Formate ester alkanol

Lipolysis is considered to be an important biochemical event during cheese ripening and the current knowledge have been discussed in detail (Collins et al., 2003, 2004 McSweeney and Sousa, 2000). The formation of short-chain FFAs by the lipolysis of milk fat by lipases is a desirable reaction in many cheese types (e.g., mold-ripened cheeses). The catabolism of FFAs, which is a secondary event in the ripening process, leads to the formation of volatile flavor compounds such as lactones, thioesters, ethyl esters, alkanols, and hydroxyl fatty acids. The contributions of lipolysis to the flavor of bacterially ripened cheeses are limited. 

Although the term methanol carbonylation is usually associated with acetic acid manufacture, an alternative carbonylation pathway involves base-catalyzed addition of CO to alkoxide ions to provide a simple route to formate esters (see also the section Direct Synthesis of Methanol from CO/H2). In the case of methanol as the alkanol, the reaction is carried out industrially on a large scale to produce formic acid. The reaction proceeds at ca 30 bar and 80°C using sodium or potassium methoxide as the catalyst and involves nucleophilic attack of methoxide on CO ... 

In the alkoxycarbonylation, the hydride mechanism initiates through the olefin insertion into a Pd - H bond, followed by the insertion of CO into the resulting Pd-alkyl bond with formation of an acyl intermediate, which undergoes nucleophilic attack of the alkanol to give the ester and the Pd - H+ species, which initiates the next catalytic cycle [35,40,57,118]. Alternatively, it has been proposed that a ketene intermediate forms from the acyl complex via /3-hydride elimination, followed by rapid addition of the alcohol [119]. In principle the alkyl intermediate may form also by protonation of the olefin coordinated to a Pd(0) complex [120,121]. 

In the other mechanism, the catalytic cycle initiates through the insertion of CO into a Pd-alkoxy bond, with formation of a Pd-carboalkoxy intermediate, which inserts the olefin with formation of an alkylcarboalkoxy /i-chelate, which undergoes protonolysis by the alkanol through the intermediacy of its enolate isomer (see Sect. 2.3.1), yielding the ester and the Pd-alkoxy species, which then initiates a new catalytic cycle [122-125]. 

Figure 2 illustrates the effect of incremental changes in ruthenium catalyst content upon the production of acetic acid and its C1--C2 alkyl acetate esters. Acetic acid production is maximized at Ru/Co ratios of ca. 1.0 1.5 however, the data in Figure 2 do show an approximate first order dependence of lOAc (acetic acid plus acetate esters) upon initial ruthenium content—at least up to the 2/1, Ru/Co stoichiometry under the chosen conditions. Selectivity to acetic acid in the liquid product peaks at 92 wt % (carbon efficiency 95 mol %) for a catalyst combination with initially low Ru/Co ratios (e.g. 1 4). The formation of C1-C2 alkanols and their acetate esters rapidly exceeds acetic acid productivity when the Ru/Co atomic ratio is raised above 1.5, although two-carbon oxygenates continue to be the predominant fraction. Smaller quantities of glycol may also be in evidence. 

Immobilisation of an Acetobacter aceti strain in calcium alginate resulted in improvement of the operational stability, substrate tolerance and specific activity of the cells and 23 g phenylacetic acid was produced within 9 days of fed-batch cultivation in an airlift bioreactor [133]. Lyophilised mycelia of Aspergillus oryzae and Rhizopus oryzae have been shown to efficiently catalyse ester formation with phenylacetic acid and phenylpropanoic acid and different short-chain alkanols in organic solvent media owing to their carboxylesterase activities [134, 135] (Scheme 23.8). For instance, in n-heptane with 35 mM acid and 70 mM alcohol, the formation of ethyl acetate and propylphenyl acetate was less effective (60 and 65% conversion yield) than if alcohols with increased chain lengths were used (1-butanol 85%, 3-methyl-l-butanol 86%, 1-pentanol 91%, 1-hexanol 100%). This effect was explained by a higher chemical affinity of the longer-chain alcohols, which are more hydrophobic, to the solvent. 

Figure 8.1. Relation of solubility parameters (solpars or Hildebrand 8 values) and carbon numbers in various homologous series of solvents. (4) Normal alkanes, (B) normal chloroalkanes, (C) methyl esters, (D) alkyl formates and acetates, (E) methyl ketones, (F) alkyl nitriles, ) normal alkanols, (H) alkyl benzenes, and (I) dialkyl phthalates.

Long chain alkyl esters of ferulic acid are common constituents in the family. From the seeds of Hyoscyamus niger even a diester, 1,24-tetracosanediol diferulate could be isolated (Ma et al. 2002). Solanum tuberosum started to accumulate long chain alkyl (mono)esters three to seven days after wound treatment. The alcohol components ranged from hexadecyl (Cj Hjj) to octacosyl (C gHj,) all even numbers plus two esters of odd chain length alkanols [nonadecyl (Cj Hj ), heneicosyl (C jH j)]. The major metabolites were represented by hexadecyl and octadecyl ferulates. The authors suppose that the formation of all these ferulates is temporally and spatially correlated with suberin formation since they were restricted to the wound periderm (Bernards and Lewis 1992). For a coherent account of suberin chemistry interested readers are directed to a review on the macromolecular aromatic domain in suberized tissues (Bernards and Lewis 1998). 

A new method for the oxidation of primary and secondary alkanols involves the formation and photolysis of the corresponding pyruvate esters the method is particularly useful when the products are acid or base sensitive. ... 

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