Thiocyanates thiocarbamates

The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight (221). Ammonium thiocarbamate is prepared from a cold saturated solution of ammonium thiocyanate, which is gradually added to dilute sulfuric acid at 25°C. The liberated carbonyl sulfide is passed into a saturated solution of alcoholic ammonia at about 10°C (221). The fairly low yield indicates that the reaction has not been greatly developed. 

Uses. There may be some captive use of carbonyl sulfide for production of certain thiocarbamate herbicides (qv). One patent (38) describes the reaction of diethylamine with carbonyl sulfide to form a thiocarbamate salt which is then alkylated with 4-chloroben2yl haUde to produce 3 -(4-chloroben2yl) A[,A/-diethylthiocarbamate [28249-77-6] ie, benthiocarb [28249-77-6]. Carbonyl sulfide is also reported to be useful for the preparation of abphatic polyureas. In these preparations, potassium thiocyanate and sulfuric acid are used to first generate carbonyl sulfide, COS, which then reacts with a diamine ... 

Substituted thiazolidin-4-ones (449) are easily prepared by the reaction between chloracetic acid, or its derivatives (447), and a thiourea, a thiosemicarbazide, or a mono-or di-thiocarbamate (448 Scheme 255). The same a-chloro acid derivatives react with metallic thiocyanates yielding an intermediate (450), the cyclization of which gives a 2-iminothiazolidin-4-one (451). In these reactions a -chloracetic acid may be replaced by... 

The isothiocyanates are transformed into thiocarbamates by reaction with alcohols or into the acetamides by reaction with acetic acid or anhydride and sodium acetate. These transformations have also been applied to the preparation of unsaturated aminosugars73,74. Thus, suprafa-cial rearrangement of ethyl 2.3,4-trideoxy-6-0-methanesulfonyl-4-thiocyan ato-a-D-t/ireo-hex-2-enopyranoside to the 2-isothiocyanatc occurs in refluxing toluene (1 h), whereas the erythro-epimer needs to be heated in dimethylformamide for 6 hours73. This difference in reactivity might be due to an unfavorable anomeric effect and C-6 in an axial orientation in the transition state of the errr/iro-epimer, respectively. 

Combination of a Diels-Alder reaction and a [3,3] sigmatropic rearrangement provides access to 1,4-substituted 2-cyclohexenyl derivatives75- 76,11 . Thus, Diels-Alder reaction of ( )-l,3-bu-tadienyl thiocyanate with methyl acrylate is followed by a [3,3] sigmatropic rearrangement to the isothiocyanate. The isothiocyanate is trapped by the solvent to give racemic 0-cthyl-/V-(4-methoxycarbonyl-2-cyclohexcnyl)thiocarbamate in a 66 33 diastereomeric ratio (cisjtram). A Lewis acid catalyzed variant of this tandem reaction showed better diastereoselectivity (90 10)111. 

Thiocyanates are converted to thiocarbamates in a similar reaction R—S—C=N + H2O R S C O NH2. Hydrolysis of cyanamides gives amines, produced by the breakdown of the unstable carbamic acid intermediates R2NCN [R2NCOOH] R2NH. 

The action of concentrated sulfuric acid followed by treatment with ice water serves to transform aryl-thiocyanates into the corresponding thiocarbamates. 

The reaction of 3-phenylpropenoyl iso thiocyanates (285) with sodium hydrogen sulfide in methanol gives thiazinones (286) and thiocarbamates (287) (Scheme 56). The thiocarbamates are derived from the thiazinones through methanolysis and can be recyclized to them by treatment with aqueous sodium hydroxide in a separate step <90MI 607-01 >. 

S-Thiocarbamic acid esters from thiocyanates SCN —>- SCONH ... 

Thioureas are obtained analogously by boiling an amine hydrochloride and an alkali thiocyanate in aqueous solution66 or an amine and a thioiso-cyanate in alcohol 67 aromatic thioisocyanates generally react even in the cold. Further, aqueous ammonia solutions are converted smoothly into mono-alkylthioureas by isothiocyanates.68 Isothiocyanates can be converted directly into symmetrical thioureas by boiling them in aqueous dimethylformamide or dimethyl sulfoxide the thiocarbamic acids formed as intermediates by partial hydrolysis add to unchanged isothiocyanate with loss of COS.69... 

Starting from 1,2-0-sulfinyl-a-D-glycopyranose or glycofuranose. Treatment of the Q -l,2-0-sulfinyl derivative with sodium thiocyanate led to a p-thiocyanate that, imder the reaction conditions was isomerized to a transient a-isothiocyanate via an oxocarbenium ion. The isothiocyanate underwent spontaneous annelation with a vicinal hydroxyl group to afford the corresponding glycopyrano and glycofurano cis-fused thiocarbamates (Scheme 13). 

This reaction was first reported by Riemschneider in 1949. It is an acidic transformation of alkyl or aryl thiocyanates into thiocarbamates and is known as the Riemschneider reaction. In this reaction, when thiocyanates are treated with concentrated sulfuric acid, the corresponding thiocarbamates are obtained. In parallel, when thiocyanates are treated with concentrated sulfuric acid in the presence of alcohol or olefin, the corresponding A -substituted carbamates are yielded. The alcohols or olefins that are stable in the presence of sulfuric acid, including isopropyl alcohol, cc-butyl alcohol, r-butyl alcohol, cyclohex-anol, isobutylene, and camphene aU are suitable for this reaction, whereas low-order alcohols such as methanol and ethanol do not react with thiocyanate to give the corresponding A -substituted thiocarbamates. hi addition, the benzyl thiocyante and some ortho-substituted phenyl thiocyanates cannot be transformed into the corresponding thiocarbamates under these conditions because they are sensitive to sulfuric acid. Some unsuitable thiocyanates are o-carboxyl, o-methoxy, o-nitrophenyl thiocyanates, and o-methyM-amino phenyl thiocyanate. ... 

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