- Surface-Mediated Reactions. 6. Effects of Silica Gel and Alumina on Acid-Catalyzed Reactions
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Absorption of a variety of acids to chromatographic silica gel results in substantial enhancement of their catalytic activity-affording easily prepared, environmentally benign heterogeneous acids that are highly effective in mediating a number of processes.This was shown for the isomerization of allene 1 and dimerization of the corresponding 1,3-diene 2; cyclization of (R)-citronellal (5), the related diester 10, and 1,5-cyclooctadiene (15); Rupe rearrangement of alkynol 18; and Friedel-Crafts cyclodehydration of alcohols 21.By contrast, commercially available Nafion-H was significantly less effective as a heterogeneous acid catalyst.Chromatographic alumina displayed enigmatic behavior, showing enhanced acidity on the adsorption of HCl but little or no acidity on the adsorption of a variety of other types of acid.The results are discussed in terms of the surface structures of silica gel and alumina.
- Kropp, Paul J.,Breton, Gary W.,Craig, Stephen L.,Crawford, Scott D.,Durland, William F.,et al.
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p. 4146 - 4152
(2007/10/02)
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- INTRAMOLECULAR CYCLOALKYLATION OF PHENYLALKANOLS IN THE PRESENCE OF SULFURIC ACID
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Te distribution of the deuterium in the benzocyclenes formed during the intermolecular cycloalkylation of 2-R-4-phenyl-2-butanol (R=CD3, CD2CH3, CH2CD3) in the presence of 85percent sulfuric acid was investigated by NMR spectroscopy and mass spectrometry.Hydrogen exchange takes place at the stage of formation of the γ-phenylalkyl cation, the average lifetime of which is sufficient for the establishment of an isotopic equilibrium by successive elimination addition of an deuteron.
- Sakhabutdinov, A.G.,Usmanova, A.G.,Proidakov, A.G.,Bazhenov, B.A.,Schmidt, F.K.
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p. 1525 - 1529
(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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- Electrosynthesis of Organic Compounds. V. Electrochemical Reduction of Selected Arylalkyl Halides
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Electrochemical reductions of some selected arylalkyl halides were carried out in methanol containing 0.1 mol*l-1 Ba(ClO4)2 on different cathodes (Hg, Zn).The compounds investigated were benzyl bromide (1); phenylethyl bromide (2); 3-phenylpropyl bromide (3); 4-phenylbutyl chloride (4); 1-methyl-3-phenylpropyl chloride (5); 1,1-dimethyl-3-phenylpropyl chloride (6) and 1,1-dimethyl-4-phenylbutyl chloride (7).The isolated products were found to include hydrogen abstraction, dehydrogenation, dimerization as well as cyclization products.Suitable mechanism involving the formation of intermediate carbanions and of free radicals was suggested to explain the results.Also, polarization curves for the compounds investigated were measured and the reduction half-wave potentials were determined.
- Ismail, M. T.,Abdel-Wahab, A. A.,Mohamed, O. S.,Khalaf, A. A.
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p. 1174 - 1176
(2007/10/02)
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