N : iso ratio

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

It is noteworthy that a clear enhancement of selectivity for the linear hydro-formylation product is observed only with cdpp (Table 5.2-1, entry e). With all other ligands, the n/iso ratios are in the 2 to 4 range. While this is in accordance with known results in the case of PPI13 (entry a) and dppe (entry c) (in comparison to monophasic hydroformylation [69]) and also with reported results in the case of Natppts (entry b in comparison to the biphasic hydroformylation of 1-pentene in [BMIM][PF(3] [46]), it is more remarkable for the bidentate metallocene ligand dppf... 

The "real" oxo precatalyst [HRh(CO)(TPPTS)3] is easily made in the oxo reactor by reacting suitable Rh salts (e.g., rhodium acetate or rhodium 2-ethylhexanoate) with TPPTS - both components freshly prepared or recovered and recycled - without any additional preformation step. The reaction starts after formation of the active species and adjustment of the whole system with water to the desired P/Rh ratio (ensuring the stability of the catalyst and the desired n/iso ratio). 

The concept of continuous flow SILP hydroformylation was also tested in the biphasic, liquid-liquid hydroformylation of 1-octene using the Rh-norbos catalyst system [78], TOFs of 44 h"1 were achieved after 3-4 h with no sign of deactivation at prolonged reaction times. At steady-state conditions an n/iso ratio of 2.6 was obtained. No leaching of rhodium metal could be detected by ICP-AES analysis of product samples at least after these short reaction times. 

In another study (102), a triarylphosphine with a sulfonyl group on each phenyl was prepared and used with rhodium in a buffered aqueous system. The hydroformylation of propylene was conducted at 80°C and 50 atm of synthesis gas. The yield of aldehydes was 98% on converted propylene with an n iso ratio of 6.7 1. 

Ruthenium source Promoter structure conversion (° ) Propionic (mole Butyric Valeric Butyric acids n/iso ratio... 

In the hydroformylation reaction, the fundamental steps that occur are essentially the same, albeit in a different sequence, to those that occur in the hydrogenation reaction, except that there is an additional CO insertion step. In the reaction, a mixture of linear and branched chain products are produced, the resulting composition being defined as the n.iso ratio. The n.iso ratio obtained is dependent upon the catalyst used and the reaction conditions, and in general, the linear products are of higher value to industry. 

With an annual production of up to 9.3 million tons in 1998, hydroformylation is the most important homogeneously catalyzed reaction [20,21], The reaction is performed almost exclusively by the use of cobalt or rhodium catalysts. The advantages of rhodium catalysts are milder reaction conditions and better n/iso ratios in product distribution. The toxicity of rhodium compounds as well as the high rhodium price [22] (between 20 and 75 g during the last five years) demand an efficient catalyst recycling. 

The catechol-based hgands 14 show fairly low selectivity similar to that of the unmodified system. In contrast, the biphenol-derived phosphites 17 gave excellent chemoselectivity. The best results were obtained with 17c, where a TOP of ca. 1900 h was achieved which is close to the maximum value of 2000 h The n-selectivity of 71% was also appreciable, corresponding to an n/iso ratio of 2.4. The substituents in the biphenol backbones in hgands 19 re-... 

In a first test reaction, the polymer support was used for the hydroformylation of 1-octene in water in the presence of Rh(CO)2acac. Within a reaction time of 10 h at 120°C and a H2/CO (1 1) pressure of 5 MPa, conversion of up to 94% was obtained. The n iso ratio was 3 1, sometimes reaching 9 1. The quantities of 3-and 4-nonanal resulting from olefin isomerization, were below 5% [74]. The versa-tihty of the polymer support was further demonstrated with the Heck reaction of styrene and iodobenzene in the presence of Pd(OAc)2 as the metal catalyst The reaction was again performed in pure water at 50 °C and product yield of up to 80% was obtained after 20 h reaction time [75]. 

The goal is to improve the ratio of straight chain to branched chain products (n iso ratio) and to keep the hydrogenation of olefin to paraffin and aldehyde to alcohol as low as possible. 

Reaction products obtained by low-temperature hydroformylation (100°-120°C) of linear a-olefins with an equimolar amount of CO and Hd at 280 atm were (% ) aldehyde, 94 1 (n iso ratio 2, 56 to 3, 16) formate, 4 0.5 alcohol, 2 0.5. Furthermore, 1% of the olefin feed is hydrogenated to paraffin and 2-3% is converted to high boiling products (aldols, ketones, and acetals). 

The fluorous solvent alone had a minimal effect on the outcome of the reaction. However, with the flnorinated ligand, the n iso ratio was found to increase with increasing phosphine concentration, reaching a valne of almost 8 1 at a phosphine to rhodium ratio of 103 1. The beauty of this system was demonstrated by its use in a semicontinnous hydroformylation experiment. After each... 

For an unmodified CojfCO) catalyst, the most influential single reaction parameter in determining the n iso ratio is the panial pressure of CO. With propylene, increasing the ( 0 pressure from 23 to 90 atm at lOO C results almost in a tripling of the n iso ratio from 1.6 to 4.4. Hydrogen partial pressure has only a small effect. 

Unlike cobalt, the rhodium catalyst exhibits little or no aldehyde hydrogenation activity, but it is 10 -10 limes more active than the cobalt analog. The rhodium system is also a highly active isomerization catalysts but gives rise to a low n iso ratio (about I compared to 4 of Co2(CO) ). 

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