- Chemo- and Regioselective Functionalization of Polyols through Catalytic C(sp3)-C(sp3) Kumada-Type Coupling of Cyclic Sulfate Esters
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This contribution describes a copper-catalyzed, C(sp3)-C(sp3) cross-coupling reaction of cyclic sulfate esters, a distinct class of electrophilic derivatives of polyols, with alkyl Grignard reagents to afford functionalized alcohol products in good yields. The method is operationally simple and highlights the potential of cyclic sulfate esters as highly reactive substrates in catalytic, chemoselective polyol transformations.
- Ramírez-Contreras, Rodrigo,Morandi, Bill
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supporting information
p. 3718 - 3721
(2016/08/16)
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- Oxidative coupling reactions of grignard reagents with nitrous oxide
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Catalysis with laughing gas: N2O in combination with transition-metal catalysts allow the oxidative homo- and cross-coupling of Grignard reagents. The reactions can be performed under mild conditions despite the inert character of N2O. Copyright
- Kiefer, Gregor,Jeanbourquin, Loic,Severin, Kay
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supporting information
p. 6302 - 6305
(2013/07/19)
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- Thermal decomposition of cyclic organic peroxides in pure solvents and binary solvent mixtures
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The thermal decomposition reaction of acetone cyclic triperoxide, acetone cyclic diperoxide, 4-heptanone cyclic diperoxide, and pinacolone cyclic diperoxide ca. 0.02 M was studied in pure solvents (acetone and 1 -propanol) and in binary mixtures of acetone/1-propanol at 150°C. The kinetics of each system was explored by gas chromatography (GC) at different solvent compositions. The reactions showed a behavior accordingly with a pseudo-first-order kinetic law up to at least 90% peroxide decomposition. The main organic products derived from these thermolysis reactions were detected by GC analysis. Among them, the corresponding ketones, methane, ethane, and propane were the main identified products. The rates of decomposition of pinacolone diperoxide in the pure solvents were practically independent of the solvent characteristics, so it was of no interest to analyze its kinetic behavior in binary solvent mixtures. In acetone/1-propanol mixtures, the solvation effect on the cyclic peroxides derived from 4-heptanone and acetone molecules was slightly dominated by specific interactions between 1-propanol and a diradical-activated complex initially formed. This species was preferentially solvated by 1-propanol instead of acetone. Specific interactions between the O atoms from the peroxidic bond and the H from the OH in 1-propanol can be taken into account.
- Iglesias, Mariangeles,Barreto, GastoN P.,Eyler, Gladys N.,Canizo, Adriana I.
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experimental part
p. 347 - 353
(2011/07/29)
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- Silver-catalyzed carbomagnesiation of terminal aryl and silyl alkynes and enynes in the presence of 1,2-dibromoethane
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Regioselective carbomagnesiation of terminal alkynes and enynes with alkyl Grignard reagents has been achieved by the combined use of a silver catalyst and 1,2-dibromoethane. The Royal Society of Chemistry 2009.
- Fujii, Yuuki,Terao, Jun,Kambe, Nobuaki
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scheme or table
p. 1115 - 1117
(2009/07/10)
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- Factors controlling photochemical cleavage of the energetically unfavorable Ph-Se bond of alkyl phenyl selenides
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(Chemical Equation Presented) Primary photochemical paths of alkyl phenyl selenides (1) were investigated, and an origin of large deviations in the chemical yields of products obtained by carbon radical reactions induced by photolysis of phenyl selenides was clarified. KrF excimer laser photolyses of n-pentyl phenyl selenide (1a) yielded 1-pentene (2a), n-pentane (3a), n-decane (4a), dipentyl selenide (5a), benzene (6), dipentyl diselenide (7a), and diphenyl diselenide (7) as major photoproducts, with compounds 2a, 3a, 4a, 5a, and 7 formed by pentyl-Se bond cleavage, and 5a, 6, and 7a by Ph-Se bond cleavage. The selectivity of the photoproducts revealed the occurrence of an unexpected amount of Ph-Se bond cleavage (35% in n-hexane at 248 nm) during photolysis. Solvent viscosity, wavelength of light, and the structure of alkyl substituents were the major factors that controlled Ph-Se bond cleavage. The ratio of Ph-Se bond cleavage decreased with increasing solvent viscosity and laser wavelength. The effect of alkyl substituents on the ratio of bond cleavages, Ph-Se/total C-Se, was investigated for five alkyl phenyl selenides; the ratio decreased in the order pentyl > 2-methylallyl > allyl > 1-ethylpropyl > tert-butyl groups. The contribution of Ph-Se bond cleavage is most probably the origin of the large deviations in the yields of radical reactions induced by photolyses of 1, which can be minimized by selecting appropriate solvents and wavelength of light.
