Question

The compound that reacts with \[\text{C}{{\text{H}}_{\text{3}}}\text{MgBr}\] to yield methane as one of the products is?
(A) \[\text{C}{{\text{H}}_{\text{3}}}\text{CHO}\]
(B) \[\text{C}{{\text{H}}_{\text{3}}}\text{COO}{{\text{H}}_{3}}\]
(C) \[\text{C}{{\text{H}}_{\text{3}}}\text{COOC}{{\text{H}}_{\text{3}}}\]
(D) \[\text{C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{\text{2}}}\text{OH}\]

Answer 1

Hint: Grignard reagents are an organo-metallic halogen compound which is represented by \[{{\text{R}}^{\text{-}}}\text{M}{{\text{g}}^{\text{2+}}}{{\text{X}}^{\text{-}}}\], where R could be an alkyl or aryl group and X represent the halogen atom.
- Zerewitinoff determination test is mainly used for the detection of acidic hydrogen in an organic compound.

Complete Solution :
The alkyl group of Grignard reagents acts as a strong base and a strong nucleophile. So Grignard reagent shows either acid base reaction or nucleophilic addition reaction and reacts with only those compounds which contain acidic hydrogen or which contains carbonyl group$\text{(-C=O)}$.
- Since, the hydrogen atom associated with the carbonyl group of aldehyde is less acidic so it will mainly prefer nucleophilic addition reaction after reacting with Grignard reagents.
- In esters there is a carbonyl group present in this compound but it is not associated with any active hydrogen atom so it will give nucleophilic addition reaction.
Since, ethyl alcohol is acid in nature and it contains acidic hydrogen (active hydrogen) so it will prefer acid base reaction and form methane after reacting with \[\text{C}{{\text{H}}_{\text{3}}}\text{MgBr}\](Grignard reagent). This reaction occurs in following manner -\[\text{C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{2}}\text{OH}\,+\,\,\text{C}{{\text{H}}_{\text{3}}}\text{MgBr}\,\to \,\,\text{C}{{\text{H}}_{\text{4}}}\,\text{+}\,\,\text{C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{2}}\text{OMgBr}\]
So, the correct answer is “Option D”.

Note: Grignard reagents are highly reactive organic compounds and it can react with any source of proton to give hydrocarbons because acid base reactions are much faster than nucleophilic addition reactions. So it is therefore necessary to avoid even trace amounts of moisture from Grignard reagent.