Nucleophilic substitutions at the pyridine ring: Kinetics of the reaction of 2-chloro-3-nitro and 2-chloro-5-nitropyridines with piperidine and morpholine in methanol and benzene

The kinetics of the reactions of 2-chloro-3-nitropyridine (ortho-like) and 5-nitro (para-like) isomer with morpholine and piperidine were studied in methanol and benzene at several amine concentrations and temperatures in the range 25–45°C. The data show that k/k ratios are less than unity in methanol. The steric hindrance in the transition state of the 3-nitro (ortho-like) isomer retards o-substitution while the stability of p-quinonoid structure of the 5-nitro (para-like) isomer favors p-substitution. In benzene, the k_3-NO2/k_5-NO2 ratios are greater than unity. The hydrogen bonding formation between the ammonium hydrogen and the ortho-nitro group in the transition state of 3-nitro isomer favors the o-substitution. © 1997 John Wiley & Sons, Inc.     

Ortho effects in schiff bases of diaminodicyanoethene

In the electron impact mass spectra of azomethines derived from various substituted aromatic aldehydes and diarninodicyanoethene the superposition of two ortho effects concurring with the azomethine group is apparent: one involving the amino group of the diaminodicyanoethene part accounts for the cyclization to [C₅H₃N₄]⁺ ions and the other involving ortho substituents of the benzylidene part which can interact with the azomethine moiety is responsible for specific fragment ions, suppressing the typical fragmentations of azomethines. The ortho effect was studied for the o-nitro derivative by labelling experiments, analysis of metastable transitions and collisional activation comparing model ions, demonstrating that the specific [M-H₂O]⁺˙ and [C₇H₅NO₂]⁺˙ ions are the result of cyclization processes.     

SYNTHESIS OF 4,6-DINITROINDOLE FROM 2,4,6-TRINITROTOLUENE

1-R-4,6-Dinitroindoles 4–6 (R = H, Me, Ts) could be obtained from 2-picrylethanol 1 (readily available from TNT) via selective reduction of ortho-nitro group by N₂H₄/FeCl₃ and subsequent treatment with TsCl, to yield a key intermediate 3. This intermediate was converted to the above mentioned indoles.     

Nitro group substitution in 2,4,6-trinitrotoluene under the action of arenethiols and transformations of the reaction products

The reactions of 2,4,6-trinitrotoluene with arenethiols in the presence of inorganic bases in dipolar aprotic solvents led to the replacement exclusively of the ortho-nitro group to form 2-arylthio-4,6-dinitrotoluenes. Substitution, oxidation, and reduction of the latter and their transformation products provided the basis for the preparation of mono- and di-ortho-S-substituted nitrotoluenes and aminotoluenes. Factors favoring the regiospecificity of ortho-substitution in 2,4,6-trinitrotoluene are discussed.     

Ortho effects in organic molecules on electron impact part 22. Competing oxygen transfers from the nitro group to sulphur and the olefinic double bond in 2-nitrophenyl styryl sulphides

Double oxygen migration to sulphur from the ortho-nitro group leading to eliminations of SO₂ and ^·SO₂H from the molecular ions and single oxygen transfer to the olefinic double bond in the side-chain giving rise to the most abundant ion at m/z 138 have been observed in 2-nitrophenyl styryl sulphides on electron impact. The proposed fragmentation mechanisms and the product ion structures were confirmed with the aid of high-resolution data, B/E linked scan and CID spectra.     

Synthesis of 5,6-Dihydrophenanthridine (DHPA) Sulfonamides and Subsequent Acid-Catalyzed Rearrangement to Diaryl Sulfones

Selective method of reduction of the ortho-nitro groups in 2,4,6-trinitrotoluene by hydrazine hydrate in the presence of FeCl₃ and charcoal has been elaborated. This method allows obtaining either 2-amino-4,6-dinitrotoluene or 2,6-diamino-4-nitrotoluene as well as 2,4,6-triaminotoluene from TNT.     

Studies in organic mass spectrometry. 12–Electron impact ionization mass spectra of some 3-nitropyrroles

The positive-ion electron impact ionization mass spectra of eight substituted 3-nitropyrroles were examined. The major fragment ions arise by ortho interactions between the 3-nitro group and the 2-methyl or 2-aryl group.     

