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Carboxylic Acids and Esters,

Carboxylic Acids

Properties of Carboxylic Acids

Esters

Esterification and Hydrolysis

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Carboxyl Group

Carboxylic acids contain the carboxyl group on carbon 1. It will be the first carbon of the parent chain.

O

CH3 — C—OH = CH3—COOH

carboxyl group

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Naming Carboxylic Acids

Formula IUPAC Common alkan -oic acid prefix – ic acid

HCOOH methanoic acid formic acid

CH3COOH ethanoic acid acetic acid

CH3CH2COOH propanoic acid propionic acid

CH3CH2CH2COOH butanoic acid butyric acid

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Naming Rules

• Identify longest chain• (IUPAC) Number carboxyl carbon as 1• Name side chains alphabetically

CH3

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CH3 — CH—CH2 —COOHIUPAC 3-methylbutanoic acid

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Naming Practice

Give IUPAC and common names:

A. CH3COOH

CH3

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B. CH3CHCOOH

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Solution

A. CH3COOH

ethanoic acid; acetic acid

CH3

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B. CH3CHCOOH

2-methylpropanoic acid

Draw the Structures

• 3-methyl-4-phenylhexanoic acid

• pentanedioic acid

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Properties

• Carboxylic acids are weak acids. They can be found in citrus fruits and others with a sour taste. Vitamin C and ASA are other common carboxylic acids.

CH3COOH + H2O CH3COO– + H3O+

• Neutralized by a base

CH3COOH + NaOH CH3COO– Na+ + H2O

Properties

• The carboxyl groups consists of a polar hydroxyl group bonded to the carbon of a carbonyl group. The presence of the polar carbonyl and polar hydroxyl groups makes carboxylic acids able to hydrogen bond with themselves and water.

• The smallest members (carbons 1-4) are soluble in water. As the alkyl group (CH) becomes longer, the polarity of the molecule decreases as does the solubility in water.

• Melting point increases with the size of the molecule. Analogous acids with multiple carboxyl groups have higher melting points.

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Learning Check

• Compare the melting point and solubility in water of:

1-butanol

• butanal

• butane

• butanoic acid

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Solution

• Lowest to highest melting point and solubility:

• Butane (nonpolar, LDF only)

• Butanal (polar, LDF, DDF, no hydrogen bonding with self )

• 1-Butanol (polar, LDF, DDF, hydrogen bonding with self and water)

• Butanoic Acid (most polar functional group, LDF, DDF, hydrogen bonding with self and water)

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Reactions of Carboxylic Acids

• Oxidation of a Primary Alcohol to Aldehyde

• Further Oxidation to a Carboxylic Acid

• *Ketones are not oxidized further

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Esters

In and ester, the H in the carboxyl group is replaced with an alkyl group (COO)

O

CH3 — C—O —CH3 = CH3—COO —CH3

ester group

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Esters in Plants

Esters give flowers and fruits their pleasant fragances and flavours.

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Naming Esters

• Name the alkyl from the alcohol –O-• Name the acid with the C=O with –ate (drop “ic” from

acid name and and “ate)

acid alcohol

O

methyl

CH3 — C—O —CH3

Ethanoate methyl ethanoate (IUPAC)

(acetate) methyl acetate (common)

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Some Esters and Their Names

Flavor/Odour

Raspberries

HCOOCH2CH3 ethyl methanoate

(IUPAC)

ethyl formate (common)

Pineapples

CH3CH2CH2 COOCH2CH3

ethyl butanoate (IUPAC)

ethyl butyrate (common)

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Practice

Give the IUPAC and common names of the following compound, which is responsible for the flavor and odour of pears.

O

CH3 — C—O —CH2CH2CH3

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Solution

Oethanoic acid propyl (propanol)

CH3 — C—O —CH2CH2CH3

propyl ethanoate (IUPAC)

propyl acetate (common)

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Practice

Draw the structure of the following compounds and name the alcohol and acid used to synthesize the ester:

A. 3-bromobutanoic acid

B. Ethyl propanoate

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Solution CA 3

A. 3-bromobutanoic acid

Br

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CH3CHCH2COOH

B. Ethyl propanoate (ethanol and propanoic acid)

O

CH3 CH2 COCH2CH3 CH3CH2COOCH2CH3

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Esterification

• Reaction of a carboxylic acid and alcohol• Acid catalyst and heat

O H+

CH3 — C—OH + HO—CH2CH3

O

CH3 — C—O—CH2CH3 + H2O

Ester Practice

• Illustrate the reaction between the acids and alcohols listed and name the ester

• (i) 3-methylbutanoic acid and methanol

• (ii) benzoic acid and ethanol

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Solution

• (i)

• (ii)

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Hydrolysis

• Esters react with water and acid catalyst• Split into carboxylic acid and alcohol

O H+

H — C—O—CH2CH3 + H2O

O

H — C—OH + HO—CH2CH3

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Saponification

• Esters react with a bases • Produce the salt of the carboxylic acid and

alcohol O

CH3C—OCH2CH3 + NaOH

O CH3C—O– Na+ + HOCH2CH3

salt of carboxylic acid

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More Practice

Write the equation for the reaction of pentanol and 3-chlorobutanoic acid in the presence of an acid catalyst.

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Solution

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Reaction Practice

What are the organic products when methylacetate (ethanoate) reacts with

A. Water and an acid catalyst?B. KOH?

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Solution

A.

O

CH3COH + HOCH3

O

B. CH3CO– K+ + HOCH3

POLYESTERS

• Esters can form long chain polymers called polyesters.

• Examples

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Properties of Esters

• The loss of the polar OH group in the esterification rxn results in esters being less polar, less soluble in water than their parent carboxylic acids and alcohols.

Lower mass esters are detected by scents because they are gases at room temperature. Larger, heavier esters tend to be waxy solids.

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