Acylarylnitrosamines. Part V. Decompositions of N-nitrosobenzanilides in carbon tetrachloride and benzene: the formation of carboxylic acids, anhydrides, and arynes

Abstract

Decomposition of a series of N-nitrosobenzanilides [R¹C₆H₄·N(NO)·CO·C₆H₄R²-p; R²= Cl; R¹= H, 2-Br, 3-Br, 4-Br, 3-Me, 4-Me, 3-NO₂, or 4-NO₂. R²= Br; R¹= 4-NO₂ or 4-Me. R¹= H; R²= NO₂ or Me] in carbon tetrachloride in the presence or absence of tetraphenylcyclopentadienone has been investigated. In the latter cases the reaction gives the corresponding benzoic acid (p-R²C₆H₄·CO₂H)(29–79%), benzoic anhydride [(p-R²C₆H₄·CO)₂O](12–38%), and aryl chloride (R¹C₆H₄Cl)(15–40%) as major products, thus indicating that removal of aromatic protons has occurred, and that attack by carboxylate anion on the nitroso-amide or the isomeric diazocarboxylate has taken place. Reactions carried out in the presence of tetraphenylcyclopentadienone lead to the trapping of arynes, with suppression, in some cases, of formation of the anhydride. The presence of water leads to the suppression of the formation of arynes. Similar results are obtained from corresponding decompositions in benzene with the exception that anhydrides are not formed. 2′,4,6′-Trichloro- and 2′,4′,6′-tribromo-4-chloro-N-nitrosobenzanilides, with their ortho-positions blocked by halogen atoms, do not give p-chlorobenzoic acid on decomposition in benzene and in carbon tetrachloride but rather react primarily by nucleophilic displacement of ortho-halogen atoms by p-chlorobenzoate anion.