Esterification with benzyl alcohols

The synthesis of trifluoromethylalkene dipeptide isosteres was reported by Wipf and coworkers [7]. As shown in Scheme 10.28, the multistep synthesis of Ala-XF[C(CF3)=CH]-Xaa type isosteres was achieved from l,l,l-trichloro-2,2,2-trifluoroethane. The carboxylation of trifluorotrichloroethane via trifluorodichloroethylzinc intermediate, esterification with benzyl alcohol, and Reformatsky addition-elimination with acetaldehyde... 

Attachment of carboxylic acids to supports as trityl esters is achieved by treatment of the corresponding trityl chloride resin with the acid in the presence of an excess of a tertiary amine (Figure 3.5 see also Section 13.4.2). This esterification usually proceeds more quickly than the acylation of benzyl alcohol linkers. Less racemization is generally observed during the esterification of A-protected a-amino acids with trityl linkers than with benzyl alcohol linkers [47], If valuable acids are to be linked to insoluble supports, quantitative esterification can be accomplished by using excess 2-chlorotrityl chloride resin, followed by displacement of the remaining chloride with methanol [64]. 

Aromatic esters may be prepared by direct esterification methods similar to those already described for aliphatic esters (Section 5.12.3, p. 695). A large range of examples of simple alkyl esters of aromatic carboxylic acids is included in Expt 6.163. Corresponding esterification of a simple aliphatic acid (e.g. acetic acid) with benzyl alcohol is illustrated in Expt 5.142. 

It is prepared by esterification of benzyl alcohol, by heating with either an excess of acetic anhydride or acetic acid with mineral acids. 

To prove our hypothesis on the organocatalytic effects of anions, we chose a series of relatively basic anions, combined with l-butyl-3-methylimidazolium cations. Surprising results were obtained in the esterification of benzyl alcohol and acetic acid, which not only showed that the yields with any of the ionic liquids investigated are much lower than in the absence of ionic liquid (27% after 5 h 75-80% after 100 h in equilibrium), but also that in none of the cases equilibrium was reached after 5 h at 100 °C (ROH R COOH ionic liquid = 1 1.5 1). However, slight effects of the nature of the anion were observed, giving decreasing reaction... 

Derivation (a) By treating benzyl chloride with sodium acetate in various solvents (b) by esterification of benzyl alcohol with acetic anhydride or acetic acid. 

The reaction catalysed by 16 was an esterification with benzoic anhydride and the best kinetic resolution obtained (s = 67) with benzylic alcohol 19 was at - 40 °C. A value of 67 is very good for a kinetic resolution. However, exceptional results were obtained using phosphine 18. This catalyst is effective with a variety of alcohols and conditions. The best result was obtained with 20, AC2O and, crucially, catalyst which had been recrystallised to >99.9% ee. In this instance s = 390 ... 

Fig. 16 Heterogeneous catalysis of the esterification of benzyl alcohol with 1-hexanoic acid using a cross-linked Hn-phase sulfonic acid resin formed by amide H-bond-assisted LLC phase formation...

R = CH3, C9H10O2, Mt 150.18, fepiookPa 215 °C, 4° 1.0550, reg1 1.5232, is the main component of jasmine absolute and gardenia oils. It occurs as a minor component in a large number of other essential oils and extracts. It is a colorless liquid with a strong, fruity, jasmine odor. Benzyl acetate is prepared by esterification of benzyl alcohol with acetic anhydride (e.g., with sodium acetate as a catalyst) or by reaction of benzyl chloride with sodium acetate. In terms of volume, benzyl acetate is one of the most important fragrance and flavor chemicals. 

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]. 

In related work a modified polymer-bound Mukaiyama reagent has been used to achieve microwave-mediated solution-phase synthesis of esters and lactones [126]. After optimization of the method by esterification of phenoxyacetic acid with benzyl alcohol, a small library of twenty esters was produced by use of the optimized procedure (Scheme 16.84). Overall reaction time was set to achieve full conversion of the starting material in cycles of 2 min irradiation and 1 min hold time. The... 

SYNTHESIS The first step involves the s)mthesis of the amino acid 7-benzyl-L-glutamate by a standard Fischer esterification reaction of L-glutamic acid with benzyl alcohol in the presence of strong acid. The amino acid is subsequently converted to the N-carboxyanhydride (NCA) monomer by reaction with phosgene gas, or by reaction with the less hazardous compound triphosgene.The NCA is polymerized by initiation with a variety compounds such as primary and secondary amines, and alkoxides. Typical comonomers include other amino acid NCAs. 

