1003-09-4Relevant articles and documents
PROTIODESILYLATION OF SUBSTITUTED 2-TRIMETHYLSILYLTHIOPHENS
Seconi, Giancarlo,Eaborn, Colin
, p. 931 - 934 (1981)
First-order rate constats at 50 deg C have been determined for cleavage of the thiophen compounds XC4H2SSiMe3-2 in mixtures of (a) MeOH (5 vol.) with aqueous HClO4 (2 vol.) and (b) CH3CO2H (4 vol.) with aqueous H2SO4 (3 vol.) Relative rates krel, in the first medium are (X =) 5-OMe, 7 200; 5-Me, 36; H, 1.00; 5-Cl, 1.08E-1; 5-Br, 9.0E-2; 3-Br, 5.0E-2; 4-Br, 4.9E-3, and in the second medium 5-Me, 36; H, 1.00; 5-Cl, 1.28E-1; 5-Br, 9.8E-2; 3-Br, 5.5E-2; 4-Br, 6.5E-3; 5-NO2, 9.1E-7; 3-NO2, 7.1E-7.Except for the nitro-compounds, the two sets of log krel values show excellent linear correlations with values for the corresponding XC6H4SiMe3 compounds, with 3-, 4-, and 5-X in the thiophen ring being taken as equivalent to o-, m-, and p-X groups, respectively, in the benzene ring, the effects of substituents being a litle larger in the thiophen than the benzene system; 3- and 5-O2NC4H2SSiMe3 are less reactive than would be expected from the correlations.Again with the exception of the data for the nitro-compound, the krel values for the 4- and 5- substituted thiophens show very good correlation with ?m+ and ?p+ constants.
Cu3(BTC)2 as heterogeneous catalyst for the room temperature oxidative hydroxylation of arylboronic acids
Dhakshinamoorthy, Amarajothi,Asiri, Abdullah M.,Garcia, Hermenegildo
, p. 2895 - 2899 (2016)
A well known copper based-metal organic framework (MOF), namely Cu3(BTC)2, is a suitable heterogeneous catalyst to promote the oxidative room-temperature hydroxylation of arylboronic acids to the corresponding phenols by H2O2. Using 0.5 equiv of H2O2, Cu3(BTC)2 exhibits 80% conversion in 60 min that is higher than 70% conversion achieved with Fe(BTC) under the same conditions and reaction time. Cu3(BTC)2 is reusable with no significant drop in the activity. Furthermore, powder XRD of the reused Cu3(BTC)2 shows no changes in crystallinity compared to the fresh Cu3(BTC)2, indicating catalyst stability is maintained under reaction conditions. The scope of Cu3(BTC)2 as heterogeneous catalyst for the oxidative hydroxylation was studied for various phenylboronic acids.
Convenient High-Yield Procedures for 2-Bromothiophene and 2,5-Dibromothiophene
Keegstra, M. A.,Brandsma, L.
, p. 890 - 891 (1988)
2-Bromothiophene is obtained in high yields by adding a solution of bromine in 48percent hydrobromic acid or a 35percent aqueous solution of hydrogen peroxide to a mixture of thiophene, diethyl ether, and 48percent hydrobromic acid. 2,5-Dibromothiophene is obtained in >90percent yields from thiophene and bromine in hydrobromic acid.
CATALYTIC REDUCTIVE DEHALOGENATION OF THIOPHENE DERIVATIVES
Sharf, V. Z.,Taits, S. Z.,Gurovets, A. S.,Vol'kenshtein, Yu. B.,Fabrichnyi, B. P.,Shcherbakova, S. I.
, p. 130 - 133 (1982)
A method for the preparation of 3-substituted derivatives of thiophene by reductive dehalogenation of 2,5-dihalo-substituted thiophenes in the presence of a palladium complex is proposed.The dehalogenation reaction is a stepwise process.The presence of an acyl group in the 3 position increases the rate of the process.
Pyridinium dichlorobromate: A new stable brominating agent for aromatic compounds
Muathen, Hussni A.
