chapter 17 carboxylic acids and esters -...

1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.

17.1 Carboxylic Acids17.2 Physical Properties of Carboxylic

Acids17.3 Acidity of Carboxylic Acids

Chapter 17 Carboxylic Acids And Esters


The carboxyl group:Is a carbonyl group (C=O) attached to a hydroxyl group (OH).Is found on carbon 1 in carboxylic acids.Is written in different ways.

O||

CH3—C—OH CH3—COOH CH3—CO2H

Carboxyl Group


Models of Carboxylic AcidsThe three-dimensional models show the geometry of atoms in carboxylic acid molecules.


The IUPAC names of carboxylic acids: Replace the -e in the alkane name with -oic acid.CH4 methane HCOOH methanoic acidCH3—CH3 ethane CH3—COOH ethanoic acidNumber substituents from the carboxyl carbon 1.

CH3|

CH3—CH—CH2—COOH4 3 2 1

2-methylbutanoic acid

IUPAC Names


The common names of simple carboxylic acids:Use formic acid (1C), acetic acid (2C), propionic acid (3C), and butyric acid (4C). HCOOH formic acidCH3—COOH acetic acidLocate substituents by assigning α, β, γ to the carbon atoms adjacent to the carboxyl carbon.

CH3γ β| αCH3—CH—CH2—COOH

β-methylbutryic acid

Common Names


Names and Sources of Some Carboxylic Acids


Aromatic Carboxylic AcidsBenzoic acid:

Is the aromatic carboxylic acid.Locates substituents by assigning 1 to the carbon attached to the carboxyl group.Has common names that assign prefixes ortho, meta, and para for 2 substituents.ortho 1, 2 locationmeta 1, 3 locationpara 1, 4 location


Aromatic Carboxylic Acids

Benzoic acid

4-Aminobenzoic acidp-Aminobenzoic acid

3-Chlorobenzoic acid m-Chlorozenoic acid

COOH

NH2

COOH

Cl

COOH


Alpha Hydroxy Acids Alpha hydroxyacids (AHAs):Occur naturally in fruit, milk, and sugarcane.Are used in skin care products.


Preparation of Carboxylic Acids

Carboxylic acid can be prepared by oxidizing primary alcohols or aldehydes.The oxidation of ethanol produces ethanoicacid (acetic acid).

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

CH3—CH2 CH3—C—H CH3—C—OH

Ethanol ethanal ethanoic acidEthyl alcohol acetaldehyde acetic acid


Give the IUPAC and common names:A. CH3—COOH

CH3|

B. CH3—CH—COOH

C.COOH

Br

Learning Check


A. CH3—COOH ethanoic acid; acetic acidCH3|

B. CH3—CH—COOH 2-methylpropanoic acid;α-methylpropionic acid

C. 2-bromobenzoic acid;o-bromobenzoic acid

COOH

Br

Solution


Boiling Points Carboxylic acids:Have higher boiling points than alcohols, ketones, and aldehydes of similar mass.Form dimers in which hydrogen bonds form between two carboxyl groups.

O H—O|| |

CH3 —C C—CH3| ||O—H O

A dimer of acetic acid


Solubility in WaterCarboxylic acids:

With 1-4 carbon atoms are very soluble in water.Form hydrogen bonds with many water molecules.


Boiling Points and Solubility


Acid Dissociation Constants

Carboxylic acids:Are weak acids.CH3—COOH + H2O

CH3—COO– + H3O+

Exist mostly as molecules and a few ions in aqueous solutions.Have small Ka values.


Salts of Carboxylic Acids

Carboxylic acid salts are:Formed when a carboxylic acid is neutralized by a strong base.CH3—COOH + NaOH CH3—COO- Na+ + H2Oacetic acid sodium acetate

(carboxylic acid salt)

Used as preservatives and flavor enhancers.


Learning CheckWrite the equation for the reaction of propanoic acid with:A. water

B. KOH


SolutionWrite the equation for the reaction of propanoic acid with:A. waterCH3—CH2—COOH + H2O

CH3—CH2—COO– + H3O+

B. KOHCH3—CH2—COOH + KOH

CH3—CH2—COO– K+ + H2O


In amides, an amino group replaces the –OH group of carboxylic acids.

O O|| ||

CH3 — C — OH CH3 — C — NH2

Amides


Preparation of AmidesAmides are produced by reacting a carboxylic acid with ammonia or an amine (1° or 2°).

O O|| heat ||

CH3—C—OH + NH3 CH3—C—NH2 + H2O

O O|| ||

CH3—C—OH + CH3—NH2 CH3—C—NH—CH3+ H2O


Amides are named as alkanamides.In the IUPAC and common names, the –oic acid or -ic acid endings are replaced by –amide.

O|| Methanamide (IUPAC)

H—C—NH2 Formamide (common)O|| Propanamide (IUPAC)

CH2—CH2—C —NH2 Propionamide (common)

Naming Amides


An alkyl group bonded to the N atom is named as N-alkyl in front of the amide name.

O||

CH—C—NH —CH3 N-methylethanamide (IUPAC)N-methylacetamide (common)

O CH3 || |

CH2—CH2—C —N —CH3 N,N-dimethylpropanamideN,N-dimethylpropionamide

Naming Amides with N Groups


Aromatic AmidesThe amide of benzene is named benzamide.

C

O

NH2

Benzamide

C

O

NH CH3

N methylbenzamide -


Classification of AmidesAmides are classified according to the number of carbon atoms bonded to the nitrogen atom.

