Gas-phase electrophilic addition promoted by CH₃S⁺== CH₂ ions on aromatic systems

• Published in: Journal of mass spectrometry 2007-10, Vol.42 (10), p.1310-1318
• Main Authors: Fileti, Eudes E, Moraes, Patrícia R.P, Domingues, Leonardo, Riveros, José M
• Format: Article
• Language: English
• Subjects: aromatic electrophilic reactions; Chemistry; Exact sciences and technology; ion/molecule reactions; Mass spectrometry; methylthiomethyl cation; Organic chemistry; Reactivity and mechanisms
• ISSN: 1076-5174; 1096-9888
• DOI: 10.1002/jms.1202

The gas-phase methylenation reaction between CH₃S⁺==CH₂ and alkylbenzenes, aniline, phenol and alkyl phenyl ethers, which yields [M + CH]⁺ and CH₃SH, has been studied by Fourier transform ion cyclotron resonance (FT-ICR) techniques and computational chemistry at the DFT level. The methylthiomethyl cation is less reactive than methoxymethyl and, unlike the latter, is unreactive toward benzene. The calculations suggest that reaction with toluene should proceed primarily by addition at the para and ortho positions resulting in a benzyl-type ion. Reaction with aniline-2,3,4,5,6-d₅ reveals that elimination of CH₃SD is kinetically favored by a factor of 5 over elimination of CH₃SH. Experiments with C₆H₆ND₂ and theoretical calculations suggest that methylenation at the nitrogen atom is energetically favorable and likely, but the observed results may reflect some H/D scrambling, which occurs after attack at a ring position. By comparison, reaction with phenol-2,3,4,5,6-d₅ reveals that methylenation followed by elimination of CH₃SD is kinetically favored by a factor of 3.8 over elimination of CH₃SH. For phenol, the theoretical calculations suggest that attack by CH₃S⁺==CH₂ at the para or ortho position is the only low-energy pathway for methylenation. However, a low-energy pathway for hydrogen scrambling is predicted by the calculations originating from the exit complex, [CH₃SH··· CH₂==C₆H₄==OH]⁺, of reaction at a ring position. Copyright © 2007 John Wiley & Sons, Ltd.