- Ouchi, Akihiko,Liu, Suyou,Li, Zhong,Kumar, S. Ajaya,Suzuki, Toshiaki,Hyugano, Takeshi,Kitahara, Haruo
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p. 8700 - 8706
(2008/03/12)
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- METHOD FOR THE PRODUCTION OF NON-AROMATIC HYDROCARBONS
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The invention relates to a method for the production of long-chain, branched-chain and/or cyclic hydrocarbons. A low molecular weight alkyl halide and a fused salt are firstly prepared. The fused salt contains an electrophilic compound and a reducing agent and is free from oxygen and oxygen compounds. The alkyl halide is then brought into contact with the fused salt such that long-chain, branched-chain and/or cyclic hydrocarbons are formed in the fused salt. The hydrocarbons formed in the fused salt are drawn off and can subsequently be separated from unreacted starting materials. By means of the above method, hydrogen can be produced during the reaction of the low molecular weight alkyl halide. The risk of oxidation of the alkane produced to give carbon monoxide or carbon dioxide is avoided by means of the reducing conditions in the fused salt. The product distribution can be controlled by means of suitable selection of the composition of the fused salt. Highly-branched hydrocarbons are produced with the preferred application of a sodium chloroaluminate fused salt.
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- Gas to liquid conversion process
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A process is disclosed for the conversion of lower molecular weight hydrocarbons, such as methane, into higher molecular weight hydrocarbon products, such as hydrocarbons having between 4 and 29 carbons. The process includes forming hydrated electrons, such as by mixing the lower molecular weight hydrocarbons with water and contacting the mixture with an energy source to form hydrated electrons. The hydrated electrons react with the methane to form hydrogen and higher molecular weight hydrocarbon products. Also disclosed is a related process for converting higher molecular weight hydrocarbons to lower molecular weight hydrocarbons by forming a mixture of higher molecular weight hydrocarbons and water and contacting the mixture with an energy source to form hydrated electrons that react with the higher molecular weight hydrocarbons to form hydrogen and lower molecular weight hydrocarbon products.
- -
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Page column 3-4
(2008/06/13)
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- Synthesis and thermal stability of O-vinylketoximes
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The O-vinylketoximes 2 were synthesized from ketoximes 1 and acetylene in superbase systems in good to excellent yields. Their thermal stability was investigated.
- Trofimov, Boris A.,Al'bina, Mikhaleva I.,Vasil'tsov, Alexander M.,Schmidt, Elena Yu.,Tarasova, Ol'ga A.,Morozova, Ludmila V.,Sobenina, Lubov' N.,Preiss, Thomas,Henkelmann, Jochem
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p. 1125 - 1132
(2007/10/03)
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- Kinetic study of the reactions of tert-butyl radicals in the liquid phase in the presence and absence of oxygen
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The photolyses of solutions of 2,2′-azoisobutane and 2,2,4,4-tetramethylpentan-3-one in decane in glass and metal cells, have been used to generate tert-butyl and, by reaction with oxygen, tert-butylperoxyl radicals. Time-dependent product yields from reactions in oxygenated and oxygen-free solutions have been measured over a range of temperatures (298-398 K). For each precursor, for a given set of conditions, the general features of the reactions are independent of the cell used, although the absolute rates of product formation are different. The major difference between the reactions of the two precursors lies in the initial photochemical step. For 2,2′-azoisobutane this leads directly to two tert-butyl radicals whereas the ketone gives a tert-butyl and a 2,2-dimethylpropanoyl radical. The product distributions can be accounted for in terms of the reactions of these radicals within a solvent cage in competition with cage escape and subsequent reaction. A single kinetic model that accounts for the reactions of both precursors, in the presence or absence of oxygen, at the temperatures studied, is described.
- Costello, Andrew R.,Lindsay Smith, John R.,Stark, Moray S.,Waddington, David J.
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p. 3497 - 3507
(2007/10/03)
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- Sterically congested molecules, 16: A convenient synthesis of di-tert-butyl ketone via its imine, 2,2,4,4-tetramethyl-3-pentanimine
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2,2,4,4-Tetramethyl-3-pentanimine (3) is efficiently prepared by a Barbier-type reaction of pivalonitrile (1) with an excess of tert-butyl chloride (2) and metallic lithium in ether. Its purification by extraction into aqueous acid and slow hydrolysis permit an inexpensive and very simple production of di-tert-butyl ketone (4). VCH Verlagsgesellschaft mbH, 1996.
- Knorr, Rudolf,Donhaerl, Angelika,Hennig, Karsten-Olaf
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p. 155 - 157
(2007/10/03)
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- Thermal reaction of (CH3)2C=C(CH3)2 in the presence of di-tert-butyl peroxide; reactions of the radicals ·CH3, (CH3)3C·C(CH3)2 and (CH3)2C=C(CH3)·CH2
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A study of the thermal reaction of (CH3)2C=C(CH3)2 (23DMB2) in the presence of di-t-butyl peroxide (PODBT) at 389-451 K yielded kinetic data on some reactions of the radicals ·CH3, (CH3)3C·C(CH3)2 (1122TMP·) and (CH3)2C=C(CH3) ·CH2 (112TMA·). The ratio of the cross-combination ratios of the radicals o(112TMA·, 122TMP·)/φ(·CH3, 1122TMP·) and the rate constant for H-abstraction from 23DMB2 by ·CH3 relative to that of the recombination reaction, ·CH3 + (CH3)2C=C(CH3)2 → CH4 + (CH3)2C=C(CH3) ·CH2 (4) 2·CH3 → C2H6 (7) have been determined. The values are φ(1122TMP·, 112TMA·)/φ(·CH3, 1122TMP·) = 0.9 ± 0.3 log(k4/k71/2) = (3.74 ± 0.21) - (36.3 ± 2.2)/Θ where Θ = RT ln 10 and the units are dm3/2 mol-1/2 s-1/2 for k4/k71/2, and kJ mol-1 for the energy of activation.
