Chaim Rav-Acha

Carbamate insecticides: Removal from water by chlorination and ozonation

A simple approach for removal of carbamates from drinking water by disinfection is presented. Four carbamates, aldicarb, methomyl, carbaryl and propoxur were reacted with excess of each of three disinfectants, Cl2, ClO2 and O3. Carbaryl and propoxur did not react with chlorine, none of the selected carbamates reacted with ClO2, and all reacted very rapidly with O3. The reaction kinetics were determined for aldicarb and Cl2 and for methomyl and Cl2. Product analysis for the reaction of aldicarb and Cl2 was carried out using reverse-phase HPLC and GC-MS. The common degradation products, aldicarb-sulfoxide and aldicarb-sulfone were found together with other by-products. A mechanism is suggested based upon an electrophilic ionic attack by hypochlorous acid. A possible mechanism of electrophilic attack by ozone is also suggested. A preliminary bioassay using Daphnia magna, to compare the toxicity of aldicarb and chlorination by-products of aldicarb showed that the by-products were less toxic. Therefore, removal/degradation of these carbamates can be achieved using Cl2 and/or O3 but not ClO2.

The different reaction mechanisms by which chlorine and chlorine dioxide react with polycyclic aromatic hydrocarbons (PAH) in water

Abstract The removal of PAH from surface water by disinfectants like chlorine or chlorine dioxide is important where contamination by these compounds is concerned and no other water treatment processes are available. Our particular interest in these reactions arise from the fact that PAH can be used as an excellent model for the investigation of the different mechanisms by which the two oxidants react with aquatic organics. The vast differences between the rates of Cl 2 and ClO 2 reactions with various PAH, as well as the physical and chemical factors influencing those reactions indicate that chlorine reacts with PAH by several possible mechanisms, e.g. addition, substitution and oxidation. Chlorine dioxide on the other hand reacts mainly as a pure oxidant and a one-electron acceptor. As a consequence, chlorine dioxide reacts much more specifically with those PAH that undergo facile oxidation. Therefore, some PAH that react quite easily with Cl 2 , do not react at all with ClO 2 , while other PAH react with ClO 2 much more rapidly than with Cl 2 . The widespread and highly carcinogenic benzo(a)pyrene and benzo(a)anthracene for example react with ClO 2 much faster than with Cl 2 .

The formation of cation-radicals by the action of chlorine dioxide on p-substituted styrenes usd other alkenes

Abstract The Hammett plot for the reaction of C10 2 with p-substituted styrenes, the solvent effect, and the order of reactivity of several alkenes towards C10 2 , indicate that the alkene-C10 2 reaction proceeds via the formation of cation-radicals.

The kBr/kCl element effect for nucleophilic vinylic substitution of the highly reactive tricyanovinyl-x system by substituted anilines

Abstract The element effects for the substitution of tricyanovinyl chloride and bromide by the p -position of three dialkylanilines are k Br /k Cl =2.37±0.18. An early transition state for the expulsion of the halide ion from the intermediate zwitterion is indicated.