Dehydration of Alcohols on Aluminum Oxide

The dehydration of alcohols on γ-aluminum oxide, which yields water, olefins, and/or ethers, was studied with the aid of kinetic methods and IR spectroscopy. The unimolecular olefin formation probably proceeds via a surface compound, in which an alcohol molecule is joined by two angular H-bonds to an OH group and an oxygen ion on the surface. The ether formation (bimolecular reaction), on the other hand, requires OH groups and oxygen and aluminum ions on the surface. The ether is formed from a surface alkoxide group and molecularly adsorbed alcohol.     

Novel branched ether formation via conjugate reduction of an unsaturated cyanohydrin derivative and its synthetic application to the EF-ring segment of ciguatoxin

A synthetic method for a branched ether system was developed. The method was based on Lewis-acid-promoted γ-position selective reduction of a γ-alkoxy β,γ-unsaturated α-silyloxy nitrile, prepared through a process including intermolecular hetero-Michael reaction of a 2-butynoate ester derivative with an alcohol. The method was efficiently applied to the synthesis of fused medium-ring ethers involving the EF-ring segment (2) of ciguatoxin (1).     

Prediction of infinite dilution activity coefficients for systems including water based on the group contribution model with mixture-type groups: II. Extension and application

Group contribution models such as ASOG or UNIFAC were known to be inaccurate in the prediction of infinite dilution activity coefficients (γ^∞) for most of the systems containing water. To overcome the weakness inherent with the UNIFAC models, Zhang et al. (Fluid Phase Equil. 149 (1998) 27) have recently proposed a group-contribution-based model with mixture-type groups, where the mixture-type group is a hypothetical concept for taking into account the particular hydrophobic effects in aqueous organic systems. The proposed methodology has been proven to be applicable to alkane/water and alcohol/water mixtures in our previous study. In this work, the proposed method was further extended to the other classes of compounds, e.g. aromatics, ketones, acids, aldehydes, esters, ethers, nitriles and halogenated compounds. Compared to the conventional UNIFAC models, the proposed method demonstrates significant improvements in accuracy for various organic compounds in water mixtures.     

Mass spectrometry in structural and stereochemical problems—CLVIII electron impact promoted fragmentation of triphenylmethyl ethers

The triphenylmethyl (trityl) moiety is frequently used for the protection of alcohols but the mass spectra of such trityl ethers have hitherto escaped scrutiny. It has now been found that triphenylmethyl derivatives of primary alcohols yield abundant molecular ions which permit the determination of the isotopic purity of the parent alcohol. Upon electron impact the triphenyl-methyl entity directs the fragmentation of trityl ethers as demonstrated by a detailed study of n-pentyl trityl ether and its deuterated analogs. Ions formed by migration of phenyl groups were observed in the mass spectra of the trityl ethers investigated as well as in the spectrum of triphenyl-methane itself.     

Water compatible gold(III)-catalysed synthesis of unsymmetrical ethers from alcohols

An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl(4), is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.     

Homopolymers and copolymers of vinyl ethers of rosin-derived alcohols

Two vinyl ethers of rosin-derived alcohols were homopolymerized with free-radical and cationic initiators. A polymer was obtained from the vinyl ether of the alcohol from Foral in good conversion by free-radical initiators but it was not a high molecular weight product. Cationic initiators were more effective; boron trifluoride etherate proved to be best. All of the homopolymers were obtained as white powders with high crystallinity. Copolymerizations of the vinyl ethers and vinyl chloride have been studied with the use of free-radical initiators. Cationic-initiated copolymers of the vinyl ethers and isobutyl vinyl ether were studied. Those containing less than 20% of the rosin vinyl ethers were rubbery, of high molecular weight, and could be crosslinked with peroxide.     

