- Synthesis of Azobenzenes from Quinone Acetals and Arylhydrazines
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Direct reaction between quinone bisacetals and arylhydrazines gives azobenzenes. The presence of catalytic amounts of cerium ammonium nitrate strongly accelerates the reaction. When the bisacetal has a substituent at the 2,5-cyclohexadiene framework, only one regioisomer is formed. The method represents a simple, mild, and novel synthetic access to differently substituted azocompounds in high to excellent yield.
- Carreno, M. Carmen,Mudarra, Gerardo Fernandez,Merino, Estibaliz,Ribagorda, Maria
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p. 3413 - 3416
(2007/10/03)
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- Quantification of the electrophilicities of diazonium ions
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The kinetics of the reactions of arenediazonium ions with arenes, alkenes, allylsilanes, allylstannanes, and silyl ketene acetals have been studied in acetonitrile solution. The reactions follow second-order kinetics, and in several cases rate-determining attack of the diazonium ion has been proven by kinetic isotope effect studies (1a + 2b), by the independence of the allylsilane reactivities of the rate of desilylation (1a + 10a, d) and by the independence of the rate constants of the diazonium counterion. A decrease of the rate constant with increasing solvent donor ability (correlation with Gutmann's donor number) was found. The reactions of diazonium ions with π-nucleophiles roughly follow the correlation lgk (20°C) = s (E + N), previously derived for the reactions of carbocations with nucleophiles. With the E parameters derived for diazonium ions, rate constants for azo couplings with aromatic and nonaromatic π-nucleophiles can be predicted with an accuracy of ≈102. On the basis of E, the electrophilic reactivities of diazonium ions can be compared with those of carbocations (Figure 9), and the combination with the nucleophilicity parameters N (Figure 10) gives a first clue on possible azo coupling reactions. Literature reports are discussed within this scheme. VCH Verlagsgesellschaft mbH, 1997.
- Mayr, Herbert,Hartnagel, Manfred,Grimm, Klaus
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- A New and Regioselective Synthesis of Aromatic Diazene Derivatives
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A new method for the preparation of aromatic diazene derivatives 3a-l, 5, 7a, b, 9 under very mild conditions is described.The reaction of trialkylarylstannanes with nitro-substituted benzenediazonium tetrafluoroborates leads, by strict ipso substitution, to the corresponding diaryldiazenes in satisfactory to high yields.Due to the excellent leaving group quality of the stannyl group azo compounds may be prepared which are not accessible by normal electrophilic azo coupling.The products can be valuable precursors, obtained by reduction of the amines or other derivatizations, for consecutive aromatic compounds.Key Words: Aromatic substitution, electrophilic / Azo compounds, synthesis of / Diazonium compounds, aromatic, coupling reaction of, with trialkylarylstannanes / Trialkylarylstannanes, application of
- Neumann, Wilhelm P.,Wicenec, Christian
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p. 2297 - 2301
(2007/10/02)
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- BASIC PROPERTIES OF 4-ARYLAZO-PHENOLS AND 4-ARYLAZO-ANISOLES
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The conditions in which 4-arylazo-phenols and 4-arylazo-anisoles have basic properties have been studied.We have also determined the equilibrium constants of the reactions between 4-arylazo-phenols or 4-arylazo-anisoles with perchloric acid in nitromethane, acetonitrile and acetic acid.Conclusions have been drawn from the influence of the nature of solvent and substituent at the benzene ring on equilibrium constant values.
- Nesterowicz, Marianna,Korewa, Ryszard
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p. 1085 - 1092
(2007/10/02)
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