Regioselective hydroformylation regioselectivity order

The regioselectivity of the hydroformylation of alkenes is a function of many factors. These include inherent substrate preferences, directing effects exerted by functional groups as part of the substrate, as well as catalyst effects. In order to appreciate substrate inherent regioselectivity trends, alkenes have to be classified according to the number and nature of their substitution pattern (Scheme 3) [4]. 

Through asymmetric hydroformylation a broad variety of chiral molecules are accessible which are valuable precursors for pharmaceuticals and agrochemicals. The potential market for synthetic chiral products in bulk form at the beginning of the 21st century is estimated to be more than US 2 billion [70], In order to obtain pure compounds, high regioselectivity and high enantioselectivity have to be combined. The desired product is the branched compound with an asymmetric carbon atom (eq. (3)). 

However, in order to attain high regioselectivity in the hydroformylation of simple 1-alkenes, a large excess of phosphines or phosphites should be added to cobalt and rhodium catalysts such as Co2(CO)8, HRh(CO)(PPh3)3, and Rh(acac)(CO)2, which decreases the reaction rate. ... 

As shown in Table 4 and Figure 5, the single PBTU impeller (Case 2) achieved a better performance with a higher initial rate and n/i aldehyde ratio accompanied by a lower power consumption than the single DT impeller (Case 1) under the same conditions of operation. This was possibly due to the better capability for overall circulation and lower agitation intensity of the PBTU impeller, which favored maintenance of the orderly micelle structure. When the novel SRFB was used (Cases 3 and 5), the initial rate of the biphasic hydroformylation increased remarkably from 0.630 10 kmol m (Case 1) to 1.24 10 and 2.03 10 kmol m respectively, by a factor of almost 2-3. However, the conversion and regioselectivity after 2 h of reaction were almost the same. Therefore, it is clear that an SRFB can increase the initial rate of 1-dodecene hydroformylation, but fails to further enhance... 

In the hydroformylation of terminal olefins, superior results in comparison to BISBI at higher temperature were noted l/b = 54.2 in comparison to BISBI Hb = 2.4) [66]. Moreover, with these tetraphosphines more than 95% linear selectivity and up to 94% yield of total aldehydes starting from 2-alkenes (2-pentene, 2-hexene, 2-octene) were observed in isomerizing hydroformylation [67]. The M-regioselectivity increased in relation to the nature of Ar in the following order, indicating a remarkable electronic effect ... 

Halide anions affect the rate of hydroformylation of internal olefins as well as the regioselective properties of the catalyst [136]. The rate of hydroformylation of thermally equilibrated internal higher alkenes increased by a factor of 6-7 by adding substoichiometric amounts (with respect to palladium) of Cl" or Br" and by a factor of 3-4 with I" [137]. When a thermally equilibrated mixture of internal Cg-Cj g olefins was subjected to isomerization-hydroformylation, a reverse effect on regioselectivity was observed [136e]. Thus, the formation of the linear aldehyde increased in the following order iodide > bromide > chloride. 

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