- REGIOSELECTIVE PARA-CHLORINATION OF ALKYLBENZENES ON CHEMICALLY-MODIFIED SILICA SURFACES
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Chlorination of alkylbenzenes was carried out with chlorine in carbon tetrachloride in the presence of chemically-modified silica catalysts.The para/ortho ratios were remarkably higher than those obtained in the FeCl3-catalyzed chlorination. t-Butylbenzene was chlorinated at para-position almost exclusively.The catalyst could be reused several times.
- Konishi, Hisatoshi,Yokota, Kiyoshi,Ichihashi, Yuji,Okano, Tamon,Kiji, Jitsuo
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- Electrochemical C-H Halogenations of Enaminones and Electron-Rich Arenes with Sodium Halide (NaX) as Halogen Source for the Synthesis of 3-Halochromones and Haloarenes
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Without employing an external oxidant, the simple synthesis of 3-halochromones and various halogenated electron-rich arenes has been realized with electrode oxidation by employing the simplest sodium halide (NaX, X = Cl, Br, I) as halogen source. This electrochemical method is advantageous for the simple and mild room temperature operation, environmental friendliness as well as broad substrate scope in both C-H bond donor and halogen source components.
- Jin, Jun,Lin, Yan,Liu, Yunyun,Wan, Jie-Ping,Wang, Chaoli
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p. 12378 - 12385
(2021/09/07)
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- C(sp3)-H methylation enabled by peroxide photosensitization and Ni-mediated radical coupling
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The “magic methyl” effect describes the change in potency, selectivity, and/or metabolic stability of a drug candidate associated with addition of a single methyl group. We report a synthetic method that enables direct methylation of C(sp3)-H bonds in diverse drug-like molecules and pharmaceutical building blocks. Visible light-initiated triplet energy transfer promotes homolysis of the O-O bond in di-tert-butyl or dicumyl peroxide under mild conditions. The resulting alkoxyl radicals undergo divergent reactivity, either hydrogen-atom transfer from a substrate C-H bond or generation of a methyl radical via b-methyl scission. The relative rates of these steps may be tuned by varying the reaction conditions or peroxide substituents to optimize the yield of methylated product arising from nickel-mediated cross-coupling of substrate and methyl radicals.
- Vasilopoulos, Aristidis,Krska, Shane W.,Stahl, Shannon S.
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p. 398 - 403
(2021/05/06)
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- Room temperature C(sp2)-H oxidative chlorination: Via photoredox catalysis
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Photoredox catalysis has been developed to achieve oxidative C-H chlorination of aromatic compounds using NaCl as the chlorine source and Na2S2O8 as the oxidant. The reactions occur at room temperature and exhibit exclusive selectivity for C(sp2)-H bonds over C(sp3)-H bonds. The method has been used for the chlorination of a diverse set of substrates, including the expedited synthesis of key intermediates to bioactive compounds and a drug.
- Zhang, Lei,Hu, Xile
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p. 7009 - 7013
(2017/10/05)
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- Mechanistic insight into the thermal 1,3-chlorine migrations of N-chloroacetanilides under neutral conditions
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The mechanistic insight of the thermal 1,3-chlorine migration reactions of N-chloroacetanilides under neutral conditions has been investigated. The results indicate that the 1,3-chorinemigration reaction is initiated by the radical reaction of the homocleavage of the Cl-N bond and subsequent radical combination of the Cl-C bond on the aromatic rings. The radical mechanism was verified by the thermal rearrangement of Nchloro- N-(4-methylphenyl)acetamide in cumene. After generation of hydrochloric acid in the radical mechanism, the migrations occurred through the acid-catalyzed rearrangement as well as the acid-catalyzed Orton reaction. The current results provide a comprehensive understanding on the mechanistic insights in the Orton reaction under different conditions.
- Cheng, Baoxiang,Xu, Jiaxi
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p. 518 - 525
(2017/05/01)
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- Microwave-assisted silica-supported aluminum chloride-catalyzed Friedel-Crafts alkylation
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Microwave irradiation is a popular method in organic synthesis to achieve high yields in shorter reaction times. This decreases total 'man-hours' in a synthetic setting. Another technique used in organic chemistry to decrease manual manipulations, is solid support reagents. The benefits of this approach is that upon completion of a reaction, a simple filtration can be performed which expedites the work-up and also produces less organic waste. Friedel-Crafts alkylation has been explored using microwave chemistry as well as with solid-supported reagents. In comparison with traditional heating, as well as with AlCl3, superior yields were observed with silica-gel bound aluminum chloride (Si-AlClx) when microwave irradiated for only 5 min.
- Zupp, Laurine R.,Campanella, Veronica L.,Rudzinski, Diandra M.,Beland, Franois,Priefer, Ronny
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p. 5343 - 5346
(2012/10/30)
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- PROCESS FOR HALOGENATION OF BENZENE AND BENZENE DERIVATIVES
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In a process of halogenation of benzene or benzene derivatives, di-substituted halobenzene derivatives having para-aromatic compounds or tri-substituted halobenzene derivatives having 1,2,4-substituted aromatic compounds are selectively produced. In halogenation of benzene or benzene derivatives, a fluorine-containing zeolite catalyst such as L-type zeolite, or a zeolite catalyst having the crystal size of at most 100 nm is used. The reaction is preferably effected in the presence of a solvent, and the solvent is preferably a halogenated compound.
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Page/Page column 18; 19
(2008/06/13)
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- Electrophilic aromatic chlorination and haloperoxidation of chloride catalyzed by polyfluorinated alcohols: A new manifestation of template catalysis
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We have demonstrated that a polyfluorinated alcohol, 2,2,2-trifluoroethanol, solvent enables haloperoxidase type activity and the oxychlorination of arenes (benzene and its alkylated derivatives) without a metal catalyst. The polyfluorinated alcohol has a dual function; it catalyzes electrophilic chlorination of less reactive arenes by several orders of magnitude and oxidation of chloride at lower H+ concentrations. DFT calculations show that a complementary charge template in the transition state explains the catalysis of the electrophilic chlorination. Copyright
- Ben-Daniel, Revital,De Visser, Samuel P.,Shaik, Sason,Neumann, Ronny
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p. 12116 - 12117
(2007/10/03)
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- Highly efficient, para-selective oxychlorination of aromatic compounds using potassium chloride and Oxone
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A highly efficient, regioselective method for oxychlorination of aromatic compounds is possible through electrophilic substitution of chlorine generated in situ from KCl as a chlorine source and Oxone as an oxidant for the first time.
- Narender,Srinivasu,Kulkarni,Raghavan
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p. 279 - 286
(2007/10/03)
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- Liquid-Phase Decarboxylation of Aromatic Haloformates: A New Access to Chloro- and Fluoroaromatics
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The treatment of phenyl chloroformates 1 with a Lewis acid in the liquid phase resulted in decarboxylation to the corresponding chloroaromatics 2. Fluoroaromatic compounds were synthesized from phenylchloroformates 1 through a sequential fluorination/decarboxylation in the liquid phase by treatment with excess anhydrous hydrogen fluoride under mild conditions. In all cases, yields were increased by performing the reaction in 1,2,4-trichlorobenzene, which is inert to Friedel-Crafts reactions.
- Lui, Norbert,Marhold, Albrecht,Rock, Michael H.
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p. 2493 - 2496
(2007/10/03)
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- Substituent Effect in C-Isopropylation of Benzene Derivatives in the Nitrobenzene-Methanesulfonic Acid-Isopropyl Methanesulfonate System
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Relative reactivities of chlorobenzene, o-dichlorobenzene, and nitrobenzene in C-isopropylation in the system nitrobenzene-methanesulfonic acid-isopropyl methanesulfonate at 298 K and the initial regioselectivity of the reaction were studied.Correlation analysis shows that sensitivity of the reaction to mesomeric effects of the substituents increses with decreasing activity of the substrate.
- Zaraiskaya, N. A.,Kachurin, O. I.
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p. 641 - 644
(2007/10/03)
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- Selective Mono-Alkylation and Arylation of Dichlorobenzenes by Palladium-Catalyzed Grignard Cross-Coupling
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Palladium(II)-phosphine complexes, especially PdCl2(dppf) where dppf stands for 1,1'-Bis(diphenylphosphino)ferrocene, are effective catalysts for the cross-coupling of Grignard reagents with dichlorobenzenes to produce selectively mono-alkylated and arylated benzenes.The addition of ligands is also effective for the cross-coupling of Grignard reagents containing a β-hydrogen(s).
- Katayama, Tatsuo,Umeno, Masayuki
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p. 2073 - 2076
(2007/10/02)
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- Selective Aromatic Chlorination and Bromination with N-Halogeno Amines in Acidic Solution
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1,2-Dimethoxybenzene and 3,4-dimethoxytoluene are efficiently chlorinated by N-chlorodialkylamines in sulphuric acid.The reaction has a very marked selectivity for monochlorination of the para-position.The chlorination and bromination of monoalkylbenzenes (toluene, ethyl-, and isopropyl-benzenes) under the same conditions is much less selective, but the para/ortho ratio can be reversed going from unsubstituted alkyl groups in the N-halogeno amines to alkyl groups substituted at the β-position by electron-withdrawing groups . m-Xylene is chlorinated with high selectivity at the 4-position.The nature of the chlorinating species is discussed.
