- Silica Supported Acids (HClO4-SiO2, KHSO4-SiO2) as Eco-friendly Reusable Catalysts for Bromodecarboxylation of α,β-Unsaturated Carboxylic Acids using KBr under Solvothermal and Solvent-Free Conditions
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A mild procedure has been developed for the bromodecarboxylation of α,β-carboxylic acids using nano silica supported SiO2-HClO4, SiO2-KHSO4 as catalysts and KBr as a bromine source in conventional solvothermal, ultrasonic assisted and solvent-free microwave assisted conditions. The α,β-unsaturated cinnamic acids were converted to corresponding β-bromo styrenes with high regioselectivity, while aliphatic α,β-unsaturated carboxylic acids afforded related β-bromo alkenes.
- Arisha, Samba Shiva Rao,Gugulothu, Yaku,Kamatala, Chinna Rajanna,Nagannagari, Maasi Reddy,Pulusu, Vijay Shekar,Utkoor, Umesh Kumar,Yelike, Hemanth Sriram
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p. 535 - 542
(2022/02/22)
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- Rethinking Basic Concepts-Hydrogenation of Alkenes Catalyzed by Bench-Stable Alkyl Mn(I) Complexes
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An efficient additive-free manganese-catalyzed hydrogenation of alkenes to alkanes with molecular hydrogen is described. This reaction is atom economic, implementing an inexpensive, earth-abundant nonprecious metal catalyst. The most efficient precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid hydrogenolysis to form the active 16e Mn(I) hydride catalyst [Mn(dippe)(CO)2(H)]. A range of mono- A nd disubstituted alkenes were efficiently converted into alkanes in good to excellent yields. The hydrogenation of 1-alkenes and 1,1-disubstituted alkenes proceeds at 25 °C, while 1,2-disubstituted alkenes require a reaction temperature of 60 °C. In all cases, a catalyst loading of 2 mol % and a hydrogen pressure of 50 bar were applied. A mechanism based on DFT calculations is presented, which is supported by preliminary experimental studies.
- Weber, Stefan,St?ger, Berthold,Veiros, Luis F.,Kirchner, Karl
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p. 9715 - 9720
(2019/10/14)
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- An efficient conversion of alcohols to alkyl bromides using pyridinium based ionic liquids: A green alternative to appel reaction
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Pyridinium based ionic liquids namely 4-alkylpyridinium bromides were prepared and used for the conversion of alcohols to alkyl bromides in the presence of p-toluenesulphonic acid in the absence of volatile organic compounds. This solvent free procedure promises to be a much improved and environmentally benign alternative to the Appel reaction.
- Das, Pranab J.,Das, Jupitara,Das, Dimpee
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p. 651 - 654
(2018/02/09)
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- Facile continuous process for gas phase halogen exchange over supported alkyl phosphonium salts
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Chloride-bromide halogen exchange was realized when a mixture of an alkyl chloride and an alkyl bromide were reacted over a supported molten alkyl phosphonium catalyst. Conversion was found to be near equilibrium in a tubular flow reactor at 150 °C and 1500 GHSV. The catalyst was prepared by impregnation of alumina or silica support and found to be highly stable for relatively long periods of time. A pathway for the catalytic cycle is proposed.
- Sharma, Priti,Sasson, Yoel
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p. 2824 - 2828
(2018/02/06)
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- A mild method for the replacement of a hydroxyl group by halogen. 1. Scope and chemoselectivity
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α-Chloro-, bromo- and iodoenamines, which are readily prepared from the corresponding isobutyramides have been found to be excellent reagents for the transformation of a wide variety of alcohols or carboxylic acids into the corresponding halides. Yields are high and conditions are very mild thus allowing for the presence of sensitive functional groups. The reagents can be easily tuned allowing therefore the selective monohalogenation of polyhydroxylated molecules. The scope and chemoselectivity of the reactions have been studied and reaction mechanisms have been proposed.
