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Question: How many of the following will from methane on reaction with CH3MgBr? C2H5OH CH3-SH CH3-NH2 H₂O C2...

How many of the following will from methane on reaction with CH3MgBr?

C2H5OH

CH3-SH CH3-NH2 H₂O C2H2

A

1

B

2

C

3

D

4

E

5

F

6

Answer

5

Explanation

Solution

The Grignard reagent, CH₃MgBr, acts as a strong base. It reacts with compounds having sufficiently acidic hydrogen (i.e. lower pKₐ values) to abstract a proton, forming CH₄. Checking each compound:

  1. C₂H₅OH (Ethanol): pKₐ ≈ 16 → reacts.
  2. CH₃COOH (Acetic acid): pKₐ ≈ 4.8 → reacts.
  3. CH₃SH (Methanethiol): pKₐ ≈ 10 → reacts.
  4. CH₃NH₂ (Methylamine): N–H is very weakly acidic (pKₐ of its conjugate acid ≈ 40) → does not react.
  5. H₂O (Water): pKₐ ≈ 15.7 → reacts.
  6. C₂H₂ (Acetylene): pKₐ ≈ 25 → is acidic enough for Grignard deprotonation → reacts.

Thus, 5 out of the 6 compounds will form methane upon reaction with CH₃MgBr.