June, 1966
CATALYTIC ISOMERIZATION OF CYCLOPBOPAKE
could be detected. This does not, however, rule out the possibility that an intramolecular hydrogen bond persists to some extent in these media as a rapid proton exchange between solvent and solute mould be expected to broaden and flatten the proton signal from the intramolecular hydrogen bond with a simultaneous merging with the solvent signal. The corresponding free acids of I-IV in DMSO gave rise t,o a very broad band a t about 6 = -5.0, a n d accordingly any internal hydrogen bond that might ha\.e been present must be disrupted in this solvent (cf. ref.6) It is widely accepted that the position of a proton resonance signal is shifted toward lower applied fields when the hydrogen atom takes part in a hydrogen bond.l0 The magnitude of the shift can be taken as a rough measure of the hydrogen bond strength.’” The difference in the behavior of the racemic and meso acid salts and an observed constancy of the alkyl proton shifts on passing from the free acid to the nionopotassium salt indicates that in the present case 110 anomalous effect arises from the presence of the cation. One would therefore expect that the proton resonance shift of 6 = -15.40 in potassium hydrogen maleate should be very close to the “lower limit” for 0....H ....0’ hydrogen bonds. Accordingly, the in(10) J. A . I’ople, R‘ G. Schneider a n d H. I. Bernstein, “High-iesolution Nuclear Magnetic Resonance,” McGraw-Hill Book Co., New York, N. Y., 1959.
769
tramolecular hydrogen bond in the salts I-IV should be comparable in strength to that of the maleate mono-anion. The slightly smaller shifts in the case of 1-117 as compared with potassium hydrogen maleate may be an indication that these hydrogen bonds are not symmetrical, but further information is needed to obtain full evidence on this point, e.g., by neutron diffraction data. It is interesting to note that short, strong hydrogen bonds can be formed in suitably substituted saturated dicarboxylic acids without there being any other path connecting 0 and 0’ through which migration of electrons can take place as in the maleate and phthalate mono-anion.“ However, some sort of O=C-C=C-C=O conjugation may be necessary for the formation of a symmetrical hydrogen bond. Acknowledgments.-The authors ~vouldlike to thank Dr. E. Forslind for his kind eiicouragement and generosity in including this work in the general research program of the XMR-group. Thanks are also due to Dr. B. R. Thomas for valuable linguisitic criticism and to Stateiis R5d for Atomforskning, Statens Naturvetenskapliga E’orskningsrid and Statens Tekniska ForskningsrHd which have provided financial support for the NMR-group. The cost of the NMR apparatus has been defrayed by grants from Knut and Alice Wallenbergs Stiftelse. (11) See ref. 4, p . 344.
A GAS ( I H R O ~ ~ , ~ T O G K B P HSTUDk’ IC OF T H E CATALYTIC ISOJIEHIZBTIOS OF CYCLOPROPANE’ BY D. W.BASSETT~ A N D H. W. HABGOOD Research Council of Alberta, Edmonton, Alberta, Canada Received December t.9,1950
The general case of a first-order catalytic reaction occurring during elution of a reactant through a chromatographic column is discussed Under conditions of low reactant partial pressure and rapid adsorption relative to the rate of the surface reaction, the fractional conversion of a pulse of reactant passed through a chromatographic column is given by an equation analogous to that for the conversion under similar conditions in a steady-state flow reactor. A major advantage of the chromatogr:rphic technique is that it permits a determination of the extent of adsorption under reaction conditions, and thus of the rate constant for the reaction on the catalyst surface. The method is illustrated by a gas chromatographic study of the catalytic isomerization of cyclopropane on Linde Molecular Sieve 13X. The rate constant of the surface reaction was found to be k = 1.3 X 10’0 exp( -30,000/RT) sec.-l. The heat of adsorption of cyclopropane under reaction conditions was 11.0 kcal. rr,ole-l.
Introduction In recent years, t8hetechniques of gas chromatography have been increasingly applied to the study of heterogeneous cat’alytic reactions. These applications are of two distinct types: those in which gas chromatography is used only as an analytical tool, and those in which gas chromatographic techniques are an integral part of the reaction study. Apart from observations of catalytic reactions occurring during analyses by gas chromatography, reported (1) C o n t r i h t i o n No. 110 from t h e Research Council of .4lberta. Presented at the Division oi Analytical Chemistry Symposium on Gas Chromatography, 137th National hfeeting of the American Chemical Society. Cleveland, Ohio, April, 1960. (‘2) Rr~sear
