In: Chemistry
1) if the cost of both the alcohol and carboxylic acid were prohibitive, how would you maximize the use of your Fischer esterification product while keeping costs down?
2) why did you wash your product with water before washing it with the solution of sodium bicarbonate? What was the purpose of washing with sodium bicarbonate? What would ha byppen if saturated NaOH solution was used instead?(the product is an ester, oil of winter green)
3) explain the function of the acid catalyst in a Fischer esterification reaction. Show a mechanism to illustrate your explanation.
1) If the cost of both the alcohol and carboxylic acid were prohibitive, one would use a acid as the catalyst for the Fischer esterification process. The acid would increase the electrophilicity of the electrophile in the reaction and alcohol would than attack this highly electrophilic species to yield maxium product from this reaction.
2) Washing with water ensures all of the acid used as the catalyst is washed off from the reaction system. Acid-base reaction is exothermic in nature, which generates a lot of heat and may cleave the ester product (reversal of esterification) formed in the reaction. Thus water wash is essential prior to addition of any base (NaHCO3 in this case) in the reaction mixture. Once this is done, NaHCO3 (aq) is added to remove any remaining acid present in the reaction. NaOH is a strong base and would end up hydrolysing the ester product back to the carboxylate. Hence NaOH cannot be used for washing the reaction mixture.
3) The acid protonates the C=O oxygen and generates a more electrophilic carbon center. This is then attacked by the nucleophile alcohol oxygen to form ester product as shown below.