10.carboxylic acids

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CHAPTER 10CARBOXYLIC ACIDS

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2

INTRODUCTION

The functional group of carboxylic acidsconsists of a C=O with -OH bonded to thesame carbon.

Carboxyl group is usually written -COOH.

Aliphatic acids have an alkyl group bondedto -COOH.

Aromatic acids have an aryl group bonded to

-COOH.

C

O

O H

C

O

O H

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3

IUPAC NAMES

Carbon atoms IUPAC name Chemical formula

1 Methanoic acid HCOOH

2 Ethanoic acid CH3COOH

3 Propanoic acid CH3CH2COOH

4 Butanoic acid CH3(CH2)2COOH

5 Pentanoic acid CH3(CH2)3COOH

6 Hexanoic acid CH3(CH2)4COOH

7 Heptanoic acid CH3(CH2)5COOH

8 Octanoic acid CH3(CH2)6COOH

9 Nonanoic acid CH3(CH2)7COOH

10 Decanoic acid CH3(CH2)8COOH

Remove -e from alkane (or alkene) name,add -oic acid.

The carbon of the carboxyl group is #1.

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4

OH group is indicated by the prefix hydroxy

3-hydroxypentanoic acid

NH2 group is indicated by amino

4-aminobutanoic acid

C O group of an aldehyde or ketone is indicated by oxo

4-oxobutanoic acid

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Dicarboxylic acids are named by adding thesuffix dioic acid

The number of the carboxyl carbons are notindicated..why???-they can be only at the ends of the parentchain.

Eg:

Ethanedioic acid Propanedioic acid

5

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Carboxylic acids bonded to cycloalkane ringis name by giving the name of the ring andadding the suffix carboxylic acid.

The atoms of the ring are numberedbeginning with the carbon bearing the COOH group.

Eg:

6

1-Aminocyclopentanecarboxylic acid

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The simplest aromatic carboxylic acid is

benzoic acid. Derivatives are named by using numbers to

show the location of substituents relative tothe carboxyl group.

Eg:

Benzoic acid 2-hydroxybenzoic acid 1,2-benzenedicarboxylic acid

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IUPAC name COMMON name

Methanoic acid

Ethanoic acid

Propanoic acid

Butanoic acid

Pentanoic acid

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COMMON NAMES

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IUPAC name COMMON name

Methanoic acid Formic acid

Ethanoic acid Acetic acid

Propanoic acid Propionic acid

Butanoic acid Butyric acid

Pentanoic acid Valeric acid

9

COMMON NAMES

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Oxidation of primary alcohols,aldehydes and alkyl benzene

Hydrolysis of nitriles Addition of grinard reagents to carbon

dioxide

10

PREPARATION OF

CARBOXYLIC ACIDS

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Oxidation of Primary Alcohols, Aldehydes and

Alkyl Benzene

11

Primary alcohol

Aldehydes

Alkyl benzene

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Hydrolysis of Nitriles The hydrolysis ofnitriles, which are organic

molecules containing a cyano group, leads tocarboxylic acid formation. These hydrolysis reactionscan take place in either acidic or basic solutions.

Eg:

12

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Addition of Grignard's reagent to

Carbon Dioxide

Grignards reagents react with carbon dioxide to formsalts of carboxylic acids which give carboxylic acids onacidification with mineral acids.

Eg:

13

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EXERCISES

1. Draw the Structural Formula for:a) 3,3-dimethylheptanoic acidb) 3-chloro-1,1-cyclopentanedicarboxylic

acid2. Complete these reactions.

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ACIDITY Weak acid The acidities: carboxylic acid > alcohol Both have O-H bond. Carboxylate ions are more stable.

Resonance stabilizes the carboxylate ions bydelocalizing its negative charge.

There is no comparable resonance stabilization ofalkoxide ions

Chapter 20 15

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Electron withdrawing groups attached to the carboxyl groupwould enhance acidity

Examples of acetic acid, chloroacetic acid and trichloroaceticacid

Chlorine atoms are electronegative and thus have anelectron withdrawing effect.

Thus they help stabilize the negative charge of the conjugate

base formed upon the ionization of an acid by electronwithdrawal through carbon-carbon bonds.

The greater the number of Cl atoms present, the greater thetotal electron withdrawing effect and the greater the ease of

ionization

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Aromatic ring substituents also influence the acidity ofcarboxylic acids

benzoic acid is more acidic than acetic acid, because itis capable of withdrawing electron density by induction Furthermore, benzoic acids with electron withdrawing

groups (i.e. NO2) are even "more acidic" than benzoicacid

Chapter 20 17

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EXERCISES

Which is the stronger acid in each pair

a) or

b) or

Chapter 20 18

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Reaction with bases Salt formation reaction of a carboxylic acid with an alkali

metal hydroxide (NaOH, LiOH, KOH)

Eg:

19

CHEMICAL REACTIONS

OF CARBOXYLIC ACIDS

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EsterificationAn ester is formed when a carboxylic acid is refluxed with an

alcohol in the presence of a small amount of concentratedsulphuric acid as a catalyst

Eg:

Chapter 20 20

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Oxidation Methanoic acid is a strong reducing agent. It can decolurise

aqueous pottasium manganate (VII) at room temperature

HCOOH + [O] CO2 + H2O

Oxidation of ethanedioic acid occurs rapidly at 60 C

COOH + [O] CO2 + H2OCOOH

Chapter 20 22

KMnO4

KMnO4

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Chapter 20 23

Reduction

Dehydration of methanoic acid can be carried out bywarming it with concentrated sulphuric acid. Carbonmonoxide gas, which is combustile, is released.

HCOOH CO + H2O

Dehydration of ethanedioic acid can also be carried out byusing concentrated sulphuric acid under the same condition

COOH

CO + CO2

+ H2

OCOOH

H2SO4Warm

H2SO4

Warm

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INDUSTRIAL USES

Widely used as foods and drink preservatives Responsible for preventing the growth of bacteria,

fungus and various microorganisms Eg: sodium benzoate, calcium propanoate and

monosodium glutamate Sodium salts of long chained fatty acids, which canbe derived from fats and oils, are used in themanufacture of soap and detergents

Zinc undercylate can be used to make components ofbaby powder

Chapter 20 24

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EXERCISES

Butanenitrile is boiled with dilutesulphuric acid to form compound W. Wreacts with sulphur oxide dichloride toproduce X. X reacts with ethanol toproduce a sweet smelling liquid, Y.

Determine the structural formulae of W,X, Y.

Chapter 20 25

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