The kinetics and thermochemistry of S 2 F 10 pyrolysis

Data on the kinetics of S 2 F 10 pyrolysis, which gives SF 4 + SF 6 , have been reinterpreted to give a value for the equilibrium constant of S 2 F 10 ⇆ SF 4 + SF 6 . This, together with statistical estimates of the entropy and heat capacity of S 2 F 10 , can be used to give for this reaction values of Δ H   298 °= 19.7 ± 1.0 kcal/mole and Δ S   300 °= 47.6 ± 2 gibbs/mole. Δ H   f ° (S 2 F 10 ) = –494 kcal/mole. A compatible mechanism is shown to beS 2 F 10 ⇆ 2SF 5 (fast); 2SF 5 ⇆ SF 6 + SF 4 (slow)with step 2 rate‐determining. The overall, best first order rate constant is proposed as k meas = 10 17.42–43.0/θ sec −1 = K 1 k 2 , where θ = 2.303 RT in kcal/mole. Independent measurements of δ H   f °and S ° for the SF 5 radical, permits the evaluation of the equilibrium constant K 1 = 10 8.92–(27.1 ± 6)/θ l./mole‐sec and yields k 2 = 10 8.50–15.9/θ l./mole‐sec. The observed homogeneous catalysis by NO and CHCl CHCl can be explained in terms of a direct abstraction of F from S 2 F 10 : C + S 2 F 10 → CF + S 2 F 9 , followed by S 2 F 9 → SF 5 + SF 4 and SF 5 + CF ⇆ SF 6 + C (C NO or C 2 H 2 Cl 2 ).