cas 2474-72-8, 2-hydroxy-1,4-benzoquinone | Articles data

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Phototransformation of resorcinol induced by excitation of nitrite and nitrate ions. II: nitrate ions
The excitation of nitrate ions in an aqueous solution of resorcinol (I) at pH = 5.5-6.5, leads to a mixture of 1,2,3-trihydroxybenzene (II), 1,2,4-trihydroxybenzene (III), 4-nitrosoresorcinol (V) and 4-nitroresorcinol (VII). A secondary formation of 2, 4-dinitrosoresorcinol (VI) was also detected.
Machado,Boule
p. 165 - 173
(1994)
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Catalytic mechanism of 5-chlorohydroxyhydroquinone dehydrochlorinase from the YCII superfamily of largely unknown function
Background:TftG is a YCII superfamily dehydrochlorinase that catalyzes conversion of 5-chlorohydroxyhydroquinone to hydroxybenzoquinone. Results:The TftG crystal structure in complex with product analog 2,5-dihydroxybenzoquinone illustrated the catalytic residues and mechanism. Conclusion:A His-Asp dyad and other conserved signature residues are implicated for catalysis and substrate binding. Significance:This is the first elucidation of a YCII superfamily protein mechanism, which helps explain their obscure nature.
Hayes, Robert P.,Lewis, Kevin M.,Xun, Luying,Kang, Chul Hee
p. 28447 - 28456
(2013)
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Kinetic studies of hydroxyquinone formation from water soluble benzoquinones
The kinetics and mechanisms of the redox reactions between hydrogen peroxide and 1,4-benzoquinone, 2-methyl-1,4-benzoquinone, 2,6-dimethyl-1,4- benzoquinone, 2-chloro-1,4-benzoquinone and 2,6-dichloro-1,4-benzoquinone were studied in aqueous media using spectrophotometric monitoring. The formation and decay of a hydroxylated 1,4-benzoquinone was detected. The formation of the intermediate was first order with respect to the parent 1,4-benzoquinone and hydrogen peroxide, whereas inverse first order dependence was revealed with respect to the hydrogen ion. The decomposition reaction had two parallel pathways: one was first order with respect to the intermediate, while the other showed second-order dependence. The values of the rate constant measured for the formation step were successfully correlated with both the redox potentials of the substituted quinone-hydroquinone systems and the pKa values of the hydroxylated quinone derivatives. Therefore, electronic effects govern the reactivity of the quinones in this process. NMR and GC-MS measurements were carried out to identify the products in the system. Quantum mechanical calculations were also carried out in these systems.
Jozsa, Eva,Purgel, Mihaly,Bihari, Marianna,Feher, Peter Pal,Sustyak, Gabor,Varnagy, Balazs,Kiss, Virag,Lado, Eszter,Osz, Katalin
p. 588 - 597
(2014)
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Synthesis, photochemical properties, and cytotoxicity of 10-alkylphenazin-2(10H)-ones
In the present study, the synthesis of a variety of 10-alkylphenazin-2(10H)-ones by oxidative coupling between N-alkylbenzene-1,2-diamine and 1,2,4-benzenetriol under an oxygen atmosphere was realized, and their photochemical and biological properties wer
Kohatsu, Haruki,Kamo, Shogo,Hosokai, Takuya,Kamisuki, Shinji,Machida, Yutaro,Kobayashi, Ryota,Kawasaki, Tsuneomi,Ohgane, Kenji,Kuramochi, Kouji
p. 871 - 885
(2021/05/19)

