http://www.cnr.it/ontology/cnr/individuo/prodotto/ID15797

New insight into solvent effects on the formal HOO + HOO reaction. (Articolo in rivista)

Type

Prodotto della ricerca (Classe)
Articolo in rivista (Classe)

Label

New insight into solvent effects on the formal HOO + HOO reaction. (Articolo in rivista) (literal)

Anno

2005-01-01T00:00:00+01:00 (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi

10.1002/chem.200400661 (literal)

Alternative label

Foti M. C.; Sortino S.; Ingold K.U. (2005)
New insight into solvent effects on the formal HOO + HOO reaction.
in Chemistry - A European Journal
(literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori

Foti M. C.; Sortino S.; Ingold K.U. (literal)

Pagina inizio

1942 (literal)

Pagina fine

1948 (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#url

http://onlinelibrary.wiley.com/doi/10.1002/chem.200400661/pdf (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#numeroVolume

11 (literal)

Rivista

Chemistry - A European Journal (Rivista)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#numeroFascicolo

6 (literal)

Note

Scopu (literal)
ISI Web of Science (WOS) (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni

Istituto di Chimica Biomolecolare - Sezione di Catania Via del Santuario 110, 95028 Valverde (CT) (Italy); Dipartimento di Scienze Chimiche Università degli Studi di Catania Viale A. Doria 8, 95125 Catania (Italy); National Research Council 100 Sussex Drive, Ottawa, ON, K1A0R6 (Canada) (literal)

Titolo

New insight into solvent effects on the formal HOO + HOO reaction. (literal)

Abstract

The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of g-terpinene (TH) at 50 8C produces pcymene and hydrogen peroxide in a radical-chain reaction having HOOC as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and tert-butyl alcohol show that chain termination involves the formal HOOC + HOOC self-reaction over a wide range of g-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, TC, with the HOOC radical under conditions of relatively high [TH] (140-1000 mm) and low [O2] (2.0-5.5 mm). This is because the formal HOOC + HOOC reaction is comparatively slow in acetonitrile (2k~8?107m?1 s?1), whereas, this reaction is almost diffusion-controlled in tert-butyl alcohol and cyclohexane, 2k~6.5?108 and 1.3?109 M?1 s?1, respectively. Three mechanisms for the bimolecular self-reaction of HOOC radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electron transfer between HOOC and its conjugate base, the superoxide radical anion, O2 ?C. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is dependent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOOC + HOOC reaction (mechanism (1)) is about 1.8? 109m?1 s?1 but in water at pH?2 where the ionization of HOOC is completely suppressed, this rate constant is only 8.6?105m?1 s?1. The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham?s HB acceptor parameter, bH2 , for water of 0.38 and an estimated HB donor parameter, aH2 , for HOOC of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOOC + HOOC reaction in water at 25 8C of 1.2?106m?1 s?1 in excellent agreement with experiment. (literal)

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