Musings about Life and Death

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I had typed, deleted and re-typed this introduction. Each paragraph had seemed superfluous, wholly incapable of describing my melancholy. Words wafted in and out of existence.

I can't be bothered with writing a proper introduction anymore. It really doesn't matter. Other events matter. Life matters. So does Death.

How, how do we justify our existence in the light of death and diseases?

Wondering. Considering. Praying.

I am sad. Or feeling sad. Or both. I can't tell the difference between the two states. I can tell the difference between an electron in the ground/excited state but I can't tell the difference between being sad and feeling sad. It's as though my emotions are in a limbo, fluxing about, eluding my attempts to conceive them.

Sad, for who? For my Music/English teacher who passed away last week from cancer and left her children behind. For my primary school friend who realised during the same week that she was suffering from Chronic Myeloid Leukemia.

What are we to do? We, who are properly concerned with achieving good grades, enlarging our social circles and learning piles of notes. We, who are concerned with DoTA, How I Met Your Mother and SNSD?

It's easy to be caught up with all this. It's easy to lose sight of what matters, of what could be and should be. It takes tragedies - not just one, perhaps one after another - to jolt us out of our stupor. 

There are stuff that we take for granted. Really, we shouldn't. 

"i’ve been diagnosed with Chronic Myeloid Leukemia (CML). the past six days felt like a stormy sea with troughs and ridges. i had the worst but also the best. i had my greatest fears but I received the greatest love. i had the greatest uncertainties, but the most reassurances. i had blood and marrow drawn from me but I received blood and medication that heals me. i vomited my food due to side effects of medication, but I had tons of home-cooked food made with love fed by my mom. i got carried out of the shower for almost fainting, but i've been showered with love and care from the nurses here. i cried for days and nights, but people cried for me more. i fight the disease, but not alone. my parents flew back from their business trip just for me. my brother was the sweetest. my sis was supportive. my relatives were more worried than i am. my friends too. i feel pain and suffering, but the heart aches the most. i love everyone whom had prayed for me and sent me their well-wishes. rest assured, they have actually been answered. i’m fighting the disease no matter what."
- an excerpt from a Facebook post by my friend

Perhaps it's time to examine our focus in life and living.

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Lab Report on Hydrolysis of tert-butyl Chloride in polar solvents

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The lab report below was submitted as part of the coursework for CM1131 Basic Physical Chemistry. Please do not plagiarise from it as plagiarism might land you into trouble with your university. Do note that my report is well-circulated online and many of my juniors have received soft copies of it. Hence, please exercise prudence while referring to it and, if necessary, cite this webpage.

Hydrolysis of tert-butyl Chloride in polar solvents

1. Aims

Measure the rate of reaction for the hydrolysis of t-butyl chloride in two polar solvent systems – namely, water/acetone and water/isopropanol mixtures – by titrating the product HCl with NaOH.

Observe and account for the change in reaction rates when different solvent systems are used.

Calculate the corresponding rate coefficients for the hydrolysis reaction in different solvent systems.

2. Introduction

2-chloro-2-methylpropane, commonly known as t-butyl chloride, is a colourless organic compound belonging to the homologous series of halogenoalkanes. It is a tertiary halogenoalkane as the carbon bonded to the chlorine atom is also directly bonded to three other methyl (-CH3) groups.

As chlorine is more electronegative than carbon, it is electron-withdrawing, thus creating a partial positive charge (δ+) on the carbon atom and a partial negative charge (δ-) on the chlorine atom. Due to this polar nature, t-butyl chloride tends to undergo spontaneous solvolysis when dissolved in water. Solvolysisis a simple nucleophilic substitution in which the nucleophile is also the solvent.

In the presence of polar water molecules, the C-Cl bond is broken and replaced by a C-OH bond. The products of this reaction are hydrochloric acid and 2-methyl-2-propanol.
This is an example of an SN1 reaction as the rate determining step (RDS), or the slowest step in a series of elementary steps, involves only one molecule as the reactant. As such, the rate of the overall reaction is influenced by the rate of the unimolecular RDS.

To initiate a chemical reaction, the reactant molecules must first possess energy ≥ activation energy. The rate of a chemical reaction is influenced by several factors, including the nature of the solvent. In this experiment, the effects of two different polar solvents on the rate of reaction will be investigated.

3. Experimental

3.1 Preparation of reaction mixtures (acetone/water and isopropanol/water)

To 50 cm3 of water in a stoppered bottle, 50 cm3 of acetone was added in. 1.00 cm3 of t-butyl chloride liquid was transferred into the stoppered bottle with a micropipette and the mixture was shaken. The stopwatch was started at the instant t-butyl chloride was added. The flask remained stoppered except when aliquots of the solution were removed for titration.

Another mixture was prepared with acetone being replaced by the same volume of isopropanol.

3.2 Preparation of an “infinity time” sample”

A 10.00 cm3 sample of the reaction mixture was removed using a pipette and added into a stoppered conical flask containing 50 cm3 of water. The mixture was left to stand for at least 90 minutes. The high concentration of water drove the reaction to completion.

3.3 Titration preparations

At every 15 minutes interval, a 10 cm3 aliquot of the reaction mixture was removed using a pipette and placed in an Erlenmeyer flask containing 15 cm3 of acetone to quench the reaction. 3 drops of bromothymol blue indicator was added to the flask, and the reaction mixture was then titrated against the standardized 0.04102M NaOH solution. When nearing the equivalence point, NaOH was added in a dropwise manner. The end point was a blue colouration that persisted for 10 seconds. The volume of NaOH used was then recorded.

After the titration of all required samples (up to 90 minutes), the reaction mixture in the “infinity time” sample was titrated against the standardized 0.04047M NaOH solution in the same way. The volume of NaOH used was then recorded.

4. Results

Volume of t-butyl chloride: 1.00 cm3

Molarity of standardized NaOH: 0.04102 M

Titration reaction: HCl + NaOHNaCl + H2O

Number of moles of HCl = Number of moles of NaOH used

=0.04102 M × (Volume of NaOH used in cm^3)/1000

[HCl] is therefore =(Number of moles of HCl)/10x 1000

4.1 For 50/50 acetone/water with t-butyl chloride

Time/mins 15 30 45 60 75 90

Volume of NaOH(aq)/cm3 6.20 9.60 12.30 14.40 16.10 17.10

[HCl]t /moldm-3 0.02543 0.03938 0.05045 0.05907 0.06604 0.07014

Volume of NaOH(aq) used for the 10cm3 infinity time sample: 19.00 cm3

Number of moles of HCl in infinity time sample = 0.04102 M ×19.00/1000 dm^3= 0.0007794mol

[HCl]∞ is therefore = 0.0007794/10 x 1000 = 0.07794 moldm-3

4.2 For 50/50 water/isopropanol with t-butyl chloride

Time/mins 15 30 45 60 75 90

Volume of NaOH(aq)/cm3 6.50 9.90 12.70 14.70 16.30 17.80

[HCl]t /moldm-3 0.02666 0.04061 0.05210 0.06030 0.06686 0.07302

Volume of NaOH(aq) used for the 10cm3 infinity time sample: 20.30 cm3

Number of moles of HCl in infinity time sample = 0.04102 M ×20.30/1000 dm^3= 0.0008327mol

[HCl]∞ is therefore = 0.0008327/10 x 1000 = 0.08327 moldm-3

4.3 ln([HCl]∞ - [HCl]t) against time for 50/50 acetone/water with t-butyl chloride

Time/mins 15 30 45 60 75 90

([HCl]∞ - [HCl]t) 0.05251 0.03856 0.02749 0.01887 0.01190 0.007800

ln([HCl]∞ - [HCl]t) -2.947 -3.256 -3.594 -3.97 -4.431 -4.854

4.4ln([HCl]∞ - [HCl]t) against time for 50/50 water/isopropanol with t-butyl chloride

Time/mins 15 30 45 60 75 90

([HCl]∞ - [HCl]t) 0.05661 0.04266 0.03117 0.02297 0.01641 0.01025

ln([HCl]∞ - [HCl]t) -2.872 -3.154 -3.468 -3.774 -4.120 -4.580

From the above diagram, it can be observed that the graphs of ln([HCl]∞ - [HCl]t)against time for both mixtures produce a straight line. It can be concluded that both reactions follow a first-order trend.