Two-Dimensional Layered Zinc Silicate Nanosheets with Excellent Photocatalytic Performance for Organic Pollutant Degradation and CO2 Conversion
Two-dimensional (2D) photocatalysts are highly attractive for their great potential in environmental remediation and energy conversion. Herein, we report a novel layered zinc silicate (LZS) photocatalyst synthesized by a liquid-phase epitaxial growth route using silica derived from vermiculite, a layered silicate clay mineral, as both the lattice-matched substrate and Si source. The epitaxial growth of LZS is limited in the 2D directions, thus generating the vermiculite-type crystal structure and ultrathin nanosheet morphology with thicknesses of 8–15 nm and a lateral size of about 200 nm. Experimental observations and DFT calculations indicated that LZS has a superior band alignment for the degradation of organic pollutants and reduction of CO2 to CO. The material exhibited efficient photocatalytic performance for 4-chlorophenol (4-CP) degradation and CO2 conversion into CO and is the first example of a claylike 2D photocatalyst with strong photooxidation and photoreduction capabilities.
Wang, Lan,Bahnemann, Detlef W.,Bian, Liang,Dong, Guohui,Zhao, Jie,Wang, Chuanyi
supporting information
p. 8103 - 8108
(2019/05/22)

Significant effect of 5,10,15,20-meso-tetraarylporphyrinatoiron(III) chloride/triflate and acidic/neutral/basic imidazolium ionic liquids in catalytic oxidation of phenols
The influence of acidic, neutral and basic ionic liquids and their binary mixture with dichloromethane on the reactivity of iron(III)porphyrins was investigated during oxidation of phenols with hydrogen peroxide catalysed by 5,10,15,20-tetraarylporphyrinatoiron(III) chloride and 5,10,15,20-tetraarylporphyrinatoiron(III) triflate. The generation of different intermediates of iron(III) porphyrin in different ILs was studied through viscosity, density, UV–Vis and 1H NMR spectroscopy. The heterolytic cleavage efficiency of (TAP)FeIII-OOH and formation of quinone using iron(III)porphyrin (TAP)FeIIICl with Cl atom as an axial ligand, is influenced by the structure of imidazolium moiety and the counteranion following the order [(CH2)4SO3HMIm]CF3COO > [Hmim]CF3COO > [bmim]TFA ?? negligible amount in [bmim]CF3SO3, [Hmim]CF3SO3, [bmim]BF4, [bmim]PF6 and [bmim]Cl. On the other hand, the heterolytic cleavage efficiency of (TAP)FeIII-OOH with iron(III)porphyrin (TAP)FeIIICF3SO3 with triflate as an axial ligand, was found in the following order [(CH2)4SO3HMIm]CF3SO3 > [Hmim]CF3SO3 > [(CH2)4SO3HMIm]CF3COO > [Hmim]CF3COO > [bmim] CF3COO > [bmim]PF6 ≈ [bmim]BF4 ≈ [bmim]CF3SO3, while epoxidation and polymerization were mainly observed in basic and neutral ILs. The reactive intermediates formed by the reaction of monooxygen donors with (TAP)FeIIICl varied with ILs, as (TAP)+?FeIV = O intermediate was dominated in acidic ILs, while (TAP)FeIV = O was formed in neutral ILs and (TAP)FeIII-OO– was formed in basic ILs.
Ahmad, Sohail,Gautam, Renu,Singhal, Anchal,Chauhan
p. 292 - 303
(2018/04/10)

A combined experimental and computational investigation on the unusual molecular mechanism of the lossen rearrangement reaction activated by carcinogenic halogenated quinones
The classic Lossen rearrangement is a wellknown reaction describing the transformation of an Oactivated hydroxamic acid into the corresponding isocyanate. In this study, we found that chlorinated benzoquinones (CnBQ) serve as a new class of agents for the activation of benzohydroxamic acid (BHA), leading to Lossen rearrangement. Compared to the classic one, this new kind of CnBQ-activated Lossen rearrangement has the following unique characteristics: (1) The stability of CnBQ-activated BHA intermediates was found to depend not only on the degree but also on the position of Cl-substitution on CnBQs, which can be divided into two subgroups. (2) It is the relative energy of the anionic CnBQ-BHA intermediates that determine the rate of this CnBQ-activated rearrangement, which is the rate-limiting step, and the Cl or H ortho to the reaction site at CnBQ is crucial for the stability of the anionic intermediates. (3) A pKa-activation energy correlation was observed, which can explain why the correlation exists between the rate of the rearrangement and the acidity of the conjugate acid of the anionic leaving group, the hydroxlated quinones. These findings may have broad implications for future research on halogenated quinoid carcinogens and hydroxamate biomedical agents.
Shan, Guo-Qiang,Yu, Ao,Zhao, Chuan-Fang,Huang, Chun-Hua,Zhu, Ling-Yan,Zhu, Ben-Zhan
p. 180 - 189
(2017/03/06)

