Bio-inspired quinone catalysis

Inspired by quinone-redox enzymes, small molecular quinone catalysts have been developed to promote C-H functionalization of amines. Recent efforts in this area have been summarized.     

Electrocoagulation of textile wastewater bearing disperse dyes

The paper describes a study on the removal of colour from textile wastewater bearing a mixture of three disperse dyes. The experiments were carried out in a reactor equipped with an Al sacrificial anode (100 cm2) and a stainless steel cathode of the same dimensions. Decolorisation occurred as a result of destabilisation of colloids due to an effect of an electric field generated between the electrodes (polarisation coagulation) and the reactions with coagulating compounds, formed in situ during anode oxidation (volumetric coagulation), followed by a subsequent flotation of agglomerates of the particles. During the study the following parameters were varied: initial pH of the solution, current density (between 100 and 300 A m-2) and an initial concentration of the dyes. The best results of elimination of colour, equal to 99%, were obtained during 5 minutes of treatment under the conditions of pH of 9 and the G factor equal to 41.     

Oxyfunctionalization of calixarene quinone rings

The epoxidation of quinone rings of calixquinones represents a valid route for the introduction of oxygenated functionalities into the de-tert-butylated calixarene walls originating cis-diepoxy-p-dione moieties. Carbonyl reduction of these systems leads to hybrid calixarenes containing dianhydroinositol moieties (calixinositols) belonging to the calixcyclitols family. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations and X-ray crystallography.     

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method.     

Synthesis of quinone derivatives of quinocarcin

O-Demethyl-DX-52-1 (3a) was prepared from quinocarcin (1) in two steps (cyanation and O-demethylation). Upon treatment with Fremy's salt, 3a and its esters 3b, 3c afforded the desired quinone 4-6 in good yields. Various substituted quinones 12-37, 47-50 were prepared from 4-6 by Thiele acetylation followed by hydrolysis of acetates and halogenation, by direct addition of amine, alcohol and mercaptan, and by epoxidation and subsequent opening of the epoxide ring with aniline. The quinonemonoketals 39b and 40 were obtained from the corresponding methoxyphenols 7b and 38b. Addition of hydroxylamine gave the quinoneoxime 44 regiospecifically. The antitumor activity of the bis-methylthioquinone (37) among the various derivatives was the most promising.     

Synthesis of quinone/hydroquinone sesquiterpenes

ent-Halimic acid has been used in the synthesis of the quinone/hydroquinone sesquiterpenes (−)-aureol, (−)-smenoqualone, (−)-neomamanuthaquinone and in the formal synthesis of (−)-cyclosmenospongine.     

Sterically congested adamantylnaphthalene quinone methides

Five new (2-adamantyl)naphthol derivatives (5-9, quinone methide precursors, QMP) were synthesized and their photochemical reactivity was investigated by preparative photolyses, fluorescence spectroscopy, and laser flash photolysis (LFP). Excitation of QMP 5 to S(1) leads to efficient excited state intramolecular proton transfer (ESIPT) coupled with dehydration, giving quinone methide QM5 which was characterized by LFP (in CH(3)CN-H(2)O, λ(max) = 370 nm, τ = 0.19 ms). On irradiation of QMP 5 in CH(3)OH-H(2)O (4:1), the quantum yield of methanolysis is Φ = 0.70. Excitation of naphthols QMP 6-8 to S(1) in CH(3)CN leads to photoionization and formation of naphthoxyl radicals. In a protic solvent, QMP 6-8 undergo solvent-assisted PT giving QM6 or zwitterion QM8 that react with nucleophiles delivering adducts, but with a significantly lower quantum efficiency. QMP 9 in a protic solvent undergoes two competitive processes, photosolvolysis via QM9 and solvent-assisted PT to carbon atom of the naphthalene giving zwitterion. QM9 has been characterized by LFP (in CH(3)CN-H(2)O, λ(max) > 600 nm, τ = 0.9 ms). In addition to photogenerated QMs, two stable naphthalene QMs, QM10 and QM11 were synthesized thermally and characterized by X-ray crystallography. QM10 and QM11 do not react with H(2)O but undergo acid-catalyzed fragmentation or rearrangement. Antiproliferative activity of 5-9 was investigated on three human cancer cell lines. Exposure of MCF-7 cells treated with 5 to 300 nm irradiation leads to an enhanced antiproliferative effect, in accordance with the activity being due to the formation of QM5.     

Synthesis of special pigments

Several TA methods (including dynamic TA, Q-TA, emanation and special conductometric TA) were used in investigations of condensed phosphate synthesis, and in the evaluation and control of the reactivity of the raw materials, when high-temperature stable pigments are developed. Conductometric TA occupies a special position because of its high sensitivity to most changes in crystal structure at the beginning of reactions.     

Photochemistry of ommochrome pigments

The ommochrome pigment present in the eyes of Loligo Vulgaris was extracted with a butanol-acetic acid-hydrochloric acid solution. The extraction mixture was examined before and after irradiation by visible light. A phenoxazinone ring opening together with a photo-induced solvent addition, causing a yellow-red batho-chromic shift, were observed and a plausible explanation of the process has been carried out and is reported on the basis of the isolated products.     

