1. In tertiary alcohols, ZnCl2 is not required. Why?

2. Heating and boiling are required for preparation of alkyl bromide and alkyl iodide. Why?

1) In the preparation of alkyl chloride from primary and secondary alcohols, ZnCl2 acts as a Lewis acid and coordinates with the oxygen atom of alcohol due to which the C-O bond weakens and a carbocation is formed. This carbocation then reacts with chloride ion to form alkyl chloride. Tertiary alcohols are very reactive due to which they donot require ZnCl2 . They readily react with concentrated HCl even in the absence of the zinc chloride.

2) Only primary alkyl bromides and iodides can be prepared from corresponding alcohols because the secondary and tertiary alcohols undergo dehydration on heating with concentrated H2SO4 to form alkenes. Heating and boiling is done to increase the rate of reaction as primary alcohols are less reactive.

  • 6
What are you looking for?