Esters are one member of the group of compounds that are referred to as carboxylic acid derivatives. As shown by the examples of the various classes of carboxylic acid derivatives below, these have the general formula RCOX where the group X has an electronegative atom bonded to the carbonyl carbon.
Acyl chlorides are the most reactive of these compounds. As shown in the scheme at the right, acyl chlorides are converted rapidly, on reaction with an appropriate reagent to an ester, an amide or a carboxylic acid. The overall reaction is substitution with HCl being a co-product of the reaction.
In addition when treated with the reagent shown over the arrow, any of the carboxylic acid derivatives can be converted to a carboxylic acid derivative below it in the diagram.
Thus esters may be prepared from reaction of an acid chloride with an alcohol.
Acyl chlorides may be prepared from the reaction of a carboxylic acid with SOCl2**. Unlike the other reactions on this page, this reaction converts a carboxylic acid to a more reactive carboxylic acid derivative. This is because SOCl2 activates the OH on the carboxylic acid so that it is displaced by Cl.
**PCl5 is an alternative reagent specified by some exam boards for courses that use BestChoice.
SOCl2 is the preferred reagent because the co-products of the reaction are gases (HCl and SO2).
This makes isolation of the product more straightforward.
 |  |
| acid chloride | ester |
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| amide | propanoic acid |
Acyl chlorides are the most reactive of these compounds. As shown in the scheme at the right, acyl chlorides are converted rapidly, on reaction with an appropriate reagent to an ester, an amide or a carboxylic acid. The overall reaction is substitution with HCl being a co-product of the reaction.
In addition when treated with the reagent shown over the arrow, any of the carboxylic acid derivatives can be converted to a carboxylic acid derivative below it in the diagram.
Thus esters may be prepared from reaction of an acid chloride with an alcohol.
Acyl chlorides may be prepared from the reaction of a carboxylic acid with SOCl2**. Unlike the other reactions on this page, this reaction converts a carboxylic acid to a more reactive carboxylic acid derivative. This is because SOCl2 activates the OH on the carboxylic acid so that it is displaced by Cl.
**PCl5 is an alternative reagent specified by some exam boards for courses that use BestChoice.
SOCl2 is the preferred reagent because the co-products of the reaction are gases (HCl and SO2).
This makes isolation of the product more straightforward.