- Superoxo radical scavenging action by common analgesic drug paracetamol: A model kinetic study
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In acid perchlorate media ([H+] = 1.0-3.0 M), each mole of paracetamol, HOC6H4NHCOCH3 (APAP), at ambient temperature quantitatively reduces two mole of the metallo-superoxo complex, μ-superoxo-bis[pentaamminecobalt(III)]5+, [(NH3)5Co(III)(μ- O2)Co(III)(NH3)5]5+ (1). Here, complex 1 is reduced to [(NH3)5Co(OH2)]3+, Co2+, O2 and NH4+ and APAP itself is oxidised to quinone oxime and acetic acid. With a large excess of APAP over 1, the reduction follows first-order kinetics. The observed first-order rate constant (ko) increases linearly with increasing [H+] as well as with TAPAP (TAPAP being the analytical concentration of APAP). The protonated form of APAP, viz. APAPH+ seems to be the kinetically reactive reductant species. The enrichment of aqueous reaction media with D2O retards the reaction and thus it appears that the reaction proceeds through an electroprotic mechanism. A relatively small ΔH≠ (57 ± 2 kJ M 1) and moderately negative ΔS≠ (-68±8JK 1 M 1) supports a compact transition state.
- Singh, Bula,Das, Ranendu Sekhar,Banerjee, Rupendranath,Mukhopadhyay, Subrata
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- Kinetics and Mechanism of Rapid Oxidation of Acetaminophen by Sodium Periodate in the Presence of Catalyst
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Abstract: Kinetic studies of the novel oxidation of acetaminophen by sodium periodate are discussed with an emphasis on structure and reactivity by using kinetic approach. The reactions were catalyzed by Os(VIII). The kinetics of the reaction was studied as a function of temperature, ionic strength, dielectric constant of the medium, concentrations of the salt and the added reaction product to learn the mechanism of the reaction. The active species of catalyst and oxidant have been identified. Activation parameters have also been evaluated using the Arrhenius and Eyring plots. A suitable mechanism consistent with the observed kinetic results has been suggested and the related rate law deduced.
- Gupta, Madhu,Srivastava, Amrita,Srivastava, Sheila
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p. 1143 - 1151
(2021/06/21)
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- Preparation method of P-benzoquinone dioxime
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The preparation method of p-benzoquinone dioxime generates intermediate p-benzoquinone monooxime and byproduct alcohol under the action of an acid reaction promoter, and the intermediate is directly reacted with hydroxylamine hydrochloride to generate p-benzoquinone dioxime. The discharge of production waste water is reduced, and the requirement of green color production is met. The by-product ethanol obtained by nitrosation reaction can be finally recovered by distillation together with an organic solvent, so that the utilization rate of raw materials is improved. The whole synthesis process adopts an inert gas to isolate air, avoids the disproportionation and decomposition and intermediate of ethyl nitrite, reduces the generation of side reactions, improves the conversion rate of the reaction, and further improves the yield and purity of the benzoquinone dioxime, the yield is 85.0% - 95.0%, the purity ≥ 99.0 wt % and the melting point are 250 °C - 255 °C.
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Paragraph 0061-0070; 0078-0087; 0095-0104
(2021/12/07)
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- Copper-mediated nitrosation: 2-nitrosophenolato complexes and their use in the synthesis of heterocycles
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A simple protocol yielding ortho-substituted nitrosophenols from phenols is demonstrated, in the form of copper(II) bis(nitrosophenolato) complexes. The developed methodology was applied to a range of substrates, confirming the role of the copper in both the formation and protection of the challenging 1, 2-substitution pattern. Using polymer supported thiourea, the Cu could be stripped from the complexes and thus enabled the isolation or identification of the uncoordinated ligands and their decomposition products, in yields generally low in line with the intrinsic high reactivity of 2-nitrosophenols. The product complexes are useful intermediates as demonstrated in revisiting a formal [4 + 2] cycloaddition with dimethylacetylene dicarboxylate to synthesise bicyclic products in variable yields, revealing the product has a novel structure different from those previously reported in the literature.
- Nicholls, Alexander J.,Batsanov, Andrei S.,Baxendale, Ian R.
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- The Diels-Alder reactions of para-benzoquinone nitrogen-derivatives: An experimental and theoretical study
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An experimental and theoretical study of the comparative reactivity and selectivity of the Diels-Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent parabenzoquinones. DFT calculations support these experimental results.
- Uliana, Marciana P.,Servilha, Bruno M.,Alexopoulos, Olga,De Oliveira, Kleber T.,Tormena, Cláudio F.,Ferreira, Marco A.B.,Brocksom, Timothy J.
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p. 6963 - 6973
(2015/11/09)
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- Synthesis of sterically hindered polychlorinated biphenyl derivatives
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A series of sterically hindered (methoxylated) polychlorinated biphenyl derivatives were synthesized using the Suzuki and the Ullmann coupling reactions. The Suzuki coupling with Pd(dba)2-dicyclohexylphosphino-2,6- dimethoxybiphenyl (DPDB) gave better yields (65-98%) compared to the classic Ullmann coupling reaction (20-38%). Despite the reactive catalyst system, no significant coupling with aromatic chlorine substituents was observed. Crystal structure analysis of four PCB derivatives revealed solid state dihedral angles ranging from 69.7 to 81.0, which indicates that these highly ortho-substituted PCB derivatives have some conformational flexibility. Georg Thieme Verlag Stuttgart.