Since the gradient of the straight line is the rate coefficient of the reaction, the pseudo first-order rate coefficient of the 50/50 acetone/water mixture with t-butyl chloride is0.0224¬ min-1and that of the 50/50 water/isopropanol mixture with t-butyl chloride is 0.0356 min-1.

Derivation to account for the determination of rate of reaction from graphs of ln([HCl]∞ - [HCl]t)against time

To determine the order of a reaction, the rate law must first be derived in the form of differential equations, and then it can be integrated to obtain an equation involving concentration as a function of time. The hydrolysis of t-butyl chloride has been found to be an SN1 reaction, which means that only one molecule is involved as a reactant in the RDS. A proposed mechanism (as demonstrated in the next section) shows that the RDS is the formation of a carbocation intermediate from t-butyl chloride. Therefore, the rate of reaction should be proportional to the concentration of t-butyl chloride.

i.e. Rate =k[CH3C-Cl] =-(d〖[CH〗_3 C-Cl])/dt where k is the rate coefficient

Integrating, we get

Therefore, ln[(CH3)3C-Cl]t = -kt + ln[(CH3)3C-Cl]0 ------(1)

Since the mole ratio (CH3)3C-Cl : HCl is 1:1, the amount of (CH3)3C-Cl at the beginning of the reaction is equal to the amount of HCl of the infinity sample,
i.e [(CH3)3C-Cl]0 = [HCl]∞ ------(2)
and the rate of consumption of (CH3)3C-Cl at any instant is equal to the rate of formation of HCl, i.e. -(d〖[CH〗_3 C-Cl])/dt = (d[HCl])/dt

Therefore the amount of (CH3)3C-Cl at any time t is equal to the initial amount of (CH3)3C-Cl minus the amount of HCl formed at time t

i.e. [(CH3)3C-Cl]t = [HCl]∞ - [HCl]t ------(3)

Substituting equations (2) and (3) into (1),

we get ln([HCl]∞ - [HCl]t) = -kt + ln[HCl]∞

Therefore, the graph of ln([HCl]∞ - [HCl]t)against time (t) will yield a straight line with gradient –k, with k as the rate coefficient of the reaction and ln[HCl]∞as the y-intercept.
Suggested mechanism for the hydrolysis of t-butyl chloride in a polar solvent

The overview of the suggested mechanism:
The schematic representation of suggested mechanism:

Step 1: Heterolytic fission of C-Cl bond to form carbocation intermediate (rate determining step)
Step 2: Nucleophilic attack of the carbocationto form a high energy transition state between the carbocation and water (fast step)
Step 3: Formation of 2-methyl-2-propanol by a hydrogen ion leaving the transition state complex (fast step)


5. Discussion

Maxwell-Boltzmann distribution curve shows that the more stable the reaction intermediates, the lower the Ea. This will favour the forward reaction and hence, result in a higher rate coefficient.

The effects of activation energy, Ea, on rate coefficient, k

The activation energy is the minimum energy that reactant molecules must possess in order to initiate a chemical reaction. In this experiment, the solventsystemsaffectthe rate of reaction by influencing the activation energy of the reaction. According to the Arrhenius’ equation,

i.e. k = Ae^(-E_A/RT)

Therefore at constant temperature, a decrease in EA will increase k, which means that the reaction rate will increase.

Accounting for the SN1 mechanism over SN2

According to literature, the hydrolysis of t-butyl chloride is an SN1 reaction. It is a nucleophilic substitution reaction where one reactant molecule is involved in the slow step, or rate determining step. The one reactant molecule involved is the one being hydrolysed, which in this case is t-butyl chloride itself. Another form of nucleophilic substitution is SN2 reaction, which means that two reactant molecules are involved in the rate determining step. For such a reaction, the two molecules are the halogenoalkane and the attacking nucleophile.

The hydrolysis of t-butyl chloride is more energetically favored as an SN1 reaction than as an SN2 reaction. This is due to steric hindrance caused by the 3 bulky methyl groups adjacent to the central C atom bonded to the chlorine atom; therefore the nucleophile cannot access and attack the electron deficient C atom effectively in an SN2 reaction. Moreover, in an SN1 reaction, the intermediate carbocation is stabilized by 3 electron-donating methyl groups surrounding the C atom, thus alleviating the positive charge on it. This occurs by hyperconjugation3which is the interaction of the C-C sigma bond electrons with the adjacent empty p-orbitals of the central carbon atom, thus supplying electrons to the electron-deficient central carbon atom to stabilize the strong positive charge. Hence, an SN1 reaction is favored.

Accounting for the pseudo first-order nature of reaction

SN1 reactions in which the nucleophile is also the solvent are commonly called solvolysis reactions. In this experiment, water is both the nuclophile and the solvent. Solvent as the nucleophile makes kinetic order indeterminate (pseudo-first-order because [solvent] is ≈ constant).

The polarity of the solvent systems

From calculations, the reaction rate for the 50/50 water/isopropanol mixture is higher than the reaction rate for the 50/50 acetone/water mixture, as the k coefficient for the former is larger than for the latter. Both isopropanol/water and acetone/water are polar solvent systems.

The polarity of the solvent affects the rate of the reaction through the solvent effect. The solvent effect is the interaction of the solvent molecules with the carbocation intermediate to stabilize it. The solvent molecules orient around the carbocation so that the electron rich ends of the solvent dipoles face the positive charge, thereby lowering the energy of the ion and favoring its formation4.

Therefore, the more polar the molecule, the stronger interaction it can have with the carbocation, resulting in a more stabilized carbocation. According to literature, the polarity of a molecule is indicated by its dielectric constant. The higher the dielectric constant, the more polar is the molecule. The dielectric constant for acetone at 25oC is 20.7 and that for isopropanol at 25oC is 18.35. According to these values, acetone is a more polar solvent than isopropanol, and so should accelerate the hydrolysis of t-butyl chloride better than isopropanol. However, given the experimental results, this is not the case. Hence another factor needs to be considered – whether the solvent is protic.

The protic/aprotic nature of the solvent systems

Isopropanol is a polar protic solvent as an H atom is bonded to an electronegative O atom, and therefore is able to dissociate to form H+ ions. Acetone is a polar aprotic solvent as all its H atoms are bonded to C atoms and are unable to dissociate.

