Polarography as a tool in organic analysis. III

Summary Rapid indirect polarographic and visual micro-methods have been developed for the determination of azo, azo and nitro, or azo and nitroso groups in the same solution. First, the azo group is reduced with titanium(III) at p_H 1.7 and then the nitro group at p_H 5.5. The excess of reductant is determined polarographically. Mixtures containing nitroso and azo groups are analysed by indirect polarography by reducing the nitroso group first in 7N acid and then the azo group at p_H 5.

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Zusammenfassung Indirekte polarographische und visuelle Mikromethoden zur Bestimmung von Azogruppen, Azo- und Nitrogruppen, oder Azo- und Nitrosogruppen in derselben Lösung wurden ausgearbeitet. Zuerst wird die Azogruppe bei p_H 1,7 mit Titan(III), dann die Nitrogruppe bei p_H 5,5 reduziert. Der Überschuß des Reduktionsmittels wird polarographisch bestimmt. Gemische mit Nitroso-und Azogruppen lassen sich indirekt polarographisch analysieren, indem man zuerst die Nitrogruppe in 7-n Säure und dann die Azogruppe bei p_H 5 reduziert.

     

Selective reduction of alkenes, α,β-unsaturated carbonyl compounds, nitroarenes, nitroso compounds, N,N-hydrogenolysis of azo and hydrazo functions as well as simultaneous hydrodehalogenation and reduction of substituted aryl halides over PdMCM-41 catalyst under transfer hydrogen conditions

Chemoselective reductions of alkenes, α,β-unsaturated carbonyl compounds, nitro and nitroso compounds, N,N-hydrogenolysis of azo and hydrazo functions as well as simultaneous reduction and hydrodehalogenation of substituted aryl halides, including bulkier substrates, were achieved by catalytic transfer hydrogenation (CTH) using mesoporous PdMCM-41 catalyst. The yields were practically unaffected upon recycling of the catalyst. Further, the CTH process is accomplished without affecting the reduction of any other reducible functional group.     

Reactions of aromatic nitro,nitroso, hydroxylamino azoxy,azo and hydrazo compounds with selenol

Relative reactivities of aromatic nitro, nitroso, hydroxylamino, azoxy, azo and hydrazo compounds in the reduction with RSe^? were found to fall in the following order :

     

Semicarbazones from N-hydroxyureas and amines: a novel entry in the reactivity of the acyl nitroso group

The condensation of carbamoyl nitroso compounds, obtained by oxidation of N-hydroxyureas, with amines unexpectedly afforded semicarbazones (aka carbamoyl hydrazones). Although the substitution of the nitrosyl moiety might compete to afford the corresponding urea, an excess of amine led to the semicarbazone as the major product, which is presumably formed via isomerization of an initially generated acyl azo compound.     

Identification of metabolites of 4,4'-diaminodiphenylmethane (methylene dianiline) using liquid chromatographic and mass spectrometric techniques.

The in vitro metabolism of 4,4'-diaminodiphenylmethane (methylene dianiline, MDA) was investigated using rabbit liver microsomes. Minimal clean-up of the microsomal incubations was carried out using zinc sulphate precipitation followed by solid-phase extraction on Sep-Pak C18 cartridges. Three metabolites were detected in hepatic microsomal incubations, namely the azodiphenylmethane (azo) azoxydiphenylmethane (azoxy) and 4-nitroso-4'-aminodiphenylmethane (nitroso) compounds. The azo and azoxy metabolites were produced enzymatically whereas the nitroso compound may have been formed via a non-enzymatic process. Reversed-phase high-performance liquid chromatography-plasma spray mass spectrometry was used to initially detect these metabolites. Fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry were utilized to further structurally characterise these compounds. Comparison of mass spectral data obtained from synthesised standards with data obtained on the putative metabolites substantiated the characterisation of these compounds.     

Oximes as intermediates or final products in reactions of nitroheteroarenes with nucleophiles in the presence of sodium methoxide‐methanol system

It has been shown that reactions of 4‐nitroimidazoles and some other nitroaromatic systems with phenyl‐acetonitrile in the presence of sodium methoxide in methanol lead to the reduction of the nitro to nitroso group and to the nucleophilic displacement of hydrogen atom at the ring by the respective carbanion followed by tautomerization of the nitroso compound to an oxime. Similar reactions of 4‐nitroimidazoles with such nucleophiles as anions generated from 4‐amino‐1,2,4‐triazole occur with the ring transformation of imidazole into 1,2,4‐oxadiazole derivatives sometimes undergoing further processes in the reaction medium. Structures of some products have been confirmed by X‐ray diffraction analysis.     

Synthesis and electrochemical studies of phenylazo substituted tetraaza macrocyclic complexes of Ni(II)

Synthesis and characterization of some phenyl azo substituted tetraaza macrocyclic complexes of Ni(II) are reported. Electrochemical behaviour of these macrocyclic complexes has been examined using polarographic, voltammetric and spectroscopic techniques. These studies show that both the ligand and the metal are electrochemically active. The electrochemical behaviour of the azo function has been shown to occur through a single four-electron process. When a nitro group is also present, the nitro function of the azo moiety is reduced in a six-electron cathodic wave.     