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... 

Imidazolium PILs and AILs with BF4, Pp6, and PTSA (para-toluenesulfonate) anions were trialed in the esterification of benzyl alcohol with acetic acid with all giving good-to-excellent conversions and selectivities in fairly short times. The AIL [BMIm][PTSA] led to 100% conversion and 100% selectivity, indicating that the esterification reaction does not require a proton for the catalytic process. However, a mechanism has been proposed by Arfan et al. that requires a proton for the esterification process. 

Complex 4 in the presence of 1 equivalent of base is an efficient dehydrogenative esterification catalyst, resulting in good turnovers and yields of esters with various alcohols at 115°C. Reaction follow-up with benzyl alcohol indicated that 91% benzyl benzoate was formed after 6 h, with TOP reaching 333 h at the level of 50% benzyl benzoate. Formation of the ester became very slow after 6 h, perhaps because of retardation of the reaction by the high ester concentration. However, almost quantitative formation of benzyl benzoate was obtained (Scheme 4). 

Benzyl acetate is usually used as jasmine flavor. It is produced in industry through the add-catalyzed esterification of acetic acid and benzyl alcohol. This is a non-green low-yield route. So Huang et al. made an attempt to biosynthesize benzyl acetate via hpase-catalyzed transesterification of vinyl acetate with benzyl alcohol in water-in-[Bmim][PFg] microemulsion stabiHzed by AOT and Triton X-100. Owing to the high dispersion of lipase, large interface, removal of the byproduct, and activation of imidazole cation, a maximum yield of 94% was obtained [99] (Figure 15.29). 

Ben /ben ate [120-51-4] CgH COOCH2CgH, mp, 21°C, cff , 1.118 bp, 323—324°C at 101.3 kPa , 1.5681. This is a colorless, oily liquid with a faiat, pleasant aromatic odor and a sharp, burning taste. It occurs naturally iu Pern and Tolu balsams, is spariugly volatile with steam, and is iusoluble iu water. Benzyl benzoate is prepared commercially by the direct esterification of benzoic acid and benzyl alcohol or by reaction of benzyl chloride and sodium benzoate. The pleasant odor of benzyl benzoate, like other benzoic esters, has long been utilized iu the perfume iadustry, where it is employed as a solvent for synthetic musks and as a fixative. It has also been used iu confectionery and chewing gum flavors. 

Esters of low volatility are accesible via several types of esterification. In the case of esters of butyl and amyl alcohols, water is removed as a binary azeotropic mixture with the alcohol. To produce esters of the lower alcohols (methyl, ethyl, propyl), it may be necessary to add a hydrocarbon such as benzene or toluene to increase the amount of distilled water. With high boiling alcohols, ie, benzyl, furfuryl, and P-phenylethyl, an accessory azeotroping Hquid is useful to eliminate the water by distillation. 

Izumi and Urabe [105] found first that POM compounds could be entrapped strongly on active carbons. The supported POMs catalyzed etherization of ferf-butanol and n-butanol, esterification of acetic acid with ethanol, alkylation of benzene, and dehydration of 2-propanol [105], In 1991, Neumann and Levin [108] reported the oxidation of benzylic alcohols and amines catalyzed by the neutral salt of Na5[PV2Mo10O40] impregnated on active carbon. Benzyl alcohols were oxidized efficiently to the corresponding benzaldehydes without overoxidation ... 

A variant that eliminates the production of water and that has proved effective for esterification of hydroxy and aromatic amino acids involves the use of thionyl chloride instead of acid. At a low temperature, the alcohol reacts with the chloride, generating methyl sulfinyl chloride, which produces the ester, probably through the mixed carboxylic acid-sulfinic acid anhydride (Figure 3.18, B). p-Toluenesulfonyl chloride added to the acid and benzyl alcohol serves the same purpose in the preparation of benzyl esters. 

Furthermore, the apphcabihty in a Mitsunobu esterification reaction and a Diels-Alder reaction was proven (Scheme 10.13). The polymer-bound benzyl alcohol (70) was reacted with 4-acetamidophenol in the presence of the Mitsunobu reagent to give phenyl ether (71) in quantitative yield. It was released from the polymeric support in high yield. 

With the methylated PAHs, another bioactivation pathway leading to benzylic carbocations becomes available through side chain oxidation to form a benzylic alcohol, followed by esterification and solvolysis. Thus, benzylic sulfate ester formation (via initial formation of benzyl alcohol) constitutes an additional route that could contribute to metabolic activation (Fig. 2). ... 

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