THE SOLVOLYSIS AND NUCLEOPHILIC SUBSTITUTION IN SERIES OF CYCLIC HALOGENALKYLISOTHIOUREAS

Abstract

Abstract Previously we reported 1, that solvolytic rearrangement of salts and bases of 2-amino-5-X-5,6-dihydro-4-H-1,3-thiazines \I a,b, where a X=C1, b X=Br\ proceeds with a contraction of cycle and results in salts and bases of 2-amino-5-X-methyl-2-thiazolines \II a-c, where a X=C1, b X=Br, c X=OH\. The reversibility of this reaction is shown now. It was found by means of radiochromatography that hydrolysis of 35S-labelled IIb bromide gives rise to rearranged Ib besides hydrolytic product lie. It was shown, also, that the solvolysis of salts IIa,b in 50% aqueous ethanol, when excess of Na36Cl is present, gives both ordinary substitution products and certain amount of rearranged Ia. In the course of 35-labelled IIb bromide solvolysis in the same conditions the return of bromide ions takes place. It was found that the addition of salts affects the composition of Ib bromide hydrolysis products. This testifies that the composition of reaction products depends on the episulphonium III form present in the medium \ scheme\. It is possible, that the formation of covalent system I is most probably due to internal return from IIIa, but covalent form II results from the other steps of the dissociation. This is confirmed by absence 2-amino-5-hydroxy-5,6-dihydro-4-H-1,3-thiazine in reaction mixture. The addition of NaC104 and NaNO3 supresses bromine ions return owing to ion exchange resulting in new external pair IIId, what leads to the increase of the relative amount of IIc. On the other hand the addition of KBr and NaCl decrease the amount of IIc, due to the increase of the degree of ions return and the probability of halogen ions attack to episulphonium III.