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Alcohols
Alcohols
Alcohols are saturated hydrocarbons in which one or more of the hydrogen atoms are
replaced by OH group.
Alcohols
they are divided into :
a- Monohydric alcohols: which contain one OH group per molecule.
b- Dihydric alcohols : which contain two OH groups per molecule
c- Polyhydric alcohols : which contain three OH groups per molecule.
Alcohols
Alcohols
According to the position of the OH group in the molecule; monohydric alcohols are subdivided into three classes :
Primary alcohols: in which the OH group is attached to the primary carbon atom.
Secondary alcohols: in which the OH group is attached to the secondary carbon atom.
Tertiary alcohols: in which the - OH group is attached to the tertiary carbon atom.
Alcohols
Preparation:
1. Hydrolysis of the corresponding alkyl halide with aqueous alkali.
Alcohols
2- Hydrolysis of esters:
Alcohols
3- Hydrolysis of ethers in presence of dil H2SO4.
Alcohols
4- Reduction of carbonyl compounds (aldehyde & ketone)
Alcohols
Reduction is usually carried out by aluminum lithium hydride.
Aldehyde on reduction gives the corresponding primary alc.
while ketones give the corresponding secondary alcohols.
Alcohols
5- Action of Grignard reagent on carbonyl compounds:
Alcohols
5- Action of Grignard reagent on carbonyl compounds:
Alcohols
5- Action of Grignard reagent on carbonyl compounds:
Alcohols
6- By hydrogenation of CO at high P and T (350 - 400°C) in the presence of zinc chromite as a catalyst (ZnO & Cr2O3)
Alcohols
7- Ethyl alcohol can be obtained on an industrial scale by the fermentation of sugars.
Alcohols
Physical properties: Alcohols are neutral, lower members are
liquids and the higher are solids. The lower members are less volatile than to
be expected from their molecular weight this is due to the hydrogen bonding
extending over a chain of molecules, thus giving rise to a large molecule its volatility would be expected to be low.
Alcohols
The lower alcohols are very soluble in water, and the solubility decreases as the molecular weight increases.
Their solubility in water is to be expected, since the oxygen atom of the hydroxyl group in alcohols can form hydrogen bonds with the water molecules.
Alcohols
In the lower alcohols the hydroxyl group constitutes a large part of the molecule, where as the molecular weight of the alcohol increases the hydrocarbon character of the molecule and hence the solubility in water decreases.
Alcohols
Chemical Reactions:
1- Esterfication:
Alcohols
Chemical Reactions:
2- Halogenation:
Alcohols
Chemical Reactions:
3- Substitution reaction:
Alcohols
Chemical Reactions:
4- Dehydration of alcohols:
Alcohols
Chemical Reactions:
4- Dehydration of alcohols: This is earned in presence of dehydrating agent
such as P2O5 or conc. H2SO4 or Al2O3, the product is always an olefin.
When 2-butyl alcohol is dehydrated, 2-butene is obtained. Here, dehydration like dehydrohalogenation follows Saytzeff’s rule.
Alcohols
Chemical Reactions:
5- Oxidation of alcohols Dehydrogenation:
Primary alcohols:
Alcohols
Chemical Reactions:
5- Oxidation of alcohols Dehydrogenation:
Secondary alcohols:
Alcohols
Chemical Reactions:
5- Oxidation of alcohols Dehydrogenation:
Tertiary alcohols:
Alcohols
Chemical Reactions: Since the carbon atom of the carbinol group
does not carry any hydrogen atoms, tertiary alcohols are not oxidized in neutral or alkaline medium.
However, in acidic medium it is first dehydrated to an alkene which is then oxidized to a ketone (with a fewer number of carbon atoms).
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