Methyl propionate, oxidation

The reaction of methyl propionate and formaldehyde in the gas phase proceeds with reasonable selectivity to MMA and MAA (ca 90%), but with conversions of only 30%. A variety of catalysts such as V—Sb on siUca-alumina (109), P—Zr, Al, boron oxide (110), and supported Fe—P (111) have been used. Methjial (dimethoxymethane) or methanol itself may be used in place of formaldehyde and often result in improved yields. Methyl propionate may be prepared in excellent yield by the reaction of ethylene and carbon monoxide in methanol over a mthenium acetylacetonate catalyst or by utilizing a palladium—phosphine ligand catalyst (112,113). 

Only with propanal are very high conversions (99%) and selectivity (> 98 0) to MMA and MAA possible at this time. Although nearly 95% selective, the highest reported conversions with propionic acid or methyl propionate are only 30—40%. This results in large recycle streams and added production costs. The propanal route suffers from the added expense of the additional step required to oxidize methacrolein to methacrylic acid. 

Esterification of the propionic acid side chain at C-13 (ring C) with a methyl group catalyzed by S-adenosyl-L-methionine-magnesium protoporphyrin 0-meth-yltransferase yields protoporphyrin IX monomethyl ester (MPE), which originates protochlorophyllide by a P-oxidation and cyclization of the methylated propionic side chain. This molecule contains a fifth isocyclic ring (ring E), the cyclopentanone ring that characterizes aU chlorophylls. 

Various nitro compounds have been condensed with carbonyl compounds in reactions catalyzed by alkaline earth metal oxides and hydroxides 145). It was found that the reactivities of the nitro compounds were in the order nitro-ethane > nitromethane > 2-nitropropane, and those of carbonyl compounds were propionaldehyde > isobutyraldehyde > pivalaldehyde > acetone > benzaldehyde > methyl propionate. Among the catalysts examined, MgO, CaO, Ba(OH)2, and Sr(OH)2, exhibited high activity for nitroaldol reaction of nitromethane with propionaldehyde. In reactions with these catalysts, the yields were between 60% (for MgO) and 26% (for Sr(OH)2) at 313 K after 1 h in a batch reactor. On Mg(OH)2, Ca(OH)2, and BaO, the yields were in the range of 3.8% (for BaO) and 17.5% (for Mg(OH)2). Investigation of the influence of the pre-treatment... 

The effect of the particular functional group on adsorption, however, is not always the same as seen on oxide surfaces. For example, carboxylic acids adsorb strongly on metal oxide surfaces, and the heat of adsorption of stearic acid is higher than that of the corresponding ester, methyl stearate (Hironaka et al., 1978). For adsorption on the nascent surface, however, propionic acid is a poor adsorbate, and the adsorption activity of propionic acid is lower than that of methyl propionate. Although propyl amine adsorbs easily on metal oxide surfaces, the adsorption activity of propyl amine is low on the fresh steel surfaces. Also, the heat of adsorption of organic sulfides on iron oxide is less than that of esters (Forbes et al., 1970b), but the results of adsorption activity on the nascent surface were the opposite. It is thus noteworthy that the chemical nature of the nascent surface of steel is often opposite to that of oxide-covered metal surfaces, with respect to adsorption. 

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

R)-3-Hydroxy-2-methyl propionic acid, an important building block for the synthesis of the widely used antihypertensive drug captopril, was obtained with 97% enantiomeric excess (e.e.) and 100% molar conversion by microbial oxidation of prochiral 2-methyl -1,3-propandiol with Acetobacter pasteurianus [25]. 

Useful whole cell asymmetric oxidations of methyl groups to carboxyl groups have been found by classical microbiological screening as for the microbial oxidation of prochiral 2-methyl-l,3-propandiol to (R)-3-hydroxy-2-methyl propionic acid with A. pasteurianus with 97% e.e. and 100% molar conversion [113],... 

Fig. 11. The effect of temperature on the maximum rate of oxidation (in torr. min ) of esters [93]. (1) Methyl acetate. (2) Methyl formate. (3) Methyl propionate. (4) Ethyl formate. (5) Methyl butyrate. (6) Propyl formate.

