- Supramolecular hydrogen-bonded liquid crystals formed from 4-(4′-pyridylazophenyl)-4″-alkoxy benzoates and 4-substituted benzoic acids
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Four pyridine-based derivatives (I10, I12, I14, and I18) with molecular formula CnH2n+1O-C6H4COOC6H4-N=N-C5H4N, that differ from each other in the number of carbon atoms, n, were prepared and characterized for their mesophase behavior. The number of carbons in the alkoxy chain varies between 10, 12, 14, to 18 atoms, respectively. Liquid crystalline properties were studied for two series of hydrogen-bonded liquid crystal complexes, consisting of the central 4-pyridylazophenyl benzoate and substituted benzoic acids. In the first series of the supramolecular complexes (group A), the lengths of the alkoxy chains on both of the azo pyridine and the benzoic acid components have varied between 10, 12, 14, and 18 carbons. In the second series (group B), the same proton-acceptors, i.e., the pyridyl azo derivatives, were used but with benzoic acids para-substituted with small compact polar groups, X. All of the newly prepared pyridine-based derivatives and their hydrogen-bonded complexes were found to be mesomorphic. The newly prepared pyridine-based derivatives and their supramolecular complexes in both groups were characterized for their mesophase behavior by differential scanning calorimetry, DSC, and polarized light microscopy, PLM. Four 4-alkoxybenzoic acids (CmH2m+1OC6H4COOH, II10, II12, II14, and II18) were used in group A series; the number of carbons (m) of their alkoxy groups also varies between 10, 12, 14, and 18, respectively. Substituents on the other group of acids (IIIa-f) in group B series vary, respectively, between CH3O, CH3, H, Br, CN, and NO2. Smectic C mesophase is induced in most of the binary mixtures investigated.
- Naoum,Fahmi,Alaasar
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- Supramolecular hydrogen-bonded liquid crystals formed from 4-(4′-pyridylazophenyl)-4″-substituted benzoates and 4-alkoxybenzoic acids
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Phase diagrams of the binary mixtures of the title compounds were constructed to investigate the effect of different polar substituents, on the pyridine-based derivatives, as well as the alkoxy-chain length, on the acids, on the extent and stability of th
- Naoum,Fahmi,Alaasar
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- Induced wide nematic phase by seven-ring supramolecular H-bonded systems: Experimental and computational evaluation
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New seven-ring systems of dipyridine derivative liquid crystalline 2:1 supramolecular H-bonded complexes were formed between 4-n-alkoxyphenylazo benzoic acids and 4-(2-(pyridin-4-yl)diazenyl)phenyl nicotinate. Mesomorphic behaviors of the prepared complexes were investigated using a combination of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Fermi bands attributed to the presence of intermolecular H-bond interactions were confirmed by FT-IR spectroscopy. All prepared complexes possessed an enantiotropic nematic phase with a broad temperature nematogenic range. Phases were confirmed by miscibility with a standard nematic (N) compound. A comparison was constructed to investigate the influence of the incorporation of the azophenyl moiety on the mesomeric behavior of corresponding five-membered complexes. It was found that the present complexes observed induced a wide nematic phase with relatively higher temperature ranges than the five aromatic systems. Density functional theory (DFT) suggested the nonlinear geometry of the formed complex. The results of the DFT explained the nematic mesophase formation. Moreover, the π-π stacking of the aromatic moiety in the phenylazo acid plays an effective role in the mesomorphic thermal stability. The energy difference between the frontier molecular orbitals, HOMO (highest occupied) and LUMO (lowest occupied), and the molecular electrostatic potential (MEP) of the prepared complexes were estimated by DFT calculations. The results were used to illustrate the observed nematic phase for all H-bonded supramolecular complexes. Finally, photophysical studies were discussed which were carried out by UV spectroscopy connected to a hot stage.