Thermochemical properties and group values for nitrogen-containing molecules

Gas-phase thermochemical group additivity values were derived from CBS-QB3 computational chemistry calculations for 105 noncyclic C/H/O/N molecules. The molecules contain nitrile, nitro, nitroso, nitrite, nitrate, amine, imino, and azo functional groups. The enthalpy of formation, entropy, and heat capacity values for 49 atom-centered groups were derived. The effect of hindered internal rotations was included via rotor potential energy scans and solution of the one-dimensional Schrodinger equation. The average 95% confidence intervals across all derived groups are 1.4 kcal mol(-1) for the enthalpy, 1.3 cal mol(-1) K(-1) for the entropy, and 1.0 cal/mol K for the heat capacity. The presented group values will be useful when employing automatic reaction mechanism generation tools to examine the role of fuel-bound or molecular nitrogen in energy-related or atmospheric processes.     

Synthesis and photochemical properties of azidohemicyanine

Photochemical activity of azidohemicyanine (1-methyl-4-(4-azidostyryl)quinolinium iodide) was predicted by quantum chemical calculations and confirmed experimentally. The azidohemicyanine, which was synthesized, is characterized by a long-wavelength absorption band (LWAB) in the spectral region 350–500 nm with a maximum at 417 nm; it decomposes with a quantum yield of 0.84±0.17 upon irradiation within the LWAB, the quantum yield being independent of the presence of oxygen. The reaction products identified by ESI mass spectrometry include the corresponding primary amine as well as azo, hydrazo, nitroso, and nitro compounds, some of them are unidentified. The azidohemicyanine possesses the longest-wavelength visible light sensitivity among aromatic azides known so far. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1402–1408, July, 2008.     

Phase I and phase II reductive metabolism simulation of nitro aromatic xenobiotics with electrochemistry coupled with high resolution mass spectrometry

Electrochemistry combined with (liquid chromatography) high resolution mass spectrometry was used to simulate the general reductive metabolism of three biologically important nitro aromatic molecules: 3-trifluoromethyl-4-nitrophenol (TFM), niclosamide, and nilutamide. TFM is a pesticide used in the Laurential Great Lakes while niclosamide and nilutamide are used in cancer therapy. At first, a flow-through electrochemical cell was directly connected to a high resolution mass spectrometer to evaluate the ability of electrochemistry to produce the main reduction metabolites of nitro aromatic, nitroso, hydroxylamine, and amine functional groups. Electrochemical experiments were then carried out at a constant potential of ?2.5 V before analysis of the reduction products by LC-HRMS, which confirmed the presence of the nitroso, hydroxylamine, and amine species as well as dimers. Dimer identification illustrates the reactivity of the nitroso species with amine and hydroxylamine species. To investigate xenobiotic metabolism, the reactivity of nitroso species to biomolecules was also examined. Binding of the nitroso metabolite to glutathione was demonstrated by the observation of adducts by LC-ESI⁺-HRMS and the characteristics of their MSMS fragmentation. In conclusion, electrochemistry produces the main reductive metabolites of nitro aromatics and supports the observation of nitroso reactivity through dimer or glutathione adduct formation. Graphical Abstract

Electrochemical simulation of nitro aromatics metabolism using hyphenation of electrochemistry and massspectrometry     

One‐pot three‐component synthesis of novel 2‐(3‐nitro‐phenyl)‐quinazoline‐4‐carboxylic acid derivatives

A simple and easy synthesis of 2‐(3‐nitro‐phenyl)‐quinazoline‐4‐carboxylic acid ( 3 ) has been successfully developed through a one‐pot three‐component condensation reaction of (2‐amino‐phenyl)‐oxo‐acetic acid sodium salt ( 1 ) obtained from the hydrolysis of isatin with ammonium acetate and 3‐nitrobenzaldehyde. Some novel quinazoline‐ester derivatives 4‐7 were then obtained by the reaction between the new compound 3 and various alcohols. Then, quinazoline‐amide derivatives 10‐14 were synthesized from the reaction of various amines and 2‐(3‐nitro‐phenyl)‐quinazoline‐4‐carbonyl chloride ( 8 ), obtained by the reaction of compound 3 with SOCl₂. Finally, some novel quinazoline‐azo derivatives 17‐19 were synthesized by the coupling reaction between β‐dicarbonyl compounds and the novel amino‐quinazoline derivative compound 15 , obtained by reduction of nitro‐quinazoline derivative compound 11 . Thus, a new series of quinazoline‐4‐carboxylic acid, ester, amide, and azo derivatives was synthesized and fully characterized by ¹H NMR, ¹³C NMR, IR, and mass spectrometry analysis.     

Atomic absorption spectrometric and potentiometric microdetermination of the nitro and nitroso groups in organic compounds

New simple, rapid, accurate, and selective methods are described for microdetermination of the nitro and nitroso groups in organic compounds. These are based on reduction with cadmium metal and 0.05 M HCl whereby 6 and 4 equivalents of the cadmium ions are released per nitro and nitroso groups, respectively. The cadmium ions are measured by atomic absorption spectrometry at 228.8 nm, potentiometrically by titration with EDTA using the cadmium ion selective electrode, and visually by EDTA titration using Eriochrome Black T indicator. Results with an average recovery of 98% and a mean standard deviation of 1.3% are obtainable and no interferences are caused by many nitrogen, oxygen, and sulfur functional groups.     

