Pyrocatecholate complexes

Shestakov, A.F. and Shilov, A.E. (2001) On the nuclearity of the vanadium(II)-pyrocatechol complex active in the reaction of molecular nitrogen reduction, Kinetics and Catalysis (Translation of Kinetika i Kataliz) 42, 653-656. 

An extractable (toluene) ion-associate of the aluminium-pyrocatechol complex and Brilliant Green is the basis of a very sensitive method (e = 2.4-10 ) [75]. 

Solvent extraction techniques are useful in the quantitative analysis of niobium. The fluoro complexes are amenable to extraction by a wide variety of ketones. Some of the water-insoluble complexes with organic precipitants are extractable by organic solvents and colorimetry is performed on the extract. An example is the extraction of the niobium—oxine complex with chloroform (41). The extraction of the niobium—pyrocatechol violet complex with tridodecylethylammonium bromide and the extraction of niobium—pyrocatechol—sparteine complex with chloroform are examples of extractions of water-soluble complexes. Colorimetry is performed on the extract (42,43). Colorimetry may also be performed directly on the water-soluble complex, eg, using ascorbic acid and 5-nitrosahcyhc acid (44,45). 

The results of the complexation study of Cu(II), Pb(II), Zn(II), Fe(III), Hg(II), Cd(II), Sn(IV), Zr(IV), Ti(IV) with arsenazo III, sulfonazo III, SPADNS, Eriochrome T, Acid Chrome Dai k Blue, Xylenol Orange, Methyl Thymol Blue, Pyrocatechol Violet, Chrome Azurol S, Eriochrome Cyanin R, Basic Blue K, Methyl Violet, Brilliant Green, Rhodamine C and Astraphoxin in solid phase. The obtained data ai e used for the working out of a new method of metal determination. 

Pyrocatechol Violet (tetraphenolictriphenylmethanesulfonic acid Na salt) [115-41-3] M 386.4, e 1.4 x 1(H at 445nm in acetate buffer pH 5.2-5.4, pKesi(i)>0 (SO3H), pK ,t(2) 9.4, pKEst(3) 13. It was recrystd from glacial acetic acid. Very hygroscopic. Indicator standard for metal complex titrations. [Mustafin et al. Zh Anal Khim 22 1808 1967.]... 

Pyrocatechol violet forms colored complexes with a variety of metal ions, the complexes are stable in differing pH ranges. 

Mono- and polyl dric phenols and enols frequently form characteristically colored complexes with Fe + ions [4, 28, 29]. Here monohydric phenols usually produce reddish-violet colors, while pyrocatechol derivatives yield green chelates [4]. Detection of acetone using Legal s test is based on the formation of an iron complex [4]. The same applies to the thioglycolic acid reaction of the German Pharmacopoeia (DAB 9) [4, 30]. 

Korenaga et al. [26] have described an extraction procedure for the spectrophotometric determination of trace amounts of aluminium in seawater with pyrocatechol violet. The extraction of ion-associate between the alu-minium/pyrocatechol violet complex and the quaternary ammonium salt,... 

Aluminium Extraction of pyrocatechol violet complex with chloroform Spectrophotometry at 590 nm < 0.1 xg/l [26]... 

The complex of Sn(IV) ions and pyrocatechol violet (2) in a flow system is concentrated on Sephadex QAE A-25 gel and subsequently determined by visible spectrophotometry at 576 nm. The linear range of the method is 2-40 pg/L with LOD 0.3 pg/L27a. 

It is known that the Ti complex acts as a reversible carrier of electrons from the cathode to the catalytically active Mo(III) complex in a Ti-Mo-pyrocatechol system for the electroreduction of CO on a mercury cathode [529]. 

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

The metal may he analyzed hy atomic absorption or emission spectrophotometry (at trace levels). Other techniques include X-ray diffraction, neutron activation analysis, and various colorimetric methods. Aluminum digested with nitric acid reacts with pyrocatechol violet or Eriochrome cyanide R dye to form a colored complex, the absorbance of which may be measured by a spectrophotometer at 535 nm. 

The neutral complexes Nil or NiL2B2 (B = py or ibipy) have been conveniently synthesized by reacting the quinone ligand and Ni(CO)4 in apolar solvents (n-pentane, n-hexane, benzene).1 0,1601 The use of anaerobic conditions gives the best results. In one case, that of Ni(C6H402)2, the complex was obtained by the peroxodisulfate oxidation of an aqueous solution of nickel(II) acetate and pyrocatechol. 

A particularly well-studied ligand is L-3,4-dihydroxyphenylalanine (l-DOPA) this may coordinate like alaninate or a pyrocatechol 700 Zn11 appears to favour binding to l-DOPA as to pyrocatechols.701 Formation constants have been measured for the ternary complexes Zn11 dopamine alanine/pyrocatechol702 and Zn11 l-DOPA L (L = penicillamine, L-alanine, glycine, 2,2 -bipyridine, citric add, tartaric acid or sulfosalicylic add). 3... 

In the presence of trace amounts of water, the tetrameric p,2-oxo complex (182) in 1,2-dimethoxyethane is transformed into a p, -oxo tetrameric complex (183 equation 254), characterized by an X-ray structure.574 In contrast, (182) 572,575 is inactive towards the oxidation of phenols. The reaction of N,N,N, AT -tetramethyl-l,3-propanediamine (TMP) with CuCl, C02 and dioxygen results in the quantitative formation of the /z-carbonato complex (184 equation 255).s76 This compound acts as an initiator for the oxidative coupling of phenols by 02. 6 Such jz-carbonato complexes, also prepared from the reaction of Cu(BPI)CO with 02 [BPI = 1,3 bis(2-(4-methyl-pyridyl)imino)isoindoline],577 are presumably involved as reactive intermediates in the oxidative carbonylation of methanol to dimethyl carbonate (see below).578 Upon reaction with methanol, the tetrameric complex (182 L = Py X = Cl) produces the bis(/z-methoxo) complex (185 equation 256), which has been characterized by an X-ray structure,579 and is reactive for the oxidatiye cleavage of pyrocatechol to muconic acid derivatives.580,581... 

In addition to the above method, based on the use of pyrocatechol violet, Tecator also describes a flow injection analysis for determining 0.5-0.5mg/l aluminium in soil extracts based on the measurement of the chromazurol-aluminium complex at 570 nm [4,5]. 

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