Ammoxidation of halogen-substituted toluenes on V-P-oxide catalysts

The ammoxidation of various halogen-substituted toluenes on crystalline vanadium phosphate catalysts was investigated. The monophosphates and the NH₄VOP₂O₇ are transformed into new NH₄-containing V-P-oxides. The (VO)₂P₂O₇ used is stable in time on stream. These structures are very active and selective ammoxidation catalysts.

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. NH₄VOP₂O₇ V-P , NH₄. (VO)₂P₂O₇ . .

     

Chromogenic polymer gels for reversible transparency and color control with temperature at a constant volume

The preparation and characterization of novel chromogenic materials has developed extremely rapid in the last years. Among them, thermotropic and thermochromic polymer gel networks have met with growing interest, because of their advanced properties. These novel polymer gels exhibit pronounced changes in transparency and/or color intensity in a practically relevant temperature range. For many future technical applications it is an essential condition, that the volume of the used gel materials is independent of temperature. A current overview of this field is given. Copyright © 2002 John Wiley & Sons, Ltd.     

5-Amino-1,2,3,4-thiatriazole: Its acylation with chloroformates and chlorothioformates as a route to 1,2,4-thiadiazoles and 1,6,6a,Δ4-trithia-3,4-diazapentalenes

Summary Pyridine catalyzed acylation of 5-amino-1,2,3,4-thiatriazole with chloroformates and chlorothioformates afforded 3,5-bis(ethoxycarbonylamino)-1,2,4-thiadiazoles in the former and 2,5-bis(phenoxy)-1,6,6a,⁴-trithia-3,4-diazapentalenes in the latter case. An unstable, but isolable intermediate 2-phenoxy-1-aza-3,4-dithiolium-5-imide has been found if the chlorothioformate acylation was performed in acetonitrile in the absence of pyridine. The bis(phenoxy)trithiapentalenes are prone to nucleophilic displacement reactions at positions 2 and 5, exchanging in a stepwise manner one or both phenoxy groups. The structures of the compounds described could be inferred from their¹H-NMR¹³C-NMR, and mass spectra and were corroborated by the comparison with the data of authentic and similar derivatives as well as by chemical means.

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Die Acylierung von 5-Amino-1,2,3,4-thiatriazol mit Chlorformiaten und Chlorthioformiaten als Route zu 1,2,4-Thiadiazolen und 1,6,6a,⁴-Trithia-3,4-diazapentalenen

Zusammenfassung Die durch Pyridine katalysierte Acylierung von 5-Amino-1,2,3,4-thiatriazol mit Chlorameisensäureethylester führt zu 3,5-bis-(ethoxycarbonylamino)-1,2,4-thiadiazolen, während mit Chlorthioameisensäureethylester 2,5-bis(phenoxy)-1,6,6a,⁴-trithia-3,4-diazapentalene erhalten werden. Ohne Pyridin entsteht bei letzterer Reaktion ein wenig stabiles, aber isolierbares Zwischenprodukt: 2-Phenoxy-1-aza-3,4-dithiolium-5-imid. Die Bis(phenoxy)trithiadiazapentalene reagieren leicht mit nukleophilen Reagenzien und tauschen dabei schrittweise eine oder beide Phenoxygruppen aus.

     

A comparison of phosphaferrocene and phospharuthenocene ligands in Rh+-catalysed enamide hydrogenation reactions: superior performance of the phospharuthenocene

Enantiopure Cp*-substituted 3,4-dimethyl-5-phenylphosphametallocene-2-methanols (M=Fe, Ru) have been prepared from the corresponding 2-carboxy-(-)-menthylphospholide anion and elaborated into 2-CH(2)PPh(2) phosphametallocenes (13: M=Fe; 14: M=Ru) and 2-CH(2)PtBuR substituted phospharuthenocenes (R=tBu, Me). The crystal structures of complexes [Rh(1,5-cod)(eta(2)-L)](+)BF(4)(-) (L=13, 14) reveal significantly different aryl group configurations. Comparative studies of the hydrogenation of para-substituted N-acetylcinnamate esters with these pre-catalysts show a superior performance for the phospharuthenocene derivative in terms of both rate and enantioselectivity.     

The Bucherer Reaction and the Preparative Use of its Intermediate Products

The study of purified intermediate products of the Bucherer reaction has shown that this reaction proceeds, not via bisulfite addition compounds of the keto form of the naphthols and the ketimine form of the naphthylamines, but via tetralonesulfonic acids and tetraloniminesulfonic acids. The intermediates lead to compounds that are otherwise difficult or impossible to obtain, and some of which are new. The mechanism of the Bucherer reaction is discussed in detail.     

Synthesis of 2-silyl substituted phospharuthenocenes and an elaboration into the first phospharuthenocene-phosphine

A [1,5] shift protocol transiently hindering the 2-position of phospholide anions provides an access to sterically unencumbered phospharuthenocenes and the first phospharuthenocene-phosphine.     

Gel dispersed liquid crystals

Microemulsion based gels (MBG) can be used as carrier materials for dispersed thermotropic liquid crystals (LC). The viscosity of the carrier material can be specifically changed by varying the gelatin content. The LC droplet sizes and their distribution in the MBG system are influenced by both the ratio between AOT surfactant and alcohol co-surfactant and the length of the carbon chain of the co-surfactant. LC droplets without or with only a small amount of alcohol co-surfactant have the same droplet size and show a radial structure.