chapter 15 carboxylic acids and esters spencer l. seager michael r. slabaugh jennifer p. harris

Chapter 15Carboxylic Acids and Esters

Spencer L. SeagerMichael R. Slabaugh

www.cengage.com/chemistry/seager

Jennifer P. Harris

CARBOXYLIC ACIDS• The functional group of carboxylic acids is the carboxyl

group.

• Many carboxylic acids have common names.

CARBOXYLIC ACID EXAMPLES

CARBOXYLIC ACID EXAMPLES (continued)

FATTY ACIDS• Fatty acids are carboxylic acids with long hydrocarbon

chains, generally 12 to 20 carbon atoms.• They were first isolated from natural fats.• These fats are known almost exclusively by their common

names.

lauric acid

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:

CARBOXYLIC ACIDS IUPAC NOMENCLATURE (continued)• 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 OF CARBOXYLIC ACIDS (continued)

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS (continued)

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS (continued)• –COOH groups can hydrogen bond with water. If the

hydrophobic –R group is not too large, carboxylic acids are very water soluble.

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS (continued)

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.

SALTS OF CARBOXYLIC ACIDS (continued)

• Examples:

SALTS OF CARBOXYLIC ACIDS (continued)

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

• Example:

SALTS OF CARBOXYLIC ACIDS (continued)

• The physical properties of carboxylic acid salts:• Solids at room temperature• Usually soluble in water because they are ionic

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.

USEFUL CARBOXYLIC ACID SALTS (continued)• A mixture of sodium citrate and citric acid is widely used as a

buffer to control pH. • The buffer can be found in:• Jelly• Ice cream• Candy• Whipped cream• Medicines• Human blood for transfusions (also an anticoagulant)

CARBOXYLIC ESTERS• The ester functional group with the ester linkage between

the carbonyl carbon and the oxygen atom:

CARBOXYLIC ESTERS (continued)• The ester functional group is a key structural feature in fats,

oils, and other lipids.• The ester functional group is also found in fruits and flowers.• Many esters are fragrant and represent some of nature’s

most pleasant odors.• Esters are commonly used as flavoring agents in foods and

scents in personal products.

CARBOXYLIC ESTERS (continued)• Esterification is the process of forming an ester linkage

between a carboxylic acid and an alcohol.

CARBOXYLIC ESTERS (continued)• Examples:

CARBOXYLIC ESTERS (continued)• 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.

CARBOXYLIC ESTERS (continued)• General reactions:

CARBOXYLIC ESTERS (continued)• Specific Examples:

CARBOXYLIC ESTERS (continued)• Polyesters are polymers made by the esterification process.• Polyesters formation is an example of a condensation

polymerization, in which monomers form a polymer and a small molecule is also formed.

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 (continued)• Examples:

ESTER REACTIONS• Ester hydrolysis is the reverse of esterification.

• Enzyme-catalyzed hydrolysis of the esters in animal fats and vegetable oils is an important process that takes place when the fats and oils are digested by the human body and other biological organisms.

ESTER REACTIONS (continued)• Specific Examples:

ESTER REACTIONS (continued)• Saponification is similar to hydrolysis, but is carried out with

a strong base to produce a carboxylic acid salt.

ESTER REACTIONS (continued)• Example:

ESTER SAPONIFICATION• Carbonyl carbon attracts hydroxide, double bond breaks

• Double bond reforms, ester linkage breaks

• Carboxylic acid forms, but donates it proton to the strongly basic anion to form alcohol

REACTION MAP FOR CARBOXYLIC ACIDS

ESTERS OF INORGANIC ACIDS• Esters can be formed by reacting alcohols with inorganic

acids such as sulfuric, nitric, or phosphoric acids.

ESTERS OF INORGANIC ACIDS (continued)

• Because phosphoric acid has three –OH groups, it can form mono-, di-, and triesters.

ESTERS OF INORGANIC ACIDS (continued)

• Mono- and diesters are very important biologically.

• At body pH, the two –OH groups of the phosphoric acid are ionized, and the phosphate group has a charge of 2-.

PHOSPHORIC ANHYDRIDES• Phosphoric anhydrides are phosphate esters that have two

or three phosphate groups linked together.

PHOSPHORIC ANHYDRIDES (continued)

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

• At the pH of body fluids, the –OH groups attached to the phosphorus lose H+ and acquire negative charges.

• At the pH of body fluids, the charge on ADP is 3-.

PHOSPHORIC ANHYDRIDES (continued)

• At the pH of body fluids, the –OH groups attached to the phosphorus lose H+ and acquire negative charges.

• At the pH of body fluids, the charge on ATP is 4-.