cas 626-64-2, 4-Hydroxypyridine | Articles data

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Fullerene soot and a fullerene nanodispersion as recyclable heterogeneous off-the-shelf photocatalysts
Metal-free heterogeneous photocatalysis, which requires no prior catalyst immobilization or chemical modification and can operate in green solvents, represents a highly-sought after, yet currently still underdeveloped, synthetic method. In this report we present a comparative study which aims to evaluate the use of unmodified fullerene soot and a fullerene nanodispersion as non-soluble and quasi-soluble carbon-based photocatalysts, respectively, for sulfide oxidation and other transformations using oxygen as an oxidant in ethanol. A wide range of sulfoxides were successfully prepared with good yields and chemoselectivity using a very low catalyst loading. The fullerene soot photocatalyst is easily recovered and shows excellent stability of the catalytic properties. The reaction was shown to proceed via a singlet oxygen pathway and has a high selectivity for aliphatic sulfides, whereas the oxidation of thioanisoles can be accomplished using an amine mediated electron transfer mechanism. The applicability of the fullerene nanodispersion as a general purpose photocatalyst was demonstrated in radical cyclization, boronic acid oxidation and imine formation reactions.
Jozeliūnait?, Augustina,Val?eckas, Domantas,Orentas, Edvinas
p. 4104 - 4111
(2021/02/02)

Isotruxene-based porous polymers as efficient and recyclable photocatalysts for visible-light induced metal-free oxidative organic transformations
Two new isotruxene-based porous polymers were prepared and demonstrated to be highly efficient, metal-free heterogeneous photocatalysts for oxidative transformations using air as the mild oxidant under visible-light irradiation. Both catalysts show excellent recyclability. In addition, the reactions can be performed in water, further indicating the greenness of this method. This journal is
Zhang, Haowen,Zhang, Xiao,Zheng, Ying,Zhou, Cen
supporting information
p. 8878 - 8885
(2021/11/27)

Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids
We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4} ? 2BF4]α (1) and [{Cd(L)2(Cl)2} ? 2H2O]α (2) (where L=N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.
Bhasin, K. K.,Husain, Ahmad,Kumar, Girijesh,Rani, Pooja
(2021/12/06)

Application of Electron-Rich Covalent Organic Frameworks COF-JLU25 for Photocatalytic Aerobic Oxidative Hydroxylation of Arylboronic Acids to Phenols
Visible-light-driven organic reactions are environmentally friendly green chemical transformations among which photosynthetic oxidative hydroxylation of arylboronic acids to phenols has attracted increasing research interest during the very recent years. Given the efficiency and reusability of heterogeneous catalysts, COF-JLU25, an electron-rich COF-based photocatalyst constructed by integrating electron-donating blocks 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTA) and 4-[4-(4-formylmethyl)-2,5-dimethoxyphenyl] benzaldehyde (TpDA), was selected as a photocatalyst for the oxidative hydroxylation of arylboronic acids. In our studies, COF-JLU25 demonstrated excellent photocatalytic activity with high efficiency, robust reusability, and low catalyst loading, showcasing an application potential of previously underexplored COF-based photocatalyst composed solely of electron-rich units.
Xiao, Guangjun,Li, Wenqian,Chen, Tao,Hu, Wei-Bo,Yang, Hui,Liu, Yahu A.,Wen, Ke
supporting information
p. 3986 - 3991
(2021/03/29)

Transforming a Fluorochrome to an Efficient Photocatalyst for Oxidative Hydroxylation: A Supramolecular Dimerization Strategy Based on Host-Enhanced Charge Transfer
The development of non-covalent synthetic strategy to fabricate efficient photocatalysts is of great importance in theranostic and organic materials. Herein, a fluorochrome N,N′-dimethyl 2,5-bis(4-pyridinium)thiazolo[5,4-d]thiazolediiodide (MPT) was transformed into an efficient photocatalyst through supramolecular dimerization in the cavity of cucurbit[8]uril (CB[8]). The host-enhanced charge transfer interaction within the supramolecular dimer 2MPT-CB[8] dramatically promoted intersystem crossing to produce triplet. In addition, the staggered conformation of 2MPT-CB[8] facilitated the energy transfer and electron transfer of the triplet. As a result, 2MPT-CB[8] could serve as a high-efficiency photocatalyst for the oxidative hydroxylation of arylboronic acids. This supramolecular dimerization strategy enriches the supramolecular engineering of functional π-systems. It is anticipated that this strategy can be extended to fabricate various π-systems with tailor-made functions.
Tang, Bohan,Xu, Weiquan,Xu, Jiang-Fei,Zhang, Xi
supporting information
p. 9384 - 9388
(2021/03/22)

