PHOTOREDUCTION OF SOME NITROBIPHENYL ETHER HERBICIDES TO NITRO RADICAL ANIONS BY β-CAROTENE AND RELATED COMPOUNDS

Abstract —The nitrobiphenyl ether herbicides; 4-nitrobiphenyl ether, bifenox, nitrofen, acifluorfen, acifluorfen-methyl, acifluorfen-ethyl, and oxyfluorfen were reduced to their corresponding nitro radical anions by visible light in the presence of β-carotene, lycopene, retinol, retinal, retinoic acid and retinyl acetate in anaerobic solutions at high pH. It was more difficult to obtain spectra of bifenox, nitrofen and oxyfluorfen than acifluorfen derivatives, probably due to their poor solubilities. In neutral solutions the steady-state concentration of the nitro radical anions was low due to their faster rate of dispropor-tionation and the poor solubility of β-carotene. In the presence of retinal, the nitro radical anion of acifluorfen was produced at pH 7.4. Compounds containing conjugated double bonds such as crotonaldehyde and 2.4-hexadienal also reduced acifluorfen and its derivatives to their respective nitro radical anions in the presence of light. Ubiquinone-50 which does not contain conjugated double bonds in the side chain did not reduce acifluorfen under similar conditions.     

Kinetics of the liquid-phase catalytic hydrogenation of chlorine-containing aromatic nitro compounds in the presence of pyridine

We have analyzed experimental kinetic data for nitro compound consumption, for the formation of the corresponding amino product, and for the accumulation of intermediate products and by-products in the hydrogenation of chlorine-containing aromatic nitro compounds. The reaction has been carried out under static conditions over a platinum catalyst on a porous support in the presence of pyridine. The effect of the admixture on different hydrogenation steps of a chlorine-containing aromatic nitro compound has been quantitatively interpreted.     

Reductive transformations of unsaturated azabicyclic nitrolactams

Using different reducing methods unsaturated indolizidine and quinolizidine lactams substituted with a nitro group were transformed into various alkaloid-like derivatives. Hydrogen transfer and palladium catalyzed hydrogenation gave compounds of ketolactam or lactam type meanwhile the nitro group was eliminated. On the other hand, in presence of Raney-nickel catalyst the nitro compounds were reduced to diastereomeric amino derivatives whose stereochemistry was elucidated by NMR spectroscopy. Using sodium bis-dimethoxy-ethoxy-aluminum-hydride (Red-Al) as reducing agent an unexpected tricyclic azetidine was isolated and characterized.     

Asymmetric synthesis of highly substituted beta-nitro alcohols and enantiomerically enriched 4,4,5-trisubstituted oxazolidinones

It is demonstrated that alpha,alpha-disubstituted-alpha-nitroketones are reduced to the corresponding trisubstituted nitro alcohols in good to excellent yield and enantiomeric excess by borane-dimethyl sulfide in the presence of a chiral oxazaborolidine catalyst. Reduction of the nitro alcohols to the corresponding amino alcohols and their subsequent conversion to enantiomerically enriched 4,4,5-trisubstituted oxazoldinones is also reported.     

Improved and new syntheses of potential molecular electronics devices

New syntheses of ethyl and nitro substituted oligo(phenylene ethynylene)s (OPEs) have been developed. To further explore whether the presence of nitro functionality in OPEs leads to switching and memory capabilities, new nitro substituted OPEs have been designed and synthesized. An isatogen-based system, a structure that is isomeric to the nitro OPE, has been synthesized. Additionally, pyridine-based and chromium-based compounds have been synthesized. We surmise that redox reactions of these candidates may impart switching capabilities and electrochemical studies are shown. U-shaped OPEs were synthesized to inhibit leakage of metals deposited during formation of top contacts on self-assembled monolayers (SAMs). The OPEs contain either thiol-based moieties or isonitrile groups to enable formation of SAMs on metal substrates.     

Dehydrogenation of nitro derivatives of bibenzyl to corresponding nitro stilbene with dioxygen catalyzed by 2,2,6,6-tetramethylpiperidine-1-oxyl

A simple and effective oxidative dehydrogenation of nitro derivatives of bibenzyl was developed using a mixture of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and metal salts as catalyst under an atmospheric pressure of oxygen. The oxidation of several nitro derivatives of bibenzyl led to corresponding nitro stilbene in good yields, and the yields increased with the increase in the substituted nitro group on the bibenzyl. For example, the aerobic dehydrogenation of 2,2??,4,4??,6,6??-hexanitrobibenzyl in the presence of a catalytic amount of TEMPO with metal salts gave 2,2??,4,4??,6,6??-hexanitrostilbene in 81?% yield and 4,4??-dinitrostilbene-2,2??-disulfonic acid (75?%) was obtained from 4,4??-dinitrobibenzyl-2,2??-disulfonic acid.     

Reactivity toward oxygen of isobenzofuranyl radicals: effect of nitro group substitution

The presence of a nitro group in the p-phenyl position dramatically slows down the oxygenation of isobenzofuranyl radicals. However, both unsubstituted and m-substituted phenyl rings have no appreciable influence on the reactivity toward oxygen. Spin delocalization on the nitro group is proposed to explain the stability of the carbon-centered radical generated. [reaction: see text]     

Acid Catalyzed tert‐Butylation and Tritylation of 4‐Nitro‐1,2,3‐triazole: Selective Synthesis of 1‐Methyl‐5‐nitro‐1,2,3‐triazole via 1‐tert‐Butyl‐4‐nitro‐1,2,3‐triazole

4‐Nitro‐1,2,3‐triazole was found to react with tert‐butanol in concentrated sulfuric acid to yield 1‐tert‐butyl‐4‐nitro‐1,2,3‐triazole as the only reaction product, whereas tert‐butylation and tritylation of 4‐nitro‐1,2,3‐triazole in presence of catalytic amount of sulfuric acid in benzene was found to provide mixtures of isomeric 1‐ and 2‐alkyl‐4‐nitro‐1,2,3‐triazoles with predominance of N2‐alkylated products. A new methodology for preparation of 1‐alkyl‐5‐nitro‐1,2,3‐triazoles from 1‐tert‐butyl‐4‐nitro‐1,2,3‐triazole via exhaustive alkylation followed by removal of tert‐butyl group from intermediate triazolium salts was demonstrated by the example of preparation of 1‐methyl‐5‐nitro‐1,2,3‐triazole.     

Liquid-phase catalytic hydrogenation of 3,4-dichloronitrobenzene over Pt/C catalyst under gradient-free flow conditions in the presence of pyridine

Experimental data on nitro compound uptake, the intermediate product accumulation, and the corresponding amine compound generation were obtained on hydrogenating 3,4-dichloronitrobenzene over Pt/C catalyst in the gradient-free flow regime in the presence and absence of pyridine. In addition, a side reaction of dehalogenation was investigated. The role of pyridine admixture on every step of the process was analyzed and the rate of hydrogenation of the nitro compound was determined both in the presence and in the absence of inhibitor.

     

ESR and electrochemical study of 5-nitroindazole derivatives with antiprotozoal activity

The electrochemistry of 3-alkoxy- and 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazole derivatives were characterized using cyclic voltammetry in DMSO. The nitro reduction process was studied and this was affected by the acid moieties present in these compounds. A nitro anion self-protonation process was observed. This phenomenon was studied by cyclic voltammetry in presence of increasing amount of NaOH. The reactivity of the nitro anion radical of these derivatives with glutathione was also studied by cyclic voltammetry. The oxidizing effect of glutathione is supported by the parallel decrease of the anodic peak current and increase of the cathodic peak in the cyclic voltammograms, corresponding to the wave of the nitro anion radical from uncharged species with the addition of glutathione. Nitro anion radicals obtained by electrolytic reduction of these derivatives were measured and analyzed in DMSO using electron spin resonance spectroscopy.     

Efficient synthesis of N-alkyl-2,7-dihalocarbazoles by simultaneous carbazole ring closure and N-alkylation

The N-alkyl-2,7-dihalocarbazole as the main product was formed by the reaction of 4,4′-dihalo-2-nitrobiphenyl with aromatic nitro compound and trialkyl phosphite. The presence and crucial role of aromatic nitro compound causes simultaneous carbazole ring closure and N-alkylation unlike the Cadogan ring closure where non-alkylated carbazole is formed as a main product. In addition, the mixture of aromatic nitro compound and trialkyl phosphite was found to be a possible N-alkylating agent for heterocycles, such as carbazole or indole.     

Studies on substitution of nitro groups in 1,3,5-trinitrobenzene with NH-azoles

Conditions were found under which NH-azoles (benzotriazole and its derivatives, 1,2,3- and 1,2,4-triazoles, pyrazole and its derivatives) replace one nitro group in 1,3,5-trinitrobenzene (TNB) to form the corresponding N-(3,5-dinitrophenyl)azoles in the presence of inorganic bases in aprotic dipolar solvents. The reaction pathway was found to depend on the structure of the starting azole. The benzotriazolyl and 1,2,4-triazolyl fragments activate the replacement of the meta-nitro group to virtually the same extent as the nitro group in TNB, which made it possible to successively replace all three nitro groups in TNB.     

Electron impact mass spectra of some tertiary aliphatic nitro compounds. Nitrocarbonyl compounds and some analogues

The mass spectra of some tertiary aliphatic nitroaldehydes, nitroketones, nitroesters, nitronitriles and related nitrocarbonyl compounds are discussed and compared with those of some analogous nitro compounds lacking the carbonyl function. The M⁺˙ ? NO₂˙ and in several cases M⁺˙ ? HNO₂ fragmentation seem to be the most characteristic features of all tertiary aliphatic nitro compounds. In the presence of the primary nitro group, the loss of NHO₂ is always observed.     