Nitration of Aromatic Compounds Catalyzed by Divanadium-Substituted Molybdophosphoric Acid,H<Subscript>5</Subscript>[PMo<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript>]

Summary. The nitration of aromatic compounds was carried out in the presence of divanadium-substituted molybdophosphoric acid, H₅PMo₁₀V₂O₄₀, as catalyst and a mixture of nitric acid and acetic anhydride as nitrating agent. In the presence of this heteropolyacid the ortho- and para-nitro compounds were obtained in good to excellent yields under mild reaction conditions.     

Nitration of Aromatic Compounds Catalyzed by Divanadium-Substituted Molybdophosphoric Acid, H5[PMo10V2O40]

The nitration of aromatic compounds was carried out in the presence of divanadium-substituted molybdophosphoric acid, H₅PMo₁₀V₂O₄₀, as catalyst and a mixture of nitric acid and acetic anhydride as nitrating agent. In the presence of this heteropolyacid the ortho- and para-nitro compounds were obtained in good to excellent yields under mild reaction conditions.     

INTERACTION OF 2,4,6-TRINITROTOLUENE AND ITS ANALOGUES WITH ALDEHYDES. SYNTHESIS OF BENZOANNELATED HETEROCYCLES FROM THE PRODUCTS OF CONDENSATION

ABSTRACT

2,4,6-Trinitrotoluene (TNT) and its sulfonyl analogue 2-isobutylsulphonyl-4,6-dinitrotoluene undergo smooth condensation with chloral and fluoral to give 2-R-4,6-dinitrophenyl-1-(trihalomethyl)ethanols which easily cyclize to give 4-R-6-nitro-2-trihalomethyl-2,3-dihydrobenzo[b]furans (R=NO₂, i-Bu; halogen = F or Cl) in the presence of K₂CO₃. 2-R′-sulphonyl-4,6-dinitrotoluenes, prepared from TNT, condense with aromatic aldehydes to form 1-(2-R′-sulphonyl-4,6-dinitro)-2-arylethenes in which the ortho-nitro group, upon interaction with NaN₃ was selectively substituted by the azido group. Thermolysis of the obtained azides gave 2-aryl-4-R′-sulphonyl-6-nitroindoles (R′ = Ph, i-Bu, PhCH₂). Such N-methylated indole (R′ = i-Bu) was regioselectively aminated.     

Structural characterization of nitro-substituted phenoxyiminato nickel complexes; inter-molecular π-π interactions in the solid states and effect of the electron drawing groups on catalytic activity

Three phenoxyiminato nickel complexes [(L)Ni(PPh₃)(Ph)] have been prepared by the introduction of the electron drawing nitro substitutes on ortho or para-position of phenoxy and characterized by X-ray crystallography. Experimental and theory calculation suggested that the ortho and para nitro groups may be equally responsible for the small net charge on the central metal atoms because the interplanar angles between o-nitro planes and aromatic rings (28.7-37.3°) are much higher than those between p-nitro planes and aromatic rings (8.2-13.8°). In the solid states of these nickel complexes there exist the short inter-molecular π-π stacking interactions with the distances of 3.5828 Å (ortho-nitro), 3.5844 Å (para-nitro), and 3.0929 Å (ortho- and para-nitro) between two neighboring nitro-phenyl moieties.     

Synthesis of 2-aryl-6-nitro-4-(<Emphasis Type="Italic">vic</Emphasis>-triazol-1-yl)-1<Emphasis Type="Italic">H</Emphasis>-indoles from <Emphasis Type="Italic">E</Emphasis>-2,4,6-trinitrostilbenes

A method is developed for the preparation of 4-(vic-triazol-1-yl)indoles that involves replacement of the ortho-NO₂ group in E-2,4,6-trinitrostilbenes by an azido group, condensation of E-2-azido-4,6-dinitrostilbenes with acetylacetone, replacement of the second ortho-NO₂ group in the resulting stilbenes by N₃, and subsequent thermolysis of the azide into the target indole. The reactions of E-2-azido-4,6-dinitrostilbenes with cyclohexane-1,3-dione gave E-2-amino-4,6-dinitrostilbenes, which can be used for selective transformation of the ortho-NO₂ group into an amino group in E-2,4,6-trinitrostilbenes. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1293–1296, May, 2005.     

