A study of the gas-phase reaction between protonated acetaldehyde and methanol.

Protonated acetaldehyde is methylated on the oxygen during interaction with methanol in the gas phase. The ionic product of the iomnolecule reaction between methanol and protonated acetaldehyde is identical with C-protonated methylvinyl ether (high-pressure ionization), and with the (M - C2H5)(+) fragment ion of sec-butyl methyl ether (following electron ionization), and also with the (M - OCH3)(+) fragment ion of acetaldehyde dimethylacetal (following electron ionization). The structures of these ions and the mechanism of their formation were established by isotope-labeling experiments and collision-induced dissociation mass spectra of model compounds obtained with three different types of tandem mass spectrometers (BEQQ, triple-quadrupole, and a penta-quadrupole instrument). Gas phase synthesis of the product ion from [(2)H3]-methanol or [(2)H 4]-acetaldehyde provided insight into its mode of formation and collision-induced dissociation. (J Am Soc Mass Spectrom 1990, 1, 481-488).