Werner Bonrath

An improved preparation of ionic liquids by ultrasound

The use of ionic liquids (ILs) as a novel class of environmentally friendly solvents is now of topical interest among the chemical community, worried about the environmental impact of chemicals. Many reactions of organic chemistry have thus been re-examined since the 1990s. Nevertheless, even if a given preparation of ILs does not represent any particular difficulty, the reaction times appear to be long and the use of large amounts of classical solvents for the synthesis and the purification steps is crucial. This article presents preliminary work performed for the ultrasound assisted preparation of several 1-butyl-3-methylimidazolium salts (BF4, PF6, CF3SO3 and BPh4). In all cases a clear yield increase results and a dramatic reduction of the reaction time accompanied by an improved quality of the products occurs. After a short and simple work-up, the ILs are ready to use without a further purification step. Moreover, an original and simple analytical way to follow the reaction in real time is also presented.

Lipase-catalyzed transformations as key-steps in the large-scale preparation of vitamins

Abstract In this account, scope and limitations for the application of hydrolytic enzymes (lipases) to large-scale syntheses of economically important bulk products (vitamins) are discussed. In three case studies, biocatalytic alternatives were compared to “classical” chemical processes. While in the first example (pantolactone) the lipase-catalyzed kinetic resolution by esterification of the hydroxy-γ-lactone did not provide superior results for the overall-process, the synthetic strategies for the preparation of key-intermediates for fat-soluble vitamins could be improved significantly by using selected robust, immobilized lipases under optimized conditions. Regioselective mono-acetylation of a primary-secondary diol for a Vitamin A synthesis as well as mono-saponification of a hydroquinone-diacetate for a route to Vitamin E provided the monoacetylated key-intermediates in excellent yields and selectivities (generally >97%). Examples of laboratory procedures and continuous production on kilogram-scale are given. In consideration of environmental, technical, and economical aspects of modern industrial syntheses, these processes are, therefore, superior to classical (de)acetylation procedures.

Synthesis of (all-rac)-α-Tocopherol Using Fluorinated NH-Acidic Catalysts

The synthesis of (all-rac)-α-tocopherol starting from trimethylhydroquinone and isophytol using fluorinated NH-acidic catalysts is described. Scope and limitations of this type of catalysts are discussed. Advantages of this new procedure are high yield and selectivity, no waste problem and mild reaction conditions. Best results in the synthesis of (all-rac)-α-tocopherol (94% yield) using NH-acidic compounds are obtained in polar solvents. The used catalyst could be recovered.

The synthesis of d,l-α-tocopherol in supercritical media

Abstract The synthesis of d , l -α-tocopherol in supercritical carbon dioxide or nitrous oxide by condensation of trimethylhydroquinone (TMHQ) with isophytol (IP) in the presence of various Bronsted or Lewis acids, especially an imide or its metal salts, as catalysts is described. The product is obtained in high yield. The method represents an interesting alternative to existing processes. A quasi-reaction mechanism is being proposed together with kinetics, which are needed for the reactor analysis and design.

Synthesis of d,l-α-tocopherol using ‘microencapsulated’ catalysts

Abstract The synthesis of d , l -α-tocopherol starting from trimethylhydroquinone and isophytol using ‘microencapsulated’ catalysts, e.g. MC-(CF 3 SO 2 ) 2 NH, is described. Scope and limitations of this type of catalysts are discussed. Advantages of this new procedure are high yield and selectivity, no waste problem and mild reaction conditions. Best results in the synthesis of d , l -α-tocopherol using MC-catalysts are obtained in polar solvents. The used catalyst could not be recovered.

Online ESI-MS Analysis of Reactions under High Pressure

A new approach for real-time mass spectrometric analysis and identification of intermediates in confined, pressurized vessels is presented. The high-pressure reaction media is depressurized, mixed with a solvent, and fed directly to the atmospheric pressure electrospray ionization source of a tandem mass spectrometer. The method was applied to track product evolution for the dehydration of hydroxenin monoacetate, a commercially, important vitamin A precursor, and for the hydrogenation of 5-norbornene-2-carbonitrile with Pd/CaCO(3) as catalyst. Faster access but comparable results as by conventional off-line methods were obtained in every case.

Synthesis and Rearrangement of 3-Methyl-1,4-pentadiyne-3-ol †

An efficient synthesis and rearrangement of 3-methyl-1,4-pentadiyne-3-ol (1) using perrhenate- and Mo(VI)-catalysts is reported. The by-products 3,6-dimethyl-1,4,7-octatriyne-3,6-diol (2) and 3-ethynyl-5-methyl-1,6-heptadiyne-3,5-diol (3) were isolated and spectroscopically characterized. A possible reaction mechanism for the formation of the by-products is discussed.

Dehydration of Aromatic Heterocyclic Carboxamides to Aromatic Heterocyclic Carbonitriles

Phosphorus pentoxide is commonly used for the dehydration of heterocyclic carboxamides to the corresponding nitriles. In this report, the use of cyanuric chloride/N,N-disubstituted formamide for this reaction is described. The advantages of this procedure are mild reaction conditions and good yields. Depending on the reaction conditions and the structures of the amides, the nitriles are obtained in yields from 51% to 99%. Several of the oxazole carbonitriles synthesized by this procedure have not yet been described.