A polar protic solvent will not only stabilize the carbocation intermediate as mentioned in the paragraph above, but it will also stabilize the leaving group, which in this case is the negative Cl- ion. With isopropanol as the solvent, theCl- ions formed from the heterolytic C-Cl fission of t-butyl chloride are solvated by electrostatic interactions between it and the partially positively-charged hydrogen of isopropanol, stabilizing the Cl¬- ions.

This interaction is known as hydrogen-bonding. This stabilization of both the carbocation and the leaving group further brings the activation energy down, and increases the rate of reaction. On the other hand, as acetone is a polar aprotic solvent, it is unable to stabilize the Cl- ions and so could not lower the activation energy further. Hence, isopropanol speeds up the hydrolysis reaction better than acetone, which is in agreement with the results of this experiment.

Titrimetric techniques

While titrating, the conical flask has to be swirled constantly throughout to ensure that the contents are mixed evenly. Also, some titrant may drip onto the sides of the conical flask and may not react with the solution in the conical flask. This reduces the accuracy of the results as extra titrant would be used to achieve the equivalence point. To prevent this, deionised water can be used to wash down the unreacted titrant when nearing the equivalence point and the conical flask should be swirled before continuing with the titration. To achieve consistent results, one important factor is to add in the titrant in a drop wise manner before the equivalence point.

Deionised water was used for washing the apparatus, instead of using tap water. This is because deionized water is pH neutral and will not negatively affect the results of the acid-base titrations. This is important as acid-base titrations are pH sensitive reactions.
Other factors that would affect the accuracy of the results include parallax error when taking the readings and making sure that no air bubbles are present within the pipette and burette while titrating.

Use of bromothymol blue as indicator

Bromothymol blue is a chemical indicator for measuring substances that would have relatively low acidic or basic levels (near a neutral pH), i.e. weak bases as well as weak acids4. With the use of bromothymol blue indicator, the course of titration stops when the blue end point persists for ten seconds. However, the blue colouration may turn back to its initial yellow/green in HCl. This is because the acetone added to the aliquot before titrating only stops the hydrolysis of tert-butyl chloride by a large amount and not completely, hence HCl is being produced gradually and the concentration of HCl increases. Despite this, since there is only a very small amount of HCl being produced, we can regard the end point to be the blue end point that persists for ten seconds. If the blue colouration disappears within ten seconds, the amount of NaOH used to neutralise the HCl is insufficient and more NaOH should be added.

To see the colour change at end-point more clearly, a blank piece of paper may be used as background screen while titrating.

Experimental errors and suggested improvement

To increase the accuracy of the experiment, multiple titrations can be carried out until duplicate determinations agree to within 0.05mL of each other. This ensures that the results are not once-off outliers. By averaging the two most consistent and accurate results, the probability of incurring random errors was accounted for and decreased.

The volatility of acetone and isopropanol causes the reaction mixture to evaporate. When removing aliquots of the reaction mixture, some of the acetone/isopropanol evaporates intoair and thus result in an inaccurate reading. To minimize errors, the pipetting should be done as quickly as possible so as to reduce the amount of solvent lost.

As the compounds are volatile and hence, hazardous to health, the experiment should be conducted in a fumehood.

Instead of manual shaking of the flask during titration, a magnetic stirrer may be used to ensure uniform and consistent stirring.

6. Conclusion

The rate of reaction is dependent on the nature of the solvent systems. Since the reaction is a SN1 mechanism, the forward reaction would be favoured by a polar protic solvent system which would stabilize both the reaction intermediate and leaving group.

As this is a pseudo first order reaction, the gradient of the graph ln([HCl]∞ - [HCl]t) against time (t) is equivalent to the rate coefficient. As such, the rate coefficients for the hydrolysis of t-butyl chloride in the respective solutions are:

Pseudo first order rate coefficient for reaction in acetone/water solvent = 0.0224 min-1

Pseudo first order rate coefficient for reaction in water/isopropanol solvent = 0.0356 min-1

7. References

http://en.wikipedia.org/wiki/Protic_solvent

http://chemistry2.csudh.edu/rpendarvis/SN1Elim.html

http://en.wikipedia.org/wiki/Hyperconjugation

John Mcmurry. 2007. Reactions of Alkyl Halides: Nucleophilic Substitution and Eliminations. In: Organic Chemistry (7th Edition). Brooks Cole. Pg 372 - 380

http://www.asiinstr.com/technical/Dielectric%20Constants.htm

http://www.organic-chemistry.org/namedreactions/nucleophilic-substitution-sn1-sn2.shtm

1 comments:

We're all old enough to be touched by tragedy

in

I found out, over Facebook, that one of my ex-teacher just passed away.

There is this vague sense of discomfort, of unsaid words, of perhaps, maybes and what-ifs.

I didn't really know her well. She taught me music and English; then, I wasn't the most attentive student. She was, by all accounts, a stranger.

In fleeting moments.

Not really sure what to say, how to feel. There is this sense of loss. Formless, yes. But there...

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Weak Anthropocentrism - Moderating between Strong and Non-anthropocentrism

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This essay is originally written for UPI2205 Ethics & The Environment.

Human beings – their future, present and past welfare – cannot be divorced from their natural surroundings. Questions regarding the ways in which human beings can and should interact with the natural environment has given rise to multiple ethical frameworks. These moral philosophies, drawing from diverse ethical traditions, may be understood according to two broad definitions – anthropocentrism and non-anthropocentrism. The anthropocentric approaches suggest that any analysis of nature must be human-centered. Their conceptual counterparts, non-anthropocentric paradigms, argue for an appreciation of nature from nonhuman perspectives and can be classified under three main positions – biocentrism, ecocentrism as well as deep ecology. Both anthropocentrism and non-anthropocentrism have ardent supporters espousing their tenets and critics arguing against their flaws. In this paper, the perceived inconsistencies of non-anthropocentrism and strong anthropocentrism will be discussed; an alternative paradigm, weak anthropocentrism will be explored and its potential to support robust environmental ethics, advocated.

I. Problems associated with non-anthropocentrism and anthropocentrism
One incongruity with non-anthropocentrism stems from its fundamental stance of ascribing nonhuman subjects with “intrinsic worth/ biospecies equality” (Devall and Sessions, 1985, p. 146). It claims that natural properties – such as integrity, beauty and biodiversity – can provide a non-human basis for valuing nature. The basis and value of subjects are assumed to lie independent of the human observers. However, according to skeptics, such qualities are neither intrinsic nor non-anthropocentric. In A Critique of Anti-Anthropocentric Ethics, Richard Watson (1983, p.157) argues that non-anthropocentric approaches are, in essence, anthropocentric:
 “The notion of a climax situation in ecology is a human invention, based on anthropocentric ideas of variety, completion, wholeness and balance. […] What would it be, after all, to think like a mountain as Aldo Leopold is said to have recommended? It would be anthropocentric because mountains do not think, but also because mountains are imagined to be thinking which human interests in their preservation or development they prefer.”
Attributing the environment with non-anthropocentric values requires us to place ourselves in their positions and imagine their viewpoints from our outsider human perspectives; this, ultimately, is a human-centered endeavor. It is “logically impossible”, Nuyen(1981, p.221) maintains, to “know how an animal thinks about itself and about human beings”. Likewise, the genuine feelings of mountains and plants cannot be rationally known. Grey (1993, p. 464) agrees and suggests that if we “attempt to step too far outside the scale of the recognizably human, rather than expanding and enriching our moral horizons, we render them meaningless, or at least almost unrecognizable.” To ascribe nature with intrinsic value is a contentious approach; from a mild anthropocentric stance, nature can be said to have inherent value as the basis of value lies within it but the source of value is in the external valuator (Nuyen, 2011, p.13). Due to this arguable attribution of intrinsic value to nature, non-anthropocentrism, at its very core, may not be as non-anthropocentric as it appears.