Application of photoactive electrospun nanofiber materials with immobilized meso-tetraphenylporphyrin for parabens photodegradation
The pollution of aqueous environment by trace amounts of anthropogenic chemical substances has a hazardous impact on regular development of plants and animals as well as on human health. The paper presents the results of studies on the heterogeneous degradation of butyl- and benzylparaben in aqueous solutions using photochemically catalyzed processes. Meso-tetraphenylporphyrin (TPP) was immobilized in the polyurethane nanofiber material by electro-spinning method. The xenon lamp was used as a simulated sunlight source. The influence of various process parameters on reaction rate was investigated. The reuse of the carrier with the immobilized photosensitizer was examined. The major role of the singlet oxygen (1Δg) during the photodegradation was proved by using sodium azide and radical scavengers. The adsorption isotherms of parabens onto nanofiber material were determined using BET model. The kinetic study showed that the heterogeneous photodegradation of parabens could be modeled using Langmuir-Hinshelwood model and rate constants have been reported. The reaction pathway for the photodegradation of parabens via 1Δg was proposed.
Gmurek,Bizukoj?,Mosinger,Ledakowicz
p. 160 - 167
(2015/02/19)

Layered silicate as an excellent partner of a TiO2 photocatalyst for efficient and selective green fine-chemical synthesis
When the partial oxidation of benzene to phenol, which is one of the most important reactions in chemical industry, was conducted using TiO2 in the presence of a phenol-philic adsorbent derived from a layered silicate, phenol was recovered in u
Ide, Yusuke,Torii, Masato,Sano, Tsuneji
p. 11784 - 11786
(2013/09/02)

The influence of hydroquinone on tyrosinase kinetics
In vitro studies, using combined spectrophotometry and oximetry together with hplc/ms examination of the products of tyrosinase action demonstrate that hydroquinone is not a primary substrate for the enzyme but is vicariously oxidised by a redox exchange mechanism in the presence of either catechol, l-3,4-dihydroxyphenylalanine or 4-ethylphenol. Secondary addition products formed in the presence of hydroquinone are shown to stimulate, rather than inhibit, the kinetics of substrate oxidation.
Stratford, Michael R.L.,Ramsden, Christopher A.,Riley, Patrick A.
experimental part
p. 4364 - 4370
(2012/08/28)

Visible light photo-oxidation of model pollutants using CaCu 3Ti4O12: An experimental and theoretical study of optical properties, electronic structure, and selectivity
Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu3Ti4O12 has distinct octahedral Ti4+ and square planar Cu2+ sites and is thus a candidate material for this approach. The sol-gel synthesis of high surface area CaCu3Ti4012 and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO4 units within the structure of CaCu3Ti4O12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu 3Ti4O12 which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.
Clark, Joanna H.,Dyer, Matthew S.,Palgrave, Robert G.,Ireland, Christopher P.,Darwent, James R.,Claridge, John B.,Rosseinsky, Matthew J.
supporting information; experimental part
p. 1016 - 1032
(2011/04/15)

Three-dimensional organotin-hexacyanoferrate polymers as effective oxidizing reagents towards phenols
Three-dimensional organotin-hexacyanoferrate polymers of the type ∞3[(R3Sn)3Fe III(CN)6] where R = Me (I), n-butyl (II) and phenyl (III), represent members of the family of supramolecular coordination polymers (SCPs) which have zeolitic-like structure containing micropores. The structures of I-III contain wide channels capable of encapsulating resorcinol, which undergoes in situ oxidation to 1,3,4-trihydroxy benzene (THB) or p-nitrophenol (PNP), which converts to 1,4-benzoquinone (BQ) and 2-hydroxybenzoquinone (2-HBQ). The oxidation products were investigated by spectroscopic methods and by HPLC. The SCP III was found to be a more effective oxidizing reagent than I and II due to the presence of terminal Sn-OH2 groups hydrogen bonded to one-sixth of the terminal CN groups, causing more wide expandable channels. In addition, mechanisms of the oxidation processes of resorcinol and PNP have been proposed. Copyright
Etaiw, Safaa El-Din H.,Werida, Amal H.
experimental part
p. 805 - 808
(2011/06/20)

