Question

4. Using your knowledge of Le Chatelier's principle and the given equation, explain why an excess of acetic acid is used in this experiment. 5. If water was added as the solvent in this reaction would this shift the equilibrium in the desired direction to form more of the product (the ester)? Explain using the given equation and LaChatelier's principle. Alcoho 6. In the two chemical structures below, identify each of the following functional groups as either carboxylic ester, carboxylic acid, or alcohol (it will help to refer to Figure 1 in your reading). carboxylic carb ester ..... Carboxylic - aridic acid - A col All aspirin carborylic ester Carboxylic acid

Answer 1

First of all, go through the reaction mechanism. This is the general mechanism for any acid and alcohol. You must have noticed that every step is reversible and reactants and products are in equilibrium.

Acid catalegsed Ester formation HO OH OH -OH +0 - carboxylic HO OH Xook Tetrahedral Intermediate Acid Path - 1 SH HO OH E I t/ - HD R our O-R +4₂0 Ester Pata - 2 ot - Rot D HO O U-H OrH on R +ROH carboxylic H Arid

There is a tetrahedral intermediate involved, and whether the reaction will give us ester or the give back the starting material carboxylic acid is dependent upon the amount of reactants.

4) If you look at the first reaction, carboxylic acid and alcohol both are at the reactant side. According to Le chatelier principle, if the amount of reactants is increased, this excess amount must be used up and hence drives the reaction forward. In other words if you do not use an excess of carboxylic acid and alcohol, the tetrahedral intermediate would collapse back to starting carboxylic acid (as every step is reversible). Hence, the reaction will keep oscillating and not give a significant yield of ester.

5) To answer this part, focus on path 1 followed by tetrahedral intermediate. Water is released in the 2nd step and hence on the product side. If we use water as the solvent, there is plenty of water to drive the reaction backward to form the tetrahedral intermediate again. Hence, reduces the ester yield.

It is advised to perform esterification in carboxylic acid or alcohol as the solvent.

6) You have solved it correctly.