O H|| |

CH3—C—N—H Primary (1°) amide O H|| |

CH3—C—N—CH3 Secondary (2°) amideO CH3|| |

CH3 —C—N—CH3 Tertiary (3°) amide


Give the common and IUPAC names for the following amides and classify as primary, secondary, or tertiary:

O||

A. CH3—CH2—CH2—C—NH2

O CH3|| |

B. CH3—C—N—CH2—CH3

Learning Check


O||

A. CH3—CH2—CH2—C—NH2butryamide (common); butanamide (IUPAC) primary(1°) amide

O CH3|| |

CH3—C—N—CH2—CH3N-ethyl-N-methylacetamide (common);N-ethyl-N-methylethanamide (IUPAC)tertiary (3°) amide

Solution


Draw the condensed structures of A. Pentanamide

B. N-methylbenzamide

Learning Check


A. PentanamideO||

CH3—CH2—CH2 —CH2—C—NH2

B. N-methylbenzamide

Solution


Amides in Health and MedicineUrea is the end product of protein metabolism.Saccharin is an artificial sweetener.Some amides such as phenobarbital, Nembutal and Seconal are barbiturates.Acetaminophen is used to reduce fever and pain.


Amides in Health and Medicine


Physical Properties of AmidesHydrogen bonds form in primary and secondary amides, but not tertiary amides. The melting points of primary amides are higher than secondary amides, which have higher melting points than tertiary amides. All amides can form hydrogen bonds with water.Amides with 1–5 carbon atoms are soluble in water.


Hydrogen Bonding of AmidesO ||

CH3—C—N—H |H Hydrogen bonding occurs

between primary amides.

O ||

CH3—C—N—H|H


Amides undergo:Acid hydrolysis to produce a carboxylic acid and ammonium salt.

Base hydrolysis to produce the salt of a carboxylic acid and an amine or ammonia.

Reactions of Amides


acid hydrolysis O ||

CH3—C—OH + NH4+Cl-

Hydrolysis Reactions

O ||

CH3—C—NH2

O ||

CH3—C—O-Na+ + NH3

HCl + H2O

NaOH

base hydrolysis


Write the products of the hydrolysis of N-ethylpropanamide with NaOH.

Learning Check


Write the products of the hydrolysis of N-ethylpropanamide with NaOH.

O ||

CH3—CH2—C—O-Na+ + CH3 —CH2 —NH2

Solution


17.4 Esters of Carboxylic Acids17.5 Naming Esters17.6 Properties of Esters

Chapter 17 Carboxylic Acids And Esters


In an ester, the H in the carboxyl group is replaced by an alkyl group.

O||

CH3—C—O—CH3CH3—COO—CH3

ester group

Esters


An ester is produced by the reaction of a carboxylic acid and alcohol in the presence of an acid catalyst.

O|| H+

CH3—C—OH + HO—CH2—CH3

O||

CH3—C—O—CH2—CH3 + H2O

Esterification


Ester ProductsAspirin:

Is used to relieve pain and reduce inflammation.Is an ester of salicylic acid and acetic acid.

Oil of wintergreen:Is used to soothe sore muscles. Is an ester of salicylic acid and methanol.

C

O

OH

O C

O

CH3

Acetylsalicylic acid(Aspirin)

C

O

O CH3

OH

Methyl salicylate(Oil of wintergreen)


Write the equation for the reaction of propionic acid and methyl alcohol in the presence of an acid catalyst.

Learning Check


Write the equation for the reaction of propionic acid and methyl alcohol in the presence of an acid catalyst.

O|| H+

CH3—CH2—C—OH + HO—CH3

O||

CH3—CH2—C—O—CH3 + H2O

Solution


Esters are named with the alkyl name of the alcohol followed by the carboxylate name from the acid. from acid from alcohol

O|| methyl

CH3—C—O—CH3

Ethanoate methyl ethanoate (IUPAC)(Acetate) methyl acetate (common)

Naming Esters


Esters give fruits their pleasant fragrances and flavors.

Some Esters In Nature


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

O||

CH3—C—O—CH2—CH2—CH3

Learning Check


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

from 1-propanolO||

CH3—C—O—CH2—CH2—CH3

Propyl ethanoate (IUPAC)Propyl acetate (common)

Solution


Draw the structure of the following compounds:

A. Butyl acetate

B. Ethyl propionate

Learning Check


A. Butyl acetateO||

CH3—C—O—CH2 —CH2 —CH2 —CH3

B. Ethyl propionateO||

CH3—CH2—C—O—CH2 —CH3

Solution


In hydrolysis: An ester reacts with water to produce a carboxylic acid and an alcohol.An acid catalyst is required.

O|| H+

H—C—O—CH2—CH3 + H2OO||

H—C—OH + HO—CH2 —CH3

Hydrolysis


In base hydrolysis or saponification, an ester reacts with a strong base to produce the salt of the carboxylic acid and an alcohol.

O||

CH3—C—O—CH2—CH3 + NaOH

O||

CH3—C—O-Na+ + HO—CH2—CH3salt of carboxylic acid alcohol

Base Hydrolysis (Saponification)


Base Hydrolysis of Fatty Acids Produces Soaps


Cleaning Action of SoapA soap:

Contains a nonpolar carbon end that dissolves in nonpolar fats and oils, and a polar end that dissolves in water.Forms groups of soap molecules called micelles that dissolve in water and are washed away.


Write the organic products when methyl acetate reacts with:A. Water and an acid catalyst

B. KOH

Learning Check


Write the organic products when methyl acetate reacts with:A. Water and an acid catalyst

O ||

CH3—C—OH + HO—CH3B. KOH

O ||

CH3—C—O- K+ + HO—CH3

Solution

chapter 17 carboxylic acids and esters -...

Documents