- A chemical oscillator based on the photoreduction of 2-methyl-1,4- benzoquinone
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This study investigated bromate-2-methyl-1,4-benzoquinone photoreaction in a batch reactor, in which the photoreduction of 2-methyl-1,4-benzoquinone plays a vital role in initiating and sustaining the reaction process. Transient oscillatory phenomena are observed over broad reaction conditions, but a phase diagram in the bromate and sulfuric acid concentration plane shows that the nonlinear behavior is more sensitive to the ratio of bromate and acid than their absolute concentrations. Light intensity and the photosensitive substance 2-methyl-1,4-benzoquinone exhibited opposite effects on the induction time of these oscillations, implying that illumination does more than just reduce 2-methyl-benzoquinone. The oscillatory behavior has been qualitatively reproduced with a generic model developed for bromate-aromatic compounds systems.
- Amemiya, Takashi,Wang, Jichang
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Read Online
- Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria
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Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.
- Bruns, David L.,Musaev, Djamaladdin G.,Stahl, Shannon S.
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supporting information
p. 19678 - 19688
(2020/12/18)
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- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Regioselective synthesis of gentisyl alcohol-type marine natural products
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Gentisyl alcohol-type natural products, possessing various important biological properties, have been synthesized from 4-methoxyphenol by using a selective phenol monohydroxymethylation/monochlorination, a CAN oxidation and a sodium dithionite reduction as the key steps. The natural product synthesis is efficient, atom- and step-economical, and requires no protecting groups.
- Wang, Hong-Shuang,Li, Hui-Jing,Wang, Long-Fei,Shen, Zhi-Lun,Wu, Yan-Chao
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supporting information
p. 1891 - 1896
(2018/05/29)
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- METHOD AND AGENT FOR TRANSPORTING HYDROGEN
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To provide techniques for transporting hydrogen in which problems of energy loss and biological safety are mitigated.SOLUTION: Provided is an agent which is used when transporting hydrogen from location A to location B. This agent is a compound represented by general formula [I] in the figure.SELECTED DRAWING: Figure 1
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Paragraph 0038; 0039; 0040; 0041; 0048; 0049; 0050; 0051
(2019/05/22)
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- Direct Synthesis of Hydroquinones from Quinones through Sequential and Continuous-Flow Hydrogenation-Derivatization Using Heterogeneous Au–Pt Nanoparticles as Catalysts
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Pt–Au bimetallic nanoparticle catalysts immobilized on dimethyl polysilane (Pt–Au/(DMPSi-Al2O3)) have been developed for selective hydrogenation of quinones to hydroquinones. High reactivity, selectivity, and robustness of the catalysts were confirmed under continuous-flow conditions. Various direct derivatizations of quinones, such as methylation, acetylation, trifluoromethanesulfonylation, methacrylation, and benzoylation were successfully performed under sequential and continuous-flow conditions to afford the desired products in good to excellent yields. Especially, air-sensitive hydroquinones, such as anthrahydroquinones and naphthohydroquinones, could be successfully generated and derivatized under closed sequential and continuous-flow conditions without decomposition.
- Miyamura, Hiroyuki,Tobita, Fumiya,Suzuki, Aya,Kobayashi, Shū
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supporting information
p. 9220 - 9224
(2019/06/13)
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- The synthesis and evaluation of thymoquinone analogues as anti-ovarian cancer and antimalarial agents
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Thymoquinone (TQ), 2-isopropyl-5-methyl-1,4-benzoquinone, a natural product isolated from Nigella sativa L., has previously been demonstrated to exhibit antiproliferative activity in vitro against a range of cancers as well as the human malarial parasite Plasmodium falciparum. We describe here the synthesis of a series of analogues of TQ that explore the potential for nitrogen-substitution to this scaffold, or reduction to a hydroquinone scaffold, in increasing the potency of this antiproliferative activity against ovarian cancer cell lines and P. falciparum. In addition, alkyl or halogen-substituted analogues were commercially sourced and tested in parallel. Several TQ analogues with improved potency against ovarian cancer cells and P. falciparum were found, although this increase is suggested to be moderate. Key aspects of the structure activity relationship that could be further explored are highlighted.
- Johnson-Ajinwo, Okiemute Rosa,Ullah, Imran,Mbye, Haddijatou,Richardson, Alan,Horrocks, Paul,Li, Wen-Wu
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supporting information
p. 1219 - 1222
(2018/03/12)
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- Pyroline derivative, and preparation method and application thereof
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The invention discloses a pyroline derivative. The pyroline derivative has a chemical structural formula which is described in the specification. According to the invention, the pyroline derivative isobtained through an esterification reaction of pyroline and ibuprofen by using dicyclohexylcarbodiimide as a dehydrating agent and 4-dimethylaminopyridine as a catalyst in an alkaline environment provided by triethylamine. Acute toxicity test results show that the pyroline derivative provided by the invention is non-toxic, while pharmacodynamic test results show that the pyroline derivative provided by the invention has better anti-inflammatory and analgesic effects compared with pyroline, ibuprofen technical and a physical mixture of the pyroline and the ibuprofen technical with equivalent amounts, and has potential application in preparation of anti-inflammatory and analgesic drugs.