Synthesis of Aryl 3,5-Dinitrophenyl Sulfones and Sulfoxides. Transformations of 3,5-Dinitrodiphenyl Sulfone in Reactions with O- and S-Nucleophiles

1-Arylthio-3,5-dinitrobenzenes are selectively oxidized to the corresponding sulfones and sulfoxides by the action of hydrogen peroxide. Reactions of 3,5-dinitrodiphenyl sulfone with O- and S-centered nucleophiles (RXH, X = O, S) in dipolar aprotic solvents in the presence of K₂CO₃ result in replacement of the nitro group by the RX fragment; the reaction with methanol occurs in aqueous medium in the presence of NaHCO₃. Substitution of the nitro group in 3,5-dinitrodiphenyl sulfone by phenylthio group, followed by oxidation of the sulfur atom to SO₂ and further replacement of the remaining nitro group yields 1,3,5-tris(phenylsulfonyl)benzene. The phenylsulfonyl group in the latter is replaced by phenylthio group by reaction with PhSH in the presence of K₂CO₃. Mononitrosulfones obtained by nucleophilic substitution in the title compound can be reduced to the corresponding anilines.     

Ph2S2-CaH2 in N-methyl-2-pyrrolidone as an efficient protocol for chemoselective cleavage of aryl alkyl ethers

CaH₂ was been found, for the first time, as a mild reducing agent to generate thiophenolate anion from Ph₂S₂ in N-methyl-2-pyrrolidone (NMP) for deprotection of aryl alkyl ethers. Excellent chemoselctivity was observed for substrates having chloro and nitro groups without displacement of the chlorine atom and the nitro group. Selective ether cleavage took place in the presence of α,β-unsaturated carbonyl and nitro groups without reduction and conjugate addition (to the α,β-unsaturated carbonyl group).     

OZONE/OXONE-MEDIATED OXIDATIONS OF AMINO AND O-BENZYLHYDROXYLAMINO SUGARS

A method for the preparation of C-methyl branched nitro sugars from the corresponding amino sugars by oxidation with mixed oxidants is described. Ozonolysis of the amino sugars in the presence of OXONE (potassium monopersulfate) and acetone (Bashir-Hashemi's procedure) gave nitro sugars in good yields. Oxidation of an O-benzylhydroxylamino sugar by this method resulted in deprotection and oxidation in a single step, giving the nitro sugar directly. The mixed oxidant method is experimentally simpler and more convenient to use than DMDO, which had been previously reported for the oxidation of amino sugars.     

An efficient route to polynitrogen-fused tricycles via a nitrene-mediated N-N bond formation under microwave irradiation

The synthesis of unprecedented fused azaheterocyclic ring systems is described. Tricycles with either a central pyrazole or a triazole ring were obtained via a nitrene-mediated reaction of nitro bis(hetaryl) derivatives in the presence of triethylphosphite. The cyclization proceeded with complete chemoselectivity for the desired N-N bond formation and was completed within minutes under microwave activation. The key nitro bicycles were synthesized using either Stille couplings or aromatic nucleophilic substitution.     

Reduction of Sulphur-containing Aromatic Nitro Compounds with Hydrazine Hydrate over Iron(III) Oxide-MgO Catalyst

Sulphur-containing aromatic amines were prepared efficiently in good to excellent yields by reduction of the corresponding sulphur-containing aromatic nitro compounds with hydrazine hydrate in the presence of iron(III) oxide-MgO catalyst. The catalyst exhibited high activity and stability for the reduction of sulphur-containing aromatic nitro compounds. The yields of sulphur-containing aromatic amines were up to 91-99 % at 355 K after reduction for 1-4 h over this catalyst.     

Catalytic deoxygenation of organic compounds by carbon monoxide: III. The reaction under pressure of aromatic nitro compounds in the presence of o-phthalaldehyde

The reaction of o-phthalaldehyde with several aromatic nitro compounds in the presence of carbon monoxide and catalytic quantities of hexarhodium-hexadecacarbonyl eventuated in the formation of the corresponding N-substituted isoindolinone as the major product. A reaction mechanism has been suggested incorporating deoxygenation of the nitro compound by carbon monoxide to a nitrene intermediate and the subsequent interception of the latter by o-phthalaldehyde.     

Spektroskopische Untersuchungen über die Rolle des Käfig-Effektes bei der Prädissoziation aromatischer Nitroverbindungen

Photolysis of the bond R_ar–NO₂ contributes to quenching of the fluorescence of aromatic nitro compounds. Since no nitro compound is known which fluoresces above 20,000 cm^?1 photolysis must occur via a predissociation process. Either a fluorine-substituted nitro compound or fluorobenzene as the solvent was used for the irradiation experiments so that ¹⁹F-NMR. spectroscopy could be used to analyse the reaction products. Cage effects play an important role. With a large distance between the radicals R _ar and NO ₂, the phenyl radical forms a diphenyl compound with a benzenetype solvent molecule, and with small distance recombination will occur. For medium to long distances geminal recombination will also occur, not to the initial nitro compound, but to the corresponding nitrite, which in the presence of oxygen forms o-nitrophenol. Mass spectrometry showed that the added oxygen atom is located in the nitro group.