Transesterification of methyl esters

Transesterifications of methyl esters with high boiling alcohols, as shown in Eq. (47), occur readily in microwave ovens because of displacement of the evaporation of the polar volatile methanol (Tab. 5.21) [11],... 

Fatty acid esters of sugars are also very important biodegradable and biocompatible surfactants that are prepared either by transesterification of methyl ester with sugar on basic catalysts or by esterification of fatty acids with sugar on acidic catalysts. Liquid acids and bases have been replaced by enzymatic catalysis with lipase, giving a higher yield of monoester [43, 44], but solid catalysts have not been used extensively so far. 

TRANSESTERIFICATION OF METHYL ESTERS OF AROMATIC AND o,p-UNSATURATED ACIDS WITH BULKY ALCOHOLS (-)-MENTHYL CINNAMATE AND (-)-MENTHYL NICOTINATE... 

TRANSESTERIFICATION OF METHYL ESTERS OF AROMATIC AND a,B-UNSATURATED ACIDS WITH BULKY ALCOHOLS (-)-NENTHYL CINNAHATE AND (-)-MENTHYL NICOTINATE (2-Propeno1c acid, 3-pheity1, 5-BethyI-2-(l- ethyIethyl)cyclohevl ester, [lR-(la,2B.Sa)-) and... 

Transesterification of Methyl Esters of Aromatic and a,8-Unsaturated Acids with Bulky Alcohols (-)-Menthyl Cinnamate and (-) Menthyl Nicotinate... 

Transesterification. Zwitterionic adduct of 4-pyrrolidinopyridine and an electron-deficient aryl isothiocyanate (e.g., p-nitrophenyl and 3,5-bis(trifluoromethyl)phenyl isothiocyanates) catalyzes transesterification of methyl esters, requiring only stoichiometric quantity of the alcohol. The reaction is best performed by azeotropic refluxing, with assistance of 5A-molecular sieves to absorb the liberated MeOH. 

Transesterification of methyl esters to 2-(trimethylsilyl)ethyl esters under mild and neutral conditions takes place in the presence of titanium tetraisopropoxide (eqs 6-8). Deprotection of the 2-(trimethylsilyl)ethyl ester in the presence of an O-TBDMS protected secondary hydroxyl group has been achieved (eq Q). An alternative method for the transesterification uses l,8-diazabicyclo[5.4.0]undec-7-ene/lithium bromide and 2-(trimethylsilyl) ethanol. ... 

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. 

Isoamyl saUcylate is perhaps the most important ester of saUcyhc acid for perfumery purposes. Generally, it is manufactured by the transesterification of methyl saUcylate. It has a characteristic flowery aroma and is useful in soap fragrances. The May 1996 price was 5.30/kg (18). Other saUcylates of commercial interest as flavor and fragrance agents include isopropyl, isobutyl, phenethyl [87-22-9] and 2-ethyIhexyl saUcylates. 

MetlylEsters. The addition product of two moles of TYZOR TPT and one mole of ethylene glycol, GLY—TI, can be used as a transesterification catalyst for the preparation of methyl esters. The low solubility of tetramethyl titanate has prevented the use of them as a catalyst for methyl ester preparation (488). 

For the delicate transesterification of a p-Lactam intermediate (for carbacephalosphorin skeleton), where originally hydrolysis of methyl ester was done homogeneously and then formation of the benzyl (or substituted benzyl) ester was done separately, Doecke et al. (1991) have devised a mild and efficient methodology using PTC. A dual use of a PT catalyst, Bu4NBr, in one pot was made in a CH2CI2 - H2O system. In the first step 5N NaOH was used, then the pH was adjusted to 7.2 to 7.8 and subsequently benzyl (or substituted benzyl) bromide was added. 

The rates of transesterification of triglycerides to methyl esters, efficiently catalyzed by boron carbide (B4C), were, on the other hand, faster under microwave conditions, probably because of superheating of the boron carbide catalyst, which is known to be a very strong absorber of microwaves [40], Scheme 10.3. Yields of methyl ester of up to 98% were achieved. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

The homogeneous acid-catalyzed transesterification process does not enjoy the same popularity in commercial application as its counterpart, the base-catalyzed process, one of the main reasons being that it is about 4000 times slower, due to the different mechanism [10]. Thus, in the reaction sequence triglyceride is converted stepwise to diglyceride, monoglyceride and finally glycerol with formation of one molecule of methyl ester at each step (Scheme 10.1). 

The esters of salicylic acid account for an increasing fraction of the salicylic acid produced, about 15% in the 1990s. Typically, the esters are commercially produced by esterification of salicylic acid with the appropriate alcohol using a strong mineral acid such as sulfuric as a catalyst. To complete the esterification, the excess alcohol and water are distilled away and recovered. The cmde product is further purified, generally by distillation. For the manufacture of higher esters of salicylic acid, transesterification of methyl salicylate with the appropriate alcohol is the usual route of choice. However, another reaction method uses sodium salicylate and the corresponding alkyl halide to form the desired ester. 

Oxotitanium acetylacetonate, TiO(acac)2, was found to be a very efficient catalyst for the transesterification of methyl (and ethyl) esters. The mechanism probably involves initial formation from reactant, ROH, of TiO(OR)2(acac)2, which upon complexation with the methyl ester, R CC Me, progresses from (13) to a tetrahedral intermediate containing a TiO bond (14), which rearranges to yield the product, R C02R, and TiO(OR)OMe)(acac)2 (Scheme 4).7... 

Fatty acid methyl esters (FAMEs) show large potential applications as diesel substitutes, also known as biodiesel fuel. Biodiesel fuel as renewable energy is an alternative that can reduce energy dependence on petroleum as well as air pollution. Several processes for the production of biodiesel fuel have been developed. Transesterification processes under alkali catalysis with short-chain alcohols give high yields of methyl esters in short reaction times. We investigated transesterification of rapeseed oil to produce the FAMEs. Experimental reaction conditions were molar ratio of oil to alcohol, concentration of catalyst, type of catalyst, reaction time, and temperature. The conversion ratio of rapeseed oil was enhanced by the alcohohoil mixing ratio and the reaction temperature. 

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. 

The molar ratio of methanol to fatty acids is also an important parameter that controls the reaction. Figure 6 shows the obtained yields of methyl esters from oleic acid, a model of fatty acids, treated at various molar ratios of methanol to fatty acid. Interestingly, compared with the transesterification reaction shownby the dashed line (13), methyl esterification proceeded more at the lower molar ratio, and it is apparent that at a molar ratio of 3, oleic acid was mostly converted to its methyl ester. This result is important in designing the production process, since a reaction with a low molar ratio requires less energy for the process. 

One-step treatment refers to a direct supercritical methanol method of rapeseed oil that involves mainly transesterification, while two-step treatment involves hydrolysis and subsequent methyl esterification. Figure 7 clearly demonstrates that at the same reaction time of 40 min, a significantly higher yield of methyl esters could be produced when the rapeseed oil was first treated with water, followed by methyl esterification of the hydrolyzed products. 

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