In the reaction of p- chlorotoluene with KNH2 in liquid NH3, the major product is:

Explanation

We know that the reaction of p-chlorotoluene with KNH2 in liquid NH3 proceeds via the benzyne mechanism. The primary stage in the mechanism is a base-promoted Dehydrohalogenation of chlorobenzene and the intermediate formed in the step will contain a triple bond in an aromatic ring called benzyne.Complete step by step answer:We know that para-Chlorotoluene initially forms benzyne with methyl as a substituent. When -NH2 attacks at carbon which is bearing triple bond it gives a mixture of Meta and para-toluidine. The major product formed is m-toluidine because of the formation of carbanion at the meta position by the attack of nucleophiles and it is more stable compared to the para position. Hence option B is correct.The mechanism by which the reaction takes place,First step: Removal of a proton by KNH2 from the Meta position of p-chlorotoluene which provides benzyne as an intermediate.Second step: Since benzyne is susceptible to nucleophilic attack and hence the nucleophile present within the solution is NH2 which may attack each side of the Benzene bond. Meta product is major as just in case of an attack on 1 the negative charge formed is going to be farthest from the methyl group which facilitates less +1 and hence more stable negative ions.We can write the chemical equation for this mechanism as,So, the correct answer is Option B.Note:Two mechanisms were proposed for the nucleophilic aromatic substitution, one among the mechanisms involves a benzyne because the intermediate form is a benzyne and so, it is named as benzyne mechanism. Arynes or benzyne are extremely reactive groups resulting from an aromatic ring by the elimination of two substituents.