Transport Effects ‐ Homogeneous

Abstract

In the present contribution, the effects of different types of mass‐transfer on homogeneous catalytic reactions are addressed. In particular, emphasis is given to the effects of mass‐transfer on the precatalytic reactions as well as the turnover frequency. Various types of transport effects are considered. These include gas–liquid and liquid–liquid mass transfer, segregation and mixing of solutions, as well as dissolution kinetics of sparingly soluble organometallics and cage effects. A number of criteria are suggested for comparing the rates of mass transfer with various rates of reaction. A checklist is proposed for the experimentalist to assist in identifying potential mass‐transfer control issues. Simple steps to mitigate these complications are suggested.

The Catalytic Binuclear Elimination Reaction: Importance of Non-linear Kinetic Effects and Increased Synthetic Efficiency

“…The first two cobalt clusters to be isolated and identified were Co 2 (CO) 8 and Co 4 (CO) 12 [39,40]. Bor and Noack [41] and Bor et al [42] using FTIR then confirmed that in solution two isomers of Co 2 (CO) 8 were observable, the all-terminal and the more favoured di-bridging. HCo(CO) 4 was discovered by Hieber et al [43].…”

“…(2) This reaction mechanism will arise from the application of one or two metallic elements in the catalytic system. (3) The system will exhibit either an unusual rate dependence and/or an unusual selectivity pattern that has its origin(s) in the structure of the reaction mechanism and not in some secondary effect due to physico-chemical issues such as transport [8]. (4) Finally, all overall reactants for the organic reaction and all organometallic intermediates for this organic reaction are solvated during all individual reaction steps present in the catalytic reaction mechanism.…”

“…Heck and Breslow [9] observed that the addition of HCo(CO) 4 to a solution of CH 3 COCo(CO) 4 resulted in the formation of the corresponding aldehyde CH 3 CHO and the homometallic dinuclear carbonyl Co 2 (CO) 8 . They postulated that such a reaction might be operating under alkene cobalt-mediated hydroformylation reaction conditions and thus contribute to aldehyde product formation.…”

“…All groups observed the simultaneous presence of the mononuclear species HCo(CO) 4 and RCOCo(CO) 4 with simple alkenes (i.e. R ¼ octyl, cyclohexyl) and the dinuclear complex Co 2 (CO) 8 under catalytic alkene hydroformylation conditions. The general conclusion from Whyman and Mirbach was that Fig.…”

“…The first hydroformylation or oxo products were identified by Roelen [44] at Ruhrchemie when a cobalt containing heterogeneous catalyst was used. Pino et al [45] carried out the first stoichiometric hydroformylation of alkenes using Co 2 (CO) 8 and this was followed by the stoichiometric hydroformylation of alkenes using HCo(CO) 4 [46]. The unmodified catalysis and kinetics were extensively studied by the Natta group [47] including the negative order in [CO] À1 .…”