Organophosphorus acids

The sensitivity of detection is usually between 0.2 and 0.5 pg per chromatogram zone. This is also true for pesticides based on organophosphorus acids [9]. 

In addition to phosphotriesterase from P. diminuta (PTE) discussed above, two other types of enzymes were found to exhibit phosphotriesterase activity. Interestingly, both are peptidases - the enzymes which in nature hydrolyse a peptide bond. The first one - organophosphorus acid anhydrolase (OPAA) from Alteromonas sp. JD6.5 - is a proline dipeptidase its original activity is to cleave a dipepfide bond with a prolyl residue at the carboxy terminus. The second one - aminopeptidase P (AMPP) from Escherichia coli - is a proline-specific peptidase that catalyses hydrolysis of N-terminal peptide bonds containing a proline residue. ° ... 

Brief notes are added on phosphorofluoridates even though their destruction by microbial activity— though clearly possible—is limited by their toxicity to the requisite microorganisms. One of the motivations for their inclusion is the fact that the hydrolytic enzyme(s) responsible for defluorination—organophosphorus acid anhydrase (OPA)—is widespread, and is found in a number of bacteria (Landis and DeFrank 1990). The microbial hydrolysis of organophosphorus pesticides and cholinesterase inhibitors is accomplished by several distinct enzymes, which are collectively termed organophosphorus acid anhydrases (OPAs). These have been reviewed (DeFrank 1991), so that only a few additional comments are necessary. 

DeFrank 11, T-C Cheng (1991) Purification and properties of an organophosphorus acid anhydrase from a halophilic bacterial isolate. / Sacfeno/ 173 1938-1943. 

The most extensively investigated reagents for the recovery of nickel and cobalt from acidic media have been the organophosphorus acids.220,222,228-234 The commercial and systematic names and the structures of the ligands used have been collected in the table presented earlier (Table 4). 

Preston, J. S. duPreez, A. C. Solvent extraction of nickel from acidic solutions using synergistic mixtures containing pyridinecarboxylate esters. 1. Systems based on organophosphorus acids. J. Chem. Technol. Biotechnol. 1996, 66, 86-94. 

Zhu, T. Structure of organophosphorus acid extractants and their steric effect. Chin. J. Inorg. Chem. 2000, 16, 305-309. 

Preston, J. S. Solvent extraction of cobalt and nickel by organophosphorus acids. I. Comparison of phosphoric, phosphonic, and phosphinic acid systems. Hydrometallurgy 1982, 9, 115-133. 

The A-esterases now classified as diisopropyl fluorophosphatases (diiso-propyl-fluorophosphate fluorohydrolase, DFPase, somanase, EC 3.1.8.2) were previously listed under EC 3.8.2.1. These enzymes, which hydrolyze P-F and P-CN bonds such as those of nerve gases, should be described as organophosphorus acid anhydrolases rather than phosphatases [56]. Diisopropyl-fluoro-phosphatases exist in different forms with contrasting substrate specificities. One form is able to hydrolyze paraoxon at a low rate, while others have no paraoxonase activity. The different forms differ in their molecular weights and in their requirements for bivalent cations for activity [56]. 

The inactivation and detoxification of paraoxon and congeners are catalyzed by the so-called A-esterases, which, as discussed, comprise aryleste-rase (sometimes still called paraoxonase, EC 3.1.1.2) and phosphoric triester hydrolases (phosphotriesterases, EC 3.1.8) subdivided into aryldialkylphos-phatase (organophosphate hydrolase, paraoxonase, EC 3.1.8.1) and organophosphorus acid anhydrolases (EC 3.1.8.2 see Sect. 9.3.7) [65][69][106-108], These activities, which occur mostly in the mammalian liver and... 

As anhydrides, such compounds are subject to spontaneous hydrolysis, which may contribute to detoxification [160]. Thus, soman hydrolysis at pH 7.5 and 37° occurs with a rate constant of 0.003 - 0.004 min-1 and an activation energy of ca. 55 kJ mol 1 [161]. However, most of the published data refer to enzymatic hydrolysis. Enzymes hydrolyzing P-X anhydride bonds are now known as organophosphorus acid anhydrolases (OPA anhydrolases) classified as EC 3.1.8.2 (also known as diisopropyl-fluorophosphatase, DFPase, tabunase, somanase), an activity related to EC 3.1.8.1 (aryldialkyl-phosphatase, paraoxonase, A-esterase) and formerly classified as EC 3.8.2.1 [64] [65] [69], Much public information on these enzymes can be found in [106],... 

