Physical and Chemical Properties of Alcohols - Practice Questions & MCQ

• Lower members of alcohols are colourless liquids whereas higher members are colourless solids.
• Alcohols have higher boiling points.
• Boiling point of alcohols increase with increase in member of OH group.
• Lower members are highly soluble in water.

Acylation of alcohols
Ethanoyl chloride reacts instantly with cold ethanol. There is a very exothermic reaction in which a steamy acidic gas is given off (hydrogen chloride) and ethyl ethanoate (an ester) is formed.

For example,

Oxidation of Alcohols
The nature of the oxidation products depends on whether the alcohol is primary, secondary or tertiary. The oxidising agents usually employed are acidified potassium dichromate, acidified or alkaline potassium permanganate or dilute nitric acid. It is a test of different alcohols as primary, secondary and tertiary alcohols give different products during oxidation.

• Primary alcohols give acids having same number of carbon atoms with acidic KMnO₄ or K₂Cr₂O₇. For example,
  
• Secondary alcohol on oxidation gives ketone which undergo further oxidation under drastic conditions by strong oxidizing agents like HNO₃ to give acid with one carbon atom less than the alcohol. For example,
  
• Tertiary alcohol cannot undergo oxidation by mild oxidizing agent as above however it can be oxidized under drastic conditions by strong oxidizing agents and the final product acid will have two carbon atom less than alcohol.
  

Ethyl alcohol when heated with iodine and sodium hydroxide or aqueous sodium carbonate forms a yellow crystalline solid, iodoform. The reaction occurs as follows:

Methyl alcohol does not respond to the iodoform test. In place of iodine, bromine or chlorine can be taken when the corresponding compounds bromoform or chloroform are to be formed. The reaction in general is known as haloform reaction.

The pinacol rearrangement is the acid-catalyzed dehydration of glycols, which converts the glycol into an aldehyde or a ketone. When pinacols are treated with mineral acids, acid chlorides, ZnCl₂, or other electrophilic reagent, they rearrange to form ketones called pinacolones with the elimination of H₂O. 

Mechanism

For example

NOTE: With unsymmetrical glycols, the product obtained is determined mainly by the OH that is lost as H₂O to give more stable carbocation and thereafter by the better migrating group.

At least 2-OH or 2 >C=O or 1-OH and 1 >C=O should be at adjacent carbons. HIO₄ works as an oxidising agent here.

Some examples include,