Both aryl and alkyl thionitrites (RSNO) were prepared quantitatively by the reaction of thiols with dinitrogen tetraoxide (N,O,) under mild conditions. Unstable thionitrites were identified by i.r. or U.V. spectra a t low temperatures (e.g. 0 " C ) or by their further reactions with nucleophiles leading to known derivatives. The spectroscopic data of these thionitrites are summarized and the highly reactive thionitrites were found to react readily with other nucleophiles such as thiols, sulphinic acids, alcohols, and secondary amines at ca. -5 "C. Treatment of thionitrites with other thiols or sulphinic acids was found to yield the corresponding unsymmetrical disulphides or thiolsulphonates in good yields. Similar treatment of thionitrites with secondary amines or alcohols gave the corresponding Nnitrosoamines, or disulphides and nitrites. versity of Tsukuba, Sakuramura, lbaraki 300-31, Japan A FEW stable alkyl thionitrites (RSNO) have been prepared by treating alkanethiols with either alkyl nitriles,2 nitrosyl chloride,, or nitrous anhydride., A few attempts to prepare aryl thionitrites have also been made, though unsuccessfully.3~ Since alkyl thionitrites of low molecular weight were characterized mainly by i.r. spectroscopic analysis in the gas phase due mainly to their instability, the yields and purities of these thionitrites were not reliable because of their ready decomposition. Recently we found that both arene-and alkane-thiols react readily with an equimolar amount of dinitrogen tetraoxide (N204) under mild conditions (-10 to 0 "C) affording the corresponding thionitrites quantitative1y.l' The highly reactive thionitrites were found to react immediately with other thiols or sulphinic acids affording the corresponding unsymmetrical disulphides (3) or thiolsulphonates (4) in good yield. In contrast, the reaction of thionitrites with alcohols is slow and yields the corresponding disulphides and alkyl nitrites. The reaction with amines is also slow and gives nitroso-compounds (6). This paper describes the synthesis of both aryl and alkyl thionitrites and a few typical reactions with nucleophiles such as thiols, sulphinic acids, and secondary amines and alcohols. These reactions are illustrated in Scheme 1.Preparation of Thionitrites.-The reaction of thiols with N,O, in an inert solvent such as CCl,, hexane, ether, or acetonitrile yields the corresponding thionitrites quantitatively, if an equivalent amount of N204 was used and the temperature was kept sufficiently low', i.e. below -10 "C. N,O, is known to be in an equilibrium with NO+ and NO3-ion6. Probably electrophilic attack of NO+ on the sulphur atom of the thiol forms the corresponding thionitrite and nitric acid. The yields are quantitative and hence remarkably high by comparison with those for the known reactions of thiols with either alkyl nitrite,2 nitrosyl ~h l o r i d e , ~ or nitrous a n h ~d r i d e . ~ Characterization of Thionitrites.-The spectra and t The gas-phase i.r. spectra of methyl and ethyl thionitrites showed vrnsx. 1 962 (-S-N=O),...
