- Photochemistry of the three carboxypyridines in water: A pH dependent reaction
-
The photochemistry of ortho, meta and para-carboxypyridines (pK a1 = 1.0-2.1 and pKa1 = 4.7-5.3) in aqueous medium was studied by laser-flash photolysis and product studies. At pH a1, hydroxylated compounds are produced with low quantum yields. Within the pH range 4-7, ortho and meta isomers undergo dimerization together with decarboxylation with a quantum yield showing a very sharp maximum around pKa2 (φmax = 0.09 and 0.01, respectively) while the para isomer is photostable. End-of-pulse transients assigned to triplet states were detected by laser-flash photolysis at pH a1 and pH > 4. Additionally, the carboxypyridinyl radicals were detected as secondary intermediates at pH a1 and 4 a1. This is in favour of an electron transfer reaction between triplet and starting compound producing a charge transfer species. The radical anion would escape as carboxypyridinyl radical while the radical cation may add water at pH a1 yielding the OH-adduct radical or may undergo decarboxylation at pH > 4. The high quantum yield of phototransformation of the ortho isomer at pH > 4 is due to an easy decarboxylation process. A reaction scheme is proposed accounting for the dependences of φ on both the pH and the carboxypyridines concentration. This study points out the distinct pattern of reactivity of carboxypyridines depending on the ionisation state of starting compounds and isomeric substitution.
- Rollet, Florence,Richard, Claire,Pilichowski, Jean-Francois,Aboab, Bettina
-
-
Read Online
- Bis(μ-6-hydroxypicolinato)-μ-oxobis[dipyridinemanganese(III)] monohydrate
-
The title compound, [Mn2(μ-O)(C6 H 3NO3)2(C5H5N) 4]·H2O, was isolated from the reaction of 2,6-pyridinedicarboxylic acid with [Mn12O12(CH 3COO)16(H2O)4] in pyridine. The dimanganese complex has twofold symmetry; the MnIII atoms are bridged by one oxo and two amidate ligands and show compressed octahedral Jahn-Teller distortion. The molecular packing comprises a three-dimensional structure constructed by means of extensive intermolecular interactions, including three kinds of hydrogen bonds and π-π interactions.
- Bian, Guo-Qing,Kuroda-Sowa, Takayoshi,Konaka, Hisashi,Maekawa, Masahiko,Munakata, Megumu
-
-
Read Online
- Infrared spectrum, molecular structure and theoretical calculation of 2-pyridone-6-carboxylic acid
-
The X-ray and infrared spectroscopic analysis of 2-pyridone-6-carboxylic acid are reported. The crystals of investigated molecule belong to P21/c of the monoclinic system, a = 11.714 ?, b = 3.7088?, c = 18.223? and β = 123.71°. The molecule is found in the ketonic form. Comprehensive studies of the molecular structures and vibrational frequencies and infrared intensities of the molecule have been performed by using Hartree-Fock, density functional B3LYP and second-order Moller-Plesset MP2 methods with the 6-31G+(d, p) basis set. The calculated geometrical parameters of investigated molecule in gas phase were compared with the experimental X-ray data.
- Arslan,?engül,Aygün,Karadayi,Bayari, S. Haman
-
-
Read Online
- Halogen–metal exchange on bromoheterocyclics with substituents containing an acidic proton via formation of a magnesium intermediate
-
A selective and practical bromine–metal exchange on bromoheterocyclics bearing substituents with an acidic proton under non-cryogenic conditions was developed by a simple modification of an existing protocol. Our protocol of using a combination of i-PrMgCl and n-BuLi has not only solved the problem of intermolecular quenching that often occurred when using alkyl lithium alone as the reagent for halogen–lithium exchange, but also offered a highly selective method for performing bromo–metal exchange on dibrominated arene compounds through chelation effect.
- Tian, Qingqiang,Shang, Suqin,Wang, Huajun,Shi, Guoqiang,Li, Zhiyao,Yuan, Jianyong
-
supporting information
(2017/12/05)
-
- Preparation of 6-Oxo-1,6-dihydropyridine-2-carboxylic Acid by Microbial Hydroxylation of Pyridine-2-carboxylic acid
-
Alcaligenes faecalis (DSM 6269) grown on pyridine-2-carboxylic acid induced regiospecific hydroxylation of the latter to 6-oxo-1,6-dihydropyridine-2-carboxylic acid on a preparative scale.
- Kiener, Andreas,Gloeckler, Rainer,Heinzmann, Klaus
-
p. 1201 - 1202
(2007/10/02)
-
- CONTROLLED, REGIOSPECIFIC OXIDATION OF PYRIDINE CARBOXYLIC ACIDS AND ESTERS WITH ELEMENTAL FLUORINE
-
Pyridine carboxylic acid salts or esters in water or water-acetonitrile mixtures were treated with elemental fluorine to give the corresponding 2-pyridones.
- Puy, Michael Van Der,Nalewajek, David,Wicks, Gene E.
-
p. 4389 - 4392
(2007/10/02)
-
- Process for the production of 2-hydroxypyridines from 2-pyridine carboxylic acid-N-oxides
-
Process for the production of 2-hydroxypyridines having the formula: STR1 from 2-pyridine carboxylic acid-N-oxides having the formula: STR2 wherein R is H, a --COOH group, an alkyl group having 1 to 8 carbon atoms or an aryl group and n designates a number between 1 and 4. The N-oxide is converted using lower aliphatic carboxylic acid anhydrides in the presence of a tertiary amine. The conversion product is then hydrolyzed.
- -
-
-
- Substituent Effects on the Isomer Ratios in the Rearrangement of Some 2- and 4-Nitraminopyridines
-
The preparation, and rearrangement in 92percent sulfuric acid, of 4-X-2-nitramino- (1), 2-X-4-nitramino- (2), and 6-X-2-nitramino-pyridines (3) is reported (X=H,Me,MeO,Br,Cl,CO2H).The product isomer ratios can be explained by differential electronic stabilization of the appropriate ? complexes for aromatic nitration and steric effects seem relatively unimportant.Deuteration had no effect on the product distribution
- Deady, Leslie W.,Korytsky, Olga L.,Rowe, Jeffrey E.
-
p. 2025 - 2034
(2007/10/02)
-
