Chapter 15: Carboxylic Acids and Esters

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CARBOXYLIC ACIDS

• The functional group of carboxylic acids is the carboxyl group.

• Many carboxylic acids have common names.

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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:

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

Example:

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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). 6

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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.

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ACIDITY OF CARBOXYLIC ACIDS

• Carboxylic acids behave as weak acids (low dissociation), forming carboxylate ions in water.

Example:

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SALTS OF CARBOXYLIC ACIDS

• Carboxylic acids react readily with strong bases (NaOH, KOH) to form salts.

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Examples:

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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: 12

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.

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CARBOXYLIC ESTERS

• The ester functional group with the ester linkage between the carbonyl carbon and the oxygen atom: 14

ESTERS, cont.

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

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Examples:

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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.

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ESTERS, cont.

Examples: 18

ESTERS, cont.

Specific Examples:

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ESTERS, cont.

• Polyesters – polymers made by the esterification process. An example of condensation polymerization.

n(monomers)  (polymer) n + nH 2 O 20

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.

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NAMING ESTERS, cont.

Examples: Click here to play Coached Problem Click here to play Coached Problem 22

ESTER REACTIONS

• Ester hydrolysis – the reverse of esterification 23

Specific Examples:

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ESTER REACTIONS, cont.

• Saponification – similar to hydrolysis, but carried out with a strong base to produce a carboxylic acid salt 25

Examples:

Click here to play Coached Problem 26

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Esters of Inorganic Acids

• Esters can be formed by reacting alcohols with inorganic acids such as sulfuric, nitric, or phosphoric acids 28

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.

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PHOSPHORIC ANHYDRIDES

• Phosphate esters that have two or three phosphate groups linked together: 30

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

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