Conversion to esters

Bois de Rose. Bois de rose oil is obtained by steam distillation of wood chips from South American rosewood trees, Aniba rosaeodora. The tree, a wild evergreen, grows mainly in the Amazon basin. The oil is used as obtained in perfumery for its sweet, woody-floral odor and as a source of linalool [78-70-6] (3), which it contains to the extent of 70%. Linalool distilled from bois de rose oil is also used directly in perfumery and for conversion to esters, eg, the acetate (1). 

Other important raw material uses of ethyl alcohol are conversion to esters and ethers, vinegar, ethyl chloride, butadiene, styrene, and chloral (for DDT). Nearly all the new developments in chemicals from ethyl alcohol, particularly the four-, six-, and eight-carbon derivatives are based on alcohol derived from petroleum. The butyl alcohol and butyl acetate so made supplement the production by fermentation and from oxidation of hydrocarbons and synthesis gas operations. The consumption of ethyl alcohol for all industrial uses (denatured alcohol) exceeded 1.2 billion pounds (100% basis) in 1950. More than 700,000,000 pounds of this were made from petroleum. 

In making acetate esters, the primary alcohols are esterilied most rapidly and completely, i.c., methanol gives the highest yield and the most rapid reaction. Under the same conditions, the secondary alcohols react much more slowly and afford lower conversions to ester products however, wide variations are observed among the different members of this scries. The tertiary alcohols react slowly and the conversions are generally low (I - l conversion at equilibrium). 

As mentioned, esterification is reversible, and with ethanol and ethanoic acid the equilibrium constant for the liquid phase is about 4 (AG° = —0.8 kcal) at room temperature, which corresponds to 66% conversion to ester ... 

In situ derivatization of the crude epoxy alcohol product becomes a viable alternative to isolation when 5-10 mol % of catalyst is used for the epoxidation. This procedure is especially useful when the product is reactive or is difficult to isolate because of solubility in an aqueous extraction phase [15,16]. Low-molecular-weight epoxy alcohols such as glycidol are readily extracted from the reaction mixture after conversion to ester derivatives such as the p-nitrobenzoate or 3-nitrobenzenesulfonate [4,17]. This derivatization not only facilitates isolation of the product but also preserves the epoxide in a synthetically useful form. 

In addition to the chain length, the effect of branching of the carbon chain was studied. Specificity of POS-PVA lipase was studied by monitoring esterification reactions of ft-butanol, sec-butanol, and ferf-butanol with butyric acid, as shown in Table 2. The highest rate of conversion to ester (60%) occurred in the presence of ft-butanol, compared with sec-butanol and ferf-butanol. The branching was found to decrease significantly the esterification yield by a factor of 0.4 for sec-butanol and 0.65 for tert-butanol. Antczak et al. (24) reported a similar conversion pattern. 

Carboxylic acid chlorides. Conventional methods for conversion of an acid into the acid chloride usually require acidic reagents. Lederle chemists have accomplished this transformation under neutral conditions by conversion of the acid into the t-butyldimethylsilyl ester. The esters react with oxalyl chloride in CH2CI2 in the presence of catalytic quantities of DMF to form the acid chloride with evolution of gas. Since DMF is essential, dimethylformiminium chloride (Vilsmeier reagent) is probably the reactive species. The acid chloride is formed in 85-95% yield, as shown by conversion to esters with ethanol-pyridine. 

Conversion to Esters. Ester formation is readily achieved by conventional alcoholysis with alkoxides such as LiOBn, NaOMe, or ROMgBr (eq 64). In hindered cases, endocyclic... 

Acylases have also been applied to the kinetic resolution of amines. Aminoacylase I from Aspergillus melleus was used for the resolution of a range of arylalkylamines and amino alcohols via acylation with methyl 2 methoxyacetate (Figure 14.13) [19]. Excellent chemoselectivity was also observed in all cases, as the amino group was preferentially acylated in the presence of a primary alcohol functionality. However, poor to moderate enantioselectivity was observed, with values <10. The best result (E = 9.3) was obtained with 1 aminoindane 10 during the conversion to ester 38. 

Direct conversion to ester is possible by treating the trityl ether with an acid chloride in CH2CI2 (12-100% yield). ... 

Hydroxyketone (72) (Scheme 6) prepared from R-carvone, was made to react with dichloromethyl lithium to yield (94) in 9 1% yield and this upon treatment with potassium carbonate in anhydrous ethanol yielded hemiacetal (95) in 75% yield. Its conversion to ester (96) was achieved by oxidation and then acetylation. This upon treatment with LDA at -78°C afforded lactone (97) whose structure was confirmed by X ray diffraction. Subjection to dehydration and cuprate addition provided compound (98) whose transformation to phytuberin has been discussed by Findlay.44... 

The chemistry of carbohydrates has sometimes been referred to as a marriage between the chemistry of alcohols and that of aldehydes and ketones. In the preceding sections, we examined oxidations and reductions of carbohydrates, cyanohydrin formation, Fischer glycosidation, and processes that involve enolization. All of these reactions involve carbonyl groups in carbohydrates. In this section, we will consider the reactions of the hydroxyl groups of carbohydrates, starting with their conversion to esters. 

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