Wax ester

A wax ester (WE) is an ester of a fatty acid and a fatty alcohol.

Wax esters are formed by combining one fatty acid with one fatty alcohol molecule. Alcohols have a hydroxyl (HO-) group. Organic acids have a carboxyl (-COOH) group. Alcohols and organic acids join to form esters. In wax esters, the hydroxyl groups of the fatty alcohols joins the carboxyl groups of the fatty acids to form ester bonds.

${\displaystyle RCOOH+R^{\prime }OH\rightleftharpoons RCOOR^{\prime }+H2O}$

There are different types of wax esters, with the main differences being between saturated and unsaturated types. Saturated wax esters have a higher melting point and are more likely to be solid at room temperature. Unsaturated wax esters have a lower melting point and are more likely to be liquid at room temperature. Both fatty acids and fatty alcohols may be of different carbon chain length. In the end, there are many different possible combinations of fatty acids and fatty alcohols and each combination will have a unique set of properties in terms of steric orientation and phase transition.

The chain lengths of fatty acids and fatty alcohols in naturally occurring wax esters vary. The fatty acids in wax esters derived from plants typically range from C12-C24, and the alcohols in plant waxes tend to be very long, typically C24-C34. The fatty acids and fatty alcohols of wax esters from different marine animals show major differences. Wax esters of sperm whales contain C12 fatty acids and C14 fatty acid and alcohols. Monounsaturated C18 is the dominant fatty acid of most fish wax esters, with the exception of roe wax esters, which have sizeable amounts of polyunsaturated fatty acids such as 20:5n-3, 22:5n-3 and 22:6n-3. The fatty acids of wax esters of certain zooplankton largely reflects the fatty acids of phytoplankton, and contain high amounts of C14 and C16, as well as 20:5n-3, 22:5n-3 and 22:6n-3 and monounsaturated C20 and C22 are the principal fatty alcohols.

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