Diazohydroxides, Diazoethers and Related Species

Abstract

Arenediazonium, ArN 2 + , ions may function as Lewis acids reacting with nucleophiles (Lewis bases, Nu − or NuH followed by loss of a proton) to give covalently bonded adducts, ArN 2 ‐Nu, at the β‐nitrogen of the arenediazonium ion, which is the electrophilic reactive center. Typical examples of covalently bonded adducts are the azo dyes (C‐coupling) but atoms other than C may be involved and the present chapter will mainly focus on the chemistry of O‐coupling adducts of the type ArN=N‐Nu, e.g., where Nu = OH − (formation and decomposition of diazohydroxides and diazoates), Nu = RO − , ArO − , ROH and cyclodextrins (formation and decomposition of diazoethers), with special emphasis on the kinetics and mechanism of the reactions involved. We will also cover, to a lower extent, those reactions with other nucleophiles leading to S‐, N‐ and P‐adducts. O‐coupling reactions are complicated by two major features. First, the formed adducts may display geometrical isomerism, leading to the E ‐( syn ) and Z ‐( anti ) forms, which show different stability and can be interconverted to each other by acid catalyzed processes. Second, some of the O‐adducts formed may be, in turn, components of a Lewis acid‐base equilibrium, for example between ArN 2 + and OH − ions, and hence may undergo further reactions.

Effects of acidity and emulsifier concentration on the distribution of vitamin C in a model food emulsion

“…As illustrated in Fig. B, no significant changes in the peak potential are obtained up to pH ~ 6, after which a relevant shift in the peak potential, attributed to the formation of the corresponding diazohydroxide 16‐ArN 2 OH, is detected …”

“…ArN 2 + ions are known to react with OH − ions to give diazotates, and the formation of these products may lead to significant changes in both the peak potential and peak currents of the voltammetric peaks of 16‐ArN 2 + ions. For this reason, we investigated the effects of acidity on the voltammetric peaks obtained in emulsions.…”

Some Theoretical and Experimental Insights on the Mechanistic Routes Leading to the Spontaneous Grafting of Gold Surfaces by Diazonium Salts

“…On the basis of the work of Bravo-Díaz and co-workers, we will briefly examine the different species that are present in a diazonium solution depending on the acidity of the medium. − In ACN, the diazonium cation is present, but in an aqueous medium, the diazonium cation, diazohydroxide, and diazoate species can be present depending on the pH. In aqueous acidic (pH <4) solutions, in the dark and in the absence of reductants, arenediazonium ions, ArN 2 + , decompose spontaneously through the rate-limiting formation of the extremely unstable aryl cation.…”

Chirality-Selective Functionalization of Semiconducting Carbon Nanotubes with a Reactivity-Switchable Molecule

“…We synthesized a pair of 3- O - p -nitro­benzene­diazo­ascorbic acid ( p -NO 2 -DZE) isomers by coupling an aryldiazonium salt to ascorbate (Figure a). First isolated by Doyle et al in 1989, the E -isomer of this ascorbate diazoether compound is stabilized in comparison to other O -coupling derivatives of aryldiazonium by its pseudo-ring structure. − In order to determine the reactivity of the two p -NO 2 -DZE isomers with semiconducting SWCNTs, we added an aliquot of a solution containing either the Z - or E -diazoether to a suspension of HiPco SWCNTs that had been enriched in the (6,5) chirality by gel chromatography and monitored the reaction progress via PL spectroscopy. The chirality enrichment of the SWCNT suspension results in a well-defined system for clear observation of the PL from both the intrinsic (E 11 ) and defect (E 11 – ) excitonic emission states that allowed us to monitor the reaction progress.…”