- Munyemana, Fran?ois,George, Isabelle,Devos, Alain,Colens, Alain,Badarau, Eduard,Frisque-Hesbain, Anne-Marie,Loudet, Aurore,Differding, Edmond,Damien, Jean-Marie,Rémion, Jeanine,Van Uytbergen, Jacqueline,Ghosez, Léon
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p. 420 - 430
(2015/12/31)
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- Influence of substructures on the spreading ability and hydrolysis resistance of double-tail trisiloxane surfactants
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Four types of novel double-tail trisiloxane surfactants of the general formula Me3SiOSiMeR1 OSiMe3 (R1 = -(CH2)3NR2 CH2CH(OH)CH 2(OCH2CH2)xOCH3; R 2 = -CH2CH(OH)CH2OCH2 (CH 2)yCH3, -CH2 (CH2) 3CH3, -CH2CH2CH(CH3) 2; x = 8.4, 12.9, 17.5, 22; y = 2, 6), have been synthesized. Their structures were characterized by proton and carbon nuclear magnetic resonance. Most of them are able to reduce the surface tension of water to less than 24 mN/m at concentration levels of 10-5 mol/L and 10-4 mol/L. The emphasis was on the influence of substructures on their spreading ability and hydrolysis resistance. The results showed that a weaker hydrophilicity of a surfactant molecule, a larger molar ratio of methyl to methylene in the whole hydrophobic groups, more flexible hydrophobic groups and introduction of a methyl group in the spacer can all improve the spreading ability of the double-tail trisiloxane surfactant solutions on low-energy solid surfaces. The double-tail trisiloxane surfactants 1F and 2F are stable for more than 270 days in a neutral environment (pH 7.0). The hydrolysis resistance of the double-tail trisiloxane surfactants can be improved by a weaker hydrophilicity of the surfactant molecule, and a larger volume of the hydrophobic groups. Copyright
- Peng, Zhongli,Lu, Caifeng,Xu, Minling
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scheme or table
p. 75 - 81
(2012/01/05)
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- Lithium carbenoids-ultra-reactive yet selective reagents for methylenation and halomethylenation of sulfones
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The first efficient, one-pot method for methylenation of p-toluyl sulfones (i.e., the transformation of p-MePhSO2CHR2 into R 2CCH2) is described. Methods for effecting that transformation involving alkylation of sulfones with reagents of the general formula MCH2X, where M = SiMe3, SnR3, and MgCl (the Julia method) have been previously described. However, the silicon reagent is completely unreactive toward many sulfones, the tin reagent typically affords only moderate yields, and the magnesium reagent typically gives incomplete reaction (9-40% starting material). This article reports that excellent yields are obtained by alkylating the sulfone with the more ionic lithium methylene carbenoids (LiCH2X, where X = Cl, Br, and I). For example, treatment of sulfone 1 with 3 equiv of n-BuLi (THF, -100 °C) followed by 2 equiv of CH2Br2 affords olefin 2 in 96% yield. Although the carbenoid is generated in the presence of a 1:2 mixture of α-lithio- sulfone and n-BuLi, it reacts selectively with the α-lithio-sulfone (Krel = 9.6 ± 0.8 with LiCH2Br). The chlorocarbenoid LiCH2Cl reacts somewhat less selectively (K rel = 3.5). The alkylsubstituted carbenoid n-BuCHBrLi reacts ≥ 40 times more slowly than LiCH2Br, suggesting that olefination occurs by the SN2 mechanism rather than by metal-assisted ionization (MAI), the mechanism by which cyclopropyl and vinylidene carbenoids react with nucleophiles. Finally, sulfones can be transformed into vinyl halides by treatment with 3 equiv of n-BuLi (THF, -78 °C), followed by >2 equiv of diisopropylamine, followed by 3 equiv of dihalomethane (CH2X 2, where X2 = Cl2, BrCl, Br2, or I2). All products are formed in high yield and purity.
- Pearlman, Bruce A.,Putt, Sterling R.,Fleming, Jeffrey A.
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p. 5646 - 5657
(2007/10/03)
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- Direct halogenation of alcohols and their derivatives with tert-Butyl halides in the ionic liquid [pmIm]Br under sonication conditions - A novel, efficient and green methodology
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A novel halogenating reagent system for direct halogenation of alcohols has been developed. tert-Butyl bromide, chloride and iodide in combination with the ionic liquid [pmIm]Br have been found to convert alcohols into the corresponding bromides, chlorides and iodides under sonication conditions (or heating) in good yields. Although a variety of primary and secondary alcohols participated in this reaction without any difficulty, tertiary alcohols remained inert. Several alcohol derivatives such as OTMS, OTBDMS, OAc, OTS and OTHP are also transformed into the corresponding halides in one-pot fashion by this procedure. A plausible rationale for this transformation is also presented. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Ranu, Brindaban C.,Jana, Ranjan
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p. 755 - 758
(2007/10/03)
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- Direct bromination and iodination of non-activated alkanes by hypohalite reagents
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The direct functionalisation of alkanes through bromination and iodination has been successfully achieved. The combination of stoichiometric mixtures of elemental halogen and sodium alkoxides leads to the formation of alkyl hypobromites and hypoiodites as reagents. The halogenation occurs without external photostimulation under thermal reaction conditions. Georg Thieme Verlag Stuttgart.