Proton-Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution

Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton-release reactions and pH values of solutions. We present the first time-resolved spectroscopic study of the excited state and proton-release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton-release mechanisms: one site acts as a photoacid generator as its pK_a value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pK_a drop of 8.7 units to −5.5 upon excitation, the latter phenolic site is regarded a super-photoacid. The 6-nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8-dinitro compound an intramolecular proton transfer to the ortho-nitro group is suggested that is involved in a rapid relaxation into the ground state.     

o-Nitrobenzylidene compounds. I—Competitive ortho interactions in the mass spectra of n-o-nitrobenzylidene-o-substituted anilines

The intense [M – 17]⁺ ion, which is a characteristic feature of the mass spectra of N-o-nitrobenzylideneaniline and its simple derivatives, may be substantially reduced in intensity when the aniline-derived ring is also ortho substituted: the intensity is lowest when this ortho substituent has a nucleophilic character and can itself interact with the CH?N group. The ortho substituents examined are Br, CH₃, OH, NH₂, SH, SC₆H₄CH₃(p), CO₂CH₃ and CO₂C₂H₅.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

 New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds.     

Chlorine-isotopic exchange between lithium chloride and substituted 2-chloropyridine in homogeneous solution

The kinetics of chlorine-isotopic exchange between lithium chloride-36 and cyano- and nitro- substituted 2-chloropyridines were measured in sulpholane, acetone or methanol solution. Activating effects of ortho-nitro and ortho-azu substitution are compared: a nitro-group is 50 × as activating as the aza-group in the p-nitrochlorobenzene system, where as it is the aza-function which is 3 times as activating as the nitro group in the o-nitrochlorobenzene system. The effect of Me substituents placed ortho to an activating nitro-group was studied by comparing 2-chloro-3-cyano-5-nitropyridine and its 6-methyl- and 4,6-dimethyl-derivatives.     

Some nitro derivatives of 1,4-benzodioxino[2,3-b]pyridine. Crystal and molecular structure of 2,7,8-trinitro-1,4-benzodioxino[2,3-b]pyridine

The electrophilic nitration of 1,4-benzodioxino[2,3-b]pyridine 1 with nitric acid in sulfuric acid has been studied. Some of the products of nitration including 7 - and 8 -nitro derivatives 2a and 2b , respectively, 7,9-, 7,8- and 6,8-dinitro derivatives 3a , 3b and 3c , respectively, and 2,7,8-trinitro derivative 4 have been isolated and characterized. The structure of isomers have been assigned for derivatives 3b and 4 while tentative structures have been proposed for the other products. The cyclopentadienyliron complex of 1 gives the same reaction products under similar conditions while for some other milder nitrating reagents no reaction was observed. 2,7,8-Trinitro-1,4-benzodioxino[2,3-b]pyridine 4 crystallizes in the monoclinic system, space group P2₁/c; the dihedral angle between the planes of outer rings was found to be 174.65(8) degrees. The planes of the nitro groups have been found to be rotated with respect to the appropriate pyri-dine and benzene ring planes by 11.13(11) degrees for the 2-nitro group and 47.56(9) and 29.80(9) degrees for the 7-nitro and 8-nitro groups, respectively.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

Summary.  New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds. Received January 22, 2001. Accepted (revised) July 18, 2001     

13C chemical shifts of phenol derivatives. A correlation with electronic structure

The ¹³C chemical shifts of twenty chloro- and nitro-substituted phenols have been measured in d-chloroform. The influence of substituents on the screening at C-1, on the total charge at this position and on the dipole moments is reported and analysed. The results of this study suggest that variations of the chemical shifts at C-1 for meta-methyl-, meta-chloro-, meta-nitro-, ortho- and para-methyl-, ortho- and para-chlorosubstituents mainly reflect charge density changes. The influence of ortho-nitro groups on the screening of C-1 is more complex.     

Synthesis and recyclization reactions of 4-(o-R-phenyl)-3-imidazolines

1-Hydroxy-4-phenyl-3-imidazoline reacts with butyllithium to give the product oforthometallation of the phenyl group. Reactions of this compound with electrophiles followed by oxidation afford 4-(o-R-phenyl) derivatives of nitroxyl radicals. When a hydroxyalkyl group is present in theortho-position, an unusual pathway of the decay of stable nitroxyl radicals of the imidazoline series has been observed due to the existence of a spirobicyclic tautomer. The reaction of theo-metallated derivative with CS₂ leads to a profound transformation of the imidazoline ring and to the formation of isoindolethione. Fast recyclization into isoquinolines occurs in the case of the 4-(o-benzoyl)phenyl derivative of 3-imidazoline. The product ofo-metallation reacts with methyl nitrate to yield the 4-(o-hydroxy)phenyl derivative (a potential paramagnetic chelate-forming reagent) and theo-nitro derivative, the starting material for further chemical transformations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 899–903, May, 1994.