Ueda et al. (37) have proposed magnesium oxide catalyst modified with a transition metal ion (M/MgO) for the vinylation of methyl propionate and acetonitrile. Acetonitrile is vinylated to acrylonitrile selectively (94% selectivity at about 10% conversion) over Cr/MgO catalysts at 350 C in the absence of oxygen. The selectivity for the vinylation of methyl propionate over Mn/MgO catalysts is not different from the value obtained with Ti -TSM in the presence of oxygen. The catalyst system, however, is not effective for the reaction of acetic acid. We conducted the reaction of acetonitrile and methanol over Ti -TSM in the presence of oxygen, and found that the vinylation does not take place but the hydrolysis to acetic acid and subsequent esterification with methanol into methyl acetate proceed preferentially. It is likely that Ti -TSM is an appropriate catalyst for the vinylation of carbonyl compounds and M/MgO is appropriate for the vinylation of nitriles. 

A unique approach to the stereochemical complexities of erythronolide A was developed by Deslongchamps as outlined in Scheme 2,19. The methyl ester of erythronolide A seco acid (212) was dehydrated to form the cyclic ketal 213. A multistep oxidation of the side chain then gave aldehyde 214 which, when condensed with the zirconium enolate of methyl propionate, afforded a 10 1 ratio of aldol diastereomers, the major being 213. Furthermore, aldehyde 214 could easily be converted into the y-lactone 215. 

Reductive removal of the halogen was achieved with tributyltin hydride and subsequent ozonolysis gave aldehyde 221. An aldol condensation of 221 with the trimethylsilyl enol ether of methyl propionate, followed by Jones oxidation... 

Methyl methacrylate (MMA) is a monomer of the so-called organic glass (Plexigals). Attempts have been made to produce MMA by a vapor-phase aldol-condensation-lype reaction between methyl propionate (f ) and HCHO in the presence of a large amount of methanol using either basic or acidic oxide catalysts [1] ... 

The reaction was also tested over a V-P oxide catalyst with a P/V atomic ratio of 1.06 consisting of (VO)2P207 at a temperature of 320 °C and a methyl propionate/HCHO molar ratio of 2.0, using methylal as the source of HCHO. The yields of methyl methacrylate, acrylic acid, propionic acid reach 25, 6, and 20 mol%, respectively, based on the charged HCHO the sum of the yields of methyl methacrylate and methacrylic acid reaches 31 mol%. By the combination of Si with the V phosphate, the yield of methyl methacrylate is markedly improved. For example, over the VSi8P2,g catalyst, the yields of methyl methacrylate, methacrylic acid, and propionic acid reach 42, 6, and 20 mol%, respectively, based on the charged HCHO the sum of yields of methyl methacrylate and methacrylic acid reaches 48 mol% based on HCHO. The yield of methyl methacrylate increases as the methyl propionate/HCHO molar ratio is increased, for example, with the molar ratio of 4.0, the sum of yields of methyl methacrylate and methacrylic acid reaches 68 mol% based on the charged HCHO. As for the selectivity, the selectivity based on HCHO increases as the methyl propionate/HCHO ratio is increased, while the selectivity based on methyl propionate decreases. With a methyl propionate/HCHO molar ratio of 4.0, the selectivity based on HCHO is 100 mol%. On the other hand, when the molar ratio is 1.2, the selectivity based on methyl propionate becomes 100 mol%. 

Aerobic Palladium-Catalyzed Oxidation of Methyl Acrylate (MA) to 3,3-Dimethoxy Methyl Propionate Process Optimization and Scale-Up... 

Dimethoxy methyl propionate is a versatile multifunctional synthetic building block, as illustrated by its use as starting material in our route to methyl cyanoac-etate [10] as precursor for cyanomethyl methacrylate [10], which finds wide application in the adhesive industry [11]. We envisaged the synthesis of 3,3-dimethoxy methyl propionate by Wacker-type oxidation of cheap methyl acrylate in methanol as the solvent (Figure 11.5). 

While studying the palladium-catalyzed oxidation of methyl acrylate in methanol using oxygen as the oxidant to form 3,3-dimethoxy methyl propionate, we encountered all three of these problems. The initial experiments were... 

Chart 11.1 Inside reactor temperature increase due to the exothermicity of the oxidation of methyl acrylate to 3,3-dimethoxy methyl propionate [9]. 

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