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Paragraph 0055; 0056; 0059-0060
(2018/06/15)
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- Pd0-PyPPh2@porous organic polymer: Efficient heterogeneous nanoparticle catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without extra oxidants and hydrogen acceptors
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In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh2@POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh2@POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh2@POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh2@POP polymer are themselves used as solid base over the Pd°-PyPPh2@POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K2CO3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts.
- Chen, Xingkun,Wang, Wenlong,Zhu, Hejun,Yang, Wenshao,Ding, Yunjie
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- Glycyrrhetinate and preparation method thereof and application thereof to preparation of antiviral medicine
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The invention discloses glycyrrhetinate. The glycyrrhetinate adopts a chemical structural formula as follows: FORMULA, and can be obtained by performing a reaction on pyroline and glycyrrhetinic acidin an oil-water two-phase system consisting of a water-insoluble organic solvent and an alkaline aqueous solution. The compound is almost non-toxic, has a relatively good therapeutic effect, which issuperior to that of the glycyrrhetinic acid, on chicken bursal disease, and can be used as a novel medicine for treating the chicken bursal disease.
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Paragraph 0050; 0053; 0054; 0055
(2018/07/30)
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- A O-methyl P-benzoquinone merabilite series of reducing agent for producing O-methyl hydroquinone method (by machine translation)
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A O-methyl P-benzoquinone merabilite series of reducing agent for producing O-methyl hydroquinone method, the O methyl hydroquinone in the extract, adding water, access sulfur series of reducing agent, the stirring reaction, sampling analysis, to the system in a non-adjacent methyl P-benzoquinone that to the end point of the reaction, the solution standing, extraction, get O-methyl hydroquinone extract, the reduction reaction to produce and mix the solution gets the extract for removing water through the pressure reducing and desolution of the extractant, ortho-methyl hydroquinone to the aqueous solution, and then by decolorization, concentrated under reduced pressure, cooling crystallization, drying to obtain the O-methyl hydroquinone product. This invention compared with the traditional process for preparing iron, mild reaction conditions, energy-efficient, clean and environmental protection, the conversion is high and the product quality is good, at the same time compared with the catalytic hydrogenation with palladium, short reaction time, low investment cost, product loss is small, and the reaction product sulfuric acid can be used as O-methyl aniline legal system to the benzoquinone raw material, more economic. (by machine translation)
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Paragraph 0009-0026
(2018/11/10)
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- Preparation method of methyl hydroquinone/2-methylhydroquinone as novel polymerization inhibitor
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The invention relates to a preparation method of methyl hydroquinone/2-methylhydroquinone as a novel polymerization inhibitor. The preparation method comprises the following steps: taking cheap o-cresol (I) as a starting raw material, taking green and environmentally-friendly hydrogen peroxide as an oxidizing agent and obtaining a methyl benzoquinone crude product (II) under the catalysis of suitable catalysts (Cat 1 and Cat 2) at a suitable temperature in a suitable organic solvent (Solvent 1) or a solvent-free solution; after simple filtration, extraction and separation, recovering the hydrogen peroxide and the catalysts (catalyst 1 and catalyst 2) for recycling and catalytically reducing the methyl benzoquinone crude product (II) through a suitable catalyst (Cat 3) and a solvent (Solvent 2) under a suitable temperature and hydrogen pressure to obtain methyl hydroquinone (III) as a target compound.
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Paragraph 0033-0046
(2020/02/07)
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- Catalytic Electrophilic Alkylation of p-Quinones through a Redox Chain Reaction
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Allylation and benzylation of p-quinones was achieved through an unusual redox chain reaction. Mechanistic studies suggest that the existence of trace hydroquinone initiates a redox chain reaction that consists of a Lewis acid catalyzed Friedel–Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. The addition of Hantzsch ester as an initiator improves the efficiency of the reaction.
- Xu, Xiao-Long,Li, Zhi
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supporting information
p. 8196 - 8200
(2017/06/30)
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- Enzyme-Catalysed Synthesis of Cyclohex-2-en-1-one cis-Diols from Substituted Phenols, Anilines and Derived 4-Hydroxycyclohex-2-en-1-ones
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Toluene dioxygenase-catalysed cis-dihydroxylations of substituted aniline and phenol substrates, with a Pseudomonas putida UV4 mutant strain and an Escherichia coli pCL-4t recombinant strain, yielded identical arene cis-dihydrodiols, which were isolated as the preferred cyclohex-2-en-1-one cis-diol tautomers. These cis-diol metabolites were predicted by preliminary molecular docking studies, of anilines and phenols, at the active site of toluene dioxygenase. Further biotransformations of cyclohex-2-en-1-one cis-diol and hydroquinone metabolites, using Pseudomonas putida UV4 whole cells, were found to yield 4-hydroxycyclohex-2-en-1-ones as a new type of phenol bioproduct. Multistep pathways, involving ene reductase- and carbonyl reductase-catalysed reactions, were proposed to account for the production of 4-hydroxycyclohex-2-en-1-one metabolites. Evidence for the phenol hydrate tautomers of 4-hydroxycyclohex-2-en-1-one metabolites was shown by formation of the corresponding trimethylsilyl ether derivatives. (Figure presented.).
- Boyd, Derek R.,Sharma, Narain D.,McIntyre, Peter B. A.,Stevenson, Paul J.,McRoberts, W. Colin,Gohil, Amit,Hoering, Patrick,Allen, Christopher C. R.