- Montoro, Raul,Wirth, Thomas
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p. 1473 - 1478
(2007/10/03)
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- Synthesis of 2-γ-N-(aminoethyl)aminopropyl-2-methyl-6-alkyl(aryl,H)-1,3-dioxa-6- aza-2-silacyclooctanes
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Some new 2-γ-N-(aminoethyl)aminopropyl-2-methyl-1,3-dioxa-6-aza-2- silacyclooctane and 2-γ-N-(aminoethyl)aminopropyl-2-methyl-6-alkyl(aryl)-1,3-dioxa-6-aza- 2-silacyclooctanes have been synthesized from γ-chloropropyldimethoxymethyl silane by ethylenediamine substitution and diethanolamine or N-alkyl(aryl)diethanolamines substitution. The resulting silocanes have been characterized by elemental analyses, IR, and 1H NMR.
- Yang,Lin,Li
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p. 2817 - 2822
(2007/10/03)
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- New versatile halogenating reagents for hydroxy groups
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Two new halogenating reagents, viz. allyltriphenoxyphosphonium bromide (ATPB) and allyltriphenoxyphosphonium chloride (ATPC) have been prepared and characterised. These have been evaluated for their potential application in bromination/ chlorination of a variety of compounds including aliphatic straight chain alcohols, branched chain alcohols and also 3′- and 5′-hydroxy groups of deoxyribonucleosides.
- Kumar,Dubey,Singh,Misra
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p. 842 - 845
(2007/10/03)
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- Study of activation energy and order of reaction of some liquid crystals
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Liquid crystals of the type p-phenylene-di-p-n-alkoxy benzoate have been prepared. Kissinger isothermal decomposition method has been used for determination of activation energy values of liquid crystals. Kissinger's assessment for shape index of DTA peaks is used to find the order of reaction. There is no direct relationship between the carbon atoms in terminal methylene groups and Ea values. Order of reaction value decreases with increase in heating rate upto carbon atoms 10 in the terminal methylene group but beyond this the order increases or decreases.
- Mundhe
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p. 246 - 249
(2007/10/03)
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- BiX3 as an efficient and selective reagent for the halogen exchange reaction
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Bismuth halides are efficient and selective reagents in the halogen exchange reactions carried out under mild conditions. This rapid, high yield reaction proceeds mainly with retention of configuration.
- Boyer, Bernard,Keramane, El Mehdi,Arpin, Severine,Montero, Jean-Louis,Roque, Jean-Pierre
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p. 1971 - 1976
(2007/10/03)
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- Primary and secondary 5-(alkyloxy)thianthrenium perchlorates. Characterization with 1H NMR spectroscopy, reactions with iodide and bromide ion, and thermal decomposition in solution
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A series of 5-(alkyloxy)thianthrenium perchlorates has been made in which the alkyl group is primary (1a-1p) and secondary (2a-2g). Preparations were carded out by reaction of the corresponding alkanol with thianthrene cation radical perchlorate in CH2Cl2 solution followed by precipitation of the perchlorate salt with dry ether. 1H NMR spectroscopy reveals that the presence of a stereogenic center in the alkyl group causes inequivalence in the ordinarily paired protons (e.g., H-4, H-6) of the thianthrenium ring. Reaction of iodide and bromide ion with primary alkyl-group compounds (e.g., methyl, ethyl, propyl, butyl) gave the alkyl halide in very good yield and by a second-order kinetic displacement. The second product was thianthrene 5- oxide (ThO). Rate constants for some of these reactions are reported. Reaction of secondary alkyl group compounds (e.g., 2-propyl, 2-pentyl, 2- hexyl, and 3-hexyl) with iodide ion gave good yields of alkyl iodide but also increasing evidence for a side reaction at the sulfonium sulfur, leading to I2, thianthrene, and secondary alkanol. Decomposition of some compounds at 100°C in solution (acetonitrile or 1,2-dichloroethane) was studied and gave alkene(s) and ThO.
- Zhao, Wenyi,Shine, Henry J.