Detailed kinetics of the Fischer-Tropsch synthesis over Co-based catalysts containing sulphur
The effect of sulphur poisoning on the activity and selectivity in the Fischer-Tropsch synthesis of a Co/γ-Al2O3 catalyst, investigated in a previous work under conditions relevant to industrial operation, has been described in this work by means of a complete kinetic model, able to predict at the same time the CO conversion and the product distribution (paraffins and olefins from C1 to C50) on the basis of the process conditions and the amount of sulphur on the catalyst. To reach this goal, a mechanistic kinetic model, developed in a previous work for an unpoisoned catalyst, has been modified introducing the dependence on sulphur of the total number of catalytic active sites (to describe the progressive decrease of the catalyst activity with increasing sulphur loading on the catalyst), of the rate of the chain growth step (to describe the decrease of the selectivity to heavy products observed with sulphur-poisoned catalysts), and of the rates of paraffins and olefins formation from the growing adsorbed intermediate (to describe the variation of the olefin/paraffin ratio in the reaction products collected with the poisoned catalysts).
Visconti, Carlo Giorgio,Lietti, Luca,Tronconi, Enrico,Forzatti, Pio,Zennaro, Roberto,Rossinic, Stefano
experimental part
p. 202 - 209
(2010/12/18)

Photohydroxylation of 1,4-Benzoquinone in Aqueous Solution Revisited
In water, photolysis of 1,4-benzoquinone, Q gives rise to equal amounts of 2-hydroxy-1,4-benzoquinone HOQ and hydroquinone QH2 which are formed with a quantum yield of ψ=0.42, independent of pH and Q concentration. By contrast, the rate of decay of the triplet (λmax=282 and ～ 410 nm) which is the precursor of these products increases nonlinearly (k= (2→3.8)×106 s-1) with increasing Q concentration ((0.2→10) mM). The free-radical yield detected by laser flash photolysis after the decay of the triplet also increases with increasing Q concentration but follows a different functional form. These observations are explained by a rapid equilibrium of a monomeric triplet Q* and an exciplex Q2* (K=5500±1000m-1). While Q* adds water and subsequent enolizes into 1,2,4-trihydroxybenzene Ph(OH) 3, Q2* decays by electron transfer and water addition yielding benzosemiquinone .QH and .OH adduct radicals .QOH. The latter enolizes to the 2-hydroxy-1,4-semiquinone radical .Q(OH)H within the time scale of the triplet decay and is subsequently rapidly (microsecond time scale) oxidized by Q to HOQ with the concomitant formation of .QH. On the post-millisecond time scale, that is, when .QH has decayed, Ph(OH)3 is oxidized by Q yielding HOQ and QH2 as followed by laser flash photolysis with diode array detection. The rate of this pH- and Q concentration-dependent reaction was independently determined by stopped-flow. This shows that there are two pathways to photohydroxylation; a free-radical pathway at high and a nonradical one at low Q concentration. In agreement with this, the yield of Ph(OH)3 is most pronounced at low Q concentration. In the presence of phosphate buffer, Q* reacts with H2PO4-giving rise to an adduct which is subsequently oxidized by Q to 2-phosphato-1,4-benzoquinone QP. The current view that .OH is an intermediate in the photohydroxylation of Q has been overturned. This view had been based on the observation of the .OH adduct of DMPO when Q is photolyzed in the presence of this spin trap. It is now shown that Q*/Q2* oxidizes DMPO (k ≈1×108M -1S-1) to its radical cation which subsequently reacts with water. Q*/Q2* react with alcohols by H abstraction (rates in units of M-1S-1): methanol (4.2×10 7), ethanol (6.7×107), 2-propanol (13×10 7) and tertiary butyl alcohol (～0.2×107). DMSO (2.7×109) and O2 (～2×109) act as physical quenchers.
Von Sonntag, Justus,Mvula, Eino,Hildenbrand, Knut,Von Sonntag, Clemens
p. 440 - 451
(2007/10/03)