- Koertvelyesi,Seres
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p. 253 - 273
(2007/10/03)
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- Synthesis and 19F and 13C NMR Studies of a Series of 4-Substituted Fluorocubanes: Resonance Dependence of 19F Chemical Shifts in a Saturated System
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The substituent chemical shifts and the carbon-fluorine coupling constants of a range of 4-substituted cubyl fluorides in solvents of varying polarity are presented.Least squares regressional analysis of the data indicates that the fluorine probe, while being somewhat less sensitive to field effects as a result of the low polarizability of the cubane C-F bond, nevertheless responds in the "reverse" manner in agreement with precedents established in other alicyclic systems.The dependence of 1J(CF) upon electronegativity has been interpreted as evidence for the occurence of ?-induction over four bonds, the longest reported to date.Significantly, resonance parameters are found to be very important in describing the effect of substituents on both the fluorine chemical shifts and the magnitude of the one-bond and four-bond 13C-19F coupling constants.This represents one of the rare occasions that resonance effects have been observed in a fully saturated system in the ground state.A possible mechanism by which these resonance effects may be transmitted is presented.
- Della, Ernest W.,Head, Nicholas J.
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p. 5303 - 5313
(2007/10/02)
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- Highly Substituted 1,3-Dienes, IV. An Experimental and Theoretical Study of the Stereochemical Properties of 2-tert-Butyl-1,3-butadiene and 2,3-Di-tert-butyl-1,3-butadiene
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The molecular structure and conformation of 2-tert-butyl-1,3-butadiene (1) and of 2,3-di-tert-butyl-1,3-butadiene (2) have been studied by the gas electron diffraction method.The monosubstituted compound is observed to have a gauche orientation (φ = 32 deg) of the conjugated C=C bonds.The forces determining the preferred conformation of this molecule (syn or gauche) appear to be similar to those operative in the case of the high-energy conformer of unsubstituted 1,3-butadiene.The disubstituted compound has an approximately perpendicular orientation of the C=C-C=C system (φ = 101.5 deg), and in this case the preferred orientation is described as a result of minimalization of the nonbonded interactions. - Theoretical calculations of the structure and conformation of the two molecules have been carried out by molecular mechanics (MM3) and by ab initio (HF/3-21G) methods.The results from both sets of calculations are in good agreement with the observed structures of the two compounds. - Key Words: Dienes, conjugated / Conformation / Butadienes, orthogonal, gauche / Gas electron diffraction
- Traetteberg, Marit,Hopf, Henning,Lipka, Helmut,Haenel, Ralf
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p. 1459 - 1468
(2007/10/02)
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- Synthesis, thermochemistry, and reactions of vicinal bis(azoalkanes). The chemistry of α- and β-azo radicals
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Two vicinal bis(azo)alkanes, 8P and 8B, were prepared from acetone phenylhydrazone (APH) and acetone tert-butylhydrazone (ATBH), respectively. Thermolysis of 8P above 130°C in the presence of thiophenol affords APH in quantitative yield, showing that the central C-C bond of 8P cleaves in preference to the usual C-N homolysis of azoalkanes. The resulting radicals 9P recombine to the C-N dimer 16P about 40 times faster than to the more stable C-C dimer 8P. From the combustion heat of 8P, we deduce that its strain enthalpy Hs is 5.5 kcal/mol, while the resonance stabilization energy (RSE) of 9P is 15.3 kcal/mol. The tert-butyl analog 8B loses 2 mol of N2, showing that C-N homolysis greatly dominates over C-C homolysis. Nevertheless, we estimate that the latter process would occur with ΔG* (150°C) > 40.3 kcal/mol, which implies that the RSE of aliphatic hydrazonyl radical 9B is at least 6 kcal/mol below that of 9P and is little or no more than the RSE of the 1,1-dimethylallyl radical.
- Engel, Paul S.,Wang, Chengrong,Chen, Yanqin,Rüchardt, Christoph,Beckhans, Hans-Dieter
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- Simultaneous scission of C-S and S-S bonds of bis(trifluoromethyl)trisulfide by Grignard reagents
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Trifluoromethyl mono-, di- and tri-sulfides, and alkyl sulfides and disulfides, as well as dimerized products, are formed as a result of the simultaneous cleavage of the C-S and S-S bonds of bis(trifluoromethyl)trisulfide by Grignard reagents at -78 deg C.The formation of various products has been rationalized on the basis of the involvement of free radicals.
- Munavalli, Shekar,Rossman, David I.,Rohrbaugh, Dennis K.,Ferguson, C. Parker,Szafraniec, Leonard J.
