Thiocyanogen chloride, thiocyanation

Entries 7 to 9 involve other reagents that react by similar mechanisms. In the case of thiocyanogen chloride and thiocyanogen, the formal electrophile is [NCS]+. The presumed intermediate is a cyanothiairanium ion. The thiocyanate anion is an... 

Thiocyanogen chloride, C1SC=N. A solution of the reagent is prepared by adding 1 mole of lead thiocyanate, Pb(SCN)2, mol. wt. 323.38 (Fisher supplies practical grade) to a solution of 2 moles of chlorine in acetic acid and filtering off the lead chloride. 

A more active agent for replacement of H by SCN is thiocyanogen chloride (C1SCN), which can be prepared from lead thiocyanate and chlorine in anhydrous acetic acid.764... 

The oxidation potential of the 2 SCN = (SCN)2 couple Mis between those of the corresponding couples for Br and 1 (Table II) (38-40). The SCN = OSCN couple is comparable to the corresponding 1 couple (41). The oxidation potential of SCN relative to the halides explains the oxidation of SCN by CI2 (42) and Br2 (43) and the oxidation of 1 by (SCN)2. The latter reaction is one that can be used to quantify (SCN)2 (44). The relative oxidation potentials also facilitate the definition of inter (pseudo)halogens like I -SCN (iodine thiocyanate) (45,46) versus Cl -SCN (thiocyanogen chloride) (47) and Br -SCN (thiocyanogen bromide), which react accordingly. 

Chlorine reacts with sodium cyanide and sodium thiocyanate to produce cyanogen chloride and thiocyanogen chloride. The reaction of chlorine with sodium thiosulfate [7772-98-7] (Antichlor) is used to remove free chlorine from solutions. 

Cyclohexene in acetic acid added at 25° to a soln. of thiocyanogen chloride, prepared from Pb-thiocyanate and chlorine in acetic acid with subsequent addition of 2,6-di-fer -butyl-p-cresol as radical inhibitor rran -l-chloro-2-thio-cyanatocyclohexane. Y 77%. F. e. s. R. G. Guy and I. Pearson, Soc. Perkin I 1973, 281. 

Uridine or 2 -deoxyuridine give the 5-thiocyanato-derivatives by substitu-ticm with thiocyanogen chloride, " opening a route to biologically active 5-mercaptopyrimidines through dithiothreitol reduction of the thiocyanate. 

This activation of the ortho position is most strikingly illustrated in the reactivity of 2,5-dimethylthiophene, which competitive experiments have shown to undergo the SnCb-catalyzed Friedel-Crafts reaction more rapidly than thiophene and even 2-methylthiophene. The influence of the reagent on the isomer distribution is evident from the fact that 2-methoxythiophene is formylated and bromi-nated (with A -bromosuccinimide) only in the 5-position. Similarly, although 3-bromo-2-methylthiophene has been detected in the bromi-nation of 2-methylthiophene with bromine, only the 5-isomer (besides some side-chain bromination) is obtained in the bromination of alkylthiophenes with A -bromosuccinimide. ° However, the mechanism of the latter type of bromination is not established. No lines attributable to 2-methyl-3-thiocyanothiophene or 2-methyl-3-chIoro-thiophene could be detected in the NMR spectra of the substitution products (5-isomers) obtained upon thiocyanation with thiocyanogen or chlorination with sulfuryl chloride. 2-Methyl- and 2-ethyl-thiophene give, somewhat unexpectedly, upon alkylation with t-butyl chloride in the presence of Feds, only 5-t-butyl monosubstituted and... 

Chemical. In addition to its intrinsic interest, sulfur serves as a starting point for the synthesis of many labeled molecules. Digestion of sulfur in aqueous sulfites yields thiosulfates, which when heated with iodine lead to tetra-thionates and trithionates. Digestion of sulfur in alcoholic cyanide solutions yields thiocyanates, thence thiocyanogen and thiourea with its derivatives and coordination complexes. Oxidation of sulfur to sulfur dioxide is a potential route to labeled sulfamic acid and its derivatives and to labeled sulfuryl chloride. The intermediate sodium sulfide readily yields hydrogen sulfide and metallic sulfides. 

A soln. of p-nitrobenzyl mercaptan in methylene chloride added with stirring at 0° during 1.5 hrs. to a soln. of thiocyanogen prepared from Pb-thiocyanate and bromine in methylene chloride, stirring continued 15 min., anhydrous Na-acetate added in one portion, then N - (2 - tritylthioethyl) - 5 - phenyl - 4,5 - dithia-pentanamide added during 15 min., stirred 45 min. at 0 and 1 hr. at room temp. -> N- [5- (4-nitrophenyl) -3,4-dithiapentyl] -5-phenyl-4,5-dithiapentanamide. Y 50%. F. e. s. R. G. Hiskey and D. N. Harpp, Am. Soc. 87, 3965 (1965). 

Treatment of ethyl rhercaptan with thiocyanogen affords ethyl thio-thiocyanate (50% yield)a compound similar to a sulfenyl chloride (RSCl) but somewhat more stable toward hydrolysis. Thiophenols... 

---