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Reactions of Alcohols and Phenols
Cleavage of O-H Bond

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Esterification

Alcohols react with carboxylic acid in the presence of conc. H2SO4 or dry HCl to form esters.

Esterification of alcohols

Due to resonance, phenols do not undergo this reaction.

Acylation

Alcohols react with acid chlorides (R−COCl) and acid anhydrides [(R−CO)2O] to form esters.

Acylation of alcohols

If the acid chloride or acid anhydride used is acetyl chloride (CH3COCl) or acetic anhydride [(CH3CO)2O] , the reaction is usually termed as acetylation. However, if benzoyl chloride (C6H5COCl) is used, the reaction is termed as benzoylation.

Phenols also undergo the reaction in the presence of base catalyst such as pyridine.

acylation in phenol requires pyridine as catalyst

In case of acetic anhydride, either acids (conc. H2SO4) or base (pyridine etc.) are used as catalysts.

acylation in phenol requires pyridine as catalyst

Schotten-Baumann reaction

Phenols react with benzoyl chloride in the presence of aqueous NaOH to form phenylesters. This reaction is called Schotten-Baumann reaction.

Schotton-Baumann reaction : Phenol reacts with benzoyl chlorides to form phenylesters

Reaction with Grignard reagents

Both alcohols and phenols react with Grignard reagents to form alkanes. The alkane thus formed corresponds to the alkyl group of the Grignard reagents.

Alkanes corresponding to grignard reagents are formed when grignard reagents react with alcohols and phenols

Example

Alkanes corresponding to grignard reagents are formed when grignard reagents react with alcohols and phenols

Example

Alkanes corresponding to grignard reagents are formed when grignard reagents react with alcohols and phenols

Questions

Question : Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanl?

  1. Prepare 2-methylpropanol with suitable grignard reagent and methanal
  2. Prepare C6H13CH2OH with suitable grignard reagent and formaldehyde

Answer : The reaction of methanal — HCHO or CH2O — with Grignard reagents is carried out as given below:

Reaction of formaldehyde with grignard reagent

Thus, to identify the reagent, we need to look for the part other than -CH2OH.

  1. Isopropyl magnesium halide is used.
    Isopropyl magnesium halide
  2. Cyclohexyl magnesium halide is used.
    Cyclohexyl magnesium halide
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