HETEROCYCLES

Heterocycles has a pay-per-view service for Non-subscribers.
You will be able to directly purchase the full text article through PayPal.
Your purchased Paper can be downloaded after the payment is completed.
An e-mail will be sent the URL to download the paper.
If you have any questions, please contact: purchase@heterocycles.com

Price: ¥ 4,400 (Yen only)
Period: This Article can be accessed for 7 days.

■ Substituent Effects on Acidities and Tautomeric Structures of 1-Aryl-3-ethoxycarbonyl-4-pyrazolones and Their 5-Arylazo Derivatives

Ahmad S. Shawali,* Hamdi M. Hassaneen, and Mokntar A. Hanna

*Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt

Abstract

Two series of 1-aryl-3-ethoxycarbonyl-4-hydroxypyrazoles (1) and 1-(m-chlorophenyl)-3-ethoxycarbonyl-4-hydroxy-5-arylazopyrazoles (2) have been prepared and their acidities determined spectrophotometrically at 25°C and ionic strength of 0.1 in 60 vol.% ethanol-water medium. The pK_a data were correlated with the simple and extended Hammett equations. The regression lines are: pK_a(1) =9.34 - 0.794 δ_X ; pK_a(1) = 9.78 - 0.794 δ_XC6H4 ; PK_a(2) = 7.49 - 1.158 δ_X ; and PK_a(2) = 7.49 -1.245 δ_I,X - 1.075 δ_R,X. It is concluded that such linear relations exclude the presence of the keto tautomers (1A) and (2A) in equilibrium with the hydroxy tautomers (1B) and (2B) respectively, in agreement with the spectral data of the compounds investigated. The electrical effect, E, of value 0.86 determined for series (2) indicates that such compounds exist in the cis-chelated hydroxyazo structure (2B).