Copper(II)-mediated autoxidation of tert-butylresorcinols
Although copper(II)-mediated oxidation of phenols results in oxidative coupling rather than in oxygenation, it was recently reported that naturally occurring 5-alkylresorcinols undergo oxygenation in the presence of copper(II). To explore the generality of this reaction, the copper(II)-mediated autoxidation of 4-tert-butylresorcinol and 4,6-di-tert-butylresorcinol was investigated and was found to result in direct oxygenation at open activated positions and, at the tert-butyl-substituted positions, in oxygenation with competing loss of (as isobutylene) and 1,2-rearrangement of the tert-butyl group. 5-tert-Butyl-2-hydroxy-1,4-benzoquinone is the major product from both starting materials, and the final product mixture reflects, in part, coupling of metastable initially formed electrophilic and nucleophilic side products. Mechanisms that are consistent with the observed products and control reactions are proposed. The key step appears to be equilibration of a copper(II)-resorcinolate with a charge-transfer radical form that reacts regioselectively with O2 as prescribed by resonance.
Ling, Ke-Qing,Lee, Younghee,Macikenas, Dainius,Protasiewicz, John D.,Sayre, Lawrence M.
p. 1358 - 1366
(2007/10/03)

Ozonolysis of phenols in aqueous solution
In the ozonolysis of phenol in aqueous solution at pH 3, 7 and 10 the following products were quantified: catechol, hydroquinone, 1,4-benzoquinone, cis,cis-muconic acid, H2O 2, 2,4-dihydroxybiphenyl and 4,4-dihydroxybiphenyl. At pH 10, material balance (products vs. phenol consumption) is obtained. Singlet dioxygen, O2(1Δg), and OH are formed as short-lived intermediates. The precursor of the latter, O3-, and a phenoxyl radical is suggested to arise from electron transfer from phenol/phenolate to ozone. Addition of OH to phenol gives rise to dihydroxyclohexadienyl radicals which add dioxygen and eliminate HO2 thereby forming catechol/hydroquinone. In competition and catalysed by H+ and OH-, the dihydroxycyclohexadienyl radical eliminates water yielding a phenoxyl radical. At pH 10, they readily oxidise catechol and hydroquinone. This reforms phenol (accounting for the low phenol consumption) and yields higher-oxidised products, eventually 1,4-benzoquinone, cis,cis-Muconic acid can be accounted for by the Criegee mechanism, while O2(1Δg) is released on the way to (some of the) catechol and hydroquinone. Similar reactions proceed with hydroquinone (products: 1,4-benzoquinone, 2-hydroxy-1,4-benzoquinone and H2O2, with high yields of O2(1Δg) and OH) and with catechol (products: 2-hydroxy-1,4-benzoquinone, cis,cis-muconic acid, H2O2 with high yields of O2(1Δg) and OH). Material balance is not obtained for these two systems. Pentachlorophenolate, pentabromophenolate and 2,4,6-triiodophenolate ions give rise to halide ions, O2(1Δg) (58%/48%/10%) and OH (27%/2%/0%). It is suggested that together with O2(1Δg) the corresponding ortho- and para-quinones plus a halide ion are formed. Further halide ion is released upon the hydrolysis of these and other products. For pentachlorophenolate the material balance with respect to the short-lived intermediates is 85%. With the bromo- and iodophenolates the O2(1 Δg) yields are substantially lowered, most likely due to release of triplet (ground state) dioxygen induced by the heavy atom effect.
Mvula, Eino,Von Sonntag, Clemens
p. 1749 - 1756
(2007/10/03)

