Methanol transesterification

As shown In Fig. 2, tensile strength of polymer A decreases more rapidly Initially In methanol than In water even though aging In methanol Is conducted at 60 C (20 C lower than In water). The rate of property loss Is observed not to Increase with time. This Is expected since the degradation reaction In methanol (transesterification) Is not autocatalytic. The reduction of tensile elongation In the two media shows a similar behavior. 

As for dihydro-1,3-oxazines, perhydro-1,3-oxazine methiodides (125) are ring-opened by reaction with sodium borohydride. The products obtained depend upon the conditions used thus, in anhydrous tetrahydrofuran tertiary amines and their borane derivatives are formed, but in ethanol or methanol transesterification occurs to give the corresponding ethyl or methyl ethers (Scheme 32) <90H(31)2079>. 

Demirbas, A. 2009a. Biodiesel from Waste Cooking Oil via Base-Catalytic and Supercritical Methanol Transesterification. Energy Conversion and Management 50 (4) 923-927. 

Samniang, A., C. Tipachan, and S. Kajomcheappun-Ngam. 2014. Comparison of Biodiesel Production from Crude Jatropha Oil and Krating Oil by Supercritical Methanol Transesterification. Renewable Energy 68 351-355. 

Puchalsky, C. B., Boron trifluoride-methanol transesterification as a means of characterizing alcohol sulfate detergents, J. Am. Oil Chem. Soc., 1970,42,803-804. 

Most large-scale industrial methacrylate processes are designed to produce methyl methacrylate or methacryhc acid. In some instances, simple alkyl alcohols, eg, ethanol, butanol, and isobutyl alcohol, maybe substituted for methanol to yield the higher alkyl methacrylates. In practice, these higher alkyl methacrylates are usually prepared from methacryhc acid by direct esterification or transesterification of methyl methacrylate with the desired alcohol. 

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. 

An analogue of the transesterification process has also been demonstrated, in which the diacetate of BPA is transesterified with dimethyl carbonate, producing polycarbonate and methyl acetate (33). Removal of the methyl acetate from the equihbrium drives the reaction to completion. Methanol carbonylation, transesterification using phenol to diphenyl carbonate, and polymerization using BPA is commercially viable. The GE plant is the first to produce polycarbonate via a solventiess and phosgene-free process. 

On the basis of bulk production (10), poly(ethylene terephthalate) manufacture is the most important ester producing process. This polymer is produced by either the direct esterification of terephthaHc acid and ethylene glycol, or by the transesterification of dimethyl terephthalate with ethylene glycol. In 1990, poly(ethylene terephthalate) manufacture exceeded 3.47 x 10 t/yr (see Polyesters). Dimethyl terephthalate is produced by the direct esterification of terephthaHc acid and methanol. 

Applications. Transesterifications via alcoholysis play a significant role in industry as well as in laboratory and in analytical chemistry. The reaction can be used to reduce the boiling point of esters by exchanging a long-chain alcohol group with a short one, eg, methanol, in the analysis of fats, oils, and waxes. For more details see References 7 and 68. A few examples are given below. 

This process differs from the direct esterification and the transesterification routes in that only ethylene glycol is released. In the former two routes, water or methanol are coproduced and the excess glycol released. 

PET methanolysis involves the reaction of PET with methanol at high temperatures and pressures in the presence of transesterification catalysts such as magnesium acetate, cobalt acetate, and lead dioxide. 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

The transesterification of fats and fatty oils by methanol into fatty acid methyl esters proceeds at 50-70°C without pressure. The deacidified fat is stirred for a short period with an excess of methanol and 0.1-0.5% caustic alkali as catalyst. On standing the reaction mixture separates forming a bottom layer of glycerin and a top layer of fatty acid esters. 

A porphinatoaluminum alkoxide is reported to be a superior initiator of c-caprolactone polymerization (44,45). A living polymer with a narrow molecular weight distribution (M /Mjj = 1.08) is ob-tmned under conditions of high conversion, in part because steric hindrance at the catalyst site reduces intra- and intermolecular transesterification. Treatment with alcohols does not quench the catalytic activity although methanol serves as a coinitiator in the presence of the aluminum species. The immortal nature of the system has been demonstrated by preparation of an AB block copolymer with ethylene oxide. The order of reactivity is e-lactone > p-lactone. 