, p. 169 - 171 (2002)
Pyridinium dichlorobromate (PyHBrCl2, 1) is a new example of iminium-trihalide complexes. The compound is prepared from pyridine and chlorine in the presence of aqueous hydrogen bromide. The crystalline trihalide is quite stable and acts as a safe source of positive bromine. It shows a remarkable reactivity towards aromatic compounds compared with other bromine complexes. It is also considered as a potential source for bromine chloride BrCl.
Halogenations of Aromatic Compounds with Halide Anions in the Presence of Nitrobenzenesulfonyl Peroxides. A Novel Method for the Formation of Positive Halogens
Yoshida, Masato,Mochizuki, Hideki,Kamigata, Nobumasa
, p. 2017 - 2020 (1988)
A novel type of positive halogens, sulfonyl hypochlorite or sulfonyl hypobromite was formed in the reactions of halide anions with nitrobenzenesulfonyl peroxides; these hypohalites could be used as effective reagents for halogenation of aromatic rings.
Electrochemical reduction of mono- and dihalothiophenes at carbon cathodes in dimethylformamide. First example of an electrolytically induced halogen dance
Mubarak, Mohammad S.,Peters, Dennis G.
, p. 8074 - 8078 (1996)
Cyclic voltammetry and controlled-potential electrolysis have been employed to probe the electrochemical reduction of a number of mono- and dihalothiophenes at carbon cathodes in dimethylformamide containing tetramethylammonium perchlorate. Reduction of 2
Green halogenation of aromatic heterocycles using ammonium halide and hydrogen peroxide in acetic acid solvent
D'Aleo, Danielle N.,Allard, Sheena R.,Foglia, Cassandra C.,Parent, Shawna L.M.,Rohr, David J.,Gottardo, Christine,MacKinnon, Craig D.
, p. 679 - 683 (2013)
The green generation of X+ (X = Br, I) using hydrogen peroxide in aqueous acetic acid allows access to aromatic heterocyclic halides in yields and purities comparable to syntheses employing N-bromosuccinimide. In activated and unsubstituted thiophene rings, regioselectivity is quantitative for positions α to the sulfur; pyrroles also give quantitative reactions, at least initially. Deactivated rings, including furans and thiazoles, as well as thiophenes with strongly electron-withdrawing groups showed little to no reactivity under the conditions investigated. The reaction shows remarkable functional group tolerance (to alcohol, nitro, alkyl, halo, and carbonyl groups), as shown through reaction with substituted phenols. In all bromination reactions, reaction yields and regiochemistry were very similar to reactions involving N-bromosuccinimide in tetrahydrofuran solvent.
Photocatalytic Selective Bromination of Electron-Rich Aromatic Compounds Using Microporous Organic Polymers with Visible Light
Li, Run,Wang, Zi Jun,Wang, Lei,Ma, Beatriz Chiyin,Ghasimi, Saman,Lu, Hao,Landfester, Katharina,Zhang, Kai. A. I.
, p. 1113 - 1121 (2016)
Pure organic, heterogeneous, metal-free, and visible light-active photocatalysts offer a more sustainable and environmentally friendly alternative to traditional metal-based catalysts. Here we report a series of microporous organic polymers containing photoactive conjugated organic semiconductor units as heterogeneous photocatalysts for a visible-light-promoted, highly selective bromination reaction of electron-rich aromatic compounds using HBr as a bromine source and molecular oxygen as a clean oxidant. Via a simple Friedel-Crafts alkylation reaction, the microporous organic polymers were obtained by cross-linking of organic semiconductor compounds with defined valence and conduction band positions. The utilization of the simply prepared porous polymer-based photocatalytic systems opens new opportunities toward a sustainable and efficient material design for catalysis.
Biphasic Electrophilic Halogenation of Activated Aromatics and Heteroaromatics with N-Halosuccinimides Catalyzed by Perchloric Acid
Goldberg, Yuri,Alper, Howard
, p. 3072 - 3075 (1993)
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.
