- On the miscibility of ethers and perfluorocarbons. An experimental and theoretical study
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Despite their significant polar character, some organic ethers such as diethyl ether were found to be miscible with perfluorocarbon solvents. Solubilities of various ethers in perfluorocarbons and miscibility temperatures were determined. These properties were found to be greatly dependent on the polarity but also size and shape of the ether molecule. Theoretical calculations of the miscibility temperatures of organic solvents and perfluorocarbons using COSMO-RS method were correlated with experimental data. Considering the difficulties in the accurate description of the macroscopic properties, such as miscibility temperatures, from the first principles, the agreement between experimental and theoretical data is reasonable.
- Babiak, Peter,Němcová, Adriana,Rulí?ek, Lubomír,Beier, Petr
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p. 397 - 401
(2008/12/21)
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- Hydrodehalogenation of 1,1-dibromocyclopropanes by Grignard reagents promoted by titanium compounds
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1,1-Dibromocyclopropanes are converted into the corresponding monobromocyclopropanes (as mixtures of stereoisomers where appropriate) by reaction with 1.0-1.3 mol equiv. of ethylmagnesium bromide and 2-10 mol% titanium isopropoxide for 90%). With ethylmagnesium bromide, the reaction occurs very slowly in the absence of catalyst; with methylmagnesium bromide, the reaction does occur in the absence of catalyst, but is only slightly promoted in the presence of titanium isopropoxide. Reactions with a number of other Grignard reagents are also discussed. In the case of phenethylmagnesium bromide, the major product containing the phenethyl-group is ethylbenzene, together with small amounts of styrene and ethyl 4-phenyl-2-butyl ether, a product of trapping of the solvent, ether. In other cases, relatively large amounts of a diether, formally derived by hydrogen ion adjacent to the ether oxygen followed by dimerisation, are isolated. No products were identified incorporating the cyclopropane and either the Grignard alkyl group or the solvent. Labelling studies indicate that the hydrogen introduced into the cyclopropane is not derived from either the α- or β-positions of the Grignard reagent. When the reduction is carried out with phenethylmagnesium bromide in d8-tetrahydrofuran both monobromides contain deuterium.
- Dulayymi, Juma'a R. Al,Baird, Mark S.,Bolesov, Ivan G.,Nizovtsev, Alexey V.,Tverezovsky, Viacheslav V.
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p. 1603 - 1618
(2007/10/03)
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- SELECTIVE DESULFURIZATION OF 1,3-DITHIANES, -OXATHIOLANES AND -THIAZOLIDINES BY TRIBUTYLTIN HYDRIDE
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Selective desulfurization of 2-alkyl-1,3-dithianes, -oxathiolanes, or -thiazolidines 1 with one equivalent of tri-n-butyltin hydride yields acyclic compounds R1R2CHX(CH2)nSSnBu3 (X=S,O,NH; n=2,3), (2) which can be destannylated to the corresponding mercaptans 3.
- Schmidt, K.,O'Neal, S.,Chan, T.C.,Alexis, C.P.,Uribe, J.M.,et al.
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p. 7301 - 7304
(2007/10/02)
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- γ-Ray-induced reduction of sterically hindered alkyl carboxylates with trichlorosilane in the presence of hydrogen chloride. Two-step mechanism for the formation of alkanes via the alkyl chloride
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γ-Irradiation of a mixture of 1-adamantyl acetate and trichlorosilane (TCS) in the presence of hydrogen chloride yields adamantane. The first step of this reaction entails cleavage of the alkyloxygen bond by the action of HCl and TCS to give the alkyl chloride. The chloride, in the second step, is dechlorinated by TCS by a known, free-radical mechanism. t-Amyl and benzyl acetates react analogously to 1-adamantyl acetate in this system to give isopentane and toluene, whereas other primary and secondary alkyl derivatives produce the corresponding dialkyl ethers by a known, free-radical mechanism.
