James M. Tanko

Free-radical side-chain bromination of alkylaromatics in supercritical carbon dioxide.

Free-radical side-chain brominations of alkylaromatics in supercritical carbon dioxide (SC-CO2) are reported. Direct bromination of toluene and ethylbenzene form the corresponding benzyl bromides in high yield. The observed selectivity in SC-CO2 is similar to that observed in conventional organic solvents. Also, SC-CO2 is an effective alternative to carbon tetrachloride for use in the classical Ziegler bromination with N-bromosuccinimide. Reaction yields are high, side products are minimized, and bromine-atom selectivities are observed. Thus, SC-CO2 must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions.

Simultaneous degradation of disinfection byproducts and earthy-musty odorants by the UV/H2O2 advanced oxidation process

Advanced treatment technologies that control multiple contaminants are beneficial to drinking water treatment. This research applied UV/H(2)O(2) for the simultaneous degradation of geosmin, 2-methylisoborneol, four trihalomethanes and six haloacetic acids. Experiments were conducted in de-ionized water at 24 ± 1.0 °C with ng/L amounts of odorants and μg/L amounts of disinfection byproducts. UV was applied with and without 6 mg/L H(2)O(2.) The results demonstrated that brominated trihalomethanes and brominated haloacetic acids were degraded to a greater extent than geosmin and 2-methylisoborneol. Tribromomethane and dibromochloromethane were degraded by 99% and 80% respectively at the UV dose of 1200 mJ/cm(2) with 6 mg/L H(2)O(2), whereas 90% of the geosmin and 60% of the 2-methylisoborneol were removed. Tribromoacetic acid and dibromoacetic acid were degraded by 99% and 80% respectively under the same conditions. Concentrations of trichloromethane and chlorinated haloacetic acids were not substantially reduced under these conditions and were not effectively removed at doses designed to remove geosmin and 2-methylisoborneol. Brominated compounds were degraded primarily by direct photolysis and cleavage of the C-Br bond with pseudo first order rate constants ranging from 10(-3) to 10(-2) s(-1). Geosmin and 2-methylisoborneol were primarily degraded by reaction with hydroxyl radical with direct photolysis as a minor factor. Perchlorinated disinfection byproducts were degraded by reaction with hydroxyl radicals. These results indicate that the UV/H(2)O(2) can be applied to effectively control both odorants and brominated disinfection byproducts.

Functionalization of Hydrocarbons by a New Free Radical Based Condensation Reaction

The Br. radical is the chain carrier of a new highly selective allylation of hydrocarbons (and other substrates): It abstracts a hydrogen atom from R−H to yield R.. Addition of R. to substituted allyl bromide (to form a β-bromo radical) followed by β-cleavage regenerates Br. and provides the product. Reaction yields and kinetic chain lengths for this reaction are highest when the allyl bromide contains a radical-stabilizing substituent.

Photochemistry in supercritical carbon dioxide. The benzophenone-mediated addition of aldehydes to α,β-unsaturated carbonyl compounds

Abstract The photo-induced addition of aldehydes to α,β-unsaturated carbonyl compounds is an effective, ‘environmentally benign’ method for the synthesis of 2-acyl-1,4-hydroquinones (from quinones) and 1,4-diketones (from enones). This process has been improved by eliminating benzene as a solvent and replacing it with supercritical carbon dioxide. Highest yields were obtained at higher CO 2 pressures, or with the addition of 5% t -butyl alcohol as co-solvent.

Comparison of Two Extraction Techniques, Solid-Phase Microextraction Versus Continuous Liquid–Liquid Extraction/Solvent-Assisted Flavor Evaporation, for the Analysis of Flavor Compounds in Gueuze Lambic Beer

Lambic is a beer style that undergoes spontaneous fermentation and is traditionally produced in the Payottenland region of Belgium, a valley on the Senne River west of Brussels. This region appears to have the perfect combination of airborne microorganisms required for lambics spontaneous fermentation. Gueuze lambic is a substyle of lambic that is made by mixing young (approximately 1 year) and old (approximately 2 to 3 years) lambics with subsequent bottle conditioning. We compared 2 extraction techniques, solid-phase microextraction (SPME) and continuous liquid-liquid extraction/solvent-assisted flavor evaporation (CCLE/SAFE), for the isolation of volatile compounds in commercially produced gueuze lambic beer. Fifty-four volatile compounds were identified and could be divided into acids (14), alcohols (12), aldehydes (3), esters (20), phenols (3), and miscellaneous (2). SPME extracted a total of 40 volatile compounds, whereas CLLE/SAFE extracted 36 volatile compounds. CLLE/SAFE extracted a greater number of acids than SPME, whereas SPME was able to isolate a greater number of esters. Neither extraction technique proved to be clearly superior and both extraction methods can be utilized for the isolation of volatile compounds found in gueuze lambic beer.