- Ahmed, Hoda A.,Al-Mutabagani, Laila A.,Alshabanah, Latifah Abdullah,Hagar, Mohamed
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- Supramolecular liquid crystals induced by hydrogen-bonding interactions between non-mesomorphic compounds. I. 4-(4′-Pyridylazophenyl)-4″- Substituted benzoates and 4-substituted benzoic acids
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Equimolar binary mixtures of the title compounds were prepared to investigate the effect of different polar substituents, either on the pyridine-based derivatives or on the acid component, on the extent and stability of the supramolecular liquid crystal p
- Naoum,Fahmi,Alaasar
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- A Rewritable, Reprogrammable, Dual Light-Responsive Polymer Actuator
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We report on the fabrication of a rewritable and reprogrammable dual-photoresponsive liquid crystalline-based actuator containing an azomerocyanine dye that can be locally converted into the hydroxyazopyridinium form by acid treatment. Each dye absorbs at
- Gelebart, Anne Helene,Mulder, Dirk J.,Vantomme, Ghislaine,Schenning, Albertus P. H. J.,Broer, Dirk J.
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- Magneto-LC effects in hydrogen-bonded all-organic radical liquid crystal
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To identify the origin of the magneto-LC effects, which refer to the enhancement of intermolecular magnetic interactions in the LC phases of all-organic radical compounds, we have designed and synthesized H-bonded all-organic radical compounds showing nem
- Uchida, Yoshiaki,Suzuki, Katsuaki,Rui, Tamura
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- Azobenzene-based supramolecular liquid crystals: The role of core fluorination
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The impact of core fluorination on the phase behaviour of supramolecular hydrogen-bonded liquid crystals (HBLCs) is investigated in detail. Therefore, different types of HBLCs were synthesized using two benzoic acid derivatives as proton donors, namely, 4-octyloxybenzoic acid and octylbenzoic acid. The two acids were combined through intermolecular hydrogen-bonding with alkoxyazopyridine derivatives as proton acceptors. Three different types of azopyridines were used either without fluorine substitution or with one lateral fluorine substituent at different positions. The study proved the importance of using core fluorination as a significant tool to modify the liquid crystalline behaviour of HBLCs, where all azopyridines are non-mesomorphic and almost all their complexes exhibit enantiotropic mesophases. The formation of the hydrogen bond between the complementary components was confirmed using FTIR and 1H NMR spectroscopy, while the liquid crystalline self-assembly of the HBLCs was investigated in detail using polarized light microscope (PLM) and differential scanning calorimetry (DSC). Depending on the type of the terminal chain on the benzoic acid derivative and on the position of the lateral fluorine substituent different types of mesophases including nematic (N), smectic A (SmA) and smectic C (SmC) phases were observed. Finally, under UV light illumination all the prepared HBLCs show cis-trans photoisomerization resulting in tuning the liquid crystalline phases, which is of importance for industrial applications.