On the mechanism for the photooxidation of aromatic azides containing a secondary N–H bond: A sequence of intramolecular transformations with the formation of heterocyclic oximes

During the photooxidation of aromatic azides containing a secondary N–H bond at the para-position, a sequence of intramolecular transformations of nitroso oxides led to the formation of heterocyclic oximes along with the corresponding nitroso and nitro compounds.     

Electronic spectra, solvatochromic behavior and acid-base properties of some azo cinnoline compounds

The electronic spectra of three azo cinnoline derivatives have been studied in pure and mixed organic solvents of different characteristics as well as the effect of concentration of the compounds in the different solvents. The different bands observed have been assigned to the proper electronic transition. The longer wavelength band displayed by the para nitro cinnoline derivative in dimethylformamide (DMF) solution is assigned to an intermolecular CT transition. The solvated H-bonding complexes formed between DMF and the para nitro derivative were investigated. DeltaG and K(f) values of these complexes have been determined. The acidity constants of the para nitro compound were determined from the spectra in aquous-methanolic solution of varying pH values. The effect of temperature on the longer wavelength visible band of p-NO(2) has been investigated.     

偶氮染料在酸性介质中的电还原性质

研究了4个偶氮染料在酸性介质中的电还原性质。偶氮基在酸性介质中的还原均为不可逆四电子一步全还原。邻、对位上有吸电子基(如—CO_2Bu-n)的偶氮基较间位有吸电子基时更易被还原。分子中同时含有偶氮基和硝基时,偶氮基先被还原。     

A convenient and general ruthenium-catalyzed transfer hydrogenation of nitro- and azobenzenes

An easily accessible in situ catalyst composed of [{RuCl(2)(p-cymene)}(2)] and terpyridine has been developed for the selective transfer hydrogenation of aromatic nitro and azo compounds. The procedure is general and the selectivity of the catalyst has been demonstrated by applying a series of structurally diverse nitro and azo compounds (see scheme).     

Effect of Additives Containing a Heavy Atom on the Yield of Photooxidation Products of Arylazides

The effect of additives containing a heavy atom on the yield of nitroso and nitro compounds, the photooxidation products of arylazides, was studied. The addition of ethyl bromide to the reaction mixture increases the total yield of photooxidation products and the contribution of nitroso compounds. The assumption was made that the intersystem crossing (ISC) of nitrene from the singlet to the triplet state is the rate-determining step of the reaction, and the ISC of the singlet adduct of nitrene with oxygen is one of the steps of the reaction path leading to the formation of nitroso compounds.     

Microgram detection of phenols and determination of nitro- and nitroso-phenols

The microgram detection of phenols and determination of nitro- and nitroso-phenols is based on their treatment in alkaline solution with a chlorinated hypochlorite solution, resulting in characteristic colours. Ion-exchange resin beads are used to make the test sensitive and selective. A few nitro and nitroso compounds have been determined spectrophotometrically.     

Étude D'une Série de Phénoxazines et D'azaphénoxazines par Spectrométrie de Masse

Mass spectra of substituted phenoxazines and azaphenoxazines have been determined and are discussed here. These compounds are characterised by hydrogen on the heterocyclic nitrogen and aromatic rings with nitro groups and chlorine as substituents. The fragmentation patterns are explained by known mechanisms. An interpretation of almost all the peaks is offered. The presence of the substituents causes a complete change in the fragmentation patterns compared with the unsubstituted phenoxazine. This is due to changes in charge localisation, caused by the substituents. Isomerisation of the nitro group to the nitroso group gives rise to a particular fragmentation route.     

Electrochemical reduction of 5-halo-5-nitro-1,3-dioxanes and 2-halo-2-nitro-1,3-propanediols

The character of the first stage of reduction of 5-X-5-nitro-1,3-dioxanes 1—10 and 2-X-2-nitro-1,3-propanediols 11 and 12 is independent of the nature of halogen (X = Br, Cl) and substituents in position 2 of the dioxane cycle. The transfer of two electrons to a molecule of compound 1—12 is accompanied by the anionoid elimination of halogen and formation of the anion of nitronic acid. The high mobility of halogen is mainly due to the acceptor nitro group capable of further transformations in the -position to halogen. The direction of further reduction involving the electron transfer to electrochemically active groups in the aromatic fragment of the molecule is determined by the nature of these groups. Chloro-, bromo-, and iodophenyl-substituted derivatives 4, 5, and 8—10 are reduced as typical halobenzenes. In the case of nitrophenyl-substituted compounds 3 and 7, the dioxane cycle opens to form dianions of p- and m-nitrobenzaldehydes along with the reduction of the nitroso group through the stages of formation of the radical anion and radical anion of the nitroso group. The radical anions of the nitro and nitroso derivatives were identified by ESR.