The controversial attribution of intrinsic value to nonhuman subjects leads to an internal inconsistency within the ethics, most aptly pointed out by Grey (1993) in Anthropocentrism and deep ecology. This, in turn, casts doubt on non-anthropocentrism’s ability to support robust environmental ethics.

On the other end of the spectrum, some anthropocentrists maintain that only humans have moral standing and intrinsic value; they claim that nature must and can only be understood from human perspectives. Of these philosophers, Immanuel Kant is perhaps the most notable. In his definitive essay, Rational beings alone have moral worth, Kant (1873, p.61) argues that “our duties towards animals are merely indirect duties towards humanity”. From his perspectives, we have no duties to nonhumans, only duties to other humans; nonhumans are appraised as instruments to human interests and values. A tree, by itself, is not valuable; it is only treasured because of its potential to be exploited as a source of fuel, paper, food, medicine or entertainment. The natural subject, by itself, has no intrinsic value; it is only valuable because it can be used to accomplish a goal desired by the valuer. In Kantian diction, they are means to an end but not an end in itself. This form of anthropocentrism has been severely criticised by non-athropocentrists as assuming moral superiority over natural organisms and systems. Rolston (1998, p.113) maintains that it is “arrogant to retreat into a human-centered environmental ethics” that presume nature only to have instrumental values dependent on human valuers.

Non-anthropocentrism has been criticised as being anthropocentric in essence and failing to convey a rational, relatable appreciation of nature. One form of anthropocentrism – such as that advocated by Kant and his supporters – has been castigated as assuming moral high grounds. Given the logical lapses in non-anthropocentrism and alienating sense of moral supremacy in anthropocentrism, there is a need to develop a different environment ethics.  Robust environmentalism can only happen if supported by a system of ethics that is both internally consistent and widely accepted – conditions which the two mentioned paradigms fail to meet. Grey (1993, p.464) proposes that the problem is not with anthropocentrism but with ill-defined anthropocentrism; he sees a need to “develop an enriched, fortified anthropocentric notion of human interest”. In view of the criticisms against existing paradigms, Bryan G. Norton argues for a philosophy based loosely on human-centered paradigms and calls this “weak anthropocentrism”.

II. Weak anthropocentrism as a moderate alternative
In Environmental Ethics and Weak Anthropocentrism, Norton (1984, p.134) maintains that environmental ethics need not “justify [difficult] claims to intrinsic values” in nature. A perfectly sufficient environmental ethic, he explains, is one which can criticize value systems purely exploitative of nature. From such a perspective, environmental ethics would be principally about “concern for the protection of the resource base through indefinite time”. Norton, as a professor of philosophy as well as public policy, expresses his concerns with “creating a theory of sustainable development that captures the key role of human values in the search for better policies to protect nature and humans of the future”. He wants a theory capable of criticizing anthropocentrism that has exploited nature and yet, does not wish to attribute nature with intrinsic values. Thus, he differentiated strong anthropocentrism from weak anthropocentrism.

To fully comprehend the differences between strong and weak anthropocentrism, we must recognize two types of human desires: felt and considered preferences. A felt preference, according to Norton, is one that may be temporarily satisfied by some specific experience. A considered preference, on the other hand, is one arrived after “careful deliberations” that determines the preference to be consistent with a “rationally adopted worldview”. By rational worldview, Norton refers to a conception of the world in accordance with established scientific research, a metaphysical framework to interpret this research as well as a set of rationally supported aesthetic and moral ideals. To illustrate the difference between a felt and considered desire, suppose, for example, the act of recycling. A desire to recycle is not a felt preference; it does not fulfill any specific desire of an individual. It is, however, a considered preference in light of the individual’s rational worldview about environmental responsibility.

Having defined felt and considered preferences, Norton then regards an ethic to be strongly anthropocentric if it focuses on felt preferences alone. In the value system of strong anthropocentrism, there is “no check upon the preferences of individuals” and as a consequence, “no means to criticize the behavior of individuals who use nature merely as a storehouse of raw materials to be extracted and used for products serving human [felt] preferences”. Strong anthropocentricism – such as that assumed by Kant – could provide no balance against felt preferences that may endanger the natural world. It allows for the rapid destruction of rainforests and its subsequent conversion to farmlands, even if it may harm nonhuman organisms and systems, as long as there are substantial tangible benefits to the general human populace.

Weak anthropocentrism, by contrast, finds value in both felt and considered preferences. It determines felt preferences to be rational or irrational based on their consistency with one’s rational worldview. As a decision-making calculus, weak anthropocentrism determines what the agent wants (felt preferences) and how these interests fit in with the agent’s rational worldview (considered preferences). The weakly anthropocentric view avoids the difficulties of justifying an environment ethic from either end of the gamut. On one hand, it avoids contention over the non-anthropocentric attribution of intrinsic values to nonhuman systems and organisms. On the other hand, it avoids strong anthropocentricism’s tendency to make felt preferences the loci of all value; it explains how considered preferences within a rational worldview can account for the value in natural environments. At this point, it may be helpful to consider how weak anthropocentrism compares to non-anthropocentrism and strong anthropocentrism.

Weak anthropocentrism encourages the protection of an organism because it holds a pivotal position in the key chain, or its genetic library could potentially cure certain human diseases, or even for the sheer pleasure that observing it may bring. It attributes value to natural organisms and systems from a human-centered perspective that most people can empathise with. A non-anthropocentrist would have to justify protection of an organism by appealing to its intrinsic value. However, why a worm or fish in an isolated lake is valuable in itself is difficult for many people to relate to.

Another advantage of weak anthropocentricism is its ease as a decision-making calculus. Weighing the intrinsic value of non-human subjects is more challenging than weighing human values. Should there be a conflict in preserving the intrinsic values of two organisms, non-anthropocentrism may reveal internal inconsistencies. Take, for example, the conservation of lions. If a lion has equal intrinsic value to a cow, would that justify the killing of the lion so that many more cows would not have to die? If the lion has to be protected on the basis of it having more intrinsic value, how much more valuable is it intrinsically? And who decides it is more valuable than cows anyway? (The very act of deciding may be an anthropocentric assignment of value.) All these questions must be answered to act on a non-anthropocentric ethic. However, the problems may be resolved – or rather, avoided – by turning to weak anthropocentrism. In a rational worldview,established scientific research indicates that extinction is forever; a metaphysical framework interprets this irreversible loss in biodiversity as a corresponding loss in aesthetic ideals and a collective failure as stewards of the natural environments. Hence, weak anthropocentrism, unlike non-anthropocentrism, allows for the weighing of a lion’s value in accordance with a rational worldview; the subsequent sacrifices of more animals, which are less rare, become justifiable. Weak anthropocentrism also differs from strong anthropocentrism. The latter philosophy may claim that lions should not be preserved for they compete for food with humans; this felt preference may be checked by considered preferences in a rational worldview (as advocated by weak anthropocentrism) and hence, argued against.