Visible-light-promoted aerobic oxidative hydroxylation of arylboronic acids in water by hydrophilic organic semiconductor
A green and sustainable catalytic system was developed based on perylenediimide (PDI) organic semiconductor for the aerobic oxidative hydroxylation of arylboronic acids in aqueous solution with visible light. By using PDI-SN, a hydrophilic organic semiconductor, which can activate oxygen to produce superoxide radicals in aqueous solution, this reaction proceeds under ambient conditions: water as the solvent and air as the oxidant, giving various phenols as products with high yields. In contrast to methods using organic solvents, this novel process has the potential of green industrial application.
Yu, Kunyi,Zhang, Hanjie,Sheng, Yuqiang,Zhu, Yongfa
supporting information

(2020/06/23)

Nickel-catalyzed oxidative hydroxylation of arylboronic acid: Ni(HBTC)BPY MOF as an efficient and ligand-free catalyst to access phenolic motifs
A straightforward and mild oxidative ipso-hydroxylation of arylboronic acids has been achieved using a simple and non-noble metal, nickel-based reusable heterogeneous catalyst Ni(HBTC)BPY MOF (HBTC = benzene-1,3,5-tricarboxylate, BPY = 4,4′-bipyridine) in the presence of benign hydrogen peroxide as an oxidant under ambient reaction condition. The Ni(HBTC)BPY MOF exhibits excellent catalytic activity towards the formation of phenols from diverse arylboronic acids within short time and can be reused up to five times without any notable loss in its activity as well as shown high functional group tolerance even in the presence of sensitive functionalities and useful to achieve hydroxyl group in heterocycles.
Latha, Ganesapandian,Devarajan, Nainamalai,Karthik, Murugan,Suresh, Palaniswamy
(2020/01/08)

Preparation method of pyridine derivative (by machine translation)
To the method, piperidine-4-one hydrochloride is used as a raw material, and a series of pyridine derivatives are obtained through halogenation reaction and elimination reaction. The reaction is eliminated by reacting piperidine-4-one hydrochloride with a specific amount of the 3,5 - halogenating agent in a halogenation 3, 3, 5 - reaction with a halogen-3, 3, 5, 5 - based reaction, followed by reaction with a pyridine derivative of a hydroxyl group, an amino group 4 - or a dimethylamino group, respectively, by eliminating the reaction with a different kind of basic agent. The method is simple and convenient to operate, mild in condition, short in technological process, low in waste water yield, environment-friendly, low in cost and beneficial to green industrial production of the pyridine derivative. (by machine translation)
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Paragraph 0075-0078; 0121-0122

(2019/12/02)

Chemoselective Demethylation of Methoxypyridine
A chemoselective demethylation method for various methoxypyridine derivatives has been developed. Treatment of 4-methoxypyridine with L-selectride in THF for 2 h at reflux temperature afforded 4-hydroxypyridine in good yield; no reaction to anisole occurred. The utility of our method was demonstrated by the efficient synthesis of the metabolic substances of the antiulcer agent omeprazole. Chemoselective demethylation at the site of 3,5-dimethyl-4-methoxypyridine in the presence of 4-methoxybenzimidazole was achieved.
Makino, Kosho,Hasegawa, Yumi,Inoue, Takahide,Araki, Koji,Tabata, Hidetsugu,Oshitari, Tetsuta,Ito, Kiyomi,Natsugari, Hideaki,Takahashi, Hideyo
p. 951 - 954
(2019/05/10)