The tert-butoxyl radical mediated hydrogen atom transfer reactions of the Parkinsonian proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and selected tertiary amines

Previous studies have shown that the hydrogen atom transfer (HAT) reactions of tert-butoxyl radical from the Parkinsonian proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) occur with low selectivity at the allylic and non-allylic alpha-C-H positions. In this paper, we report a more comprehensive regiochemical study on the reactivity of the tert-butoxyl radical as well as on the associated primary kinetic deuterium isotope effects for the various hydrogen atom abstractions of MPTP. In addition, the results of a computational study to estimate the various C-H bond dissociation energies of MPTP are presented. The results of the present study show the allylic/non-allylic selectivity is approximately 73:21. The behavior of the tert-butoxyl radical mediated oxidation of MPTP contrasts with this reaction as catalyzed by monoamine oxidase B (MAO-B) that occurs selectively at the allylic alpha-carbon. These observations lead to the conclusion that the tert-butoxyl radical is not a good chemical model for the MAO-B-catalyzed bioactivation of MPTP.

ORAChromatography and Total Phenolics Content of Peanut Root Extracts

A large number of compounds have been reported in peanut plants. Many of these compounds are phytoalexins, which are produced by plants experiencing environmental stress and often exhibit antioxidant activity. It is difficult to determine which of the many compounds has the greatest impact on total antioxidant capacity in a mixture. The objectives of this research were to examine the oxygen-radical absorbing capacity (ORAC) value and total phenolic contents of peanut root extracts and peanut root extract fractions collected via HPLC. Peanut roots were extracted from four different cultivars (Brantley, NC-12, Phillips, and Wilson) with 70% aqueous ethanol with ultrasonic assistance. Each cultivar was sampled in duplicate. The extracts were fractionated into 18 3-min fractions by HPLC using a C-18 column. Fractions and crude extracts were freeze dried. ORAC values and total phenolic content were then determined for all fractions and crude extracts. Fractions had a significant effect on the μM TE/mg gallic acid equivalents (GAE). ORAC values ranged from -46.89 μM TE to 185 μM TE in HPLC fractions. ORAChromatography can be used to focus on antioxidants in complex samples.

Characterization of a ‘hypersensitive’ probe for single electron transfer to carbonyl compounds

The radical anion generated from 1,1-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1) undergoes facile ring opening yielding both the 3° and 1° distonic radical ions in a ratio of 9 : 1 with a rate constant ≥107 s–1(relief of cyclopropane ring strain and the generation of an aromatic ring provide the thermodynamic driving force for this rearrangement), the facility of C–C bond cleavage in this radical anion and the observed electrochemistry are reminiscent of the reductive cleavage of carbon–halogen bonds in alkyl and benzylic halides: on the basis of these results, 1 emerges as a viable substrate for use as a hypersensitive SET probe in mechanistic studies.

Reaction of benzophenone triplet with aliphatic amines. What a potent neurotoxin can tell us about the reaction mechanism

A photochemical model study of benzophenone triplet ((3)BP) with the MAO-B substrate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [MPTP (1)] and two of its derivatives, 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (2) and (±)-[trans-2-phenylcyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (3) were performed. Literature precedent and calculations reported herein suggest that the barrier to ring opening for aminyl radical cations derived from N-cyclopropyl derivatives of tertiary amines (such as MPTP) will be low. The LFP results reported herein demonstrate that pathways for the reaction of (3)BP with 1, 2, and 3 are very similar. In each instance, disappearance of (3)BP is accompanied solely by appearance of bands corresponding to the diphenylhydroxylmethyl radical and neutral radical derived from MPTP and its two derivatives 2 and 3. These results suggest that the reaction between benzophenone triplet and tertiary aliphatic amines proceed via a simple hydrogen atom transfer reaction. Additionally these model examinations provide evidence that oxidations of N-cyclopropyl derivatives of MPTP catalyzed by MAO-B may not be consistent with a pure SET pathway.

Funktionalisierung von Kohlenwasserstoffen über eine neuartige, radikalische Kondensationsreaktion

Br\.-Radikale sind die Kettentrager einer neuartigen selektiven Allylierung von Kohlenwasserstoffen (und anderen Substraten): Sie abstrahieren unter Bildung von R\. ein Wasserstoffatom vom Kohlenwasserstoff RH. Die Addition von R\. an ein substituiertes Allylbromid (unter Bildung eines β-Bromradikals) mit anschliesender β-Spaltung fuhrt zur Ruckbildung von Br\. und zur Bildung des Produkts. Die Reaktionsausbeuten und die kinetischen Kettenlangen dieser Reaktion sind dann am hochsten, wenn das Allylbromid einen radikalstabilisierenden Substituenten tragt.