- Insights into a novel class of azobenzenes incorporating 4,6- O -protected sugars as photo-responsive organogelators
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A novel class of 4,6-O-butylidene/ethylidene/benzylidene β-d-glucopyranose gelator functionalized with photo-responsive azobenzene moieties were designed and synthesized and also characterized using different spectral techniques. These azobenzene-based or
- Bhavya,Rabecca Jenifer,Muthuvel, Panneerselvam,Mohan Das
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- Porphyrin Co(III)-nitrene radical mediated pathway for synthesis of o-aminoazobenzenes
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Azobenzenes are versatile compounds with a range of applications, including dyes and pigments, food additives, indicators, radical reaction initiators, molecular switches, etc. In this context, we report a general method for synthesizing o-aminoazobenzene
- Goswami, Monalisa,De Bruin, Bas
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- Porphyrin cobalt(III) "Nitrene radical" reactivity; Hydrogen atom transfer from Ortho-YH substituents to the nitrene moiety of cobalt-bound aryl nitrene intermediates (Y = O, NH)
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In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier.
- Goswami, Monalisa,Rebreyend, Christophe,De Bruin, Bas
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- Fast synthesis of hydrazine and Azo derivatives by oxidation of rare-earth-metal-nitrogen bonds
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A novel N-N coupling reaction was developed through the oxidation of rare-earth-metal-nitrogen bonds produced by treatment of the easily available rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl) Li(THF)3 with aromatic primary or secondary amines. The reaction provides the symmetrical or unsymmetrical azo compounds and hydrazine derivatives in good to high yields within a very short time under mild conditions.
- Zhang, Lijun,Xia, Jing,Li, Qinghai,Li, Xihong,Wang, Shaowu
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scheme or table
p. 375 - 378
(2011/03/21)
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- Synthesis and photochemical properties of oligo-ortho-azobenzenes
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Azobenzenes have attracted great interest in recent years because of their ability to change conformation upon irradiation. This property has been featured in several applications not only in organic chemistry but also in biology. Even though monoazobenzenes have been extensively studied and documented in the literature, only a few methods are available for the synthesis of oligo-ortho-azobenzenes. Also, their photochemical properties have not been reported so far. This study shows an efficient strategy for the preparation of oligo-ortho-azobenzenes and the investigation of their photochemical properties. It is demonstrated that the absorption spectra are highly influenced by the substituents. Interestingly, none of the ortho-bis-, tris-, or tetra-azobenzenes showed any E → Z isomerization. Only the ortho-nitrogen-substituted monoazobenzenes' photochromic behavior upon UV irradiation was observed.
- Bellotto, Silvia,Reuter, Raphael,Heinis, Christian,Wegner, Hermann A.
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p. 9826 - 9834
(2012/01/06)
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- Ag-TiO2/clay composite photocatalyst for the oxidation-cyclization of 1,2-diamine compounds with propylene glycol or alcohols
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Silver-loaded TiO2 (Ag-TiO2) and acidic clay (K10 montmorillonite) composite photocatalyst has been successfully applied for the light-induced conversion of o-phenylenediamine (OPD) and its derivatives to substituted benzimidazoles with various alcohols in acetonitrile using UV-A and solar light. The influence of the various photocatalysts, solvents, and substituents on the yield and selectivity of the products has been investigated. The mechanism of photocatalysis is proposed. Loading silver on TiO2 enhances product yield and selectivity both in UV and solar light. In the presence of primary alcohols, 2-aminothiophenol forms only disulfide and hence Ag-TiO2/ clay can be used as a green catalyst for the synthesis of disulfides.
- Selvam, Kaliyamoorthy,Annadhasan, Mari,Velmurugan, Rengasamy,Swaminathan, Meenakshisundaram
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experimental part
p. 831 - 837
(2010/09/06)
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- A new class of azobenzene chelators for Mg2+ and Ca 2+ in buffer at physiological pH
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A new class of azobenzene-based chelators, trans-3a and trans-3b (3a and 3b), were designed and synthesized in two steps. Both 3a and 3b were readily dissolved in a buffer solution at physiological pH. The values of the dissociation constant of 3a and 3b for Mg2+ and Ca2+ were determined by the Hills plot; KdMg=1.12 mM and K dCa=660 μM for 3a and KdMg=158 μM and KdCa=200 μM for 3b, respectively. On irradiation at 489 nm light, 3a isomerized to give cis-form, which underwent cis-to-trans thermal isomerization in darkness at room temperature. The change in the absorption spectrum of the irradiated solution of 3a in the presence of Mg2+, showing the cis-to-trans thermal isomerization, indicates that the affinity of cis-3a for Mg2+ is lower than that of 3a.
