16. carboxylic acids

8/2/2019 16. Carboxylic Acids

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Chapter 16 Carboxylic Acids and

Esters

16.1

Carboxylic Acids

Copyright 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings


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A carboxylic acid

Contains a carboxyl group, which is a carbonyl group(C=O) attached to a hydroxyl group (OH).

Has the carboxyl group on carbon 1.

carbonyl group

O

CH3 COH hydroxyl group or CH3COOH

carboxyl group

Carboxylic Acids


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Models of Carboxylic Acids

The three-dimensional models show the geometryof atoms in carboxylic acid molecules.



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The IUPAC names of carboxylic acids

Replace the -ein the alkane name with -oic acid.

CH4 methane HCOOH methanoic acid

CH3CH3 ethane CH3COOH ethanoic acid

Number substituents from the carboxyl carbon 1.

CH3 O|

CH3CHCH2COH4 3 2 1

3-methylbutanoic acid

IUPAC Names


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The common names of simple carboxylic acids

Are formic acid (1C), acetic acid (2C), propionic acid(3C), and butyric acid (4C).

HCOOH formic acidCH3COOH acetic acid

Locate substituents using , , for the carbonatoms adjacent to the carboxyl carbon.

CH3 | CH3CHCH2COOH

3-methylbutanoic acid (-methylbutryic acid)

Common Names


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Alpha Hydroxy AcidsAlpha hydroxy acids

(AHAs)

Occur naturally in

fruit, milk, andsugarcane.

Are used in skincare products.



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Names and Sources of Some

Carboxylic Acids

TABLE 16.1

Copyright 2007 by Pearson Education, Inc.

Publishing as Benjamin Cummings


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Aromatic Carboxylic Acids

Benzoic acid

Is the aromatic carboxylic acid.

Locates substituents by assigning 1 to the carbonattached to the carboxyl group.

Has common names that assign prefixes ortho,meta, and parafor 2 substituents.

ortho 1, 2 locationmeta 1, 3 location

para 1, 4 location


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Aromatic Carboxylic Acids

OHC

O

OHC

O

OHC

O

Cl

NH2

benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid

m-chlorobenzoic acid p-aminobenzoic acid


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Give the IUPAC and common names:

A. CH3COOH

CH3|

B. CH3CHCOOH

C.

Learning Check

COOH

Br


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A. CH3COOH ethanoic acid (acetic acid)CH3|

B. CH3CHCOOH 2-methylpropanoic acid(-methylpropionic acid)

C. 2-bromobenzoic acid

(o-bromobenzoic acid)

Solution

COOH

Br


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Preparation of Carboxylic Acids

Carboxylic acids can be prepared by oxidizingprimary alcohols or aldehydes.

The oxidation of ethanol produces ethanoic acid

(acetic acid).

OH O O| [O] || [O] ||

CH3CH2 CH3CH CH3COH

ethanol ethanal ethanoic acid(ethyl alcohol) (acetaldehyde) (acetic acid)


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Learning Check

What alcohol could be used to prepare the following:

1. butanoic acid

2. propanoic acid


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Solution

What alcohol could be used to prepare the following:

[O] [O]

1. butanol butanal butanoic acid

[O] [O]

2. 1-propanol propanal propanoic acid


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16.2Properties of Carboxylic Acids


Esters



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Polarity of Carboxylic AcidsCarboxylic acids

Are strongly polar.

Have two polar groups:

hydroxyl (OH) and carbonyl (C=O).

-

O

+

- +

CH3COH


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Boiling Points of Carboxylic AcidsThe boiling points of carboxylic acids

Are higher than alcohols, ketones, and aldehydes ofsimilar mass.

Are high because they form dimersin whichhydrogen bonds form between the polar groups in thetwo carboxyl groups.

O HO|| |CH3C CCH3

| ||OH O

A dimer of acetic acid


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Comparison of Boiling Points

Compound Molar Mass Boiling Point

O

CH3CH2CH 58 49C

CH3CH2CH2OH 60 97C

O

CH3COH 60 118C


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Solubility in Water

Carboxylic acids

Form hydrogenbonds with many

water molecules.

With 1-4 carbonatoms are very

soluble in water.

Water molecules



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Boiling Points and Solubility

TABLE 16.2

Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings


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Acidity of Carboxylic Acids

Carboxylic acids

Are weak acids.

