Carboxylic Acids (R-COOH)
The carboxylic acid family contains the carboxyl group (-COOH), which is a combination of the carbonyl group and the hydroxyl group.
If wine is left open, vinegar is produced, thus carboxylic acids are produced from alcohols.
Carboxylic acids are found in citrus fruit, crab apples, rhubarb and other foods with a sour taste. The muscle ache we feel after exertion is caused by lactic acid.
Physical Properties of the Carboxylic Acids
Carboxylic acids are polar (C=O and –OH groups) and can hydrogen bond (–OH group)
They have high melting points when compared to similar hydrocarbons.
They are similar in solubility to the alcohols, i.e. simple carboxylic acids are water soluble, while larger carboxylic acids are insoluble.
They have all the properties of acids and can react with bases in neutralization reactions.
Esters (R-COO-R′)
An ester is similar to an acid, with an alkyl group is attached to the oxygen in the chain.
Esters are responsible for the odours of fruit and flowers; synthetic esters are often added to foods and cosmetics.
Physical Properties of the Esters
With the loss of the –OH group, esters are less polar than carboxylic acids and are unable to H-bond.
They are less water soluble, have lower mp and bp.
It is the low molecular weight esters that have detectable scents, since they are gases at RT.
Preparing Esters
An ester is created by combining an alcohol and an acid in an esterification reaction.
Homework:
Practice, p. 220 #1-4
Practice, p. 225 #1-3
Answers:
