Vanadium complexes thiocyanates

Unisulf [Unocal sulfur removal] A process for removing sulfur compounds from petroleum fractions, similar to the Stretford process, but including in the catalytic solution vanadium, a thiocyanate, a carboxylate (usually citrate), and an aromatic sulfonate complexing agent. Developed by the Union Oil Company of California in 1979, commercialized in 1985, and operated in three commercial plants in 1989. 

SNC, Thiocyanate, gold complex, 26 90 SNOjCjH, 1,2-Benzisothiazol-3(2//)-one 1,1-dioxide, chromium and vanadium complex, 27 307, 309 SOOsPCvH45. Osmium, carbonyl(thiocar-bonyl)tris(triphenylphosphine)-,... 

Vanadium thiocyanate complex adsiorbed on Dowex 1-X8 anion exchange resin, desorbed with nitric acid... 

The ability of vanadium(II) chloride to facilitate sulfoxide deoxygenation has been discussed (Section IV,C), and it appears that vana-dium(III) sulfoxide complexes may be prepared by air oxidation of van-adium(II) salts in the presence of the sulfoxide. In this manner, [V(Me2S0)6][C104]3 was prepared from vanadium(II) perchlorate (119) and the kinetics of substitution with thiocyanate ion detailed. Care is necessary in handling the pure compound, as it is reported to be sensitive to detonation. A large number of oxovanadium(IV) species have... 

Table 5 Data on the Complexation of Vanadium(II) with Thiocyanate in Water at 25 °C...

Iron. Industrial hygiene chemists have analyzed iron as the o-phenanthrollne or thiocyanate complexes (6,13). In the AAS analysis at 248.3 nm with air-acetylene atomization, nickel and silica are interferences. If iron in ferro-vanadium must be analyzed, a more oxidative solution than the ntiric acid wet ashing of P CAM 173 is required. Nitric acid-hydrofluoric acid will solubilize refractories containing iron. 

Some Thiocyanate Complexes op Vanadium, Niobium, and Tantalum... 

The rates for these reactions are 7.1 + 0.4 sec" and 0.99 seo, respectively. At the concentrations used the rate of isomerization of CrSCN " was negligible relative to these values. Sutin et al. (62) suggest that these results indicate that, in contrast to the V(II)-Fe(III) reactions, the reaction of CrSCN with proceeds via an anion-bridged intermediate. It would be entirely consistent with what is now known of vanadium-thiocyanate complexes, and with the foregoing, for this intermediate to have the structure [(HaO)5V—NCS—Cr(H20)5]. ... 

The ability of phosphines to act as both a metal oxidation states and as a 7r acceptor to relieve electron density from lower metal oxidation states explains, in part, the observation that diphosphines stabilize the +3, +1, and 0 oxidation states at the expense of the +2 oxidation state.870 Vanadium(II) diphosphine halides, [V(dmpe)2X2] (dmpe = dimethyl-dimethylphosphinoethane, X = Br or I), were prepared as side products in the synthesis of [XV(CO)2(dmpe)2].885 The structurally characterized diphosphino V11 tetrahydroborate complex, tra .s-[V(BH4)2(dmpe)2], (223) was synthesized via the reduction of similar vanadium(III) precursors.832 The reaction of a vanadium(II) chloride salt with dmpe afforded the tra s-[VCl2(dmpe)2] complex which can be alkylated with MeLi or MgMe2 to afford the organometallic trans-[V(Me)2(dm pcVJ compound, which in turn reacts with thiocyanate to form tnms -[V(NCS)2(dmpe)2].8 87 Acetonitrile or propionitrile readily displace the chlorides from trans- WCl2(dmpe)2] to form // tf/ ,v-[V( NCR)2(dmpc)2][BI>h4]2 (R = Me or Et) the acetonitrile derivative reacts with HCPh(S02CF3)2 in acetonitrile solvent to yield the hexaacetonitrile species [V(NCMe)6]2+.887... 

