Phosphoric acid analytical data

Phosphorus acid (260 mg, 3.17 mol) was placed into a 250-ml, threenecked, round-bottomed flask suspended in an oil bath. The flask was equipped with a three-way adapter, carrying a pressure-equalizing addition funnel, a reflux condenser with a drying tube, a mechanical stirrer, and a thermometer. Acetonitrile (33 g, 0.80 mol) was introduced to the reaction flask dropwise over a 2-h period while the phosphorous acid was agitated and maintained at a temperature of 138 to 142°C. After completion of the addition, the reaction mixture was maintained at that temperature for an additional 12 h. Methanol was then added to precipitate the pure l-aminoethane-l,l-diphos-phonic acid (13.9 g, 85%), which exhibited spectral and analytical data in accord with the proposed structure. 

Benzylamine (53.5 g, 0.5 mol) and crystalline phosphorous acid (82 g, 1.0 mol) were dissolved in water (100 ml), concentrated hydrochloric acid (100 ml) was added, and the mixture was heated to reflux. Over the course of 1 h, 37% aqueous formaldehyde (160 ml, 2.0 mol) was added dropwise, and the reaction mixture was maintained at reflux for another hour. After cooling, the solvent was evaporated, and the residual syrup was dissolved in hot ethanol. Upon cooling, the crude benzyliminodimethylenediphosphonic acid precipitated and was recrystallized from hot dilute hydrochloric acid to give the pure material (127 g, 85.7%) of mp 248°C, which exhibited analytical data in accord with the proposed structure. 

The metabolic and/or hydrolytic products of parathion encountered as residues in the urine include both diethyl phosphoric acid and diethyl phosphorothioic acid, most probably as their salts (potassium or sodium). Derivatization of these residues with diazomethane would result in the formation of three trialkyl phosphate compounds, namely, 0,0-diethyl O-methyl phosphate (DEMMP), 0,0-diethyl 0-methyl phosphoro-thionate (DEMMTP), and 0,0-diethyl S-methyl phosphorothiolate (DEMMPTh). Earlier (15), it had been shown by combined gas chromatography-mass spectrometry and other analytical data that a later-eluting major product ca. 85%) of the methylation of diethyl phosphorothioic acid formed under the conditions of the analytical method was DEMMPTh, and the minor product formed (ca. 15%) was DEMMTP. Accordingly, all three trialkyl phosphates were observed and confirmed by mass spectrometry in the analysis of the human urine extract. Sufficient internal bond energy differences are associated with the isomeric structures DEMMPTh and DEMMTP that qualitatively and quantitatively dissimilar fragmentation patterns are observed for both isomers as can be seen from the mass spectra of these compounds shown in Figure 4. 

The application of standard electrode potential data to many systems of interest in analytical chemistry is further complicated by association, dissociation, complex formation, and solvolysis equilibria involving the species that appear in the Nemst equation. These phenomena can be taken into account only if their existence is known and appropriate equilibrium constants are available. More often than not, neither of these requirements is met and significant discrepancies arise as a consequence. For example, the presence of 1 M hydrochloric acid in the iron(Il)/iron(llI) mixture we have just discussed leads to a measured potential of + 0.70 V in 1 M sulfuric acid, a potential of -I- 0.68 V is observed and in 2 M phosphoric acid, the potential is + 0.46 V. In each of these cases, the iron(II)/iron(III) activity ratio is larger because the complexes of iron(III) with chloride, sulfate, and phosphate ions are more stable than those of iron(II) thus, the ratio of the species concentrations, [Fe ]/[Fe ], in the Nemst equation is greater than unity and the measured potential is less than the standard potential. If fomnation constants for these complexes were available, it would be possible to make appropriate corrections. Unfortunately, such data are often not available, or, if they are, they are not very reliable. 

Fig. 7-13. Comparison of Th(IV) binding to whole marine colloidal organic matter and the acid polysaccharide fraction (data from Murphy, 2000). The data are plotted in the form of a classic Schubert plot (Schubert, 1948). The analytical method is a ligand competition, liquid-liquid extraction technique using HDEHP (di-2-ethylhexyl phosphoric acid) in toluene to compete against the colloidal organic matter (COM) in an aqueous phase. Xq is the toluene/aqueous phase distribution of the Th in the absence of the COM X is the partitioning in the presence of the COM.

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