|
Abstract
|
The electrochemical reduction of 9 substituted aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones (DBXT) and 10 substituted 3-methyl-1,4-diphenyl-1,4-dihydrobenzo [6,7]chromeno[2,3-c]pyrazole-5,10 diones (DCPD) in water/DMF mixture (30/70 v/v) has been studied by cyclic voltammetry, choronoamperometry and differential pulse voltammetry at a glassy carbon electrode. Our data show that the electrochemical reduction of DBXTs takes place in two consecutive two-electron processes, ErEq, corresponding to two successive reductions of naphthoquinone moieties to 1,4-naphthalenediol groups (13- phenyl-13H-dibenzo[b,i]xanthene-5,7,12,14-tetraol). On the other hand, electrochemical reduction of DCPDs shows a reversible two-electron process corresponding to the reduction of naphthoquinone moiety to 1,4-naphthalenediol group. Our data also show that DBXT derivatives containing electronwithdrawing groups participate in the comproportionation reaction, while the fully reduced DBXT derivatives with electron-donating groups are unstable and readily undergoes side reactions. The calculated diffusion coefficient of some DBXT (5 107 cm2/s) and DCPD (2 107 cm2/s) derivatives shows that there is no significant relationship between the diffusion coefficients and substituent groups. The smaller diffusion coefficient of DCPD than that of the DBXT derivatives can be related to the formation of more and stronger hydrogen bonds by DCPD than DBXT derivatives. In this work, also, the correlation of E1/2 with s constants and the adsorption behavior of DBXTs and DCPDs has been investigated
|