Pertechnic acid

Radiochromatographic techniques have been used to determine the rates of oxidation of cysteine by pertechnate ion, Tc04. The technetium(vu) is reduced by the thiol (and cysteine ethyl ester) to form a Tc complex which involves both S- and 7V-co-ordination of the amino-acid. The rate law is first order with respect to both [Tc ] and [RSH]. A hydrogen-ion dependence observed is attributed to the formation of pertechnic acid, the rate-determining step being the nucleophilic attack by the thiol at the metal centre of HTCO4. The oxidation of RSH (R=Et, Pr, or Bu) has been studied over the range 20—40 °C in aqueous alkaline solutions in the presence of metal phthalo-cyanines. The reaction is zero order with respect to [thiol], first order in phthalocyanin and decreases in the order M = Co>Mn> V>Feii. No effects are observed from the nature of the alkali cation. 

Extraction with a solution of methyltricaprylammonium chloride in chloroform results in nearly quantitative isolation of pertechnetate from aqueous media, ranging from 4 M sulfuric acid or 9 M hydrochlorid acid to pH 13 . A 1 1 pertechne-tate-organic cation adduct seems to be formed at any pH an excess of the organic reagent is only necessary if extraneous anions can compete with pertechnetate. 

The preparation of uranyl pertechnate, U02(Tc04)2,2H20 from UO3 with per-technetic acid has been described and the dehydration shown to follow the course... 

A 50-mL beaker equipped with a Teflon-jacketed stirbar is filled with 32 mL 12 N hydrochloric acid. To the stirred solution, 4.0 mL 0.32 M (1.28 mmole) NH4[Tc04] in water is added. After 10 minutes, 4.0 mL of a 75% w/w tetrabutylammonium chloride solution (Pfaltz Bauer) is added dropwise to the green solution. The resultant gray-green microcrystalline powder is filtered and collected on a medium-porosity fritted filter. The solid is washed, and any residual product transferred to the filter with 3.0 mL 12 N hydrochloric acid, followed by five 3.0-mL aliquots of isopropyl alcohol or 1-methylethanol. The solid is dried in vacuo for 2 hours. The yield, based on ammonium pertechne-tate, is 0.63 g (99%). 

The active ingredients are diphosphonic acids - dicarboxypropane diphosphonic acid (DPD), hydroxymethylene diphosphonic acid (HDP or HMDP), hydroxyethylidene diphosphonic acid (EHDP), methylene diphosphonic acid (MDP) - or their sodium salts. As stabilizers are used N-(4-aminobenzoyl)-L-glutaminic acid, gentisic acid (2,5-dihydroxybenzoic acid), ascorbic acid, or carbamide. For reduction of Tc-pertechne-tate to lower oxidation states, tin(II) chloride and tin(II) fluoride are employed. 

Passivators are inorganic substances possessing oxidative properties whose reaction products with metals form a passive film on the substrate surface, which shifts the corrosion potential of the substrate to the positive side by a few tens of volts. Like a depolarizer, the passivator generates a current on the anodic areas of the substrate of 1 > i density, where i is the critical density of the passivation current. This means that the chemical composition of the passivating film on a metal substrate is the same whether the substrate is passivated by anodic polarization in an acid or is treated with solutions of chromates (CrO ), nitrates (NO ), molybdates (MoO ), tungstates (WO ), ferrates (FeO ) or pertechnates (TcOj). 

The same Flade potential is obtained whether iron is passivated by concentrated nitric acid or is anodically polarized in sulfuric add, indicating that the passive film is essentially the same in both instances. In fact, when iron is passivated by immersion in solutions of passivators, whether chromates (CrOl ), nitrites (NOi), molybdates (MoO ), tungstates (WO4 ), ferrates (FeOl ), or pertechne-tates (TcOi), the corresponding Flade potentials are close to values obtained... 

The pertechnate ion oxidizes ascorbic acid to give a red species... 

---