Acetic acid, vanadium complex

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Vanadium(n) Complexes.—Dehydration of VSO. THjO has been shown to proceed via the formation of VS04,mH20 (where n = 6, 4, or 1) and V(OH)-(SO4), which were characterized by X-ray studies. The polarographic behaviour and the oxidation potential of the V -l,2-cyclohexanediamine-tetra-acetic acid complex, at pH 6—12, have been determined.Formation constants and electronic spectra have been reported for the [Vlphen),] " and [V20(phen)] complexes. The absorption spectrum of V ions doped in cadmium telluride has been presented and interpreted on a crystal-field model. The unpaired spin density in fluorine 2pit-orbitals of [VF ] , arising from covalent transfer and overlap with vanadium orbitals, has been determined by ENDOR spectroscopy and interpreted using a covalent model. " ... 

The kinetics of the reaction between [V(salen)] in pyridine and oxygen have been determined and interpreted in terms of the formation of a [V(salen)] -oxygen adduct. This reinforces the view that vanadium(iii) complexes can act as oxygen carriers. The oxidation of the 1,2-cyclohexanediaminetetra-acetic acid complex of V " has been studied in solutions of pH 6—12. ... 

Acetic acid is formed when methane reacts with CO or C02 in aqueous solution in the presence of 02 or H202 catalyzed by vanadium complexes.327 A Rh-based FeP04 catalyst applied in a fixed-bed reactor operating at atmospheric pressure at 300-400° C was effective in producing methyl acetate in the presence of nitrous oxide.328 The high dispersion of Rh at sites surrounded by iron sites was suggested to be a key factor for the carbonylation reaction. 

The vanadium(V) oxidation of the sulfide PhCH=CHSPh has been studied in aqueous acetic acid containing perchloric acid. The reaction is first order in vanadiiun(V) and fractional order in sulfide. An intermediate complex of vanadium and the sulfide forms and its decomposition is the slow step of the reaction.181 Two Indian groups have reported on the use of ruthenium(VI) and ruthenium(III).182 183 The kinetics and mechanism of the oxidation of diethylene glycol by aqueous alkaline potassium bromate in the presence of Ru(VI)182 and the Ru(III)-catalysed oxidation of aliphatic alcohols by trichloroisocyanuric acid183 have been examined. 

Oxidations. Ketones are cleaved to afford carboxylic acids in moderate yields by ReiOv-t-BuOOH in acetic acid at 100°. Vanadium-catalyzed epoxidation of unsaturated alcohols in liquid carbon dioxide is feasible.- A resin-bound cobalt-phosphine complex is also effective as a catalyst for oxidation. ... 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

The drawback of this reaction is that trifluoroacetic acid for the solvent and excess K2S2O8 for the oxidant are required. Although a bimetallic system based on Pd and Cu was initially used as the catalyst, it was determined that the reaction can proceed using only the copper catalyst. A radical mechanism is proposed. Vanadium complexes such as VO(acac)2 also effectively catalyze acetic acid formation from methane and CO (57). The yield reached 93% based on methane. 

Hydroxyquinoline (oxine) reacts with numerous metal ions, in neutral, ammoniacal, or acetic acid solution, to produce inner complex salts of the coordination structure (II). Anions of metallo acids (molybdic, tungstic, vanadic) react in acetic acid solution to form insoluble compounds of a different structure probably the oxine esters of the particular metallo acid are formed. The vanadium compound is represented by (III). ... 

The black vanadium complex precipitates immediately. Heat the mixture briefly, filter, wash the complex with dilute acetic acid and dry it. Dissolve the blue-black solid in a mixture (1 1) of xylene and glacial acetic acid by warming, and dilute the solution with xylene— glacial acetic acid (1 1) until it has a convenient intensity of colour (about lO" M). Store the reagent solution in a dark bottle. 

Cobalt(II) complexes (such as cob(II)alamin, formerly called B,2,) can be obtained by several methods including controlled potential reduction [14,15], anaerobic photolysis of some organocobalt species [16] (see Section 5.2(b)), partial oxidation of cobalt(I) complexes, in some cases acidification of solutions of cobalt(I) complexes (see below) and chemical reduction. Chemical reduction of cobalt(III) cobalamins to the +2 oxidation state has been achieved with hydrogen over platinum oxide [16], with neutral and acidic solutions of vanadium(III) [17], with chromous acetate at pH 3 [18] and with amalgamated zinc in 0.1 M aqueous perchloric acid [19]. All such cobalt(II) species are probably 5-coordinate, and are low spin d systems containing an unpaired electron and thus displaying an ESR spectrum [20]. 

---