Photoprocesses of p-Benzoquinones in Aqueous Solution
The photochemistry of 1,4-benzoquinone (BQ) and several derivatives, for example, duroquinone, trimethyl-2,5- or 2,6-dimethyl-, and methyl-BQ in aqueous solution or mixtures with polar media, for example, acetonitrile or 2,2,2-trifluoroethanol, was studied by time-resolved UV-vis spectroscopy after pulses at 248 and 308 nm. The triplet state and the semiquinone radical (?QH/Q?-) of BQs are spectroscopically and kinetically separated intermediates. The radical yield in the absence of H-atom donors is low and significantly increased in the presence of alcohols. Efficient photoinduced charge formation, because of Q?- and H+ after H-atom transfer from 2-propanol to the triplet state, and small effects in the absence of a donor were observed by transient conductivity. The quantum yield of photodecomposition, λirr = 254 nm, is substantial for BQ, MeBQ, and Me2BQs in aqueous solution, but small for Me 4BQ. To account for the efficient photoconversion of BQs into hydrobenzoquinones and 2-hydroxy-1,4-benzoquinones, a novel water-mediated reaction not involving free radicals is proposed as major step. This mechanism is consistent with the prediction that the observed triplet state is monomeric and the yield of Q?-, detected by both transient absorption and conductivity, is low for sub-millimolar BQ, MeBQ, and Me2BQs at pH 5-6. In addition, H-atom abstraction from a polar organic solvent or by self-quenching plays a role in mixtures with water or at enhanced quinone concentration, respectively.
Goerner, Helmut
p. 11587 - 11595
(2007/10/03)

Regioselective oxidation of phenols to o-quinones with o-iodoxybenzoic acid (IBX)
Chemical equation presented An efficient regioselective method for oxidation of phenols to o-quinones is reported. When this procedure is combined with a subsequent reduction, it proves to be useful for the construction of a variety of catechols.
Magdziak, Derek,Rodriguez, Andy A.,Van De Water, Ryan W.,Pettus, Thomas R. R.
p. 285 - 288
(2007/10/03)

Photochemical behaviour of 1,4-dichlorobenzene in aqueous solution
Several photoproducts were identified in the direct photolysis of 1,4-dichlorobenzene (1,4-DCB) in air-saturated aqueous solution, namely 4-chlorophenol, hydroquinone, hydroxybenzoquinone, and 2,5-dichlorophenol. In the absence of oxygen the latter is not formed and phenol was detected, but the unexpected formations of 4,4′-dichlorobiphenyl, 2,4′,5-trichlorobiphenyl, and a terphenyl derivative are observed. Mechanisms are proposed to explain the formations of identified photoproducts. The phototransformation of 1,4-DCB may be photoinduced by NO3- or FeIII salts. The main primary product is 2,5-dichlorophenol, which results from a hydroxylation without dechlorination. Some other products have been identified in particular 4-chlorophenol and 2,5-dichlorobenzoquinone in the case of FeIII salts.
Meunier,Pilichowski,Boule
p. 1179 - 1186
(2007/10/03)

Synthetic analogs of ecteinascidin-743
The present invention is directed to the synthesis and characterization of compounds having the formula: wherein R1, R2, R3, R4, R5, R6, R7, R8 and R9 are each independently selected from the group consisting of H, OH, OR', SH, SR', SOR', SO2R', NO2, NH2, NHR', N(R)2, NHC(O)R', CN, halogen, =O, C(=O)H, C(=O)R', CO2H, CO2R', C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, and substituted or unsubstituted heteroaromatic; wherein each of the R' groups is independently selected from the group consisting of H, OH, NH2, NO2, SH, CN, halogen, =O, C(=O)H, C(=O)CH3, CO2H, CO2CH3, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, aryl, aralkyl, and heteroaromatic; wherein each dotted circle represents one, two or three optional double bonds; wherein R7 and R8 may be joined into a carbocyclic or heterocyclic ring system; and wherein X1 and X2 are each independently defined as above for R1-R8, and each further includes specific preferred groups as defined herein.
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(2008/06/13)

