- Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo
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Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.
- Rana, Sujoy,Biswas, Jyoti Prasad,Sen, Asmita,Clémancey, Martin,Blondin, Geneviève,Latour, Jean-Marc,Rajaraman, Gopalan,Maiti, Debabrata
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p. 7843 - 7858
(2018/10/31)
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- Catalytic Bromination of Alkyl sp3C-H Bonds with KBr/Air under Visible Light
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Alkyl sp3C-H bonds of cycloalkanes and functional branch/linear alkanes have been successfully brominated with KBr using air or O2 as an oxidant at room temperature to 40 °C. The reactions are carried out in the presence of catalytic NaNO2 in 37% HCl (aq)/solvent under visible light, combining aerobic oxidations and photochemical radical processes. For various alkane substrates, CF3CH2OH, CHCl3, or CH2Cl2 is employed as an organic solvent, respectively, to enhance the efficiency of bromination.
- Zhao, Mengdi,Lu, Wenjun
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supporting information
p. 5264 - 5267
(2018/09/12)
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- Silica gel-mediated hydrohalogenation of unactivated alkenes using hydrohalogenic acids under organic solvent-free conditions
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Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under organic solvent-free conditions proceeded to give the corresponding chlorides in good yields. Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid afforded the corresponding halides, respectively. Silica gel could be recycled five times without any significant loss of activities.
- Tanemura, Kiyoshi
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supporting information
p. 4293 - 4298
(2018/11/10)
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- Preparation method of alkane brominated material
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The invention relates to a preparation method of an alkane brominated material. The preparation method comprises the following steps: adding alkane, a bromine-containing compound or elemental bromine,a catalyst and acid into a solvent; adding the solvent into a light-transmission reaction container under air or oxygen atmosphere; sealing; performing stirring reaction under constant pressure and light illumination conditions; then analyzing a nuclear magnetic yield, and performing extraction, drying, filtration, distillation under reduced pressure and column separation to obtain the alkane brominated material. Compared with the prior art, the preparation method disclosed by the invention has the advantages that by using low-cost and safe bromic salt as a bromine source, the air as an oxidizing agent and a nitrogen-containing reagent as the catalyst, reaction is carried out under the conditions of constant temperature and constant pressure, so that energy conservation and economy are realized, and the preparation method is convenient and safe to operate and is environmentally friendly.
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Paragraph 0046-0047
(2018/09/08)
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- A General Strategy for Aliphatic C-H Functionalization Enabled by Organic Photoredox Catalysis
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Synthetic transformations that functionalize unactivated aliphatic C-H bonds in an intermolecular fashion offer unique strategies for the synthesis and late-stage derivatization of complex molecules. Herein we report a general approach to the intermolecular functionalization of aliphatic C-H bonds using an acridinium photoredox catalyst and phosphate salt under blue LED irradiation. This strategy encompasses a range of valuable C-H transformations, including the direct conversions of a C-H bond to C-N, C-F, C-Br, C-Cl, C-S, and C-C bonds, in all cases using the alkane substrate as the limiting reagent. Detailed mechanistic studies are consistent with the intermediacy of a putative oxygen-centered radical as the hydrogen atom-abstracting species in these processes.
- Margrey, Kaila A.,Czaplyski, William L.,Nicewicz, David A.,Alexanian, Erik J.
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supporting information
p. 4213 - 4217
(2018/04/05)
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- Highly selective halogenation of unactivated C(sp3)-H with NaX under co-catalysis of visible light and Ag@AgX
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The direct selective halogenation of unactivated C(sp3)-H bonds into C-halogen bonds was achieved using a nano Ag/AgCl catalyst at RT under visible light or LED irradiation in the presence of an aqueous solution of NaX/HX as a halide source, in air. The halogenation of hydrocarbons provided mono-halide substituted products with 95% selectivity and yields higher than 90%, with the chlorination of toluene being 81%, far higher than the 40% conversion using dichlorine. Mechanistic studies demonstrated that the reaction is a free radical process using blue light (450-500 nm), with visible light being the most effective light source. Irradiation is proposed to cause AgCl bonding electrons to become excited and electron transfer from chloride ions induces chlorine radical formation which drives the substitution reaction. The reaction provides a potentially valuable method for the direct chlorination of saturated hydrocarbons.