- Oka, Kunio,Nakao, Ren
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- Chemistry of Carbenes: Part I - Reactions of Methylene with Diethyl Ether
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The carbene biradical, methylene, reacts with diethyl ether to give in addition to insertion products (ethyl n-propyl and ethyl isopropyl ethers), a methyl alkyl ether by a displacement reaction and acetaldehyde by an abstraction reaction in which the biradical behaves like a monoradical.The insertion reactions have been found to show clear discrimination.The bond reactivity of secondary C-H bond is 2.53 at 20 and 2.85 at 100 deg C, whereas for that of Et-O bond is 0.90 at 20 and 1.14 at 100 deg C in comparison to 1.00 for primary C-H bond.At 100 deg C the H-abstraction rate is 1.00 although individual runs show variation.The cumulative rate of attack at 100 deg C is thus about 3.8 times greater on secondary bond as compared to that at the primary bond.The addition of oxygen to the system not only alters the course of the reactions but results in the formation of novel peroxy biradicals and monoradicals which give rise to large amounts of ethyl acetate and ethyl formate.
- Mehta, R. K. S.
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p. 1239 - 1243
(2007/10/02)
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- Thioalkanoyl-carnitines, process for their preparation and mucolytic pharmaceutical compositions containing same
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Thioalkanoyl-carnitines of general formula (I) STR1 wherein R is a straight alkylene radical having from 2 to 6 carbon atoms, or is a branched alkylene radical having from 3-6 carbon atoms, or is a branched alkylene radical having from 3-6 carbon atoms, R1 is a straight or branched lower alkyl radical having from 1 to 4 carbon atoms, and X- is a halogen anion are prepared by reacting a thio-acid (II) of general formula R1 COSH (a) if in (I) the thioalkanoyl radical R1 COS-- is in terminal position, with a compound of general formula (III) STR2 wherein n is an integer comprised between 0 and 4 or (b) if in (I) the thioalkanoyl radical R1 COS-- is not in terminal position, with a compound of general formula (IV) STR3 wherein m and m1 are integers comprised between 0 and 3, and R2 is a lower alkyl radical having from 1 to 4 carbon atoms. The pharmaceutical compositions containing the thioalkanoyl-carnitines (I) possess mucolytic and antitussive activity.
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- Onium Ylide Chemistry. 3. Evidence for Competing Oxonium Ylide Formation with C-H Insertion in Meerwein's Reaction of Methylene and Methylene-d2 with Dialkyl Ethers
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Meerwein's reaction of singlet methylene, produced by photolysis of diazomethane, with dialkyl ethers has been reinvestigated on the basis of reactions using CD2N2.In competition with methylene insertion into the various C-H bonds, about 10percent of methyl alkyl ether and small amounts of dimethyl ether formation are also observed.This indicates evidence for competing attack of methylene on oxygen leading to the corresponding intermediate methylenedialkyloxonium ylides which are immediately protonated by methyl alkohol (or water)impurity present in the reaction medium togive the corresponding methyldialkyloxonium ions.Dealkylative cleavage of the latter gives the observed methyl alkyl ethers.By the use of deuterium-labeled diazomethane CD2N2 it has been shown that ethylene and propylene formed under the reaction conditions are coming predominantly from diazomethane itself and not via intramolecular β-elimination of the oxonium ylides.
- Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.
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p. 2116 - 2120
(2007/10/02)
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- Oxonium Ions. Solvation by Single Acetonitrile Molecules in the Gas Phase and by Bulk Solvents
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The standard free energy of formation of gaseous complexes between monoprotonic oxonium ions and acetonitrile have been obtained by using the ion cyclotron resonance equilibrium constant method for exchange of acetonitrile between the ions.The results show that the "solvation" by a single molecule of acetonitrile in the gas phase reproduces the important diverse effects of molecular structure on oxonium ion solvation by bulk water.It is estimated from the present results that the effects of solvation by bulk water are only about three times as great as the corresponding effects of "solvation" by a single water molecule in the gas phase.Internal charge delocalization from the protonic site of the oxonium ions may be reversed by differential solvation, both with single H-bonding molecules in the gas phase and with bulk solvent.Further evidence for the site of preffered protonation of esters and amides is provided.
- Bromilow, J.,Abboud, J. L. M.,Lebrilla, C. B.,Taft, R. W.,Scorrano, G.,Lucchini V.
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p. 5448 - 5453
(2007/10/02)
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