A Green Alternative for the Conversion of Arylboronic Acids/Esters into Phenols Promoted by a Reducing Agent, Sodium Sulfite
Hydroxylation of arylboronic acids and arylboronic esters using sodium sulfite and oxygen as the source of ultimate oxidant proceeds rapidly in water under transition metal-free conditions. This remarkable mild and environmentally benign protocol represents a green alternative to synthesize phenols using inexpensive starting materials in a simple methodology. This new application for sodium sulfite shows a wide tolerance of functional groups, and it is compatible with oxidizable functionalities.
Castro-Godoy, Willber D.,Schmidt, Luciana C.,Argüello, Juan E.
p. 3035 - 3039
(2019/05/15)

Photoinduced Hydroxylation of Organic Halides under Mild Conditions
Presented in this paper is photoinduced hydroxylation of organic halides, providing a mild access to a range of functionalized phenols and aliphatic alcohols. These reactions generally proceed under mild reaction conditions with no need for a photocatalyst or a strong base and show a wide substrate scope as well as excellent functional group tolerance. This work highlights the unique role of NaI that allows a challenging transformation to proceed under mild reaction conditions.
Cai, Yue-Ming,Xu, Yu-Ting,Zhang, Xin,Gao, Wen-Xia,Huang, Xiao-Bo,Zhou, Yun-Bing,Liu, Miao-Chang,Wu, Hua-Yue
supporting information
p. 8479 - 8484
(2019/10/16)

Development of a novel protocol for chemoselective deprotection of N/O-benzyloxycarbonyl (Cbz) at ambient temperature
Abstract: A novel protocol for the deprotection of N-benzyloxycarbonyl and O-benzyloxycarbonyl groups by nickel boride generated in situ from NaBH4 and NiCl2·6H2O in methanol at room temperature has been developed to give the corresponding amines and phenols. This protocol is chemoselective as groups like chloro, bromo, amide, ester, pyridine, and tert-butyloxycarbonyl moiety are unaffected under these conditions. The deprotection has also been validated in gram scale reactions, to establish the wider appropriateness of this protocol. Graphical abstract: [Figure not available: see fulltext.].
Saroha, Mohit,Aggarwal, Komal,Bartwal, Gaurav,Khurana, Jitender M.
p. 2231 - 2235
(2018/10/02)

Photoreductive Removal of O-Benzyl Groups from Oxyarene N-Heterocycles Assisted by O-Pyridine-pyridone Tautomerism
Facile photoreductive protocols have been developed to remove benzyl O-protective groups from oxyarene N-heterocycles at positions capable for 2-/4-O-pyridine-2-/4-pyridone tautomerism. Blue light irradiation, a [Ru] or [Ir] photocatalyst, and ascorbic acid in a water-acetonitrile solution debenzylates a variety of aryl N-heterocycles cleanly and selectively. Ascorbic acid has two functions in the reaction. On the one hand, it protonates the N-heterocycles that reduces their reduction potentials notably and on the other hand it acts as a sacrificial reductant. Reduction potentials and free energy barriers calculated at the CPCM-B3LYP/6-31+G? level can predict the reactivities of the studied substrates.
Todorov, Aleksandar R.,Wirtanen, Tom,Helaja, Juho
p. 13756 - 13767
(2017/12/26)

Kinetic study on aminolysis of 4-pyridyl benzoate and O-4-pyridyl thionobenzoate in acetonitrile: Factors influencing reactivity and reaction mechanism
A kinetic study on nucleophilic substitution reactions of 4-pyridyl benzoate (2a) andO-4-pyridyl thionobenzoate (2b) with a series of cyclic secondary amines in acetonitrile at 25.0°C is reported. Plots of pseudo-first-order rate constant (kobsd) vs. [amine] are linear and pass through the origin for the reactions of 2a but curve upward for those of 2b. The upward curvature observed for the reactions of 2b is typical for reactions that proceed through a stepwise mechanism with a zwitterionic intermediate T±, which decomposes to the products via uncatalyzed and catalyzed routes competitively. The reaction of 2a has been suggested to proceed through a stepwise mechanism with T±, in which expulsion of the leaving group occurs in the rate-determining step on the basis of a linear Br?nsted-type plot with βnuc = 0.77. The catalyzed reaction of 2b from T± has been proposed to proceed through a concerted mechanism with a six-membered cyclic transition state rather than via a stepwise pathway with an anionic intermediate T-. Factors influencing reactivity and reaction mechanism are discussed in detail.
Um, Ik-Hwan,Kim, Min-Young,Lee, Jae-In
p. 1577 - 1581
(2016/10/13)