Critics, however, may claim that even weak anthropocentrism falls prey to the same problem of assigning values to organisms. Whether or not one believes a lion or a cow is more valuable is always a relevant question when following a weakly anthropocentric ethic. What that may constitute a rational worldview to one may not be so to another. Admittedly, weak anthropocentrism faces the same issue in determining the value of one human’s worldview compared to another’s, but this problem is easier to resolve given more experience with and greater empathy within homocentric perspectives. This problem, on the other hand, will be more pronounced with non-anthropocentric paradigms, given that they are projecting their human perspectives on and attempting to sympathise with non-human subjects, a “logically impossible” endeavor, as Nuyen (1981, p.221) has pointed out. Also, to resort to a tu quoque response, this problem of recognizing what is valuable to different individuals is a problem for all ethical systems, and not unique to a weakly anthropocentric environmental ethic.

Non-anthropocentric ethicists often claim that weak anthropocentricism is impossible, that any anthropocentrism “taints the whole ethic because it always devolves into appeals to existing human desires” (Mendenhall, 2009, p.35). This, however, is not problematic as long as there is a clear distinction between felt and considered preferences. Maintaining this distinction will place a constraint on felt preferences, deeming them irresponsible and destructive if they are inconsistent with a rational worldview. The key here is finding a worldview that values things like ecological diversity and human consciousness. Naess (2003, p. 264), one of the founders of deep ecology, further argues against weak anthropocentrism, claiming that it is “indecent for a teacher to proclaim an ethic for tactical reasons only”. Naess’s strongly-worded criticism wholly misses the perspectives of weak anthropocentrism. The supporters of this philosophy want to expedite an agreement between environmental ethicists with strongly anthropocentric or non-anthropocentric persuasions, ultimately to campaign for the common goals of protecting the natural environments.

Weak anthropocentrism’s relation to other philosophies
Norton (1984) envisions weak anthropocentrism as an environmental ethic that eschews the contentious assignment of intrinsic value, in order to focus on pragmatic principles intended to “protect nature and humans of the future”. Weak anthropocentrism, however, did not go so far as to adopt a strong stance counter to non-anthropocentrism. Instead, it adopts a moderate position which allows for the criticism of exploitative acts towards nature – one which strong anthropocentrism does not allow. Weak anthropocentrism, thus, is amoderate foundation capable of supporting robust environmental ethics.

Felt preferences stem from the anthropocentric tendencies of humans to assign values according to their needs and wants. Because it is a must to sustain oneself through the provisions of nature, there is an element of felt preferences in all environmental ethics. Considered preferences, on the other hand, depends on adherence to a rational worldview. The protection of nature “can be justified as being implied by the ideal of harmony with nature,” Norton (1984, p.315) rationalizes, “(and) this ideal, in turn, can be justified either on religious grounds referring to human spiritual development or as being part of a rationally defensible world view”. The broadness of what constitutes a “rationally defensible world view” – be it based on logic or spiritual sensibilities –allows many philosophies to be subtended under weak anthropocentrism.

Social ecology, as advocated by Murray Bookchin (1987), is a weakly anthropocentric paradigm. It has considered preferences in terms of socio-cultural ideals and regards environmental degradation as the result of social inequalities.

Ecofeminism,in the manner envisioned by Karen Warren (1990), may be considered weakly anthropocentric too. It weighs the felt preferences of women in general and their considered preferences of an ideal whereby nature and women are treated with respect and not oppressed.

Confucian role-based ethics, as supported by A.T. Nuyen (2011), suggests that the attribution of inherent value to nature is part of a rational worldview. It may also be interpreted as weakly anthropocentric.

Even non-anthropocentric philosophies, such as biocentrism, ecocentrism and deep ecology, can be interpreted with the tenets of weak anthropocentrism. After establishing that these ethics are, essentially, anthropocentric, what constitutes a rational worldview to these philosophies may be further defined.

To biocentrists, a rational worldview attributes moral standing to all and only living things.  To ecocentrists, species, ecosystems, natural processes and earth itself are deserving of respect. To deep ecologists, a rational worldview is one in which there is spiritual harmony with the natural environment.

One must recognize that these aforementioned environmental ethics are different and espouse multifarious approaches towards the treatment of nature; it will not be fair to ignore the nuances in their philosophical inclinations. However, through the common lenses of weak anthropocentrism, environment ethicists will be able to see a thread of camaraderie running through paradigms that appear dissimilar. Through this, it is hoped that there will be greater empathy between ethicists from various fractions.

Conclusion
In this paper, I began with an explanation of the flaws associated with non- and strong anthropocentrism. I then moved on to explain how weak anthropocentrism differs from these two strong paradigms and offers a moderate ethical alternative. The discourse progresses to a focus on how different philosophies may, in one way or another, be weakly anthropocentric.

Even as I write this paper, the British Broadcasting Channel (BBC) reports the death of the last Javan rhino in Vietnam. The degradation of natural systems and exploitation of its creatures continue. It is critical for environmental ethicists to work together in a concerted fashion to protect the natural environment.

Nobutsugu, an ethicist supporting Norton’s weak anthropocentrism, explains the problems of ideological conflicts between different ethical frameworks:
“Norton sees ideological polarization in the American conservation movement since the age of Gifford Pinchot and John Muir. He thinks that preexperiential commitments of environmentalists to one’s own ideology (e.g. anthropocentrism and non-anthropocentrism) profoundly influence their rhetoric in environmental debates and that “outbursts of ideologically motivated rhetorics are unlikely to result in improved environmental policies” (Norton, 2005).”
While there may be flaws associated with weak anthropocentrism – such as what constitutes a rational worldview – it remains an adequate ethics that may serve as a meeting point between strong anthropocentrists and non-anthropocentrists. It is not the most ideal, but it is sufficient.

Weak anthropocentrism cannot cater to the beliefs of everyone. Because of the inherent biological differences in people and disparities in their external socio-cultural-political-geographical upbringing (which shaped their beliefs), it is difficult – perhaps, even impossible – to develop an ethics that everyone could agree with. There will be deep ecologists who seek spiritual harmony with nature and strong anthropocentrists interested only in viewing nature through economic costs-benefits calculus.

Weak anthropocentrism, while not the most ideal ethics that appeal to everyone, is an adequate basis for robust environmental ethics.The weakly anthropocentric view avoids the difficulties of justifying an environmental ethics from either end of the spectrum. It does not lapse into the questionable attribution of intrinsic value to non-human organisms, biospheres and ecologies. It avoids the short-sightedness of strong anthropocentrism, which judges mainly on felt preferences.

As Nuyen (2011, p.215) writes in An anthropocentric ethics towards animals and nature, most people, if not all, agrees that it is wrong to treat animals and nature without respect, to inflict needless destruction. The ecological world desperately needs the damaging human population to adopt an ethic that will slow or reverse environmental degradation. It is important to expand our moral horizons through debates on what constitutes an ideal environmental ethics. But, we must not miss the forest for the trees. It is pressing to focus on protecting what we now have, to focus on protecting our natural environment. In this regard, weak anthropocentrism’s pragmatism serves well. Certain aspects of nature, once destroyed, may not be reversible. Vietnam’s last Javan rhino is a startling example.

