Esters methyl, transesterification

Acrylic Esters. A procedure has been described for preparation of higher esters from methyl acrylate that illustrates the use of an acid catalyst together with the removal of one of the products by azeotropic distillation (112). Another procedure for the preparation of butyl acrylate, secondary alkyl acrylates, and hydroxyalkyl acrylates using -toluenesulfonic acid as a catalyst has been described (113). Alurninumisopropoxide catalyzes the reaction of amino alcohols with methyl acrylate and methyl methacrylate. A review of the synthesis of acryhc esters by transesterification is given in Reference 114 (see... 

In a similar sequence, reaction of ketoester 52 with 2-thienylmagnesium bromide gives a modest yield of the benzilic ester 53. Transesterification of this with aminoalcohol 51, prepared analogously to 45 by starting with methylamine, gives, after quaternization with methyl bromide, heteronium bromide... 

Bradshaw A soapmaking process in which glyceryl esters (fats) are first converted to their corresponding methyl esters by transesterification, and then hydrolyzed. Invented by G. B. Bradshaw. 

Methyl benzoate, [93-58-3], CTfCOOCI Ig, bp, 198—200°C at 101.3 kPa d [ , 1.094 n], 1.5205. Insoluble in water, this is a colorless, transparent liquid solidifying at about 15°C. Methyl benzoate is prepared by the direct esterification of benzoic acid and methanol. It is used in the fragrance industry and in the production of other benzoate esters (via transesterification). A technical-grade methyl benzoate is available as a by-product in the manufacture of dimethyl terephthalate [120-61 -6]. 

Figure 3. 3,5-Dinitrobenzoic acid esters from transesterification of some plasticizers Kieselgel G Eluent benzene,methyl acetate (150 1 pt. by vol.)...

Fig. 5. Comparison in yield of methyl esters between transesterification of triglycerides and methyl esterification of fatty acids by supercritical methanol treatment at various temperatures. , Transesterification at 270°C A, transesterification at 300°C , transesterification at 350°C O, methyl transesterification at 270°C A, methyl transesterification at 300°C , methyl transesterification at 350°C.

Figure 5 shows a comparison of the yields of methyl esters between transesterification of triglycerides (rapeseed oil) and methyl esterification of fatty acids by supercritical methanol at various temperatures. At 350°C, both reactions could produce very similar results. At 300°C, transesterification produced about 90% methyl esters at 12 min of treatment, whereas methyl esterification resulted in a complete conversion. When triglycerides were transesterified at 270°C, a plateau was reached at about 40 min of treatment with a yield of about 76%. However, much higher yield could be achieved by methyl esterification at 20 min of treatment. These results, therefore, indicate that the reaction rate in methyl esterification is higher than that in transesterification. 

To obtain substantial yields of surfactant hydrophobes, especially in the most useful C12— 14 range, the choice is restricted to coconut, palm and palm kernel oils. In the C16-18 range, the same oils are also used but animal (normally beef) tallow can be used. The use of animal fats raises some ethical issues but these are not commonly used to produce anionic surfactants. The oils may be converted to methyl esters by transesterification which allows easier distillation to remove heavy/light fractions and the esters are finally hydrogenated to fatty alcohols. Alternatively, the fat or oil can be hydrolysed to fatty acid prior to esterification... 

Shieh et al. (2003) indicated a biodiesel transesterification using soybean oil and methanol and commercial immobilized lipase from R. miehei (Lipozyme IM-77). The response surface analysis showed that the following variables were important reaction time, temperature, enzyme amount, molar ratio of methanol to soybean oil, and added water content on percentage weight conversion to soybean oil methyl ester by transesterification. The optimum yield based on ridge max analysis gave a 92.2% weight conversion. 

Resolution by transesterification. Using vinylic acetates to esterify allyl alcohols, propargyl alcohols, 2-phenylthiocycloalkanols, a-hydroxy esters," methyl 5-hydroxy-2-hexenoates, and 2-substituted 1,3-propanediols, the enantioselective esterification provides a means of separation of optical isomers. Vinyl carbonates are also resolved by lipase-mediated enantioselective conversion to benzyl carbonates. Other esters that have also been used in the kinetic resolution include 2,2,2-tri-fluoroethyl propionate. There is a report on a double enantioselective transesterification" of racemic trifluoroethyl esters and cyclic meso-diols by lipase catalysis. 

Cambou and Klibanov have used transesterifications catalyzed by PLE and yeast lipase to resolve a variety of alcohols with great effectiveness. Their novel approach employed a biphaslc system of aqueous enzyme solution absorbed in a porous solid phase placed in a mixture of "matrix ester" (methyl propionate or tributyrin) and racemic alcohol (Scheme I). 

Fig. 5.5 3 Schematic representation of Crieco s reaction in a droplet microreactor. Photographs of droplet displacement during the Crieco s reaction are shown on the right ofthis figure. The droplet containing 1 was allowed to converge towards the droplet containing 2 and TFA. After mixing, the obtained droplet was directed towards the droplet containing 3, thus leading quantitatively to adducts 4 which could be cleaved to the corresponding methyl esters by transesterification.

Due to the instability of the feri-butyl ester, and the resistance of the ethyl ester to transesterification, installation of the methyl ester prior to glycosylation was clearly required. Conversion of tert-butyl enol ester 51b to the methyl ester 51a was achieved in 78% yield over two steps, with hydrolysis of the tert-bvAy ester using trifluoroacetic acid at 0 °C, followed by methylation with trimethylsilyl diazomethane (Scheme 21). Gratrfyingly, when methyl enol ester 51a was... 