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- A CONVENIENT PREPARATION OF PIVALALDEHYDE: SOME REMARKS ON THE BOUVEAULT SYNTHESIS
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A simple and versatile procedure of pivalaldehyde synthesis is described.The synthesis is based on the formylation of tert-butyl magnesium chloride with excess of DMF in low temperature and can be easily performed in bulk scale.The application of DMF for the formylation of tertiary Grignard compounds is briefly discussed in terms of steric effects.
- Nazarski, Ryszard B.,Tasz, Maciej K.,Skowronski, Romuald
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p. 817 - 820
(2007/10/02)
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- Thermal Decomposition of Nitrate Esters
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Rates of thermal decomposition and solvent rate effects have been measured for a series of nitrate esters.The alkoxy radicals formed by homolysis together with some of their further degradation products have been stabilized by hydrogen donation.Internal and external return of nitrogen dioxide have been demonstrated by solvent cage effects and isotope exchange.Radical-stabilizing substituents favor β-scission.Dinitrates in a 1,5 relationship behave as isolated mononitrates.Dinitrates in a 1,3 or 1,4 relationship exhibit intramolecular reactions.Tertiary nitrate esters in diethyl ether undergo elimination rather than homolysis.
- Hiskey , Michael A.,Brower, Kay R.,Oxley, Jimmie C.
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p. 3955 - 3960
(2007/10/02)
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- Mercury-Photosensitized Sulfination, Hydrosulfination, and Carbonylation of Hydrocarbons: Alkane and Alkene Conversion to Sulfonic Acids, Ketones, and Aldehydes
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Mercury-photosensitized sulfination of alkanes, RH, with SO2 forms sulfinic acids (RSOOH) and sulfinate esters (RSOOR) in high conversion and yield; oxidation of the mixture produces RSO2OH in high yield.Mercury-photosensitized hydrosulfination of alkenes with H2 and SO2 gives RSO2OH after oxidative workup.Mercury-photosensitized carbonylation of alkanes with CO gives RCHO and R2CO.
- Ferguson, Richard R.,Crabtree, Robert H.
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p. 5503 - 5510
(2007/10/02)
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- Homocoupling of Alkyl Halides and Cyclization of α,ω-Dihaloalkanes via Activated Copper
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The homocoupling of alkyl halides utilizing a highly activated form of zerovalent copper has been studied.Allyl and benzyl halides produce high yields of their respective homocoupled dimers 1,5-hexadiene and 1,2-diphenylethane.An 83percent yield of tetradecane was produced from n-heptyl iodide.The yield drops substantially for the corresponding bromo and chloro compounds.The yield is also strongly solvent and temperature dependent.Secondary and tertiary alkyl iodides and bromides produce moderate to low yields of homocoupling accompanied by substantial amounts of the corresponding alkane and alkenes.The copper-mediated cyclization of α,ω-dihaloalkanes has also been examined.The yield of cycloalkanes is moderate to high for the smaller rings with the yield decreasing substantially as the ring size increases.The compound meso-1,2-dibromo-1,2-diphenylethane was found to produce exclusively trans-stilbene in high yield.The activated copper was produced by reducing CuI*PR3 with a preformed solution of lithium naphthalenide.Complexes using triethylphosphine and tri-n-butylphosphine were both studied.The product yields were found to be similar in both cases.
- Ginah, Francis O.,Donovan, Thomas A.,Suchan, Scott D.,Pfennig, Deborah R.,Ebert, Greg W.
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p. 584 - 589
(2007/10/02)
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- Allylic and Propargylic Substitution Reactions Involving Radicals Generated from Alkylmercury Halides
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Addition of alkyl radicals to allyl or propargyl derivatives forms adduct radicals which can undergo β-elimination with substituents such as halogen, PhS, PhSO2, Bu3Sn, or HgCl to form the alkyl-substituted propene or allene and an eliminated radical which regenerates the alkyl radical by displacement from an alkylmercurial.With β-oxy substituents, such as O2CR, OP(O)(OEt)2, O3SAr, OPh, OSiMe3, or OH, the adduct radicals can displace the alkyl radical from the alkylmercurial to yield β-substituted alkylmercurials which spontaneously, or in the presence of nucleophiles, undergo an elimination reaction to yield the alkene or allene.Relative reactivities toward tert-butyl radical attack, such as k(allyl chloride)/k(propargyl chloride) = ca. 10, have been determined.A similar relative reactivity is observed in reaction with (t-Bu)2CuLi implicating attack by free tert-butyl radicals.With allyl or propargyl iodide, radical attack leads to iodine atom abstraction.Reaction of propargyl iodide with t-BuHgCl/hν, (t-Bu)2CuLi, or (t-Bu)3ZnLi leads to a mixture of hydrocarbons in which tert-butylallene is present in only trace amounts.Benzene is an important reaction product which seems to be formed via the cyclodimerization of two "propargyl" (C3H3.) radicals.
- Russell, Glen A.,Ngoviwatchai, Preecha,Wu, Yuh Wern
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p. 4921 - 4927
(2007/10/02)
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- Making Mercury-Ptotosensitized Dehydrodimerization into an Organic Synthetic Method: Vapor Pressure Selectivity and the Behavior of Functionalized Substrates
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Mercury-photosensitized dehydrodimerization in the vapor phase can be made synthetically useful by taking advantage of a simple reflux apparatus (Figure 1), in which the products promptly condense and are protected from further conversion.This vapor pressure selectivity gives high chemical selectivity even at high conversion and on a multigram scale.Mercury absorbs 254-nm light to give the 3P1 excited state (Hg*), which homolyses a C-H bond of the substrate with a 3o>2o>1o selectivity.Quantitative prediction of product mixtures in alkane dimerization and in alkane-alkane cross-dimerizations is discussed.Radical disproportionation gives alkene, but this intermediate is recycled back into the radical pool via H atom attack, which is beneficial both for yield and selectivity.The method is very efficient at constructing C-C bonds between highly substituted carbon atoms, yet the method fails if a dimer has four sets of obligatory 1,3-syn methyl-methyl steric repulsions, as in the unknown 2,3,4,4,5,5,6,7-octamethyloctane.We have extended the range of substrates susceptible to the reaction, for example to higher alcohols, ethers, silanes, partially fluorinated alcohols, and partially fluorinated ethers.We see selectivity for dimers involving C-H bonds α to O or N and for S-H over C-H.An important advantage of our experimental conditions in the case of alcohols is that the aldehyde or ketone disproportionation product (which is not subject to H. attack) is swept out of the system by the stream of H2 also produced, so it does not remain and inhibit the rate and lower the selectivity. kdis/krec is estimated for a number of radicals studied.The very hindered 3o 1,4-dimethylcyclohex-1-yl radical is notable in having a kdis/krec as high as 7.1.
- Brown, Stephen H.,Crabtree, Robert H.
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p. 2935 - 2946
(2007/10/02)
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- Photochemistry of Azocyclopropane
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trans-Azocyclopropane (1t) has been irradiated in the gas phase at 254 nm and in hydrocarbon solution at several wavelengths.As with most acyclic azoalkanes, the dominant reaction is isomarization to the cis-azoalkane 1c.In the gas phase or with short wavelength light, 1t undergoes competitive C-N homolysis, giving cyclopropyl radicals, and ring fragmentation to ethylene.Triplet-sensitized isomerization of the azo linkage proceeds with unusually high efficiency (Φt->c=0.2), but no experimental support could be found for the notion that cyclopropane ring cleavage leads to azo group isomerization.Since azocyclopropane behaves as a "reluctant azoalkane" that undergoes multiple photoreactions, it is not a particularly useful source of cyclopropyl radicals.
- Engel, Paul S.,Bodager, Gregory A.
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p. 4748 - 4758
(2007/10/02)
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- Reactions of the formyl radical with alkyl radicals
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The 308-nm exciplex laser flash photolyses of gas-phase CH3CHO, C2H5CHO, n-C3H7CHO, i-C3H7CHO, and t-C4H9CHO were studied by using both time-resolved and en
- Baggott,Frey,Lightfoot,Walsh
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p. 3386 - 3393
(2007/10/02)
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- REACTION OF THIANTHRENE CATION RADICAL WITH GRIGNARD REAGENTS; EVIDENCE FOR ELECTRON TRANSFER AND TRAPPING OF ALKYL RADICALS BY THE THIANTHRENE CATION RADICAL
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Reactions are reported between RMgCl and thianthrene cation radical perchlorate (Th+ClO4-) suspended in ether and tetrahydrofuran (THF).In ether solutions reactions R=Bu, s-Bu, t-Bu, 5-hexenyl, and cyclopentylmethyl.Major products were the alkane, the alkene R(-H) in some cases, and, in the cases of R=Bu, 5-hexenyl, and cyclopentylmethyl, the 5-alkylthianthrenium perchlorate (ThR+ClO4-).When 5-hexenylMgCl was used a mixture of 5-(5-hexenyl)- and 5-(cyclopentylmethyl)thianthrenium perchlorates in the ratio of approximately 2 was obtained.Since the ratio of 5-hexenyl/cyclopentylmethyl in the Grignard reagent was 10.4, it is concluded that the C6 sulfonium ions were formed by radical trapping by Th.+ after single electron transfer from Grignard to cation radical had occurred, thus allowing for cyclization of 5-hexenyl radical.Formation of ThBu+ClO4- is attributed to the trapping of butyl radical by Th.+, while formation of RH and R(-H) is in all cases also attributed to alkyl radical reactions.Reactions in THF (R=Me, i-Pr, Bu, s-BU, t-Bu, Ph) led almost exclusively to RH and Th.Polymerization of THF was also initiated and took place slowly giving rise to low molecular weight poly(THF).By using THF-d8 as solvent for reaction between BuMgCl and Th.+, it was possible to find Bu groups (1H-NMR) in the poly(THF-d8).Polymerization of THF is attributed, in some cases (R=Me, Bu), to alkyl-cation transfer from ThR+ to THF.In other cases initiation of polymerization by R+ and THF(-H)+ is considered.