- Liu, Shouxin,Zhang, Qi,Tian, Xia,Fan, Shiming,Huang, Jing,Whiting, Andrew
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p. 4729 - 4737
(2018/10/23)
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- Coupling molecular and nanoparticle catalysts on single metal?organic framework microcrystals for the tandem reaction of H2O2 generation and selective alkene oxidation
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A molecular catalyst, (sal)MoVI, and a heterogeneous catalyst, either Pd or Au nanoparticles (NPs), were integrated into one UiO-66 MOF microcrystal. The resulting dually functionalized catalysts, Pd@UiO-66-(sal)Mo and Au/UiO-66-(sal)Mo, have been utilized for a one-pot tandem reaction of H2O2 generation and selective liquid-phase alkene oxidation. The NPs serve as catalysts for the production of H2O2 from H2 and O2 gases, while the (sal)Mo moieties function as the oxidation catalyst. When the metal NPs are fully encapsulated within the MOF microcrystals, the alkene hydrogenation side reaction is largely suppressed, with a 6-fold decrease in the hydrogenation/oxidation product ratio for 5-bromo-1-cyclooctene favoring the epoxide as the major product. For Au/UiO-66-(sal)Mo, where the two catal sts are in close roximit on the MOF microcr stal the enhancement in oxidation productivity is increased by 10 times in comparison to the [Au/UiO-66-NH2 + UiO-66-sal(Mo)] physical mixture of the two singly functionalized MOFs.
- Limvorapitux, Rungmai,Chou, Lien-Yang,Young, Allison P.,Tsung, Chia-Kuang,Nguyen, SonBinh T.
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p. 6691 - 6698
(2017/11/09)
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- A alkane halogenation method (by machine translation)
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The invention relates to a cycloalkane of halogenation method, comprises the following steps: S1: taking inorganic hydrohalide salt M+ X- And the inorganic acid or organic acid, stirring to dissolve in water, containing the halide X- Aqueous solution; S2: light in the reactor will be put aqueous solution, add nanometer metal/semiconductor composite material photocatalyst, phase transfer catalyst and reaction substrate cycloalkane; S3: under the stirring condition, in the sunlight or 300W xenon lamp or LED light shifted to catalytic reaction; S4: reaction after the fluid is static set, filtering and recycling photocatalyst, separating and recovering the aqueous phase and then, drying the organic phase, and the dried organic phase rectification separation purification, to obtain the corresponding organic halogenated product. The present invention provides a method halide of the cycloalkanes, low cost, the apparatus is simple and easy to operate, high selectivity, easy separation, can be large-scale production, is a novel, environmental protection, high selectivity, low energy consumption of the new organic halide, viable green channels, with potential industrial application value. (by machine translation)
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Paragraph 0056; 0057
(2017/07/21)
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- Preparation of manganese/Graphite oxide composite using permanganate and graphite: Application as catalyst in bromination of hydrocarbons
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A highly efficient one-pot preparation of manganese/graphite oxide (MnOX/GO) composite from graphite and KMnO4 is described. Hummers preparation method of GO requires a stoichiometric amount of KMnO4, as a result, the method produces a large amount of reduced Mn species. The Mn residue generally is a waste, therefore, we envisioned converting it to value-Added materials. A MnOX/GO composite was prepared in one-pot by treating the unpurified GO with aqueous KOH. The composite was characterized by XRD, XAFS, SEM and TEM. Among various applications of the MnOX/GO composite, we applied it as a recyclable catalyst for bromination of saturated hydrocarbons, one of the most basic but important chemical transformations. The MnOX/GO composite is expected to be an efficient catalyst because of the high surface area and high accessibility of substrates derived from the 2- dimensional sheet structure. When the reaction of a saturated hydrocarbon and Br2 in the presence of catalytic MnOX/GO was performed under fluorescent light irradiation, a brominated product was formed in high yield in a short reaction time. GO could strongly bind with Mn to prevent elution to the liquid phase, enabling the high recyclability.
