Title: On the gas-phase reactivity of complexed OH+ with halogenated alkanes
Authors : Adlhart, Christian
Sekiguchi, Osamu
Uggerud, Einar
Published in : Chemistry - A European Journal
Volume(Issue) : 11
Issue : 1
Pages : 152
Pages to: 159
Publisher / Ed. Institution : Wiley VCH
Publisher / Ed. Institution: Weinheim
Issue Date: 2005
License (according to publishing contract) : Licence according to publishing contract
Type of review: Peer review (Publication)
Language : English
Subjects : C-h activation; Proton affinities; Oxidation; Peroxide
Subject (DDC) : 540: Chemistry
Abstract: OH+ is an extraordinarily strong oxidant. Complexed forms (L-OH+), such as H2OOH+, H3NOH+, or iron-porphyrin-OH+ are the anticipated oxidants in many chem. reactions. While these mols. are typically not stable in soln., their isolation can be achieved in the gas phase. We report a systematic survey of the influence on L on the reactivity of L-OH+ towards alkanes and halogenated alkanes, showing the tremendous influence of L on the reactivity of L-OH+. With the help of with quantum chem. calcns., detailed mechanistic insights on these very general reactions are gained. The gas-phase pseudo-first-order reaction rates of H2OOH+, H3NOH+, and protonated 4-picoline-N-oxide towards isobutane and different halogenated alkanes CnH2n+1Cl (n = 1-4), HCF3, CF4, and CF2Cl2 have been detd. by means of Fourier transform ion cyclotron resonance measurements. Reaction rates for H2OOH+ are generally fast (7.2 × 10-10-3.0 × 10-9 cm3 mol-1 s-1) and only in the cases HCF3 and CF4 no reactivity is obsd. In contrast to this H3NOH+ only reacts with tC4H9Cl (kobs = 9.2 × 10-10), while 4-CH3-C5H4N-OH+ is completely unreactive. While H2OOH+ oxidizes alkanes by an initial hydride abstraction upon formation of a carbocation, it reacts with halogenated alkanes at the chlorine atom. Two mechanistic scenarios, namely oxidn. at the halogen atom or proton transfer are found. Accurate proton affinities for HOOH, NH2OH, a series of alkanes CnH2n+2 (n = 1-4), and halogenated alkanes CnH2n+1Cl (n = 1-4), HCF3, CF4, and CF2Cl2, were calcd. by using the G3 method and are in excellent agreement with exptl. values, where available. The G3 enthalpies of reaction are also consistent with the obsd. products. The tendency for oxidn. of alkanes by hydride abstraction is expressed in terms of G3 hydride affinities of the corresponding cationic products CnH2n+1+ (n = 1-4) and CnH2nCl+ (n = 1-4). The hypersurface for the reaction of H2OOH+ with CH3Cl and C2H5Cl was calcd. at the B3LYP, MP2, and G3m* level, underlining the three mechanistic scenarios in which the reaction is either induced by oxidn. at the hydrogen or the halogen atom, or by proton transfer.
Departement: Life Sciences und Facility Management
Organisational Unit: Institute of Chemistry and Biotechnology (ICBT)
Publication type: Article in scientific Journal
DOI : 10.1002/chem.200400699
ISSN: 0947-6539
URI: https://digitalcollection.zhaw.ch/handle/11475/2108
Appears in Collections:Publikationen Life Sciences und Facility Management

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