Extraction of cobalt by organophosphorus acids, especially CYANEX 272, from acidic solutions... 

Both carboxylic (e.g., Versatic acid) and organophosphorus acids have been used commercially to extract the lanthanides. The extraction follows the formation of the metal-extractant complex [Eq. (11.21)] and so depends on the pH of the feed. 

Kabachnik and co-workers have determined the pKa s of a number of dithio- and monothio-organophosphorus acids and considered the thiol-thione tautomeric equiUbria of monothiophosphoric acids. For most monothio acids the tautomeric equlibrium is shifted toward the thione form. There are slight changes in the pKa s of O, O -dialkyldithiophosphoric acids with substituent variation. Other data U4,29i) indicates that the pKavalues are rather substituent dependent, e.g., Ref. gives pKa values of -1.10 and +0.22 for HSP(S)(OC2Hs h... 

Organophosphorus acid pesticides Parathion and methylparathion Insecticide 300-800... 

Solvent extraction of base metals by organophosphorus acids 792... 

The use of organophosphorus acids, such as di(2-ethylhexyl)phosphoric acid (D2EHPA di(2-ethylhexyl) monohydrogen phosphate 2 R = C4H9CH(Et)CH2), is now well established in the recovery of base metals. This reagent has found commercial application in the separation of cobalt from nickel,67 68 the separation of zinc from impurities such as copper and cadmium,69 the recovery of uranium,68 beryllium70 and vanadium,71 and in separations involving yttrium and the rare-earth metals.72 73... 

Other commercial operations known to have used organophosphorus acids for the recovery of rare earths are those of Thorium Ltd. in England,39the Megon Company in Norway,73-95 and Denison Mines in Canada.96,97... 

Few details have been revealed concerning the commercial extraction of beryllium by organophosphorus acids. However, alternative processes involve the stripping of the loaded organic phase... 

Organophosphorus acids were among the first extractants to be used in the commercial recovery of uranium from solutions obtained by the leaching of low-grade ores with sulfuric acid. In the so-called Dapex process,70 114 the leach liquor is extracted with a solution of about 0.1 M D2EHPA in kerosene, and the pH value of the aqueous phase is adjusted to close to 1.0 in order to prevent the coextraction of vanadium impurities. Since iron(III) also extracts under these conditions, the leach liquor is reduced with metallic iron prior to extraction to convert any iron(III) present to the iron(II) state. 

Organophosphorus acid extractants have found considerable use in recent years for the recovery of uranium as a byproduct in the manufacture of wet-process phosphoric acid. This acid is obtained by the digestion of phosphate rock with sulfuric acid, and typically contains 0.1 to 0.2 g of uranium per litre.120 It has been estimated that, in 1976, the wet-process acid produced in the USA alone contained some 2500t of dissolved uranium 121 this therefore represents a valuable potential source of this strategic metal. 

In contrast to the chemistry of extraction of uranium(VI) by organophosphorus acids, that of uranium(IV) has not been widely studied. It is known,135 however, that the extraction of U4+ by mono(2-ethylhexyl)phosphoric acid (2-ethylhexyl dihydrogen phosphate), for example, exceeds that of U022+ by a factor of 105. This clearly provides the basis for the strong extraction of uranium(IV) from phosphoric acid solutions by extractants containing monoalkyl phosphates. The existence of a synergistic effect in the extraction of uranium(IV) by mixtures of mono(2-ethylhexyl)phosphoric acid and neutral organophosphorus compounds was also reported recently.136... 

Organophosphorus acid extractants have also been used commercially to recover thorium from barren solutions obtained from uranium ion-exchange plants. For instance, Rio Tinto Dow Ltd of Canada installed a plant at Elliot Lake in 1959 to extract thorium(IV) from solutions containing only 0.15 g of thorium per litre.137 The loaded organic phase is stripped with 5 M sulfuric acid, from which the product subsequently crystallizes as an acid thorium(IV) sulfate. 

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