Fatty acid methyl ester of soybean oil is an excellent biobased solvent, and is produced by transesterification of soy oil with methanol resulting in a mixture of soy fatty acid methyl esters. Methyl soyate-based solvents have been introduced in the market in the recent years. They match or even surpass the performance of some conventional solvents while being cost competitive. Methyl soyate exhibits superior solvency, is readily biodegradable, and has a low toxicity when compared to other common chemicals. 

A monoester of sucrose prepared from a pure fatty acid methyl ester by transesterification is a mixture of positional isomers (15-20). Each isomer could behave differently in bread. Data in Figure 4 show a dramatic example of how positional isomers function differently in breadmaking (2) ). L-Ascorbyl 6-palmi-tate is an excellent dough strengthener, which showed a +92 cc volume response above a no-shortening control loaf (905 cc). On the other hand, L ascorbyl 2-palmi-tate decreased loaf volume 165 cc below the control. 

With lipid samples from animal tissues, it is sometimes necessary to purify methyl esters after transesterification has been carried out in order to eliminate cholesterol, which can be troublesome when the esters are subjected to gas chromatography. This can be accomplished by adsorption chromatography with a short column (approx. 2 cm) of silica gel or Florisir in a Pasteur pipette plugged with glass wool, and eluted with hexane-diethyl ether (95 5, v/v 10 mL). The cholesterol and other polar impurities remain on the column. Commercial pre-packed columns (Bond Elut or Sep-Pak ) can be used in a similar way. Methyl esters can also be purified by preparative TLC, with hexane-diethyl ether (9 1, v/v) as the mobile phase. 

Esterification.—iVAWW -Tetramethylchloroformamidinium chloride, which is readily prepared from iVAWW -tetramethylurea and oxalyl chloride, is an efficient reagent for the esterification of carboxylic acids with alcohols yields of between 66 and 97% are obtained, and the method has also been applied to macrolide synthesis. A modified one-pot procedure for the esterification of carboxylic acids, using phenyl dichlorophosphate-dimethylformamide complex, has appeared. A simple method of activation of carboxylic acids, using methanesulphonyl chloride and triethylamine followed by addition of the alcohol and 4-dimethylaminopyridine, leads to esters in 57— 96% yield for thirteen examples. 0-Methylcaprolactim reacts with carboxylic acids to give methyl esters in 73—91 % yield for seven examples and 2-iodoethyl esters are prepared from acyl chlorides, ethylene oxide, and sodium iodide. Transesterification, catalysed by titanium(iv) alkoxides, provides an effective method for synthesis of esters. Diethyl trichloromethylphosphonate reacts with carboxylic acids to give ethyl esters via transesterification, in 52 to 98 % yield. ... 

Nishilddo et al reported two methods for the synthesis of a variety of carboxylic esters using Sn[N(S02C8Fi7)2]4 as a Lewis acid catalyst in FBS (Scheme 10.48) [73]. They showed that the Sn(IV) complex effectively functions for the preparation of carboxylic esters by transesterification from methyl esters with the corresponding alcohols, whereas Hf[N(S02C8Fi7)2]4 is more effective than Sn[N(S02C8Fi7)2]4 in the direct esterification of free carlx)xylic acids. 

The latter was converted into corresponding hydroxy ester through transesterification with NaOMe and further converted into iodide 253 (Scheme 29.32). A chemoselec-tive copper-catalyzed alkylation of iodide 253 was performed using /-PrMgCl and catalytic amounts of LiaCuCLj in the presence of A -methyl-2-pyrrolidinone without affecting the ester moiety, and further reduction with DIBAL-H at -90°C furnished aldehyde 254 in good overall yield. Aldehyde 254 was finally converted into (-l-)-vittatalactone 255 via reaction sequence boron aldol... 

Some esters of substituted alcohols have been synthesized by transesterification. Treatment of 4-methyl-5-thiazolecarboxylic acid (14) with 3-chloroethyldiethylamine in acetone in the presence of anhydrous potassium carbonate gives the desired ester (15) in good vield (60%) (Scheme 10) (163). 

Esters. Neopentyl glycol diesters are usually Hquids or low melting soflds. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Manufacture. Cyanoacetic acid and cyanoacetates are iadustrially produced by the same route as the malonates starting from a sodium chloroacetate solution via a sodium cyanoacetate solution. Cyanoacetic acid is obtained by acidification of the sodium cyanoacetate solution followed by organic solvent extraction and evaporation. Cyanoacetates are obtained by acidification of the sodium cyanoacetate solution and subsequent esterification with the water formed being distilled off. Other processes reported ia the Hterature iavolve the oxidation of partially oxidized propionittile [107-12-0] (59). Higher esters of cyanoacetic acid are usually made through transesterification of methyl cyanoacetate ia the presence of alumiaiumisopropoxide [555-31-7] as a catalyst (60). 

Transesterification of methyl methacrylate with the appropriate alcohol is often the preferred method of preparing higher alkyl and functional methacrylates. The reaction is driven to completion by the use of excess methyl methacrylate and by removal of the methyl methacrylate—methanol a2eotrope. A variety of catalysts have been used, including acids and bases and transition-metal compounds such as dialkjitin oxides (57), titanium(IV) alkoxides (58), and zirconium acetoacetate (59). The use of the transition-metal catalysts allows reaction under nearly neutral conditions and is therefore more tolerant of sensitive functionality in the ester alcohol moiety. In addition, transition-metal catalysts often exhibit higher selectivities than acidic catalysts, particularly with respect to by-product ether formation. 

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