Hydrogenation of CO2 under Supercritical Conditions

7 pmol of complex 1 [28], is placed into an oven-dried 50 mL reaction vessel in an argon-filled glove bag. The vessel is then connected via an adapter to a gas/vacuum manifold, evacuated for 10 min under high vacuum and 

Baiker and co-workers reported that the complex tranj-[Ru(Cl)2(dppe)2] (3) (dppe = l,2-bis(diphenylphosphino)ethane) catalyzes the formation of DMF very efficiently, despite the insolubility of the complex in SCCO2 [31]. They were even able to use a heterogenized silica-grafted ruthenium complex, which was obtained from the five-coordinated precursor 4 and tetraalkoxysi-lanes in a sol-gel process [32]. With these catalysts, the reaction occurs in the liquid dimcarb phase. The fact that high rates can be achieved with such heterogenized metal complexes makes them attractive materials for other processes involving SCFs or compressed gases. 

5 mmol of CF3(CF2)eCH20H, 0.70 mmol of tiglic acid, and 4.5 pmol of [Ru(OAc)2(6)] [37] are placed into an oven-dried 50 mL reactor in an argon-filled glove bag. The reactor is closed, flushed with CO2, and pressurized to 

Note that the above procedure requires a compressor to supply H2 at a sufficiently high pressure for most of the experiments summarized in Table 4.7-1. In the absence of such equipmeht, the H2 could be introduced after the temperature equilibratiori and immediately before adding the remainder of the CO2. As long as the CO2 is pumped in very quickly thereafter, little hydrogenation would take place during the pumping time. This technique could not be used if the reaction were fast (t 1/2 30 min). 

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Scheme 4.7-1 Synthesis of formic acid and its derivatives by hydrogenation of CO2 under supercritical conditions. Species 1-4 are some ruthenium complexes that have been used as catalysts or catalyst precursors.

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