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The thermal decomposition of ethanethiol was studied using a 1 mm x 2 cm pulsed silicon carbide microtubular reactor, CH3CH2SH + Δ → Products. Unlike previous studies these experiments were able to identify the initial ethanethiol decomposition products. Ethanethiol was entrained in either an Ar or a He carrier gas, passed through a heated (300-1700 K) SiC microtubular reactor (roughly ≤100 μs residence time) and exited into a vacuum chamber. Within one reactor diameter the gas cools to less than 50 K rotationally, and all reactions cease. The resultant molecular beam was probed by photoionization mass spectroscopy and IR spectroscopy. Ethanethiol was found to undergo unimolecular decomposition by three pathways: CH3CH2SH → (1) CH3CH2 + SH, (2) CH3 + H2C=S, and (3) H2C=CH2 + H2S. The experimental findings are in good agreement with electronic structure calculations. (Chemical Equation Presented).

The photochemistry of methyl thioglycolate (MTG), CH3OC(O)CH2SH, in gas phase and in matrix isolation conditions was studied by means of FTIR spectroscopy, and the influence of the presence of molecular oxygen on the photochemical me

The products of the gas-phase pyrolysis of two regioisomeric 1,2,4-trithiolane S-oxides were collected in an argon matrix at 1OK and studied by means of spectroscopic as well as computational methods. Whereas the main products of the pyrolysis of the symmetrical S-oxide were identified as thioformaldehyde S-oxide and thioformaldehyde S-sulfide, the non-symmetrical S-oxide gave predominantly dithioformic acid, which exists as a mixture of s-cis and s-trans conformers. We present a rationalization of the reaction pathways including density functional theory computations.

The CH + CH4 and H2S reactions were studied, at room temperature, in a low-pressure fast-flow reactor. CH (X2π, v = 0) radicals were obtained from the reaction of CHBr3 with potassium atoms. The overall rate constants were found at 330 K to be (0.76 ± 0.20) x 10-10 and (2.8 ± 0.8) x l0-10 cm3 molecule-1 s-1, respectively. The absolute atomic hydrogen productions were determined by resonance fluorescence in the vacuum ultraviolet: H production from the CH + CH4 reaction is 100% and from the CH + H2S reaction is 99-4+1%, the H production from the CH + H2 reaction being the reference. Ab initio studies of the different stationary points relevant to the CH + CH4 reaction have been performed at the CCSD(T)/cc-pVTZ level and comparison is made with experimental results. The experimental results for the CH + H2S reaction is compared with those of a recent theoretical study [Chem. Phys. 242 (1999) 1].

Matrix isolation spectroscopy allows the direct identification of ylide 1 and its cyclic isomer 2. They were obtained by pyrolysis of 1,2,4-trithiolane under high vacuum; the cyclic compound forms from 1 by thermal ring closure in a kinetically controlled reaction.

The dissociative photoionization of CH3SSCH3 has been investigated in the photon energy range of ～8-25 eV with a molecular beam/photoionization mass spectrometry/threshold photoelectron spectrometry system using synchrotron radiation as an ionization source. For dissociation above photon energy of 11.5 eV, six fragment ions of CH3+, C2H3+, SH3+, HCS+, S2+, and CH2S2+ were reported for the first time. The photoionization efficiency spectra for the parent ion and for 12 observed fragment ions, CH3+, C2H3+, SH3+, HCS+, CH2S+, CH2SH+, CH3SH+, CH3SH2+, CH3SCH2+, S2+, CH2S2+, and CH2S2H+, were measured; their branching ratios as a function of photon energy were derived. Ionization energy of 8.20±0.04eV for CH3SSCH3 and the appearance energy for each fragment ion were determined from the onsets of the photoionization efficiency spectra. Based on the appearance energy and existing thermochemical data, plausible structures of the fragment ions and their neutral counterparts are proposed. Fragmentation mechanisms that involve H migration and structural rearrangement in the dissociative photoionization processes are discussed.

N-Phthaloyl cysteine derivatives 1a-d were photochemically transformed by elimination, decarboxylation, and via electron transfer cyclization to the products 2,3,4 and 6-8. The spin selectivities of the singlet and triplet pathways were investigated in acetonitrile and acetone . The excited singlets were prone to elimination and γ-H abstraction (e.g. formation of 5) whereas the triplets cyclized to thiazinoisoindoles. This behavior can be correlated with efficiencies of forward and return electron transfer stepsversus homolytic hydrogen abstraction as exemplified for the cysteine substrate.

