ALKANOIC ACIDS

ALKANOATES

General molecular formula, nomenclature,  preparation,  properties and uses.

 

SOURCES

The alkanoic acid or carboxylic acids are also called fatty acids because some of them are found in natural fats and oils.  They contain the functional group called carboxy group.

 

NOMENCLATURE

The IUPAC name of each homologue is obtained by changing the “-e” endind of the corresponding alkane to “-oic” acid e.g. mathanoic, ethanoic etc.

 

STRUCTURE

Alkanoic acid has a general molecular fomular of CnH₂n + 1COOH where n > 0. or RCOOH.  Thus it has the following structure.

O

RC

OH

 

E.g.Ethanoic acid CH₃COOH

H

O

H          C       C

 

H            OH

PREPARATION   e.g.Ethanoic acid

Ethanoic acid can be prepared by the complete oxidation of ethanol by acidified sodium heptaoxo dichromate (VI) solution.  The oxidation reaction is a two stages of reaction

1. Ethanol oxidized to ethanol; CH₃CH₂OH             O₃         CH₃CHO

 

1. Ethanol oxidized to ethanoic acid; CH₃CHO        O₃          CH₃COOH

Or

CH₃CH₂OH  +    [O]            CH₃CHO  +     [O]               CH₃COOH

PHYSICAL PROPERTIES

1. It is colourless liquid with a sharp and pungent smell.
2. It has sour taste.
3. It is soluble in water.
4. It freezes into ice-like at temperature below 17⁰C therefore called gluciaethanoic acid (anhydrous ethanoic acid).
5. It has boiling point of 118⁰C
6. It turns blue litmus papers to red.

 

CHEMICAL PROPERTIES

1. It libratescarbon(IV) oxide from either trioxocarbonate (IV) or hydrogen trioxocarbonate (IV) salts. 2CH₃COOH  + Na₂CO₃          2CH₃CONa  +  H₂O + CO₂.
2. It librates hydrogen gas when it reacts with highly electropositive metals e.g.

Mg &Ca;              2CH₃COOH + Ca               (CH₃COO)₂Ca + H₂.

3. As an acid, it neutralizes boxes or alkalis to form salts known as ethanoate and water only

CH₃COOH + NaOH              CH₃COONa + H₂O.

4. It reacts with alkanols to form ester e.g. CH₃COOH + CH₃CH₂OH CH₃COOCH₂CH₃ + H₂O
5. Reduction:

It can be reduced to ethanol in the presence of lithiumtetrahydridoaluminate III as

reducing agent (LiAlH₄)

CH₃COOH  + 4H          CH₃CH₂OH + H₂O

6. It reacts with chlorme successively to form chloroethanoic acid e.g.

CH₃COOH       +  Cl₂                CH₂C_lCOOH   +    HCl

CH₂ClCOOH   +   Cl₂                CHCl₂ COOH  +HCl

CHCl₂ COOH  +   Cl₂                CCl₃COOH     +    HCl

 

EVALUATION

1. (a) State four (4) chemical properties of ethanoic acid.

(b) Give two (2) physical properties of ethanoic acid.

2. How would you prepare ethanoic acid in the laboratory.

 

CLASSIFICATION OF ALKANOIC ACID

Alkanoic acids are classified based on the number of carbonxylic groups present per molecules.

1. Monocarboxylic Acids: these have one carboxylic group per molecule e.g.

methanoic acid (HCOOH)

 

 

O

 

H          C

OH

 

Ethanoic acid CH₃ COOH

 

H

O

H          C          C

 

H                 OH

2. Dicarboxylic Acids: these have two carboxyl groups per molecules e.g. ethan -1, 2-dioe acid

(oxalic acid)

COOH               O          O

or                  C     C

COOH             HO                  OH

 

3. Tricarboxylic acids: these have 3 carboxylic acid per molecule e.g. 2-hydroxy propan 1,2, 3-

tricaboxylic acid.

