Thiocyanogen hydrolysis

The application of thiocyanogen in volumetric analysis is restricted by the necessity of using anhydrous solvents and dry vessels, to avoid hydrolysis. With a sufficient excess of sodium thiosulphate or hydrogen sulphide, respectively, thiocyanogen reacts quantitatively according to the equations ... 

All methods that have been suggested for the preparation of thiocyanogen solutions involve the use of strictly anhydrous solvents, since the presence of moisture causes rapid hydrolysis and decomposition to take place. It is possible, howeyer, to stabilize thiocyanogen in aqueous solution to a limited extent by the presence of large quantities of potassium thiocyanate. 

The hydrolysis of thiocyanogen (SCN)2 in warm base yields sulfate, cyanide, and thiocyanate ions. Show how this hydrolysis is in conformity with the picture of the —SGN as a pseudo-halogen group. (Hint recall the hydrolysis of the halogens under similar conditions.)... 

The rates of hydrolysis of thiocyanogen, (NCS)2, have been studied by a pulse-radiolytic method, monitoring the optical absorbance due to SCN and the conductance. In acidic solutions the reactions involved are said to be... 

Cycloalkenes may be converted into episulphides by reaction with an ethereal or dichloromethane solution of iodine and thiocyanogen, in equimolar proportions, followed by alkaline hydrolysis. Iodine thiocyanate (ISCN) appears to be present in the solution, and to add diaxially to the olefinic bond hydrolysis then closes the episulphide ring. 5a-Cholest-2-ene (156), for example, gave the 2/ff,3)5-epithio-derivative (157) in acceptable yield. 

There exist three fundamental ways to prepare OSCN (1) hydrolysis of thiocyanogen, (SCN)2 in aqueous base (2) enz5une-catalyzed oxidation of SCN by H2O2 and (3) oxidation of SCN by electrophilic halogenating agents. The advantages and disadvantages of each of these methods will be discussed next. 

C.l. Preparation by hydrolysis of thiocyanogen under alkaline conditions... 

In accord with the view that thiocyanogen may be regarded as a pseudohalogen, it has recently been shown that a wide range of aliphatic and steroidal ketones undergo a-thiocyanation when their solutions in methanol are stirred at room temperature with a suspension of copper(ii) thiocyanate (Scheme 53). Cyclic ketones, as well as undergoing thiocyanation, may also be converted into their dimethyl acetals, from which the free a-thiocyanato ketones are readily obtained by hydrolysis. 

Selective hydrogenation of a -unsaturated carbonyl compounds can be carried out by reduction with iron pentacarbonyl and a small amount of base in moist solvents. The method is applicable to oc -unsaturated aldehydes, ketones, esters, and lactones with negligible over-reduction of the carbonyl group and is susceptible to the steric environment of the olefin. Spectroscopic evidence suggests that solutions of equimolecular amounts of iodine and thiocyanogen contain an appreciable concentration of iodine thiocyanate. Addition of alkenes results in tran.r-addition to yield jS-iodo-thiocyanates which in base suffer rapid hydrolysis of the thiocyanate followed by ring closure to the episulphide (516). As a synthetic procedure this does not appear to be applicable to acyclic olefins. ... 

The extreme sensitivity of thiocyanogen toward hydrolysis and polymerization probably accounts for the long interval between its formulation by Berzelius and its preparation by Bjerrum and Kirshner and by Soderback. For this same reason, when thiocyanogen is employed in chemical reactions, it is prepared in solution and more commonly is produced in situ. 

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... 

The triaryl derivatives of phosphorus, arsenic, antimony, and bismuth add thiocyanogen, with decreasing reactivity in the order indicated. The primary products are sufficiently stable to hydrolysis to be isolable... 

Moderate yields (26—57%) of thiirans are obtained directly from olefins, e.g. (1), on treatment with iodine-thiocyanogen, followed by hydrolysis of the thiocyanate (2) so formed and the displacement of iodide ion. The... 

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