SYNTHESIS OF 1,5-DIPHENYL-3-ARYLVERDAZILS

Abstract

The reaction between verdazyls and CH-acids was studied for checking common views on the stable radicals reactivity which is usually associated with the spin density values of the reaction centers and its alterations due to the influence of substituents. The synthesis of row l,5-diphenyl-3-arylverdazyls that contains the different types of substituents in the phenyl rings that are situated at C3 verdazyl radical atom was carried out for this purpose. This also includes the previously non-described 1,5-diphenyl-3-(4-hydroxyl)phenyl-, 1,5-diphenyl-3-(4-bromo)phenyl-, 1,5-diphenyl-3-(3- nitro)phenylverdazyls. In this case, the availability and nature of the substituents in the phenyl rings at C3 verdazyl radical atom may not be affected by the change in the spin density values on the N2 and N4 nitrogen atoms that are verdazyl radicals’ reaction centers. The synthesis of verzdazyls was carried out according to the conventional scheme, on the basis of arylhydrazones. It was observed that during azocoupling reacting of phenyldiazonium chloride with arylhydrazones in the synthesis of formazans the reaction proceeds with a higher yield when the solvent dimethylformamide-pyridine is being used. Transformation of formazans into verdazyl radicals was being carried out at room temperature with formaldehyde exposured to formazan in the presence of potassium hydrogen sulfate under the constant air going through the reactor feed. The availability of substituents in the phenyl ring at C3 formazan atom was increasing reaction time significantly in comparison with 1,3,5- trifenylformazan regardless of the substituent’s nature at C3 formazan atom. During the reaction between 1,5-diphenyl-3-arilverdazyls and CH-acids (acetylacetone and dimedone), it was discovered that the reaction rate depends on both the acidity of the CH-acid (dimedone reacts faster than acetylacetone) and the nature of the substituents situated in phenyl ring at C3 verdazyl atom. At the same time, the electron-donating substituents increase the rate of reaction between verdazyls and CH-acids while electron-donor substituents decrease it. Therefore, as it was formerly reported, when we deal with monochloroacetic acid, the rate of a reaction between verdazyl radicals and CH-acids is increasing in front of the electron-donor substituents and decreasing in front of electron-acceptor substituents. These regularities are not connected with the spin density values of the verdazyls’ reaction centers.Forcitation:Tsebulayeva Yu.V., Pryanichnikova M.K., Tanaseichuk B.S. Synthesis of 1,5-diphenyl-3-arylverdazils. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 1. P. 23-29