Free Radical Atom Research Articles

Does bromine atom-free radical (Br·) undergo a chemical reaction before dimerization to dibromine (Br2)? An electrochemical investigation

The important question, does bromine atom free radical, Br·, undergo a chemical reaction with a substrate before it dimerizes to dibromine Br2, is investigated through electrochemical oxidation of bromide ion Br−. Cyclic voltammetry and spectrophotometry were used as electro-oxidation and monitoring devices. Simulation of cyclic voltammogram was used to obtain information about the mechanism of electro-oxidation process as well as reaction with substrates. It is shown that the primary electro-oxidation product (PEOP) of Br−, Br· (bromine atom-free radical), reacts with chemicals like chloroform, glycine, cytosine, etc. It can also dimerize, for example in acetonitrile. Reactions of PEOP Br· with substrate chloroform, acetone, DNA components adenine, cytosine, thymine and amino acid glycine were studied and their kinetics are reported here.

“Long-life” atom-free radical: Generation and reactions of bromine atom-free radical

In order to study the damaging or beneficial properties of bromine atom-free radical, reaction of the free radical (Br•) with some biologically important compounds were investigated. Br• was generated through electrochemical oxidation of bromide ion (Br–). First the reactivity of Br• atom-free radical vis a vis its dimerization to form Br2, was studied using cyclic voltammetry and spectroelectrochemistry. Through these techniques it was ascertained that the substrates understudy and the under experimental conditions used, underwent reactions with Br• and not with dibromine (Br2). The monitoring of the reactions of Br• with glycine and cytosine led us to conclude that whereas cytosine reacted with Br• as simple chemical reaction (EC mechanism), glycine underwent a catalytic reaction (EC′ mechanism).

Lewis acid-promoted Kharasch-Curran additions: a competition kinetics study of bromine atom transfer addition of N-alpha-bromoacetyl-oxazolidinone to 1-hexene.

Lewis acids can efficiently promote free radical atom transfer reactions of an oxazolidinone imide substrate, 1, derived from alpha-bromo acetic acid. Thus, 1 undergoes a radical chain addition to 1-hexene giving the atom transfer addition compound, 6, in the presence of scandium or ytterbium triflate in 1,2-dichloroethane or a cosolvent mixture of 1/9 THF/dichloromethane. In 1,2-dichloroethane the solution is heterogeneous, while the cosolvent mixture gives a homogeneous solution, even at temperatures of -78 degrees C. Competition experiments were carried out in both solvent systems with added carbon tetrachloride to study how Lewis acid affected the product distribution. In the presence of carbon tetrachloride, chloride 7 is formed in addition to 6 and the ratio of these two products depends on the amount of Lewis acid present. In the presence of ytterbium triflate, in the cosolvent system, the reaction rate of bromine atom transfer was enhanced up to 400-fold compared to the reaction without added Lewis acid. Significant rate enhancements were also obtained in the solvent 1,2-dichloroethane, although the analysis of the system is complicated by the heterogeneous nature of the medium. Computation of C-Br bond dissociation energies (BDE) of the complexed and uncomplexed oxazolidinone bromide suggest that complexation lowers the BDE due to the effect of the strong electron-withdrawing group on the C-Br bond dipole.

The generality of metal atom-free radical reactions and synthesis of new trifluoromethylalkyls of gold(III) and silver

The cocondensation reaction of trifluoromethyl radicals with gold and silver vapors is an effective and efficient synthesis for the new compounds, Au(CF 3) 3 and AgCF 3. Addition of trimethylphosphine to these alkyls yielded the room temperature stable compounds, Au(CF 3) 3PMe 3 and AgCF 3(PMe 3).