Dimethyl oxalate, oxidation

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

Finally, mention should be made of the oxidative coupling to yield dimethyl oxalate, the isomerization into acetaldehyde and the reaction to acetone. 

Oxidative carbonylation of MeOH with PdCl2 affords dimethyl carbonate (233) and dimethyl oxalate (232) [137,138], Selectivity of the mono- and dicarbonylation depends on CO pressure and reaction conditions. 

Oxidative Carbonylation of Methanol to Dimethyl Carbonate and Dimethyl Oxalate... 

The choice of liquid phase can affect the course of ozonation. This has been shown with phenylindenes by Miura et al. (1985) and with lignin models by Kratzl et al. (1976), who found that 4-methylveratrole gave a higher yield of dimethyl -methyl-cis,cis-muconate in 45% aqueous acetic acid than in dichloromethane and that the yield of dimethyl oxalate from acetoveratrone was markedly dependent on the solvent. Eriksson and Gierer (1985) found that in methanol the benzene ring of vanillin is cleaved (albeit only very slowly, after acetalization has occurred), but that in nonprotic solvents, such as acetone, the initial reaction is oxidation of the aldehyde function to a carboxyl group. 

The most promising process is also an oxidative carbonylation based on alkyl nitrites and was developed for dimethyl oxalate mainly by Ube. It uses supported palladium catalysts, modified with Fe, Ni, or Mo on y-Al203 [82, 83, 136]. 

The synthesis of kifunensine (1) was also achieved from the 5-deoxy-5-azidomannolactone derivative 8, obtained from cw-cyclohexadienediols by microbial oxidation using Pseudomonas putida 39D, ° by isopropylidenation followed by reduction to furnish 9 in 30% yield. Treatment of 9 with dimethyl oxalate followed by methano-lic ammonia furnished intermediate 10 (55%), which underwent oxidation of the primary alcohol to the aldehyde followed by cycUzation in methanolic ammonia to afford 11. Removal of the diacetoiude groups from 11 with 75% trifluoroacetic acid gave (+)-l. 

More recently, Bouwman carried out a detailed study on the carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes as catalysts [29-31]. After a careful analysis of the reaction, mixtures revealed that besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MFC), A, 7/-diphenylurea (DPU), aniline, azobenzene (Azo) and azoxyben-zene (Azoxy)], large quantities of oxidation products of methanol were co-produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H2O, and CO). They proposed the Pd-imido species P2Pd = NPh, which is the central key intermediate that can link together all the reduction products of nitrobenzene and all the oxidation products of methanol into one unified mechanistic scheme. 

Indirect, or multistep, routes to ethylene glycol use either formaldehyde or methanol derived from synthesis gas as the feed. In the former case, several approaches based on either glycolic acid or glycolaldehyde intermediates have been proposed and developed by different groups of workers. The principal route based on methanol involves the oxidative coupling of CO to dimethyl oxalate via methyl nitrite. 

The synthesis of diethyl oxalate 2b by carbonylative oxidation of ethanol with O2 in the presence of PdCl2-CuCl2 catalyst was originally discovered by Fenton and Steinwand. Utilizing triphenylphosphine and cobalt acetate(ll) as additives, dimethyl oxalate 2a was obtained in high yield (Scheme 2). Oxalate 2b was not formed in the presence of water, so this reaction was carried out with a considerable excess of orthoformate 4 as the dehydrating agent in order to maintain anhydrous conditions in the system. 

Palladium metal catalyst supported on the activated carbon affords dimethyl oxalate 2a selectively. On the other hand, dimethyl carbonate 3a is selectively formed when the same catalyst is treated with methyl nitrite la and HCl. This may be due to the oxidation of the Pd(0) to Pd(ll) by la and HCl (Table 3). To keep the oxidation state of palladium at +2, the presence of halogen ion like Cl and Br is important for the formation of 3a in the gas phase reaction. 

Carbonylation of alcohol group, methanol to dimethyl carbonate (DMC) and dimethyl oxalate (DMO), phenol to diphenyl carbonate (DPC), is very important chemical process in the current chemical industry. Dialkoxyl carbonate is key material for phosgene free process. The electrocarbonylation has great advantages to compare with a conventional catalytic carbonylation with O2. A particular advantage of electrocarbonylation is to be able to suppress CO2 formation by oxidation of CO because oxidizing power can be controlled as finely as one millivolt and there is no oxygen. 

The oxidative carbonylation of methanol yields dimethyl carbonate or dimethyl oxalate ... 

If palladium/copper halide catalysts are used, C—C coupling occurs and dimethyl oxalate is formed. The by product water can be trapped by addition of orthoformates and, instead of oxygen, quinones can also be used as the oxidizing agent. Typical conditions are 70 bar of CO and temperatures of 125 C. Based on results of Rivetti et aL, product formation can be envisioned via alkoxycarbonyl species [73] ... 

