Hydrogenation of Interesting Substrates and Renewable Sources

Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 

The residual carbon-carbon double bond in nitrile butadiene rubber (NBR) can be catalytically hydrogenated to yield its tougher and more stable derivative, hydrogenated nitrile butadiene rubber (HNBR).2 This class of specialty elastomer was developed to expand the range of operating environments possible for nitrile butadiene rubber NBR in environments that expose the rubber to chemical and thermal attack. 

The efficiency of Crabtree s catalyst as a catalyst for small molecule hydrogenation has been known for many years. Unlike many homogeneous hydrogenation catalysts, Crabtree s catalyst is able to reduce hindered olefins at favourable rates.7 It has never been reported as a catalyst for the hydrogenation of rubber except for its use in the hydrogenation of bulk PBD.8 This paper describes the first use of Crabtree s catalyst in the hydrogenation NBR. Kinetic data are presented and analyzed to understand the underlying chemistry. 

Crabtree s catalyst was obtained from Strem Chemicals. The NBR grade used throughout was Krynac 38.50 (NBR containing 38% acrylonitrile units) from Bayer Rubber Inc. Solvents employed (chlorobenzene, acetone and 2-butanone) were used as received from Fisher Chemical Co. The purity of H2 and D2 (02 free) from Linde-Union Carbide was reported to be 99.99%. 

In the kinetic study, data were obtained from the amount of hydrogen consumed by the reaction over time using an automated gas uptake control system. The apparatus is designed to maintain isothermal and isobaric conditions while monitoring H2 consumption. Procedures used were as described previously.3 5 

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