Transesterification alcohol used

Commercial Hydrolysis Process. The process of converting poly(vinyl acetate) to poly(vinyl alcohol) on a commercial scale is compHcated on account of the significant physical changes that accompany the conversion. The viscosity of the poly(vinyl acetate) solution increases rapidly as the conversion proceeds, because the resulting poly(vinyl alcohol) is insoluble in the most common solvents used for the polymeri2ation of vinyl acetate. The outcome is the formation of a gel swollen with the resulting acetic acid ester and the alcohol used to effect the transesterification. 

In lipase-catalyzed transesterifications, frequent use of enol esters as acyl agents has been seen [1, 5], since the leaving unsaturated alcohol irreversibly tautomerizes to an aldehyde or a ketone, leading to the desired product in high yields. The polymerization of divinyl adipate and 1,4-butanediol proceeded in the presence of lipase PF at 45 °C [39]. Under similar reaction conditions, adipic acid and diethyl adipate did not afford the polymeric materials, indicating the high polymerizability of bis(enol ester) toward lipase catalyst. 

There are basically two approaches to the synthesis of enantiomerically pure alcohols (i) kinetic resolution of the racemic alcohol using a hydrolase (lipase, esterase or protease) or (ii) reduction mediated by a ketoreductase (KRED). Both of these processes can be performed as a cascade process. The first approach can be performed as a dynamic kinetic resolution (DKR) by conducting an enzymatic transesterification in the presence of a redox metal [e.g. a Ru(ll) complex] to catalyze in situ racemization of the unreacted alcohol isomer [11] (Scheme 6.1). We shall not discuss this type of process in any detail here since it forms the subject of Chapter 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. 

Naturally occurring fatty alcohols used in the fragrance industry are produced principally by reduction of the methyl esters of the corresponding carboxylic acids, which are obtained by transesterification of natural fats and oils with methanol. Industrial reduction processes include catalytic hydrogenation in the presence of copper-chromium oxide catalysts (Adkins catalysts) and reduction with sodium (Bouveault—Blanc reduction). Unsaturated alcohols can also be prepared by the latter method. Numerous alcohols used in flavor compositions are, meantime, produced by biotechnological processes [11]. Alcohols are starting materials for aldehydes and esters. 

As with inorganic solid catalysts, the most extensively studied system was acetic acid—ethanol [428,432,434,444—448]. Other alcohols used in kinetic studies were methanol [430,449,450], 2-propanol [438], 1-bu-tanol [429,431,433,451—458], allyl alcohol [459], 1-pentanol [434] and ethyleneglycol [460] besides acetic acid, the reactions of formic [450], propionic [443,461], salicylic [430,449], benzoic [453—457] and oleic acids [430,451—453] and of phthalic anhydride [462] have been reported. Investigation of a greater variety of reactants is reported in only one paper [463] six alcohols (C4, Cs and C8) and five acids (mainly dicarboxylic were studied. Transesterification kinetic studies were performed with ethyl formate [437,439,441], isobutyrate [437,439—441] acetate [402, 435—437,439—442], methoxyacetate [441] and acrylate [403,404,464, 465] the alcohols used were methanol [402,435,437,439—442,450],... 

Figure 14 Lipase-catalyzed transesterification of secondary alcohols using isopropenyl acetate as acyl donor in...

Ghanem, A. Schurig, V. Lipase-catalyzed transesterification of secondary alcohols using isopropenyl acetate as acyl donor in organic solvents. Monateshefte fur chemie, 2003, 134, 1151-1157. 

The KR of aryl alkyl sec-alcohols using various chiral nucleophilic N-heterocyclic carbenes (NHCs) has also recently been achieved by the groups of Suzuki [125, 126] and Maruolca [127]. These studies build on an emerging body of information showing that achiral NHCs are extremely efficient nucleophilic organocatalysts for transesterification [128]. The levels of selectivity achieved by Maruoka using the Cj-symmetric NHC 29b for the KR of aryl alkyl sec-alcohols (and two allylic alcohols) lie in the range 16 to 80 (Scheme 8.8). 

