AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

White phosphorus in tetrahydrofuran under argon reacts in a long radical chain reaction with carbon radicals derived from Barton PTOC esters. The reaction is initiated by traces of oxygen and strongly inhibited by TEMPO. From the duration of the induction period the chain length can be measured as approximately one million. Each P4 molecule can add up to two carbon radicals. Oxidation of the adducts provides a convenient synthesis of phosphonic acids in high yield. With H2O2 at 0°C oxidation to the appropriate phosphinic acids is fast. For sensitive natural products the further transformation to phosphonic acids is best carried out at room temperature with an excess of SO2. In this way even linoleic acid can be converted to the corresponding phosphonic acid in good yield without any attack on the skipped diene unit. TEMPO is also remarkable for its stabilization of white phosphorus in solution when exposed to oxygen. Likewise an ordinary phosphine, like tributyl phosphine, is also stabilized by small amounts of TEMPO.

A simple water soluble diselenide derivative 1 shows radical scavenger properties towards alkyl and hydroxyl radicals (k3 (0°C)=6.8×108 M−1 s−1) in Fenton-type chemistry. The reaction rate between produceded alkyl radicals 2 and the diselenide overwhelms self-termination and halogen transfer reactions.

A method is reported for the determination of both the primary and secondary kinetic isotope effects at a reactive center based on staring material reactivities. This allows the determination of the separate KIEs in reactions for which neither product analysis nor absolute rate measurements are applicable. The methodology is applied to the FeCl3-catalyzed oxidation of ethylbenzene with tert-butyl hydroperoxide, which exhibits both a primary isotope effect and a substantial secondary isotope effect.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An improved procedure for the phenylselenation of saturated hydrocarbons has been developed. The reaction of tributylphosphine with diphenyl diselenide in the presence of FeII picolinate in pyridine-acetonitrile-trace of water affords a quantitative yield of phenylselenol. Subsequent or prior addition of the saturated hydrocarbon and final addition of 30% hydrogen peroxide gives phenylselenation in excellent yield based on the oxidant added. The mechanism of this reaction has been further studied; carbon and hydroxyl radicals are not part of the mechanism.

By maintaining the iron catalyst in the ferrous [iron(II)] state, the oxidation chemistry of TBHP was dominated by the tert-butoxyl radical. Saturated hydrocarbons were readily oxidized.

The xanthate of a hindered secondary alcohol can be deoxygenated easily with phosphine-boranes and AIBN in a high yielding radical chain reaction. A similar efficient olefin forming reaction has been seen with a 1,2-dixanthate under the same conditions. In contrast to tin hydride based reagents phosphine-boranes do not reduce chlorides or bromides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Gif systems permit the selective functionalization of saturated hydrocarbons under mild conditions and with high efficiencies. A newly discovered Fe-II-Fe-IV manifold is shown to form alkyl chlorides by a process involving carbon-centered radicals as intermediates. This is distinct from the usual ketonization process (Gif Chemistry) produced by an Fe-III-Fe-V manifold. The importance of certain carboxylic acids such as picolinic acid for hydrocarbon activation has been demonstrated. The ligand environment of the catalyst in solution is clarified using quantitative C-13-NMR spectroscopy. Evidence for a mu-peroxo dimer species as a key intermediate in solution is provided and recent mechanistic studies are reported.

In the FeIII-FeV manifold the formation of the iron-carbon bond was found to be very fast, but the evolution to give ketone was slow at −20 °C and −40 °C. However, the efficiency at the latter temperature was good. The iron-carbon bond can be captured rapidly by I− or by PhSeH. We have confirmed that either way to measure the iron-carbon bond gives essentially the same results. In contrast to the FeIII-FeV manifold the reactions at −20 °C in the FeII-FeIV manifold are very fast for both iron-carbon bond formation and evolution to final products. In this manifold the reactions at −20 °C are more efficient than those at −5 °C.

Further aspects of the chemistry of TBHP in the presence of Fe-II and Fe-III species have been investigated. Now all the results previously reported with TBHP can be understood in terms of radical chemistry. Oxidation states of iron higher than Fe-III are not involved. (C) 1998 Elsevier Science Ltd. All rights reserved.

It is demonstrated by a study of cyclohexane phenylselenation that the synergistic oxidation of cyclohexane with H2S and O-2 does not involve carbon or oxygen radicals.

By comparing the reactivities of alcohols and alkanes towards TBHP radical oxidation and non-radical Gif oxidation, we bring additional evidence regarding the non-radical nature of Gif chemistry.

The binuclear MnIVMnIV manganese complex 1 catalyzes the periodic acid oxidation of sulfides to sulfones under mild conditions. The reaction was found to be highly selective giving almost quantitative yields of the sulfones even in the presence other easily oxidized groups. Only amines were found to hinder the reaction.

The reaction of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) with I-butyl hydroperoxide, in the presence of catalytic amounts of Fem yields oxygen. This reaction, which has never been described in the literature so far, led us to envisage a totally new concept, involving the reaction of TEMPO with oxygen-centered radicals. The formation of an intermediate has been detected during the course of the reaction. A mechanism based on the experimental facts and literature data is proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.

The role of pyridine and of many substituted pyridines in Gif oxidation chemistry has been examined. In the presence of a suitable pyridine type base most of the solvent can be replaced by acetonitrile without diminishing the yield of oxidation products. The use of 4-tert-butylpyridine permits the isolation of cyclohexanone and cyclohexanol by simple distillation.

Under Gif conditions using ascorbic acid as reductant and oxygen as oxidant in pyridine, the selectivity for secondary hydrogen functionalization is exceptional. EDTA (ethylenediamine-tetra-acetic acid) is not needed as a ligand for iron.

By maintaining the iron catalyst in the feme state, the oxidation of 2,4,6-tri-tert-butylphenol with TBHP affords exclusively tert-butyl-peroxylated products. Mechanistic interpretation does not require a higher valence state of iron than Fe-III.