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p. 4002 - 4014
(2017/11/22)
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- Candida antarctica lipase B-catalyzed regioselective deacylation of dihydroxybenzenes acylated at both phenolic hydroxy groups
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Candida antarctica lipase B proved to be highly active in the deacylation of substituted hydroquinones and resorcinols acylated at both phenolic hydroxy groups. The deacylation reactions were much faster than the corresponding direct acylations of these dihydroxybenzenes catalyzed by the same lipase. More importantly, they took place generally in a markedly regioselective manner: the acyloxy group remote from the substituent was preferentially cleaved. The main or exclusive products obtained were the regioisomers of those produced through the direct acylation of the dihydroxybenzenes. In the case of alkyl-substituted hydroquinone derivatives, the regioselectivity increased with an increase in the bulk of the substituent. In the case of 4-substituted diacylated resorcinols, the 3-O-monoacyl derivatives were obtained generally as the sole products. Quite interestingly, some secondary alcohols proved to act as better acyl acceptors than the corresponding primary alcohols in these enzymatic deacylations.
- Miyazawa, Toshifumi,Hamada, Manabu,Morimoto, Ryohei
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- Biocatalytic One-Pot Synthesis of l-Tyrosine Derivatives from Monosubstituted Benzenes, Pyruvate, and Ammonia
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l-Tyrosine derivatives were obtained in >97% ee via a biocatalytic one-pot two-step cascade using substituted benzenes, pyruvate, and NH3 as starting materials. In the first step, monosubstituted arenes were regioselectively hydroxylated in the o-position by monooxygenase P450 BM3 (using O2 as oxidant with NADPH-recycling) to yield the corresponding phenols, which subsequently underwent C-C coupling and simultaneous asymmetric amination with pyruvate and NH3 using tyrosine phenol lyase to furnish l-DOPA surrogates in up to 5.2 g L-1. Instead of analytically pure arenes, crude aromatic gasoline blends containing toluene were used to yield 3-methyl-l-tyrosine in excellent yield (2 g L-1) and >97% ee.
- Dennig, Alexander,Busto, Eduardo,Kroutil, Wolfgang,Faber, Kurt
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p. 7503 - 7506
(2015/12/11)
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- Complex reaction dynamics in the cerium-bromate-2-methyl-1,4-hydroquinone photoreaction
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Spontaneous oscillations with a long induction time were observed in the bromate-2-methyl-1,4-hydroquinone photoreaction in a batch reactor, where removal of illumination effectively quenched any reactivity. A substantial lengthening of the oscillatory window and a dramatic increase in the complexity of the reaction behavior arose upon the addition of cerium ions, in which separate bifurcation regions and mixed mode oscillations were present. The complexity has a strong dependence on the intensity of illumination supplied to the system and on the initial concentrations of the reactants. 1H NMR spectroscopy measurements show that the photoreduction of 2-methyl-1,4-benzoquinone leads to the formation of 2-methyl-1,4-hydroquinone and the compound 2-hydroxy-3-methyl-1,4-benzoquinone. Spectroscopic investigation also indicates that the presence of methyl group hinders the bromination of the studied organic substrate 2-methyl-1,4-hydroquinone, resulting in the formation of 2-methyl-1,4-benzoquinone.
- Bell, Jeffrey G.,Green, James R.,Wang, Jichang
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p. 9795 - 9800
(2015/01/09)
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- Multitargeted drug development: Discovery and profiling of dihydroxy substituted 1-aza-9-oxafluorenes as lead compounds targeting Alzheimer disease relevant kinases
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Alzheimer disease (AD) turned out to be a multifactorial process leading to neuronal decay. So far merely single target structures which attribute to the AD progression have been considered to develop specific drugs. However, such drug developments have been disappointing in clinical stages. Multitargeting of more than one target structure determines recent studies of developing novel lead compounds. Protein kinases have been identified to contribute to the neuronal decay with CDK1, GSK-3β and CDK5/p25 being involved in a pathological tau protein hyperphosphorylation. We discovered novel lead structures of the dihydroxy-1-aza-9-oxafluorene type with nanomolar activities against CDK1, GSK-3β and CDK5/p25. Structure-activity relationships (SAR) of the protein kinase inhibition are discussed within our first compound series. One nanomolar active compound profiled as selective protein kinase inhibitor. Bioanalysis of a harmless cellular toxicity and of the inhibition of tau protein phosphorylation qualifies the compound for further studies.
- Tell, Volkmar,Mahmoud, Kazem Ahmed,Hilgeroth, Andreas,Holzer, Max,Herrmann, Lydia,Schaechtele, Christoph,Totzke, Frank
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p. 6914 - 6918,5
(2020/09/02)
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- The phototransformation of 4-chloro-2-methylphenoxyacetic acid under KrCl and XeBr excilamps irradiation in water
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The effect of UV radiation of a KrCl and a XeBr on the photodegradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) was studied. The main photoproducts were identified by gas chromatograph/mass spectrometry (GC/MS). The variation of chlorine-ion and active chlorine in MCPA aqueous solution exposed to excilamp radiation was also defined by analytical methods. Irradiation of MCPA solution with a KrCl excilamp emitting mainly at 222 nm yield 2-methylhydroquinone and lactone of 2-hydroxy-3-methyl-5-chlorophenoxyacetic acid as the main photoproducts. Irradiation of MCPA solution with a XeBr excilamp emitting mainly at 283 nm yield 2-methylhydroquinone as the main photoproduct. Biological processes are not suitable for MCPA removal due to low or total absence of biodegradability of this class of pollutants. Estimation of biodegradability of phototreated MCPA solution was carried out according to ratios of biological oxygen demand (BOD5) to chemical oxygen demand (COD). The biodegradability of MCPA solutions increased after irradiation.
