Antioxidant Activity of <i>o</i>-Bisphenols:  the Role of Intramolecular Hydrogen Bonding

Amorati, Riccardo; Lucarini, Marco; Mugnaini, Verónica; Pedulli, Gian Franco

doi:10.1021/jo0342931

Cited by 84 publications

(77 citation statements)

References 28 publications

(46 reference statements)

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“…Hindered phenolic compounds (ArOH) represent the major family of both natural and synthetic antioxidants. 5 They are an excellent additive in polymers and lubricants. 6 In general, efficient phenol antioxidants have substituents in ortho-and/ or para-positions.…”

Section: Introductionmentioning

confidence: 99%

Antioxidant activity of cashew nut shell liquid (CNSL) derivatives on the thermal oxidation of synthetic cis-1,4-polyisoprene

Rodrigues¹,

Feitosa²,

Ricardo³

et al. 2006

J. Braz. Chem. Soc.

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LCC (Líquido da Castanha de Caju), ou CNSL (Cashew Nut Shell Liquid), é uma mistura de meta-alquilfenóis, que variam no grau de insaturação do grupo ligado ao núcleo benzênico. A degradação térmica do poli(1,4-cis-isopreno) sintético a 140 °C foi estudada na presença do LCC técnico e de alguns derivados (cardanol, cardanol hidrogenado e cardanol hidrogenado e alquilado), através de FTIR. A quantidade de grupamentos OH/OOH e C=O formados e de C=C consumidos foi determinada durante a degradação. Todos os materiais aumentaram o tempo de indução e diminuíram as constantes aparentes de velocidade. Com base nos parâmetros cinéticos, a ordem de atividade antioxidante é: LCC >> cardanol ≅ cardanol hidrogenado e alquilado > cardanol hidrogenado. O efeito do LCC pode ser atribuído à contribuição extra de seus outros componentes, além do cardanol, e à insaturação na longa cadeia lateral. Essa maior atividade é importante, considerando que o LCC tem mais baixo custo do que seus derivados.CNSL is a mixture of meta-alkylphenols with variable degree of unsaturation attached to the benzene ring. The kinetic study of the thermal degradation at 140 °C of synthetic cis-1,4-polyisoprene film, in the presence of technical CNSL and some derivatives (cardanol, hydrogenated cardanol and alkylated hydrogenated cardanol) was carried out by FTIR. The amount of OH/OOH and C=O formed and also of C=C consumed during the degradation was determined. All materials increase the induction period and decrease the apparent rate constants of thermal-oxidation. Based on kinetic parameters, the order of antioxidant activity was: CNSL >> cardanol ≅ hydrogenated and alkylated cardanol > hydrogenated cardanol. The effect of CNSL could be attributed to the extra contribution of the other components besides cardanol and to the unsaturation on the long side chain. This greater activity is important because CNSL is much more cost effective than its derivatives.

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Section: Introductionmentioning

confidence: 99%

Antioxidant activity of cashew nut shell liquid (CNSL) derivatives on the thermal oxidation of synthetic cis-1,4-polyisoprene

Rodrigues¹,

Feitosa²,

Ricardo³

et al. 2006

J. Braz. Chem. Soc.

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“…Only for reaction (12) the energy gain calculated with allowance for isomerism increases by 4.31 kcal mol -1 . At the same time comparison of the ∆G M and ∆G eff values for reactions (8), (10), and (12) shows that |∆G eff | = |∆G M | + (0.01-0.05) kcal mol -1 . For reac tion (9) one gets |∆G eff | = |∆G M | + 0.16 kcal mol -1 while for reactions (11) and (13) one has |∆G eff | = |∆G M | -(0.14-0.24) kcal mol -1 .…”

Section: Methodsmentioning

confidence: 91%

7-Ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (echinochrome A): A DFT study of the antioxidant mechanism. 1. Interaction of echinochrome A with hydroperoxyl radical

2007

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The molecular geometry and electronic structure of hydroxy substituted naphthazarin (NZ) 7 ethyl 2,3,5,6,8 pentahydroxy 1,4 naphthoquinone (echinochrome A, (Et)NZ(β OH) 3 , 1) were calculated by the B3LYP/6 311G(d) method. The influence of the (i) character of the β OH groups dissociation and (ii) conformational mobility of molecule 1 and the anions, radicals, and radical anions derived from 1 on the energy of their reactions with hydroperoxyl radical was studied by the (U)B3LYP/6 31G and (U)B3LYP/6 311G(d) methods. The enol enolic tautomerism due to the transfer of hydrogen atoms of α OH groups and rotational isomerism of the β OH groups at the C(2) and C(3) atoms and of the α OH groups at the C(5) and C(8) atoms were studied. The equilibrium in the gas phase reaction 1 + • OOH (Et)(HO β) 2 NZ(β О • ) + НOOH (1) (quenching of hydroperoxyl radical) is shifted to the separated reagents. Heterolysis of the O-H bond in one of the three β hydroxy groups considerably reduces the energy of subsequent O-H bond homolysis in either of the two remaining β hydroxy groups. As a consequence, the reaction (Et)(HO β) 2 NZ(β O -) + • OOH (Et)(HO β, -О β)NZ(β О • ) + НOOH (2) (quenching of hydroperoxyl radical) becomes exothermic and the equilibrium is shifted to the formation of hydrogen peroxide. The Gibbs energy gain in reaction (2) varies from -6.4 to -10.9 kcal mol -1 depending on which β hydroxy group is involved in the O-H bond homolysis.

