Formation of mixed organic layers by stepwise electrochemical reduction of diazonium compounds

This work describes the formation of a mixed organic layer covalently attached to a carbon electrode. The strategy adopted is based on two successive electrochemical reductions of diazonium salts. First, bithiophene phenyl (BTB) diazonium salt is reduced using host/guest complexation in a water/cyclodextrin (β-CD) solution. The resulting layer consists of grafted BTB oligomers and cyclodextrin that can be removed from the surface. The electrochemical response of several outer-sphere redox probes on such BTB/CD electrodes is close to that of a diode, thanks to the easily p-dopable oligo(BTB) moieties. When CD is removed from the surface, pinholes are created and this diode like behavior is lost. Following this, nitrophenyl (NP) diazonium is reduced to graft a second component. Electrochemical study shows that upon grafting NP insulating moieties, the diode-like behavior of the layer is restored which demonstrates that NP is grafted predominately in the empty spaces generated by β-CD desorption. As a result, a mixed BTB/NP organic layer covalently attached to a carbon electrode is obtained using a stepwise electrochemical reduction of two diazonium compounds.     

Cathodic reduction of diazonium salts in aprotic medium

Cathodic reduction of diazonium salts in acetonitrile led to the formation of azobenzenes, in good to moderate yields, and diarylamines as minoritary products. The reactions were carried out at the second reduction potential of the diazonium salts, involving aryl anions in the formation of the products.     

Spontaneous grafting of diazonium salts: chemical mechanism on metallic surfaces

The spontaneous reaction of diazonium salts on various substrates has been widely employed since it consists of a simple immersion of the substrate in the diazonium salt solution. As electrochemical processes involving the same diazonium salts, the spontaneous grafting is assumed to give covalently poly(phenylene)-like bonded films. Resistance to solvents and to ultrasonication is commonly accepted as indirect proof of the existence of a covalent bond. However, the most relevant attempts to demonstrate a metal-C interface bond have been obtained by an XPS investigation of spontaneously grafted films on copper. Similarly, our experiments give evidence of such a bond in spontaneously grafted films on nickel substrates in acetonitrile. In the case of gold substrates, the formation of a spontaneous film was unexpected but reported in the literature in parallel to our observations. Even if no interfacial bond was observed, formation of the films was explained by grafting of aryl cations or radicals on the surface arising from dediazoniation, the film growing later by azo coupling, radical addition, or cationic addition on the grafted phenyl layer. Nevertheless, none of these mechanisms fits our experimental results showing the presence of an Au-N bond. In this work, we present a fine spectroscopic analysis of the coatings obtained on gold and nickel substrates that allow us to propose a chemical structure of such films, in particular, their interface with the substrates. After testing the most probable mechanisms, we have concluded in favor of the involvement of two complementary mechanisms which are the direct reaction of diazonium salts with the gold surface that accounts for the observed Au-N interfacial bonds as well as the formation of aryl cations able to graft on the substrate through Au-C linkages.     

Functionalization of carbon nanotubes by electrochemical reduction of aryl diazonium salts: a bucky paper electrode.

Small-diameter (ca. 0.7 nm) single-wall carbon nanotubes are predicted to display enhanced reactivity relative to larger-diameter nanotubes due to increased curvature strain. The derivatization of these small-diameter nanotubes via electrochemical reduction of a variety of aryl diazonium salts is described. The estimated degree of functionalization is as high as one out of every 20 carbons in the nanotubes bearing a functionalized moiety. The functionalizing moieties can be removed by heating in an argon atmosphere. Nanotubes derivatized with a 4-tert-butylbenzene moiety were found to possess significantly improved solubility in organic solvents. Functionalization of the nanotubes with a molecular system that has exhibited switching and memory behavior is shown. This represents the marriage of wire-like nanotubes with molecular electronic devices.     