Photocatalytic degradation of 4-chlorophenol. 2. The 4-chlorocatechol pathway
The TiO2-mediated photocatalytic degradation of 4-chlorocatechol is studied as a branch of the degradation of 4-chlorophenol. In addition to some basic kinetic studies, the identities of many of the cyclic and acyclic intermediates, verified in most cases with authentic samples, are reported. From 4-chlorocatechol, the major product is hydroxylation to form 5-chloro- 1,2,4-benzenetriol. A small amount of 4-chloropyrogallol is also produced. Substitution to give 1,2,4-benzenetriol is observed as is oxidative cleavage of the C1-C2 bond to give the diacid. The major products of all of the triols are those of oxidative cleavages, occurring mainly between ortho hydroxy- substituted carbons to give diacids but also between one hydroxy and one unsubstituted carbon to give acid-aldehydes. Many smaller intermediates in the degradations are identified, and pathways are proposed for the larger compounds.
Li, Xiaojing,Cubbage, Jerry W.,Jenks, William S.
p. 8525 - 8536
(2007/10/03)

Study of the aqueous photochemistry of 4-fluorophenol, 4-bromophenol and 4-iodophenol by steady state and nanosecond laser flash photolysis
The mechanisms of the aqueous photoreactions of 4-fluorophenol, 4-bromophenol and 4-iodophenol have been studied by steady state photolysis and by nanosecond laser flash photolysis. The same photoproducts are obtained as were found in the photolysis of aqueous 4-chlorophenol although the photoreaction quantum yields vary considerably across the series of compounds. As for 4-chlorophenol the carbene 4-oxocyclohexa-2,5-dienylidene is formed from the halogenophenol by loss of HX and this species reacts efficiently with oxygen to form 1,4-benzoquinone O-oxide which subsequently yields 1,4-benzoquinone. Consideration of the reaction quantum yields together with the photophysical properties of the four halogenophenols suggests that the carbene is derived from the first excited singlet state rather than a triplet excited state.
Durand, Anne-Pascale,Brown, Robert G.,Worrall, David,Wilkinson, Francis
p. 365 - 370
(2007/10/03)

Hydrothermal formation of 1,2,4-benzenetriol from 5-hydroxymethyl-2-furaldehyde and D-fructose
Thermolysis of 0.05 M aqueous 5-hydroxymethyl-2-furaldehyde (HMF) at 27.5 MPa and 290 to 400°C led to the formation of 1,2,4-benzenetriol in yields of up to 46% at 50% HMP conversion. The reaction temperature and water density have a significant effect on the product composition. Pseudo-first-order reaction rate constants for HMF conversion under these conditions range from 0.107 to 0.308 min-1. For the region 290 to 350°C, the activation energy for HMF conversion was found to be 47.7 kJ.mol-1. When subjecting D-fructose to hydrothermolysis, the main products are HMF, 1,2,4-benzenetriol, and furfural. Thermolysis of 0.05 M aqueous 5-hydroxymethyl-2-furaldehyde (HMF) at 27.5 MPa and 290 to 400°C led to the formation of 1,2,4-benzenetriol in yields of up to 46% at 50% HMF conversion. The reaction temperature and water density have a significant effect on the product composition. Pseudo-first-order reaction rate constants for HMF conversion under these conditions range from 0.107 to 0.308 min-1. For the region 290 to 350°C, the activation energy for HMF conversion was found to be 47.7 kJ.mol-1. When subjecting D-fructose to hydrothermolysis, the main products are HMF, 1,2,4-benzenetriol, and furfural.
Luijkx,Van Rantwijk,Van Bekkum
p. 131 - 139
(2007/10/02)

Flash Photolysis-HPLC Method applied to the Study of Photodegradation Reactions
A new method, involving UV flash photolysis followed shortly by HPLC analysis of products, has been applied to the study of the partial photooxidation of 4-chlorophenol as an example of an oxidative photodegradation reaction of pollutants.
Lipczynska-Kochany, Ewa,Bolton, James R.
p. 1596 - 1597
(2007/10/02)