In a interesting example of organocatalysis, Suzuki et al. studied the enantioselective acylation of secondary alcohols using chiral NHCs [11,12]. The approach was partly based on the work of Nolan and Hedrick who had independently reported NHC-catalyzed transesterifications [13,14]. The enantioselective acylation was subsequently improved by using more sterically hindered acylating agents such as diphenylacetate derivatives (Scheme 4), leading to selectivity factors (s = kn, ) of up to 80 [15,16]. 

Metal-oxides of the type (Al203)x(Sn0)Y(Zn0)z were also studied as heterogeneous catalysts for the transesterification reaction of soybean oil (Macedo et al., 2006). It was observed that these materials are active for soybean oil alcoholysis with different alkyl-chain alcohols using several alcohols, including branched ones. The best result was achieved using methanol, with conversion yields up to 80% in 4 h. As observed for the complex 1 in homogenous conditions, the catalytic activities are strongly dependent on the nature of the alcohol. For alcohols with a linear chain, the reaction activities decrease with... 

Scheme 7.1. Base-catalyzed transesterification of triacylglycerols (TAGs) to produce fatty acid esters (biodiesel). Methyl esters (shown) are the most common but others, such as ethyl esters, can be produced depending on the alcohol used in the reaction. Ri, R2 and R3 represent unique fatty acids attached to the glycerol backbone of the TAG.

Direct esterification of methacrylic acid with alcohols using sulfuric acid or other catalysts can be used to prepare methyl methacrylate (MMA) and other esters. Commercial routes for the direct preparation of MMA and some lower alkyl esters also exist. In the 1990s, researchers at Shell developed a direct route to MMA from propyne (methylacetylene), carbon monoxide, and methanol using a Pd(II) catalyst. The limited availability of propyne may slow the expansion of this highly efficient route to high purity MMA. Transesterification of MMA is often the preferred route for the preparation of other esters. 

Esterification and transesterification. Tetracyanoethylene used at about 10 mol% is the first Jt-acid catalyst for esterification of carboxylic acids with various alcohols. Transesterification requires higher temperature. 

The storage stability of other lipases has been also analysed. For instance, the storage stability of PsL in hydrophobic ILs for a period of 20 days at room temperature, measured with the variation of the transesteriiication activity of this enzyme during transesterification of ethyl 3-phenylpropanoate with different alcohols, resulted in an increased yield of 62-98% in [bmim fNTfj ] and 45-98% in [bmim ] [PFg ], respectively, depending on the nature of alcohol used in the tiansesterifica-tion reaction. In these ionic liquids, the operational stability was also measured and found that the P.yL-IL mixture was recycled live times without any decrease in the transesterification activity [13]. 

Transesterification. Ethyl esters from carboxylic acids and acetic esters of benzylic alcohols are obtained in the catalyzed transesterification processes, using ethyl acetate as the donor of ethoxy or acetyl group. 

Vinyl alcohol monomer does not exist because its keto tautomer is much more stable. Poly(vinyl alcohol) can be prepared from either poly(vinyl ester)s or from poly(vinyl ether)s. Commercially, however, it is prepared exclusively from poly(vinyl acetate). The preferred procedure is through a transesterification reaction using methyl or ethyl alcohols. Alkaline catalysts yield rapid alcoholyses. A typical reaction employs about 1% sodium methoxide and can be carried to completion in one hour at 60 °C. The product is contaminated with sodium acetate that must be removed. The reaction of transesterification can be illustrated as follows ... 

The first reaction designed specifically as an N-heterocyclic carbene catalyzed process was the transesterification of esters in the presence of IMes 13. This process, reported simultaneously by Hendrick and Waymouth and by Nolan, allowed the facile transesterification of esters with an added alcohol (Scheme 14.3). A number of researchers have also developed chiral NHCs for kinetic resolutions of alcohols using these processes. ... 

Cambou, B. and Klibanov, A. M. (1984) Preparative production of optically active esters and alcohols using esterase-catalyzed stereospecific transesterification in organic media J. Am. Chem Soc. 106,2687-2692... 

The most common use of In(III) salts in the catalysis of nucleophilic substitutions is in nucleophilic acyl substitutions, specifically esterifications and transesterifications. The traditional acetylation of alcohols using strong acids or bases are often plagued by problems of substrate compatibility with the reaction conditions, especially for tertiary alcohols with their low Sn2 reactivity and propensity to eliminate instead of undergoing SnI reactions. Thus, the use of mild conditions offered by In(III) salts provided solutions to these problems. 

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