Ekkehard Bartmann

Liquid Crystals with Polar Substituents Containing Fluorine: Synthesis and Physical Properties

Abstract Liquid crystalline compounds with various polar terminal groups containing fluorine have been prepared (see below formula 1 with Z = S‒CHF2, S‒CF3, SO‒CHF2, SO‒CF3, SO2‒CHF2, SO2‒CF3, SO2F, OCH2CF3, CO‒OCH2CF3, CO‒CF3, CO‒CF2Cl, CO‒CF2H, CO‒CF2‒CH3, CO‒CF2‒C3H7). The synthesis of these compounds is outlined here and their physical properties (phase transitions, dielectric anisotropy, birefringence, viscosity) are discussed.

Ether cleavage by activated metals: I. Cleavage of tetrahydrofuran by transition-metal activated magnesium

Abstract Transition metal complexes obtained by reduction of transition metal chlorides with magnesium catalyze a slow insertion reaction of magnesium into carbon-oxygen bonds of tetrahydrofuran and other ethers. The order of reactivity of the transition metals tested is Ti ≈ Co > V > Cr > Zr > Rh > Mn > Nb > Fe ≈ Ni. The effects on the reaction of modifications of the catalysts are discussed.

Ether cleavage by activated metals. II: Cleavage of allyl and benzyl ethers by activated magnesium

Abstract Activated magnesium (prepared by reduction of magnesium halides with potassium) reacts with allyl and benzyl ethers to give the corresponding allyl or benzyl magnesium compounds.

Synthesis of α,α-difluoronitriles from acyl cyanides

Abstract Aromatic α,α-difluoronitriles (aryl α,α-difluoroacetonitriles) have been synthesized by reaction of aroyl cyanides with diethylamino sulphur trifluoride. Some liquid crystalline difluoronitriles have been prepared by this method.

Reaction of acceptor-substituted carbonyl compounds with diethylamino sulfur trifluoride

Abstract The reaction of carbonyl compounds with SF 4 or its derivatives like diethylamine sulfur trifluoride (DAST) is a well-established method for the introduction of fluorine into organic systems. However, in contrast to ‘normal’ aldehydes and ketones (eqn. 1; R and AH, alkyl or aryl), compounds containing an electron-withdrawing group adjacent to the carbonyl group have been used rather infrequently in carbonyl-fluorination. (Reaction with DAST have been described only for few examples.) R = alkyl, aryl A = CO 2 R′, CF 3 , CF 2 R″ We have found that various acceptor-substituted carbonyl compounds react very easily with DAST (faster than ‘normal’ aldehydes and ketones). This opens up a facile route to α, α-difluoro-substituted carboxylic esters as well as to compounds containing pentafluoroethyl groups or tetrafluoroethylene moieties (eqn. (1). The use of this method is demonstrated in the synthesis of new liquid crystalline materials [ DE Pats 4 002 374 and 4 101600 (Aug. 1, 1991), 4 015 681 (Nov. 21,1991)] to E. Bartmann, E. Poetsch, U. Finkenzeller and B. Rieger (for Merck-Patent GmbH).