Determination of Cd and Pb on glassy carbon electrode modified by electrochemical reduction of aromatic diazonium salts

Carbon modified by the reduction of aromatic diazonium derivatives was first used as electrode for the electrochemical stripping analysis of heavy metals. As a model, the glassy carbon electrode was modified with benzoic acid by electrochemical reduction of diazobenzoic acid, and the resulting modified electrodes were used for determination of Cd²⁺ and Pb²⁺. The anodic peak currents of cadmium and lead at the benzoic acid-modified glassy carbon electrode are 7.2 and 6 times of that at the bare glassy carbon electrode. A linear response was observed for Pb²⁺ and Cd²⁺ in the range of 0.5–50 μg/l. The detection limits are 0.20 μg/l for Pb²⁺ and 0.13 μg/l for Cd²⁺. The relative standard deviations for six consecutive measurements of 50 μg/l Cd²⁺ and 50 μg/l Pb²⁺ are 0.82% and 3.02%, respectively. Applicability of the sensor to the determination of Cd²⁺ and Pb²⁺ in sewerage samples was demonstrated.     

Stimulation by Sn+2 or ascorbic acid on diazonium salts reactions

Use of a mild reducing agent and ligand transfer for the transformation of diazonium salts into aryl halides provides an alternative to the Sandmeyer procedure.     

Covalent modification of iron surfaces by electrochemical reduction of aryldiazonium salts.

Electrochemical reduction of aryldiazonium salts (in acetonitrile or acidic aqueous medium) on an iron or mild steel surface permits the strong bonding (which resists an ultrasonic cleaning) of aryl groups on these surfaces. Attachment of aryl groups was demonstrated by the combined used of electrochemistry, infrared spectroscopy and polarization modulation infrared reflection spectroscopy (PMIRRAS), Rutherford backscattering, X-ray photoelectron spectroscopy, and capacity measurements. The substituents of aryl groups, which can be widely varied, include NO2, I, COOH, and long alkyl chains. It is shown that the attachment of the aryl groups is to an iron and not to an oxygen atom and that the bond is covalent.     

Reaction of 5-alkylidenerhodanines with diazonium salts

In the action of diazonium salts on 5-alkylidenerhodanines, azo compounds are formed by the replacement of one or two hydrogen atoms in the methyl group. In the case of 5-ethylidenerhodanines, the formation of an azorhodanine through the replacement of the alkylidene residue by an arylazo group takes place simultaneously. In the formazyl derivatives the long-wave absorption maximum is displaced hypsochromically by 15–20 nm as compared with the dyes having a single azo group.     

Aryl diazonium salts: a new class of coupling agents for bonding polymers, biomacromolecules and nanoparticles to surfaces

This critical review summarizes existing knowledge on the use of diazonium salts as a new generation of surface modifiers and coupling agents for binding synthetic polymers, biomacromolecules, and nanoparticles to surfaces. Polymer grafts can be directly grown at surfaces through the so-called grafting from approaches based on several polymerization methods but can also be pre-formed in solution and then grafted to surfaces through grafting onto strategies including "click" reactions. Several routes are also described for binding biomacromolecules through aryl layers in view of developing biosensors and protein arrays, while the use of aryl diazonium coupling agents is extended to the attachment of nanoparticles. Patents and industrial applications of the surface chemistry of diazonium compounds are covered. This review stresses the paramount role of aryl diazonium coupling agents in adhesion, surface and materials sciences (114 references).     

Reaction of heterocyclic diazonium salts with hydrazones

Depending on the nature of the heteroring and the hydrazone, a formazan or a heterylazophenylhydrazone are formed in the reaction of an aryl hydrazone with the diazonium salt obtained from a heterocyclic amine. Disproportionate to form a triphenylformazan is also possible.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1062–1064, August, 1972     

Photochemical grafting of diazonium salts on metals

4-Nitrobenzenediazonium may be photochemically grafted onto gold, copper and iron under visible and UV light. Thin nanometre layers are obtained and characterized by IRRAS, electrochemistry and ellipsometry.     

Reaction of some organomercury compounds with diazonium salts

Summary We were the first to replace a mercury atom attached to a saturated carbon atom by the arylazo group. The reaction of the p-nitro- and 2,4-dinitrophenyldiazonium fluoborates with ethyl -bromomercuriphenylacetate and with bromomercurimethyl tert-butyl ketone give the corresponding arylhydrazones in good yields.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1711–1712, September, 1964     

Electrochemical transformation of diazonium salts into diaryl disulfides

Electrolyses of aryldiazonium tetrafluoroborates in CS₂/EtOH and Bu₄NClO₄, as the solvent-supporting electrolyte system, led to the corresponding diaryl disulfides in good yields.