Bibliography
Bookchin, Murray. 1987. Social Ecology versus Deep Ecology. Environmental Ethics, Readings in Theory and Application, Sixth Edition, p. 165 – 176.
Devall, Bill and Sessions, George. 1985. Deep Ecology. Environmental Ethics, Readings in Theory and Application, Sixth Edition, p. 143 – 148.
Grey, William. 1993. Anthropocentrism and Deep Ecology. Australian Journal of Philosophy, Vol. 71, No 4, p. 463 – 475.
Holmes, Rolston III. 1998. Value In Nature And The Nature of Value. Press Syndicate of the University of Cambridge, pg 113.
Kant, Immanuel. 1873. Rational beings alone have moral worth.Environmental Ethics, Readings in Theory and Application, Sixth Edition.
Mendenhall, Beth. 2009. The Environmental Crises: Why We Need Anthropocentrism. Stance, Vol. 2, April 2009.
Naess, Arne. 1972. The Shallow and the Deep, Long Range Ecology Movements. Environmental Ethics, Readings in Theory and Application, Sixth Edition, p. 129 – 133.
Nobutsugu, Kanzakaki. 2011. Communication, Community and Commitment: Environmental Virtue Ethicist’s Interpretation of Bryan Norton’s “Sustainability”.Kyoto University.
Norton, Bryan. 1984. Environmental Ethics and Weak Anthropocentrism. Environmental Ethics 6:2 (1984).
Nuyen, Anh Tuan. 1981. An Anthropocentric Ethics Towards Animals and Nature. Martinus Nijhoff Publishers, p. 215 – 223.
Nuyen, Anh Tuan. 2011. Confucian Role-Based Ethics and Strong Environmental Ethics. Environmental Values, The White Horse Press, p.215.
Warren, Karen. 1990. The Power and the Promise of Ecological Feminism. Environmental Ethics, Readings in Theory and Application, Sixth Edition, p. 589 – 601.
Watson, Richard. 1983. A Critique of Anti-Anthropocentric Ethics. Environmental Ethics, Readings in Theory and Application, Sixth Edition, p. 156 – 163.

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On the nature of Art

in

Art isn’t ugly or malicious or pretentious. It isn’t angry. Nor does it assume a position of superiority.  To be honest, I was disappointed in the way the final critique in NUS Museum unfolded. The video on the Changsha bowl’s journey from the kiln to a display cabinet was amazing. The camera work was confident, the choice of music and variety of visual effects, great. When everyone started pointing out flaws with the film, I was aghast.
Honest commentary is laudable for it helps to hone the film makers’ craft. Some of the points raised were indeed valid. There was a barrage of comments for this video; most of them were, unfortunately, delivered in a negative, not-so-tactful manner. At one point of the critique, I complimented the video; I didn’t want the film makers to have no one recognize their labour; I didn’t want the critique session to be all about criticisms. Yes, it was a critique session. But no, it wasn't a criticism session. 
It wasn’t because I didn’t agree with some of the criticisms raised; it was because I disagreed with the way they were raised. There is a need to respect the efforts of the film makers. Some people were downright rude but dressed it up as professionalism.
Art is beautiful; people have no right to pass rude comments in its name. It isn’t ugly or malicious or pretentious. It isn’t angry. It is about beauty and life. Spreading beauty, understanding life.
People who criticise unreservedly, they are not artists.

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Lab Report on Multistep Synthesis of p-Tolilic Acid from p-Tolualdehyde

in

The lab report below was submitted as part of the coursework for CM3291 Advanced Experiments in Organic and Inorganic Chemistry. Please do not plagiarise from it as plagiarism might land you into trouble with your university. Do note that my report is well-circulated online and many of my juniors have received soft copies of it. Hence, please exercise prudence while referring to it and, if necessary, cite this webpage.
Aim

To carry out a multistep synthesis of p-Tolilic acid from p-Tolualdehyde. The first step involves the preparation of 4,4’-dimethylbenzoin from p-Tolualdehyde using thiamine hydrochloride as the catalyst. In the subsequent step, the 4,4-dimethylbenzoin is converted to 4,4’-dimethylbenzil using copper(II) acetate as the catalyst. Finally, the 4,4’-dimethylbenzil is used to prepare p-Tolilic acid by reaction in basic conditions followed by an acidic work-up. The IR and melting point of the p-Tolilic acid was also determined.

Results & Calculations

Part A: Preparation of 4,4’-dimethlbenzoin from p-Tolualdehyde
Mass of thiamine hydrochloride: 1.9858 g
Volume of p-Tolualdehyde: 7.01 ml
Density of p-Tolualdehyde: 1.015 g ml-1
Mass of p-Tolualdehyde: 1.015 x 7.00 = 7.1152 g
Molar mass of p-Tolualdehyde: 8 x 12.01 + 8 x 1.0079 + 16.00 = 120.14 g mol-1
No. of moles of p-Tolualdehyde: 7.1152 / 120.14 = 0.05922 mol

Mole ratio of p-Tolualdehyde to 4,4’-dimethylbenzoin is 2:1.
Expected no. of moles of 4,4’-dimethylbenzoin: 0.05922 / 2 = 0.02961 mol

Molar mass of 4,4’-dimethylbenzoin: 16 x 12.01 + 16 x 1.0079 + 2 x 16.00 = 240.29 g mol-1
Expected mass of 4,4’-dimethylbenzoin produced: 0.02961 x 240.29 = 7.1155 g
Mass of 4,4’-dimethylbenzoin obtained: 4.7308 g
Percentage yield of 4,4’-dimethylbenzoin: 4.7308 / 7.1155 x 100% = 66.5%

Part B: Preparation of 4,4’-dimethylbenzil from 4,4’-dimethylbenzoin

Mass of copper (II) acetate: 0.0603 g
Mass of 4,4’-dimethylbenzoin used: 4.7305 g
No. of moles of 4,4’-dimethylbenzoin: 4.7305 / 240.29 = 19.686 mmol
Mass of ammonium nitrate: 2.3652 g

Mole ratio of 4,4’-dimethylbenzoin to 4,4’-dimethylbenzil is 1:1.
Expected no. of moles of 4,4’dimethylbenzil: 19.686 mmol

Molar mass of 4,4’-dimethylbenzil: 16 x 12.01 + 14 x 1.0079 + 2 x 16.00 = 238.27 g mol-1
Expected mass of 4,4’-dimethylbenzil: 19.686 x 10-3 x 238.27 = 4.6907 g
Mass of 4,4’-dimethylbenzil obtained: 2.901 g
Percentage yield of 4,4’-dimethylbenzil: 2.901 / 4.6907 x 100% = 61.8%
Part C: Preparation of p-Tolilic acid from 4,4’-dimethylbenzil


Mass of 4,4’-dimethylbenzil used: 2.850 g
No. of moles of 4,4’-dimethylbenzil: 2.850 / 238.27 = 11.961 mmol

Mole ratio of 4,4’-dimethylbenzil to p-Tolilic acid is 1:1.
Molar mass of p-Tolilic acid: 16 x 12.01 + 16 x 1.0079 + 3 x 16.00 = 256.29 g mol-1
Expected mass of p-Tolilic acid: 11.961 x 10-3 x 256.29 = 3.0655 g
Mass of p-Tolilic acid obtained 0.1120 g
Percentage yield of p-Tolilic acid: 0.1120 / 3.0655 x 100% = 3.65%

