Ralf Miethchen

Symptoms and treatment of hydrogen fluoride injuries

Abstract Accidents with hydrogen fluoride are causes of the most hazardous injuries in laboratories. The effects of HF on human tissues are substantially different from those of ordinary acids. Therefore, the paper deals with the symptoms, first-aid and medical treatment of lesions caused by skin contact, inhalation or ingestion of HF. Furthermore, selected cases of accidents with hydrogen fluoride are reported to exemplify the unique dangers of such events. Some proper protection measures are also described.

Amphiphilic and mesogenic carbohydrates - II. sysnthesis and Characterisation of mono-o-(n-alkyl)-d-glucose derivates

Abstract The synthesis of various amphiphilic o-(n-alkyl)-D-glucopyranoses, having the long alkyl chain (C8H17 - C16H33) in 2-, 3,- 4-, or 6- position are described. The investigations of the thermal behavior of 6-0-( 13a-e ), 4-0( 14a-e ), 3-0( 15a-e ) and 2-0- (n-alkyl)-D-glucopyranoses ( 16a-e ) and the corresponding methyl-α-D-glucosides 4a-e , 8a-e and 12a-e , respectively, are summarized in this paper.

Liquid crystals based on fluorinated carbohydrates

Fluorine introduced in the hydrophilic or the hydrophobic region of amphiphiles influences the thermomesomorphy of amphiphilic and monophilic fluorosugars in a very specific manner. This paper is the first review about chiral mesogens based on fluorinated carbohydrates. It covers the literature published so far. Analytical objectives are given to: (i) Effects of fluorine atoms on the H-bonding network of the hydrophilic region of sugar amphiphiles; (ii) Effects of perfluoroalkyl chains compared to alkyl chains; (iii) Polymorphism, e.g., also formation of smectic S(C)* phases.

Organofluorine compounds and fluorinating agents Part 16: Monoalkylations and cycloadditions with trans-3,3,3-trifluoro-1-nitropropene

Abstract Monoalkylations of different nucleophilic azoles were investigated with the electron-deficient trans-3,3,3-trifluoro-1-nitropropene (1) as alkylating reagent without addition of any catalyst. In each case, the bonding of the alkene at the azole occurs regioselectively at the trifluoromethyl-substituted C atom of the alkene, whereas the azoles react at different positions depending on the electron density of the heterocycles. Thus, 1-methyl-pyrrole (2) reacted with 1 under C-C bond formation giving the two regioisomers 2-(1-trifluoromethyl-2-nitroethyl)-1-methyl-pyrrole (3) (major product) and 3-(1-trifluoromethyl-2-nitroethyl)-1-methyl-pyrrole (4). The less nucleophilic pyrazole (5), 1,2,4-triazole (7), 3-bromo-1,2,4-triazole (9), and 3,5-dibromo-1,2,4-triazole (12) gave exclusively the corresponding N-alkyl azoles 1- (1-trifluoromethyl-2-nitroethyl )-pyrazole (6), 1-(1-trifluoromethyl-2-nitroethyl) -1,2,4-triazole (8), 3-bromo-1- (1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole (10)/5-bromo-1-(1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole (11), and 3,5-dibromo-1-(1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole (13), respectively. The enantiomeric pairs of the chiral monoalkyl-azoles could not be separated. Moreover, we used trans-3,3,3-trifluoro-1-nitropropene (1) as a dienophile in Diels-Alder cycloadditions with cyclopentadiene (14), cyclohexa-1,3-diene (16), and furan (18). Two diastereomeric products (15A/15B, 17A/17B, and 19A/19B), which could not be separated by column chromatography, are formed from each diene. All compounds were characterized by 1H, 13C, and 19F NMR data.

Perfluorozinc aromatics by direct insertion of zinc into C–F or C–Cl bonds

Abstract For the first time perfluoroaromatic organozinc compounds were obtained by direct action of zinc on C–F bonds in the presence of metal salts (SnCl 2 , CuCl 2 , ZnBr 2 ). The reactions are accelerated by ultrasound. The scope of the method can be extended to polyfluoroaromatics which contain other halogen atoms (Cl) in the aromatic ring.

