Marko Zupan

Oxidative Halogenation with "Green" Oxidants: Oxygen and Hydrogen Peroxide

It is difficult to imagine organic chemistry without organo-halogen compounds and the molecular halogens needed for their preparation. The halogens have very different reactivity, with iodine usually requiring some form of activation, while others are reactive and hazardous chemicals. To avoid their use, various modified reagents have been discovered (N-bromo- and N-chlorosuccinimide, Selectfluor..), but halogens are used to prepare these reagents and when they are used the atom economy is poor. A better approach, which is based on biomimetric research on oxidative halogenation in nature, consists of generating the halogenating reagent in situ under acidic conditions from a halide salt. The result of such a reaction has been halogenation with 100 % halogen atom economy. Suitable oxidants for the oxidation of halides are hydrogen peroxide and oxygen.

Bromination of ketones with H2O2–HBr “on water”

Various 1,3-diketones, β-ketoesters, cyclic ketones, aryl alkyl and dialkyl ketones were effectively brominated with an aqueous H2O2–HBr system “on water” at room temperature without the need for a catalyst or organic solvent. The resultant brominated ketones were isolated in yields of 69–97% with high selectivity for monobromination vs. dibromination. Reactivity was manipulated by using more diluted aqueous solutions of H2O2 and HBr and the use of an excess of HBr where necessary. Dilution also increases selectivity of ring bromination vs. α-bromination of aryl ketones with an activated phenyl ring. Finally, an aqueous H2O2–HBr system was used for a tandem oxidation–bromination process and alcohols were transformed into α-bromoketones. This simple but effective “on water” bromination of ketones with an aqueous H2O2–HBr system is characterised by the use of inexpensive reagents, a lower impact on the environment and the absence of organic waste that make it a good alternative to existing bromination methods.

Selective aerobic oxidative dibromination of alkenes with aqueous HBr and sodium nitrite as a catalyst

Various alkenes (internal, terminal, aryl and alkyl substituted) and 1,2-diphenylethyne were efficiently and selectively dibrominated using 2 equivalents of 48% aqueous hydrobromic acid, with air as an oxidant and sodium nitrite as a catalyst. Despite the presence of water, only trans dibromination occurred producing anti-1,2-dibromoalkanes and (E)-1,2-dibromo-1,2-diphenylethene. A comparison of resource demand, waste production and environmental, health and safety issues of the NaNO2 catalyzed aerobic bromination with molecular bromine and other oxidative bromination methods revealed that the proposed method is not only selective and effective but has a better environmental profile.

Relationship of Soil Properties to Fractionation of Pb and Zn in Soil and Their Uptake into Plantago lanceolata

Soil samples (0 to 5 cm) from 30 locations in the Celje region, Slovenia, an area that has been subjected to severe industrial emissions of Pb and Zn, were analyzed for selected soil properties and subjected to a six-step sequential extraction of Pb and Zn. Phyto-available forms of heavy metals: soluble in soil solution and exchangeable from soil colloids to soil solution together accounted for 0 to 1.68% of Pb and 0 to 40.8% of total soil Zn. Most of the Pb and Zn was found to reside in less labile forms bound to carbonate (2.04 to 43.5% Pb, 3.9 to 35.1% Zn), bound to Fe and Mn oxides (0 to 16.1% Pb, 1.4 to 25.4% Zn), bound to organic matter (35.8 to 71.1% Pb, 14.8 to 56.2% Zn), and in the residual fraction (10.4 to 53.4% Pb, 14.2 to 75.3% Zn). Factor analysis and stepwise multiple regression revealed that the concentration of Pb in the proposed indicator plant, narrow leaf plantain (Plantago lanceolata) did not correlate with the measured soil properties, Pb fractionation in soil, and total soil Pb. Plant uptake of Zn, however, significantly correlated with soil pH and with the share of phyto-available forms of Zn in the soil (R2 = 86.9). A statistically significant correlation (P<0.01) was found between the fractions of Pb and Zn carbonates and soil organic matter content (R2 = 90.6 and 90.9, respectively); the fraction of Pb bound to organic matter and soil organic matter content (R2 = 90.6); the residual fraction of Pb and total Pb content in soil (R2 = 95.7); the fraction of Zn bound to Fe an Mn oxides, the fraction of Zn bound to organic matter, the residual fraction of Zn and total Zn content in soil (R2 = 75.9, 93.2, and 87.4, respectively). Soil texture, pH, and cation exchange capacity did not affect the relative proportions of Pb and Zn forms in soil.

High yield direct fluorofunctionalisation of ketones using AccufluorTM-NFTh fluorinating reagent

Abstract Direct regioselective conversion of a variety of cyclic and acyclic ketones to α-fluoroketones was achieved in high to excellent yield using 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2,2,2]octane bis(tetrafluoroborate) [AccufluorTM - NFTh] in acetonitrile solution.

Effective and selective iodofunctionalisation of organic molecules in water using the iodine–hydrogen peroxide tandem

Efficient hydrogen peroxide enhanced iodofunctionalisation of ketones, 1,3-dicarbonyl derivatives and activated aromatic molecules using elemental iodine in water is achieved, whereas alkynes were stereoselectively converted into (E)-1,2-diiodoalkenes.

α-Substituted organic peroxides: synthetic strategies for a biologically important class of gem-dihydroperoxide and perketal derivatives

In this paper we review the recent developments in the synthesis of alpha-substituted hydroperoxides. Alpha-substituted hydroperoxides are interesting compounds due to their chemistry and bioactivity and as intermediates for the synthesis of other peroxides, of which cyclic peroxides are of major importance. Although the emphasis of this report will be on the derivatives of gem-dihydroperoxides, perketals, as well as the less studied nitrogen and sulfur derivatives, will also be covered.

Room Temperature Regioselective Iodination of Aromatic Ethers Mediated by SelectfluorTM Reagent F-TEDA-BF4

Abstract Monosubstituted phenyl ethers were regioselectively iodinated with a mixture of iodine and F-TEDA in acetonitrile at room temperature at the para position, while 1-methoxy-4-substituted benzene derivatives were converted to 2-iodo products in high yield.

Fluorination with xenon difluoride; Part IX. Reaction with phenylsubstituted sulphides

Abstract Fluorination of phenyl-methylsulphide with xenon difluoride yields phenyl-fluoromethylsulphide. Further fluorination leads to phenyl-difluoromethylsulphide. Reaction with cis-2,6-diphenyltetrahydro-1-thio-4-pyrone results in the dehydrogenated product 2,6-diphenyldihydro-1-thio-4-pyrone, while further reaction leads to 2,6-diphenyl-1-thio-4-pyrone; thiochroman-4-one yields thiochromen-4-one. No evidence for precursors of the products isolated at room temperature was found.

1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) as a new, effective reagent for selective fluorofunctionalisation of alkenes under mild reaction conditions

Abstract 1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) ( Accufluor ™ NFTh) is confirmed as a highly effective reagent for introducing a fluorine atom into organic molecules across a phenyl-substituted carbon-carbon double bond. Quantitative and Markovnikov-type regioselective formation of vicinal fluoro-hydroxy, fluoro-methoxy or fluoro-acetoxy adducts was achieved when phenyl-substituted alkenes were treated with a MeCN solution of NFTh In the presence of water, methanol or acetic acid. The stereochemical course of fluoro-methoxylation reactions in the case of cyclic phenyl-substituted alkenes depends strongly on the structure of the alkene.