Alkanoic acids  – sources, nomenclature, structure, preparation, properties and uses. Alkanoates, general molecular formular, nomenclature, preparation, properties and Uses.

ALKANOIC ACIDS

 

CONTENT

Sources

Nomenclature

Structure

Preparation

Properties and Uses

 

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 carboxyl group.

 

NOMENCLATURE:

The IUPAC name of each homologue is obtained by changing the “-e” ending 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.

E.g. Ethanoic acid CH3COOH

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.

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

CH3COOH + NaOH                 CH3COONa + H2O.

  1. It reacts with alkanols to form ester e.g.
  2. CH3COOH + CH3CH2OH            CH3COOCH2CH3 + H2O
  3. Reduction:

It can be reduced to ethanol in the presence of lithium tetrahydrido aluminate III as reducing agent (LiAlH4)

CH3COOH  + 4H          CH3CH2OH + H2O

  1. It reacts with chlorine successively to form chloroethanoic acid e.g.

CH3COOH       +  Cl2                     CH2ClCOOH   +    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.

  1. 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)

 

 

 

Ethanoic acid CH3 COOH

 

 

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

(oxalic acid)

COOH

or

COOH

 

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

 

 

 

 

N.B:    Two important aromatic carboxylic acid 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.

 

READING ASSIGNMENT

New School Chemistry by O.Y. pages.504-506

 

ALKANOATES

General molecular formula.

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

It has structural formula of

 

e.g.     ethyl ethanoate 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

 

  1. REACTION WITH AMMONIA

Ethyl ethanoate reacts with ammonia to produce ethanol and then amide

CH3COOC2H3 + NH3                  C2H5OH + CH3COOH2

 

  1. 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?

 

READING ASSIGNMENT

New School Chemistry by Osei Yaw Ababio page.504-509

 

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 enthanoic acid appears in
  5. Unripe pawpaw B. Carrot    C.  Vinegar     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.

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

 

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