- Medium effect on the rotational barrier of carbamates and its sulfur congeners
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The solvent effect on rotation about the conjugated C-N bond has been studied for methyl N,N-dimethylcarbamate (1), S-methyl N,N-dimethylthiocarbamate (2), O-methyl N,N-dimethylthiocarbamate (3), and methyl N,N- dimethyldithiocarbamate (4). The present investigation included experimental determination of activation parameters (ΔH?, ΔS?, and ΔG?) combined with theoretical calculations via both quantum and classical approaches. Rotational barriers were measured through dynamic NMR experiments in solvents of varied polarity and proton donor ability. In the less polar solvents, the values were 15.3 ± 0.5 (CS2), 14.0 ± 1.1 (CS2), 17.5 ± 0.4 (CCl4), and 14.6 ± 0.5 kcal/mol (CCl4) for 1, 2, 3, and 4, respectively. Upon changing to an aqueous solution, the greatest variations occurred for 2 and 4, whereas for 1 and 3, there was no observable effect. Quantum chemical calculations at the HF/6-311+G(2d,p) and B3LYP/6-311+G(2d,p) levels, with the inclusion of solvation effects via the isodensity polarizable continuum model (IPCM), correctly reproduced the experimentally observed trends but failed to account for some of the measured rotational barrier's magnitudes. Hydrogen-bonding effects were included by performing molecular dynamic simulations. For these latter calculations, it was necessary to parametrize the force field against energies of water-solute complexes calculated at B3LYP/6-31+G-(d,p). Through the results of radial distribution functions, solution rotational barriers could be calculated, presenting good agreement with experimental determinations and revealing the role of hydrogen bonding. Interestingly, only for 2, the rotational barrier is predicted to increase as a result of complexation with water. For the remaining compounds, hydrogen bonding causes the barrier to decrease, contrasting with most of the molecular systems studied up to now.
- Pontes, Rodrigo M.,Basso, Ernani A.,Dos Santos, Francisco P.
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- Conversion of thiocarbamates to carbamates
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Treatment of methyl N-methylthionocarbamate (2a) with a catalytic amount of iodine or conc. H2SO4 results in the unexpected formation of the isomer, methyl N-methylthiolcarbamate (3a) in 90% yield. This has subsequently been transformed into methyl N-methylcarbamate (4a), by sodium methoxide. A curious transformation of methyl N-methyldithiocarbamate (1a) to (4a) on prolonged treatment with sodium methoxide is also discussed.
- Tandel, Sagun K.,Rajappa, Srinivasachari,Pansare, Sunil V.
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- VIBRATIONAL SPECTRA OF MONOTHIOCARBAMATES. I. ASSIGNMENT AND TENTATIVE FORCE FIELD OF S-METHYL-N,N-DIMETHYLTHIOCARBAMATE
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FT-IR and Raman spectra of S-methyl-N,N-dimethylmonothiocarbamate and its d3-, d6-, d9-, and 13C-substituted isotopomers have been recorded and analysed.Normal coordinate calculations were performed to support the assignment and to derive a simplified valence force field which would be characteristic of the monothiocarbamate moiety, =N-(C=O)-S-, and is consistent with the known bond length vs force constant correlations.
- Keresztury, G.,Besenyei, G.,Holly, S.
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- O,S-Dimethyl carbonodithioate as a phosgene substitute for the preparation of S-methyl alkylcarbamothioates and dialkylcarbamothioates
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O,S-Dimethyl carbonodithioate is proposed as a suitable and safely handled reagent that can be used as a replacement for phosgene in the synthesis of S-methyl alkyl- and dialkylcarbamothioates. The former were obtained by a two-step procedure, which can also be carried out in a one-pot fashion without isolating the intermediates O-methyl alkylcarbamothioates; the overall yields of the pure S-methyl alkylcarbamothioates were 94-98%. Optimal conditions for the synthesis of S-methyl dialkylcarbamothioates involved a one-step procedure in a solvent-free system in the presence of triethyl(methyl)ammonium methyl carbonate as a catalyst; yields of the pure products were 85-98%. A mechanism is proposed for the carbamothioate-formation reaction. Georg Thieme Verlag Stuttgart.