Melting point of product: 126.80 – 127.50 oC

Overall yield
Expected mass of p-Tolilic acid: 0.05922/2 x 256.29 = 7.5887 g
Overall yield = 0.1120 / 7.5887 x 100% = 1.48%

Discussion

In the first part of the experiment, 4,4’-dimethylbenzoin was prepared from p-Tolualdehyde using thiamine hydrochloride as the catalyst. Thiamine hydrochloride was first dissolved in water to yield chloride ions and thiamine. Upon addition of ethanol, a white precipitate forms because thiamine is less soluble in ethanol. Next, NaOH solution was added and this creates a basic environment changing the structure of a thiamine. The white precipitate dissolves and form a yellow solution. Thiamine reacts with hydroxyl ions in basic solutions in the following manner:

Figure 1: Thiamine under basic conditions

Under basic conditions, the amino group in thiamine attacks the carbon-nitrogen double bond in a nucleophilic reaction, causing the loss of a proton and yielding a tricyclic dihydrothiachromine intermediate form. As it is an intramolecular nucleophilic attack, the reaction occurs rapidly and in preference to an external attack by an OH- at the same electrophilic carbon. Subsequently, another proton is lost in the second step to open the thiazole ring to form the yellow thiol form. The presence of this thiol gives rise to the yellow colour of the solution observed.  

For the reaction to form 4,4’-dimethylbenzoin, an ylid is first formed from thiamine. An acidic proton is extracted by the hydroxyl ions present in the solution to form the ylid.

Figure 2: Formation of the ylid

The ylid is stabilized by the adjacent electronegative atoms of N and S. The positive charge on nitrogen further draws away the electron density from the carbon which further stabilizes the ylid. To this ylid that is present in solution, p-tolualdehyde was added to it.

Figure 3: Mechanism for Part A reaction (benzoin condensation)

The mechanism for the reaction is that of a thiamine-catalyzed benzoin condensation reaction. The nucleophilic ylid formed by deprotonation of thiamine attacks the p-tolualdehyde at the electrophilic carbonyl carbon to form the tetrahedral intermediate. From this intermediate, the oxoanion extracts the adjacent acidic proton whilst forming an enamine in the process. The enamine then acts as a nucleophile to add on another equivalent of p-tolualdehyde by similarly attacking the electrophilic carbonyl carbon. Eventually, the lone pair on the hydroxyl group donates itself to a  bond and kicks out the ylid to give the products of 4,4’-dimethylbenzoin and the ylid catalyst. Overall, two equivalents of p-tolualdehyde have been condensed to give one equivalent of 4,4’-dimethylbenzoin.

Thiamine, with the common name of vitamin B1, decomposes readily upon heating hence the reaction mixture was cooled in an ice/water bath to prevent this. NaOH was added until the pH was equal to or above 9 to ensure that the thiamine could be deprotonated by the base to form the ylid. The composition of the reaction mixture also needed to be taken into account because an overly aqueous medium would prevent the p-tolualdehyde from being present in the solution. The p-tolualdehyde is slightly soluble in aqueous medium which was why only 3 ml of water and about 5 ml of NaOH was added. 20 ml ethanol was used to form the bulk of the mixture and to enable p-tolualdehyde to dissolve in it more readily as ethanol is a polar solvent. Furthermore, ethanol is miscible with water and the thiamine present in water can interact freely with the p-tolualdehyde in ethanol. The reaction mixture was stored in the dark to prevent p-tolualdehyde from being oxidised to p-toluic acid by exposure to light. The reaction took place at room temperature hence the rate of reaction was slow, and it was left to react for a week to ensure the reaction goes to completion as much as possible.

In part B of the experiment, 4,4’-dimethylbenzoin that was obtained from part A was oxidized to 4,4’-dimethylbenzil using a Cu2+ salt and ammonium nitrate. The Cu2+ salt here is Cu(OAc)2 and only catalytic amounts of Cu2+ are necessary because they are continuously recycled. The Cu+ ions formed by reaction with 4,4’-dimethylbenzoin are reoxidized to Cu2+ by ammonium nitrate which is present in excess. The overall reaction can be summed up as two paired redox reactions taking place as shown by the diagram on the left. A stronger oxidising agent like potassium dichromate was not used as it might cause the cleavage of the C-C bond in the benzoin molecule, causing the reformation of p-tolualdehyde instead. Meanwhile, the entire reaction mechanism is depicted as follows:

Figure 4: Mechanism for Part B reaction (oxidation of 4,4’-dimethylbenzoin to 4,4’-dimethylbenzil)
In the first redox cycle, the 4,4’-dimethylbenzoin donates an electron to Cu2+, forming Cu+ and a benzoin radical cation. The benzoin radical cation then loses a proton to acetate ion to form acetic acid and a resonance-stabilized radical. Another redox cycle between Cu2+ and the radical takes place, forming a second Cu+ ion and cation. This cation then loses a proton to another acetate ion, forming 4,4’-dimethylbenzil. Meanwhile, for the second redox cycle, the Cu+ is reoxidized back to Cu2+ by NH4NO3 which acts as an oxidizing agent:

Figure 5: Second redox cycle – Cu+ to Cu2+

The mixture was refluxed for an hour to speed up the oxidation reaction. It could be observed that for every equivalent of 4,4’-dimethylbenzoin that was oxidized to 4,4’-dimethylbenzil, 2 equivalents of Cu2+ were required and this was regenerated by 1 equivalent of NH4NO3. Hence, the NH4NO3 added was roughly 0.5 by mass of the benzoin added, which is more than the required molar equivalent of NH4NO3 required. After reflux, the reaction mixture was poured unto crushed ice to precipitate out the 4,4’-dimethylbenzil which is insoluble in water.
Figure 6: Mechanism for Part C reaction (oxidation of 4,4’-dimethylbenzil to p-Tolilic acid)


For part C of the experiment, p-Tolilic acid was prepared from 4,4’-dimethylbenzil using an potassium hydroxide solution which was mixed with ethanol. The reaction is known as a benzilic acid rearrangement because a phenyl group migrates from one carbon to another. The mechanism for the reaction is as shown in Figure 6.

The first step involves the attack by the nucleophile OH- on one of the electrophilic carbonyl carbons in a nucleophilic addition reaction to form a tetrahedral intermediate. The next step involves a conformational change or a rearrangement as the phenyl group migrates to the other carbonyl carbon as the tetrahedral intermediate collapses. The reaction is analogous of a semipinacol rearrangement in which a deprotonated hydroxyl group provides the impetus to push the phenyl group to the other carbon and at the same time, the electrons in the carbonyl bond migrate to the carbonyl oxygen atom to make way for the incoming group. A semipinacol rearrangement involves a carbocation adjacent to a carbon with a hydroxyl group. The rearrangement involves the transfer of an R group from the carbon with the hydroxyl group to the carbocation. As such, the semipinacol rearrangement is similar to that of the benzilic rearrangement reaction. After the rearrangement, a proton transfer occurs in which the more basic oxoanion pulls the proton from the carboxylic acid in an intramolecular deprotonation. The proton could also have come from a molecule of water instead of from the carboxylic acid group. This deprotonated p-Tolilic acid was then acidified by treating it with cold hydrochloric acid. The pH was ensured to be less than pH 2 to obtain as much of the product as possible from the solution.

