The Pyrolytic Reaction of Ketonic Hydrazones fromS-Methyl Dithiocarbazate: A Combined Online GC-MS Pyrolysis and DFT Study

Abstract

The gas-phase pyrolysis of ketonic hydrazones from S-methyl dithiocarbazate R(1)R(2)C=N-NHC(=S)SCH(3) (R(1), R(2) = alkyl or aryl) was investigated by online GC-MS pyrolysis and theoretical calculation. Both of these pyrolytic products, ascribed to methanethiol and the corresponding N-isothiocyanate imines, were detected in the total ion chromatography (TIC) of GC-MS. Calculation results exhibit two stable configurational structures for reactants (Re), which can interconvert with relatively low barriers (<78 kJ/mol). DFT calculations showed that the two unimolecular pyrolytic processes, a direct 1,2-elimination of CH(3)SH for syn-Re and a two-step reaction pathway for trans-Re involving tautomer interconversion followed by decomposition of CH(3)SH, are competitive in the reaction. Both syn-Re and trans-Re exhibit lower critical energies in the propagation step of the radical pyrolysis than that in the unimolecular pyrolysis process (187.76 kJ/mol via 131.91 kJ/mol for syn-Re, and 159.15 kJ/mol via 98.92 kJ/mol for trans-Re). However, much more energy is needed to excite the compound to produce the methylthio radical, with 262.03 and 253.60 kJ/mol for syn-Re and trans-Re, respectively. Therefore, the unimolecular pyrolysis rather than the radical one occurs in the condition of this study.

Investigation on the Gas-Phase Decomposition of Trichlorfon by GC-MS and Theoretical Calculation

“…Vibrational frequencies and zero point energies (ZPE) for all the key species were calculated at the same level of theory. Scaled frequencies were not considered since the errors on the calculated thermodynamical properties are almost negligible at this theoretical level [ 14 , 18 ]. Data for the geometries of all of the structures that were determined are available in the Supporting Information ( S1 – S9 Tables).…”

“…Methods for analyzing OPs generally include gas chromatography (GC) [ 7 , 8 ] and high performance liquid chromatography (HPLC) [ 9 , 10 ]. Some OPs have been found to undergo pyrolysis in the heated GC injector port when they are analyzed by GC or GC-mass spectrometry (MS) [ 11 – 14 ]. TCF is a common OP but, unusually, it has no garlic-like odor.…”

Rapid differentiation ofortho-,meta-, andpara-isomers of halogenated phenylmethylidene hydrazinecarbodithioates by metal complexation and electrospray ionization mass spectrometry

“…Thiosemicarbazones are an important class of sulfur ligands for transition metal ions because of their mixed hard‐soft donor character and versatile coordination behavior, and their metal‐chelating abilities that partially account for their biological activities . Substituted phenylmethylidene hydrazinecarbodithioates ( M ) are an important intermediate in thiosemicarbazone synthesis and exhibit a considerable chemical activity . In our previous work, dissociation of the complex of [2 M – H + Ni] + results in an active complex [ M + SCH 3 + Ni] + ion that undergoes ligand‐exchange reactions with residual gas molecules, such as water, acetonitrile, and nitrogen, in the ion trap in MS 3 experiments .…”

“…[49][50][51] Substituted phenylmethylidene hydrazinecarbodithioates (M) are an important intermediate in thiosemicarbazone synthesis [46] and exhibit a considerable chemical activity. [54,55] In our previous work, dissociation of the complex of [2M -H + Ni] + results in an active complex [M + SCH 3 + Ni] + ion that undergoes ligand-exchange reactions with residual gas molecules, such as water, acetonitrile, and nitrogen, in the ion trap in MS 3 experiments. [56] To advance our work, the gas-phase ligand-exchange reactions were applied to differentiate the positional isomers of halogensubstituted M, since halogen is the common substituent on the aryl group.…”

Descrição teórica de complexos de metais de transição com ligantes hidrazona com potencial aplicação farmacológica

“…Hidrazonas 1a-3a estudadas por Ros e colaboradores. [9] ....................6 Figura 1.5. Hidrazonas relatadas por Veljkovic´ e colaboradores.…”