More recently, Ube Industries have published an indirect process to carbonylate methanol oxidatively to dimethyl oxalate utilizing nitrous acid methyl ester as the oxidant. A supported Pd/Fe catalyst is used and methyl nitrite can be generated either in situ or in a separate reactor from methanol and NO [74] ... 

Oxalic ester synthesis—Enolesters from ketones. 6 g. dl-zl5,14-3.Ethylenedioxy-lly ,18-oxido-16-oxo-18-tetrahydropyranyloxyandrostadiene and dimethyl oxalate in benzene added dropwise to NaH in oil (Metal Hydrides, Inc., Beverly, Mass., USA) and benzene, stirred 48 hrs. at 30° in a slow Ng-stream, the crude product dissolved in benzene, and allowed to stand at room temp, overnight with acetic anhydride and pyridine 6.61 g. methyl dl-J5,14,17(20)-3-ethylene-dioxy-1 ly, 18- oxid o-16- oxo-18- tetrahydropyranyloxy - 20 - acetoxypregnatrien-21-ate, 6 g. suspended in an ice-cold 10 1 mixture of morpholine and water, stirred 3-4 hrs. until a clear soln. results, allowed to stand 24 hrs. at ca. 10°, evaporated almost to dryness at 35-40°/0.05 mm., a mixture of benzene and ether then pyridine added, ice-cooled, acetic anhydride added, and allowed to stand 24 hrs. at room temp. 5.55 g. dl-j5,14,17(20)-3-ethylenedioxy-ll, 18-oxido-16-oxo-18-tetrahydropyranyloxy-20-acetoxypregnatrien-21-ic acid morpholide.—Morpholine is preferred to other sec. amines because of its good solvent properties (cf. Synth. Meth. lA, 87). Use of anhydrous amines caused decomposition. K. Heus-ler, P. Wieland, and A. Wettstein, Helv. A2, 1586 (1959). 

Carbonylation acetic acid, acetic anhydride, methyl acetate, methyl formate Reductive carbonylation acetaldehyde, ethanol, ethyl acetate, ethylidene diacetate Oxidative carbonylation dimethyl carbonate, dimethyl oxalate... 

Of the large volume of tin compounds reported in the Hterature, possibly only ca 100 are commercially important. The most commercially significant inorganic compounds include stannic chloride, stannic oxide, potassium staimate, sodium staimate, staimous chloride, stannous fluoride, stannous fluoroborate, stannous oxide, stannous pyrophosphate, stannous sulfate, stannous 2-ethyUiexanoate, and stannous oxalate. Also important are organotins of the dimethyl tin, dibutyltin, tributyltin, dioctyltin, triphenyl tin, and tricyclohexyltin families. 

The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethyl aniline in aqueous acid (Fig. 2). The reaction mass is made alkaline and the excess dimethylaniline is removed by steam distillation. The resulting leuco base is oxidized with freshly prepared lead dioxide to the carbinol base, and the lead is removed by precipitation as the sulfate. Subsequent treatment of the carbinol base with acid produces the dye, which can be isolated as the chloride, the oxalate [2437-29-8] or the zinc chloride double salt [79118-82-4]. 

The addition of various Kolbe radicals generated from acetic acid, monochloro-acetic acid, trichloroacetic acid, oxalic acid, methyl adipate and methyl glutarate to acceptors such as ethylene, propylene, fluoroolefins and dimethyl maleate is reported in ref. [213]. Also the influence of reaction conditions (current density, olefin-type, olefin concentration) on the product yield and product ratios is individually discussed therein. The mechanism of the addition to ethylene is deduced from the results of adsorption and rotating ring disc studies. The findings demonstrate that the Kolbe radicals react in the surface layer with adsorbed ethylene [229]. In the oxidation of acetate in the presence of 1-octene at platinum and graphite anodes, products that originate from intermediate radicals and cations are observed [230]. 

Treatment of D-glucoascorbic acid (XV) with diazomethane gives a 2,3-dimethyl derivative (LXXIX) and this upon repeated treatment with silver oxide and methyl iodide yields 2,3,5,6,7-pentamethyl-D-glucoascorbic acid (LXXX). Ozonization of the latter followed by hydrolysis gives oxalic acid and 3,4,5-trimethyI-D-arabonic acid (LXXXI). This acid was shown to possess a free hydroxyl group at C2 by reason of the fact that the amide of LXXXI gives a positive Weerman reaction for a-hydroxy amides, i.e., when the amide is treated with sodium hypochlorite, sodium isocyanate is produced, the latter being identified by... 

---