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Tetrafluorosilane–amine adducts: stoicheiometry, thermodynamics of dissociation, stability, and hydrolysis

1972; Royal Society of Chemistry; Issue: 18 Linguagem: Inglês

10.1039/dt9720001953

2050-5671

B. J. Aylett, Ian A. Ellis, C. J. Porritt,

Silicone and Siloxane Chemistry

Tetrafluorosilane combines with the following amines under varying conditions to give 1 : 2 adducts: NHxMe3 –x(x= 0–3), NHxEt3 –x(x= 0–2), NH2R (R = Prn, Bun, Bus, But, or Ph), NHR2(R = Prn or Bun; R2= C4H8 or C5H10), NC5H5, NMexEt3 –x(x= 1 or 2), and with NHR·[CH2]n·NHR (n= 2, R = Me or Et; n= 3, R = Me) to give 1 : 1 adduct. Solid tetrafluorosilane also reacts with a deficit of liquid pyridine to yield an approximately 1 : 1 adduct. Solid–vapour or liquid–vapour equilibria are reported for adducts of NHxMe3 –x(x= 0–3), NHxEt3 –x(x= 0 or 1), NMeEt2, and NC5H5; the extent of dissociation in the vapour phase is estimated, and values of ΔH, ΔG, and ΔS for dissociation from the condensed phase are calculated. Competition experiments indicate the order of adduct stability: NH3 NH2Me > NH2Ph > NHMe2 > NMe3. First-order rate constants for hydrolysis of SiF4,2NH3 and SiF4,2NH2Me are 1·0 × 10–3 and 1·9 × 10–3 s–1 at 25 °C; qualitatively hydrolysis becomes more rapid in the order ammonia < primary amines < secondary amines < tertiary amines. Ease of dissociation and hydrolysis are related to hydrogen-bonding and steric factors.