ENERGETICS AND REACTION PATHWAYS OF SOME REACTIONS LEADING TO SNSASF6 AND SNASF6

Our previously reported preparation of SNSAsF6 from S4N4, S8 and AsF5 was investigated in situ by N-14 NMR spectroscopy with, and without, traces of Br2. Reaction pathways are proposed, which were separately investigated by N-14 NMR spectroscopy, and an efficient high-yield synthesis of highly crystalline SNSAsF6 developed. The enthalpy of reaction was estimated as -104.6 +/- 2 kJ mol-1 per SNSAsF6. The compound SNSAsF6 was also formed rapidly and quantitatively from SNAsF6 and S8 with no observable intermediates (A reaction mechanism is proposed and the enthalpy and entropy of the reaction estimated as -66 +/- 28 kJ mol-1 and -1.6 J K-1 mol-1), from reactions of S4(AsF6)2 with (S3N2)2(AsF6)2 (1:1) and S4N4 (2:1), and very slowly in small amounts from S4N4(AsF6)2 with S8, S8(AsF6)2 or S4(AsF6)2. The compounds S4(AsF6)2 and S4N4 gave (S3N2)2(AsF6)2 and an IR spectrum of the pure material is reported. The compounds (S3N2)2(AsF6)2 was oxidised by AsF5 to give equimolar amounts of SNAsF6 and SNSAsF6 in SO2 solution, the reaction proceeding faster with traces of Br2. The enthalpy of reaction of S4N4 and AsF5 leading to SNAsF6 was estimated as -40 +/- 28 kJ mol-1 per SNAsF6 and subsequently the reaction was shown to occur in about 30% yield. As part of an investigation into the course of this reaction, polymeric (S5N5AsF6)x was prepared in high yield, from S4N4 and S4N4(AsF6)2, which on oxidation with AsF5 and traces of Br2 gave SNAsF6 in a 30% yield. In addition, (S3N2)2NAsF6 was oxidised by AsF5 with traces of Br2 to give SNSAsF6, SNAsF6 and N2.