Chapter 15: Carboxylic Acids and Esters

CARBOXYLIC ACIDS The functional group of carboxylic acids is the carboxyl group. Many carboxylic acids have common names.

CARBOXYLIC ACIDS IUPAC NOMENCLATURE Find the longest carbon chain that contains the –COOH group. Drop the –e from the end of the hydrocarbon name and substitute –oic acid. Number the longest chain. Carbon number 1 is the carboxyl carbon. Name and number other substituents. Examples:

Aromatic acid names are derived from the parent compound, benzoic acid. Example:

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS Low molecular weight carboxylic acids are liquids at room temperature and have characteristically sharp or unpleasant odors. The –COOH group is very polar. Hydrogen bonding between –COOH groups creates dimers (two identical molecules bonded together). This gives carboxylic acids high boiling points (greater than alcohols).

PHYSICAL PROPERTIES, cont. –COOH groups can hydrogen bond with water. If the hydrophobic –R group is not too large, carboxylic acids are very water soluble.

ACIDITY OF CARBOXYLIC ACIDS Carboxylic acids behave as weak acids (low dissociation), forming carboxylate ions in water. Example:

SALTS OF CARBOXYLIC ACIDS Carboxylic acids react readily with strong bases (NaOH, KOH) to form salts.

Examples:

SALTS, cont. To name a carboxylic acid salt, name the metal ion first and change the –ic ending of the acid name to –ate. Example:

USEFUL CARBOXYLIC ACID SALTS Na+ and K+ salts of long-chain acids are used as soaps (sodium stearate). Calcium and sodium propanoate are used as preservatives in bakery products. Sodium benzoate is a food preservative used in ketchup and soda pop. Zinc 10-undecylenate is used to treat athlete’s foot.

CARBOXYLIC ESTERS The ester functional group with the ester linkage between the carbonyl carbon and the oxygen atom:

ESTERS, cont. Esterification is the process of forming an ester linkage between a carboxylic acid and an alcohol.

Examples:

ESTERS, cont. Because of the reversible nature of the esterification reaction, carboxylic acid chlorides and carboxylic acid anhydrides are used instead of the carboxylic acid to obtain higher product (ester) yields.

ESTERS, cont. Examples:

ESTERS, cont. Specific Examples:

n(monomers)  (polymer)n + nH2O ESTERS, cont. Polyesters – polymers made by the esterification process. An example of condensation polymerization. n(monomers)  (polymer)n + nH2O

NAMING ESTERS The first word of the name of an ester is the name of the alkyl or aromatic group (R') contributed by the alcohol. The second word is the carboxylic acid name, with the –ic acid ending changed to –ate.

NAMING ESTERS, cont. Examples: Click here to play Coached Problem Click here to play Coached Problem

ESTER REACTIONS Ester hydrolysis – the reverse of esterification

Specific Examples:

ESTER REACTIONS, cont. Saponification – similar to hydrolysis, but carried out with a strong base to produce a carboxylic acid salt

Click here to play Coached Problem Examples: Click here to play Coached Problem

Esters of Inorganic Acids Esters can be formed by reacting alcohols with inorganic acids such as sulfuric, nitric, or phosphoric acids

INORGANIC ACID ESTERS, cont. Because phosphoric acid has three –OH groups, it can form mono-, di-, and triesters. Mono- and diesters are very important biologically.

PHOSPHORIC ANHYDRIDES Phosphate esters that have two or three phosphate groups linked together:

Adenosine diphosphate (ADP) and adenosine triphosphate (ATP) are two phosphoric anhydrides of great biological importance. In each case, the R group is adenosine.