- Soroka, Miroslaw,Shine, Henry
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p. 6111 - 6122
(2007/10/02)
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- Electrolytic-Reduction of tert-Butyl Bromide at Mercury Cathodes in Dimethylformamide
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A polarogram or cyclic voltammogram for reduction of tert-butyl bromide at mercury in dimethylformamide containing a tetraalkylammonium salt exhibits two waves, signaling stepwise generation of the tert-butyl radical and carbanion.Electrolyses of the alkyl bromide at a mercury pool cathode and at potentials corresponding to the first wave produce isobutane (40-43percent), isobutylene (43-45percent), and 2,2,3,3-tetramethylbutane (9-10percent).Experiments with perdeuterated tert-butyl bromide have revealed that the first two products arise via disproportionation of tert-butyl radicals, whereas the third compound is formed by combination of radicals.At potentials on the second wave for tert-butyl bromide, electrolyses in dimethylformamide containing either tetramethylammonium or tetra-n-butylammonium perchlorate yield equal quantities of isobutane (47-50percent) and isobutylene (47percent), but little 2,2,3,3-tetramethylbutane (1percent) is formed; interestingly, when tetraethylammonium perchlorate is the electrolyte, the products are isobutane (55percent), isobutylene (30percent), pivalaldehyde (14percent), and 2,2,3,3-tetramethylbutane (1percent).Electrolyses done in the presence of deuterated reagents have demonstrated that electrogenerated tert-butyl carbanions are protonated by water and, to a lesser extent, tetramethylammonium and tetraethylammonium cations to yield isobutane.Hydroxide ion, formed when water is deprotonated by the alkyl carbanion, attacks unreduced tert-butyl bromide to give isobutylene.
- Vieira, Kenneth L.,Peters, Dennis G.
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p. 1231 - 1239
(2007/10/02)
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- -
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In dimethylformamide or N-methylpyrrolidone the Ni-bipyridyl system catalyses the electrochemical reduction of functionalised or non-functionalised aliphatic halides. High yields of dimeric products are obtained besides primary mono- or di-bromides. Analysis of the reaction products shows the formation of dialkylnickel which can be isolated by coulometry. This species acts as a reducing agent for aliphatic halides.
- Mabrouk, Salah,Pellegrini, Sylvain,Folest, Jean-Claude,Rollin, Yolande,Perichon, Jacques
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p. 391 - 400
(2007/10/02)
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- CONTRIBUTION A L'ETUDE DES REACTIONS DE COMBINAISON DES RADICAUX ALCOYLE TERTIAIRES EN PHASE SOLIDE
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Disproportionation/combination ratios of self-reacting t-alkyl radicals are estimated in solid phase at low temperature.The low temperature solid state limit was estimated to be 7-25, this value is considerably lower than ratios of the literature (100 to 500) and is compatible with the FISCHER limit in liquid state.In the present work, the ratios are determined by product analysis from the gamma radiolysis of isobutane.
- Gourdin-Serveniere, C.,Fontaine, L. M.,Tilquin, B.
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p. 177 - 188
(2007/10/02)
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- Direct Geminal Dimethylation of Ketones and Exhaustive Methylation of Carboxylic Acid Chlorides Using Dichlorodimethyltitanium
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The reaction of ketones with an excess of (CH3)2TiCl2 (6) leads to the replacement of the carbonyl oxygen atom by two methyl groups.This mild method of direct geminal dimethylation involves Grignard-type addition followed by formation of tertiary carbocations which are captured by methyltitanium species.Additional functional groups such as primary alkyl chlorides, thioethers, aromatics, ethers and esters are tolerated, but not thioketals.The procedure has been applied to the synthesis of (+/-)-cuparene (44).Similarly, carboxylic acid chlorides are converted to tert-butyl derivatives.
- Reetz, Manfred T.,Westermann, Juergen,Kyung, Suk-Hun
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p. 1050 - 1057
(2007/10/02)
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- Isomerisation des radicaux insatures. III. Radicaux α,α,β-, α,β,γ- et α,α,γ-trimethallyles
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α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0-nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively.Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes.An internal sigmatropic 1,2-hydrogen atom transfer process is part of the proposed mechanism to explain such products.Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C-C) bond, then one β(C-H), and, to a lesser extent, one central C-CH3 bond.
- Deslauriers, Helene,Collin, Guy J.
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p. 3168 - 3173
(2007/10/02)
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- Reactions of Oxygenated Radicals in the Gas Phase. Part 14. Reactions of t-Butylperoxyl Radicals
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The photo-oxidation of trans-2,2'-azoisobutane has been studied between 313 and 393 K.The principal products are acetone, t-butyl alcohol, t-butyl hydroperoxide, and formaldehyde.The yields of hydroperoxide and formaldehyde come to a limiting value during photolysis.Detailed analyses of products were carried out at different temperatures and total pressures.Further experiments were performed in which t-butyl hydroperoxide was added.The reaction was simulated over this wide range of conditions.The importance of reactions between the various alkylperoxyl radicals is emphasised.
- Osborne, David A.,Waddington, David J.