Oxidative hydroxylation of arylboronic acids to phenols catalyzed by copper nanoparticles ellagic acid composite
Copper nanoparticles (Cu NPs) were prepared by in situ reduction of CuSO4·5H2O using ellagic acid (EA) as the reducing agent as well as stabilizer and its catalytic activity is tested in the oxidative hydroxylation of phenylboronic acids to phenol without any added base or ligand. The synthesized Cu NPs-EA composite was characterized by UV-Vis., FT-IR, powder XRD and HRTEM analyses. The average particle size of Cu NPs is found to be in the range of 20-25 nm as evident from HRTEM and copper content is estimated to be 3.18 wt%. EA acts both as a reducing agent as well as a stabilizer for the in situ formation of Cu NPs. A small portion of Cu NPs is also found to undergo aerobic oxidation to give Cu2O NPs which does not take part in the reactions. A series of arylboronic acids are converted to the corresponding phenols in high yields at short reaction time under milder reaction conditions. It is also observed that Cu NPs-EA composite can be reused at least four times with a significant decrease in the yield.
Affrose, Abdullah,Azath, Ismail Abulkalam,Dhakshinamoorthy, Amarajothi,Pitchumani, Kasi
p. 500 - 505
(2014/12/10)

Electronic nature of substituent X governs reaction mechanism in aminolysis of 4-pyridyl X-substituted-benzoates in acetonitrile
A kinetic study is reported for aminolysis of 4-pyridyl X-substituted-benzoates 5a-i. Plots of pseudo-first-order rate constants (k obsd) vs [amine] curve upward for the reactions of substrates possessing a strong electron-withdrawing group in the benzoyl moiety (5a-d) but are linear for the reactions of those bearing an electron-donating group (5e-i), indicating that the electronic nature of substituent X governs the reaction mechanism. The k1k2/k-1 and k1k 3/k-1 values were calculated from the intercept and slope of the linear plots of kobsd/[amine] vs [amine], respectively. The Hammett plot for k1k2/k-1 consists of two intersecting straight lines, while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρX = 0.41 and r = 1.58, implying that the nonlinear Hammett plot is not due to a change in rate-determining step but is caused by stabilization of substrates possessing an electron-donating group through resonance interactions. The small ρX suggests that the k2/k-1 ratio is little influenced by the nature of substituent X. The Bronsted-type plots for aminolysis of 4-pyridyl 3,5-dinitrobenzoate 5a are linear with βnuc = 0.98 and 0.79 for k1k2/k-1 and k1k3/k -1, respectively. The effect of amine basicity on the microscopic rate constants is also discussed.
Um, Ik-Hwan,Bae, Ae Ri
supporting information; experimental part
p. 5781 - 5787
(2012/08/29)

Kinetic study on aminolysis of 4-pyridyl X-substituted benzoates: Effect of substituent X on reactivity and reaction mechanism
A kinetic study is reported for nucleophilic substitution reactions of 4-pyridyl X-substituted benzoates 7a-e with a series of alicyclic secondary amines in H2O. The Bronsted-type plot for the reactions of 4-pyridyl benzoate 7c is linear with βnuc = 0.71. The corresponding reactions of 2-pyridyl benzoate 6, which is less reactive than 7c, resulted in also a linear Bronsted-type plot with βnuc = 0.77. The fact that the more reactive 7c results in a smaller βnuc value appears to be in accord with the reactivity- selectivity principle. The aminolysis of 7c has been suggested to proceed through a stepwise mechanism in which breakdown of the intermediate is the rate-determining step (RDS). The Hammett plot for the reactions of 7a-e with piperidine consists of two intersecting straight lines, i.e., ρX = 1.47 for substrates possessing an electron-donating group (EDG) and ρX = 0.91 for those possessing an electron-withdrawing group (EWG). In contrast, the corresponding Yukawa- Tsuno plot exhibits excellent linear correlation with ρX = 0.79 and r = 0.56. Thus, it has been concluded that the nonlinear Hammett plot is not due to a change in the RDS but is caused by stabilization of the ground state of the substrates possessing an EDG through resonance interaction between the EDG and the C=O bond of the substrates.
Lee, Jong Pal,Bae, Ae Ri,Um, Ik-Hwan
experimental part
p. 1907 - 1911
(2012/01/14)

2-(Trimethylsilyl)ethanol as a new alcohol equivalent for copper-catalyzed coupling of aryl iodides
2-(Trimethylsilyl)ethanol as a new alcohol equivalent has been employed for copper-catalyzed coupling of aryl iodides. Using mild reaction conditions, it has been observed that substituted phenols and phenols with sensitive functional groups can be readily prepared.
Dibakar, Mullick,Prakash, Anjanappa,Selvakumar, Kumaravel,Ruckmani, Kandasamy,Sivakumar, Manickam
supporting information; experimental part
p. 5338 - 5341
(2011/10/19)

Efficient and selective demethylation of heteroaryl methyl ethers in the presence of aryl methyl ethers
A new and efficient method for the demethylation of 6-membered aza-heterocyclic methyl ethers is described using lithium chloride and para-toluenesulfonic acid. This process is chemoselective for aza-heterocyclic methyl ethers in the presence of aryl methyl ethers.
Soni, Ajay,Dutt, Akhilesh,Sattigeri, Viswajanani,Cliffe, Ian A.
experimental part
p. 1852 - 1857
(2011/06/20)

NOVEL AROMATIC COMPOUND AND POLYARYLENE COPOLYMER HAVING NITROGEN-CONTAINING HETEROCYCLE INCLUDING SULFONIC ACID GROUP IN SIDE CHAIN
Provided is a solid polymer electrolyte having increased heat resistance and high proton conductivity and a proton conductive membrane composed of the electrolyte. Also provided is a copolymer having a sulfonic acid group. The copolymer includes a repeating unit represented by Formula (1): (in the formula, Y denotes at least one kind of structure selected from the group consisting of —CO—, —SO2—, —SO—, —CONH—, —COO—, —(CF2)l— (l is an integer of 1 to 10), and —C(CF3)2—; W denotes at least one kind of structure selected from the group consisting of a direct bond, —CO—, —SO2—, —SO—, —CONH—, —COO—, —(CF2)l— (l is an integer of 1 to 10), —C(CF3)2—, —O—, and —S—; Z denotes a direct bond or at least one kind of structure selected from the group consisting of —(CH2)l—(l is an integer of 1 to 10), —C(CH3)2—, —O—, —S—, —CO—, and —SO2—; R30 denotes a nitrogen-containing aromatic ring having a substituent represented by —SO3H, —O(CH2)hSO3H, or —O(CF2)hSO3H (h is an integer of 1 to 12); p is an integer of 0 to 10; q is an integer of 0 to 10; r is an integer of 1 to 5; and k is an integer of 0 to 4).
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(2010/06/22)

A simple and practical copper-catalyzed approach to substituted phenols from aryl halides by using water as the solvent
Water surprise! A simple and practical copper-catalyzed approach to substituted phenols by hydroxylation of aryl halides has been developed by using environmentally benign water as the solvent (see scheme). The method proceeds under mild conditions and is tolerant towards various functional groups in the substrates.
Yang, Daoshan,Fu, Hua
supporting information; experimental part
p. 2366 - 2370
(2010/06/15)

Thiapyran formation via an unexpected thioaldehyde intermediate by the thermal decomposition of phenacyl sulfoxides bearing some heterocycles
Thermolysis of phenacyl sulfoxide bearing some nitrogen-containing heterocycles in the presence of 2,3-dimethyl-2,3-butadiene led to 6-benzoyl-5,6-dihydro-3,4-dimethyl-2H-thiapyran. This product was considered to be formed by the Diels-Alder reaction of the diene with thioaldehyde formed initially by the thermal decomposition of the sulfoxide.
Morita, Hiroyuki,Takeda, Masahiro,Kamiyama, Hideo,Hashimoto, Tadaaki,Yoshimura, Toshiaki,Shimasaki, Choichiro,Tsukurimichi, Eiichi
p. 3739 - 3740
(2007/10/03)

