Esters dimethyl oxalate

The above example serves to iUustrate the basis of the procedure employed for the characterisation of aUphatic esters, viz., hydrolysis to, and identification of, the parent acids and alcohols. Most esters are liquids a notable exception is dimethyl oxalate, m.p. 54°. Many have pleasant, often fruit-hke, odours. Many dry esters react with sodium, but less readily than do alcohols hydrogen is evolved particularly on warming, and a sohd sodio derivative may separate on coohng (e.j/., ethyl acetate yields ethyl sodioacetoacetate ethyl adipate gives ethyl sodio cj/cZopentanone carboxylate). 

Oxahc acid reacts with various metals to form metal salts, which are quite important as the derivatives of oxahc acid. It also reacts easily with alcohols to give esters. Crystalline dimethyl oxalate is, for example, produced by the reaction of oxahc acid dihydrate and methanol under reflux for a few hours. When oxahc acid is treated with phosphoms pentachloride, oxalyl chloride, ClCOCOCl, is formed (6). 

The treatment of kasuganobiosamine with dimethyl ester of oxalic acid followed by concentrated aqueous ammonia gave two kinds of amides. The amide (11a) with pK a 7.6 was identical with the amide of kasugamycinic acid, which was prepared from kasugamycinic acid by treatment with anhydrous hydrogen chloride-methanol followed by concentrated aqueous ammonia. The other isomer (lib) with pK a 7.8, was named amide of isokasugamycinic acid. 

Assumed tto be similar to that of other esters (like dimethyl oxalate) in Table 1. Assumed to equal that of O,. ... 

Two of these forms suggest possible bimolecular rate-controlling steps. The kinetic data cannot be used to decide between them, although other tests might. For example, one could test whether dimethyl oxalate reacts with OCl , and the monomethyl ester with HOC1. 

In addition to the successful hydrogenation of the two fluorinated esters, this report describes the hydrogenation of dimethyl oxalate. Using the reactive anionic ruthenium catalyst, a 70% conversion to methyl glycolate could be achieved (TON = 235 TOF 12 h-1) (Scheme 15.19, Table 15.14, final entry). 

It is worthy of note that the melting points of the methyl esters are generally higher than those of the corresponding ethyl esters thus, to take a well-known example, dimethyl oxalate (melting point 54°) is a solid whilst the diethyl ester is a liquid. 

Reaction CII. Direct Action of an Acid on an Alcohol. (A. Ch., 58, 44.) —Few normal esters are prepared in this way—dimethyl oxalate being an exception in this case the water formed is probably prevented from including the back reaction by the presence of anhydrous oxalic acid—but the yield is only 40%. With acid esters, however, good yields can be obtained, since only partial esterification is required. 

Some esters, e.g. methyl formate, dimethyl oxalate, dimethyl succinate, dimethyl and diethyl tartrate, are appreciably soluble in water. These are usually easily hydrolysed by alkali. 

When cyanuric chloride reacts with DMF in t-butyl methyl ether it forms Gold s salt, [3-(dimethylamino)-2-azaprop-3-enylidene]dimethylammonium chloride, in almost quantitative yield. Methylate-promoted condensation of this salt with the methyl ester of sarcosine gives methyl 1-methylimidazole-5-carboxylate in up to 75% yield. The synthetic utility of this method is dependent on interception of the eliminated dimethylamine by addition of dimethyl oxalate and the bubbling of nitrogen through the solution [38]. 

Esters of dicarbonic acids are partially reduced with the elimination of alcohol in this fashion methyl glycolate is obtained from dimethyl oxalate... 

Dimethyl oxalate [29SS], diketene [2789], an acetoacetate [3489], 3-amino-crotonic ester [3489] and the Vilsmeicr reagent [2994] have also been demonstrated to be useful synthons. 

Japanese workers76 claim the superiority of a phosgene-triethylamine mixture (ratio 1 2) over other conventional dehydrating agents. Thus, they devised a novel synthesis of 4-methyl-5-alkoxyoxazole-2-carboxylic acid esters (17) by condensation of alkyl alaninate hydrochloride with diethyl or dimethyl oxalate followed by cyclization of the product (16). 

In the model reaction of the oxalate ester synthesis [10c], the efficiency and selectivity (oxalate vs. carbonate) of carbonylation of methanol with a stoichiometric amount of Pd(OAc)2 were examined as a function of added phosphine, base, and CO pressure. Without added phosphine, Pd(OAc)2 is very effective in forming dimethyl oxalate at room temperature. Use of PPhs slowed the formation of the oxalate, a reaction temperature of ca. 50°C being required. At room temperature Pd(COOMe)(OAc)(PPh3)2 was isolated. More basic phosphine, e.g. PBu3 almost completely inhibited the oxalate formation. The formation of oxalate decreased and that of dimethyl carbonate increased by the use of low CO pressure and some bases (e.g. EtsN). A reaction scheme accounting for these observations was presented (Scheme 8.7). 

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