Dediazoniation of 1‐naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

Abstract

We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV-vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (k obs ) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase k obs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic D N + A N mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles.

Kinetics of brilliant green fading in the presence of TX-100, DTAB and SDS

“…The rates of chemical reactions are known to be changed by self-organized assemblies such as micelles [1][2][3][4][5][6][7][8][9]. Effects of micelles on these reactions can be attributed to electrostatic and hydrophobic interactions.…”

Effects of Surfactants on the Rate of Chemical Reactions

“…In the presence of SDS micelles, 1-naphthalenediazonium (ArN + 2 ) is incorporated into the micellar aggregates, given the estimated of 290 M −1 and = 9 × 10 −4 s −1 . It shows that a significant fraction of 1-naphthalenediazonium is incorporated into the micellar pseudophase at low-surfactant concentrations, where it undergoes thermal decomposition in the Stern layer [40].…”

Reactivity in organised assemblies

“…Fernandez-Alonso and co-workers 4 studied the dediazoniation of 1-naphthalenediazonium tetrafluoroborate in acidic aqueous solutions, in the presence and absence of sodium dodecyl sulfate micelles. Calculations based on a pseudophase model showed that the substrate binds to micelles in a significant fraction, even at low surfactant concentration (but above the critical micelle concentration, cmc).…”