Thiocyanate and iodine

A single report of the addition of sodium azide to cyclohexene in the presence of iodine under phase-transfer catalytic conditions to produce 2-iodocyclohexanyl azide has the potential for extension to other alkenes [17], The analogous reaction of cyclohexene with potassium thiocyanate and iodine produces 2-iodocyclohexyl isothiocyanate (17%) and 2-iodocyclohexanyl thiocyanate (61%). Similar products are obtained with other alkenes [17],... 

Replacement of iodine in (perfluoroalkyl)ethyl iodides predominates over the usual conversion to olefins when the reagent is very nucleophilic and weakly basic Soft nucleophiles like sodium thiocyanate and sodium thiolates react well in displacements [46, 47] (equation 42)... 

Potassium permanganate and iodine, which are important redox reagents, are both self-indicating, i.e. the colour of the reagent in each case is intense and will impart a perceptible colour to a solution when present in very small excess. One drop of a solution of potassium permanganate (0.02 mol dm 3) can be detected in a titrand solution of 100 cm3, and a similar amount of iodine by shaking the titrand with 5 cm3 of chloroform or carbon tetrachloride to produce an intense purple colour. Specific indicators react in a specific manner with one participant in the reaction. The best examples are starch, which produces an intense blue colour with iodine and potassium thiocyanate, which forms an intense red compound with iron(III). 

According to Kerstein and Hoffmann 2 a further analogy between thiocyanogen and iodine lies in the formation of trithiocyanates (cf. tri-iodides) by the union of thiocyanogen with thiocyanates. These trithiocyanates behave like free thiocyanogen, except for their lesser sensitiveness towards water. 

Evolution of nitrogen from sodium azide-iodine mixture is brought about by traces of thiocyanate, and the latter may readily be detected by this means in the presence of most inorganic oxy-acids and the common organic acids.2 Sulphides and thiosulphates interfere (see pp. 65, 205) and must previously be removed by means of mercuric "hloride. 

Special test Catalysis of iodine-azide reaction solution of sodium azide (NaN3) and iodine reacts with a trace of a sulfide to evolve nitrogen thiosulfates and thiocyanates act similarly and therefore must be absent... 

Anodic halogenation proceeds usually as the thiocyanation discussed above (Section VI, F), but may also involve the free halogen or a halogen cation. Anodic halogenation may be advantageous in fluorination and iodination reactions, and in halogenations where a low, easily measured concentration of halogen is desirable. 

Chlorinated, brominated, and iodinated derivatives have been prepared by halogenation of phenothiazine. Direct fluorination is unknown. All fluorinated phenothiazines (see, for example. Roe and Little ) have been made by ring closure. Thiocyanation of phenothiazine has also been reported. 

The full paper on the reactions of iodine(l) thiocyanate and 5a-androst-2-ene and other alkenes has appeared." An investigation into the stereochemistry of the addition of BrCl to cholesterol revealed that the ratio of a /8 attack was 4.5 1, which was higher than that for other electrophilic additions. It was suggested that the reaction involved rapid reversible formation of the bromonium ions followed by attack by chloride ion and that the opening of the 5/8,6/3-bromonium ion was slow relative to that of the 5a,6a-bromonium ion owing to steric interactions with the la-, 3a-, 7a-, and 9a-axial hydrogen atoms. 

The reaction catalyzed by thiocyanate ion may also proceed through intermediates of appreciable stability. There is again a chain reaction , and 80-150 moles of azide may react per mole of thiocyanate. The results are consistent with competition between oxidation of an intermediate by iodine and its reaction with azide liberating thiocyanate and nitrogen. At pH values greater than 6, the former reaction becomes progressively more prominent it is probably pH-dependent. Both triiodide and hydrazoic acid are relatively unreactive in the system. 

In the following pages particular attention is paid to the bromination procedures that are most easily carried out on the laboratory scale, but most of the processes of fluorination, chlorination, iodination, and of formation of thiocyanates customarily used in the laboratory are also included (for detailed accounts of the preparation of organic fluorine and chlorine derivatives see reference, la, li and for bromine and iodine compounds see reference). The material is classified according to the type of reaction and the class of compound produced. 

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