- Joshi,Vyas,Duffel,Parkin,Lehmler
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scheme or table
p. 1045 - 1054
(2011/06/20)
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- An efficient tandem oxidative-protection reaction of benzylic alcohols to corresponding arylhydrazones and oximes
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A mild and efficient one-pot synthesis of hydrazones and oximes from the reaction of the oxidation product of benzyl alcohols and phenols by 3,6-bis(triphenylphosphonium)cyclohexene dichromate with phenylhydrazine, 2,4-dinitrophenylhydrazine, and hydroxylamine is described. Copyright Taylor & Francis Group, LLC.
- Badri, Rashid,Shushizadeh, Mohammad Reza
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p. 601 - 605
(2007/10/03)
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- Reactivity of phenolic nucleophiles towards nitroso compounds
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The reactivities of a series of mono- and poly-phenolic ambident nucleophiles with the ambident electrophile N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) were studied.Reaction with the MNTS sulfonyl group afforded the corresponding sulfonic esters, and reaction with the MNTS nitroso group afforded the C-nitrosophenol and/or NO.However, the rate of reaction with the nitroso group correlated well with the basicity of the phenolic oxygen atom, suggesting that both the sulfonyl and nitroso groups of MNTS react with phenolates exclusively through this single nucleophilic centre.Similar behaviour in the reaction between ascorbic acid and 2-ethoxyethyl nitrite suggests that in vivo generation of NO from alkyl nitrites may result from their reaction with biological reductones.
- Leis, J. Ramon,Rios, Ana
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p. 857 - 864
(2007/10/03)
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- Nitrosation of phenolic substrates under mildly basic conditions: Selective preparation of p-quinone monooximes and their antiviral activities
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Nitrosation of 3-methoxyphenol and 1-naphthol were examined under both acidic (NaNO2-EtCO2H-H2O) and basic (i-AmNO2-K2CO3-DMF) conditions. Acidic nitrosations afforded ortho-directed products, whereas para-directed nitrosations were observed under basic conditions to yield p-quinone monooximes. The basic para-directed nitrosation was further examined using 15 phenols, two naphthols, and four phenolic heterocyclics. A one-pot operation of the basic nitrosation followed by methylation with dimethyl sulfate gave the corresponding methyl ethers in high yield. Two p-quinone monooximes derived from 3-methoxyphenol and 8-hydroxyquinoline showed a moderate activity against HSV-1, and the latter oxime was also effective against HSV-2. On the other hand, p-quinone monooximes derived from methyl salicylate, 1-naphthol, 7-hydroxy-2-methylbenzo[b]furan, and 8-hydroxycoumarin showed the comparable activity to that of DDI against HIV-1.
- Ishikawa, Tsutomu,Watanabe, Toshiko,Tanigawa, Hisashi,Saito, Tatsuru,Kotake, Ken-Ichiro,Ohashi, Yoshiaki,Ishii, Hisashi
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p. 2774 - 2779
(2007/10/03)
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- Alkyl Nitrenes from N-Alkylbenzoquinone Imine N-Oxides
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Alkyl nitrenes have been generated by photolysis of two N-t-alkylbenzoquinone imine N-oxides.These mainly abstract hydrogen to give the corresponding amines which are trapped by reaction with benzoquinone.Intramolecular hydrogen abstraction followed by cyclisation to give a pyrrolidine is a minor process in one case.Attempts to generate α-substituted benzyl nitrenes in this way led mainly to the production of substituted benzyl radicals by C-N bond cleavage of the N-benzylbenzoquinone imine N-oxides.
- Baldry, Peter J.,Forrester, Alexander R.,Ogilvy, Munro M.,Thomson, Ronald H.
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p. 2027 - 2034
(2007/10/02)
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- N-Hydroxyacetaminophen: A Postulated Toxic Metabolite of Acetaminophen
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The decomposition of N-hydroxyacetaminophen has been shown to occur via an initial first-order dehydration step to N-acetyl-p-benzoquinone imine with a rate constant at pH 7.6 of 8.66*10-3 min-1 and a half-life of 80 min.This is followed by a complex reaction between the quinone imine and the N-hydroxy compound to ultimately yield p-nitrosophenol and acetaminophen.The glucuronide and sulfate conjugates of N-hydroxyacetaminophen have been observed as urinary metabolites of N-hydroxyacetaminophen.No N-hydroxylated metabolites were found among the metabolites of acetaminophen.These results have been interpreted to show that N-hydroxyacetaminophen is not a metabolite of acetaminophen.It is proposed that the hepatotoxicity and nephrotoxicity of acetaminophen are mediated by a direct oxidation of acetaminophen to the toxic reactive intermediate N-acetyl-p-benzoquinone imine by the cytochrome P450 dependent mixed-function oxidase system.
- Calder, Ian C.,Hart, Sandra J.,Healey, Kevin,Ham, Kathryn N.
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p. 988 - 993
(2007/10/02)
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- Nitrosation process
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In the process of subjecting a compound selected from phenols, N,N-dialkylanilines and mixtures thereof to nitrosation reaction conditions using a nitrite in an aqueous system to prepare nitrosated products selected from benzoquinone oximes and p-nitroso-N,N-dialkylanilines, the nitrosation reaction is advantageously carried out in the presence of an acid stronger than nitrous acid an organic acid of pKa 2 to pKa 5 or a salt thereof and water, the quantities of the organic acid and water being up to 5 times by mole and up to 10 times by weight the quantity of the compound to be nitrosated, respectively.
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