- Tchaikovskaya, Olga N.,Karetnikova, Elena A.,Sokolova, Irina V.,Mayer, Georgy V.,Shvornev, Dmitry A.
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experimental part
p. 8 - 14
(2012/04/10)
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- Degradation of fenitrothion by ultrasound/ferrioxalate/UV system
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The sonochemical photodegradation of fenitrothion, which is one of phosphorothiate insecticides, was carried out in the presence of Fe(III) and oxalate. The degradation rate was strongly influenced by initial concentrations of Fe(III) and oxalate. An initial fenitrothion concentration of 10 mg L-1 was completely degraded after 30 min at pH 6 under the optimum conditions. Therefore, the photo-Fenton reaction combined with sonication in the presence of oxalate was available around neutral pH. The decrease of TOC as a result of mineralization of fenitrothion was observed during ultrasound (US)/ferrioxalate/UV process. In addition, the formations of nitrite and sulfate ions as end-products were observed during this degradation system. The decomposition of fenitrothion gave two kinds of intermediate products. The degradation mechanism of fenitrothion was proposed on the base of the evidence of the identified intermediates. Based on these results, US/ferrioxalate/UV system could be useful technology for the treatment of wastewater containing fenitrothion.
- Katsumata, Hideyuki,Okada, Toshiko,Kaneco, Satoshi,Suzuki, Tohru,Ohta, Kiyohisa
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experimental part
p. 200 - 206
(2010/11/18)
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- An efficient reduction of quinones by formate-palladium/carbon system
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Ammonium formate in presence of palladium-carbon is an efficient system for catalytic transfer hydrogenation of several functional groups under mild conditions. However, this system was not found effective for reduction of quinones to hydroquinones, although reduction could be effected with phosphinic acid, phosphinates or cyclohexene as donors. A reexamination of this reaction suggested that formates were good hydrogen donors in this reduction but the reaction was inhibited due to quinhydrone formation. A simple expedient of maintaining low concentration of quinone during catalytic transfer hydrogenation reduction gave excellent yields of the hydroquinone. Compared to formates, formic acid was found to be a poor hydrogen donor.
- Pande, Poorn Prakash
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experimental part
p. 2549 - 2553
(2010/11/05)
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- Spectral and GC-MS analysis of phototransformation of herbicides in water
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The phototransformation of 2,4-dichlorophenoxyacetic and 2-methyl-4-chlorophenoxyacetic acids in water was studied using the KrCl*(λrad 222 nm) and XeBr*(λrad 283 nm) excilamps as UV radiation source.
- Chaikovskaya,Sokolova,Karetnikova,Mal'Kov,Kuz'Mina
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experimental part
p. 396 - 401
(2009/07/10)
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- Secondary alcohols act as better nucleophiles than primary alcohols in the lipase-catalyzed regioselective deacylation of dihydroxybenzenes acylated at both phenolic hydroxyls
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Candida antarctica lipase B (CAL-B) was found to be highly regioselective as well as active in the deacylation of resorcinols and hydroquinones acylated at both phenolic hydroxyls. Contrary to expectation, secondary alcohols acted as better nucleophiles than primary alcohols in these enzymatic deacylations.
- Miyazawa, Toshifumi,Hamada, Manabu,Morimoto, Ryohei,Murashima, Takashi,Yamada, Takashi
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p. 8334 - 8337
(2008/03/14)
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- 2,5-Dihydroxybenzyl and (1,4-dihydroxy-2-naphthyl)methyl, novel reductively armed photocages for the hydroxyl moiety
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(Chemical Equation Presented) Irradiation of alcohols, phenols, and carboxylic acids "caged" with the 2,5-dihydroxybenzyl group or its naphthalene analogue results in the efficient release of the substrate. The initial byproduct of the photoreaction, 4-hydroxyquinone-2-methide, undergoes rapid tautomerization into methyl p-quinone. The UV spectrum of the latter is different from that of the caging chromophore, thus permitting selective irradiation of the starting material in the presence of photochemical products. These photoremovable protecting groups can be armed in situ by the reduction of photochemically inert p-quinone precursors.
- Kostikov, Alexey P.,Popik, Vladimir V.
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p. 9190 - 9194
(2008/03/14)
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- Processes for preparing benzoquinones and hydroquinones
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A process for the preparation of hydroquinone compounds comprising, reacting an aromatic hydroxy compound with an oxidizing agent in a biphasic solvent system. The reaction is carried out in the presence of a transition metal hydroxy phosphate catalyst to produce the corresponding hydroquinone compound.