- Suzuki, Hideyuki,Nishina, Yuta
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- Revisiting the bromination of c-h bonds with molecular bromine by using a photo-microflow system
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The photobromination of C-H bonds by using molecular bromine was reinvestigated under microfluidic conditions. The continuous-flow method suppressed the production of dibrominated compounds and effectively produced the desired monobrominated products with high selectivity. Rapid bromination of benzylic substrates containing a photoaffinity azide group was achieved without any decomposition. Go with the (micro)flow: Photobromination of C-H bonds by using molecular bromine under microfluidic conditions has been investigated (see scheme). The continuous-flow method suppressed the production of dibrominated compounds and effectively produced the desired monobrominated compounds with high selectivity. Rapid bromination of benzylic substrates containing a photoaffinity azide group was achieved without any decomposition.
- Manabe, Yoshiyuki,Kitawaki, Yuriko,Nagasaki, Masahiro,Fukase, Koichi,Matsubara, Hiroshi,Hino, Yoshiko,Fukuyama, Takahide,Ryu, Ilhyong
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supporting information
p. 12750 - 12753
(2015/03/30)
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- Site-selective aliphatic C-H bromination using N -bromoamides and visible light
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Transformations that selectively functionalize aliphatic C-H bonds hold significant promise to streamline complex molecule synthesis. Despite the potential for site-selective C-H functionalization, few intermolecular processes of preparative value exist. Herein, we report an approach to unactivated, aliphatic C-H bromination using readily available N-bromoamide reagents and visible light. These halogenations proceed in useful chemical yields, with substrate as the limiting reagent. The site selectivities of these radical-mediated C-H functionalizations are comparable (or superior) to the most selective intermolecular C-H functionalizations known. With the broad utility of alkyl bromides as synthetic intermediates, this convenient approach will find general use in chemical synthesis.
- Schmidt, Valerie A.,Quinn, Ryan K.,Brusoe, Andrew T.,Alexanian, Erik J.
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supporting information
p. 14389 - 14392
(2014/12/10)
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- Bromination of hydrocarbons with CBr4, initiated by light-emitting diode irradiation
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The bromination of hydrocarbons with CBr4 as a bromine source, induced by light-emitting diode (LED) irradiation, has been developed. Monobromides were synthesized with high efficiency without the need for any additives, catalysts, heating, or inert conditions. Action and absorption spectra suggest that CBr4 absorbs light to give active species for the bromination. The generation of CHBr3 was confirmed by NMR spectroscopy and GC-MS spectrometry analysis, indicating that the present bromination involves the homolytic cleavage of a C-Br bond in CBr4 followed by radical abstraction of a hydrogen atom from a hydrocarbon.
- Nishina, Yuta,Ohtani, Bunsho,Kikushima, Kotaro
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p. 1663 - 1667
(2013/10/22)
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- Direct bromination of hydrocarbons catalyzed by Li2MnO 3 under oxygen and photo-irradiation conditions
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A method for the direct bromination of hydrocarbons with Br2 using a ubiquitous and inexpensive catalyst is highly desirable. Herein, we report the selective mono-bromination of hydrocarbons in good yield using Li2MnO3 as a catalyst under irradiation with a fluorescent room light. This new catalyst can be recycled. The effect of light was investigated using action spectra, which revealed that the reaction occurred on the surface of the catalyst.
- Nishina, Yuta,Morita, Junya,Ohtani, Bunsho
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p. 2158 - 2162
(2013/03/13)
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- A photoirradiative phase-vanishing method: Efficient generation of HBr from alkanes and molecular bromine and its use for subsequent radical addition to terminal alkenes
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A triphasic phase-vanishing (PV) system comprised of an alkane, perfluorohexanes, and bromine was successfully combined by photoirradiation to efficiently generate hydrogen bromide, which underwent radical addition with 1-alkenes in the hydrocarbon layer to afford terminal bromides in high yields. Georg Thieme Verlag Stuttgart.
- Matsubara, Hiroshi,Tsukida, Masaaki,Ishihara, Daisuke,Kuniyoshi, Kenji,Ryu, Ilhyong
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experimental part
p. 2014 - 2018
(2010/10/02)
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- Hexabromoacetone and ethyl tribromoacetate: a highly efficient reagent for bromination of alcohol
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A new and efficient method for the bromination of alcohols utilizing Br3CCOCBr3/PPh3 and Br3CCO2Et/PPh3 is described. Various alcohols can be converted smoothly into their corresponding alkyl bromides in high yields under mild conditions with short reaction times. Based upon 1H NMR studies using competitive reactions between selected brominating agents and Cl3CCN, Br3CCOCBr3 displays the highest reactivity approximately nine times that of CBr4.
