Ethylene glycol formation

There are many related compounds, including rhodium carbonyl cluster anions, which are present in the solutions cataly2ing ethylene glycol formation and which may be the catalyticaHy active species or in equiUbrium with them (38). 

The distribution of products in these reactions can change very substantially with reaction time, as illustrated in Fig. 1. The rate of ethylene glycol formation remains quite constant, but rates to other products change markedly as the reaction proceeds, indicating that secondary reactions are taking place. Some of the plausible secondary reactions in this system have been listed by Feder et al. (37) ... 

The reaction rates in this system are presumably first-order in catalyst concentration, as implied by the scaling of product formation rates proportionately to rhodium concentration (90, 92, 93). Responses to several other reaction variables may be found in both the open and patent literature. Fahey has reported studies of catalyst activity at several pressures in tet-raglyme solvent with 2-hydroxypyridine promoter at 230°C (43). He finds that the rate to total products is proportional to the pressure taken to the 3.3 power. A large pressure dependence is also evident in the results shown in Table VII. Analysis of these results indicates that the rate of ethylene glycol formation is greater than third-order in pressure (exponents of 3.2-3.5), and that for methanol formation somewhat less (exponents of 2.3-2.8). The pressure dependence of the total product formation rate is close to third-order. A possible complicating factor in the above comparisons is the increased loss of soluble rhodium species in the lower-pressure experiments, as seen in Table VII. Experiments similar to those of Fahey have also been... 

Kaplan has proposed that ion pairing between rhodium complex anions and the positively charged counterions has an adverse effect on catalytic activity for ethylene glycol formation (96, 109, 110). The following scheme ... 

Fig. 18. Effect of pressure on methanol and ethylene glycol formation rates by an iodide-promoted ruthenium catalyst (191). Reaction conditions 75 ml A -methylpyrrolidone solvent, 15 mmol Ru, 45 mmol Nal, H2/CO = 1, 230 C. 1 MPa = 9.87 atm.

Reaction of ethylene oxide with water is accomplished using a large molar excess of water to favor ethylene glycol formation over... 

A particularly broad potential for application in syngas reactions is shown by ruthenium carbonyl clusters. Iodide promoters seem to favor ethylene glycol (155,156) the formation of [HRu3(CO),]- and [Ru(CO)3I3]- was observed under the catalytic conditions. These species possibly have a synergistic effect on the catalytic process. Imidazole promoters have been found to increase the catalytic activity for both methanol and ethylene glycol formation (158-160). Quaternary phosphonium salt melts have been used as solvents in these cases the anion [HRu3(CO)u] was detected in the mixture (169). Cobalt iodide as cocatalyst in molten [PBu4]Br directs the catalytic synthesis toward acetic add (163). With... 

The use of [,3CJformaldehyde resulted in the formation of 80% of the dilabeled ethylene glycol, indicating that the ethylene glycol formation proceeds preferentially via reductive carbon-carbon coupling over hydro-formylation of formaldehyde the catalytic turnover is not given (166). Ru3(CO),2 was also found to catalyze the reductive alkylation of active methylene compounds with formaldehyde under synthesis gas. For example, pentan-2,4-dione is converted into 3-methylpentan-2,4-dione... 

Catalyst in MeOH, HCOOMe, and ethylene glycol formation ... 

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