Combination tables carboxylic esters

Hexachlorocyclotriphosphatriazeneb (also known as phosphonitrilic chloride trimer, PNC) has also been found to promote the polycondensation of carboxylic acids and phenols to yield carboxylic esters in high yields. This process has been successfully applied to the preparation of polyesters directly from p- and m-hydroxy-benzoic acids and also from a combination of dicarboxylic acids and bisphenols (Table 18)13, especially from 4-hydroxy 3,5-dimethoxy benzoic acid (syringic acid) in high yield. 

It has been pointed out earlier that the anti/syn ratio of ethyl bicyclo[4.1,0]heptane-7-carboxylate, which arises from cyclohexene and ethyl diazoacetate, in the presence of Cul P(OMe)3 depends on the concentration of the catalyst57). Doyle reported, however, that for most combinations of alkene and catalyst (see Tables 2 and 7) neither concentration of the catalyst (G.5-4.0 mol- %) nor the rate of addition of the diazo ester nor the molar ratio of olefin to diazo ester affected the stereoselectivity. Thus, cyclopropanation of cyclohexene in the presence of copper catalysts seems to be a particular case, and it has been stated that the most appreciable variations of the anti/syn ratio occur in the presence of air, when allylic oxidation of cyclohexene becomes a competing process S9). As the yields for cyclohexene cyclopropanation with copper catalysts [except Cu(OTf)2] are low (Table 2), such variations in stereoselectivity are not very significant in terms of absolute yields anyway. 

Enantioselective carbenoid cyclopropanation of achiral alkenes can be achieved with a chiral diazocarbonyl compound and/or chiral catalyst. In general, very low levels of asymmetric induction are obtained, when a combination of an achiral copper or rhodium catalyst and a chiral diazoacetic ester (e.g. menthyl or bornyl ester ) or a chiral diazoacetamide ° (see Section 1.2.1.2.4.2.6.3.3., Table 14, entry 3) is applied. A notable exception is provided by the cyclopropanation of styrene with [(3/ )-4,4-dimethyl-2-oxotetrahydro-3-furyl] ( )-2-diazo-4-phenylbut-3-enoate to give 5 with several rhodium(II) carboxylate catalysts, asymmetric induction gave de values of 69-97%. ° Ester residues derived from a-hydroxy esters other than ( —)-(7 )-pantolactone are not as equally well suited as chiral auxiliaries for example, catalysis by the corresponding rhodium(II) (S )-lactate provides (lS, 2S )-5 with a de value of 67%. 

Synthesis of Carboxylic Acid Esters. The preparation of aliphatic carboxylic acid esters from synthesis gas and the corresponding acid is illustrated by the experimental data summarized in Table VI. Here propionic acid is the coreactant (eq. 21) and CO hydrogenation yields substantial quantities of Cx C4 alkyl propionates. Some 14 catalyst combinations of ruthenium with quaternary Group 5B and alkali metal promoters have been considered. The important features of the catalysis are as follows ... 

Olestra is a zero-calorie commercial fat substitute with the look and feel of natural fats. It Is a synthetic compound whose structure involves a novel combination of natural components. The core of olestra Is derived from sucrose, ordinary table sugar. Six to eight of the hydroxyl groups on the sucrose framework have long-chain carboxylic acids (fatty acids) appended to them by ester linkages. These fatty acids are from Cs to C22 in length. In the industrial synthesis of olestra, these fatty acids derive from... 

The alkylation of carboxylate ions has also been catalyzed by crown ethers. Ordinarily, the reaction is conducted with the alkyl halide in an organic phase such as acetonitrile which is in contact with the solid carboxylate salt. The combination of the crown and the solvent (at least for the more polar solvents like acetonitrile) aid in the dissolution of the salt. The poorly solvated carboxylate anion is an effective nucleophile in such situations and alkylates readily. The potassium acetate-crown ether ion pair is a reactive nucleophile but appears to be a relatively weak base. The synthesis of several esters by crown ether phase transfer of carboxylate salts is recorded in Table 6.5. 

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