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Page/Page column 4
(2008/06/13)
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- Synthesis of triprenylated toluquinone and toluhydroquinone metabolites from a marine-derived Penicillium fungus
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Two triprenylated toluquinone and toluhydroquinone marine fungal metabolites, 5-methyl-2-[(2′E,6′E)-3′,7′,11′-trimethyl-2′,6′,10′-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione and 5-methyl-2-[(2′E,6′E)-3,7,11-trimethyl-2′,6′,10′-dodecatrienyl]-1,4-benzenediol, were synthesized in four and five steps, respectively, from 2-methyl-1,4-benzoquinone. The synthesis extends the applicability of the oxidative ether cleavage of hydroquinone dimethyl ethers with argentic oxide under acidic conditions to include the oxidative demethylation of polyprenylated-1,4-dimethoxy-toluhydroquinones with a quantitative survival of the oxidation- and acid-sensitive polyprenyl side chain.
- Scheepers, Brent A.,Klein, Rosalyn,Davies-Coleman, Michael T.
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p. 8243 - 8246
(2007/10/03)
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- Simple, mild, and efficient method for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN3
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A simple, mild, and efficient method is presented for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN3 under neutral conditions in the presence of water. Copyright Taylor & Francis Group, LLC.
- Algi, Fatih,Balci, Metin
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p. 2293 - 2297
(2007/10/03)
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- Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke
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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.
- Chouchane, Salem,Wooten, Jan B.,Tewes, Franz J.,Wittig, Arno,Mueller, Boris P.,Veltel, Detlef,Diekmann, Joerg
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p. 1602 - 1610
(2008/12/22)
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- PROCESS FOR CONVERSION OF PHENOL TO HYDROQUINONE AND QUINONES
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The present invention relates to a process for the conversion of phenol to hydroquinone and quinones. More particularly this invention relates to a process for the oxidation of phenol to a mixture of 1,4-benzoquinone and hydroquinone using an oxidant in the presence of titanium superoxide as a reusable catalyst in a liquid phase condition.
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Page/Page column 7
(2008/06/13)
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- An easy two-step reduction of salicylic acids and alcohols to 2-methylphenols
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Salicylic acids and alcohols can be reduced to 2-methylphenols by a simple two steps procedure. Reaction conditions were optimized carrying out a study on the solvent effect and the amount of the reducing agent. The improved procedure resulted particularly useful in the synthesis of deuterated building blocks of biological interest. Georg Thieme Verlag Stuttgart.
- Mazzini, Francesco,Salvadori, Piero
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p. 2479 - 2481
(2007/10/03)
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- The hydrolysis of 4-acyloxy-4-substituted-2,5-cyclohexadienones: Limitations of aryloxenium ion chemistry
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The title compounds serve as potential precursors to aryloxenium ions, often proposed, but primarily uncharacterized intermediates in phenol oxidations. The uncatalyzed and acid-catalyzed decomposition of 4-acetoxy-4-phenyl-2,5-cyclohexadienone, 2a, generates the quinol, 3a. 18O-Labeling studies performed in 16O-H2O, and monitored by LC/MS and1 13C NMR spectroscopy that can detect 18O-induced chemical shifts on 13C resonances, show that 3a was generated in both the uncatalyzed and acid-catalyzed reactions by C alkyl-O bond cleavage consistent with formation of an aryloxenium ion. Trapping with N3- and Br- confirms that both uncatalyzed and acid-catalyzed decompositions occur by rate-limiting ionization to form the 4-biphenylyloxenium ion, 1a. This ion has a shorter lifetime in H2O than the corresponding nitrenium ion, 7a (12 ns for 1a, 300 ns for 7a at 30 °C). Similar analyses of the product, 3b, of acid- and base-catalyzed decomposition of 4-acetoxy-4-methyl-2,5-cyclohexadienone, 2b, in 18O-H2O show that these reactions are ester hydrolyses that proceed by Cacyl-O bond cleavage processes not involving the p-tolyloxenium ion, 1b. Uncatalyzed decomposition of the more reactive 4-dichloroacetoxy-4-methyl-2,5-cyclohexadienone, 2b′, is also an ester hydrolysis, but 2b′ undergoes a kinetically second-order reaction with N3- that generates an oxenium ion-like substitution product by an apparent SN2′ mechanism. Estimates based on the lifetimes of 1a, 7a, and the p-tolylnitrenium ion, 7b, and the calculated relative stabilities of these ions toward hydration indicate that the aqueous solution lifetime of 1b is ca. 3-5 ps. Simple 4-alkyl substituted aryloxenium ions are apparently not stable enough in aqueous solution to be competitively trapped by nonsolvent nucleophiles.
- Novak, Michael,Glover, Stephen A.
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p. 8090 - 8097
(2007/10/03)
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- Processes for preparing benzoquinones and hydroquinones
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A process for the preparation of benzoquinones and hydroquinones includes oxidizing an aromatic hydroxy compound with oxygen or an oxygen containing gas, a copper containing catalyst, and a promoter to form the benzoquonone. A reduction reaction is employed to form the hydroquinone.
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- Processes for preparing benzoquinones and hydroquinones
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A process for the preparation of benzoquinones and hydroquinones includes oxidizing an aromatic hydroxy compound with oxygen or an oxygen containing gas, a copper containing catalyst, and optionally a promoter to form the benzoquinone. A reduction reaction is employed to form the hydroquinone.
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- PROCESS FOR THE MONOALKYLATION OF DIHYDROXY AROMATIC COMPOUNDS
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A continuous process comprising: contacting a mixture comprising dihydroxy aromatic compound, water and an alkylating agent with a catalyst system in the presence of a flowing carrier gas, to form a mono alkylated dihydroxy aromatic compound, wherein the catalyst system is obtained by the calcination of a catalyst precursor system comprising a metal oxide precursor, a transition metal element and a pore former.