- Tongkate, Pratoomrat,Pluempanupat, Wanchai,Chavasiri, Warinthorn
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p. 1146 - 1148
(2008/09/18)
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- Chemoselective monobromination of alkanes promoted by unactivated MnO 2
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Reaction of alkanes with bromine promoted by unactivated MnO2 gave the corresponding alkylbromides in excellent yield with good chemoselectivity. The MnO2 could be easily recovered and reused.
- Jiang, Xuefeng,Shen, Meihua,Tang, Yu,Li, Chaozhong
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p. 487 - 489
(2007/10/03)
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- Carbonylation of C7-C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds
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Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr4·2AlBr3 at -40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic aci
- Akhrem,Afanas'eva,Petrovskii,Vitt,Orlinkov
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p. 9903 - 9907
(2007/10/03)
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- A putative monooxygenase mimic which functions via well-disguised free radical chemistry
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The hydroxylation of cycloalkanes at 25°C by the syringe pump addition of tert-alkyl hydroperoxides (10 and 1 equiv based on catalyst) to deoxygenated acetonitrile containing cycloalkanes (0.64 M) and 0.61 mM of the catalyst, [Fem(III)2O(TPA)2(H2O)2]4+, is demonstrated to be a reaction which involves freely diffusing cycloalkyl radicals, i.e., free alkyl radicals.
- MacFaul, Philip A.,Ingold,Wayner,Que Jr., Lawrence
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p. 10594 - 10598
(2007/10/03)
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- The functionalization of saturated hydrocarbons. Part 31. The Fe(pa)3 - and [Fe(tpa)Cl2]ClO4 - catalyzed oxidations of saturated hydrocarbons by hydrogen peroxide: A comparative mechanistic study
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The Fe(pa)3 and [Fe(tpa)Cl2]ClO4 catalyzed (pa = picolinic acid, tpa = tris(2-pyridylmethyl)amine) functionalization of saturated hydrocarbons by H2O2 in pyridine/acetic acid follows a common reaction pathway. Regioselectivity studies indicate, that a high valent iron species is responsible for the activation of the alkane. Alkyl hydroperoxides are the precursors for ketone and alcohol formation. Dioxygen provides the oxygen atoms in the alkyl hydroperoxide.
- Barton,Beck,Taylor
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p. 5245 - 5254
(2007/10/02)
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- The functionalization of saturated hydrocarbons. Part 23. Gif-type bromination and chlorination of saturated hydrocarbons: A non-radical reaction
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The bromination of saturated hydrocarbons was studied in the GoAggIII system using CBrCl3 and other polyhaloalkanes. This bromination reaction was compared to free radical processes by (i) evaluating the rates of reactions for a series of polyhaloalkanes, by (ii) measuring the selectivity of the different systems towards various saturated hydrocarbons and by (iii) analyzing the product distribution arising from the bromination of cyclohexyl bromide under both the GoAggIII type conditions and from known processes for alkyl radical generation. Some chlorine containing reagents were also examined for C - Cl bond formation in the GoAggIII system. All the experimental findings support a mechanism for the reaction that is different from one involving free radicals. This non-radical pathway is common in all Gif-type systems, as seen in common patterns of selectivity, conditions is in agreement with a non-radical reaction pathway for the Gif-type bromination and chlorination reactions.
- Barton, Derek H. R.,Csuhai, Eva,Doller, Dario
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p. 9195 - 9206
(2007/10/02)
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- Comparison of gif-type reactivity towards alkanes with standard radical reaction selectivity. Gif oxidation of n-butane and propane
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A precise comparison has been made between radical bromination of a series of saturated hydrocarbons using BrCCl3 and the bromination of the same series with the same reagent under Gif-type (GoAggIII) conditions. The relative reactivities in the two series are completely different and confirm a difference in mechanism. Experiments with n-butane and with propane have shown that these gases react with the usual Gif selectivity to furnish 2-butanone and acetone respectively.
- Barton, Derek H. R.,Csuhai, Eva,Doller, Dario,Ozbalik, Nubar,Senglet, Nathalie
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p. 3097 - 3100
(2007/10/02)
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