- Minisci, Francesco,Vismara, Eelena,Fontana, Francesca,Platone, Eduardo,Faraci, Giovanni
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p. 123 - 126
(2007/10/02)
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- Halogenation Using Quaternary Ammonium Polyhalides. XIX. Aromatic Chlorination of Arenes with Benzyltrimethylammonium Tetrachloroiodate
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The reaction of arenes with a calculated amount of benzyltrimethylammonium tetrachloroiodate in acetic acid at room temperature or at 70 deg C gave nuclear chloro-substituted arenes in fairly good yields.
- Kajigaeshi, Shoji,Ueda, Yasuhiro,Fujisaki, Shizuo,Kakinami, Takaaki
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p. 2096 - 2098
(2007/10/02)
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- Molar enthalpies of formation of isopropylchlorobenzenes derived from equilibrium measurements
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Isomerization equilibria have been studied between 1-chloro-3-isopropyl-4-methylbenzene (I) and 1-chloro-2-isopropyl-4-methylbenzene, between 1-chloro-2,6-diisopropyl-4-methylbenzene (III) and 1-chloro-2,5-diisopropyl-4-methylbenzene (IV), and between 1-chloro-4-methylbenzene (VI) with the formation of (I) and (II) has also been studied.These experiments have been performed for the compounds in the liquid state between 303 and 403 K.From the values of the equilibrium constants following pairs of results have been calculated for ΔfH0m/(kJ.mol-1) and ΔfS0m/(J.K-1.mol-1): I=II, -(3.12 +/- 1.08) and (4.04 +/- 3.18); III=IV, (0.43 +/- 0.17) and (2.68 +/- 0.25); V=IV, -(10.08 +/- 4.86) and (5.40 +/- 13.14); IV+VI=I+II, -(0.72 +/- 0.50) and (3.42 +/- 1.46).The effects bj/(kJ.mol-1) of double and triple interactions of the functional groups have been calculated for alkylchlorobenzenes: b0Me-i-Pr=(7.6 +/- 3.9); b0i-Pr-Cl=(4.6 +/- 1.3); bpi-Pr-Cl=(1.5 +/- 1.1); bmi-Pr-Cl=0; b1.2.3i-Pr-Me-i-Pr=(7.1 +/- 5.6); b1.2.3i-Pr-Cl-i-Pr=(3.2 +/- 2.9).The effects of para- and meta-interactions of alkyl groups are equal to zero.The molar enthalpies of formation at 298.15 K of 20 alkylchlorobenzenes in the liquid state have been calculated.
- Nesterova, T. N.,Rozhnov, A. M.,Malova, T. N.,Kovzel, E. N.
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p. 649 - 656
(2007/10/02)
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- New Reagent Systems for Electrophilic Chlorination of Aromatic Compounds: Organic Chlorine-Containing Compounds in the Presence of Silica
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In the presence of silica, a number of chlorine-containing organic compounds, such as N,N-dichlorourethane, dichloramine-T, and t-butyl hypochlorite, become active electrophilic reagents capable of controlled monochlorination of aromatic compounds under mild conditions; for example, t-butyl hypochlorite/silica chlorinates alkylbenzenes, naphthalene, and anisole readily at 25 deg C; N,N-dichlorourethane/silica chlorinates benzene within 2 days 50 deg C.
- Smith, Keith,Butters, Michael,Paget, Walter E.,Nay, Barry
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p. 1155 - 1156
(2007/10/02)
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- Highly para-Selective Mono-Chlorination of Aromatic Compounds Under Mild Conditions by t-Butyl Hypochlorite in the Presence of Zeolites
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t-Butyl hypochlorite supported on H(1+), Na(1+) faujasite X (zeolite X) produces para-selective monochlorination of alkyl-, phenyl-, and halobenzenes under mild conditions; for example, chlorobenzene in acetonitrile (at 40 deg C) is chlorinated in high yield of isolated product (92percent) to give dichlorobenzene with an isomer ratio 97percent para/3percent ortho.
- Smith, Keith,Butters, Michael,Nay, Barry
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p. 1157 - 1158
(2007/10/02)
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- Alkylation of aromatic hydrocarbons
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A process for the alkylation of aromatic hydrocarbons with alkylating agents having from one to five, and preferably three to five, carbon atoms. The reactants are brought into contact, preferably in the liquid phase, in the presence of a crystalline zeolite catalyst characterized by a silica to alumina ratio of at least 12 and a constraint index within the approximate range of 1-12. The reaction is conducted at 100° C. to 300° C. and a pressure of from about 105 N/m2 to about 2×107 N/m2.
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