Question

How will you convert methyl bromide (bromomethane) to acetic acid (ethanoic acid)?

Answer 1

Methyl bromide (CH₃Br) can be converted to acetic acid (CH₃COOH) through two main methods: 

1. Nitrile Hydrolysis Method:

1. Formation of acetonitrile (CH₃CN): Methyl bromide (CH₃Br) is treated with alcoholic potassium cyanide (alc. KCN). In this nucleophilic substitution, the bromine atom is replaced by the –CN group, forming acetonitrile (CH₃CN).
   \[\ce{CH3Br + KCN -> CH3CN + KBr}\]
2. Hydrolysis of acetonitrile: Acetonitrile is then hydrolyzed with dilute hydrochloric acid (or dilute NaOH). Hydrolysis converts the –CN group into a –COOH group, producing acetic acid (CH₃COOH).
   \[\ce{CH3CN + 2H2O ->[H^+ or OH^-][] CH3COOH + NH3}\]

2. Grignard Synthesis Method:

1. React methyl bromide with magnesium in dry ether to form methyl magnesium bromide (CH₃MgBr).
   \[\ce{CH3Br + Mg ->[dry ether][] CH3MgBr}\]
2. Treat CH₃MgBr with solid carbon dioxide (CO₂) to form a magnesium acetate complex.
   \[\ce{CH3MgBr + CO^-_2 -> CH3COOMgBr}\]
3. Hydrolyze this intermediate with dilute acid to obtain acetic acid.
   \[\ce{CH3COOMgBr + HCl -> CH3COOH + MgBrCl}\]