The kinetics of n-pentane isomerization over a Pt-A!203 catalyst were investigated at 372°. The reaction was carried out in a flow reactor in the presence of added hydrogen at pressures ranging from 7.7 to 27.7 atm. and hydrogen to n-pentane ratios ranging from 1.4 to 18. The rate of isomerization was found to correlate with the n-pentane to hydrogen mole ratio and to be independent of total reactor pressure at a fixed n-pentane to hydrogen ratio. These results can be explained in terms of the postulated mechanism by which isomerization proceeds via an olefin intermediate present in equilibrium concentration. According to this mechanism n-pentane dehydrogenates on platinum sites to n-pentene, which in turn migrates to acidic sites to isomerize, presumably by a carbonium ion mechanism. The rate-controlling step is the isomerization of the intermediate olefin on acidic sites.

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NotesYol. 65 in methanol and precipitation by excess ether. It was then heated in vacuo to constant weight.Absorption spectra were measured on a Cary recording spectrophotometer. The time dependence of the spectra was checked. Over a period of several days at room temperature the peak positions remained constant but slight changes in absorbance occurred. KINETICS OF THE CATALYTIC DEHYDROCYCLIZATIOX OF -HEPTANE

CEC 21-210 dual-collector mass spectrometer using the 29/ 28 ratio. Two sets of equilibrations were carried out a t 281 and 253'K. and atmospheric pressure. From five independent equilibrations a t each temperature the effective separation factors were evaluated according to (1). Results T(OK)p(mm.) a (N"/N") 281 754 1.0024 i 0.0008 253 750 1.0046 rt 0.0005 DiscussionThe reason for the small values of the effective a(N15/K14) is that the degree of dissociation of the gaseous SOBr into KO and Brz is comparatively low; the gas phase consists predominantly of NOBr. Since the composition of the gas phase a t 263'K. is not known, the approximate determination of the interesting cr4 from the effective a-(N16/N14) is possible only for 2 8 1 O K . ; according to (4)This result is in good agreement vvith the spectroscopic data available for the KO-NOBr system.Although the rate of exchange probably is much faster in the SO-NOBr than in the NO-SOC1 system and the liquid FOBr easily could be decomposed by electrolysis or heat (exchangedistillation), the low effective separation factor makes this system unfeasible for the separation of the nitrogen isotopes.Acknowledgments.-The author is indebted to Prof. T. I. Taylor of Columbia University for his continued interest in this work and for helpful discussions, and to Prof. W. Spindel of Rutgers University for the use of his mass spectrometer.