Carbon-13 NMR of quinone methides

The ¹³C NMR spectra of four ortho- and seven para-quinone methides were assigned using chemical shift and long-range carbon-proton coupling information. The carbonyl shifts are compared with those in ortho- and para-benzoquinones. The chemical shifts of the carbonyls of the p-quinone methides are observed at δ 186.2–186.4 for the three ortho-di-tert-butyl-substituted compounds and at δ 180.7–181.5 for the four ortho-oxy-substituted compounds. In the three o-quinone methides with meta, para-dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o-quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.     

Amine–quinone polyimides

Two dianiline monomers were prepared by the reaction of either 4,4′‐methylenedianiline or 4,4′‐oxydianiline with 1,4‐benzoquinone. These monomers were used to synthesize a series of amine–quinone polyimides by condensation with either 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride or 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride to make the corresponding polyamic acid. The polyamic acids were converted to the polyimides by thermal imidization at 290 °C. The amine–quinone polyimides gave freestanding films with tensile strengths in the range of 90 to 150 MPa and Young's moduli of 0.9 to 1.5 GPa. The thermal decomposition temperature under nitrogen was 440 to 480 °C and the glass‐transition temperature was in the range of 280 to 310 °C. The amine–quinone polyimides had the excellent thermal and mechanical properties that one expects for polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4044–4049, 2001     

Studies in the quinone field

The condensation of p-benzoquinone with substituted N-benzyl-β-aminocrotonic esters has been studied. A series of derivatives of 1-benzyl-5-hydroxyindole containing various substituents in the benzene nucleus of the benzyl radical has been obtained.     

On the Performance of Free Radicals Combined Electrocoagulation Treatment Processes

The electrocoagulation (EC) combined treatment processes have shown promising performances in which the removal of pollutants from industrial wastewater was greatly enhanced. The integration of a free radical producing step with EC has been considered as one of these new combinations that show synergy and improvements in the overall cleaning process performance. This review is devoted to discuss and analyze references on free radicals-assisted EC processes. Different combinations of free radical mechanisms were cited in the literature during the last two decades. They included ozone, advanced oxidation and ultrasound energy-assisted EC. It was noted that most of those studies were lab-scale processes that used synthetic wastewaters rather than real wastewaters. In addition the performances of those combined processes were improved compared to the EC process alone. This review considers the main parameters of free radical EC processes such as mechanisms, kinetic models, scale-up and cost estimation. Many concluding remarks were stated to give insights for possible future investigations. It seems from the results that the ozone-assisted EC is the most efficient combination since its removal efficiency is high in most applications. On the other hand, the combination of ultrasonic energy with EC was reported to reduce electrode passivation.     

Electrocoagulation of waterborne polymers in the presence of carbon black

Electrodeposition of paint is an electrochemical process, starting from water-borne polymers. The electrode reactions are water decomposition, leading to diffusion layers of an extreme pH. Coagulation of polymers proceeds in these layers as an acid / base reaction rather than as a direct discharge of macroions at the electrodes. The electrodeposited film behaves like a weak acid or alkaline ion exchanger. Under polarization, high electric field strength leads to charge separation and the formation of a double space charge. Current / voltage-behavior is nonlinear. The mechanism of charge transport is purely ionic. Resistivities are in the order of p = 10⁸ Ohm·cm in the wet film. The stoved film is an insulator. Electrodeposition of a second film is impossible. However, electrodeposition of the primary film in the presence of dispersed carbon black, studied in detail for the first time, leads to an appreciable electronic conductivity in the stoved film. ρ is in the order of 10⁵ - 10⁷ Ohm·cm even with a carbon black concentration of only a few wt.-%. This has been explained in terms of a stick percolation model and the preferential formation of transversal carbon black chains in the film. The relatively high resistivities found along these chains is due to the need of electron tunneling through ultrathin polymer films around the polymer wetted individual carbon black particles. Temperature behavior of resistivities, field effect and other proofs are given for this model. For practical application, the most important findung is the possibility of an electrodeposition of a coherent second layer and even of multilayers in the presence of only 1 - 5 wt.-% of an appropriate carbon black filler.     

Amine–quinone polyurethanes containing N‐alkylated amine–quinone monomers

A series of amine–quinone diol monomers, containing the 2,5‐diamino‐1,4‐benzoquinone group, were synthesized where the alkyl group on the amine was varied from methyl to ethyl to n‐propyl. Polyurethanes were prepared from these monomers by condensation polymerization in N,N‐dimethylformamide solution with toluene diiscyanate and poly(tetrahydrofuran) diol (M_n = 650). These amine–quinone polyurethanes were used as binders in metal particle tape. Samples were exposed to pH 2.0 aqueous buffer and the all amine–quinone polymers were shown to be superior in their ability to protect the iron particle against corrosion, relative to the commercial binders. There was no significant difference in the ability of the three amine–quinone polymers to inhibit corrosion. Clearly the increasing the steric bulk at the nitrogen did not affect their ability to inihibit corrosion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3284–3292, 2000