Reaction of Imidazoles with Cyanogen Bromide: Cyanation at N 1 or Bromination at C 2?

Abstract

The reaction in acetonitrile solution of a number of imidazoles(1H-, 1-methyl-, 2-methyl-, 4-methyl-, 1,2-, 1,4- and1,5-dimethyl-, 1-ethyl-, 1-benzyl- and 1-butyl-imidazole) and imidazolecomplexes([Co(NH₃)₅(imH)](ClO₄)₃,[Co(NH₃)₅(im)](ClO₄)₂ and[Co(NH₃)₅(1-Meim)](ClO₄)₃) with BrCN has beenstudied. Those imidazoles bearing an N-alkyl substituent and having a hydrogenat C2 react to give the 2-bromo products, while the N-H imidazoles react togive N-cyano derivatives. The product(s) from thereaction of 1,2-dimethylimidazole with BrCN could not be characterized. Of thecomplexes, only[Co(NH₃)₅(im)](ClO₄)₂ reacts, giving the 2-bromoproduct. Our observations suggest a lone pair on a ring nitrogen atom isnecessary for an imidazole to react with BrCN, and a possible mechanism issuggested. The X-ray structure of 2-methylimidazole-1-carbonitrile isreported. Crystal data (–143°C) forC₅H₅N₃:monoclinic, P2₁/c, a10·201(5), b 7·110(3),c 7·227(3) Å, β 100·47(2)°,V 515·4(4) Å 3 , Z 4,d_calcd 1·380 gcm^¯3 . Refinement of the structure converged withR₁ 0·0444 for 1183reflections with F_o >4F(F_o) andwR₂ 0·1259 for all 1278data.