Site of alkylation of N‐methyl‐ and N‐ethylaniline in the gas phase: a tandem mass spectrometric study Journal Articles uri icon

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abstract

  • AbstractN‐Methylaniline (NMA) was ethylated and N‐ethylaniline (NEA) was methylated under chemical ionization conditions using C2H5I and CH3I, respectively, as reagent gases. The structures of the resulting m/z 136 adduct ions have been probed using metastable ion and collision‐induced dissociation (CID) methods. From the similarity of the spectra obtained and from the presence of structure‐diagnostic ions at m/z 59 (CH3NHC2H5+•) and m/z 44 (CH3NHCH2+), it is concluded that predominantly N‐alkylation occurs in both systems. This interpretation was aided by the use of C2D5I and CD3I as reagents. Adduct ions of m/z 136 were also formed by ethylation of the isomeric toluidines and by methylation of the ring‐ethylanilines. The resulting CID mass spectra were distinctly different from those obtained for the m/z 136 ions obtained by alkylation of NMA and NEA. Protonation of N‐ethyl‐N‐methylaniline using CH3C(O)CH3 as Brønsted acid reagent produced an m/z 136 species whose CID mass spectrum also featured intense ion signals at m/z 59 and 44. This observation led to the conclusion that protonation with acetone as reagent results, in this case, in dominant N‐protonation. However, the CID mass spectrum of the m/z 136 ion formed when CH3OH was the protonating agent featured a weak signal at m/z 44 and no signal at m/z 59. Hence it was concluded that the latter m/z 136 ion contains a larger contribution from the ring‐protonated adduct. Copyright © 2004 John Wiley & Sons, Ltd.

publication date

  • June 2004