Effect of micelle formation of quaternary pyridinium salts on their recyclization to anilines

The recyclization of N-alkyl--methylpyridinium salts with an N-alkyl chain consisting of 12 and 16 carbon atoms under the influence of aqueous solutions of sulfites of various amines was studied. It was established that the formation of micellar structures in aqueous solutions of these salts affects the direction of the reactions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 508–510, April, 1981.     

Alkylamino group exchange upon recyclization of pyridinium salts into anilines

Nitropyridiniium salts react with primary or secondary amines to form alkyl or dialkylanilines as result of recyclization of pyridine nuclei. The alkylamine or dialkylamine group is included in the reaction final product at the open form stage. Aqueous methylamine may open even non-quatèrnized nitropyridines with the following ring closure to alkylanilines.     

Preparation of quaternary pyridinium salts as possible proton conductors

On basis of earlier experimental experience, the transfer of protons in salts of the organic cation-inorganic anion type occurs primarily through directional arrangement of the anion-anion type short hydrogen bonds. The submitted work presents the preparation of quaternary pyridinium salts of inorganic hydrogen anions in the absence of solvent molecules in their crystal structure. These substances can form only the above-described anion-anion type hydrogen bonds; in addition, the absence of solvate anions increases the stability of the prepared compounds. A total of six substituted pyridinium salts were prepared, four of which have not been described yet: 1,2,4,6-tetraphenylpyridinium perchlorate, 1-benzyl-2,4,6-trimethylpyridinium perchlorate, 1,4-dimethylpyridinium hydrogen sulphate, 1,4-dimethylpyridinium dihydrogen phosphate, 1,4-dimethylpyridinium hydrogen sulphate, and 1,2-dimethyl-5-ethylpyridinium dihydrogen phosphate. Three of these substances were characterised by X-ray structural analysis: 1,2,4,6-tetraphenylpyridinium perchlorate crystallises in the orthorhombic system, space group Pbca; 1-benzyl-2,4,6-trimethylpyridinium perchlorate crystallises in the monoclinic system, space group P2₁/c; and 1,4-dimethylpyridinium dihydrogen phosphate crystallises in the monoclinic system, space group C2/c. This structure contains an oriented anion network bond by short anion-anion type hydrogen bonds with the donor acceptor lengths of 2.567(3) Å and 2.557(3) Å and thus fulfils the requirements of a good proton conductor.     

Dealkylation of quaternary 1-alkylazolo[a]pyridinium salts

A convenient method is proposed for the preparation of new derivatives of free heterocyclic bases of imidazo[1,2-a]pyridine, pyrido[1,2-a]benzimidazole, and [1,2,4]triazolo[4,3-a]pyridine series. This method entails the dealkylation of N-(2-cyanoethyl)- or N-benzylazolopyridinium quaternary salts in the presence of bases and reaction with ammonium formate in the presence of Pd/C, respectively.     

One-pot synthesis of quaternary pyridinium salts and tetrahydropyridine derivatives of fusidane triterpenoids

Chemistry of Heterocyclic Compounds - An efficient one-pot method was developed for the preparation of quaternary pyridinium salts and tetrahydropyridine derivatives of fusidane triterpenoids,...     

Steric effects in the recyclization of nitropyridinium salts to nitroanilines

The effect of the degree of branching of alkyl groups attached to the amine nitrogen atom on the recyclization of 1,2,4,6-tetramethyl-3-nitropyridinium iodide to nitroanilines was studied.Decreased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1271, September, 1980.     

The relative stability of pyridinium and 1,7-diaza[12]annulenium quaternary salts

Theoretical calculations (energies and chemical shifts) at the B3LYP/6-311++G(d,p) level confirm that the compounds described as 1,7-diaza[12]annulenium quaternary salts are in fact pyridinium quaternary salts.     

Skeletal remodeling of chalcone-based pyridinium salts to access isoindoline polycycles and their bridged derivatives

Simultaneous deconstructive ring-opening and skeletal reconstruction of an inert, aromatic pyridinium ring is of great importance in synthetic communities. However, research in this area is still in its infancy. Here, a skeletal re-modeling strategy was developed to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines through a dearomative ring-opening/ring-closing sequence. Two distinct driving forces for the deconstruction of the pyridinium core were involved in these transformations. One was the unprecedented harnessing of the instability of in situ generated cyclic β-aminoketones, and the other was the instability of the resultant N,N-ketals. The desired isoindoline polycycles could undergo the Wittig reaction with various phosphorus ylides to achieve structural diversity and complexity. Notably, by tuning the Wittig conditions by addition of one equivalent of base, an additional bridged ring was introduced. A plausible mechanism was proposed on the basis of control experiments and theoretical calculations.

A novel skeletal remodeling strategy to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines was achieved through a dearomative ring-opening/ring-closing sequence.     

Features of the molecular structure of pyridinium salts and their dissolving power with respect to cellulose

Main geometric parameters and electronic structure of molecules of alkylpyridinium chlorides, bromides, and acetates were calculated by a quantum-chemical method. The influence of the electronic structure of molecules on their dissolving power with respect to cellulose was analyzed.     

Catalytic hydrogenation of pyridinium salts

Catalytic hydrogenation of polysubstituted pyridinium salts leads to piperidines and their condensed analogs The spatial properties and conformational properties of the saturated azaheterocycles have been determined by¹³C NMR spectorscopy. It was shown that hydrogenation of the pyridinium salts occurs stereoselectively to form cis isomers in most cases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 68–72, January, 1994.     

Redox behavior of pyridinium salts and their polymers having radical stabilizing groups

The redox behavior of pyridinium salts having various substituents capable of stabilizing pyridinyl radicals at the 4-position was investigated by cyclic voltammetry in water with a platinum electrode, and their redox potentials were more positive in the order of 4-substituents of acetyl > cyano > carbomethoxy > carbamide groups. Sodium dithionite was found to be suitable for a chemical reducing agent of the pyridinium salts. Two types of homopolymers with pendant 4-carbamido-pyridinium groups were prepared and their redox potentials were more positive than the corresponding model compounds. The positive shift might be caused by charge repulsion between the neighboring pyridinium cations on the polymer main chain in the oxidized state.     

13C NMR spectra of azolopyridines and their quaternary salts

¹³ C NMR spectra of some azole series have been investigated: 2-pyridylbenzimidazoles, 2-pyridylimidazo [4,5-b]-pyridines, 2-pyridylimidazo[4,5-c]-pyridines, analogous oxazole compounds, as well as their mono- and bisquaternary salts. Some problems, related to the structure of these compounds in solution, have been discussed.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow 117975. Torino University, Italy. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 866–872, April, 1992.     

Novel pyridinium salts as cationic thermal and photoinitiators and their photosensitization properties

Novel pyridinium salts [N‐(α‐phenylbenzyl)‐, N‐(1‐naphthylmethyl)‐, or N‐cinnamyl p‐ or o‐cyanopyridinium hexafluoroantimonates] were synthesized by the reaction of p‐ or o‐cyanopyridine and the corresponding bromides followed by anion exchange with KSbF₆. These pyridinium salts polymerized epoxy monomers at lower temperatures than previously reported for N‐benzyl‐2‐cyanopyridinium hexafluoroantimonate. The o‐substituted pyridinium salts showed higher activity than the p‐substituted ones, and the crosslinked epoxy polymers cured with these initiators showed higher glass‐transition temperatures. These pyridinium salts photoinitiated radical polymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic ketones as photosensitizers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1037–1046, 2002