The reactions of the HO-, CH3S-, CH2S- and CH2=C(CH3)-CH2- ions with three ketones (CF3COR; R=CH3, CF3, C6H5) and three esters of trifluoroacetic acid (CF3CO2R; R=CH3, C2H5 and C6H5) have been studied with use of Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry. All four negative ions react exclusively by proton transfer with CF3COCH3. With the other substrates, the HO- ion reacts by various pathways, such as proton transfer, SN2 substitution, E2 elimination and attack on the carbonyl group. The CH3S- ion is unreactive towards CF3COC6H5 but is able to react by hydride transfer, SN2, E2 and/or carbonyl attack with the remaining neutral species. The CH2S- radical anion reacts by electron transfer to afford stable molecular radical anions of CF3COCF3 and CF3COC6H5, whereas the main reaction with the two esters, CF3CO2CH3 and CF3CO2C2H5, is dissociative electron transfer leading to CF3CO2- and CF3- ions. The CH2=C(CH3)-CH2- anion displays a more complex reactivity pattern involving electron transfer, SN2, E2 as well as attack on the carbonyl group. Direct evidence for the occurrence of electron transfer as the initial step in an overall BAC2 type process has not been obtained for the systems studied. The reaction of the CH2S- ion with CF3CO2C6H5 was observed, however, to yield exclusively a CF3COCHS-. radical anion. Based upon the absence of a BAC2 process in the reaction of CH2S- with the methyl and ethyl esters of trifluoroacetic acid in combination with the facile occurrence of electron transfer from this radical anion, it is suggested that the CF3COCHS-. ion is formed by an initial electron transfer followed by coupling between the CH2S molecule and the CF3CO2C6H5- radical anion and subsequent loss of C6H5OH from the collision complex.

Thermolysis of methyl methanethiosulfinate and methyl tert-butyl sulfoxide has been studied by photoelectron (PE) spectroscopy. The electronic structure of methanesulfenic acid (1) generated from both compounds has been determined, and the thermal stability of 1 was checked. 1 appears rather stable in the gas phase, giving rise to thioformaldehyde and water at high temperature. Thermolysis of vinyl tert-butyl sulfoxide gives rise to ethanethial S-oxide (6). At the thermolysis onset, sulfine 6 is observed in a mixture with a compound identified as ethenesulfenic acid (4). These results imply either an easy isomerization of 4 to 6, in agreement with previous theoretical evaluations, or an alternative thermolysis pathway of the starting sulfoxide, directly leading to sulfine 6. The obtained PE spectra complement previous microwave and/or mass spectrometry data and provide a further insight in the electronic structure and thermal stability of sulfenic acids 1 and 4. The experimental ionization potentials are compared throughout this study with ab-initio calculated vertical ionization potentials either within Koopmans' approximation or by difference between the ionic and ground state energies.

The thermal decomposition of γ-thiovalerolactone, α-methyl-γ-thiobutyrolactone and β-methyl-γ- thiobutyrolactone has been studied in a gaseous flow system, by monitoring the changes in the photoelectron spectra recorded during the course of the reactions. Three modes of decomposition were observed, two involve loss of carbon monoxide (decarbonylation) and one involves loss of carbonyl sulfide (decarboxylation). The decarbonylation reaction producing an olefin and a thioaldehyde and the decarboxylation producing an olefin are similar to those observed for the unsubstituted thiobutyrolactone. The third reaction, observed only in the methylated compounds, is decarbonylation with the formation of hydrogen sulfide and butadiene. It is proposed that the last reaction can be attributed to the relatively facile elimination reaction of a butenethiol intermediate.

High-resolution intracativity dye laser spectroscopy has been used to obtain sub-Doppler spectra of transitions to 350 rotational levels in the 401 band of the 1A2- 1A1 electronic transition of thioformaldehyde.Ground state combination differences from the sub-Doppler spectra, combined with microwave and infrared data, have been used to improve the ground state rotational and centrifugal distortion constants of H2CS.The upper state shows a remarkable number of perturbations.The largest of these are caused by nearby triplet levels, with matrix elements of 0.05-0.15 cm-1.A particularly clear singlet-triplet avoided crossing in Ka' = 7 has been shown to be caused by interaction with the F1 component of the 3162 vibrational level of the 3A2 state.At least 53percent of the S1 levels show evidence of very small perturbations by high rovibronic levels of the ground state.The number of such perturbations is small at low J, but increases rapidly beyond J=5 such that 40percent-80percent of the observed S1 levels of any given J are perturbed by ground state levels.Model calculations show that the density and J dependence of the number of perturbed levels can be explained if three is extensive rotation-induced mixing of the vibrational levels in the ground state.