- Momotake, Atsuya,Arai, Tatsuo
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p. 7277 - 7280
(2007/10/03)
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- Structure-reactivity correlation of anilines in acetic acid
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The oxidation of aniline in glacial acetic acid with percarbonate, a dry carrier of hydrogen peroxide, is a second-order reaction conforming to the isokinetic relationship. The hitherto followed method of correlation of the reaction rates in terms of the structure-reactivity relationships is unsatisfactory and erroneous. But the reaction rates of molecular anilines, obtained for the first time, conform to the structure-reactivity relationships.
- Karunakaran, Chockalingam,Kamalam, Ramasamy
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p. 1118 - 1124
(2007/10/03)
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- Rates of thermolysis of azidobenzenes in solution: Large stabilizations of transition states by charge transfer from electron-donor substituents
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Introduction of +R type para substituents into azidobenzenes causes very large increases in rate of thermolysis, up to 225-fold. The rates of nitrobenzene solutions at 120°C follow a Hammett-type linear free energy relationship log k = -5.44 - 2.33σ1 - 1.48R+ which indicates conjugative stabilization of a nitrene-like transition state. ortho-Substituents of the +R type causes still larger rate enhancements, up to 456-fold for 2-amino, which identify a special resonance proximity effect. It is suggested that the very high rates reported for such α-azidoheterocycles as 2-azidothiophene are due to similar resonance stabilizations and not to ring-opening concerted with nitrogen loss.
- Dyall, Leonard K.,L'abbe, Gerrit,Dehaen, Wim
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p. 971 - 975
(2007/10/03)
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- 1H AND 13C NMR SPECTRA OF 2,2'-DISUBSTITUTED TRANS AZOBENZENES SUITABLE FOR PREPARATION OF METALLIZED AZO DYES
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The 1H and 13C NMR spectra have been measured of six trans-azobenzenes substituted at 2 and 2' positions with substituents favourable for complex formation with a metal (OH, NH2, NHCOCH3, COOH).From the standpoint of NMR such substituted trans-azobenzenes are present in solution in a rapid equilibrium following from rotation around the bond between C-1 of phenyl group and N atom of azo linkage.The predominant form has the substituent in the syn-position with respect to the free electron pair of the nearer azo nitrogen atom.The equilibrium is affected by dipolar aprotic solvents (such as hexadeuteriodimethyl sulfoxide) by decreasing the presence of the predominant form by 1 to 11percent .
- Jirman, Josef
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p. 2160 - 2168
(2007/10/02)
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- Photochemical Conversion of o-Phenylenediamine and o-Aminophenol into Heterocyclics
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o-Phenylenediamine is photo-oxidized to phenazine-2,3-diamine in ethanolic or aqueous hydrochloric acid solution.In acetic or propionic acid solutions it forms benzimidazole derivatives. o-Aminophenol in ethanol is photo-oxidized to 2-amino-3H-phenoxazin-3-one and two tetracyclic solvent addition products.
- Crank, G.,Makin, M.I.H.
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p. 1163 - 1165
(2007/10/02)
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- Method for the preparation of tetranitrodibenzotetrazapentalene
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Tetranitrodibenzo-1,3a,4,6a-tetrazapentalene is prepared from diaminobenzene by reacting diaminobenzene and lead dioxide in ethylacetate to produce diaminoazobenzene, isolating the product by silica-gel elution, reacting diaminoazobenzene with an inorganic azide in a dilute aqueous nitrous acid solution at a temperature not in excess of 10° C. to produce diazidoazobenzene, isolating the product, heating diazidoazobenzene slowly to about 190° C. until nitrogen stops evolving to form dibenzotetrazapentalene, isolating the product, nitrating dibenzotetrazapentalene with concentrated sulfuric acid and forming nitric at a temperature not in excess of about 65° C. to product tetranitrodibenzo-1,3a,4,6a-tetrazapentalene.
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- Oxidations of Aromatic Amines by Superoxide Ion
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Superoxide ion acts as a mild and highly selective oxidizing agent for aromatic amines.Aniline and α-naphthylamine were not oxidized, but β-naphthylamine formed dibenzophenazine, dibenzophenazine and 2,2'-azonaphthalen-1-ol. o- and p-Diamines are oxidized to diaminoazobenzenes but m-diamines are unreactive.Similarly o- and p-aminophenols are oxidized to dihydroxyazobenzenes but m-aminophenols are unaffected, and o-mercaptoaniline forms the disulfide.The oxidations are considered to be free-radical processes, initiated by hydrogen abstraction by superoxide from the substrates.The biological significance of the results is discussed.
- Crank, George,Makin, Mohammad I. H.
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p. 845 - 855
(2007/10/02)
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- Organic chemistry of superoxide. I. Oxidations of aromatic compounds.
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Potassium superoxide is a selective oxidant for aromatic compounds with the order of susceptibility of substituent groups being -SH>-NH2-OH. Only o- and p- disubstituted amines and phenols are oxidized but monosubstituted thiols react.
- Crank,Makin
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p. 2169 - 2170
(2007/10/05)
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