Synthesis of aryl diethers and diamines via C-X (X = O, N) Ullmann cross-coupling of 1,4-dibromobenzene

Abstract

and amines which serve as important aryl molecular scaffolds in functional materials. This study explored the synthesis and characterization of C-O and C-N coupled products derived from 1,4-dibromobenzene with various phenols/alcohols and amines. Reactions were carried out in dimethyl sulfoxide (DMSO) using activated copper bronze/Cu2O/CuCl2.2H2O catalysts with Cs2CO3 as a base under atmospheric or nitrogen conditions at varying temperatures and time periods. Reaction progress was monitored by thin layer chromatography and crude products were purified by column and preparative chromatography. The purified products were characterized using FTIR and UV-visible spectroscopy. In the C-O coupling, the reaction of 1,4-dibromobenzene with benzyl alcohol (1:2 molar ratio) using 2 eq. Cs2CO3 and 10 mol % CuCl2·2H2O, in DMSO at 130 oC overnight afforded a new ether product. FTIR spectra exhibited characteristic peaks at 3174, 1029 and 720 cm-1, consistent with phenyl / -OH, C-O-C and C-Br stretching vibrations confirming ether bond formation. UV-vis analysis showed a λmax at 272 nm indicating π- π* transitions of a conjugated π system. In C-N coupling, the reaction of 1,4- dibromobenzene with benzyl amine (1:2 molar ratio) under similar conditions but with 5 mol % CuCl2·2H2O at 130 oC for 4 h produced a new amine product. The FTIR spectrum exhibited the disappearance of characteristic stretching vibration peaks of -NH2 around 3300– 3500 cm⁻¹ supports successful C-N coupling. Further structural confirmation of both ether and amine derivatives requires 1H and 13C NMR spectroscopy.