Pyrocatechol, also formation

On distillation at atmospheric pressure, vanillin undergoes partial decomposition with the formation of pyrocatechol. This reaction was one of the first to be studied and contributed to the elucidation of its stmcture. Exposure to air causes vanillin to oxidize slowly to vanillic acid. When vanillin is exposed to light in an alcohoHc solution, a slow dimerization takes place with the formation of dehydrodivanillin. This compound is also formed in other solvents. When fused with alkaU (eq. 3), vanillin (I) undergoes oxidation and/or demethylation, yielding vanillic acid [121 -34-6] (8) and/or protocatechaic acid (2). 

A-Benzoylphenylhydroxylamine (BPHA) reacts with Nb20 in bioling acidic aqueous solutions to yield a monomeric seven-coordinated niobium compound [NbO(BPHA)3]. The hydroxylamine ligand could be displaced by tropolone or 8-quinolinol, and the ratedetermining step was shown to be associative (equation 38).427 Oxoniobium and tantalum(V) 8-quinolinolates have also been reported. The optimal conditions for the formation and extraction of the [Nb0(C6H402)3]3 ion formed in the niobium(V)-pyrocatechol system, have been investigated.428... 

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... 

Aluminum is extracted from sea water into chloroform after complexation with pyrocatechol violet and the formation of an ion associate of the aluminum complex with zephiramine (tetradecyldimethylbenzylammonium chloride). With 5 ml of chloroform as much as 94.7% of the aluminum was separated from 110 ml of sea water, i.e. a 20-fold aluminum concentration could easily be achieved. Several ions, such as manganese, iron(II), iron(III), cobalt, nickel, copper, zinc, cadmium, lead, and uranyl also react with pyrocatechol violet and to some extent are extracted together with aluminum. However, the interferences of these ions and other metal ions present in sea water could be eliminated by masking with sodium diethyl-dithiocarbamate and 8-hydroxyquinaldine. In presence of these agents all the above metal ions except aluminum were extracted into chloroform51). 

In contrast to monohydric phenols, also non-alkylated pyiocatechol or hydro-quinone and their monomethyl derivatives are antioxidation effective. During the oxidation in water-alcoholic alkaline medium, 2,5-dihydroxy-l,4-benzoquinone CLII189 190,193 and 2-hydroxy-5-methyl-1,4-benzoquinone19 are formed from pyrocatechol and 4-methylpyrocatechol, respectively. The oxidation of 2-methyl-hydroquinone is more complex and more products are formed. Besides ion radicals CXXXVII and CXLI, also the ion radical CLIII was identified198 in the study of reaction mechanism. Intermediate CLIII corresponds to the formation of dimeric hydroxybenzoquinone CLIV. 

---