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Upstream product

• 553-97-9 2-Methyl-1,4-benzoquinone 
• 95-71-6 2-methylbenzene-1,4-diol 
• 59-50-7 4-Chloro-3-methylphenol 

Downstream Products

• 95-71-6 2-methylbenzene-1,4-diol 
• 553-97-9 2-Methyl-1,4-benzoquinone 

Relevant academic research and scientific papers

Radicals formed by Ultraviolet Irradiation of Substituted 4-Chlorophenols

Aqueous akaline solutions (pH 8) of (I) 2-methyl-4-chlorophenol, (II) 2-cyclohexyl-4-chlorophenol, (III) 2-benzyl-4-chlorophenol, (IV) 2,2'-methylene-bis-(4-chlorophenol), (V) 2-methoxy-4-chlorophenol, have been irradiated in situ with u.v. light and studied by electron spin resonance spectroscopy with a view to investigating further the free radicals formed by photoallergens with this basic chemical structure.Radical species were observed in all cases within minutes of irradiation.The radical spectra were interpreted and assigned as arising from substituted semiquinone radical anions, showing the initial replacement of the 4-chloro group with OH to give the corresponding hydroquinones.In the presence of oxygen, the hydroquinones are oxidised to the corresponding semiquinone radicals.There was no direct evidence of the presence of initial carbon-centred aryl radicals formed by the loss of chlorine; radicals of this type were, however, demonstrated by spin-trapping experiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO).

Electron Paramagnetic Resonance, ENDOR and TRIPLE Resonance Studies on Substitution Reactions of 2-Methyl-1,4-benzoquinone and 2,3-Dimethoxy-5-methyl-1,4-benzoquinone in Alkaline Methanol

Substitution of 2-methyl-1,4-benzoquinone wih methanol takes place in alkaline methanol, giving rise to methoxy-substituted methyl-1,4-benzoquinone radical anions.The relative signs and absolute values of the hyperfine coupling constants (hfcs) of the various mono-, di- and tri-substituted methoxymethyl-1,4-benzoquinones have been measured by EPR, ENDOR and TRIPLE resonance spectroscopy.The hfcs of OCH3 and CH3 protons had the same positive sign, except in the 3,5-dimethoxy-2-methyl-1,4-benzoquinone radical anion.The ENDOR signals of the methoxy protons could be distinguished from the methyl proton signals by using perdeuterated methanol as solvent.Partial optimization of the geometry of the radicals were performed by using the unrestricted MNDO method.In the most stable conformers the methoxyl groups had twisted out of the aromatic plane.INDO calculations were performed by using optimized structures, and the hfcs were compared with those obtained using standard bond lengths and angles.The hfcs of the ring protons were assigned by McLachian calculations and support of the assignment was provided by the additivity relationship method.The general TRIPLE technique allowed identification of the methyl, methoxy and ring protons of the different methoxy-substituted methyl-1,4-benzoquinone radical anions.

Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke

Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.

Electron transfer barriers for ground- and excited-state redox couples: trans-dioxo(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) osmium(VI)/osmium(V)

Pulse radiolysis methods were used to measure rate and equilibrium constants for the reaction of the OsVI(TMC)(O)22+/ OsV(TMC)(O)2+ couple with semiquinone/quinone couples, OsVI(TMC)(O)22+ + Q- ?caret; OsV(TMC)(O)2+ + Q, where TMC = tetramethylcyclam and Q is 1,4-benzoquinone or 2-methyl-1,4-benzoquinone. This work yields a self-exchange rate constant of 1.1 × 106 M-1 s-1 and a reduction potential of +0.048 V versus NHE for the dioxoosmium ground-state couple at 0.1 M ionic strength and 25°C. [Os(TMC)(O)2](PF6)2 crystallizes in the monoclinic space group, P21/c, with a = 6.712(2) A, b = 17.756(6) A, c = 10.150(2) A, β = 95.59(2)° and Z = 2. Single crystal X-ray diffraction results for the PF6- salt of the OsVI(TMC)(O)22+ indicate that the dominant isomer present in the crystal is the RSSR isomer in which one pair of N-methyl groups is 'up' while the other is 'down'. The average Os-O and Os-N distances are 1.735(6) and 2.126(8) A, respectively.

Entropy Changes and Electron Affinities from Gas-Phase Electron-Transfer Equilibria: A(-) + B = A + B(-)

By measuring the electron-transfer equilibria 1, A(-) + B = A + B(-), at 150 deg C with a pulsed electron high-pressure mass spectrometer we determined the ΔGo1 values involving 12 new compounds.Measurements of the temperature dependence of K1 for 21 reactions involving some of the new compounds and many compounds whose ΔGo1 had been determined previously led, via van't Hoff plots, to ΔHo1 and ΔSo1 values.These were interconnecting such that ΔHo and ΔSo continuous scales (ladders) were obtained.These were anchored to SO2 whose electron affinity is accurately known.Available geometries and vibrational frequencies for SO2 and SO2(-) permit the evaluation of So(SO2(-)) - So(SO2).Through the ΔSo scale the So(B(-)) - So(B) for the other compounds B could be obtained also.Certain regularities in the So(B(-)) - So(B) data permitted entropy estimates to be made also for compounds for which no van't Hoff plots were made.In this manner a table of ΔHo, ΔSo, and ΔGo data for the electron capture e + B = B(-) was obtained, which contains some 50 compounds B.Most of the compounds are substituted benzenes, quinones, conjugated acid anhydrides, and perfluorinated organics.