[Jazzified]

Hello.  I need help with the following questions:

All of the questions relate to the equation:
benzoic acid + methanol + sulfuric acid <--> methyl benzoate + water

1. Suppose that during extraction, the washes with aqueous base were omitted in the workup of methyl benzoate.  What problems could result?

2. Why would the choice of solid potassium hydroxide as a drying agent for the ester be a bad one?

I know I won't get answers simply given to me, but may I please get some guidance on how to approach these questions?  Thanks in advance.

[Custos]

1. After the reaction is complete what has happened to the sulfuric acid? What might help to get rid of it?

2. The reverse of esterification is hydrolysis. What kind of reagents could you use for this (unwanted) reaction?

[Jazzified]

1. After the reaction is complete what has happened to the sulfuric acid? What might help to get rid of it?

2. The reverse of esterification is hydrolysis. What kind of reagents could you use for this (unwanted) reaction?

1. The sulfuric acid enhances the reactivity of the benzoic acid to make it reactive enough to be attacked by methanol.  A lack of water might help to get rid of it?

2. Water is needed for hydrolysis.

This is leading up to something, right lol?

This made me think...would these be appropriate answers:

1. If the washes with aqueous base were omitted in the workup of methyl benzoate, the problems that could result are a lower yield during ether extraction, the acidity of the mixture would increase, and hydroxide ions and hydrogen gas would form as products (instead of water).

2. The choice of solid potassium hydroxide as a drying agent for the ester would be a poor one.  Since it is a strong base, it would cause the reaction to go in the reverse direction, moving towards the reactant side of the reaction.

[Custos]

1. Yes, the sulfuric acid enhances the reactivity of the benzoic acid to make it reactive enough to be attacked by methanol. But in the final product there is still someresidual sulfuric acid. Washing with aqueous base helps neutralise that reside and wash it out of your product.

2. That's correct. You have probably heard the term "saponification". That's a process of treating fatty esters with hydroxide (early soap makers used potash or lye) to hydrolyse the ester and form soaps - the soaps are actually long chain acid salts.

[Jazzified]

1. Yes, the sulfuric acid enhances the reactivity of the benzoic acid to make it reactive enough to be attacked by methanol. But in the final product there is still someresidual sulfuric acid. Washing with aqueous base helps neutralise that reside and wash it out of your product.

2. That's correct. You have probably heard the term "saponification". That's a process of treating fatty esters with hydroxide (early soap makers used potash or lye) to hydrolyse the ester and form soaps - the soaps are actually long chain acid salts.

Thank you for your help.  For #1 though, is my answer of If the washes with aqueous base were omitted in the workup of methyl benzoate, the problems that could result are a lower yield during ether extraction, the acidity of the mixture would increase, and hydroxide ions and hydrogen gas would form as products (instead of water). correct?  Or should I just say that the problems that could result are residual sulfuric acid remaining in the product?

[Custos]

The problems that could result is residual sulfuric acid remaining in the product. When you then evaporate off the ether the residual sulfuric acid will become concentrated and this can lead to decomposition of your product.

[Jazzified]

The problems that could result is residual sulfuric acid remaining in the product. When you then evaporate off the ether the residual sulfuric acid will become concentrated and this can lead to decomposition of your product.

Okay cool, thank you for your *delete me*