Demethylation of methoxypyridines with sodium trimethylsilanethiolate
Demethylation of methoxypyridines was accomplished in 55-87percent yield by use of ca. 1.5-2.5 equivalents of NaSSiMe3 in 1,3-dimethyl-2-imidazolidinone at 120-180 deg C.This method was found applicable to a methoxyquinoline and methoxypyridines containing a second substituent, such as Cl, OMe, and COOMe.
Shiao, Min-Jen,Ku, Wei-Shen,Hwu, Jih Ru
p. 323 - 328
(2007/10/02)

Quinolinoxy phenylsulphonamides
New phenylsulphonamide of the formula in which STR1 R1 represents a pyridyl, quinolyl or isoquinolyl radical which is unsubstituted or substituted by halogen, alkyl, cycloalkyl, alkoxy, cyano, nitro, halogenoalkyl, halogenoalkoxy, alkoxycarbonyl or alkylsulphonyl, R2 represents hydrogen, cyano, nitro, halogen, alkyl, alkoxy, halogenoalkyl, halogenoalkoxy or alkoxycarbonyl, R3 represents an aryl radical which is unsubstituted or monosubstituted, disubstituted or trisubstituted by halogen, halogenoalkyl, halogenoalkoxy, alkyl, alkoxy, alkylthio, alkylsulphonyl, cyano, nitro or alkoxycarbonyl, the substituents being identical or different, or represents pentafluorophenyl or represents a straight-chain, branched or cyclic alkyl which is unsubstituted or substituted by halogen, aryl, aryloxy, cyano, alkoxycarbonyl, alkoxy, alkylthio or trifluoromethyl, and X represents an --O--, --A--B-- or --B--A-- group where A denotes --O--, STR2 and B denotes --CH2 -- or STR3 where R1 does not represent a pyridyl radical when x represents an --O-- group, and salts thereof are prepared by reacting appropriate amines with sulphonyl halides. The substituted phenylsulphonamides can be employed as active compounds for inhibiting enzymatic reactions and for inhibiting thrombocyte aggregations.
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(2008/06/13)

EPOXIDATION WITH PYRIDINE-TRIFLUOROACETIC ANHYDRIDE-MOLECULAR OXYGEN AND ITS MECHANISTIC ASPECTS
Epoxidation of cholesteryl acetate (3) with pyridine-trifluoroacetic anhydride-molecular oxygen afforded bis(trifluoroacetate) (4), β-epoxide (5), α-epoxide (6), hydroxy trifluoroacetates A (7) and B (9), and enone (8).An oxidation mechanism proceeding via the hydroperoxide intermediate (A) is presented.
Harayama, Takashi,Sakurai, Osamu,Fukushi, Hideto,Tezuka, Yasuhiro,Yoneda, Fumio
p. 2335 - 2338
(2007/10/02)

Preparation of 4-substituted pyridines using quaternary pyridine salts
A process for preparing a 4-substituted pyridine product from a starting pyridine substituted in the 4-position by a leaving group susceptible to nucleophilic displacement when the starting pyridine is in quaternized form, comprises, quaternizing the starting pyridine under effective acidic conditions with acrylamide, N-monoalkylacrylamide or N-dialkylacrylamide, subjecting the resultant, corresponding quaternized starting pyridine, to a nucleophilic displacement reaction with a reagent which reacts with it to produce the corresponding quaternary salt of the 4-substituted pyridine product, and dequaternizing the latter under effective basic conditions to liberate the 4-substituted pyridine product.
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(2008/06/13)

EFFECT OF THE POSITION OF THE NITROGEN ATOM IN HETERO- AND HOMOAROMATIC HYDROXY COMPOUNDS ON THE CONTENT OF THE HIGHLY POLAR TAUTOMER OF AN ORGANIC AMPHOLYTE IN WATER
In the transition from 3-hydroxypyridine to 3-aminophenol the content of the highly polar tautomer is reduced by 1E4 times, while in the transition from 4-hydroxypyridine to 4-aminophenol it is reduced by 1E5 times.In the series of aminophenols the transition from the 3- to the 4-isomer leads to an increase of an order of magnitude in the content of the highly polar tautomer.The results from calculations of the content of the highly polar tautomer in the 3- and 4-aminophenol systems by a method where the acid-base constants of the systems and model compounds were used show that it is large enough at the isoelectric point (1E-3 and 1E-4 mole percent respectively) to be taken into account during discussion of the characteristics of these systems.The content of the highly polar tautomer is determined not only by the acidity of the hydroxy group in the molecule of the low-polarity tautomer and by the basicity of the endo- or exocyclic nitrogen atom in it but also by the stability of the molecule of highly polar tautomer.The latter, in turn, depends on the possibility of conjugation in its molecule.
Zaionts, V. I.,Korovitskaya, L. A.,Agrest, F. B.,Gutshabach, E. Sh.,Yachkula, S. S.
p. 1153 - 1158
(2007/10/02)