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Page/Page column 9-10
(2010/02/14)
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- Alkylation and acetal formation using supercritical alcohol without catalyst
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The aromatic ring alkylation of phenols, N-alkylation of aniline, O-alkylation of phenols and acetal formation from acetaldehyde or acetone were examined using supercritical (SC) alcohol without any catalyst. Highly selective syntheses of monoalkylated compounds were achieved for the aromatic ring alkylation and N-alkylation. The O-alkylation proceeded more preferentially than the aromatic ring alkylation for phenols which have a deactivating group. The acetal formation went on in more than 96% selectivity.
- Horikawa, Yoshiteru,Uchino, Yuki,Sako, Takeshi
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p. 232 - 233
(2007/10/03)
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- Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution
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The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.
- Goerner, Helmut
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p. 440 - 448
(2007/10/03)
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- Polymer electrolyte and process for producing the same
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A polymer electrolyte having, in a main chain, a structural unit represented by the following formula (1):-[Ar1-(SO2-N-(X+)-SO2-Ar2)m-SO2-N-(X+)-SO2-Ar1-O]- wherein Ar1 and Ar2 independently represent a divalent aromatic groups, m represents an integer of 0 to 3, and X+ represents an ion selected from hydrogen ion, an alkali metal ion and ammonium ion, which is excellent in proton conductivity, thermal resistance and strength. The polymer electrolyte is soluble in solvents and has excellent film forming property and recycling efficiency.
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- Supported metalated phthalocyanine as catalyst for oxidation by molecular oxygen. Synthesis of quinones and carbonyl compounds
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Supported metalated phthalocyanine on K1O or on lamellar zirconium phosphate catalyses the oxidation of hydroquinones (and phenols) into quinones. Some interesting natural napthoquinones were also prepared (Juglone, Menadione, Lawsone, Phthiocol). Supported metalated phthalocyanine was also used in re-oxidation by oxygen of palladium and ruthenium, in the Wacker oxidation of olefins into ketones, in the oxidation of cyclohexadiene and in oxidation of benzylic alcohols in aldehydes.
- Villemin, Didier,Hammadi, Mohamed,Hachemi, Messaoud
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p. 1501 - 1515
(2007/10/03)
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- Copper(II)-Catalyzed Reactions of Activated Aromatics
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The catalytic reaction of cis-bisglycinato copper(II) monohydrate in the presence of hydrogen peroxide leads to hydroxylation of phenol to give catechol and hydroquinone (1:1.2 ratio) in good yield. 2,6-Dimethylphenol can be hydroxylated by hydrogen peroxide and a catalytic amount of cis-bisglycinato copper(II) monohydrate to give an aggregate of 1,4-dihydroxy-2,6-dimethylbenzene and 2,6-dimethylphenol. A similar reaction of o-cresol gives 2,5-dihydroxytoluene. The reactivity of cis-bisglycinato copper(II) monohydrate in hydrogen peroxide with o-cresol is 4.5 times faster than that of a similar reaction by trans-bisglycinato copper(II) monohydrate. A catalytic reaction of cis-bisglycinato copper(II) monohydrate with aniline in aqueous hydrogen peroxide gives polyanilines in the form of pernigraniline with different amounts of Cu(OH)2 attached to them. The two major components of polyanilines obtained have Mn values of 1040 and 1500, respectively. Resistance of films of these polyanilines increases with temperatures from 40°C to a maximum value at 103°C and then decreases in the region of 103-150°C, showing the property of a thermoelectric switch. The aggregate prepared from hydroxylation of 2,6-dimethylphenol shows a similar property in the region of 30-180°C.
- Puzari,Baruah, Jubaraj B.
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p. 2344 - 2349
(2007/10/03)
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- Polymer pyrolysis and oxidation studies in a continuous feed and flow reactor: Cellulose and polystyrene
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A dual-zone, continuous feed tubular reactor is developed to assess the potential for formation of products from incomplete combustion in thermal oxidation of common polymers. Solid polymer (cellulose or polystyrene) is fed continuously into a volatilization oven where it fragments and vaporizes. The gas-phase polymer fragments flow directly into a second, main flow reactor to undergo further reaction. Temperatures in the main flow reactor are varied independently to observe conditions needed to convert the initial polymer fragments to CO2 and H2O. Combustion products are monitored at main reactor temperatures from 400 to 850 °C and at 2.0-s total residence time with four on-line GC/FIDs; polymer reaction products and intermediates are further identified by GC/MS analysis. Analysis of polymer decomposition fragments at 400 °C encompasses complex oxygenated and aromatic hydrocarbon species, which range from high-molecular-weight intermediates of ca. 300 amu, through intermediate mass ranges down to C1 and C2 hydrocarbons, CO, and CO2. Approximately 41 of these species are positively identified for cellulose and 52 for polystyrene. Products from thermal oxidation of cellulose and polystyrene are shown to achieve complete combustion to CO2 and H2O at a main reactor temperature of 850 °C under fuel-lean equivalence ratio and 2.0-s reaction time. A dual-zone, continuous feed tubular reactor is developed to assess the potential for formation of products from incomplete combustion in thermal oxidation of common polymers. Solid polymer (cellulose or polystyrene) is fed continuously into a volatilization oven where it fragments and vaporizes. The gas-phase polymer fragments flow directly into a second, main flow reactor to undergo further reaction. Temperatures in the main flow reactor are varied independently to observe conditions needed to convert the initial polymer fragments to CO2 and H2O. Combustion products are monitored at main reactor temperatures from 400 to 850°C and at 2.0-s total residence time with four on-line GC/FIDs; polymer reaction products and intermediates are further identified by GC/MS analysis. Analysis of polymer decomposition fragments at 400°C encompasses complex oxygenated and aromatic hydrocarbon species, which range from high-molecular-weight intermediates of ca. 300 amu, through intermediate mass ranges down to C1 and C2 hydrocarbons, CO, and CO2. Approximately 41 of these species are positively identified for cellulose and 52 for polystyrene. Products from thermal oxidation of cellulose and polystyrene are shown to achieve complete combustion to CO2 and H2O at a main reactor temperature of 850°C under fuel-lean equivalence ratio and 2.0-s reaction time.
