Alcohol long-chain, esterification with

Deactivation of silica surfaces by grafting of alkyl chains [esterification with short-chain (Ci) or long-chain (Ci6) alcohols] was reported (24) to be associated with strong decreases in 7sd as well as 7sp, which for Ci6-modified samples are very close to those exhibited by polyethylene (known to be a... 

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated co-hydroxy acids and dicarboxylic acids are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic acid and a>-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

Resolution of branched alkanoic adds. Hydrolase-catalyzed esterification of 2-methylalkanoic acids can be fairly efficient, especially for acids with long chains, provided that the conditions are carefully adjusted by immobilization of the enzyme (in some cases), by control of the water activity, and by proper choice of the appropriate alcohol as nucleophile as well as the correct solvent [134]. The alcohol concentration does also influence the E-value [133]. It is important to note that the esterifications are reversible, thus preventing easy access to the remaining substrate in high ees. Some representative examples are given in Table 4.4. A procedure based on iterative resolutions can be used to provide both enantiomers of 2-methyloctanoic acid in high ees (>99%) and reasonable yields (25% for S- and 43% for R-acid based on the starting racemic acid) [137]. 

The synthesis of long-chain fatty acid esters of carbohydrates is inherently more demanding. It was found that glucose did not react with vinyl laurate in a pure ionic liquid medium, but in biphasic tert-butyl alcohol/[BMIm][PF6], glucose could be acylated by the vinyl esters of O, 2-Cu, fatty acids. The best results were obtained with CaLB, which was twice as active as TIL, and the selectivity for acylation at C-6 was high [114]. The esterification of glucose with palmitic acid, which is, in an industrial context, to be preferred over transesterification, has recently been demonstrated in tert-butyl alcohol/[BMIm][PF6] medium [115]. 

The direct esterification of undec-lO-enoic acid with phenylalkanols using DCC and 4-(N,N-dimethylamino)pyridine affords the corresponding esters in quantitative yields. Esterification of the secondary alcohol 655 with long chain aliphatic acids in the presence of DCC and DMAP affords the dioxane esters 656 in yields of 80-93 %. ... 

Other possibilities to prepare chiral cyanohydrins are the enzyme catalysed kinetic resolution of racemic cyanohydrins or cyanohydrin esters [107 and references therein], the stereospecific enzymatic esterification with vinyl acetate [108-111] (Scheme 2) and transesterification reactions with long chain alcohols [107,112]. Many reports describe the use of fipases in this area. Although the action of whole microorganisms in cyanohydrin resolution has been described [110-116],better results can be obtained by the use of isolated enzymes. Lipases from Pseudomonas sp. [107,117-119], Bacillus coagulans [110, 111], Candida cylindracea [112,119,120] as well as lipase AY [120], Lipase PS [120] and the mammalian porcine pancreatic lipase [112, 120] are known to catalyse such resolution reactions. 

This alcoholysis of carboxylic esters under the influence of alkaline catalysts is important for the preparation of esters of long-chain alcohols with heat-sensitive carboxylic acids, e.g., with /ff-keto carboxylic acids,858-864 and of esters of acid-sensitive alcohols860-863 that cannot be subjected to the usual methods of esterification. For such reactions sodium alkoxides,853 sodium hydroxide,854 855 and potassium carbonate856 have proved useful as catalysts. 

Other new methods used in heterogeneous catalytic reactions include the use of ionic liquids as catalysts and simultaneous applications of ultrasound and microwave irradiation. An ionic liquid as an acidic catalyst has been used for synthesis of cou-marins [78], in esterification of acetic acid with benzyl alcohol [79], in catalytic esterification at room temperature [80], in alkylation of a-methylnaphthalene with long-chain alkenes [81], and in hydrogenation of benzene [82]. 

Linko et al. 1998). Lipases have been extensively used in the production of surfactants of different chemical nature by esterification of alkyl glycosides and fatty acids, by transesterification of natural oils and alcohols, by transesterification of phospholipids and alcohols, and also by esterification of amino acids and amides (Saxena et al. 1999). Personal care products, hke isopropyl myristate and isopropyl palmitate, have been produced in solvent-free media with immobilized lipase and wax esters (esters from long-chain fatty acids and fatty alcohols) are also being produced with lipases (Hasan et al. 2006). 

In the third step, proteins act as amides and react with the free hydroxyl of the citric acid. The hydroxyl of the citric acid reacts like the hydroxyl of an alcohol in a standard esterification process. During the reaction of the amide with the citric acid, the substitution of the amide hydroxyl by an alkoxy radical (-OR) takes place. At the end of the process, the oxygen in the -OH group of the citric acid remains in the chain whereas the hydroxyl oxygen in the amino acids is eliminated in the form of water. This mechanism results in long chains containing metal cations tightly bond and evenly distributed. 

Selective oxidations of benzylic and aliphatic alcohols to aldehydes and esters, by O2 in the presence of the ligand Q, o -bis(di-f-butyl phosphino)-o-xylene or Bu"P(l-adamantyl)2 and the additive AgPFg in toluene and in the presence of various alcohols, were achieved using Pd(OAc)2 as the catalyst without the need for additional organic hydrogen acceptors. " In a parallel study, the [PdCl2(MeCN)2]-catalysed esterification of benzylic alcohols with methanol and various long-chain aliphatic alcohols in the... 

The hydrophobicity of the surface of this material resulted in a high tolerance toward water and free fatty acids present in the feed oils. As such, in contrast to other solid or homogeneous catalysts, the Zn-Fe(II)-DMC was found to be active for the simultaneous transesterification of triglycerides and the esterification of free fatty acids present in the feed mixture [25,26], On a similar note, the use of Zn-Fe(II)-DMC as a catalyst for the production of lubricant oils by reacting methyl oleate with long-chain alcohols (C8-C12) also resulted in good product yield and avoided the production of undesired side products typically found when using other acid catalysts [27]. 

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