Vanadium stability constants

The stepwise stability constants for V complexes with glutamic, aspartic, W -ethylenediaminedisuccinic, and W -ethylenediamine-bis-(a-glutaric acid) have been reported.The 1 1 oxovanadium(iv) complex of 5-nitrosalicylic acid has been characterized = 710 nm), and the mixed species formed between vanadium(iv) with protocatechuic acid (H3L ) or gallic acid (H L ) and 4-aminoantipyrine (aant) have been identified spectroscopically as the 1 1 1 and 1 2 2 HL (HL ) aant complexes. The species present in solutions of and tartaric acid below pH 2 have been identified as [VO-... 

Vanadium(m) forms more stable complexes with NCSe- ion in acetone and methyl cyanide than in DMF.383 Spectroscopic detection of the 1 3 and 1 2 complexes in acetone, the 1 2 complex in methyl cyanide, and the 1 1 complex in all three solvents has been achieved. Stepwise stability constants of the complexes are reported as are their electronic spectral parameters. V(antipyrene)3(NCSe)3 and V(diantipyrrylmethane)(NCSe)3 have been isolated from ethanol solutions. 

The presence of vanadium(III) complexes in the very acidic medium of the vacuoles of the signet ring cells in Ascidia ceratodes, containing one or two sulfato/hydrogensulfato ligands, has focused interest on sulfatovanadium complexes as model systems. " ] Whereas readily forms a 1 1 complex with sulfate K = 300 m ), the affinity of V to sulfate is less pronounced. Selected stability constants and pA a values obtained from... 

We therefore determined the complex stability constants of a larger variety of ligands related to HIDP, which are shown for the V(IV)- and Cu(II)-chelates in table 2. Only N-hydroxy-iminodiacetic acid forms a vanadium compound with similar stability as amavadin. All other ligands like the isomeric compound N-hydroxy-D,D -iminodipropionic acid or the bidentate ligand N-hydroxy- -alanine form much weaker complexes. 

NO ligand with a stability constant of 145 at 25°C and 1.5 M ionic strength. The complex decays to [Fe(CN)5NO] and 5RSSR with a rate constant of 1.8 x 10 s but is subject to equilibria involving loss or attack by CN . A purple vanadium(IV) complex has been detected as a product in the vanadium(V) oxidation of cysteine.It is thought to be a bis-cysteine adduct. Acid decomposition of [(en)2Co(SCH2CH2NH2)] is first order in the complex, independent of [H" ], with a rate constant of 2.10 x 10 s ... 

There are less data available for the stability constant of V2(OH)2 than were available for those of the monomeric vanadium(III) hydrolysis species, but nevertheless, the majority of the data still come from the work of Pajdowski and co-workers (see Table 11.4). As was the case with V(OH)2, the data have been acquired in chloride media across the temperature range of 20-25 0. It is believed that utilisation of these data without correction will not significantly impact calculations for obtaining the stability constant at zero ionic strength since the change in each constant is likely to be within the uncertainty assigned to each constant. 

Table 11.4 Data for the stability constants of vanadium(lll) hydrolysis species (reaction (2.5), M = V +). 

The determination of the maj ority of the stability constants for the vanadium( V) hydrolysis species has not been related to reaction (2.5) (M = V02 ). This is because other reactions better facilitate the calculation of the relevant stability constants at zero ionic strength, as is illustrated in the following. For consistency with data given for other cations. Table 11.9 contains the stability constants for all vanadium(V) species that relate to reaction (2.5) (M=V02" ). To undertake these calculations, the derived stability constants at zero ionic strength have been combined with the relevant stability constant of a monomeric vanadium) V) species (also given in the following) and that for water, as given in Chapter 5. 

Table 11.9 Stability constants for vanadium(V) species in accord with reaction (25) (M = VOj+).

Data are also available for three tetrameric vanadium(V) species. The stability constants for these three species can be described with respect to the generic reaction (11.4) from the same monomeric species, V02(0H)2- ... 

Three decameric vanadium( ) species have reported stability constants. The formation of the first ofthese species, ( 02)2q(OH)j, has been described using reaction (2.5) M=V02, p= 10, q= 14). The stability constants reported for the formation of ( 02)20(011)24 according to reaction (2.5) have been utilised, with the extended specific ion interaction theory, to determine the stability constant at zero ionic strength and the associated ion interaction coefficients. The variation of the stability constants as a function of ionic strength is illustrated in Figure 11.19. The zero ionic strength stability constant and ion interaction coefficients obtained are... 

The stability constants for the formation of the monomeric hydrolysis species of vanadium(V) are given in Table 11.11. The table contains data for the reaction of V02" with water to form the species V02(0H)(aq) (or HVOjCaq)), V02(OH)2-(or VO3-), V02(0H)32- (or HVO -) and V02(0H)/- (or VO/-). The data from Borgen, Mahmoud and Skauvik (1977) or Schiller and Thilo (1961) are not included in Table 11.11 as the complete experimental conditions used are not clear in either study. Moreover, the stability constants derived in these studies appear to be inconsistent with those of other studies. 

Heath and Howarth (1981) studied the hydrolysis of vanadium(V) at 0"C and in 2.0 mol 1 LiClO. They determined stability constants for species in addition to those fisted in Tables 11.11 and 11.12. However, in the absence of data for the dissociation constant of water for the conditions used, it is not possible to report these values in the tables. They did indicate that their stability constant for the formation of V02(0H)2 through reaction (2.11) (M = VOj, q = 3) was equivalent to log Ag = -7.1 and that this value was about 1 log unit more than the equivalent value at 20 °C in the same medium and 0.9 log units more than that in the absence of lithium perchlorate. This appears to be reasonably consistent with the stability constant for this reaction that can be derived from the data presented in Table 11.9. 

Use of excess air levels of 5 percent or less has been shown to reduce fuel ash corrosion in furnaces, most likely by stabilizing the vanadium as a refractory suboxide, VO2 or V2O3. Utility plants have had some success using this method to control vanadium ash corrosion. However, practical application of excess air control in refinery and chemical plant operations is difficult, and has not been particularly successful. Problems with particulates, smoke, pollution, and flame control are encountered unless the necessary expensive control systems and operator attention are constantly available. 

Another study of the variation of trace element concentrations with ashing time at 500°C in covered and uncovered platinum crucibles indicated that ashing time had no effect (Table V). As previously noted, the loss of boron from the uncovered crucibles stabilized at a relatively constant concentration in less than 5 hrs. Molybdenum and vanadium, which show losses with increasing temperatures, show no apparent ashing time dependence. 

The ultimate measurement of trap performance is if microactivity increases at constant fresh catalyst additions and metals levels or if the improved stability provides the flexibility to reduce additions or process higher vanadium containing feed. From an evaluation standpoint, it helps to have additional methods of determining success. 

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