Catechols copper catalysts

Reaction conditions Catalyst wt = 0.75 g phenol H2O2 = 3 1, mole reaction time = 8 h Temp = 353 K solvent = acetonitrile PBQ = para benzoquinone CAT = Catechol HQ = hydroquinone TON = moles of phenol converted per mole of copper in the catalyst... 

The development of catalysts for the efficient oxidation of catechol and its derivatives in water is topic of ongoing work in this laboratory. Towards this end, polyethylene glycol side-chains were incorporated in a pentadentate salen ligand to enhance the water solubility of the complexes derived thereof. A dinuclear copper(II) complex is found to catalyze the oxidation of 3,5-di-tert.-butylcatechol into 3,5-di-tert-butyl-o-benzoquinone more than twice as fast in aqueous organic solution as in purely organic solvents (ly,at/knon= 140,000). Preliminary data are discussed. 

Carboxy-3,5-dichlorophenyl diazo-nium chloride, 31, 97 Catalyst, ammonium acetate, 31, 25, 27 copper chromite, 31, 32 ferric nitrate, hydrated, 31, 53 piperidine, 31, 35 piperidine acetate, 31, 57 Catechol, 33, 74... 

In non-aqueous solution, the copper catalyzed autoxidation of catechol was interpreted in terms of a Cu(I)/Cu(II) redox cycle (34). It was assumed that the formation of a dinuclear copper(II)-catecholate intermediate is followed by an intramolecular two-electron step. The product Cu(I) is quickly reoxidized by dioxygen to Cu(II). A somewhat different model postulated the reversible formation of a substrate-catalyst-dioxy-gen ternary complex for the Mn(II) and Co(II) catalyzed autoxidations in protic media (35). 

The results were interpreted in terms of the model proposed by Balia and co-workers (36). It is reasonable to assume that the micelle formation produces a somewhat organized pattern of the metal centers and, due to the shortened distance between the copper(II) containing head groups, the coordination of catechol to two metal centers may increase the stability of the catalyst substrate complex. Perhaps, the same principles... 

While only tyrosinase catalyzes the ortho-hydroxylation of phenol moieties, both tyrosinase and catechol oxidase mediate the subsequent oxidation of the resulting catechols to the corresponding quinones. Various mono- and dinu-clear copper coordination compounds have been investigated as biomimetic catalysts for catechol oxidation [21,194], in most cases using 3,5-di-tert-butylcatechol (DTBC) as the substrate (Eq. 16). The low redox potential of DTBC makes it easy to oxidize, and its bulky tert-butyl groups prevent un-... 

The interest in catechol oxidase, as well as in other copper proteins with the type 3 active site, is to a large extent due to their ability to process dioxygen from air at ambient conditions. While hemocyanin is an oxygen carrier in the hemolymph of some arthropods and mollusks, catechol oxidase and tyrosinase utilize it to perform the selective oxidation of organic substrates, for example, phenols and catechols. Therefore, establishment of structure-activity relationships for these enzymes and a complete elucidation of the mechanisms of enzymatic conversions through the development of synthetic models are expected to contribute greatly to the design of oxidation catalysts for potential industrial applications. 

Catalyst, alumina, 34, 79, 35, 73 ammonium acetate, 31, 25, 27 boron tnfluonde etherate, 38, 26 copper chromite, 31, 32, 36, 12 cupric acetate monohydrate, 38, 14 cuprous oxide silver oxide, 36, 36, 37 ferric nitrate, hydrated, 31, 53 phosphoric acid, 38, 25 piperidine, 31, 35 piperidine acetate, 31, 57 Raney nickel, 36, 21, 38, 22 sulfuric acid, 34, 26 Catechol, 33, 74 Cetylmalonic acid, 34, 16 Cetylmalonic ester, 34,13 Chlorination, by sulfuryl chloride, 33, 45, 37, 8... 

METHYL STYRENE or 3-METHYL STYRENE or 4-METHYL STYRENE or m-METHYL STYRENE or p-METHYL STYRENE mixed Isomers (25013-15-4) C,H,o Flammable liquid. Forms explosive mixture with air (flash point 125°F/51°C). An inhibitor, usually 10 to 50 ppm of tert-butyl catechol, must be present in adequate concentrations to avoid explosive polymerization. Violent reaction with strong oxidizers, strong acids, peroxides and hydroperoxides. Incompatible with catalysts for vinyl or ionic polymers aluminum, aliuninum chloride, ammonia, aliphatic amines, alkanolamines, caustics, copper, halogens, iron chloride, metal salts (e.g., chlorides, iodides, sulfates, nitrates). The uninhibited monomer vapor may block vents and confined spaces by, forming a solid polymer material. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or CO extinguishers. a-METHYL STYRENE (98-83-9) C,H, Flammable liquid. Forms explosive mixture with air [explosion limits in air (vol %) 0.9 to 6.1 flashpoint 129°F/54°C autoignition temp 1066°F/574°C Fire Rating 2]. Easily polymerizable. Unless inhibited, forms unstable peroxides. Reacts with heat and/or lack of appropriate inhibitor concentration. Reacts with catalysts for vinyl or ionic polymerization, such as aluminum, iron chloride or 2,5-dimethyl-2,5-di(ieri-butylperoxy)hexane. Violent reaction with... 

The hydroxylation of DPQ (steps F-H in Figure 7) is mimicked by the copper(II)-catalyzed aqueous autooxidation of 4-alkylcatechols to 2-alkyl-5-hydroxybenzoquinones (Figure 10). The role of the catalyst here is to promote oxidation of the catechol precursor the subsequent hydrolysis step is promoted by base, but not by copper. Interestingly, the hydrolysis is in fact a result of 1,4-addition of H2O2 to C5 of the catechol, rather than H2O (Figure 10) " H2O2 is produced in the reaction mixture as a by-product of catechol oxidation. Hence, this apparently simple synthetic reaction does not accurately model the biogenesis of TPQ, in which the C2 O atom in the final product is derived from water. 

Some mononuclear Cu(II) complexes have been also reported to act as catalysts in the catechol oxidation 146,151,165). The efficiency of these systems is very low and in general it is always possible that the actual species responsible for catechol oxidation is a dimeric species resulting from aggregation of two mononuclear units, as it has been recently shown for an amino-carbohydrate-copper(II) system 156). 

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