Argon-matrix isolated thietane at 10 K decomposed by irradiation (λ > 290 nm) to form ethylene and thioformaldehyde.The photolysis of thietane under these conditions has been shown to be a clean source of thioformaldehyde.The CH2S and CD2S molecules generated this way are indefinitely stable and their infrared spectra could be recorded.

The anion [CH3)2Alo]- (1) has prepared In a flowing afterglow selected ion flow tube (FA-SIFT) by ion selection from the reaction mixture of trimethylaluminum dimer and hydroxide. This unusual ion is quite reactife and has extensively studied. It with halogen-containing compounds of several types, including fluorobenzene, chlorobenzene, bromofluorobenzene, acetyl chloride, and HF, to give {(CHj^AKOHJX] , where X = F, Cl, and Br. Its chemistry with hexafteorabenzene and silicon tetrafluoride has also detailed as have a number of reactions with carboxylic adds, esters, anhydrides, sulfur-containing neutrals, alcohols, water, and ammonia. The dominant reaction pattern of 1 involves six-centered processes which require a relatively acidic hydrogen and a lone pair donor atom in the neutral reactant. In these reactions, ion 1 abstracts a proton as the lone pair atom to aluminum, often with concomitant extrusion of a small, neutral molecule. We have compared the reactifity of 1 with that of [(CH3)3SiO]- and briefly examined other aluminum oiide ions. The kinetics of several reactions as well the thermochemical relationships among some of these ions have studied, Acidity studies coupled with thermochemical analysis establish that the conjugate acid of [A1O]~ is A1OH, not HA1O. Computational studies out to the reaction of trimethylaluminum and hydroxide, and the acidities and of A1OH and HA1O.

Mono- and dialkylated thiocyanohydrins are prepared by alkylation of the parent compound 2 (NCCH2SH) under mild conditions. Some examples of the reactivity of this new class of compounds are also given.

Thioxoethanal has been generated in the gas phase by vacuum thermolysis of 2,3-dihydro-1,4-oxathiin.Its characterization was performed by chemical trapping and photoelectron spectroscopy (PES).The PE HeI-HeII study led to the conclusion that thioxoethanal was obtained, with ethylene, as the only thermolysis product at 720 deg C.At higher temperatures, a cleavage into methanethial and carbon monoxide was observed.The results from the PE study, as well as MNDO calculations, indicate a very weak interaction between the formyl and thioformyl moieties of the molecule through the ? C-C bond.The HOMO sulfur lone pair is only slightly stabilized by the inductive effect of the carbonyl group.These conclusions account for the observed dienophilic reactivity of thioxoethanal.

Methanethial 2a and ethanethial 2b are obtained by a vacuum gas-phase dehydrocyanation of the corresponding thiocyanohydrins and characterized by mass spectroscopy experiments.

The matrix isolation technique has been used to study the initial intermediate products of the reaction of molecular fluorine, F2, with several alkyl sulfides, as well as with trimethylphosphine.While previous studies of the reaction of these bases with ClF and Cl2 demonstrated that charge transfer complexes are formed, no evidence has been observed here for complex formation.Rather direct reaction occurs for each system studied, leading in several cases to hydrogen displacement products, while in other systems the spectral evidence supports a direct addition reaction.For example, in the F2/H2S system, initial formation of H2SF2 is postulated, followed by HF elimination to form HSF upon Hg arc irradiation.

The flash vacuum pyrolysis of Diels-Alder adducts of anthracene constitutes a rapid and selective route to methanethial 1 and methanithial S-oxide 2, as analyzed in the gas phase by photoelectron spectroscopy.Low temperature infrared and nuclear magnetic resonance (1H, 13C) spectra are also reported for sulfine 2.

