Esters, hydroformylation

Higher alcohols are produced from three routes that involve H2. These three routes differ in feed stocks and the nature of the process, so alcohols can be produced for specific process needs. The three routes are hydrogenation of fatty acids or esters, hydroformylation, and the Alfol process [108,109]. 

Alkenyl esters. Hydroformylation of vinyl acetate gives exclusively the branched aldehyde 49 (Eq. while the linear aldehyde 50 is the predonii ... 

Metal-semiconductor transitions, 135 Metazellerite structure, 848 Metazidoheraerythrin structure, 690 Melhacrylic acid methyl ester hydroformylation, 261 Methane... 

Isobutyraldehyde is commonly available as a by-product of propylene/Oxo hydroformylation. Methyl isoamyl ketone is used as a solvent for ceUulose esters, acryHcs, and vinyl polymers. It is available in the United States from Eastman (Kingsport, Tennessee) (47) and Union Carbide (South Charleston, West Virginia) and was priced at 1.42/kg in October 1994. 

Hydroformylation. Esters of maleate and fumarate are treated with carbon monoxide and hydrogen in the presence of appropriate catalysts to give formyl derivatives. Dimethyl fumarate [624-49-7] is hydroformylated in 1 1 CO/H2 at 100°C and 11.6 MPa pressure with a cobalt [7440-48-4] catalyst to give an 83% yield of dimethyl formylsuccinate [58026-12-3] product (72). 

Obviously, the use of a nonvolatile ionic liquid simplifies the distillative workup of volatile products, especially in comparison with the use of low-boiling solvents, where it may save the distillation of the solvent during product isolation. Moreover, common problems related to the formation of azeotropic mixtures of the volatile solvents and the product/by-products formed are avoided by use of a nonvolatile ionic liquid. In the Rh-catalyzed hydroformylation of 3-pentenoic acid methyl ester it was even found that the addition of ionic liquid was able to stabilize the homogeneous catalyst during the thermal stress of product distillation (Figure 5.2-1) [21]. This option may be especially attractive technically, due to the fact that the stabilizing effects could already be observed even with quite small amounts of added ionic liquid. 

Methyl-l-hexanol has also been prepared by the reaction of 2-hexylmagncsium halides with formaldehyde,3 the reduction of 2-mctliylliexanoic acid or its ester,4 5 and by hydroformylation of 1-hexene6"8 among others. 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

Hydro carbonylation of olefins, hydroformylation, hydroesterification and hy-droxycarbonylation are reactions which appear to be of particular interest. Indeed, they allow the simultaneous creation of a new C - C bond as well as the introduction of a functional group (aldehyde, ester and acids). One or two new stereogenic centres can thus be formed at the same time (Scheme 26). Despite the difficulty of using high carbon monoxide pressure, the aheady existing industrial processes prove that such reactions can be performed on a very large scale [107]. 

An unusual enhancement of catalytic activity in a two-phase system has been reported by Fremy et al. (1998) for the hydroformylation of acrylic esters using Rh complex of TPTS as catalyst. Even though acrylic esters have reasonable solubility in water, rate enhancements in two-phase systems by a factor of 2 to 14 have been reported. It seems that water is not an inert solvent but also acts as a reactant or a co-ordinating solvent which can modify elementary steps of the catalytic cycle (Cornilis, 1997). 

Branched-regioselective hydroformylation of unsaturated esters has been achieved [41]. The use of the phosphaadamantane ligand 1, which is readily available from acetylacetone and phenylphosphine (Eq. 1), proved particularly useful in terms of reaction rate, regio-, and chemoselectivity [42-44]. 

Hydroformylation of a range of 1,1-di- and 1,1,2-trisubstituted unsatur-ated esters yields quaternary aldehydes (Table 1, entries 1-8). Hence, the regiochemistry-directing influence of the electron-withdrawing ester function overcompensates Keuleman s rifle. Furthermore, hydroformylation of 1,2-disubstituted unsaturated esters occurred with high a-selectivity and chemoselectivity (Table 1, entries 9 and 10). As a side reaction hydrogenation of the alkene has been observed [41]. 

Table 1 Results of branched-selective hydroformylation of a.fi-unsaturated esters with a rhodium/phosphaadamantane (1) catalyst...

From a library of mixtures of monodentate ligands an excellent catalyst for branched-selective hydroformylation of methacrylic esters was identified (Scheme 5) [45]. The best catalyst employs a 1 1 mixture of triphenylphos-phine and a phosphabenzene ligand 2 [32]. 

An interesting one-pot hydroformylation/Fischer indole sequence can be achieved by running the hydroformylation in the presence of a phenylhy-drazine. This protocol gave access to the methyl ester of the plant growth regulator 3-indole butanoic acid (IBA) (Scheme 16) [61-63]. A review on related tandem processes involving the hydroformylation as a key step has appeared recently [9]. 

C02Me)CH2-C02Me was regioselectively prepared in >82% enantiomeric excess by homogeneous catalytic hydroformylation. For other vinylidene esters, the asymmetric induction was lower.318... 

Aldehyde dimers and trimers are common byproducts produced during the hydro formylation of propene. Union Carbide addressed the problem in a creative way when it was discovered that the dimers and trimers could be used as the principal reaction solvent for hydroformylation.[32] Elimination of an extraneous solvent simplified the process. The Ester-diol Trimers may equilibrate, as shown in Equation 2.9 to give a mixture of diol, a dimer, and the diester of the diol, which is a tetramer of butanal. 

The hydroformylation reaction has been the subject of excellent reviews (for example I, 6-8) therefore, the object of this particular treatise is not to provide comprehensive coverage of all aspects. The basic chemistry is presented, along with recent developments of interest as reported in the literature, although not in chronological order. Stereochemical studies (6) are included only when pertinent to another point under consideration. Carbonylations or hydrocarboxylation reactions which produce ketones, esters, acids, esters, or amides are not included (/). Also not included is the so-called Reppe" synthesis, which is represented by Eq. (1). 

A small amount of formate esters (4%) is formed in the cobalt hydroformylation cycle (46). The amount is undetectable in the rhodium-catalyzed reaction. 

In the hydroformylation of crotonate esters, three different aldehydes. may be formed, denoted as the a-, / -, or -y-isomers ... 

Early studies of the cobalt hydroformylation (4) included vinyl acetate as the olefinic reactant. A mixture of a- and /3-formyl esters was reported. 

---