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p. 1861 - 1868
(2007/10/02)
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- Selective Formation of Solute Radicals in the Radiolysis of Neopentane-Cyclopentane Mixtures at 4 and 77 K as Studied by Capillary Gas Chromatography and ESR Spectroscopy
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The dimer yields in the radiolysis of the neo-C5H12-cyclo-C5H11 (1 molpercent) mixtures at 77 and 4 K have been measured by capillary gas chromatography.Analysis of the results indicates that cyclopentyl radicals are produced selectively at 77K, while their selective formation is suppressed at 4K.This result coincides well with the data obtained by ESR spectroscopy.
- Tilquin, Bernard,Gourdin-Serveniere, Catherine,Miyazaki, Tetsuo,Fueki, Kenji
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p. 2029 - 2030
(2007/10/02)
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- ELECTRON TRANSFER FREE RADICAL MECHANISM IN THE REACTIONS OF ARENEDIAZONIUM CATIONS WITH GRIGNARD REAGENTS
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The major pathway in the reactions of arenediazonium cations with certain Grignard reagents is found to involve an electron transfer from the latter to the ?-system of the former reactant and radicals are the immediate precursors of the final products.
- Singh, P. R.,Khanna, R. K.,Jayaraman, B.
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p. 5475 - 5478
(2007/10/02)
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- Disproportionation-Combination Reactions of Caged Geminate Radical Pairs Formed from the Photodecomposition of 2,2'-Azoisobutane. Anisotropic Reorientation of tert-Butyl Radicals in Viscous Media and Birth Effects in Very Viscous Media
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The solvent viscosity dependence of the self-termination reactions of tert-butyl radical pairs generated from the photolysis of 2,2'-azoisobutane, in a number of inert solvents admixed with thiophenol, shows a linear relationship between the cage efficiency, 1/cage yield, and fluidity, 1/η, of the solvent.The viscosity dependence of the ratio of disproportionation/combination rate constants, kd/kc, for these cage reactions was compared to the values observed for the reactions of encounter pairs generated by the photolysis of di-tert-butyl ketone.At viscosities between 0.5 and 2.7 cP the kd/kc ratios obtained for geminate radical pairs were the same as those obtained from the reaction of the encounter pairs, while at higher viscosities of 12-808 cP the orientation of the geminately formed radicals at birth appeared to bias the radicals to undergo a higher proportion of combination.
- Tanner, Dennis D.,Rahimi, Parviz M.
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p. 225 - 229
(2007/10/02)
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- Chemistry of the tert-Butyl Radical: Polar Character, ρ Value for Reaction with Toluenes, and the Effect of Radical Polarity on the Ration of Benzylic Hydrogen Abstraction to Addition to Aromatic Rings
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We have reexamined the reactions of tert-butyl radicals with toluenes and have obtained a ρ value of 0.49 +/- 0.04 at 80 deg C.The new, independent system involves the quantification of all of the principal products from the reaction of tert-butyl radicals with mixtures of toluene and substituted toluene.Five major products contain benzyl fragments and are formed in significant yields: two symmetrical bibenzyls, the cross bibenzyl, and the two neopentylbenzenes that result from combination of tert-butyl and the two benzyl radicals.Attack on the side chain is a major reaction of free tert-butyl radicals and is the only significant reaction that they undergo other than cage and termination reactions. tert-Butyl radicals do not add to the ring of toluenes.Data on the relative rates of addition to benzenes and hydrogen abstraction from toluenes are collected for a series of radicals including hydrogen atoms; methyl, isopropyl, and tert-butyl radicals; and p-nitrophenyl, p-bromophenyl, and phenyl radicals.The data demonstrate that more electrophilic radicals have a larger tendency to add to rings whereas more nucleophilic radicals have a larger tendency to abstract benzylic hydrogens.
- Pryor, William A.,Tang, Felicia Y.,Tang, Robert H.,Church, Daniel F.
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p. 2885 - 2891
(2007/10/02)
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- Gas-Phase Photolysis of 2,2-Dimethylbutane, 2,2,3-Trimethylbutane, 2,2,3-Trimethyl-2-silabutane, and 2,2,3,3-Tetramethyl-2-silabutane at 147 nm.
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The 147-nm photolyses of 2,2-dimethylbutane, 2,2,3-trimethylbutane, 2,2,3-trimethyl-2-silabutane (isopropyltrimethylsilane), and 2,2,3,3-tetramethyl-2-silabutane (tert-butyltrimethylsilane) are reported.In addition, the mercury-sensitized photolyses of i-C4H10, trimethylsilane, and mixtures of i-C4H10 and trimethylsilane are reported which give disproportionation to combination (D/C) ratios of 2.1+- 0.2 and 0.28+-0.05 for (CH3)3C + (CH3)3C and (CH3)3Si + (CH3)3Si, respectively, and D/C ratios of 1.86+- 0.15and 0.55+- 0.08 for (CH3)C + (CH3)3Si to form 2-methyl-2-silapropene and i-C4H8, respectively.With the completion of this work, several trends and generalizations can be drawn concerning the importance of various processes in linear vs. branched alkanes and alkylsilanes.These conclusions are summarized in this report.
- Doyle, Daryl J.,Tokach, S. K.,Gordon, M. S.,Koob, R. D.
