3013-02-3Relevant articles and documents
Medium effect on the rotational barrier of carbamates and its sulfur congeners
Pontes, Rodrigo M.,Basso, Ernani A.,Dos Santos, Francisco P.
, p. 1901 - 1911 (2007)
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.
VIBRATIONAL SPECTRA OF MONOTHIOCARBAMATES. I. ASSIGNMENT AND TENTATIVE FORCE FIELD OF S-METHYL-N,N-DIMETHYLTHIOCARBAMATE
Keresztury, G.,Besenyei, G.,Holly, S.
, p. 237 - 242 (1990)
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.
Preparation of N,N-Dimethyl-N′-arylureas using S,S-dimethyl dithio-carbonate as a carbonylating reagent
Degani, Iacopo,Fochi, Rita,Magistris, Claudio,Migliaccio, Mara
experimental part, p. 801 - 808 (2009/08/07)
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.
Oxidation of dithiocarbamates and synthesis of a stable sulfine
Chevrie, David,Metzner, Patrick
, p. 8983 - 8986 (2007/10/03)
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.
