NBR hydrogenation

Scheme 1 Mechanism of NBR hydrogenation catalyzed by RhCKPPhsls. Source Ref. 8.

Hydrogenation of olefinic unsaturation using ruthenium (Ru) catalyst is well known. It has been widely used for NBR hydrogenation. Various complexes of Ru has been developed as a practical alternative of Rh complexes since the cost of Ru is one-thirtieth of Rh. However, they are slightly inferior in activity and selectivity when compared with Rh catalyst. 

Martin et al. [69] undertook a study of the kinetics and mechanism of NBR hydrogenation using various Ru complexes. They examined the activity of RuXCl-(C0)L2 (X = H, Ph, or CH=CHPh L = PCy3, PPr,... 

The most widely used homogeneous palladium catalyst is palladium carboxylate. Table 6 lists the palladium-based catalyst systems developed for NBR hydrogenation [75-87]. They are regarded as homogeneous cata-... 

Acetone is the best solvent for NBR hydrogenation in the presence of palladium carboxylates. No hydrogenation is achieved when chloroform or chlorobenzene are the solvents. Since it is understood that palladium is reduced to colloidal metal in the presence of hydrogen, attempts have also been made to reduce the palladium by hydrazine [76], methylaluminoxane [84], and trialky] aluminum [85] to improve the catalytic activity. 

Figure 6 A catalytic pathway of NBR hydrogenation with Crabtree s catalyst.

RhCl(PPh3)3 oxidatively adds molecular hydrogen to form a five-coordinate dihydride complex which is consistent with the previous understanding [82] for olefin hydrogenation. This was also confirmed by experiments conducted by Mohammadi and Rempel [83] for NBR hydrogenation, where at 65 °C under 1 bar H2 the reaction is quantitative towards formation of the dihydride ... 

Scheme 19.5 Mechanism of nitrile butadiene rubber (NBR) hydrogenation catalyzed by Ru(CH=CH(Ph))CI(CO)(PCy3)2.

Scheme 19.8 (a, b) Alternative mechanisms of NBR hydrogenation catalyzed by OsHCI(CO) (02) (PCy3)2. 

HCV heat-curable vulcanizate H-NBR hydrogenated nitrile rubber... 

Likozar et al. [148] obtained NBR/hydrogenated NBR mixed with MWCNTs using a melt compounding method, cured with peroxide, and further mixed with a two-roll mill. The resulted composites showed improved hardness, elastic modulus, tensile strength, elongation at break, and tear strength compared with noncured... 

The results are reported of a study of the effects of gaseous oil, gaseous sour oil, oily gas and dry gas at different temperatures and pressures on several elastomers. These elastomers were CR, NBR, hydrogenated NBR, FKM and EPDM. 13 refs. 

The Handbook of Specialty Elastomers was conceived as a single reference source for the rubber compounder with some experience in designing parts in the rubber industry. The definition of specialty elastomers referenced in this publication is heat, oil, fuel, and solvent-resistant polymers that include polychloroprene (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), fluoroelastomer (FKM), polyacrylate (ACM), ethylene acrylic elastomer (AEM), polyepichlorohydrin (CO, ECO), chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSM), ethylene vinyl acetate (EAM), and thiokol (T). 

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