Question

The above conversion can be carried out by:

• A. Zn-Hg/ Conc.HCL
• B. i. H2NNH2 ii. NaOH in ethylene glycol, △
• C. i. HSCH2CH2SH/H⨁ ii. H2/Ni
• D. Bromine water

Answer 1

The Correct Option is A, B, C

• Clemmensen Reduction (Zn-Hg/Conc.HCl): This method uses zinc amalgam (Zn-Hg) and concentrated hydrochloric acid (HCl) to reduce aldehydes and ketones to alkanes. It's particularly useful for substrates that are stable in acidic conditions.
• Wolff-Kishner Reduction (i. H₂NNH₂ ii. NaOH in ethylene glycol, Δ): This reaction involves converting the carbonyl group to a hydrazone (using hydrazine, H₂NNH₂) followed by treatment with a strong base (NaOH) in a high-boiling solvent like ethylene glycol at high temperatures. This reduction is best for compounds that are unstable in acidic conditions.
• Desulfurization (i. HSCH₂CH₂SH/H⁺ ii. H₂/Ni): First, a carbonyl is converted to a thioketal using ethanedithiol and an acid catalyst. The thioketal is then reduced using Raney nickel (Ni) and hydrogen, which removes the sulfur and replaces it with hydrogen atoms.
• Bromine water: Bromine water is used to test for unsaturation (double or triple bonds) in alkenes and alkynes. It does not reduce carbonyl groups to alkanes.

Therefore, the Clemmensen reduction, the Wolff-Kishner reduction, and desulfurization are viable methods for reducing a carbonyl to a methylene.

Correct Answer: Zn-Hg/ Conc.HCl, i. H₂NNH₂ ii. NaOH in ethylene glycol, Δ, i. HSCH₂CH₂SH/H⁺ ii. H₂/Ni