4-Carboxyl-2, 6-dinitrobenzene diazonium ion (CDNBD): a new diazonium for the detection of phenol ether homologues

Abstract

Pharmaceutical phenol ethers are a heterogeneous group of compounds possessing ether linkage to an aromatic nucleus. Diazo coupling is rare with these compounds and no physicochemical method of analysis has been reported based on the reaction of these ethers with a diazonium ion. The high reactivity of 4-carboxyl-2,6-dinitrobenzene diazonium ion (CDNBD) is therefore investigated in this work. Comparative coupling reaction was done with two other diazonium ions (derived from p-nitroaniline and sulphanilic acid). Twenty-two phenol ethers were selected for evaluation of their reactivity with the three diazonium ions. Such ethers consist of those with naphthalenes, indole and bridged rings. Spot tests were used to establish coupling at room and elevated temperatures. Visual inspection and thin layer chromatographic (TLC) analysis of the reaction mixture provided evidence of coupling or otherwise. UV-VIS absorption spectra were used to characterize brightly coloured adducts, as a preliminary test for the estimation of these ethers by spectrophotometry. Of all the ethers screened, fourteen gave instant and distinct colour from CDNBD while seven of these gave colours of deeper intensity at elevated temperature. Only three of the ethers gave instant colour with diazotized p-nitroaniline while one compound gave instant colour with diazotized sulphanilic acid. UV absorption spectral analysis reveals the superiority of CDNBD for the detection and possible estimation of these ethers. CDNBD is shown to be a highly reactive arenediazonium ion with the possibility of finding usefulness for the determination of phenol ethers by ultraviolet/visible spectrophotometry and precolumn derivatization in high performance liquid chromatographic (HPLC) analysis.

Journal of Pharmacy & Bioresources Vol. 2(2) 2005: 146-161