Energetics and reaction pathways of some reactions leading to SNSAsF6 and SNAsF6

Abstract

Our previously reported preparation of SNSAsF₆ from S₄N₄, S₈ and AsF₅ was investigated in situ by ¹⁴N NMR spectroscopy with, and without, traces of Br₂. Reaction pathways are proposed, which were separately investigated by ¹⁴N 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.