Gas-phase dimerization of dimethylaniline in an external electrospray Fourier transform mass spectrometer

Abstract

N,N-Dimethylaniline (DMA) is a common starting material in graft copolymerization and photopolymerization processes when combined with an organic acid. Several anodic oxidation studies of DMA, in an acidic medium, have been performed. Numerous electrochemical studies imply that DMA has a tendency to dimerize, forming the tail-to-tail coupling product N,N,N',N'-tetramethylbenzydine (TMB). Here, external electrospray ionization Fourier transform mass spectrometry was used to investigate the dimerization and charging characteristics of DMA in an acidic medium in the absence of an applied electrochemical technique. DMA forms both tail-to-tail and head-to-tail dimer products, and the different linkage types were determined by employing tandem mass spectrometry for structure elucidation. In addition, it was found that desolvated protonated DMA ions accumulated and stored in the hexapole ion guide for 1-10 s before transport to the trapped ion cell can undergo gas-phase ion-molecule reactions to form dimeric products, including doubly charged species. Hence the hexapole storage region can be used to conduct ion-molecule reactions away from the low-pressure ion trap.