Variamin Blue

Variamine blue (C.I. 37255). The end point in an EDTA titration may sometimes be detected by changes in redox potential, and hence by the use of appropriate redox indicators. An excellent example is variamine blue (4-methoxy-4 -aminodiphenylamine), which may be employed in the complexometric titration of iron(III). When a mixture of iron(II) and (III) is titrated with EDTA the latter disappears first. As soon as an amount of the complexing agent equivalent to the concentration of iron(III) has been added, pFe(III) increases abruptly and consequently there is a sudden decrease in the redox potential (compare Section 2.33) the end point can therefore be detected either potentiometrically or with a redox indicator (10.91). The stability constant of the iron(III) complex FeY- (EDTA = Na2H2Y) is about 1025 and that of the iron(II) complex FeY2 - is 1014 approximate calculations show that the change of redox potential is about 600 millivolts at pH = 2 and that this will be almost independent of the concentration of iron(II) present. The jump in redox potential will also be obtained if no iron(II) salt is actually added, since the extremely minute amount of iron(II) necessary is always present in any pure iron(III) salt. 

The visual detection of the sharp change in redox potential in the titration of an iron(III) salt with EDTA is readily made with variamine blue as indicator. 

Procedure. Prepare the indicator solution by dissolving 1 g variamine blue in 100 mL de-ionised water as already pointed out (Section 10.48), variamine blue acts as a redox indicator. 

BPR = bromopyrogallol red FSB = fast sulphone black F M = murexide MTB = methylthymol blue SB = solochrome black TPX = thymolphthalexone VB = variamine blue XO = xylenol orange. 

Iron (III) solution, 0.05M. Dissolve about 12.0 g, accurately weighed, of ammonium iron(III) sulphate in water to which a little dilute sulphuric acid is added, and dilute the resulting solution to 500 mL in a graduated flask. Standardise the solution with standard EDTA using variamine blue B as indicator (Section 10.56). 

Variamine blue B hydrochloride 0.712J 0.310 1.5-6.3 Colorless to blue... 

Goto et al. (2004) measured the reaction kinetics of one-electron oxidation of A -methyl-p-anisidine in AN. In the electrode process, oxidation was performed at the platinum disk-shaped anode, in the chemical process, by means of the tris(p-bromophenyl)amine cation-radical. In both the cases, after one-electron oxidation, dimerization took place leading to the formation of the dye variamine blue. According to the kinetic data, the mechanism of this dye formation is different in the electrode and chemical processes (see Scheme 2.34). Namely, in the electrode oxidation, the cation-radical appears to be surrounded by a huge amount of the initial (nonoxidized) A-methyl-p-anisidine... 

Variamine Blue RT (salt) [4477-28-5] M 293.3, Xmax 377 nm. Dissolved lOg in 100ml of hot water. Sodium dithionite (0.4g) was added, followed by active carbon (1.5g) and filtered hot. To the colourless or slightly yellow filtrate a soln of saturated NaCl was added and the mixture cooled. The needles were filtered off, washed with cold water, dried at room temperature, and stored in a dark bottle. [Erdey Chem Analyst 48 106 1959]. 

Bathophen,b bathophen sulfonic acid, TPT,b bipy, phen, variamine blue Oxinec... 

A-Benzoyl-A-phenylhydroxylamine, variamine blue, vanadox, PAN,b PAR,b TTAb... 

The redox potential of an indicator depends strongly on pH because hydrogen ions are directly involved in the redox process, as the following example of Variamine Blue (7 C.I. 37255) shows. 

In the presence of a small amount of ascorbic acid, the I2 formed is reduced back to iodide. When all the ascorbic acid is consumed, iodine is liberated, and the sudden appearance of iodine can be made visible with variamine blue (Landolt effect). The time to the appearance of iodine is measured. The reaction of hydrogen peroxide and iodide is much faster in the presence of molybdate, probably because of the reactions... 

Eugenol and thymol can also be qualitatively detected on silica gel by use of visualizing reagents based on a saturated aqueous solution of variamine blue hydrochloride." ... 

More recently, the detailed kinetics of the decay reaction of p-anisidine radical cations 68a+ in ACN was investigated by the ETSF method66 using spectral analysis of 68a+ (absorption band at 450 nm) and products variamine blue dication 72a2+ (absorbance at 580 nm) and radical cation 72a+ (absorbance at 595 nm). Contrary to previous results of Simon and coworkers65 in DMF, the formation of dication 72a2+ as well as of radical cation 72a 1 was observed with the overall stoichiometry shown in equations 4a and 4b. 

Perchlorate ions form extractable ion-associates with basic dyes such as Brilliant Green (e= 9.4-10 ) [34,35], Malachite Green [36,37], Crystal Violet [38], Methylene Blue [39], and the oxidized form of Variamine Blue [40]. Chloroform, dichloroethane, benzene, nitrobenzene and toluene have been used as extractants. Perchlorate impurities in potassium chlorate have been determined by these sensitive methods [34]. The FIA technique has been applied in the determinations [35]. 

N-(p-Methoxyphenyl)-p-phenylenediamine, N-(4-Aminophenyl)-p-anisidine 1,4-Benzenediamitie, N-(4-methoxyphenyl)- EINECS 202-962-9 N-(p-Methoxy-phenyl)-p-phenylenediamine Variamine Blue Base. Us in nnanufacture of azoic dyestutfe. Crystals tup = 102° bpi2 = 238°. Hoechst AG. 

Redox indicators include indophenols for example, 2,6-dichlorophenolindophenol azine dyes such as the well-known thiazine dye methylene blue indigo carmine and other indigo derivatives derivatives of diphenylamine including diphenylamine-4-sulfonic acid and variamine blue and the 1,10-phenanthro-line-ferrous complex. 

Most organic redox indicators contain groups that can ionize (e.g., OH, NH) or can be protonated (e.g., amine N, ketonic O). As pH is changed, the specia-tion of the oxidized and reduced form of the indicator can change, depending upon the pK values of these acid/base groups. Thus for variamine blue, there are two nitrogen atoms that can be protonated or not. For the reduced indicator, any of (4-6) can be present. 

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