- Alaasar, Mohamed,Darweesh, Ahmed F.,Schmidt, Jaques-Christopher,Tschierske, Carsten
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- Azopyridines salt compound and preparation method
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The invention provides a preparation method of an azopyridines salt compound. The preparation method comprises the following synthesis steps: (1) enabling 4-aminopyridine and phenol to be subjected todiazo coupling reaction in the presence of nitrite to o
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Paragraph 0037; 0038; 0039; 0040
(2018/03/28)
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- AZO-QUATERNARY PYRIDINIUM SALTS WITH ACID-ENHANCED ANTIBACTERIAL EFFICACY, METHODS OF USE, METHODS OF SYNTHESIS, AND USES THEREOF
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A new azo-type quaternary pyridinium salt (Azo-QPS) shows enhanced activity at acidic conditions (e.g., pH=5); in neutral or basic conditions, this new Azo-QPS shows a much lower level (2-50 times less) anti-bacterial activity. The use of such a “stimulus
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Paragraph 0019; 0020
(2018/04/26)
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- Optical devices for the detection of cyanide in water based on ethyl(hydroxyethyl)cellulose functionalized with perichromic dyes
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Films of three polymers, based on ethyl(hydroxyethyl)cellulose functionalized with protonated perichromic dyes, were used for anion sensing. The polymer functionalized with protonated Brooker's merocyanine acts as a chromogenic/fluorogenic system for the
- Nandi, Leandro Guarezi,Nicoleti, Celso Rodrigo,Marini, Vanderléia Gava,Bellettini, Ismael Casagrande,Valandro, Silvano Rodrigo,Cavalheiro, Carla Cristina Schmitt,Machado, Vanderlei Gageiro
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p. 1548 - 1556
(2016/12/22)
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- Compound assisting metal in enhancing fluorescence and preparation method thereof
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The invention provides a preparation method of a compound assisting metal in enhancing fluorescence. The preparation method includes following steps: 1), synthesizing silver nanoparticles in situ in dye containing pyridine group; 2), dissolving an obtaine
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Paragraph 0012; 0013; 0036; 0037; 0038; 0039; 0048; 0050-51
(2017/01/02)
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- Mirror symmetry breaking in cubic phases and isotropic liquids driven by hydrogen bonding
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Achiral supramolecular hydrogen bonded complexes between rod-like 4-(4-alkoxyphenylazo)pyridines and a taper shaped 4-substituted benzoic acid form achiral (Ia3d) and chiral “Im3m-type” bicontinuous cubic (I432) phases and a chiral isotropic liquid mesophase (Iso1[*]). The chiral phases, resulting from spontaneous mirror symmetry breaking, represent conglomerates of macroscopic chiral domains eventually leading to uniform chirality.
- Alaasar, Mohamed,Poppe, Silvio,Dong, Qingshu,Liu, Feng,Tschierske, Carsten
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supporting information
p. 13869 - 13872
(2016/12/06)
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- Photoresponsive liquid crystals based on halogen bonding of azopyridines
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A series of photoresponsive halogen-bonded liquid crystals (LCs) were successfully constructed using molecular halogen and azopyridine compounds, which show interesting properties of photoinduced phase transition upon UV irradiation. In addition, bromine-bonded LCs were first obtained with high mesophase stability. This journal is the Partner Organisations 2014.
- Chen, Yinjie,Yu, Haifeng,Zhang, Lanying,Yang, Huai,Lu, Yunfeng
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supporting information
p. 9647 - 9649
(2014/08/18)
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- Janus ultrathin film from multi-level self-assembly at air-water interfaces
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Ultrathin free-standing Janus films were fabricated at air-water interfaces using azopyridine derivatives and poly(acrylic acid) via multi-level self-assembly on molecular and microscopic scales, which showed distinct asymmetric water wetting abilities on
- Zhang, Hongbin,Hao, Rui,Jackson, John K.,Chiao, Mu,Yu, Haifeng
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supporting information
p. 14843 - 14846
(2015/02/19)
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- Ruthenium acetate cluster amphiphiles and their Langmuir-Blodgett films for electrochromic switching devices
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We synthesized a long-chain phenylazopyridine ligand and used it to obtain three new amphiphilic trinuclear ruthenium acetate clusters. The amphiphilicity and anisometric form of the long-chain ligand allowed the complexes to self-assemble at the liquid-air interface and enabled their deposition by the Langmuir-Blodgett technique. We obtained the linear complex [Ru3O(C2H3O2)6(py)2L]+ [L = 4-(4-dodecyloxyphenylazo)pyridine, py = pyridine], which was more stable than the triangular [Ru3O(C2H3O2)6L3]+ and more suitable for application in electrochromic switching devices, as attested by its fast switching and optical changes in the near-IR region. Indeed, our electrochromic device remained stable for hundreds of switching cycles. Amphiphilic triruthenium clusters containing a long-chain phenylazopyridine ligand are presented. Langmuir-Blodgett (LB) film formation and its electrochemical characterization are discussed. An LB film of the linear amphiphilic triruthenium cluster was applied for a near-IR (NIR) electrochromic switching device.
- Naidek, Karine P.,Hoffmeister, Denize M.,Pazinato, Jaqueline,Westphal, Eduard,Gallardo, Hugo,Nakamura, Marcelo,Araki, Koiti,Toma, Henrique E.,Winnischofer, Herbert
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p. 1150 - 1157
(2015/04/27)
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- Ruthenium acetate cluster amphiphiles and their langmuir-blodgett films for electrochromic switching devices
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We synthesized a long-chain phenylazopyridine ligand and used it to obtain three new amphiphilic trinuclear ruthenium acetate clusters. The amphiphilicity and anisometric form of the long-chain ligand allowed the complexes to self-assemble at the liquid-a
- Naidek, Karine P.,Hoffmeister, Denize M.,Pazinato, Jaqueline,Westphal, Eduard,Gallardo, Hugo,Nakamura, Marcelo,Araki, Koiti,Toma, Henrique E.,Winnischofer, Herbert
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p. 1150 - 1157
(2014/03/21)
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- Functionalized gold nanoparticles as an approach to the direct colorimetric detection of DCNP nerve agent simulant
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New functionalized gold nanoparticles have been synthesized and their ability to act as colorimetric molecular probes for the naked-eye detection of nerve agent simulant DCNP has been studied. The detection process is based on the compensation of charges
- Marti, Almudena,Costero, Ana M.,Gavina, Pablo,Gil, Salvador,Parra, Margarita,Brotons-Gisbert, Mauro,Sanchez-Royo, Juan Francisco
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p. 4770 - 4779
(2013/08/23)
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- Light-controlled real time information transmitting systems based on nanosecond thermally-isomerising amino-azopyridinium salts
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Aminoazopyridines are valuable molecules for stable information transmitting systems as well as for light-controlled optical oscillators. Amino-substituted azopyridinium methyl iodide salts transmit optical information within the time scale of nanoseconds, and moreover, show oscillation frequencies up to 1 MHz at room temperature.
- Garcia-Amoros, Jaume,Nonell, Santi,Velasco, Dolores
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scheme or table
p. 3421 - 3423
(2012/05/05)
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- Supramolecular liquid crystals induced by intermolecular hydrogen bonding
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A series of new hydrogen-bonded liquid-crystal complexes formed between parasubstitued alkoxybenzoic acids (OBAm, where m denotes the number of the carbon in the alkoxy group, m=4, 5, 6, 7, 8, 10) and 4'-pyridylazophenyl-4- alkoxybenzoate (PEAPn, where n represents the number of the carbon in the alkoxy group, n=5, 6, 7 8, 10, 12, 14, 16) have been investigated by Fourier transform infrared (FTIR) Spectroscopy, differential scanning calorimetry (DSC), Polarizing optical microscopy (POM), and variable-temperature X-ray diffraction analysis. All PEAPn themselves are smectic mesogens and the hydrogen-bonded complexes show entiotropic smectic phases. The hydrogen bonding can raise the clear points of the complexes and, at the same time, decrease the melting points. The complexes were found to possess a much wider mesophase range than their corresponding individual components. The influence of the terminal chain lengths of OBAm and PEAPn on the phase transition temperatures is discussed. The results indicate that mostly the mesogenic behavior of the hydrogen-bonded assemblies exhibits a slight odd-even effect. Copyright Taylor & Francis Group, LLC.
- Lu, Huidan,Wang, Jianxiu,Song, Xiangzhi
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experimental part
p. 93 - 102
(2012/04/17)
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- Photo-driven optical oscillators in the kHz range based on push-pull hydroxyazopyridines
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Push-pull azophenols are valuable target molecules for stable photo-driven optical oscillators. Hydroxyazopyridinium methyl iodide salts show oscillation frequencies up to 10 kHz with no signs of fatigue upon continuous work. The Royal Society of Chemistry.
