Hydrogenation in supercritical carbon dioxide

Hydrodebromination. The tin hydride (CgF,3CH2CH2)3SnH participates in radical reactions such as replacement of bromine by hydrogen in supercritical carbon dioxide. Cyclization of l-bromo-6,6-diphenyl-5-hexene to give diphenylmethylcyclopentane is observed. 

Lange, S. Brinkmann, A. Trautner, P. Woelk, K. Bargon, J. Leitner, W. Mechanistic aspects of dihydrogen activation and transfer during asymmetric hydrogenation in supercritical carbon dioxide. Chirality 2000, 72 (5/6), 450-457. 

Aminodiphosphane (P,N,P)-ligands form active catalysts with iridium(I) for transfer hydrogenation (249). A novel phosphino-dihydrooxazol, modified with perfluoroalkyl groups proved to be excellent ligand for enantioselective hydrogenation in supercritical carbon dioxide (250). 

Meric P, Yu KMK, Tsang SC. Micelle-hosted palladium nanoparticles catalyze dtral molecule hydrogenation in supercritical carbon dioxide. Langmuir 2004 20 8537-45. 

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

Keurentjes et al. performed a continuous hydrogenation of 1-butene in supercritical carbon dioxide.[9,10] A fluorous derivative of Wilkinson s catalyst was prepared in situ by mixing the ligand with [(COD)RhCl]2 under hydrogen / carbon dioxide pressure (Figure 4.37). 

S. Kainz, A. Brinkmann, W. Leitner, A. Pfaltz, Iridium-Catalyzed Enantioselective Hydrogenation of Imines in Supercritical Carbon Dioxide , J. Am Chem Soc 1999, 121, 6421-6429. 

P. G. Jessop, Y. Hsiao, T. Ikariya, R. Noyori, Homogeneous Catalysis in Supercritical Fluids Hydrogenation of Supercritical Carbon Dioxide to Formic Acid, Alkyl Formates, and Formamides ,J. Am Chem Soc 1996,118, 344-355. 

J.-L Xiao, S. C. A Nefkens, P. G. Jessop, T. Ikariya, R. Noyori, Asymmetric Hydrogenation of a, -Unsaturated Carboxylic Adds in Supercritical Carbon Dioxide , Tetrahedron Lett. 1996,37,2813-2816. 

Catalytic hydrogenation in supercritical carbou dioxide has been studied. The effects of temperature, pressure, and CO2 concentration on the rate of reaction are important. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-supported palladium catalyst were measured in a continuous gra-dient-less internal-recycle reactor at different temperatures, pressures, and C02-to-feed ratios. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pressure inside the reactor provided reproducible values of the product stream compositions, which were measured on-line after separation of the gaseous components (Bertucco et al., 1997). 

Kainz, S., Brinkmann, A., Leitner, W. and Pfaltz, A. (1999) Iridium-catalyzed enantioselective hydrogenation of imines in supercritical carbon dioxide. /. Am. Chem. Soc., 121, 6421. 

Burk MJ, Feng S, Gross MF et al (1995) Asymmetric catalytic hydrogenation reactions in supercritical carbon dioxide. J Am Chem Soc 117(31) 8277-8278... 

The enantioselective hydrogenation of imines, such as the Metolachlor intermediate, in supercritical carbon dioxide has been investigated by Walter Leitner et al., Max Planck Institute for Coal Research, Miilheim, Germany but as always, replacing an established technology is a difficult task. 

The oxidation of hydrogen to hydrogen peroxide in supercritical carbon dioxide is a case in point Hancu, D., and Beckman, E. J. Green Chemistry, 2001, 3, 80. 

Catalytic asymmetric hydrogenations have also been performed in supercritical carbon dioxide [79-81]. For example, a-enamides were hydrogenated in high enantioselectivities comparable to those observed in conventional solvents, using a cationic rhodium complex of the EtDuPHOS ligand (Fig. 7.24) [79]. More recently, catalytic asymmetric hydrogenations have been performed in scC02 with... 

Xiao, J., Nefkens, S. C. A., Jessop, P. G., Ikariya, T., Noyori, R. Asymmetric hydrogenation of a,P-unsaturated carboxylic acids in supercritical carbon dioxide. Tetrahedron Lett. 1996, 37, 2813-2816. 

The products are the same as those in the homogeneous reactions (Table 1). Sodium undec-10-enoate and sodium dodecyl sulfate were used as detergents at concentrations exceeding the critical micelle concentration. The differences in the cisjtrans ratios of both the hydroformyl-ation and hydrogenation products in the homogeneous and micellar reactions have been discussed. Performed in supercritical carbon dioxide, 10 and 11 are obtained in similar distribution from 9 and HMn(CO)5. ... 

Jessop, P.G. Hsiao, Y. Ikariya, T. Noyori, R. Homogeneous catalysis in supercritical fluids hydrogenation of supercritical carbon dioxide to formic acid, alkyl formates, and formamides. J. Am. Chem. Soc. 1996, 118 (2), 344-55. 

Bianchini, C. Glendenning, L. Catalytic production of dimethylformamide from supercritical carbon dioxide. Methyl formate synthesis by hydrogenation of supercritical carbon dioxide in the presence of methanol. Selectivity for hydrogenation or hydroformylation of olefins by hydridopentacarbonylmanganese(I) in supercritical carbon dioxide. Chemtracts Org. Chem. 1996, 9 (6), 318-321. 

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