Long Optical Path Length Thin-Layer Spectroelectrochemistry. Catalytic Oxidation of Hydroquinones by Oxygen at Platinum
A clean, open-circuited Pt electrode, in the presence of dissolved oxygen, catalyzes the oxidation of hydroquinones in 1 M H2SO4.The oxidation rate is independent of hydroquinone, but dependent upon O2 concentration.If iodine is preadsorbed onto the Pt surface, the catalysis is inhibited, although reversible electron transfer to electrolyze the dissolved hydroquinone is not.
Gui, Yupeng,Kuwana, Theodore
p. 231 - 234
(2007/10/02)

Kinetics of the Reduction of a Tetra-μ-acetato-dirhodium Cation by Substituted 1,2- and 1,4-Dihydroxybenzene Compounds in Aqueous Perchlorate Media
The kinetics of the reduction of the tetra-μ-acetato-dirhodium cation, +(+), by substituted 1,2- and 1,4-dihydroxybenzene compounds (H2Q) have been investigated in aqueous perchlorate media.The observed rate equation (below) is interpreted in terms of a rate- -d+>/dt=2(k1+k2K1/+>)+> determining one-electron oxidation of H2Q or HQ- to a semiquinone radical intermediate.The rate constants for the cross-reactions are correlated with the semiquinone reduction potentials by means of the Marcus relationship.Self-exchange rate constants for the dihydroxybenzene/semiquinone and semiquinone/quinone couples are discussed in terms of the inner-sphere and solvent reorganization energies for electron exchange.
Herbert, John W.,Macartney, Donal H.
p. 1931 - 1936
(2007/10/02)

Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder
The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors in vestigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5.The products at the initial stage of the reaction were hydroquinone, pyrocatechol. 1,2,4-benzenetriol, pyrrogallol, and 2-hydroxy-1,4-benzoquinone.These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O.A reaction scheme involving hydroxyl radicals as real reactive species has been proposed.Although H2O2 was formed via O2(-) produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction.About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction.These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2(-).It was interesting from the viewpoint of wastewater treatment that phenol was completely mineralized to CO2 in the presence of TiO2 powder under solar irradiation without both aeration and mixing of the solution.
Okamoto, Ken-ichi,Yamamoto, Yasunori,Tanaka, Hiroki,Tanaka, Masashi,Itaya, Akira
p. 2015 - 2022
(2007/10/02)

Oxidative Decarbonylation of Phenolic Acids by Singlet Oxygen
Phenolic acids containing in addition to p-OH, at least one more activating OH/OCH3 group, on reaction with singlet oxygen generated by the dye-sensitized method, have been foud to undergo replacement of the carboxyl group by a hydroxyl.
Chibber, S. S.,Dutt, S. K.
p. 352 - 353
(2007/10/02)

PHOTOCHIMIE ET ENVIRONMENT II. PHOTOCHIMIE DES TRIPHENOLS EN SOLUTION AQUEUSE DILUEE
In aqueous solution the formation of phenoxy radicals from elecronically excited triphenols occurs through a primary photochemical process assisted by oxygen.Products observed in the photooxidation of triphenols are accounted by secondary reactions of these radicals.The nature of the major secondary processes depends on the triphenol under investigation.The phenoxy radicals formed from 1,2,4-trihydroxybenzene are poorly reactive with oxygen and disappear through a disproportionation.A fairly unstable hydroxybenzoquinone is formed.The corresponding phenoxy radicals of 1,2,3-trihydroxybenzene lead to purpurogallin and are oxidized into dihydroxybenzoquinone.The material balance in the photooxidation of the 1,3,5-trihydroxybenzene is poor; the radicals formed are readily oxidized and unstable oxidation products are formed.No accumulation of the primary photoproducts is observed in a long term photooxidation of triphenols.
Perbet, Gilles,Boule, Pierre,Lemaire, Jacques
p. 95 - 100
(2007/10/02)