Interfering elements include other metals which form coloured thiocyanate complexes (e.g., V, Bi, U, Cu, Mo, and W), and metals which give preeipitates [Ag, Cu(l)] or consume thiocyanate ions to form colourless complexes ( e.g. Hg). Finally, ions which are themselves coloured (e.g., Ni and Cr) interfere when present at high eoneentrations. Copper(ll) can be masked by means of thiosulphate or thiourea, and vanadium can be masked with tartaric acid. 

Tungsten, molybdenum, and vanadium interfere in the determination of niobium. In contrast to the corresponding tungsten complex, the niobium-thiocyanate complex is decomposed by oxalic acid. Fe(ni), U, Ti, and Ta do not interfere if they are present in no greater than hundred-fold amounts relative to niobium. Phosphate and fluoride interfere, but the latter can be masked with aluminium ions [37]. 

Vanadium(V) is reduced to V(II) in 1 M H2SO4 by zinc amalgam. After addition of thiocyanate and pyridine, and adjustment of the pH to 5.2-5.5, the ternary complex is extracted with CHCI3. Hydrogen peroxide is used to strip vanadium [4]. 

Formation constants of 3d metal ions with A-m-tolyl-p-substituted benzohydroxamic acids and of rare earths with thenoylhydroxamic acid have been determined. Formation constants of proton and metal complexes of iV-phenyl-2-thenoyl- and A-p-tolyl-2-thenoyl-hydroxamic acids have also been determined. In addition, study has been made of the mixed ligand complexes involving nicotine- and isonicotino-hydroxamic acids. A method of extraction and spectrophotometric determination of vanadium with chlorophenylmethylbenzohydroxamic acid has also been published. It may be mentioned that hydroxamic acids (in particular, the A-phenylbenzohydroxamic acid) have been widely used as analytical reagents for metal ions. Solvent extraction of titanium by benzo- or salicyl-hydroxamic acid in the presence of trioctylamine in the form of coloured complexes has been reported. A-w-Tolyl-p-methoxybenzohydroxamic acid has been used for extraction and spectrophotometric determination of Mo and W from hydrochloric acid media containing thiocyanate. 

Trivalent vanadium exists only as a (hexahydrated) ion, V(H20)8, m an aqueous solution. The most readily formed complexes are the halogens and halogenoids. The following complexes are formed with fluoride ions VfI , VFi -H20, VF4-2H20 [6]. Chloride ion forms the VC1 -H20 complex. The cyanide complex [7] has been isolated but is unstable in aqueous solution. However, several thiocyanate complexes have been reported [7,8]. Only the V(SCN) and the V(SCN) appear to be stable in water, the latter only at high concentrations of thiocyanate. 

Transition Metal Complexes Related to the Simon test is a family of color-producing reactions based on transition metal complexes (coordination complexes) and tightly associated ion pairs. Coordination complexes arise from a Lewis acid-base interaction between a metal cation, such as cobalt, and an atom with unshared electrons, such as water or, in the case of drugs, basic nitrogen found in alkaloids and amines. Metals that have been used in these reagents include copper, vanadium, bismuth, and cobalt Cobalt, as part of two common reagents (cobalt thiocyanate and Dilli-Koppanyi) is perhaps the most versatile. Cobalt has an electron structure of 3d 4s, while ttie cation has a 3d (2 ) or 3d (3 ") structure. 

Twenty per cent TBF dissolved In kerosene was used as extractant. The partition coefficient, increases with Increased TBF concentration. Increases with increased pH, and decreases with increased sulfate concentration. Vanadium and Iron (ill) are appreciably extracted by TBP from thiocyanate solutions. Copper, titanium, cobalt are weakly extracted. Iron (ll), cadmium, molybdenum, magnesium and aluminum are essentially not extracted. Phosphate Ion may cause the precipitation of uranium or complex formation when present in large amounts. Okada, et al. report the extraction of uranium by TBP, mesityl oxide, and methyl ethyl ketone from phosphoric acid solutions having 20 times as much ammonium thiocyanate as uranium. 

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