A NEW GROUP OF LIQUID CRYSTALS BASED ON PERFLUOROALKYLATED CARBOHYDRATES

The mesogenic fluoroalkyl β-d-glucopyranosides 5a-d (smectic A) were generated via a dithionite initiated addition of the homologous 1-iodo-perfluoroalkanes 1a-d to allyl 2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside (2) forming 3a-d followed by hydrodeiodination to 4a-d and deacetylation.

Amphipilic and mesogenic carbohydrates XII. New thermotropic mesogens based on perfluoroalkyl-substituted carbohydrates

In continuing studies of amphiphilic and mesogenic carbohydrates, the mesomorphic properties of a new group of perfluoroalkylated amphiphilic mesogens are discussed. Smectic A phases dominate the mesomorphic behaviour of the new materials, but one compound exhibits a columnar mesophase and three others have SmA-SmC* transitions. The synthesis of these materials has already been reported and involved dithionite-mediated O- and S-perfluoroalkylations with 1-iodoperfluoroalkanes.

Organofluorine compounds and fluorinating agents. Part 25. Dithionite mediated C- and S-perfluoroalkylations of monosaccharide derivatives

Abstract Allyl 2,3,4,6-tetra-O-acetyl-β- d -glucoside (1), 2,3,4,6-tetra-O-acetyl-1-thio- d -glucopyranose (6), and 2,3,4,6-tetra-O-acetyl-1-thio- d -galactopyranose (9) were alkylated with 1-iodo-perfluoroalkanes (C4F9I, C6F13I, C8F17I, C10F21I) giving the corresponding (2-iodo-3-perfluoroalkyl-propyl) glucosides 2a–d, perfluoroalkyl s- d -thioglucosides 7b,c, and perfluoroalkyl s- d -thiogalactosides 10a-c, respectively. From these compounds the amphiphilic sugars 4a–d, 8b,c, and 11b,c were synthesized. The deacetylation of 3a–d, 7b,c, and 10b,c was carried out by treatment with alumina-supported CsF. Finally, 4c was converted to 5 by a regioselective 6-O-decanoylation. The “single tailed” amphiphiles 4a–d, 8b,c, and 11b,c are liquid crystals (SA-type), whereas compound 5, which contains a lipophilic as well as a fluorophilic chain, forms a columnar mesophase.

Reactions with and in anhydrous hydrogen fluoride systems. Part 8. Triethylamine trishydrofluoride — a convenient reagent for the stereoselective synthesis of glycosyl fluorides

Abstract Stereoselective fluorinations are effected by bromine—fluorine exchange at glycosyl bromides of the D - and L -series using triethylamine trishydrofluoride. Pyranosyl fluorides of D -xylose, L -arabinose, D -glucose, D -mannose and L -rhamnose derivatives, as well as of D -galacturonic acid esters, have been prepared. The influence of neighbouring groups in the 2-position is considered.

New Stereospecific Rearrangements of Pyranosides

Abstract Methyl β-D-arabinopyranoside (1), phenyl 1-thio-β-D-galactopyranoside (3), methyl β-L-fucopyranoside (7), methyl β-L-fucopyranoside (9), 1,6-anhydro-β-D-galactopyranoside (D-galactosan; 11), and 1,6-anhydro-β-D-mannopyranoside (D-mannosan; 14) were stereospecifically converted in moderate up to good yields into methyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-lyxopyranoside (2), phenyl 4-(9-cyclohexyIcarbamoyl-6-O-formyl-2,3-O-(2,2,2-trichloroethylidene)-1-thio-β-D-gulopyranoside (4) / phenyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-1-thio-β-D-gulopyraoside (5), methyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-6-deoxy-α-L-gulopyranoside (8), methyl 2,3-O-(2,2,2-trichloroethylidene)-4-O-cyclohexylcarbamoyl-6-deoxy-β-L-gulopyranoside (10), 1,6-anhydro-4-O-cyclohexyl-carbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (12), and 1,6-anhydro-2-O-cyclohexylcarbamoyl-3,4-O-(2,2,2-trichloroethylidene)-β-D-altropyranoside (15), respectively, ...