Alkanols: Molecular formular, Source, Classification, Types, Properties and Uses

CONTENT

-Source

-General molecular formula

-Nomenclature

– Classification  

-Types, Preparation, Properties and Uses.

Test for Alkanols

SOURCES OF ALKANOLS

–           From destructive distillation wood.

–           From starchy food and sugar

General molecular formular

Alkanol is a homologous series with general molecular formular of C_n H_2n+1OH or ROH.

Or (C_nH_2n+2O).

Nomenclature:

The names of alkanols are obtained by substituting “e” in alkanes with “Ol” in alkanol e.g. methanol

(CH₃OH), ethanol (CH₃CH₂OH).

Classification

The alkanols are classified based on the number of alkyl groups directly linked to the carbon atom

holding the hydroxyl group.

N.B:      Examine the structure of the alkanol, identify the carbon atom bonded to the –OH, count the number of alkyl groups that are directly attached to the carbon atom.  Then you can say whether it is 1⁰, 2⁰ or 3⁰.

EVALUATION

1.         Name the functional group in the alkanol.

2.         Give an example each by writing the structure and names of the classes of alkanols.

Types of Alkanol

The type of alkanols is determined by the number of the hydroxyl group –OH, present in the molecule.

PREPARATION   e.g. ethanol

1.         Laboratory preparation

            –           Hydrolyzing ethyl esters with hot alkali

            –           Reducing ethanol with nascent hydrogen

2.         Commercial preparation

            –           From ethene

Ethene is obtained by the cracking of petroleum. It is then absorbed in 95% H₂SO4 at 80⁰C and

30 atoms to form C₂H₅HSO4

C₂H₄  +  H₂SO₄ →  C₂H₃HSO₄

The C₂H₃HSO₄ is bedded in water to produce ethanol; C₂H₃HSO4 + H₂O   →    C₂H₃OH + H₂SO₄.

The ethanol is distilled off leaving the acid behind which can be used again.

-Preparation by fermentation ethanol is prepared industrially from raw materials containing

starch or sugar by the process of fermentation.

-The fermentation is an enzymatic process which involves the decomposition of large organic

molecules to simple molecule by micro-organism.

-The common micro-organism used is YEAST

EVALUATION

1.         Name three (3) types of alkanol and give one example each.

2.         State two methods by which ethanol can be prepared industrially.

CHEMICAL PROPERTIES

1.         Combustion:  the lower members of alkanols burn with clean flames in plenty air

            2CH₃OH  +  3O₂           →    2CO_{2        4} +H₂O

2.         Oxidation

            The products of oxidation depend on the structure of the alkanol.

USES OF ETHANOL

1.         It is used as organic solvent

2.         It is the main constituent of methylated spirit used to clean wounds and to dissolve paint.

3.         It is used as petrol addictive for use as fuel in vehicles.

4.         Used to manufacture other chemicals such as ethanol and ethanoic acid.

5.         It is used as ingredient in making alcoholic drinks e.g. beers, wines and spirits.

6.         It is used as anti-freeze in automobile radiator because of its low freezing point (-117⁰C).

TEST FOR ALKANOLS

–           It librates hydrogen gas on reacting with sodium methal.

–           It changes to alkanoic acid (primary alkanol) on exposure to air or reacting with oxidizing agent.

EVALUATION

1.         State five (5) chemical properties of ethanol.

2a.       Identify two (2) physical properties of ethanol

  b.       State two (2) uses of alkannol.

READING ASSIGNMENT

–           New School Chemistry By O.Y. Osei Yaw Ababio pages 496-501

WEEKEND ASSIGNMENT

1.         The functional groups of the alkanol is

            A.  CnH_{2n + 1} OH     B.  carboxylic group    C.  hydroxyl group    D.  CnH_{2n+ 2}

2.         Primary alkanols are oxidized to carbonylic acid, secondary alkanols are oxidized to alkanones while tertiary alkanols are    A.  oxidized to alkanols    B.  oxidized to alkanones    C.  not oxidized    D.  oxidized to alkene

3.         The soluble of alkanols in water is due to

            A.  the covalent nature    B.  hydrogen bonding    C.  their low melting point 

D.  their low melting point

4.         When acidified KMnO4 is used as oxidizing agent for alkanol, the colour change observed is

            A.  yellow to red     B.  purple to colourless    C.  orange to green    D.  white to black

5.         Which of the following enzymes converts glucose to ethanol?

            A.  maltose       B.  zymase        C.  diastase       D.  amylase

THEORY

1(a)      Write the structural formula of two named secondary alkanols.

  (b)     Explain the structural difference between primary and tertiary alkanols.

2(a)      What is fermentation?

  (b)     Describe the preparation of ethanol from table sugar.