Q17P - Organic Chemistry (Mcmurry)

Question

2-Butene-1-thiol is one component of skunk spray. How would you synthesize this substance from methyl 2-butenoate? From 1,3-butadiene?

Step-by-Step Solution

Answer

Answer

The Synthesis of 2-Butene-1-thiol from methyl 2-butenoate and 1,3-butadiene is shown as,

Step-by-Step Solution Step 1: Preparation of Thiols

For the preparation of thiols, thiourea ((NH₂)₂ C=S) is often used as a nucleophile, and the halide ion is displaced by forming an alkyl isothiourea salt intermediate. When hydrolyzed with an aqueous base, this intermediate forms a thiol compound.

Step 2: Synthesis of 2-Butene-1-thiol from methyl 2-butenoate

When methyl 2-butenoate is treated with LiAlH₄, and then with H₃O⁺, it forms but-2-en-1-ol. On further treating with PBr₃, it forms 1-bromobut-2-ene. At last, this 1-bromobut-2-ene on reacting with thiourea ((NH₂)₂ C=S), results in the formation of 2-Butene-1-thiol.

Synthesis of 2-Butene-1-thiol from methyl 2-butenoate

Step 3: Synthesis of 2-Butene-1-thiol from 1,3-Butadiene

When 1,3-Butadiene is treated with HBr, it forms 1-bromobut-2-ene. On further treatment with thiourea ((NH₂)₂ C=S) , it results in the formation of 2-Butene-1-thiol.

Synthesis of 2-Butene-1-thiol from 1,3-Butadiene