Hydroformylation Aldehydes from ethylene

Hydroformylation s. Aldehydes from ethylene derivatives Hydrogen prepared in situ 17, 96 18,115 G-Hydrogen... 

The mechanism of the cobalt-cataly2ed oxo reaction has been studied extensively. The formation of a new C—C bond by the hydroformylation reaction proceeds through an organometaUic intermediate formed from cobalt hydrocarbonyl which is regenerated in the aldehyde-forrning stage. The mechanism (5,6) for the formation of propionaldehyde [123-38-6] from ethylene is illustrated in Figure 1. 

Synthetic precursors for aliphatic materials mirror the pattern of their naturally derived counterparts in that the commonest units are even in carbon chain length. This is because they are usually derived from ethylene through oligomerisation. Thus, coupling of two ethylene molecules produces a four-carbon chain, three produces six, and so on. In order to obtain an odd number of carbon atoms in the chain, one of the simplest techniques is to add a single carbon to an even chain which can be achieved, for example, by hydroformylation. Hydroformylation also introduces an alcohol function and opens the way for oxidation to aldehydes and acids. Three carbon units are available from propylene as well as by reaction of ethylene with a one-carbon unit. 

The structure written for I is satisfactory for olefins which can have only internal or only terminal double bonds (ethylene, propylene, cyclohexene). We find, however, that although internal olefins are thermodynamically more stable than terminal olefins under reaction conditions, the products obtained in the hydroformylation reactions are largely derived by addition to the terminal carbons. For example, the distribution of alcohols secured from 1-pentene and 2-pentene is about the same 13, 14), 50-55% of n-hexanol, 35-40% of 2-methylpentanol-l, and 10% of 2-ethylbutanol-l. In each case the chief product can be obtained only by the addition of the formyl group to the No. 1 carbon atom. If we assume that hydroformylation occurs only at the double bond, we may ask how it is possible to form a straight-chain aldehyde from an internal olefin. 

Hydroformylation usually involves the production of an aldehyde from hydrogen, carbon monoxide and ethylene using a catalyst such as RhH(CO)(PPh3)3, HCo(CO)3P Bu3, R3P(CO)3Co+ Co(CO)4 or [Bu3PPtCl2l2SnCl2. These catalysts enable the process to work at lower temperatures and pressures than were required by previously used catalysts such as Co2(CO)s. Most in current use is RhH(CO) (PPh3)3 which can secure over 95% conversion in scheme (12.352). 

Carbon monoxide is efficiently incorporated into aldehydes and alcohols by the hydroformylation reaction presented in Section 9.3, but methods are now being sought to incorporate CO into other organic compounds and to reduce the oligomerize it to produce long-chain alkanes or alcohols. Most organic chemicals are currently made commercially from ethylene, a product of oil refining. It is possible that in the next several decades we may have to shift toward other carbon sources for these chemicals as depletion of our oil reserves continues. Coal can be converted into CO/H2 mixtures with air and steam (Eq. 12.1), and it is possible to convert such mixtures, variously called... 

Chemical processes dominate the production of short-chain organic acids. The primary route of synthesis employs the "Oxo process (Billig and Bryant 1991). Propionic acid is made by oxo synthesis of propionaldehyde from ethylene, CO, and H2 with a rhodium catalyst. liquid-phase oxidation of the aldehyde yields propionic add. Butyric acid is made by air oxidation of butyraldehyde, which is synthesized by the 0x0 process fi-om propylene, CO, and H2. The triphenylphosphine-modified rhodium 0x0 process, termed the LP Oxo process, is the industry standard for the hydroformylation of ethylene and propylene (Billig and Bryant 1991). Also pure propionic acid can be obtained from propionitrile or by oxidation of propane gas. 

The catalyst formed in this manner exhibited carbonyl infrared absorptions, as shown in Table XXX. These catalysts were tested by hydroformylation of ethylene or propylene at 100°C and atmospheric pressure. Both were effective, with (A) being better than (B), probably because of the higher surface area. The aldehyde formed from propylene was a mixture of 63% n- and 37% isobutyraldehyde. The rate expression for ethylene hydroformylation was ... 

Metal-catalysed hydrocarboxylation of olefins (Equation 3) is the poor relative of the more famous hydroformylation. It generally requires forcing reaction conditions and suffers from mediocre activities and selectivities (n/i ratio). Moreover, the same products can be made via hydroformylation and oxidation of the aldehyde product.431 Consequently, there are few industrial applications of hydrocarboxylation e.g. Ni(CO)4-catalysed production of propionic acid by hydrocarboxylation of ethylene.432,433... 

The ethylene spacer is necessary as a shield from the strong electron-withdrawing effect of the perfluoroalkyl chain, which would decrease the donor properties of the phosphane. This phosphorous-ligand is extremely soluble in per-fluorinated solvents such as perfluoromethylcyclohexane (CFgCsFn) and only trace amounts of it can be extracted with organic solvents. The in situ prepared rhodium(l) complex 14 is a useful catalyst for the hydroformylation of terminal alkenes under FBS-conditions. The aldehydes 16 and 17 were formed in 85% yield by hydroformylation of 1-octene (15) with an linear to iso ratio of nearly 3 1 Eq. (8). 

With the Ziegler displacement process the higher alkyl group is displaced from the chain growth product by ethylene. This yields a mixture of even-numbered linear alpha olefins with the trialkyl aluminum being recycled. The odd-numbered linear alcohols are produced through hydroformylation of the olefin and hydrogenation of the odd-numbered aldehydes. 

In principle, the hydroformylation-acetalization sequence can be performed in two separate steps as sometimes described in the older literature. Thus, hydroformylation of cyclohexene was carried out with Co2(CO)g as catalyst at 180 bar syngas pressure [45]. The formed aldehyde was separated from the catalyst and subsequently reacted with ethylene glycol in the presence of sulfuric acid to give the corresponding cyclic acetal. ... 

The mechanism of ethylene l ydroformy1at1on with Pt/Sn catalysts has been invest gated.279 j, e diphenyl phosphine oxide complex (58) catalyses the hydroformylation of 1-hexene and even 2-hexene to give mainly linear aldehydes and alcohols best results were obtained from an in-situ mixture of PtCcodlj, Ph2P0H and dppe (1 1 1). There is no activity without Ph2P0H.280... 

---