Ionize in water to produce carboxylate ions

and hydronium ions.O O

CH3COH + H2O CH3CO + H3O+



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Neutralization of Carboxylic Acids

Carboxylic acid salts

Are a product of the neutralization of a carboxylic acidwith a strong base.

CH3COOH + NaOH CH3COONa+ + H2O

acetic acid sodium acetate

(carboxylic acid salt)

Areused as preservatives and flavor enhancers.




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Learning Check

Write the equation for the reaction of propanoic acid with

A. water

B. KOH


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Solution

Write the equation for the reaction of propanoic acid with

A. water

CH3CH2COOH + H2O CH3CH2COO + H3O+

B. KOH

CH3CH2COOH + KOH CH3CH2COO K+ + H2O


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Esters

16.3 Esters

16.4 Naming Esters



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Esters

In an ester,

The H in the carboxyl group is replaced

with an alkyl group.

OCH3 COCH3

ester group



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Esterification is

The reaction of a carboxylic acid and alcohol in thepresence of an acid catalyst to produce an ester.

O H+

CH3COH + HOCH2CH3

O

CH3COCH2CH3 + H2Oethyl acetate (an ester)

Esterification


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Write the equation for the reaction of propanoic acidand methanol in the presence of an acid catalyst.

Learning Check


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Write the equation for the reaction of propanoic acid

and methanol in the presence of an acid catalyst.

O

H+CH3CH2COH + HOCH3

propanoic acid methanolO

CH3CH2COCH3 + H2O

Solution


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Naming Esters

The name of an ester contains the names of

The alkyl group from the alcohol.

The carbon chain from the acid withateending.from alcohol from acid

O

methyl

CH3OC CH3ethanoate (acetate)

IUPAC: methylethanoate

common:methyl acetate


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Ester Products

Aspirin

Is used to relieve pain andreduce inflammation.

Is an ester of salicylic acidand acetic acid.

Oil of wintergreen

Is used to soothe sore

muscles. Is an ester of salicylic acid

and methanol.

CH3

O

CO

OH

O

C

OH

CH3O

O

C


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Esters in Plants

Esters giveflowers and

fruits their

pleasantfragrances andflavors.

TABLE 16.4



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Learning Check

Give the IUPAC and common names of the followingcompound, which is responsible for the flavor and odorof pears.

O

CH3COCH2CH2CH3


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Give the IUPAC and common names of the followingcompound, which is responsible for the flavor and odorof pears.

from 1-propanol

O

CH3COCH2CH2CH3

Propyl ethanoate (IUPAC)Propyl acetate (common)

Solution


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Learning Check

Name the following esters:O

A. CH3

CH2

CH2

C

O

CH3

O

B. CH3

CH2

COCH2

CH3


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Solution

A. Methyl butanoate (methyl butyrate)

B. Ethyl propanoate (methyl propionate)


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Learning Check

Write the structure of the following esters:

A. Ethyl pentanoate

B. Propyl butyrate


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Solution

A. Ethyl pentanoateO

CH3CH2CH2CH2COCH2CH3

B. Propyl butyrateO

CH3CH2CH2COCH2CH2CH3


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Esters

16.5

Properties of Esters



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In acid hydrolysis

An ester reacts with water to produce a carboxylicacid and an alcohol.

An acid catalyst is required.O H+

HCOCH2CH3 + H2O

OHCOH +HOCH2CH3

Acid Hydrolysis of Esters


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Base hydrolysis (also called saponification)

Is the reaction of an ester with a strong base.

Produces the salt of the carboxylic acid and analcohol.

O||

CH3COCH2CH3 + NaOHO

CH3CONa+ + HOCH2CH3salt of carboxylic acid alcohol

Base Hydrolysis (Saponification)


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Soaps

The base hydrolysis of long chain fatty acids

produces acid salts called soaps.



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Cleaning Action of Soap

A soap Contains a nonpolar

end that dissolves innonpolar fats and

oils, and a polar endthat dissolves inwater.

Forms groups ofsoap molecules

called micelles thatdissolve in waterand are washedaway.




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Write the organic products when methyl acetate reactswith

A. Water and an acid catalyst

B. KOH

Learning Check


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Write the organic products when methyl acetate reactswith:

A. Water and an acid catalystO

CH3COH + HOCH3

B. KOHO

CH3CO K+ + HOCH3

Solution

16. carboxylic acids

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