In order to convert the raw oils into useful material, transesterification technology is used. The oil is reacted with a low molecular weight alcohol, commonly methanol, in the presence of a catalyst to form the fatty acid ester and glycerol (Scheme 6.1). The ester is subsequently separated from the glycerol and used as biodiesel, the glycerol being used as a raw material for fine chemicals production. Although the chemistry is simple, in order to make biodiesel commercially viable the process must be... 

The transesterification reactions were conducted in a sealed 250 ml autoclave equipped with a stirrer. The molar ratio of methanol to oil was 12 1, reaction temperature was 200 C-230°C, and the ratio of catalyst to oil was about 2 wt%. Samples were taken out from the reaction mixture and biodiesel portions were separated by centrifuge. 

Synthesis of dimethyl carbonate by transesterification of ethylene carbonate and methanol using quaternary ammonium salt catalysts... 

In our previous works[8,9] on the synthesis of various 5-membered cyclic carbonate, quaternary ammonium salts such as tetrabutylammonium halides showed excellent catalytic activities in relatively mild reaction conditions, under atmospheric pressure and below 140 U. hi this work, several kinds of quaternary ammonium salts have been used for the transesterification reactions of the ethylaie carbonate with methanol to DMC and ethylene glycol. 

The transesterification reaction was carried out in a 50 mL stainless steel autoclave equipped with a magnetic stirrer. For each typical reaction, quaternary ammonium salt (2 mmol), propylene carbonate (25 mmol) and excess methanol (200 mmol) were charged into the reactor, and the CO2 was introduced at room temperature to a preset pressure. The reaction was started by stirring when the desired tranperature and pressure were attained The reachon was performed in a batch operation... 

In order to imderstand the effects of the cation structure in the transesterification between methanol and EC, quaternary ammonium chloride catalysts of different alkyl cations such as TPAC, TBAC, THAC, TOAC, and TDodAC were used at 140 C. Table 1 shows EC conversions after 1 h... 

In the synthesis of DMC fiom the transesterification of EC and methanol, quaternary ammonium salt catalysts showed good catalytic activity. The main byproduct was ethylene glycol. The quaternary salt with the cation of bulkier alkyl chain laigth and witii more nucleophilic anion showed better reactivity. Hi temperature and large amount of catalyst increased the conversion of EC. The EC conversion and DMC selectivity increased as the pressure of CO2 increased from 250 to 350 psig. 

One of the most important characteristics of IL is its wide temperature range for the liquid phase with no vapor pressure, so next we tested the lipase-catalyzed reaction under reduced pressure. It is known that usual methyl esters are not suitable for lipase-catalyzed transesterification as acyl donors because reverse reaction with produced methanol takes place. However, we can avoid such difficulty when the reaction is carried out under reduced pressure even if methyl esters are used as the acyl donor, because the produced methanol is removed immediately from the reaction mixture and thus the reaction equilibrium goes through to produce the desired product. To realize this idea, proper choice of the acyl donor ester was very important. The desired reaction was accomplished using methyl phenylth-ioacetate as acyl donor. Various methyl esters can also be used as acyl donor for these reactions methyl nonanoate was also recommended and efficient optical resolution was accomplished. Using our system, we demonstrated the completely recyclable use of lipase. The transesterification took place smoothly under reduced pressure at 10 Torr at 40°C when 0.5 equivalent of methyl phenylthioacetate was used as acyl donor, and we were able to obtain this compound in optically pure form. Five repetitions of this process showed no drop in the reaction rate (Fig. 4). Recently Kato reported nice additional examples of lipase-catalyzed reaction based on the same idea that CAL-B-catalyzed esterification or amidation of carboxylic acid was accomplished under reduced pressure conditions. ... 

We first examined the lipase-catalyzed resolution of azirine-2-methanol I, which we expected to have a versatile synthetic utility. As expected for primary alcohols, the enantioselectivity obtained in the transesterification with lipase PS in ether was low (E = 17 at best) at room temperature despite considerable efforts such as screening of lipases, solvents, additives, and acylating agents. 

One of the most interesting side reactions taking place during the enantioselective hydrogenation is the transesterification of the substrate or the reaction product. If the enantioselective hydrogenation of ethyl pyruvate was performed in methanol as a solvent the formation of methyl pyruvate and methyl lactate was observed. CD appeared to be an effective catalyst for the above transesterification reaction. 

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