Oxalic ester chlorides

Acid moieties include formic acid itself, formates and orthoesters, formamide, DMF dimethyl acetal and ethyl diethoxyacetate, acids, acid chlorides and anhydrides, the last including a rare [3,4-oxalate esters, 2-acyl or 2-ethoxycar-bonyl derivatives e.g. 180) are formed. 

Two different approaches have been used to determine phenols without derivatization. In the first, the corresponding oxalate esters were synthesized in the traditional way (i.e., using oxalyl chloride and triethylamine) [111, 112]. Pen-tachlorophenol, 1-naphthol, bromofenoxim, bromoxynil, and /t-cyanophenol were treated this way, after which the POCL resulting from their reaction was measured in a static system. The second approach exploits the oxidation reaction between imidazole and hydroxyl compounds at an alkaline pH, where hydrogen peroxide is formed [113]. Polyphenols, e.g., pyrogallol, pyrocatechol, and dopa-... 

By means of oxidation of the initially formed 3,4-disubstituted 5-bromo-2-bromomethylpyrrole, bromine converted 3,4-disubstituted-2-methylpyr-roles and their 5-carboxylic acids into 5-bromo-5 -bromomethyl-2,2 -dipyrrolylmethanes. Similar reaction with sulfuryl chloride led to the analogous chloro species (77MI2). Whereas treatment of 2-aroyl-l,3-dimethylpyrrole-5-acetic esters with NBS brominated the vacant ring carbon, the related oxalate ester gave the 3-bromomethyl derivative (80JMC98). 

Thus, as shown by the example in Scheme 42, sequential treatment of the trime-thylsilyl ethers of a variety of tertiary alcohols with oxalyl chloride and the parent thionohydroxamic acid furnishes mixed oxalate esters which undergo reductive deoxygenation on subsequent reaction with a tertiary thiol in refluxing benzene [46]. The selectivity of this method for tertiary alcohols arises as a consequence of the relativity slow rates of decarboxylation of primary and secondary alkoxycarbonyl radicals. 

As anticipated, by analogy with the chemistry of Barton esters, the same mixed oxalate esters can be used to prepare tertiary alkyl chlorides, simply by refluxing in carbon tetrachloride [47], and also for the creation of quaternary carbon centers through selection of either a Michael acceptor [46] or 2-(carboethoxy) allyl tert-butyl sulfide [46] as the radicophile. 

The methyl ester chloride of oxalic acid Potassium ethyl oxalate (50 g) is covered with dry ether, and SOCl2 (80 g) is dropped in with ice-cooling. The cooling bath is then removed and the mixture left at room temperature until reaction starts, then finally heated for 15 h under reflux on a water-bath. The precipitated KC1 is filtered off and washed with ether, and the liquids are fractionated. The fraction distilling at 125-138° consists mainly of the ester chloride and can be used directly for Friedel-Crafts reactions. Yields are up to 70%. A further amount of the ester chloride can be obtained by re-treating the foreruns with SOCl2. 

Ethyl (cMoroformyl)formate (oxalic acid monoethyl ester chloride), b.p. 130-132° (cf. page 247), can be obtained by way of ethyl dichlorodiethoxyacetate which splits off ethyl chloride, sometimes spontaneously and always in the presence of a little metallic plat-... 

To obtain good yields of the ester chloride it is important to use an excess of the oxalic ester so as to avoid conversion of both C=0 groups into CC12 and the reactions that follow therefrom also the temperature must be kept as low as possible and the POCl3 formed must be separated before the dichloro ethoxy ester can decompose 1139... 

A mixture of PC15 (2 kg powdered immediately before use) and diethyl oxalate (1.8 kg) is heated at 95-100° for 4 days with exclusion of moisture. The reaction time can be shortened by shaking. POCl3 (b.p. 27°/18 mm) is then distilled off in a vacuum, and the residue is heated with palladium black (0.5 g) at 95-98°, until no more ethyl chloride is split off (2 h), and it is worked up by vacuum-distillation. The ester chloride (1150 g) has b.p. 39.7°/18 mm. 

Figure 4 L-(+)-ascorbic acid 244, L-(+)-tartaric acid ethyl ester 245, and (S)-phenylethyl amide of oxalic acid chloride 246.

Oxalic ester synthesis 16, 812 Oxalyl chloride, reaction with amines 16, 502 Oxamic acid derivatives... 

One route to o-nitrobenzyl ketones is by acylation of carbon nucleophiles by o-nitrophenylacetyl chloride. This reaction has been applied to such nucleophiles as diethyl malonatc[l], methyl acetoacetate[2], Meldrum s acid[3] and enamines[4]. The procedure given below for ethyl indole-2-acetate is a good example of this methodology. Acylation of u-nitrobenzyl anions, as illustrated by the reaction with diethyl oxalate in the classic Reissert procedure for preparing indolc-2-carboxylate esters[5], is another route to o-nitrobenzyl ketones. The o-nitrophenyl enamines generated in the first step of the Leimgruber-Batcho synthesis (see Section 2.1) are also potential substrates for C-acylation[6,7], Deformylation and reduction leads to 2-sub-stituted indoles. 

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). 

Oxidative Garbonylation. Carbon monoxide is rapidly oxidized to carbon dioxide however, under proper conditions, carbon monoxide and oxygen react with organic molecules to form carboxyUc acids or esters. With olefins, unsaturated carboxyUc acids are produced, whereas alcohols yield esters of carbonic or oxalic acid. The formation of acryUc and methacrylic acid is carried out in the Hquid phase at 10 MPa (100 atm) and 110°C using palladium chloride or rhenium chloride catalysts (eq. 19) (64,65). 

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