Diazonium reduction

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different... 

From the discussion earlier, it is clear that the use the electrochemical reduction of diazonium reagents on carbon leads to reproducible molecular layers that can withstand fabrication and packaging procedures. In addition to the ability to readily fabricate reproducible junctions, another aspect of the excellent stability of this system is the excellent temperature stability of PPF/molecule/Cu MJs [73]. While the stability of Au/SAM/PEDOT/Au MJs was shown to be limited to temperatures of 50 °C [84] or 60 °C [85], molecular layers on PPF made using diazonium reduction are stable to 400 °C, while completed PPF/molecule/Cu MJs are stable to at least 250°C [73]. Moreover, when employing a covalent top contact material, also made of carbon, both temperature and bias stability are improved, as discussed later. 

Kibena, E., M. Marandi, U. Maeorg, L. B. Venarusso, G. Maia, L. Matisen, A. Kasikov, V. Sammelselg, and K. Tammeveski. Electrochemical modification of gold electrodes with azobenzene derivatives by diazonium reduction. Chem. Phys. Chem. 14, 2013 1043-1054. 

Brooksby, P. A. and A. J. Downard. Electrochemical and atomic force microscopy study of carbon surface modification via diazonium reduction in aqueous and acetonitrile solutions. Langmuir 20, 2004 5038-5045. 

Anariba, F., S. H. DuVall, and R. L. McCreery. Mono- and multilayer formation by diazonium reduction on carbon surfaces monitored with atomic force microscopy scratching. Ana/. Chem. 75, 2003 3837-3844. 

The pioneering work of Delamar et al. [14] demonstrated the coating of glassy carbon by an organic layer of 4-nitrophenyl by the electrochemical reduction of (4-nitrophenyl)diazonium tetrafluoroborate (typical concentration 1-10 mM) from an ACN solution. Cyclic voltammetry shows two reduction phenomena in the first scan. The first peak centered at —0.04 V versus SCE is irreversible and corresponds to the diazonium reduction, whereas the second one is reversible and appears at a more cathodic potential (—1.20 V vs SCE) that is related to the electroactivity of the nitro group. A second voltammogram recorded on the same electrode shows... 

Zigah, D., Noel, J. M., Lagrost, C., Hapiot, P. Charge transfer between electroactive species immobilized on carbon surfaces by aryl diazonium reduction. SECM investigations. J. Phys. Chem. C 2010, 114, 3075-3081. 

Azo-compounds can be obtained by reduction of nitro-compounds, or by oxidation of hydrazo-compounds. They are usually prepared, however, by reacting a phenol or amine with a diazonium salt. The coupling usually takes place in the position para to the hydroxyl or amino group, but if this position is occupied it goes to the ortho position, e.g. 

It is prepared commercially by treating benzene diazonium chloride with sodium sulphite and then reducing the mixture with zinc dust and ethanoic acid. It can also be prepared by reduction of benzene diazonium chloride with SnCl. ... 

In absolute ethanol solution, the ethyl ether and the corresponding hydrocarbon are formed, the latter by reduction of the diazonium compound by the ethanol, which is itself oxidised to acetaldehyde ... 

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

Nitrophenylhydrazine may be similarly prepared from p-nitroplienyl-diazonium chloride by reduction with sodium or ammonium sulphite ... 

The preparation of 5-azothiazoles uses the nucleophilic character of C-5 carbon in reaction with the appropriate diazonium salt (402, 586). These 5-azothia2oles form 1 1 complexes with Ag (587). 2-Amino-4-methyl-5-arylazothiazoles give reduction waves involving two-electron transfer the Ej/ values correlate to the angle between the thiazole and phenyl rings (588). 

Sodium borohydride has also been used to reduce aryl diazonium salts m reductive deam mation reactions... 

Reductive deamination of primary arylamines The ammo substituent of an arylamine can be replaced by hydrogen by treatment of its de rived diazonium salt with ethanol or with hypophosphorous acid... 

Aromatic Hydrazines. A general synthesis for aryUiydraziaes is via diazotization of aromatic amines, followed by reduction of the resulting diazonium salt (18) ... 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

The most important synthesis of pyrazolones involves the condensation of a hydrazine with a P-ketoester such as ethyl acetoacetate. Commercially important pyrazolones carry an aryl substituent at the 1-position, mainly because the hydrazine precursors are prepared from readily available and comparatively inexpensive diazonium salts by reduction. In the first step of the synthesis the hydrazine is condensed with the P-ketoester to give a hydrazone heating with sodium carbonate then effects cyclization to the pyrazolone. In practice the condensation and cyclization reactions are usually done in one pot without isolating the hydrazone intermediate. 

SnCl2 reduction produced the 4-hydrazinoisoxazole (243). In ethanol the diazonium salt reacted with the 4-aminoisoxazole to produce the linear triazine (244) (Scheme 85). Diazoisoxazoles can also be treated with KI or H20/urea to produce the 4-iodo or 4-hydroxy derivatives (63AHC(2)365). These Sandmeyer reactions have been extended to a variety of isoxazole systems (77JMC934, 63AHC(2)365). 

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