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Znd. Eng. Chem. Res. 1988, 27, 915-920 915 energy values have been determined. These, along with k h e n i u s correlations for the rate constants, are presented in Table V. The calculated activation energy values are consistent with the low values normally observed with free-radical reactions. ConclusionsQuantitative and selective oxidation of styrene to benzaldehyde was achieved with Wilkinson complex. The reaction initiation period was independent of temperature. The reaction induction period strongly depended upon the catalyst concentration below the critical catalyst concentration. Co-oxidation of aldehyde to acid was found to be significant above a temperature of 75 "C and a styrene conversion of 25%. The optimum reaction conditions have been determined as (C/So) = 5.0 X lo4, (So/T) = 0.5, and T = 75 OC. A second-order kinetic model has been found to fit satisfactorily the experimental kinetic data both in the presence and absence of co-oxidation reactions.Nomenclature AI, A2, A3 = constants (B) = concentration of benzaldehyde, mol/L (C) = concentration of the catalyst, mol/L (C/So) = mole ratio of the catalyst to initial styrene kf = first-order rate constant, l / h k'f = pseudo-first-order rate constant, l / h k, = second-order rate constant, L/(mol h) (S) = styrene concentration, mol/L (So) = initial concentration of styrene, mol/L (So/T) = mole ratio of initial styrene to toluene (T) = toluene concentration, mol/L T = temperature, K t = time, h r = [(So) -(S)]/(So) = mole fraction of styrene converted xB = (B)/(So) = mole ratio of benzaldehyde to initial styrene Registry No. RhCl(PPh3)The kinetics and product distributions of the thermal cracking of cyclohexane were investigated in a stainless steel annular reactor using the pulse method. Experiments were conducted a t 1-atm pressure and with excessive nitrogen dilution. Data were obtained at temperatures of 700-860 OC and space times of 0.40-1.14 s. A kinetic analysis of the conversion-space time data revealed that conversion was autocatalytic at 700-800 "C, while at higher temperatures (820-860 O C ) it was governed by first-order kinetics. The activation energies for the two kinetic regimes were 192.5 and 240.0 k J mol-', respectively. The autocatalysis was ascribed to the participation of methylallyl radicals in a new bimolecular propagation sequence. The product distributions and the first-order kinetic rate parameters were consistent with those obtained in the continuous-flow mode.

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