- Park, Byung-Ik,Bozzelli, Joseph W.,Booty, Michael R.,Bernhard, Mary J.,Mesuere, Karel,Pettigrew, Charles A.,Shi, Ji-Chun,Simonich, Staci L.
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p. 2584 - 2592
(2007/10/03)
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- Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones
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Absorption spectra and rate constants for the disproportionate of 12 alkyl- and methoxy-substituted semiquinone anion free radicals (Q?-) produced by the one-electron reduction (using CO2?- as a reductant) of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation (using N3? as an oxidant) of the corresponding hydroquinones (QH2) were determined by pulse radiolysis in 50 mM sodium phosphate buffer, pH 7.40 at room temperature. Both spectral and kinetic characteristics of Q?- only moderately depended on whether Q?- was produced from Q or QH2. Spectra of benzosemiquinones display two peaks with maximum at 310-320 nm and ca. 430 nm with the ratio of about 2-2.5. Molar absorption coefficients were determined. Rate constants for Q?- disproportionation (2k1) were correlated with the nature of substituents. While 2k1 was scarcely affected by methyl substitution, Q?- containing isopropyl, tert-butyl and methoxy substituents were visibly more stable than non-substituted and methyl-substituted Q?-.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa,Saran, Manfred
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p. 1835 - 1840
(2007/10/03)
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- Redox reactions of phenylhydroquinone with quinones in water
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The reversible reaction of hydrogen transfer between phenylhydroquinone and quinones (p-benzo-quinone, chlorobenzoquinone, and methylbenzoquinone) was studied as depending on water pH and composition and the procedure for water pretreatment. A spectrophotometric technique for measuring low concentrations of phenylbenzoquinone produced in the reaction was developed, and the rate constants for the forward and back reactions and the equilibrium constants were calculated. The reaction rate increased drastically (by more than 4 orders of magnitude) as pH grew from 4 to 8. The dependence of the reaction rate in water on pH was explained by the formation of hydroquinone anions in the alkaline region. These anions are strong electron donors and readily react with quinone molecules. The mechanism of the redox reaction in the hydroquinone-p-benzoquinone system is considered in quantum-chemical terms.
- Kalnin'sh,Pavlova
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p. 1596 - 1600
(2007/10/03)
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- Hydroxylation of chlorotoluenes and cresols: a pulse radiolysis, laser flash photolysis, and product analysis study
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The reactions of ·OH, O·- and SO4·- with 2-, 3-, and 4-cresols were studied by pulse radiolysis, laser flash photolysis, and product analysis techniques. The rates of OH reaction with cresols are very high (k ≈ 1 × 1010 M-1 s-1), whereas O·- was found to be less reactive (k ≈ 2.4 × 109 M-1 s-1). The second-order rate constants for SO4·- reaction with cresols are in the range (3-6) × 109 M-1 s-1. The transient absorption spectra measured in OH reaction exhibited peaks in the range 295-325 nm with a red shift for the meta isomer. The absorption spectra obtained for O·- reaction with 2-cresol has a peak at 360 nm. The absorption spectra of the transient species in SO4·- reaction obtained by pulse radiolysis and flash photolysis techniques are similar, with absorption maxima centered around 290 and 390 nm in all three isomers. The intermediates formed in ·OH, O·-, and SO4·- reactions are assigned to OH adducts, substituted benzyl radicals, and radical cations, respectively.
- Choure,Bamatraf,Rao,Das,Mohan,Mittal
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p. 9837 - 9845
(2007/10/03)
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- Free-Radical Ring Expansion by one Carbon Atom by Decomposition of the Thiohydroxamic Esters of (1-Alkoxycarbonyl-2-oxocycloalkyl)acetic Acids
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A free-radical ring expansion by one carbon atom has been achieved by thermal decomposition of thiohydroxamic esters of (1-alkoxycarbonyl-2-oxocycloalkyl)acetic acids, 8.Thus, by decomposition of thiohydroxamic esters 8a-f in boiling toluene, ethyl 3-oxocycloalkenecarboxylates 9a-f are obtained as principal ring-enlarged products in 27-58percent yield; accompanied by ethyl 1-(4-methyl-2-thiazolylthio)-3-oxocycloalkane-1-carboxylates 10c,d (24percent yield) with the ring expanded by one carbon atom.Unrearranged ethyl 1-(4-methyl-2-thiazolylthiomethyl)-2-oxocycloalkane-1-carboxylates) 11a-f are formed as side products (8-17percent yield).Ring expansion involves the following sequence of reactions: 3-exo-cyclization (to C=O grup), cleavage of the cyclopropane ring, intermolecular addition to the thione group of thiohydroxamic esters and elimination reaction.