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“…10% NaOH (15 mL) were then added to the aqueous solution and the basic products were extracted with ethyl acetate. The reaction products were identified by gc-ms analysis and comparison with authentic samples prepared according to known procedures [2][3][4], [12] and analysed by gc with internal standard. Compound 4 was utilised as internal standard for reaction products 1-3 and 5-20, while compound 5 was used as internal standard for compound 4.…”

Section: General Procedurementioning

confidence: 99%

“…7). Moreover, we have evaluated [12] that hydrogen abstraction from the =N-OH group in NHPI by peroxyl radical ROO• , (7.2 × 10 3 M -1 s -1 at r.t.) is much faster than from C-H bonds (10 -3 -10 -1 M -1 s -1 ) and we can reasonably expect that hydrogen abstraction by the acylperoxyl radical, RCO-OO . , should also be much faster from =N-OH (eq.…”

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confidence: 99%

Polar effects in free‐radical reactions. A novel homolytic acylation of heteroaromatic bases by aerobic oxidation of aldehydes, catalysed by N‐hydroxyphthalimide and Co salts

Minisci¹,

Recupero²,

Cecchetto³

et al. 2003

Journal of Heterocyclic Chem

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A new process for the homolytic acylation of protonated heteroaromatic bases is described; an N-oxyl radical (PINO) generated from N-hydroxyphthalimide by air oxygen and Co(II) abstracts a hydrogen atom from an aldehyde. The resulting nucleophilic acyl radical adds to a heteroaromatic base, which is then rearomatised in a chain process. Quinazoline has an anomalous behaviour, giving 3H-quinazolin-4-one as the only reaction product.J. Heterocyclic Chem., 40, 325 (2003).The great synthetic interest of the substitution of protonated heteroaromatic bases by nucleophilic carbon-centred radicals results from the high regio-and chemoselectivity, due to polar effects, the large variety of inexpensive radical sources and the simple experimental conditions. The overall polar effect in these reactions is the result of the polarity and the polarisability of both the radicals and the substrates. While carbon-centred radicals usually do not show an extremely marked nucleophilic character, the electrophilic polarity of heteroaromatic bases is greatly increased by protonation. The strongly induced activation of heteroaromatic bases towards nucleophilic species, due to protonation, cannot be exploited with ionic nucleophiles, whose primary effect is deprotonation of the base. This problem is overcome by the use of free-radical nucleophiles, which react with protonated heteroaromatic bases in a large variety of substitutions characterised by high reactivity and selectivity. These reproduce most of the features of the FriedelCrafts aromatic substitutions, but with opposite reactivity and selectivity, so as to represent one of the main general reactions of this class of aromatic compounds [1].Because of their high reactivity (absolute rate constants in the range of 10 5 -10 8 M -1 s -1 at r.t.) the most reactive bases are effective traps for revealing the presence of carbon-centred radicals in a reaction medium. Basically any carbonyl (acyl, carbamoyl, alkoxycarbonyl) or alkyl radical not bearing electron-withdrawing groups directly bonded to the radical centre can be successfully utilised to this purpose [1].In previous works we have developed two general sources of acyl radicals, useful for the acylation of heteroaromatic bases:1. the t-BuOOH/Fe(III) redox system in the presence of aldehydes [2] (eqs. 1, 2) 2. the oxidative decarboxylation of α-ketoacids by the S 2 O 8 = Ag + redox system [3] (eqs.3, 4) In this Note we report a new homolytic acylation of heteroaromatic bases by aerobic oxidation of aldehydes, catalysed by N-hydroxyphthalimide (NHPI) and Co salts. The overall stoichiometry is given by eq. 5, [HetH 2 ] + being the protonated base.The reaction is carried out by bubbling air in a CH 3 CN or PhCN solution of the heteroaromatic base protonated by CF 3 COOH, the aldehyde, NHPI and the Co(II) salt. In the absence of NHPI no reaction occurs under the same conditions. The reactivity of acyl radicals towards protonated heteroaromatic bases is so high that, even in the case of aldehydes R-CHO where R is a tertiary alkyl gr...

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Antioxidant Activity of o-Bisphenols: the Role of Intramolecular Hydrogen Bonding

Cited by 84 publications

References 28 publications

Antioxidant activity of cashew nut shell liquid (CNSL) derivatives on the thermal oxidation of synthetic cis-1,4-polyisoprene

Antioxidant activity of cashew nut shell liquid (CNSL) derivatives on the thermal oxidation of synthetic cis-1,4-polyisoprene

7-Ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (echinochrome A): A DFT study of the antioxidant mechanism. 1. Interaction of echinochrome A with hydroperoxyl radical

Polar effects in free‐radical reactions. A novel homolytic acylation of heteroaromatic bases by aerobic oxidation of aldehydes, catalysed by N‐hydroxyphthalimide and Co salts

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