- Garcia-Amoros, Jaume,Nonell, Santi,Velasco, Dolores
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body text
p. 4022 - 4024
(2011/06/25)
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- Rearrangement mechanisms for azoxypyridines and azoxypyridine N-oxides in the 100% H2so4 region -The Wallach rearrangement story comes full circle
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Kinetic studies of the Wallach rearrangements of four azoxypyridines, four azoxypyridine N-oxides, and one azoxypyridine JV-methiodide have been, carried out in the 100% H2SO4 acidity region. For all of the ss-isomers in the study th
- Buncel, Erwin,Keum, Sam-Rok,Rajagopal, Srinivasan,Cox, Robin A.
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supporting information; experimental part
p. 1127 - 1134
(2009/10/23)
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- Acid-catalysed aryl hydroxylation of phenylazopyridines: Reaction intermediates, kinetics and mechanism
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A kinetic and product analysis study of the reactions of the three isomeric phenylazopyridines (PAPys) in aqueous sulfuric acid media (30-97 wt% H2SO4) is reported. The final products obtained from the reaction of 4-(phenylazo)pyridine (4-PAPy) are the hydroxylated product 4-(4-hydroxyphenylazo)pyridine, the reduction products 4-aminophenol and 4-aminopyridine, and a small amount of a dimerized product. 3-(Phenylazo)pyridine is unreactive, but 2-(phenylazo)pyridine gives the equivalent 2-(4-hydroxyphenylazo)pyridine, 4-aminophenol and 2-aminopyridine products. This product pattern, an oxidized azo-compound and two reduced amines, is similar to that found in the disproportionation of di-p-substituted hydrazinobenzenes observed in benzidine rearrangement studies. Consequently it has been proposed that the corresponding [N′-(4-hydroxyphenylhydrazino)]pyridines were formed as reaction intermediates in the present system; this is confirmed by showing that [N′-4-(4-hydroxyphenylhydrazino)-pyridine synthesized independently gave the same products as 4-PAPy under the same conditions. The kinetic study shows that the 4-isomer reacted faster than the 2-isomer at all the acid concentrations investigated (the 3-isomer being inert). Rate maxima are observed, at ~72 wt% H2SO4 for 4-PAPy and ~86 wt% H2SO4 for 2-PAPy. To facilitate the kinetic analysis, values of pKBH22+ for the protonation of the substrates and the possible hydroxy products at the azo-group were determined, using the excess acidity method; the first protonation occurs on the pyridine nitrogen in the pH region. An excess acidity analysis of the observed pseudo-first-order rate constants as a function of acidity indicate an A2 mechanism, with the diprotonated substrate and either one HSO4- ion or one H2O molecule in the activated complex. The proposed mechanism thus involves nucleophilic attack of HSO4- or H2O at an aryl carbon of the diprotonated substrate in the slow step, resulting in an intermediate hydrazo species which gives the observed products in a subsequent fast step (cf. benzidine rearrangement).
- Cheon, Kap-Soo,Cox, Robin A.,Keum, Sam-Rok,Buncel, Erwin
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p. 1231 - 1239
(2007/10/03)
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- Acid-catalysed disproportionation and benzidine rearrangement of phenylhydrazinopyridines: Reaction pathways, kinetics and mechanism
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A kinetic and product analysis study of the reaction of 4-[N′-(4-hydroxyphenylhydrazino)]pyridine (1) and 4-(N′-phenylhydrazino)pyridine (2) in 10-55 wt% aqueous sulfuric acid media is reported. The final products obtained from 1 are the oxidation product, 4-(4-hydroxyphenylazo)pyridine (3), and the two reduction products 4-aminophenol and 4-aminopyridine. This product pattern resembles that of the disproportionation products observed in some cases of the benzidine rearrangement. The reaction of 2 gives a complex product mixture including the disproportionation products 4-(phenylazo)pyridine (4), aniline and 4-aminopyridine, and other benzidine-type products including a p-semidine. Complicating the situation is the concurrent hydroxylation and disproportionation of 4 which take place in these media, giving 3, 4-aminopyridine and 4-aminophenol. The observed pseudo-first-order rate constants for the disproportionations increase steeply with acid concentration without showing any downturn at higher acidities. The disproportionation rate constants for 1 and 2 are much larger than those for the hydroxylation of 4. A reasonable mechanism which explains the observations is a benzidine-type rearrangement with accompanying disproportionation. To our knowledge this work is the first description of this type of reaction in substrates containing pyridinium rings.
