Esterification
Esters are highly volatile organic compounds with distinctively sweet aromas and tastes. They are responsible for flavours and smells of many fruits.
Esters can be formed in two distinct methods.
The first you may have practised is the reaction of a carboxylic acid with an alcohol. This forms the ester and water. The hydrogen from the COOH group in the acid is removed, as is the -OH group from the alcohol. This leaves the RC=OO from the acid and the CR3 from the acid which react together to form the functional ester group C=OOC. Hence the standard reaction can be written thusly:
Alcohol + Carboxylic Acid 
Ester + Water
or
R3C-OH + RC=OOH R3COO=CR + H2O
This method requires the warming of the acid (in glacial form, that is the pure acid, free of water) and alcohol together in presence of a sulphuric acid catalyst.
The second way is the reaction of an acid anhydride (in place of the carboxylic acid) and alcohol. The acids anhydrides are reactive compounds which can be made from carboxylic acids and their salts. Their structure can be represented as such:
RC=OOO=CR (My attempt to represent an acid anhydride using displayed formula can be seen below).
Benefits of this method include the fact that this reaction is non-reversible - unlike the acid/alcohol route - and that no catalyst is required.
The reaction is also different in that in place of water, a carboxylic acid is formed alongside the ester. Hence we can write the equation generally as:
Acid anhydride + Alcohol → Ester + Carboxylic acid
or
RC=OOO=CR + R3COH → RCOOCR3 + RCOOH
