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. 2018 Mar;29(3):588-599.
doi: 10.1007/s13361-017-1858-x. Epub 2018 Jan 8.

Gas-Phase Reactions of Dimethyl Disulfide with Aliphatic Carbanions - A Mass Spectrometry and Computational Study

Barbara Franczuk  1 , Witold Danikiewicz  2
Affiliations

Gas-Phase Reactions of Dimethyl Disulfide with Aliphatic Carbanions - A Mass Spectrometry and Computational Study

Barbara Franczuk et al. J Am Soc Mass Spectrom. 2018 Mar.

Abstract

Ion-molecule reactions of Me2S2 with a wide range of aliphatic carbanions differing by structure and proton affinity values have been studied in the gas phase using mass spectrometry techniques and DFT calculations. The analysis of the spectra shows a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the carbanion. Product ions of thiophilic reaction (m/z 47), SN2 (m/z 79), and E2 elimination - addition sequence of reactions (m/z 93) can be observed. Primary products of thiophilic reaction can undergo subsequent SN2 and proton transfer reactions. Gibbs free energy profiles calculated for experimentally observed reactions using PBE0/6-311+G(2d,p) method show good agreement with experimental results. Graphical Abstract ᅟ.

Keywords: Aliphatic carbanions; DFT calculations; Dimethyl disulfide; Gas-phase ion-molecule reactions; Thiophilic reaction.

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Figures

Graphical Abstract
Graphical Abstract
ᅟ
Scheme 1
Scheme 1
SN@S reaction of dialkyl disulfides with nucleophiles
Scheme 2
Scheme 2
Formation of CH3-S-CH2-S- ion
Figure 1
Figure 1
Mass spectra of the reaction products of Me2S2 with: (a) –CH2-CN, (b) –CH2NO2, (c) CHF2-, (d) –C≡C-CO2Me, (e) –C≡C-Ph, (f) –CH2-COOEt, (g) –CH=C=O, (h) –CH2COOH
Scheme 3
Scheme 3
Possible reactions between Me2S2 and primary or secondary carbanions in the gas phase
Scheme 4
Scheme 4
Reactions between Me2S2 and cyanomethyl anion in the gas phase
Figure 2
Figure 2
Calculated Gibbs free energy diagram of possible paths of the reaction between cyanomethyl anion and dimethyl disulfide in the gas phase. Blue trace: thiophilic reaction, red trace: SN2 reaction, green trace: elimination – addition reaction, thin black line: the results of G4(MP2) calculations
Figure 3
Figure 3
Calculated Gibbs free energy diagram of possible paths of the reaction between nitromethyl anion and dimethyl disulfide in the gas phase. Blue trace: thiophilic reaction, red trace: SN2 reaction, green trace: elimination – addition reaction
Figure 4
Figure 4
Calculated Gibbs free energy diagram of possible paths of the reaction between difluoromethyl anion and dimethyl disulfide in the gas phase. Blue trace: thiophilic reaction, red trace: SN2 reaction, green trace: elimination – addition reaction
Scheme 5
Scheme 5
Reactions of substituted acetylenide anions with Me2S2 in the gas phase
Figure 5
Figure 5
Calculated Gibbs free energy diagram of the thiophilic path of the reaction between methyl acetylenecarboxylate anion and dimethyl disulfide in the gas phase. Blue and green traces: thiophilic reaction, red trace: SN2 reaction
Figure 6
Figure 6
Calculated Gibbs free energy diagram of possible paths of the reactions between (ethoxycarbonyl)methyl anion and dimethyl disulfide in the gas phase. Blue and green traces: thiophilic reaction, red trace: SN2 reaction
Figure 7
Figure 7
Calculated Gibbs free energy diagram of possible paths of the reaction between ketene anion and dimethyl disulfide in the gas phase. Blue trace: thiophilic reaction, red trace: SN2 reaction
Figure 8
Figure 8
Calculated Gibbs free energy diagram of possible paths of the reaction between carboxymethyl anion and dimethyl disulfide in the gas phase
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