Application of the Dropping Mercury Electrode to Diazo Chemistry

Abstract

The reduction of diazotized aromatic amines has been observed to occur at the dropping mercury electrode. The reduction is irreversible and the polarographic waves are too complex to treat with electrochemical equations. Nevertheless distinct waves whose heights vary directly with concentration are obtained. One wave of the reduction occurs at a potential well below that of the azo or nitro groups or nitrite ion. Therefore, it is possible to use the dropping mercury electrode with an applied potential of 0.3 volt vs. the saturated calomel electrode as an indicator for the measurement of the concentration of diazotized amines. In this manner, amperometric coupling titrations, diazotization rates, coupling rates, etc., may be studied. The new technique is more generally applicable than either the gasometric or colorimetric methods of measuring the concentration of diazotized amines. In certain cases, such as measuring the rapid formation of an insoluble azo compound, the polarographic technique is the only practical method available.

Electrochemical determination of rate constants and product yields for the spontaneous dediazoniation ofp-nitrobenzenediazonium tetrafluoroborate in acidic aqueous solution

“…At a specific pH [21,22], the diffusion currents are proportional to the arenediazonium salt concentration. Therefore, a DME electrode can be used to determine arenediazonium salts [17] both qualitatively and quantitatively by comparing the measured diffusion current with a calibration curve obtained from diffusion current-salt concentration profile.…”

“…A number of methods have been developed to monitor dediazoniations [26 -28]; however, little attention has been paid to the use of electrochemical methods [6,14,15,17,32]. Here we examined the dediazoniation of p-nitrobenzenediazonium tetrafluoroborate, pNBD, in aqueous solution by employing differential pulse polarography (DPP) at a DME and differential pulse voltammetry (DPV) on glassy carbon electrode (GCE) combined with a recently reported method [28] for using coupling reagents to quench the dediazoniation process at convenient times (Scheme IV).…”

Coupling rates and kinetics of arenediazonium cations with couplers utilized in the diazo reprographic process

“…and even as low as 0.62, in analogous plots [15]. If the monoionized form were the exclusive form of the coupler, the gradient should fall off near the pK, value (of 8.24) and become zero a t about p H 9.…”

Electrochemical Reduction of Aromatic Diazonium Salts: I . Electrochemical Behavior of p‐Tolyl‐ and p‐Anisyldiazonium Fluoborates at a Mercury Cathode: Evidence for the Corresponding Hydrazines Formation

“…Ar--NH----N -b e -> Ar--NH~N[:], is [5] 2Ar~NH--N[~ -> Ar--NH--NH--Ar q-N2 [6] Ar~NH--N[~ -b 2H + ~-Ar--NH----NH2 2+ [7] Ar--NH:NH2 2+ -~ 2e-> Ar--NH--NH2 i4 [8] Ar--NH--NH2 -~ H + ~_ Ar--NII--NH3 + [9] Thus the present paper demonstrates formation of a primary hydrazine derivative by a direct electrochemical reduction of the corresponding diazonium fluoborate.…”

“…Elofson and co-workers (6,13) have furthermore found that, for diazonium concentrations above 10-aM, the limiting current of the first wave reaches a constant value independent of concentration, and the occurrence of a polarographic maximum on the second one, which was interpreted by adsorption phenomena. In acidic medium, they have also observed a splitting of the second wave.…”