- Synthesis and structural characterization of 2,5-dihalo-3,4- dinitrothiophenes
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Using new nitration protocols, we have been able to efficiently dinitrate 2,5-dihalothiophenes with yields of ~80-95%. The resulting products 2,5-dibromo-3,4-dinitrothiophene (1), 2,5-dichloro-3,4-dinitrothiophene (2), 2-bromo-5-chloro-3,4-dinitrothiophene (3), as well as the analogous 2-bromo-3,4-dinitrothiophene (4), all crystallize easily allowing their characterization via X-ray crystallography. Crystallization of 1 occurs in the monoclinic space group C2/c with a=14.547(3)A, b=7.3534(15)A, c=10.775(2)A, β=128.89(3)°, and Z=4. Crystallization of 2 occurs in the tetragonal space group I-42d with a=9.9398(14)A, b=9.9398(14)A, c=16.866(3)A, and Z=8. Crystallization of 3 occurs as a pseudo-merohedral twin in the triclinic space group P-1 with a=7.340(5)A, b=8.094(5)A, c=9.112(5)A, α=82.059(5)°, β=66.232(5)°, γ=63.021(5)°, and Z=2. Crystallization of 4 occurs in the triclinic space group P-1 with a=7.1787(14)A, b=7.4092(15)A, c=8.3151(17)A, α=101.67(3)°, β=96.00(3)°, γ=116.13(3)°, and Z=2. The structures of all compounds exhibit the formation of interesting solid-state assemblies due to halogen-bonding interactions between the halogen and nitro groups. Springer Science+Business Media, LLC 2007.
- Wen, Li,Rasmussen, Seth C.
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p. 387 - 398
(2008/02/05)
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- Biphasic Electrophilic Halogenation of Activated Aromatics and Heteroaromatics with N-Halosuccinimides Catalyzed by Perchloric Acid
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Catalytic amounts of 70percent perchloric acid (0.1 - 10, mostly 0.1 - 1, mol percent, based on substrate) initiate the regioselective halogenation of activated aromatics and heteroaromatics with N-halosuccinimide (NXS, X = Cl or Br) in two-phase solid-liquid systems (NXS/hexane or NXS/CCl4) at room temperature to give ring-halogenated products in high yields.For example, thiophene is transformed to 2-halo or 2,5-dihalo derivatives (yield 82-98percent) using 1 or 2 equiv of NXS, respectively.Unsymmetrical 2,5-dihalothiophenes are obtained in 70-82percent yield by reacting 2-halothiophenes with an appropriate NXS.The reaction of 3-bromothiophene with NBS affords 2,3-dibromothiophene in 93-99percent yield. 1,3-Dimethoxybenzene and 2,3-dimethylanisole are halogenated regiospecifically at the 4-position to give the corresponding products in 81-94percent yield.
- Goldberg, Yuri,Alper, Howard
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p. 3072 - 3075
(2007/10/02)
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- Charge Density - Activation Energy Correlations in Electrophilic Bromination of Thiophenes
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Charge density calculations are made on eleven thiophenes by Hueckel LCAO MO and Del Re methods and correlated with experimental activation energies(Ea) obtained for the molecular bromination of these compounds.The need for the inclusion of ?-charges in any correlation of charge density with kinetic data is stressed. - Keywords: Charge density/ Activation energy / Bromination of thiophenes
- Nanjan, M. J.,Kannappan, V.,Ganesan, R.
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- Kinetics of Bromination of Certain Substituted Thiophenes in Solution
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The general features of the kinetics of bromination of thiophene and substituted thiophenes have been investigated in dry and 15percent aq. acetic acid (v/v) and the Arrhenius activation energy (Ea) accurately determined for ten thiophene derivatives and interpreted.The mechanism proposed is supported with the detection of a ?-complex between bromine and 2-bromothiophene.
- Kannappan, V.,Nanjan, M. J.,Ganesan, R.
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p. 1183 - 1187
(2007/10/02)
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