- Degani, Iacopo,Fochi, Rita,Magistris, Claudio
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experimental part
p. 3807 - 3818
(2010/03/30)
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- Preparation of N,N-Dimethyl-N′-arylureas using S,S-dimethyl dithio-carbonate as a carbonylating reagent
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A new, general method for the preparation of N,N-di-methyl-N′- arylureas using S,S-dimethyl dithiocarbonate as a phosgene substitute is reported. The method has been set up according to four procedures, all including three steps: (1) reaction of S,S-di- methyl dithiocarbonate with dimethylamine to give S-methyl N,N-dimethylthiocarbamate; (2) halogenation with various halogenating reagents (chlorine, methanesulfenyl chloride, bromine, and meth-anesulfenyl bromide) to give N,N-dimethylcarbamoyl chloride or bromide; (3) in situ reaction with primary arylamines. All the target products were obtained in high yields (85-98%; 16 reactions, average yield 93%) and with high purity. Also noteworthy is the recovery of byproducts of industrial interest, namely methanethiol and dimethyl disulfide, with complete exploitation of the reagent S,S- dimethyl dithiocarbonate. Georg Thieme Verlag Stuttgart.
- Degani, Iacopo,Fochi, Rita,Magistris, Claudio,Migliaccio, Mara
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experimental part
p. 801 - 808
(2009/08/07)
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- Synthesis of aromatic urea herbicides by the selenium-assisted carbonylation using carbon monoxide with sulfur
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Commercially useful aromatic urea herbicides were synthesized in good yields from lithium amides of aromatic amines with thiocarbamates, which were prepared by the selenium-assisted carbonylation of secondary amines with carbon monoxide and sulfur under mild conditions.
- Mizuno, Takumi,Kino, Takanobu,Takatoshi, Ito,Miyata, Toshiyuki
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p. 1675 - 1688
(2007/10/03)
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- Oxidation of dithiocarbamates and synthesis of a stable sulfine
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Investigation of the oxidation reaction of various dithiocarbamates demonstrated that the corresponding sulfines (S-oxides) are formed. Though their stabilities are very moderate, a number of sulfines could be isolated and characterised. When left at ambient temperature they decomposed to thiolocarbamates and dithiocarbamates. The sulfines from secondary dithiocarbamates led to disulfides which formation was explained. With a sterically hindered aryl group present on the sulfur atom, a stable sulfine was prepared and its crystal structure was analysed.
- Chevrie, David,Metzner, Patrick
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p. 8983 - 8986
(2007/10/03)
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- Vibrational spectra of monothiocarbamates-II. IR and Raman spectra, vibrational assignment, conformational analysis and ab initio calculations of S-methyl-N,N-dimethylthiocarbamate
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The IR (3200-30 cm-1) spectra have been recorded for S-methyl-N,N-dimethylthiocarbamate, (CH3)2NC(O)SCH3, and its isotopomers, S-d3, N-d6 and N-d9, for the gas and liquid.Additionally, the Raman spectra (3200-10 cm-1) for the solid and liquid, with qualitative depolarization ratios, have been obtained for all the isotopes.These data are interpreted on the basis that the s-cis conformer (the S-methyl group oriented cis to the carbonyl group) with CS symmetry is the only form existing in all three phases for this molecule.A complete vibrational assignment proposed for the -d0 molecule is facilitated by the availability of spectral data for five different isotopomers.A normal coordinate analysis has been carried out utilizing ab initio calculations with the 3-21G* basis set.The potential energy distributions and ab initio calculated frequencies have allowed a clarification of some of the corresponding results obtained from experiment.Structural optimizations and potential surface scan have also been carried out by ab initio calculations with the 3-21G* basis set.These results are compared with some previous studies on this molecule as well as on similar molecules.
- Keresztury, G.,Holly, S.,Besenyei, G.,Varga, J.,Wang, Aiying,Durig, J. R.
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p. 2007 - 2026
(2007/10/02)
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- Gas-phase Pyrolysis of Methyl Dimethylcarbamate and the Correponding Mono- and Dithio Analogs
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Gas-phase pyrolysis of methyl dimethylcarbamate (1), O-methyl dimethylthiocarbamate (2), S-methyl dimethylthiocarbamate (3), and methyl dimethyldithiocarbamate (4) has been carried out in the temperature range 1043-1404 K applying the gas-phase Curie-point pyrolysis technique.Real-time analysis of the pyrolyses were carried out by field ionization- and collision activation mass spectrometry. 1 and 4 were found to be thermally very stable even after pyrolysis at 1404 K.N-Methyl methanimine was found in moderate yield following pyrolysis of 2 and 3.The possible isomerization of the ester functions were studied by application of collision activation mass spectrometry in combination with 18O and 34S labeling.The results are discussed considering available data on the simple acetic acid esters with special emphasis on the effect of increasing sulfur content.
- Carlsen, Lars,Egsgaard, Helge
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p. 987 - 990
(2007/10/02)
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