- Matovic, Radomir,Cekovic, Zivorad
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p. 483 - 488
(2007/10/03)
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- Thermodynamics of semiquinone disproportionation in aqueous buffer
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The thermodynamic parameters, Kdisp, ΔH° and ΔS°, controlling the disproportionation of semiquinones derived from 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 2-methylbenzoquinone (MBQ), menadione (MNQ), naphthazarin (NZQ) and quinizarin (QNZ), have been determined. Smaller disproportionation constants, Kdisp, are observed upon addition of a fused benzene ring to the semiquinone structure. Negative enthalpies and positive entropies of disproportionation govern the disproportionation equilibria. Addition of OH groups to the 5 and 8 positions in NQ?- displaces the disproportionation equilibrium to the semiquinone probably due to intramolecular hydrogen bonding.
- Alegria, Antonio E.,Lopez, Marcos,Guevara, Norberto
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p. 4965 - 4968
(2007/10/03)
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- Titanium Silicate Molecular Sieve (TS-1)/H2O2 induced Triphase Catalysis in the Oxidation of Hydrophobic Organic Compounds with Significant Enhancement of Activity and Para-Selectivity
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Triphasis conditions (solid and two immiscible liquid reactants) when compared with more commonly employed biphasic ones (solid and immiscible liquids along with a cosolvent), significantly enhance the catalytic activity and para selectivity in the hydroxylation/oxidation of various hydrophobic organic compounds (viz. toluene, anisole, benzyl alcohol, cyclohexanol etc.) over crystalline, microporous, titanium silicate, TS-1, using dilute H2O2 (30 masspercent, aq.).
- Bhaumik, Asim,Kumar, Rajiv
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p. 349 - 350
(2007/10/02)
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- REACTIONS OF IMINODIMAGNESIUM REAGENTS WITH 1,4-QUINONES: THEIR STRUCTURAL FACTORS GOVERNING THE MODES OF REACTIONS
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Reactions of benzo-, naphtho- and anthraquinone derivatives (unsubstituted and substituted) with aryliminodimagnesium and aryloxymagnesium of a weak electron-donating ability were studied.In addition to the reduction products (quinhydrones and hydroquinones), nuclear substitution and condensation (with =C=O) products were formed.The efficiency of single electron transfer (SET) from ArN(MgBr)2, evaluated by the relative values of the difference between the oxidation and reduction potentials of the reactants (ΔE=Eox-Ered), varies with the electron-accepting power of quinones. ΔE governs the modes of semiquinone appearance (ESR signals) and the relative amounts of the heat of reactions, reflecting the types and yields of the products.It is concluded that condensation products of both components are produced in the reactions of quinones with the lower SET efficiency by the presence of a fused benzene ring or MeO substituent.The structure-reactivity relationship proposed previously for reactions of various magnesium reagents is extended in the reactions with a variety of quinones even in cases of higher SET efficiency.
- Matsuo, Koji,Shiraki, Ryuji,Okubo, Masao
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p. 567 - 577
(2007/10/02)
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- Synthesis of (+/-)-6-hydroxy-3,4-dihydro-4,7-dimethylbenzo-1-pyran-2(H)-one, a tetranorsesquiterpenoid
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Synthesis of the title compound (1), a naturally occuring C11 coumarin, isolated from Heritiera ornithocephala Kosterm has been achieved.A probable biogenesis of 1 involving the mode of elimination of four carbon atoms of the sesquiterpenoid precursor 2 has been suggested.Preparation of benzo-1-pyran-4-ones 7 and 8 has also been reported.
- Nadkarni, K. K,Kamat, S. P.,Paknikar, S. K.
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p. 432 - 435
(2007/10/02)
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- Acid-catalyzed amino-migration of O-phenylhydroxylamines
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The mechanism of amino-migration of O-phenylhydroxylamine (1a) was studied. It was found that 1 rearranges to give 2-aminophenol (50%) and 4-aminophenol (7%) in trifluoroacetic acid (TFA). The predominance of the ortho rearrangement of 1 clearly distinguishes this process from the Bamberger rearrangement. From cross-coupling experiments employing stable isotopes, it was clarified that the ortho rearrangement proceeds intramolecularly and the para rearrangement involves both intra- and intermolecular processes. Good first-order kinetics were obtained for the rearrangement. The Hammett plot (σ+) with a large negative slope (ρ = -7.8) indicates that initial heterolytic N-O bond cleavage of 1 occurs and generates a positive charge on the oxygen atom with considerable delocalization into the aromatic ring. An ion-molecule pair involving a phenoxenium ion and an ammonia molecule as an intermediate rationalizes all of the results. In this pair, intramolecular combination to the ortho position proceeds preferentially over that to the para position. Formation of catechol and hydroquinone can be explained in terms of nucleophilic attack of TFA on the phenoxenium ion in a solvent-separated pair.
- Haga, Naoki,Endo, Yasuyuki,Kataoka, Ken-Ichiro,Yamaguchi, Kentaro,Shudo, Koichi
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p. 9795 - 9806
(2007/10/02)
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