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Alcohol

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The compounds commonly known as alcohols are molecules containing only one OH group; they have the general formula $C_{n}H_{2n+1}OH$ and should more correctly be called the "monohydric alcohols"

The alcohol compounds could also be considered to be "hydroxy alkanes" but they are more unusually called alcohols. The alcohols are named using a system that clearly locates the position of the OH group on the carbon chain.

Definition

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"Alcohols are organic compounds containing a hydroxyl group, -OH attached to an alkyl group."
The general formula for an alcohol is R-OH and the IUPAC names of alcohols end in -ol. The alcohols are hydrocarbons with one or more hydrogen atoms substituted by hydroxyl (-OH) groups. A compound with one hydroxyl group is an alcohol while with two, the group is called glycols and with three hydroxyls it is called glycerols.

Synthesis

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Alcohols are extremely versatile starting materials for organic synthesis, since they can be converted to a wide variety of functional groups. Many simple alcohols are commercially available, but this will focus on the preparation of alcohols. These synthetic strategies will be useful not only for complex alcohol target molecules, but also for alcohols that may be intermediates within a larger synthesis.

Hydrolysis of alkyl halides

Hydrolysis of alkyl halides with aqueous alkali or moist sliver oxide or aqueous potassium carbonate yield alcohol.

Preparation of Alcohol

Hydration of alkenes

Dilute acid catalyzed hydration of alkenes give alcohols. The major product is formed in accordance with the Markovnikov's rule.

Hydration of Alkenes
In the IUPAC system, the longest chain of carbon atoms containing the -OH group is selected as the parent alkane and numbered from the end closer to -OH. Common names for alcohols are derived by naming the alkyl group bonded to -OH and then adding the word alcohol.

Here are IUPAC names and in parentheses, common names for several low-molecular weight alcohols. 

Alcohol Nomenclature
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Types

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There are three types of alcohols.
  1. Primary alcohol - On the carbon with the -OH group, there are two hydrogen.
  2. Secondary alcohol - On the carbon with the -OH group, there is only one hydrogen.
  3. Tertiary alcohol - On the carbon with the -OH group there are no hydrogen.
Examples :

Primary Secondary Tertiary
Butan-1-ol
CH3CH2CH2CH2OH
Butan-2-ol
CH3CH2CH(OH)CH3
2-metyl-propan-2-ol
(CH3)3COH

Physical Properties

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The -OH group dominates the physical properties of short chain alcohols. Hydrogen bonding takes place between alcohol molecules resulting in 
  • High melting and boiling points than alkanes.
  • Solubility in water.
The solubility of alcohols in water decreases with increasing carbon chain length as the non-polar contribution to the molecule becomes more important. 

Physical Properties of Alcohol

Chemical Properties

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Some of the Alcohol Reactions are listed below.

1. Combustion

Methanol burns in air or oxygen to form carbon-dioxide and water with the release of heat.

2CH3OH + 3O2 $\rightarrow$ 2CO2 + 4H2O + Heat

2. Reaction with sodium

Alcohol reacts with sodium methoxide with the evolution of hydrogen.

CH3OH + 2Na $\rightarrow$ 2CH3ONa + H2

3. Reaction with halogen acids

Methanol reacts with hydrogen chloride in the presence of anhydrous ZnCl2 to form cloromethane.

CH3OH + HCl $\rightarrow$ CH3Cl + H2O

4. Halogenation

Methanol reacts with phosphorus pentachloride to form chloromethane.

CH3OH + PCl5 $\rightarrow$ CH3Cl + POCl3 + HCl

5. Esterification

Methanol reacts with ethanoic acid in the prsence of conc.H2SO4 to form a sweet smelling ester methyl acetate. The process is known as esterification.

CH3OH + CH3COOH $\rightarrow$ CH3COOCH3 + H2O

Applications

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  1. Ethanol is well known as a powerful bactericide that is widely used in hospitals and in food premises to sterilize instruments, utensils, working surfaces etc.
  2. Methanol has been used in feed stock for other chemicals, fuel use and other direct uses as a solvent, inhibitor or substrate.
  3. Propyl alcohol is a primary alcohol mainly used as a solvent and carrier for a variety of natural products and synthetic polymers.
  4. n-buthyl alcohol is used extensively in a large number of industries.For instance it is used as a solvent in industries associated with the manufacturing of paints, varnishes, synthetic resins, gums, pharmaceuticals, vegetable oils, dyes and alkaloids.