Esters oxyacid

Lipase-catalyzed polymerizahon of oxyacid esters was reported. PPL catalyzed the polymerizahon of methyl 6-hydroxyhexanoate. ° The polymer with DP up to 100 was synthesized by polymerization in hexane at 69°C for more than 50 days. The PPL-catalyzed polymerization of methyl 5-hydroxypentanoate for 60 days produced the polymer with DP of 29. Solvent effects were... 

Enzymatic enantioselective oligomerization of a symmetrical hydroxy diester, dimethyl /Lhydroxyglutarate, produced a chiral oligomer (dimer or trimer) with 30-37% ee [24]. PPL catalyzed the enantioselective polymerization of e-substituted-e-hydroxy esters to produce optically active oligomers (DP < 6) [25]. The enantioselectivity increased with increasing bulkiness of the monomer substituent. Optically active polyesters with molecular weight of more than 1000 were obtained by the copolymerization of the racemic oxyacid esters with methyl 6-hydroxyhexanoate. 

By Valence Change of an Oxyacid Ester or Related Species. Many of the two-electron oxidations of alcohols of use to preparative chemists involve formation of an ester-type intermediate of general formula >CH 0-X"<, followed by formation of the carbonyl group in what is essentially an El... 

Compounds with phosphorus as the key element that have been investigated for extreme-pressure additive activity add up to an impressively long list. But only a few of them have turned out to be of practical utility and these are predominantly esters of phosphoric acid or derivatives of thiophosphoric acid. In this section we shall be concerned only with those compounds in which phosphorus in combination with oxygen constitutes the key structure dithiophosphates and related derivatives are discussed in Section 11.2.6. The four main types of phosphorus oxyacid esters treated in the present section are shown in Table 11-12. Phosphoric and phosphorous acids are trifunctional hence there are three or-ganophosphorus structures to be considered the neutral triester, the monoacidic diester and the diacidic monoester. 

Lipase-catalyzed polymerization of oxyacid esters was reported. PPL catalyzed the polymerization of methyl 6-hydroxyhexanoate [89]. A polymer with a DP of up to 100 was synthesized by polymerization in hexane at 69 °C for more than 50 d. The PPL-catalyzed polymerization of methyl 5-hydroxypentanoate for 60 d produced a polymer with a DP of 29. Solvent effects were systematically investigated hydrophobic solvents such as hydrocarbons and diisopropyl ether were suitable for the enzymatic production of high-molecular-weight polymer. Various hydroxyesters, ethyl esters of 3- and 4-hydroxybutyric acids, 5- and 6-hydroxyhexanoic acids, 5-hydroxydodecanoic acid, and 15-hydroxypentadecanoic acid were polymerized by Pseudomonas sp. lipase at 45 °C to give the corresponding polyesters with molecular weights of several thousand [90]. 

In vitro synthesis of polyesters using isolated enzymes as catalyst via non-biosynthetic pathways is reviewed. In most cases, lipase was used as catalyst and various monomer combinations, typically oxyacids or their esters, dicarboxylic acids or their derivatives/glycols, and lactones, afforded the polyesters. The enzymatic polymerization often proceeded under mild reaction conditions in comparison with chemical processes. By utilizing characteristic properties of lipases, regio- and enantioselective polymerizations proceeded to give functional polymers, most of which are difficult to synthesize by conventional methodologies. 

Lipase-Catalyzed Polycondensation of Oxyacids and their Esters 243... 

Quite often, we find nonsystematic nomenclature used in the literature dealing with organophosphorus compounds. This results in unnecessary confusion, as systematic nomenclature is easy to use and understand. Nomenclature based on the oxidation state of the phosphorus center eliminates the confusion and helps to promote understanding of the chemistry as well as to facilitate communication. Table 1.1 shows structures for tricoordinate and tetracoordinate phosphorus compounds related to oxyacids with their English general names. Also noted are the names for simple esters of the parent acids. They are organized based on oxidation state and the number of bonds of the carbon-phosphorus type. 

Hata, T. and Sekine, M., Silyl- and stannyl-esters of phosphorus oxyacids — intermediates for the synthesis of phosphate derivatives of biological interest, in Phosphorus Chemistry Directed Toward Biology, Stec, W.J., Ed., Pergamon, New York, 1980, p. 197. 

Hydroxides and oxides of the non-metals and less electropositive metals behave as oxyacids and react with alcohols to form esters (alkoxides) and water. Typically such reactions involve an equilibrium and removal of the generated water by fractionation is necessary to obtain the pure... 

Oxides and oxyacids of Cr(VI) are powerful oxidants. The oxidative power of chromic acid is comparable to that of nitric acid. Chromic esters have been proposed as intermediates in these oxidations, thus isopropyl chromate has been isolated and converted into acetone by pyridine-catalyzed elimination in benzene solution [Eq. (2)]. Decomposition of the chromate ester involves removal of the proton attached to the... 

Ester. A compound formed from an alcohol and an oxyacid by elimination of water here used specifically in the sense of an alkoxy- or aroxysilane, such as may be considered to result from the combination of an alcohol with the hypothetical silicic acids a compound comprising the structure SiOR where R is an organic group. 

The Lunge nitrometer provides a simple and very useful means for controlling nitrations carried out in concentrated sulfuric acid solution. Its usefulness for the determination of the oxyacids of nitrogen, especially nitric and nitrous acids, depends on the fact that these acids (and their salts and esters) are quantitatively and rapidly reduced to NO by metallic mercury in the presence of concentrated sulfuric acid, even at ordinary temperatures, according to the reaction ... 

Esters of various oxyacids have been isolated the anhydrous sulfate (equation 31), formed at 160 °C, is unstable. 

Alcohols react with common inorganic oxyacids to produce inorganic esters. For instance, nitric acid reacts with alcohols to produce nitrates by substitution of nitrate, —ONO2, for hydroxyl, —OH. 

The same change, from classical general base to nucleophilic catalysis by selected nucleophilic bases, has been observed and studied recently for the hydrolysis of activated amides (an example is l-benzoyl-3-phenyl-l,2,4-triazole 2.2, Scheme 2.11) [21], and is observed also for esters of various oxyacids of phosphorus. The changeover to general base catalysis of the hydrolysis of aryl dialkyl phosphates... 

In Section 10.6 of the preceding chapter it was shown that tricresyl phosphate, a widely used organophosphorus additive, left an interaction film of ferrous phosphate on the steel surface that it lubricated. In terms of a mechanism generally applicable to the esters of phosphorus oxyacids, two reaction paths immediately suggest themselves. One is the thermal decomposition of the ester linkage, catalyzed by the activated metal interface ... 

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