A QSRR Study on the Relative Retention Time of Halogenated Methyl-phenyl Ethers

1 INTRODUCTION Halogenated methyl-phenyl ethers (anisoles) are ubiquitous organic compounds in the environment. There are 134 possible congeners consisting of 19 chloroanisoles, 19 bromoanisoles and 96 bromo- chloroanisoles. Although they are not produced…     

Synthesis of the EF-ring segment of ciguatoxin CTX1B based on novel regioselective reduction of unsaturated cyanohydrins and ring-closing olefin metathesis

Aiming at a convergent total synthesis of ciguatoxin CTX1B, its EF-ring segment has been synthesized. During the synthesis, a novel method for the construction of branched ethers, based on regioselective reduction of γ-alkoxy β,γ-unsaturated α-silyloxy nitriles with borontrifluoride etherate and trialkyl silane or tributyltin hydride, has been developed. Combination use of the method and ring-closing olefin metathesis successfully provided medium-sized cyclic ethers. Efficient site-selective reduction of vinyl epoxides into homoallyl alcohols has also been developed.     

Photochemische Reaktionen. 83. Mitteilung. Verbindungen der 3,4-Dihydrojonon-Reihe als Modelle zur Photochemie γ, δ- bzw. δ, ϵ-ungesättigter Ketone und Aldehyde

Compounds of the 3,4-dihydro-ionone series as models for the photochemistry of γ, δ- and δ,?- unsaturated ketones and aldehydes . The photochemistry of γ, δ- and δ,?-unsaturated carbonyl compounds of the dihydro-ionone series has been studied, with special attention to the investigation of oxetane formation versus hydrogen abstraction. UV.-irradiation of the dihydro-β-ionone compounds with structure A ( 1 , 7 , 14 , 18 , 24 , 29 ) led to isomeric ethers with structures B ( 2 , 8 , 15 , 19 , 25 , 30 ), C ( 3 , 9 , 16 , 20 , 26 , 31 ) and D ( 4 , 21 , 27 ), isomeric bicyclic alcohols with structure E ( 5 , 10 , 17 , 22 , 28 ), and photoreduction products with structure F ( 6 , 11 , 12 , 13 ). Photolysis of dihydro-γ-ionone ( 32 ) gave a complex mixture containing fragmentation product 35 , hydrocarbon 36 , β-ambrinol ( 34 ), oxetane 33 , as well as dihydro-β-ionone ( 1 ) and three of its photoproducts ( 2 , 3 , 5 ). The dihydro-α-ionone compounds 37 and 40 gave mixtures of fragmentation products and the oxetanes 38 and 41 . Irradiation of the side-chain homologues 42 and 45 yielded 43 , which photo-cyclizes to 44 . In contrast, 3 , 4 -dihydro-3′,4′-dehydro-β-ionone ( 46 ) gave merely the isomeric open-chain triene-ketone 47 . The structures assigned to the ethers 2 , 3 , 33 , 38 and to the alcohols 5 , 10 , 13 could be confirmed by chemical reactions and mutual interconversions. The structure of the ether 21 had to be established by X-ray analysis, details of which are described. A novel intramolecular hydrogen transfer is involved in formation of ethers B . The photocyclization A → D probably proceeds by addition of the carbonyl-C atom to the double bond ( A → h ), followed by methyl (1 → 2)-shift ( h → i ). Process A → h may also be involved in formation of compounds of type C and E .     

The breakdown of vinyl ethers as a two-center synchronous reaction

The experimental data on the molecular decomposition of vinyl ethers of various structures to alkanes and the corresponding aldehydes or ketones in the gas phase were analyzed using the method of intersecting parabolas. The enthalpies and kinetic parameters of decomposition were calculated for 17 reactions. The breakdown of ethers is a two-center concerted reaction characterized by a very high classical potential barrier to the thermally neutral reaction (180–190 kJ/mol). The kinetic parameters (activation energies and rate constants) of back reactions of the formation of vinyl ethers in the addition of aldehydes or ketones to alkanes were calculated using the method of intersecting parabolas. The factors that influenced the activation energy of the decomposition and formation of ethers were discussed. Quantum-chemical calculations of several vinyl ether decomposition reactions were performed. Ether formation reactions were compared with the formation of unsaturated alcohols as competitive reactions, which can occur in the interaction of carbonyl compounds with alkenes.