silicon and trimethylfluorosilane

In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH3)3F- (R = CH3CH2O, CF3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH3)3F- leads to loss of the nucleophile R- and FSi(CH3)3, except in the case of (CH3)3SiNHSi(CH3)3F-, where HF loss is also observed. Ion affinities for FSi(CH3)3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of deltaH(acid) values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R = CH3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH). We use the fluoride affinity of the silanes and the FSi(CH3)3 affinity of the departing nucleophilic anion to assess the feasibility of fluoride-induced desilylation of the silanes examined in this work.

Topics: Anions; Computer Simulation; Electron Transport; Feasibility Studies; Fluorides; Membranes, Artificial; Models, Chemical; Models, Molecular; Silicon; Spectrometry, Mass, Electrospray Ionization; Trimethylsilyl Compounds

A flow-through system is described for rapid purification of [18F]fluoride for nucleophilic substitution reactions. It depends on generation of [18F]fluorotrimethylsilane from aqueous 18F solutions and subsequent collection of the gas and its hydrolysis by base in near anhydrous acetonitrile. Potassium t-butoxide plus Kryptofix 2.2.2 was found to be a more effective base than K2CO3 plus Kryptofix or than tetraethylammonium hydroxide. The procedure takes 2-3 min and is thus faster than controlled removal of water from [18F]fluoride by evaporation. The trapped and hydrolyzed 18F was used in several nucleophilic substitution reactions. The flow-through system is also convenient for recovery of fluoride from impure and otherwise unreactive solutions, including residues from large scale 18F syntheses, and can thus lead to more efficient use of 18F where production of the radionuclide is limited.

Topics: Fluorine Radioisotopes; Isotope Labeling; Silicon; Trimethylsilyl Compounds

[18F]Fluorotrimethylsilane was prepared in 80% decay corrected yield by reaction of no-carrier added tetramethyl-ammonium fluoride (hydroxide as bulk anion) with chlorotrimethylsilane in 65% aqueous acetonitrile. The 18F gas was collected in a cold-trap at -130 degrees C and found to have an Ostwald solubility coefficient of 11.5 in paraffin oil. Accurate measurement of its aqueous solubility was precluded by hydrolysis. When rats were allowed to inhale [18F]fluorotrimethylsilane extensive uptake of 18F occurred in bone, demonstrating ready release of fluoride in vivo.

Topics: Animals; Bone and Bones; Fluorine; Isotope Labeling; Radioisotopes; Radionuclide Imaging; Rats; Silicon; Tissue Distribution; Trimethylsilyl Compounds

18F-Labeled fluorotrimethylsilane was prepared by nucleophilic substitution of chlorotrimethylsilane with reactor produced [18F]fluoride. Hydrolysis of fluorotrimethylsilane by aqueous tetraethylammonium hydroxide followed by removal of water with a mechanical pump gave a powerful source of no carrier added nucleophilic 18F. Reaction of this purified 18F preparation with 4,6-benzylidene-1-beta-O-methyl D-mannopyranoside-2.3-cyclic sulfate was complete in 2 min at 80 degrees C and gave two labeled products with similar retention times on reverse phase HPLC. Allowing for decay and handling losses during deprotection, the maximum yield of [18F]2-deoxy-2-fluoro-D-glucose from no-carrier added tetraethylammonium fluoride was 50%. Incorporation of 18F into organic products was 30% complete in 10 min at room temperature. An identical time-course was observed for reaction of 3-O-triflyl-1,2-5,6-diisopropylidene-D-allofuranose, the starting material for 3-deoxy-3-fluoro-D-glucose. Reaction of tetraethylammonium fluoride with chlorotrimethylsilane was more rapid and much more tolerant of water than the fluorosugar reactions. Chlorotrimethylsilane can be used to recover unreacted 18F from reaction mixtures.

Topics: Chemical Phenomena; Chemistry; Chromatography, High Pressure Liquid; Deoxy Sugars; Deoxyglucose; Fluorine; Fluorodeoxyglucose F18; Hydrolysis; Isotope Labeling; Kinetics; Radioisotopes; Silicon; Tetraethylammonium; Tetraethylammonium Compounds; Trimethylsilyl Compounds

Topics: Adsorption; Chromatography, Gas; Environmental Pollutants; Fluorides; Polyethylenes; Silicon; Trimethylsilyl Compounds