- Buncel, Erwin,Cheon, Kap-Soo
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p. 1241 - 1247
(2007/10/03)
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- Studies of azo and azoxy dyestuffs. Part 18. Kinetics and mechanism of the mechanism of the hydrolysis of 3- and 4-(p'-methoxyphenyazo)pyridines in aqueous sulfuric acid media
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The kinetics of hydrolyis of 4-(p'-methoxyphenylazo)pyridine, 1, and its 3-isomer,2, have been studied in moderately concentrated sulfuric acid media at 25 deg C.In all the acid solutions investigated, 1 reacted faster than 2; rate differences between the two compounds varied from ca. 1000-fold in the dilute region of acidity to ca.250-fold in the more concentrated acid solutions.The observed first-order rate constants, kφ, for both substrates exhibit a maximum, at ca. 42percent H2SO4 and 47percent H2SO4 for 1 and 2, respectively.Activation paramaters have been determined.The pKa values for the second protonation equilibria of 1 and 2 have been evaluated and structures of the diprotonated species are discussed.Hydrolysis is shown to occur from the diprotonated substrates and two main mechanisms are operative.The first is an A-2 type mechanism, which involves rate-limiting attack of H2O on the aryl carbon center giving delocalized transition states and intermediates in which the pyridinium and azonium functions are involved in charge delocalization.Substituent transfer of a proton and detachment of the leaving group are fast processes.In the second A-SE2 type mechanism, nucleophilic attack and transfer of the proton are fast steps preceding the slow general acid catalyzed separation of the leaving group.The difference in reactivity of the two compounds is attributed to differences in extent of charge delocalization in the transition states of the reactions: for 1 both the pyridinium and protonated azonium functions are involved whereas for 2 only the azonium function participates in charge delocalization.
- Buncel, Erwin,Onyido, Ikenna
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p. 2115 - 2126
(2007/10/02)
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- STUDIES OF AZOXY DYESTUFFS-16 INVESTIGATIONS OF THE PROTONATION AND TAUTOMERIC EQILIBRIA OF 4-(p'-HYDROXYPHENYLAZO)PYRIDINE AND RELATED SUBSTRATES
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A study of the protolytic equlibria undergone by the title compound 1 and the related substrates 2-4 has been carried out by spectrophotometric methods.Compound 1 is associated with two macroscopic protolytic equilibrium constants (pKa1=7.73, pKa1=4.65) while compounds 2, 3 and 4 are associated with a single protolytic equilibrium in each case (pKa2=6.31, pka3=6.31, pka4=4.53).Compounds 2 and 3 exhibit identical spectral behaviour as function of pH, which provides clues to interpretation of the equilibria involved in this series.Further consideration of possible protolytic and tautomeric equilibria (Schemes 1-3) has allowed the various microscopic equilibrium constants to be assigned, the first intance in the hydroxyphenylazopyridine series.It is concluded that hydrazone tautomeric forms are not important in these systems.The equilibrium between the neutral (HA) and zwitterionic (AH+/-) forms of 1 is predominantly on the former side, whereas the equlibrium between 4-hydroxypiridine and 4-pyridone greatly favours the latter form.Discussion of various eqilibrium contants is given in terms of structural and electronic effects.
- Buncel, Erwin,Keum, Sam-Rok
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p. 1091 - 1101
(2007/10/02)
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