- Anodic Oxidation of Alkyl Isocyanates and Their Thio Derivatives in Acetonitrile
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Seven alkyl isocyanates (RNCO), five alkyl isothiocyanates (RNCS), and two aromatic cyanato derivatives (ArNCO) were electrochemically investigated by cyclic voltammetry and anodic controlled-potential electrolysis in acetonitrile at platinum anodes.It was found that RNCS compounds exhibited considerably lower anodic potentials than RNCO derivatives.The preparative electrochemical oxidation of RNCS was dependent on the nature of the alkyl group.Primary RNCS afforded mainly five-membered heterocyclic products while tertiary ones gave largery amides due to α-cleavage or isocyanates due to substitution of sulfur for oxygen processes.RNCO compounds were oxidized at the onset of the solvent electrolyte region and yielded amides and carbonyl products due to nucleophilic involvement of either acetonitrile or water, respectively, or formed products due to radical reactions (mono-, di-, and tricyanomethyl derivatives).ArNCO gave mostly polymeric products.Mechanistic routes for the formation of the various products are discussed.
- Becker, James Y.,Zinger, Baruch,Yatziv, Shimon
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- Selective Formation of Five-Membered Heterocyclic Products by Anodic Oxidation of Alkyl Isothiocyanates (RNCS) in Dichloromethane and Their Thermal Isomerization and Decomposition
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Anodic oxidation of primary and secondary alkyl isothiocyanates (RNCS) in dichloromethane yielded two isomers of five-membered heterocyclic products, 4-alkyl-5-(alkylimino)-1,2,4-dithiazolidine-3-one 2 and 2,4-dialkyl-5-oxo-1,2,4-thiadiazolidine-3-thione 3.Their relative ratio was found to be depedent on the length or bulkiness of the alkyl group in RCNS.Isomer 2 was favorable for R = Me and Et and exclusive for R = n-Pr, n-Bu, and cyclohexyl.Upon GLC injection (at 150-200 deg C), compounds of type 2 isomerized completely to 3 (when R = Me, Et), mostly to 3 and partially decomposed to RN=C=NR (11) (when R = n-Pr, n-Bu), and exclusively decomposed to 11 for R = cyclohexyl.Tertiary RNCS did not yield cyclic products but instead underwent chlorination to substitute a hydrogen (or "NCS" group) by chlorine.Plausible mechanistic schemes are suggested and discussed.
- Becker, James Y.,Yatziv, Shimon
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p. 1744 - 1748
(2007/10/02)
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