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p. 695 - 702
(2007/10/03)
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- Reactivity of Alkaneselenyl Bromide: Conversion of Alcohols into the Corresponding Alkyl Bromides with Dialkylselenium Dibromide
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The reaction of alcohols with dialkylselenium dibromide gave the corresponding bromides in moderate to high yields.Alkaneselenyl bromide, produced by the thermal decomposition from dialkylselenium dibromide, acts as a brominating agent.The reaction of alcohol with dialkylselenium dichloride afforded the corresponding chlorides, although the yields were realtively low compared with those of the bromide.
- Akabori, Sadatoshi,Takanohashi, Yoshinori
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p. 3482 - 3484
(2007/10/02)
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- Kinetics and Mechanism of the Exo Cyclizations of ω-Formylalkyl Radicals
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Kinetic analysis of the reactions of 5-bromopentanal (1) and 6-bromohexanal (7) indicates that both the formylbutyl radical (2) and the formylpentyl radical (8) undergo fast exo cyclization.In each case the reaction is reversible and the equilibrium lies in favor of the open-chain form.The reactions are complicated by the propensity of aldehydes to undergo abstraction of formyl hydrogen atoms.Rate constants were measured by competition against reactions of the formylalkyl radicals, 2 and 8, and the cycloalkoxy radicals, 3 and 9, with tributylstannane.Values obtainedat 80 deg C include 8.7E5 s-1 and 1.0E6 s-1 for cyclization of 2 and 8, respectively, and 4.7E8 s-1 and 1.1E7 s-1 for the reverse reactions.The Arrhenius parameters for cyclization of 2 and its alkenyl analogue, 5-hexenyl radical, are very similar, but the activation energy for cyclization of 8 is unexpectedly low.Molecualar orbital (AM1) and molecular mechanics (MM2) calculations of transition structure strain energies are consistent with these observations.
- Beckwith, Athelstan L. J.,Hay, Benjamin P.
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p. 2674 - 2681
(2007/10/02)
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- Electron Spin Resonance Spectra and Structure of the Radical Cations of Dibromoalkanes and Monobromoalkanes
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The radical cations of dibromoalkanes containing two bromines separated by an alkyl chain, have been generated by exposing dilute solutions of the dibromoalkanes in freon to X-rays at 77 K.Two types of e.s.r. spectra were observed for these cations.The spectra obtained for Br(CH2)nBr, n = 1-7, show septet features characteristic of two equivalent Br nuclei.The coupling constant of the septet increases and reaches a plateau, with increased n in these dibromoalkanes.This indicates that a positive hole in these cations is shared, not by the two Br nuclei connected through ?-delocalization over the chain, but by the two Br nuclei directly bonded to each other, in accordance with conclusions recently drawn from e.s.r. studies of dichloroalkane cations.In contrast, the e.s.r. spectra obtained for Br(CH2)nBr, n > 7, are more complicated.When similar experiments were carried out with H(CH2)nBr, n > 7, analogous spectra were obtained, indicating that the spectra observed for these dibromoalkanes can be interpreted in terms of hyperfine interactions to only one of the two Br nuclei and to two nuclei with nuclear spins of 1/2.This result, considered together with the fact that similar cationic centres were detected for H(CH2)nBr, n > 3, and with the spectral change observed for Br(CH2)nBr and H(CH2)nBr cations in different matrices (CCl2FCClF2, CCl3F, and CCl4) indicates that cyclization also occurs for these cations, the positive hole being occupied in a three-centre bond comprising a Br nucleus, a C nucleus (four atoms away from the Br nucleus), and an H nucleus bonded to the C nucleus.
- Hasegawa, Akinori,Symons, Martyn C. R.,Shiotani, Masaru
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p. 657 - 666
(2007/10/02)
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- New Reagents, XXXII, Alkyldiphenylbismutanes: Synthesis, Properties, and Halogenolysis
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Alkyldiphenylbismutanes 1 have been synthesized for the first time (61-92 percent).These compounds are air sensitive, not spontaneously inflammable liquids which decompose not below ca. 170 deg C.The diphenylbismutino group is very good equivalent for Cl- or Br-substituents at aliphatic residues since halogenolysis of the Bi-Alk bond with SO2Cl2 or Br2 already occurs at -40 to 0 deg C (corresponding fissions of As-Alk and Sb-Alk bonds afford heating to ca. 130 or ca. 220 deg C).