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p. 3626 - 3634
(2007/10/02)
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- PHOTOCHEMICAL STUDIES ON THE TERTIARY BUTYL RADICAL ISOLATED IN ARGON MATRICES
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The t-Bu radical was isolated in an argon matrix and exposed to short wavelength UV light.Two major photoproducts were observed using IR spectroscopy: the first, isobutylene, was formed by cleavage of a βCH bond; the second was the i-Bu radical which could have been formed by a photoisomerisation, or recombination of a H atom with isobutylene.
- Pacansky, J.,Chang, J. S.,Brown, D. W.
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p. 257 - 260
(2007/10/02)
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- SELECTIVE COUPLING OF FREE RADICALS VIA ORGANOCHROMIUM COMPLEXES.
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Free radicals can be coupled in high yield to give either symmetric dimers or cross coupling products by reacting chromous chloride in THF with alkyl halides.
- Sustmann, Reiner,Altevogt, Rudolf
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p. 5167 - 5170
(2007/10/02)
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- MEASUREMENT OF RATE PROCESSES OF FREE RADICALS IN HOMOGENEOUS AND MICELLAR SOLUTIONS BY CIDNP
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CIDNP is used to study rate processes of free radicals in both homogeneous and micellar solutions.An estimate of the lifetime of the phenyl-acetyl radical at ambient temperature (τ-CO>/=1E-7sec) produced during photolysis of dibenzyl ketone is made based on quantitative CIDNP measurements and computer simulations.Observation of CIDNP in micellar solution is shown to be consistent with an isotropic medium which restricts diffusion on a short time scale, allowing for an increased tendency toward cage reaction.In the case of t-butyl/pivaloyl radical pairs, escape of the radical fragments from the micelle is shown to be competitive with decarbonylation of the pivaloyl radical.Likewise, CIDNP is consistent with product yield results which show the enhanced tendency of triplet born benzyl radical pairs to undergo cage reaction when they are sequestered in a micelle.
- Lehr, Gary F.,Turro, Nicholas J.
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p. 3411 - 3420
(2007/10/02)
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- Ketone-derived Peroxides. III. Decompositions of Cyclic Diperoxides derived from Dialkyl Ketones
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The decompositions of diperoxides from acetone, pentan-3-one, 1,5-diphenylpentan-3-one, pinacolone, benzyl methyl ketone and dibenzyl ketone have been studied.The yield of ketone decreases in this series, from 68percent with acetone to 1-2percent with dibenzyl ketone, i.e. with the increasing stability of the more stable radical fragment.The major products from the decompositions of diperoxides from the dibenzyl ketone and di(p-methylbenzyl) ketone were bibenzyl and 4,4'-dimethylbibenzyl respectively formed through coupling of benzyl radicals; crossover experiments showed that this was primarily an out-of-cage process.Most of the peroxides gave significant yields (5-20percent) of esters formed by an in-cage reaction between the alkyl radical and diacyl peroxide generated from decomposition of the biradical formed in the initial O-O bond homolysis of the peroxide.
- McCullough, Kevin J.,Morgan, Alistair R.,Nonhebel, Derek C.,Pauson, Peter L.
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p. 651 - 676
(2007/10/02)
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- Self-Termination of Benzoyl Radicals to Ground- and Excited-State Benzil. Symmetry Control of a Radical Combination
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Benzoyl radicals (C6H5C.O) are generated in liquid solutions together with tert-butyl radicals by photocleavage of pivalophenone.The rate constant for their termination to benzil is determined by ESR and optical spectroscopy.It is well described by von Smoluchowski's equation employing a spin-statistical factor of 1/4.Energetically, the combination may lead to ground- and excited-state benzil.The latter reaction is ruled out by the kinetic data and the absence of recombination luminescence.Auxiliary data are presented on the photochemistry of pivalophenone and on the photophysics of benzil.
- Huggenberger, Christian,Lipscher, Juraj,Fischer, Hanns
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p. 3467 - 3474
(2007/10/02)
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- Azoperoxides. VII. Thermolysis of α-Alkylazoalkylhydroperoxides
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The thermal decomposition of 1-methylazo-1-hydroperoxycyclohexane 1 and 1-tert.-butylazo-1-hydroperoxycyclohexane 2 was studied in ethylbenzene and in the case of 2 also in other solvents.Decomposition products and decomposition rates of the azo and the peroxy groups were selectively estimated.The title compounds decompose faster than the analogous azo compounds and alkylhydroperoxides.A induced homolysis of both initiator groups is proposed; the compounds are not "bifunctional initiators".
- Schulz, Manfred,Missol, Udo
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p. 417 - 422
(2007/10/02)
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- Efficient Coupling of Tertiary Alkyl Halides with Dialkylzinc and Titanium Compounds
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Dialkylzinc compounds react with tertiary halides to afford the corresponding coupling products containing a quaternary carbon atom, thereby making geminal dialkylation of ketones or hydroalkylation of olefins possible.
- Reetz, Manfred T.,Wenderoth, Bernd,Peter, Roland,Steinbach, Rainer,Westermann, Juergen
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p. 1202 - 1204
(2007/10/02)
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