Exposure of a solid argon matrix containing the molecules OCS and PX3 (X = F or Cl) at ca. 20 K to broad-band ultraviolet radiation leads to the formation of CO and the corresponding thiophosphorus(V) halides SPX3, as witnessed by the infrared spectrum of the matrix.Photolysis of a solid methane matrix containing OCS at 13-20 K on exposure to radiation with wavelengths near 230 nm gives rise to CO, methanethiol, CH3SH, thioformaldehyde, H2C=S, and carbon disulfide, CS2, as the only products to be detected by their infrared spectra.Yet there is no sign of either CH3SH or H2C=S on photolysis of OCS in a CH4-doped argon matrix with the composition Ar:CH4:OCS = 100:20:1.Evidently the photolysis of OCS generates 1D sulfur atoms which add to an adjacent CH4 molecule with the formation of a vibrationally activated intermediate *; this relaxes to give CH3SH or decomposes to give H2C=S.Similar experiments have been carried out with solid argon matrices including OCS and either C2H4 or C2H2.In the presence of C2H4 there is no hint of C-H insertion; instead the C2H4 undergoes sulfur atom addition at the double bond to give thiirane, , as the sole product to be identified by its infrared spectrum.By contrast, C2H2 yields thioketene, H2C=S, ethynethiol, HCCSH, and carbon disulfide, CS2, as the main products, as well as thiirane, , as a minor product.The response of the hydrocarbon molecules in argon matrices can be interpreted in terms of the diffusion and reaction of ground-state 3P sulfur atoms but not of 1D sulfur atoms which are too short-lived to undergo significant migration.It appears that 3P sulfur atoms react with both C2H4 and C2H2 to yield a triplet diradical: that derived from C2H4 favors cyclization, whereas that derived from C2H2 rearranges preferentially to H2C=C=S and this in turn enters into secondary reactions to give HCCSH and CS2.

A mild, efficient and general method for the generation of reactive thioaldehydes from α-silyldisulfides is described.

Measurements have been made of the asymmetry doublings in the lines of the rR3 branch of the 401 band of the 1A2- 1A1 system of thioformaldehyde by using the technique of intermodulated fluorescence.Line widths of ca. 5 MHz have been achieved and many small irregular perturbations up to ca. 300 MHz have been observed.These perturbations are not magnetically sensitive and must be caused by high vibrational levels of the ground state.The mixing of ground- and excited-state rovibronic levels produces irregularities in the fluorescence efficiencies of the latter.

N-Methylthiophthalimide undergoes a photochemical cycloaddition reaction with 2,3-dimethylbut-2-ene or with stilbene to give products containing a spiro-thietane system; with 1,1-diphenylethene the product isolated is a diphenylmethyleneisoindoline.

The products of very low pressure pyrolysis (VLPP) of hexamethylcyclotrisilthiane (I), tetramethylcyclodisilthiane (II) and 3,3-dimethyl-3-silathietane (III) were isolated in Ar matrices and were studied by IR spectroscopy.The only pyrolysis product of I was cyclosilthiane II, a dimer of transient dimethylsilanthione (Me2Si=S) (IV).The starting material was recovered on pyrolysis of II.Thermal decomposition of III involves three intermediate unsaturated compounds: dimethylsilaethylene (Me2Si=CH2) (V) and thioformaldehyde (H2C=S) (VI), both isolated in Ar matrix at 10 K, as well as silanthione IV fixed in the matrix in a form of the cyclic diemr II.The latter was also observed in the study of copyrolysis of 1,1-dimethyl-1-silacyclobutane and thietane, being authentic sources of intermediates V and VI.IR spectra of starting compounds I, II and III isolated in Ar matrices were obtained.The theoretical structure of IV and force constant F(Si=S) were determined by the CNDO/2 method.With regard to CNDO/2 errors, Si=S bond distance and F(Si=S) are equal to 1.993 Angstroem and 4.72 mdyn/Angstroem, respectively.Calculation of normal vibrations resulted in the following values of vibrational frequencies of dimethylsilanthione (cm-1): 884 νs(SiC2) (A1), 735 νas(SiC2) (B2), 626 νs(Si=S) (A1), 200 1).

Very low pressure vapor phase pyrolysis (flash thermolysis) of four-membered ring compounds was followed by microwave spectroscopic detection of the reaction products.The molecules studied included substituted cyclobutanes, thietanes, oxetane and azetidine.Microwave spectroscopy is well suited not only to observe stable reaction products but also to detect unstable species formed during pyrolysis.The investigation provided a wealth of information on typical decomposition patterns during pyrolysis of four-membered ring compounds.In addition, new methods were found for producing some unstable molecules with improved efficiency.

Fluorescence spectra of single vibronic levels of the first excited singlet state of H2CS have been measured under effusive flow conditions as a function of pressure.Weak non-resonance bands grow in with increasing pressure, demonstrating the existence of collisional vibrational relaxation of the 41 level to the 40 level.

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Thiocarbonyl derivatives R1R2C=S with R1, R2 = H, CH3, C6H5 can be generated thermally in the gas phase from a variety of precursors.Especially advantageous are the cleavage of propene from allyl sulfides or, for their preparation in pure form, the pyrolysis of dithietane or trithiolane derivatives.Photoelectron spectroscopy proves to be well-suited for gas analysis in the flow tube used, for the optimization of the decomposition conditions, and via assignment of the observed ionization patterns for the characterization of the thioaldehydes and thioketones prepared.

