2. You are working for a company that many years ago conducted a number of polyc

Question

2. You are working for a company that many years ago conducted a number of polycon- densation reaction experiments between diol and diacid monomers. You need data on the kinetics of one of these reactions from the archives, but much was lost in a flood. All you find are the results of the original experiments, where small aliquots of sample were withdrawn from the reaction vessel quenched to low temperature to stop the reac- tion and titrated to determine the amount of unreacted acid functional groups. The results

Explanation / Answer

Polyesterification reactions, if allowed to carry out without a catalyst, generally take >1000 minutes to complete, as they are slow and are inhibited by a number of side reactions. To enable us to understand the kinetics of the reaction, we will calculate the value of p, the extent of the reaction at different time intervals.

We have the titer values of NaOH required to neutralize the dicarboxylic acid, which we can use to determine the amount of carboxylic acid present.

One mole of the diacid will be neutralized by two moles of NaOH, at each step, the amount of acid present= titer value/ 2.

We will use this amount of acid to calculate the value of p.

p= (Amount of acid initially present- Amount of acid present at time interval of t minutes) / t.

We notice the extent of reaction proceeds steadily till it becomes very small after 100 minutes.

Additionally, at 700 minutes, 0.822cm3/g of acid remains unreacted in the reaction mixture, out of the 68.45cm3/g initially present, that is, approximately 1%. So, we can conclude that the reaction has almost proceeded to completion.

Using these observations, it is safe to conclude that the reaction was catalyzed by an external catalyst.

P at various time intervals Time (Min) Amount of acid (cm3/g) p (cm3/g/min) 0 68.45 - 25 34.235 1.368 50 17.115 0.6848 100 8.56 0.1711 150 5.275 0.0657 200 3.424 0.037 300 2.053 0.01371 400 1.506 0.00547 500 1.081 0.00425 600 0.959 0.00122 700 0.822 0.00137

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