Linear/branched ratio

The introduction of rhodium has allowed the development of processes which operate under much milder conditions and lower pressures, are highly selective, and avoid loss of alkene by hydrogenation. Although the catalyst is active at moderate temperature, plants are usually operated at 120°C to give a high n/iso (linear/ branched) ratio. The key to selectivity is the use of triphenylphosphine in large excess which leads to >95% straight chain anti-Markovnikov product. The process is used for the hydroformylation of propene to n-butyraldehyde, allyl alcohol to butanediol, and maleic anhydride to 1,4-butanediol, tetrahydrofuran, and y-butyrolactone. 

Casey observed a linear/branched ratio of 66 1 using a BISBI-Rh complex to hydroformylate 1-hexene. This is a huge increase over the linear/branched ratio of only 2.6, which Casey observed when a Rh-dppe40 complex is used for hydro-formylation of 1-alkenes.41 The (3n of BISBI is 113-120°, whereas that of dppe is much lower, at 85°. 

These ligands allow hydroformylation of propene to occur at 100 °C and less than 20 bar, resulting in a linear/branched ratio of 30 1 and a 98% conversion of propene to product in one pass over the catalyst—truly an impressive achievement. 

Hydroformylation reactions have been one of the most well researched areas of CO2 reaction chemistry. Hydroformylation reactions are necessary for the formulation of complex chemicals. The first complete kinetic study of a hydroformylation reaction was in CO2 and was first published in 1999. Prior to this, most studies had considered the effect of dense CO2 on linear branch ratios or other forms of selectivity. Carbon dioxide has an effect on the selectivity of a variety of hydroformylation reactions and can enhance the rate of reaction Hydroformylation is by its nature regioselective and typically the linear branch or n iso ratio is used as the measure of selectivity. The use of asymmetric catalysts to achieve chiral products has introduced a second degree of selectivity to catalyst design. Advancements in catalyst design, together with solvent selection, are expected to make... 

The linear/branched ratio was 7.5 1, which was greater than that found with the control catalyst in solution. Rhodium(III) chloride has been immobilized on a support made by polymerization of vinylpyridine and divinylben-zene in the presence of silica. The best activity for the conversion of methanol to acetic acid by carbon monoxide was obtained after 20% of the pyridine groups were quaternized with methyl iodide. This suggests ionic bonding of a tetra-halorhodate ion to the polymer.211... 

A variety of ligand-modified cobalt catalysts have been investigated and a commercial process known as the Shell Process was developed The Shell Process uses tributylphosphine as the modifier, which generates HCo(CO)3PBu3 as the active catalyst species and is substantially more stable than HCo(CO)4. This process gives a higher linear/branched ratio (7.3/1, i.e., 88% linear and 12% branched for the reaction of 1-propene), but the products are alcohols and not aldehydes, and ca. 15% of 1-propene is hydrogenated to propane. These... 

Phosphine Cone angle (°) Rel. rate Linear branched ratio... 

It should be mentioned here that soluble supports are not always innocent systems but can in fact alter the reaction in rather unexpected ways Cole-Hamilton and coworkers reported on dendrimers with 16 PPh2 groups on the periphery. This system was applied in the Rh-catalyzed hydroformylation of 1-octene and linear/branched ratios (l/h) of 13.9 were obtained, while a small-molecule analogue showed an l/b ratio of 3.8 (13) [24]. 

Rh(acac)(CO)]2 and P(C6H4-/ -C6Fi3)3. These conditions resulted in faster rates and better linear branched ratios of the products. At room temperature, the substrate 1-octene is miscible with perfluoromethylcyclohexane but nonanal (1) is not, resulting in the phase separation of the product and the catalyst layer. 

Rhodium-catalyzed hydroformylation of 1-octene using a continuous flow reactor was conducted with a phosphine ligand immobilized on silica (Scheme 84). A linear/branched ratio >30 was achieved, although the conversion was rather low. In addition, no activity loss was observed over several days. 

A pyridal formate group is used for hydroesterification of an olefin (Equation (42)). Use of a benzyl ester in place of the pyridyl group gave 0% yield. Pyridyl formamides were also found to give hydroamidation products with high linear/branched ratios. "" ... 

Hydroformylation of A-allyl phthalimide on 200-g scale was described in a recent patent by Dow [10]. Using the Rh-biphephos catalyst, the desired linear aldehyde (10) was produced in 11.5 1 linear/branched ratio. Acetal protection of the aldehyde and cleavage of the phthalimide gave the protected amino aldehyde (11), useful as a pharmaceutical intermediate. 

Dissociation of PPhs from 1 gives 3t, dissociation of CO from 2ee also gives 3t, while dissociation of CO from 2ae will give 3c. Dissociation of PPhs from 2 gives the isomers lOt and 10c. The use of diphosphines such as dppe and dppp gives modest linear-branched ratios and their putative intermediates 3 must have cis structure 3c. Therefore, 3c is not a likely intermediate for the selective hydroformylation. For linear-branched ratios of 4 1 we don t have to invoke mono-phosphine species of type 10, as already structure 3c suffices for the production of moderate I b ratios (3 1). 

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