ALKANOL
Alkanols are a homologous series of organic compounds containing one or more hydroxyl groups linked to an alkyl or aryl radicals. They have the general molecular formular of CnH2n+1OH and a functional group of OH. The first – two members of the series are both liquids. They are methanol (CH3OH) and ethanol (CH3CH2OH). Alkanols are named by replacing the "–e" in the parent alkanes by "–ol".
CLASSES OF ALKANOLS
Alkanols are classified based on the number of hydroxyl groups in the molecule.
1.MONOHYDRIC ALKANOLS: These are alkanols that have only one hydroxyl group (OH) per molecule e.g
CH3OH
Methanol
CH3CH2OH ethanol
CH3CHCH3 propan-2-ol
| OH
CH3CH2CHCH3
|
OH
butan-2-ol
2.DIHYDRIC ALKANOLS: These are alkanols that contain two hydroxyl group (OH) per molecule.g
CH2CH2
| |
OH OH
Ethan-1,2-diol
CH3CHCH2CH2
| |
OH OH
Butan-1,3-diol
3.TRIHYDRIC ALKANOLS: Alkanols that contains three hydroxyl group (OH) per molecule are know as trihydric alkanols. e.g
CH2CHCH2
| | |
OH OH OH
Propan-1,2,3-triol
CH2-CH-CH2-CH2
| | |
OH OH OH Butan-1,2.4-triol
MONOHYDRIC ALKANOLS
The table below shows the formular of the first 10 members of monohydric alkanol derived from the general molecular formular (CnH2n+1OH)
|
When n= |
General Molecular Formulae CnH2n+1OH |
Name |
|
1 |
CH3OH |
Methanol |
|
2. |
C2H5OH |
Ethanol |
|
3. |
C3H7OH |
Propanol |
|
4. |
C4H9OH |
Butanol |
|
5. |
C5H11OH |
Pentanol |
|
6. |
C6H13OH |
Hexanol |
|
7. |
C7H15OH |
Heptanol |
|
8. |
C8H17OH |
Octanol |
|
9. |
C9H19OH |
Nonanol |
|
10. |
C10H21OH |
Decanol |
MOLECULAR STRUCTURES OF FIRST 10 MONOHYDRIC ALKANOLS
|
N |
ALKANOL |
STRUCTURAL FORMULAR |
MOLECULAR FORMULAR |
|
1. |
CH3OH Methanol |
|
CH3OH |
|
2. |
C2H5OH Ethanol |
H H |
CH3CH2OH |
|
3. |
C3H7OH Propanol |
H H H |
CH3(CH2)2OH |
|
4. |
C4H9OH Butanol |
H H H H |
CH3(CH2)3OH |
|
5. |
C5H11OH Pentanol |
H H H H H |
CH3(CH2)4OH |
|
6. |
C6H13OH Hexanol |
H H H H H H |
CH3(CH2)5OH |
|
7. |
C7H15OH Heptanol |
H H H H H H H |
CH3(CH2)6OH |
|
8. |
C8H17OH Octanol |
H H H H H H H H |
CH3(CH2)7OH |
|
9. |
C9H19OH Nonanol |
H H H H H H H H H |
CH3(CH2)8OH |
|
10. |
C10H21OH Decanol |
H H H H H H H H H H |
CH3(CH2)9OH |
H
(i) |
CH3-C-OH
|
CH3
Propan-2-ol
(ii) CH3CH2C- OH
|
CH3 Butan-2-ol
CH3
(iii) |
CH3-C-CH2OH
CH3
2,2-dimethylpropan-1-ol
CH3
(iv) |
CH3-C-CH2CH2CH3
|
OH
2-methylpentan-2-ol
CH3
(v) |
CH3-C-CH2CHCH2CH3
| |
CH3 OH
5,5-dimethylhexan-3-ol
OH
|
(vi) OH-C-OH
|
OH
methan-1,1,1,1-tetraol
CH3 OH OH
(vii) | | |
CH3-CH2CH2-C—CH—CH-CHCH3
| |
CH3 CH2CH3
5,5-dimethyl, 4-ethyloctan-2,3-diol
(viii) CH3CHCH2CHCH2CHCH3
| | |
OH OH OH
heptan-2,4,6-triol
TYPES OF ALKANOLS
Alkanols can be classified into three types depending on the number of the alkyl group or H- atom attached to the C-atom carrying (attached to) the functional group (-OH). We have
1. PRIMARY ALKANOLS: These are alkanols in which the hydroxyl group (OH) is directly attached to a carbon atom. i.e H
Examples include
H H H H H
H H
| | | | | | |
H—C—OH H—C
– C – OH H – C – C
– C – C – OH
| | | | | | |
H H H H H
H H
Methanol ethanol propanol
2. SECONDARY ALKANOLS: These are alkanols in which the Carbon atom carrying the hydroxyl group (OH) is itself attached to two alkyl group (or two other carbon atoms) or one hydrogen atom.
i.e, H
|
R—C—OH
|
R
Examples include
H H
H
(i) | (ii) | (iii) |
CH3—C—OH CH3—C – CH2CH3 CH3
– C – CH2CH2CH3
| | |
CH3 OH
OH
Propan-2-ol Butan-2-ol Pentan-2-ol
3. TERTIARY ALKANOLS: These are alkanols in which the carbon-atom carrying the hydroxyl group (OH) is itself attached to three other alkyl group that is, no hydrogen attached to the carbon atom carrying the -OH group.
R
|
R—C—OH
|
R
Examples include
(i) CH3 CH3 CH3
| | |
CH3—C—OH CH3—C – CH2CHCH3
| |
CH3 OH
- 2-methylpropan-2-ol 2,4-dimethylpentan-2-ol
ETHANOL: This is the second and greatly used member of the series. it has a molecular formula of C2H5OH and a structural formula of
H H
| |
H—C – C – OH
| |
H H
LABORATORY PREPARATION OF ETHANOL
Ethanol is prepared in the laboratory by the process hydrolysis iodoethane with an alkali
CH3CH2I + NaOH → CH3CH2OH + NaI
Industrially ethanol is prepared by
(i) Hydrolysis of ethene
STAGE 1:
C2H4 + H2SO4 → C2H5HSO4
Ethylhydrogen tetraoxosulphate (IV)
STAGE: II
C2H5HSO4 + H2O →C2H5OH
(ii) Fermentation: -This is a reaction in which simple sugar such as glucose (C6H12O6) is converted into ethanol (C2H5OH) and carbon (IV) oxide (CO2) by the action of an enzyme called zymase present in the yeast.
C6H12O6 → 2C2H5OH + CO2
Glucose ethanol
PREPARATION OF ETHANOL FROM STARCHY FOODS
The starchy food (like sweet potato) is first crushed, and pressure cooked using a pressure cooker for some time. The crushed potato releases starch granules and this starch granules are treated with malt (partially germinated barley) for an hour at about 600C. Malt contains the enzyme diastase. The starch contained in the potato is then converted by the enzyme diastase into maltose by hydrolysis.
Diastase
2(C6H10O5)n(s) + H2O(l) → C12H22O11(aq)
maltase
C12H10O11(aq) + H2O(l) → 2C6H12O6(aq)
Zymase
C6H12O6(aq) → 2 C2H5OH(aq) + 2CO2(g)
reacts with
OBJECTIVES
1. What is the major product formed when C2H5OH with
a. C2H5COOH
b. C2H5COCH3
c. CH3COOC2H5
d. C3H7COOH
2.
THEORY
1. What is fermentation
1a. with chemical equations only, show how ethanol can be produced from starch
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