The thiocarbonyl 'S' is softer than thiolate 'S': A catalyst-free one-pot synthesis of isothiocyanates in water
Treatment of the preformed or the in situ generated aryl/alkyl dithiocarbamates triethylammonium salt (ArNHCSS-.Et 3NH+) with methyl acrylate in an aqueous medium gave solely arylisothiocyanate (ArNCS), whereas the in situ generated aryl dithiocarbamic acid (ArNHCSS-.H+) yielded exclusively the thia-Michael adduct (ArNHCSSCH2CH2COOMe). This differential reactivity can be explained by two alternative mechanisms which is dependent both on the nature of the counter cation and on the pH of the reaction medium. Irrespective of the counter cations, the thiocarbonyl sulfur (=S) atom, having large orbital-coefficient, is softer compared to the thiol/thiolate sulfur (-SH/S-) in a dithiocarbamate salt and the former adds to the Michael acceptor by a 1,4-addition.
Jamir, Latonglila,Ali, Abdur Rezzak,Ghosh, Harisadhan,Chipem, Francis A. S.,Patel, Bhisma K.
A novel one-pot synthesis of isothiocyanates and cyanamides from dithiocarbamate salts using environmentally benign reagent tetrapropylammonium tribromide
A highly efficient and simple protocol for the synthesis of isothiocyanates and cyanamides from their respective amines in the presence of a mild, efficient, and non-toxic reagent tetrapropylammonium tribromide is described. High environmental acceptability of the reagents, cost effectiveness and high yields are the important attributes of this methodology.
Kuotsu, Neivotsonuo Bernadette,Jamir, Latonglila,Phucho, Tovishe,Sinha, Upasana Bora
p. 832 - 841
(2018/01/17)
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