- Kauffmann, Thomas,Steinseifer, Fritz
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p. 1031 - 1038
(2007/10/02)
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- Antibiotics and derivatives thereof having β-lactamase inhibitory activity and production thereof
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A novel antibiotic substance of the formula STR1 wherein R1 is CH3 and R2 is --CH2 --CH2 -- or R1 is H and R2 is --CH=CH--; and R3 represents hydrogen, lower alkyl or triphenylmethyl, and including the salts of the compound of formula (I) wherein R3 is hydrogen, said antibiotic substance having strong antibiotic activity and β-lactamase inhibiting effect, and a method for producing the same by aerobic cultivation of Streptomyces A271.
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- Direct Photolysis of 1-Halo-1-hexynes. Lack of Ionic Behavior
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Direct photolyses at >200 nm of 1-bromo- and 1-iodo-1-hexynes were performed in polar and nonpolar solvents.Only radical-derived products were obtained even in polar solvents, contrary to the previously reported ionic photochemical behavior of alkyl and vinyl halides.The results are discussed from an energy point of view; the ionization potential of the initially formed organic radical well accounts for the obvious difference in photobehavior between alkynyl and alkyl or vinyl halides.
- Inoue, Yoshihisa,Fukunaga, Takao,Hakushi, Tadao
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p. 1732 - 1737
(2007/10/02)
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- Silylaminyl Radicals. Part 2. Free Radical Chain Halogenation of Hydrocarbons using N-Halogenobis(trialkylsilyl)amines
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The liquid-phase halogenation of a number of hydrocarbons and of 1-chlorobutane by N-halogenobis(trialkylsilyl)amines has been studied using product analysis techniques.The reactions take place by free radical chain mechanisms which involve the propagation steps generalised in equations (A) and (B) (X=Br or Cl).At 353 K, the molar reactivities of toluene (benzylic C-H) and cyclohexane towards (R3Si)2N+RH(R3Si)2NH+R (A) R+(R3Si)2NXRX+(R3Si)2N (B) (Me3Si)2N are approximately equal and toluene is 5.2 times more reactive than perdeuteriotoluene.The relative rates of hydrogen abstraction by (Me3Si)2N and (ButMe2Si)2N from the primary, secondary, and tertiary C-H groups in 2-methylbutane show that the silylaminyl radicals are not only highly reactive but also sterically demanding.Thus, at 333 K the average primary C-H reactivity is 0.6 times that of the tertiary C-H towards attack by (Me3Si)2N, but 4.2 times that of the tertiary C-H towards attack by the more bulky (ButMe2Si)2N.Silylaminyl radicals are much more reactive in hydrogen abstraction than are analogous dialkylaminyl radicals and this difference is interpreted in terms of thermodynamic and polar effects which arise because of the ?-donor-?-acceptor nature of the trialkylsilyl substituent.
- Cook, Malcolm D.,Roberts, Brian P.,Singh, Karamjit
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p. 635 - 644
(2007/10/02)
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- LIQUID CRYSTALLINE PROPERTIES OF 4-N-ALKOXYPHENYL 4-NITROBENZOATES.
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Twelve 4-alkoxyphenyl esters of 4-nitrobenzoic acid were synthesized. The mesophases were identified and the transition temperatures and enthalpies determined. The above series shows considerable similarity to the reverse analogues, i. e. , the 4-nitro-phenyl 4-n-alkoxybenzoates.
- Galewski,Sobczyk
-
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- STABILIZATION IN THE ORDER I>Br>Cl AMONG TRIMETHYLSILYLMETHYL HALIDES, COMPARED TO CARBON ANALOGS. POSSIBLE ROLE OF ELECTRONEGATIVITY IN ORGANOSILICON CHEMISTRY
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Electronegativities may be used to rationalize the observation that the equilibrium, CH3(CH2)3I + (CH3)3SiCH2Cl CH3(CH2)3Cl + (CH3)3SiCH2I, lies to the right.
- Peterson, Paul E.
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p. 1295 - 1298
(2007/10/02)
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- A NOVEL ZIRCONIUM-CATALYZED HYDROALUMINATION OF OLEFINS
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Sterically hindered trialkylalanes, such as triisobutylalane, react with olefins at or below room temperature under the influence of a catalytic amount of Cl2ZrCp2 to effect hydroalumination of the olefins.The reaction can tolerate certain hetero-functional groups, such as OH, SPh and Br, which tend to interfere with previously reported hydroalumination procedures.
- Negishi, Ei-ichi,Yoshida, Tadao
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p. 1501 - 1504
(2007/10/02)
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