Theoretical Description of Solvent Effects. V. The Medium Influence on the Lactim-Lactam Tautomerism of Hydroxyazines
Der Loesungsmitteleffekt auf die Tautomeriegleichgewichte der Titelverbindungen wird mit Hilfe klassischer und quantenchemischer Versionen der Solvatonen- und der Reaktionsfeldtheorie berechnet.In Uebereinstimmung mit dem Experiment ergeben alle getesteten Verfahren eine Gleichgewichtsverschiebung zugunsten der Lactamform.Zur quantitativen Beschreibung dieses Effektes ist jedoch das Reaktionsfeldmodell besser geeignet.
Krebs, C.,Foerster, W.,Weiss, C.,Hofmann, H.-J.
p. 369 - 378
(2007/10/02)

TOTAL REACTIVITY OF PYRIDINE AND QUINOLINE VIA THE REACTIONS OF ARYLBENZOATES WITH HYDROXIDE ION. APPARENT SUBSTITUENT CONSTANS FOR SOME N-HETEROAROMATIC GROUPS
A new set of apparent ? values was evaluated for the aza substitution of all positions in pyridyl and quinolyl groups on the basis of the alkaline hydrolysis of aryl benzoates.The enhanced reactivities of 4-pyridyloxy- and 4-quinolyloxy- groups were first estimated quantitatively.
Sawada, Masami,Ichihara, Masaharu,Ando, Takashi,Yukawa, Yasuhide,Tsuno, Yuho
p. 4733 - 4736
(2007/10/02)

Displacement of Protomeric Equilibria by Self-Association: Hydroxypyridine-Pyridone and Mercaptopyridine-Thiopyridone Isomer Pairs
Values of both self-association and protomeric equilibrium constants are reported for 2-hydroxypyridine-2-pyridone, 4-hydroxypyridine-4-pyridone, and 2-mercaptopyridine-2-thiopyridone isomer pairs in different solvents.These results provide quantitative evidence for significant differences in the positions of protomeric equilibria for self-associated and monomeric species.The 2-substituted isomers are associated as well-known dimers while the 4-substituted systems form oligomers.In polar and hydrogen-bonding solvents self-association is substantially reduced.Sterically hindered 2- and 4-pyridones are less associated than unhindered systems.The implication of these results, that determinations and interpretations of protomeric equilibrium should take into account the possible dominance of self-association, is discussed.
Beak, Peter,Covington, Johnny B.,Smith, Stanley G.,White, J. Matthew,Zeigler, John M.
p. 1354 - 1362
(2007/10/02)

Reaction of OH with Pyridine. Pulse-Radiolytic and Product-Analysis Studies
The products obtained from the reaction of OH radicals, generated radiolytically, with pyridine under conditions where the intermediate 1-azahydroxycyclohexadienyl radicals are oxidized to isomeric hydroxypyridines have been examined by high-performance liquid chromatographic methods.From product-analysis data, the initial radiation chemical yields of o-, m-, and p-hydroxypyridines are 1.0, 3.8, and 0.3, respectively.The high yield of m-hydroxypyridine exemplifies the electrophilic nature of OH.The low yield of p-hydroxypyridine is attributed to the failure to quantitatively oxidize the 1-aza-p-hydroxycyclohexadienyl radical by the more powerful oxidant such as IrCl62-.The isomeric OH adducts of pyridine exhibit selectivity in reactivity with the two oxidants examined, and their reducing strength follows the order meta > ortho > para.From optical pulse radiolysis the second-order rate constant for the electron-transfer processes between hexachloroiridate and meta and ortho pyridine-OH adducts was determined to be 5.8 * 1E8 M-1 s-1.
Selvarajan, N.,Raghavan, N. V.
p. 2548 - 2551
(2007/10/02)