H

H          C          COOH

HO       C          COOH

H          C          COOH

H

N.B:      Two important aromatic caborxylicacid are

(1)        Benzoic acid

(2)        2-hydroxy benzoic acid

USES OF ETHANOIC ACID

1. It is used in making compounds like cellulose ethanoate, dyes etc.
2. It is used as organic solvent.
3. It is used in the food industries for preserving and flavoring food.
4. Used for coagulating rubber latex.

 

EVALUATION

1. Give three (3) classes of alkanoic acid.
2. State four (4) uses of ethanoic acid.

 

ALKANOATES

General molecular formula.

The alkanoates are called esters.  They have general molecular formula of RCOOR’.

It has structural formula of

O

R     C

OR

e.gethylethanoate CH₃COOCH₂CH₃

NOMENCLATURE

Naming of alkanoates are obtained by substituting “e” ending in alkane with “oates” in

alkanoates.

Preparation e.g. ethyl ethanoate .

Ethyl ethanoate is prepared by the esterification between ethanol and glaciusethanoic acid at 150⁰C  in the presence of concentrated tetraoxosulphate (VI) acid

C₂H₅OH + CH₃COOH                 CH₃COOC₂H₅ + H₂O

 

PHYSICAL PROPERTIES

1. Ethyl ethanoate is a colourles volatile liquid with a pleasant smell.
2. It is slightly soluble in water.

3..It has boiling point of 75⁰C.

 

CHEMICAL PROPERTIES

1.  Hydrolysis.

Ethyl ethanoate can be hydrolysed by water to produce ethanoic acid and ethanol.

CH₃COOC₂H₅  + H₂O                     CH₃COOH + C₂H₅OH.

 

N.B:If an alkali is used instead of water, it will produce the salt of the acid e.g.

CH₃COOC₂H₅ + NaOH                 CH₃COONa + C₂H₅OH

 

2. REACTION WITH AMMONIA

Ethyl ethanoate reacts with ammonia to produce ethanol and thenamide

CH₃COOC₂H₃ + NH₃               C₂H₅OH + CH₃COOH₂

 

3. REDUCTION

Ethyl ethanoate can be reduced by hydrogen from lithium tetrahydridoalluminute (III) as reducing agent          CH₃COOC₂H₅ + 4[H]                2C₂H₅OH

 

USES OF ALKANOATES/ESTERS

– They are used as food flavours.

– Used in perfumes and cosmetics

– Used as solvent for cellulose nitrate .

– Used for quick-drying substances like paints, nail varnishes etc.

 

EVALUATION

1.Write the general structure of the ester.

2.Write a balanced equation for the reaction between propanol and butanoic acid.

(a) Name the products formed.

(b) What type of reaction is involved.

 

WEEKEND ASSIGNMENT

1. The name of (CH₃)₂ CHCOOH is
2. Propane acid    B. 2-methylhutanoic acid  C.           Dimethyl butanoic acid
3. Propanoic acid
4. Citric acid appears in unripe orange while enthanwie acid appears in
5. Unripe pawpaw B. Carrot    C.  Vineger     D.  Rice
6. Esters are employed in the following except.
7. Making perfumes   B.  Making cement    C. Nail varnishes    D.  Making yeast
8. An alkanoic acid reacts reversibly with an alkanol to produce.
9. a salt  B.  an ester     C.  a sugar     D.  an alkene
10. Ethan-1, 2-dioe acid is
11. a mineral acid    B.  dicarboxylic acid    C.  citric acid    D.  a soap

 

THEORY

1a.       Give the formula of ethanoic acid and indicate its functional group.

1. Ethanoic acid reacts with both sodium hydroxide and ethanol, suing equations to comparethe reactions and classify the products.

2a.       Ethylethanoate reacts with both water and alkali; using equation to compare the reaction.

b.       What happens when ethanoic acid is heated strongly with soda-line

 

See also

ALKANOLS

AROMATIC HYDROCARBONS

ALKYNES

UNSATURATED HYDROCARBONS

Saturated Hydrocarbons