Solvolysis of Some Arenediazonium Salts in Binary EtOH/H 2 O Mixtures under Acidic Conditions

• Published in: European journal of organic chemistry 2003-09, Vol.2003 (17), p.3421-3428
• Main Authors: Pazo‐Llorente, Román, Bravo‐Díaz, Carlos, González‐Romero, Elisa
• Format: Article
• Language: English
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200300183

We have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2‐, 3‐, and 4‐methylbenzenediazonium ions (2‐, 3‐, and 4‐MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants ( k obs ) for substrate loss are equal to those for product formation, and they remain essentially constant (2‐MBD) with changing solvent composition but increase by a factor of ≈︁2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products − cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) − were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity ( S ) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log k obs and Y Cl (solvent ionizing power) were observed for the three ArN 2 + ions. All data are consistent with the rate‐determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)