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Reactions of Neopentane and 1,1-Dimethylcyclopropane with Deuterium Over Metal Films

C. Kemball and J. C. Kempling
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 329, No. 1579 (Sep. 12, 1972), pp. 391-403
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/78240
Page Count: 13
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Reactions of Neopentane and 1,1-Dimethylcyclopropane with Deuterium Over Metal Films
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Abstract

The simultaneous exchange and hydrogenolysis of neopentane have been examined over cobalt and nickel films by using a combined gas chromatographic-mass spectrometric technique. Exchange was mostly limited to one methyl group, yielding (CH3)3(CH2D)C and (CH3)3(CD3)C as the major products. With cobalt the multiply exchanged species predominated but nickel was selective towards the mono-deuterated product. Some of the initial exchanged neopentanes had more than three deuteriums and therefore were due to an α γ -exchange process. Methane was the major product from hydrogenolysis; nickel yielded more of the intermediate hydrocarbons (isobutane, propane and ethane) than cobalt. All of the hydrogenolysis products were completely exchanged. With cobalt, hydrogenolysis and exchange are comparable in rate but over nickel exchange occurs 6.5 times faster than hydrogenolysis. The hydrogenolysis of 1,1-dimethylcyclopropane was examined over iron, cobalt and nickel films at the same temperatures as were used for the neopentane reactions. Ring opening was favoured at the carbon-carbon bond opposite the substituent methyl groups to form neopentane. Considerable multiple carbon-carbon bond rupture occurred; over cobalt, methane was the major product but with nickel the reaction was specific to isobutane and methane. Iron was intermediate in behaviour. All the hydrogenolysis products were fully exchanged except neopentane, the major isotopes of which were (CH3)2(CH2D)$_{2}$C and (CH3)2(CH2D)(CD 3)C. These products are analogous to those formed from neopentane exchange. The relative amounts of singly and multiply deuterated methyl groups formed from the two processes show a linear relation for the three metals, suggesting that ring opening occurs via a neopentane species which is adsorbed at only one methyl group. No exchanged 1,1-dimethylcyclopropanes were observed.

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