Dimethyl carbonate alkylation

CycHc carbonates are made by treating 1,2-diols with dialkyl carbonates using an alkyl ammonium and tertiary amine catalyst. The combination of propylene glycol and dimethyl carbonate has been reported to result in a 98% yield of propylene carbonate (21). 

As seen in Figure 1, the organo sulfur compounds are methylated at the boiling point (90°C) of dimethyl carbonate, whereas methylation (or alkylation with other alkyl groups) of other functional groups requites higher temperatures. This has resulted in the selective methylation of sulfhydryl groups of compounds that contain other substituents that can be alkylated. The other substituents can then be alkylated at elevated temperatures (63). 

The reaction of tertiary alkylthioenyne alcohols (205) with carbon dioxide [70-73 atm, 70-75°C, Cu(I) salts, triethylamine] leads to 4,4-dimethyl-5-(alkyl-thioethenylmethylene)-l,3-dioxolan-2-ones (206) (79KGS1617 79ZOR1319). 

In contrast with the reactions involving sulphide or hydrogen sulphide anions, aryl alkyl thioethers and unsymmetrical dialkyl thioethers (Table 4.3) are obtained conveniently by the analogous nucleophilic substitution reactions between haloalkanes and aryl or alkylthiols under mildly basic conditions in the presence of a quaternary ammonium salt [9-15] or polymer-supported quaternary ammonium salt [16]. Dimethyl carbonate is a very effective agent in the formation of methyl thioethers (4.1.4.B) [17]. 

Comparison of the configuration of the stannane with the prodncts of reaction reveals that primary alkyl halides that are not benzyhc or a to a carbonyl react with inversion at the lithium-bearing carbon atom. In the piperidine series, the best data are for the 3-phenylpropyl compound, which was shown to be >99 1 er. In the pyrrolidine series, the er of the analogous compound indicates 21-22% retention and 78-79% inversion of configuration. Activated alkyl halides such as benzyl bromide and teri-butyl bromoacetate afford racemic adducts. In both the pyrrolidine and piperidine series, most carbonyl electrophiles (i.e. carbon dioxide, dimethyl carbonate, methyl chloroformate, pivaloyl chloride, cyclohexanone, acetone and benzaldehyde) react with virtually complete retention of configuration at the lithium-bearing carbon atom. The only exceptions are benzophenone, which affords racemic adduct, and pivaloyl chloride, which shows some inversion. The inversion observed with pivaloyl chloride may be due to partial racemization of the ketone product during work-up. 

Electrolyte solutions of various aprotic organic solvents are used in primary lithium batteries. Among the organic solvents are alkyl carbonates [PC (er = 64.4-), ethylene carbonate (EC, 89.640°c)> dimethyl carbonate (DMC, 3.1), diethyl carbonate (DEC, 2.8)], ethers [DME (7.2), tetrahydrofuran (THF, 7.4), 2-Me-THF (6.2),... 

Dimethyl carbonate is an interesting material which can be used instead of toxic dimethyl sulfate as a multipurpose alkylating reagent.438-578 Its synthesis can be performed in one step from cheap methanol, CO and oxygen materials in the presence of copper salts (e.g. copper(ll) methoxychloride or CuCl/py) at ca. 100 °C and 15-70 atm (equation 290).578,62S This reaction is thought to proceed in two steps 578 (a) formation of copper(II) methoxychloride from the reaction of copper(I) chloride, 02 and methanol (equation 291) and (b) reduction of copper(II) methoxychloride with CO to form dimethyl carbonate and regenerate copper(I) chloride (equation 292).626... 

Aresta and Quaranta studied the reactivity of alkylammonium N-alkylcarbamates (RNH3)02CNHR towards a different acylating substrate, such as dimethyl carbonate (DMC) [62a, b]. Carbamate salts (RNH3)02CNHR (R = benzyl, allyl, cyclohexyl), prepared in situ from aliphatic primary amines and C02, reacted with DMC to afford N-alkyl methylcarbamates (Equation 6.6). The reaction requires mild conditions (343-363 K 0.1 MPa C02 pressure) and can be carried out in DMC used as solvent and reagent. At 363 K, carbamate esters were obtained in satisfactory yield (45-92%) with high selectivity, as side products such as ureas, N,N-dialkylcarbamate esters, and alkylated amines were formed in very small amounts. 

Lipid-Protein-Carbohydrate Interactions. Evidence for such complex interaction was recently reported by Huang et al (36) who observed that the addition of corn lipids to zein and corn carbohydrates enhanced the formation of alkylpyrazines, indicating that lipid-derived free radicals may accelerate the rate of Maillard reactions. Two of the alkylpyrazines, identified in such mixtures after heating for 30 minutes at 180°C, have 5-carbon alkyl substitution at the pyrazine ring and could only be explained by interaction of lipid or lipid decomposition products. These authors suggested that condensation of amino ketones, formed by protein-carbohydrate interaction, may yield 3,6-dihydropyrazine which would in turn react with pentanal, a lipid oxidation product, to form 2,5-dimethyl-3-pentylpyrazine. 

Cesium-exchanged zeolite X was used as a solid base catalyst in the Knoevenagel condensation of benzaldehyde or benzyl acetone with ethyl cyanoacetate [121]. The latter reaction is a key step in the synthesis of the fragrance molecule, citronitrile (see Fig. 2.37). However, reactivities were substantially lower than those observed with the more strongly basic hydrotalcite (see earlier). Similarly, Na-Y and Na-Beta catalyzed a variety of Michael additions [122] and K-Y and Cs-X were effective catalysts for the methylation of aniline and phenylaceto-nitrile with dimethyl carbonate or methanol, respectively (Fig. 2.37) [123]. These procedures constitute interesting green alternatives to classical alkylations using methyl halides or dimethyl sulfate in the presence of stoichiometric quantities of conventional bases such as caustic soda. 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

The dimethyl carbonate decomposition has been shown to proceed heterogeneously at relatively high temperatures on a quartz surface - By contrast, alkyl and aryl carbonates with j8-carbon hydrogens, decompose smoothly homogeneously and unimolecularly in surface conditioned reactors at appreciably lower temperatures T > 600 °K) to give olefin, alcohol, and carbon dioxide. Gas phase kinetic results for some 1-arylethyl methyl carbonates S for methyl ethyl carbonate, and for diethyl carbonate are shown in Table 14. Some gas phase relative rate results for substituted 1- and 2-arylethyl carbonates have also been determined (Table 15). 

The Williamson reaction, discovered in 1850, is still the best general method for the preparation of unsymmetrical or symmetrical ethers.The reaction can also be carried out with aromatic R, although C-alkylation is sometimes a side reaction (see p. 515). The normal method involves treatment of the halide with alkoxide or aroxide ion prepared from an alcohol or phenol, although methylation using dimethyl carbonate has been reported. It is also possible to mix the halide and alcohol or phenol directly with CS2CO3 in acetonitrile, or with solid KOH in Me2SO. The reaction can also be carried out in a dry medium,on zeolite-or neat or in solvents using microwave irradiation. Williamson ether synthesis in ionic liquids has also been reported. The reaction is not successful for tertiary R (because of elimination), and low yields are often obtained with secondary R. Mono-ethers can be formed from diols and alkyl halides. Many other... 

The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on CrP04 and CrP04-AlP04 catalysts gives a mixture of O- and C-alkylation products, the latter being predominantly orf/zo-isomers (equation 19) . 

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