Titanium oxalate complexes

If a chemical reaction regenerates the initial substance completely or partially from the products of the electrode reaction, such case is termed a chemical reaction parallel to the electrode reaction (see Eq. 5.6.1, case c). An example of this process is the catalytic reduction of hydroxylamine in the presence of the oxalate complex of TiIV, found by A. Blazek and J. Koryta. At the electrode, the complex of tetravalent titanium is reduced to the complex of trivalent titanium, which is oxidized by the hydroxylamine during diffusion from the electrode, regenerating tetravalent titanium, which is again reduced. The electrode process obeys the equations... 

The NH2 radical rapidly reacts with excess oxalic acid required to form the oxalate complexes of titanium. 

The absorption spectrum of the Ta complex and the interferences owing to other elements (particularly Nb and Ti) vary according to the reaction conditions. A solution of 4 M HCl and 0.02 M (NH4)2C204 is a suitable medium, since the colour from pyrogallol complexes with niobium and titanium is insignificant. In this medium, a ternary tantalum complex with pyrogallol and oxalic acid, and the colourless Nb oxalate complex are formed. To reduce the interference by Nb, tartrate is sometimes added. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Titanium(III) chloride in the presence of oxalate ions or complexed with other ligands such as EDTA, NTA, DTPA or HETA is a developer.40 The TiIH—DTPA developer maintains constant activity over a wide pH range (3—10), is relatively non-toxic and safe to handle, and has some desirable properties as a single-use developer.41... 

Solid, water-soluble a-hydroxycarboxylic acid and oxalic acid titanium complexes can be formed by reaction of the acid and a tetraalkyl titanate in an inert solvent, such as acetone or heptane. The precipitated complex is filtered, rinsed with solvent, and dried to give an amorphous white solid, which is water- and alcohol—water-soluble (81,82). 

TiO " (in a less acidic medium). At pH 1 basic salts precipitate, followed by the hydroxide, which displays very weak amphoteric properties. Titanium(IV) forms stable fluoride, peroxide, tartrate, oxalate, and EDTA complexes, and weak sulphate, thiocyanate and... 

In the presence of DCTA, only Nb, U and Ti interfere in the determination of V. In the presence of DCTA the reaction proceeds slowly the maximum absorbance is attained after 30 min. EDTA breaks down the V-PAR complex, but tartrate, oxalate, phosphate and fluoride have little influence. Interference by titanium decreases in the presence of propanol... 

The photodegradation of hexabromocyclododecane in aqueous solution has been obtained by Fe -oxalate and Fe -citrate complexes, in the presence of H2O2 and simulated sunlight. " Fe-g-C3N4 (Fe-CN) and titanium silicate zeolite (TS-1) hybrid materials have been produced from dicyandiamide, metal chloride as precursors and TS-1 as a support. The material has been applied as heterogeneous catalyst for the photo-catalytic selective oxidation of benzene to phenol, in the presence of H2O2 as benign oxidant under ambient conditions. Noticeably, the hybrid... 

An oxalato complex can also be regarded as a source of the aqueous precursor. The oxalato ion, Ti(0H)2(C204)2, was reported to be present in aqueous solution at low concentrations of <0.02 mol/1 and imder acidic conditions (pH 1—4) (Van de Velde, 1977). A concentrated and acidic aqueous solution could be prepared by directly adding titanium tetraisopropoxide into double molar oxalic acid solution. An opaque colloidal... 

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