The benzilic acid rearrangement reaction could be understood from a molecular orbital point of view. After the nucleophilic attack by the OH- ion, the central C-C bond rotation brings the HOMO ( bond of the methylbenzyl group) into closer proximity to the LUMO of the tetrahedral intermediate. The LUMO is a linear combination of two * MOs of the carbonyl groups giving a set of bonding and antibonding MOs. Combination of these MOs in-phase produces a 4-electron system without any nodes and this is the LUMO which interacts with the pair of electrons from the HOMO. As the HOMO and the LUMO approach each other with the orbitals in-phase, the transition state which forms consists of 6 electrons and this is an aromatic system as it follows Huckel’s rule of 4n+2 whereby n = 1. The process is depicted as shown below:

As shown in the diagram, the  bond of the methylbenzyl group acts as the HOMO to attack the in-phase bonding LUMO of the C=O * MOs. The equivalent transition state is shown on the far right side of the figure. As realigning the orbitals to ensure that they are in-phase with each other requires a relatively high amount of energy, this is the rate-determining step of the reaction.

The reaction mixture was heated under reflux for half an hour to ensure that the benzilic acid rearrangement occurs. It could be noted that as the reaction proceeded, the mixture turned brown due to the formation of potassium 4,4’-dimethylbenzilate. This salt is soluble in water, hence it was dissolved in warm water with heating and stirring. The acid work-up was done using HCl in ice, which forms the p-tolilic acid from the salt. The low temperature was to quench the reaction, prevent the decomposition of the product as well as to precipitate out as much of the product as possible. There were globules of unreacted organic compounds and side products at this point in time which would be filtered off later. The crude yellow product obtained by suction filtration was recrytallized by dissolving in a minimal amount of boiling water upon which gravity filtration was done to remove the oily globules that were present as impurities. The filtrate was left to stand to allow crystallization to occur.

IR Analysis

Wavenumber / cm-1
Vibrational mode
Intensity
3405.5
O-H stretching (alcohol)
Strong and sharp
2923.3
O-H stretching (carboxylic acid)
sp3 C-H stretching
Weak and broad
1719.1
C=O stretching (carboxylic acid dimer)
Strong and sharp
1513.2
C=C stretching
Weak and sharp
1256.8
C-O stretching (carboxylic acid dimer)
Medium and sharp
1173.1
C-O stretching (carboxylic acid monomer)
Medium and sharp
1068.4
C-O stretching (alcohol)
Strong and sharp
817.9
Aromatic OOP bending (para-substituted)
Strong and shrap

From the IR analysis, the peak at 3405.5 cm-1 was due to the O-H stretch of the alcohol’s hydroxyl functional group. The peaks at 1256.8 and 1173.1 cm-1 which corresponds to C-O stretching provides further evidence of the presence of an alcohol. The peak at 1719.1 cm-1 was assigned to the C=O stretch, which is part of the carboxylic acid functional group when the molecule is in its dimeric form. Monomeric carboxylic acids absorb at higher wavenumbers of around 1760 – 1730 cm-1. There are three C-O stretches in total. Two of them at 1256.8 cm-1 and 1173.1 cm-1 are due to the carboxylic acid dimeric and monomeric forms respectively. The C-O stretch at a lower wavenumber of 1068.4 cm-1 was due to the C-O of the alcohol. The dimeric form of the carboxylic acid tends to be present in the solid state and the IR was indeed done using a KBr disc. This dimerization also weakens the C=O bond and lowers its stretching force constant k, resulting in the lowering of the carbonyl stretching frequency to around 1710 cm-1. The aromaticity of the compound was also shown by the OOP bending at 817.9 cm-1 and this peak corresponds to the para-substituted benzene rings in the product. Besides doing IR analysis, 1H and 13C NMR could be done also to ascertain the synthesis of the desired product.

Percentage Yield and Melting Point Determination

The experiment which consists of three parts – Part A, B and C – had percentage yields of 66.5%, 61.8% and 3.65% respectively, with an overall yield of 1.48%. The first yield is reasonable at 66.5% and could be due to the amount of 4,4’-dimethylbenzoin remaining in solution even after crystallization. Other possible reasons might be that initial exposure to light has caused some of the p-tolualdehyde to be oxidized to p-toluic acid which decreased the amount of the limiting reagent available. Meanwhile, the second yield is 61.8% which is also reasonable, and this is probably due to the efficient work of the Cu2+ catalyst which was regenerated continuously in the synthesis. In the last part of the experiment, however, yield was considerably low at only 3.65%. The low yield could be due to the reaction of 4,4’-dimethylbenzil to form side products like 4,4’-dimethylbenzhydrol or 4,4’-dimethylbenzophenone  when the 4,4’-dimethylbenzilate was heated to dissolve it. Thus, less of the p-tolilic acid was crystallized out due to lesser amount of the 4,4’-dimethylbenzilate present in the reaction mixture. On hindsight, it might have been more appropriate to evaporate the solvent instead to generate a higher yield of the fine white powder. The overall percentage yield of the experiment is 1.48%. This overall yield is considerably low as it is dependent on the individual yields of the three parts of the multi-step synthesis.

The melting point of the p-tolilic acid was determined to be 126.80 – 127.50 oC, which is lower than the literature value of 128 – 129 oC. This may be due to the presence of impurities. Recrystallization might be carried out to purify the product further though this risks losing more products in the recrystallization step.

Conclusion

The multistep synthesis of p-Tolilic acid from p-Tolualdehyde was carried out in a sequence of three steps – part A, B and C – having the percentage yields of 66.5%, 61.8% and 3.65% respectively. The overall yield was calculated to be 1.48%. IR analysis gave evidence for the formation of the target molecule of p-Tolilic acid as seen by the characteristic peaks from the carboxylic and alcohol functional groups. The melting point was determined to be 126.80 – 127.50 oC.

References

1. Carl T. Wigal. Copper-Catalyzed Oxidation of Benzoin to Benzil. H. A. Neidig, 2000. Pg 1 – 12.
2. Carl. T. Wigal. Thiamine-Catalyzed Benzoin Condensation. H.A. Neidig, 2000. Pg 1 – 12.
3. Carl T. Wigal and Jerry Manion. Converting Benzaldehyde to Benzilic Acid: A Multistep Synthesis. H.A. Neidig, 2000. Pg 1 - 4.
4. Clayden, Greeves, Warren and Wothers. Organic Chemistry, Oxford University Press, 2006. Pg 987, 989 – 990.
5. Floyd L. James and Anthony L. Ippolito. Rearrangement of p,p’-Disubstituted Benzils. Miami University, Ohio. The Ohio Journal of Science 53 (1) : 31, January, 1953. Pg 1 – 6.
6. Jon Landis and R. Minard (Penn State Univ.). Thiamine Catalyzed Benzoin Condensation. Adapted from K. L. Williamson: Macroscale and Microscale Organic Experiments, 2nd Ed. 1994, Houghton Mifflin, Boston. Revised 2/22/02.
7. George D. Maier and David E. Metzler. Structures of Thiamine in Basic Solution, Department of Chemistry, Iowa State College. Pg 4386 – 4391.


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Bubbling Joy In Barcelona

Sycophany/ Self-preservation

Romance of the two wisdom teeth

Art Appreciation 101