Photoelectron spectroscopy has proven valuable for the analysis and optimization of numerous gas phase reactions in flow-systems - especially in search for heterogeneous catalysts, which can be tested within a single day using gas mixtures of varying composition over the temperature range from 300 K to 1300 K.In academic research, this real-time measuring probe allows one to determine - with millimol quantities and within a few hours - the temperatures for different decomposition channels.Simultaneously, main products can be characterized by the comparison of their ionization fingerprints with calculated (SCF) eigenvalue sequences making use of Koopmans theorem.If need be, the yield of a certain reaction product e. g. a short-lived intermediate can be improved by optimizing the reaction conditions aiming at maximum intensity of the corresponding bands.In this way, many short-lived and/or reactive molecules such as thioformaldehyde, P2 or silabenzene, which are discussed as examples, have been detected or reaction channels like vinyl azide -> 2H-azirine -> acetonitrile visualized, PE-spectrometers are well-suited for on-line connection to computers; portable instruments for laboratory use are under development.

Syntheses of 1,3-dithietane (1), 1,3-dithietane 1-oxide (2), 1,3-dithietane 1,1-dioxide (3), cis-1,3-dithietane 1,3-dioxide (4), trans-1,3-dithietane 1,3-dioxide (5), and 1,3-dithietane 1,1,3-trioxide (6) are reported for the first time.These compounds are converted in high yield to the previously described sulfene dimer 1,3-dithietane 1,1,3,3-tetraoxide (7).The structures of 2 and 7 are found to be respectively puckered (by microwave spectroscopy) and planar (by X-ray crystallography).Spectroscopic and physical data are discussed (photoelectron (PE) and NMR spectros copy, pKa values, oxidation potentials) along with some data on base-catalyzed H/D exchange.The PE spectra are assigned using MO models on different levels, including PNO/CEPA for thioformaldehyde (CH2S).Thermal decomposition is investigated using three independent methods: mass, microwave, and PE spectroscopy.Two types of decomposition channels are observed: retro 2+2 and retro 3+1.Among others, species like thioformaldehyde and sulfine (CH2SO, thioformaldehyde S-oxide) are produced.They are characterized by their microwave structure as well as by their PE ionization patterns and IR spectra.

The experimental advantages of the optimization of gasphase reactions using a photoelectron spectrometer are exemplified by investigating the reaction of cyanogen with white phosphorus and with dimethyl disulfide.Whereas NCCN does not react with any of the components of the thermal equilibrium P4 P2 even at 1470 K (!), H3CSSCH3 at 950 K is quantitatively converted, the main product being CH3SCN.

The thermal decomposition of the dialkyl chalcogenide derivatives RSR, RSSR and RSeSeR (R = CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, C(CH3)3) in a heated flow tube is analyzed and optimized using PE spectroscopy.Whereas high-temperature pyrolysis >1000 K yields mixtures of thermodynamically favored final products like H2, CH4, CS2, and HCCH, the lowest thermal reaction channel produces homogeneously olefin, H2S, and sulfur or olefin, alkaneselenol, H2Se, and selenium, respectively.The decomposition temperatures increase from RSeSeR via RSSR towards RSR and also with decreasing size of the alkyl groups.Based on the experimental data the possible course of the thermal decomposition is discussed.

The photolysis of inert matrix isolated methylene trithiocarbonate at 10 K has been shown to be a clean source of thioformaldehyde.The CH2S and CD2S molecules produced this way are indefinitely stable under these conditions and their FTIR spectra could be recorded.A normal coordinate analysis has been carried out and all the normal frequencies of both molecules have been assigned.

The gas-phase negative ion-molecule chemistry of 1,3-dithianes and 1,3-dithiolanes differs considerably from the in solution.When treated with anionic bases, 1,3-dithiane undergoes successive elimination reactions giving thiolates, in competition with deprotonation at the 2-carbon, which is the sole solution phase reaction channel.The appearence of the various product ions with changing base strength agrees with their calculated thermochemical onset.The gase-phase acidity of 1,3-dithiane is measurable if the elimination reaction is blocked by gem-dimethyl substitution at the 5 carbon.For 1,3-dithiolane, no deprotonation product is pbserved; even at thermochemical treshold, cycloreversion to RCS2- and ethylene occurs.This competes with successive elimination to thiolates, as with the six-membered ring.The differences between the gas phase and solution reactivities are rationalized in terms of counterion effects.