Structure reactivity relationship in the accelerated formation of 2,3-diarylquinoxalines in the microdroplets of a nebuliser

Competition experiments in which 1,2-phenylenediamine, C6H4(NH2)2, condenses with equimolar quantities of benzil, (C6H5CO)2, and a 3,3′- or 4,4′-disubstituted benzil (XC6H4CO)2 (X = F, Cl, Br, CH3 or CH3O) to form a mixture of 2,3-diphenylquinoxaline and the corresponding 2,3-diarylquinoxaline (Ar = XC6H4) in the microdroplets produced in a nebuliser allow a Hammett relationship with a ρ value of 1.85 to be developed for this accelerated condensation in the nebuliser. This structure reactivity relationship reveals that an appreciable amount of negative charge builds up on the carbon of the carbonyl group of the benzil during the rate-limiting step of the reaction, thus confirming that this process involves nucleophilic addition of the 1,2-phenylenediamine to the benzil. In general, the presence of an electron donating substituent, particularly in the 4 and 4′ positions, in the benzil retards the reaction, whereas an electron attracting substituent, especially in the 3 and 3′ position, accelerates it.

THEORETICAL STUDY ON OXYGEN–OXYGEN HOMOLYTIC BOND DISSOCIATION ENTHALPIES OF PEROXIDES

Seven theoretical methods (B3LYP, B3P86, X3LYP, BMK, MP2, CBS-QB3, G3B3) were employed to calculate oxygen–oxygen homolytic bond dissociation enthalpies of 13 peroxides. Comparison of the performances of these methods with the available experimental data showed that ROBMK method is suitable and economical for calculating O–O homolytic bond dissociation enthalpies of peroxides. Then ROBMK method was used to calculate O–O homolytic bond dissociation enthalpies of a series of peroxides. Meanwhile, the α-substituent effect and Hammett relationship were also discussed.

Kinetics and mechanism of the C-S coupling reactions of aryl Grignard reagents with aryl arenesulfonates

The kinetics of the C-S coupling of arylmagnesium bromides with phenyl tosylate has been studied in THF: toluene at 90°C. The reaction is first order in Grignard reagent and first order in phenyl tosylate. Kinetic data, Hammett relationship and activation parameters are consistent with a nucleophilic addition mechanism involving rate determining attack of carbanion to sulfonyl group followed by a fast phenoxide group leaving.