Frank J. Weigert

Selective synthesis and equilibration of methylamines on sodium mordenite

Abstract Sodium mordenite catalyzes the sequential reactions of methanol and ammonia to give methylamine and dimethylamine, but little trimethylamine. The kinetics of this selective reaction are compared to the nonselective reaction catalyzed by Bronsted acids. Selective adsorption, not shape selectivity, is the critical factor in determining the catalysts selectivity.

A fluorine NMR database

Abstract We have established a fluorine chemical shift database for compounds with the empirical formula C x F y . Each record contains the compounds name, literature reference, empirical formula, functional group information, and a nine digit location code and chemical shift for each resonance. The database has over 500 compounds and 3000 chemical shifts. We can ask questions both about compounds as a whole or individual flourines. Some structures in the literature are inconsistent with the reported nmr parameters. Chemical shift assignments which were not possible earlier can now be made because of the correlations developed in this work.

Fluorine NMR parameters of two-carbon chlorofluorohydrocarbons

Abstract A complete database of fluorine nmr parameters for compounds with two carbons and all possible combinations of fluorine, chlorine, and hydrogen substituents now exists. These include the saturated compounds from CH 3 CH 2 F to CF 3 CF 3 and olefins from CH 2 =CHF to CF 2 =CF 2 . The chemical shifts cannot all be explained in terms of simple additive substituent effects. With this database as a guide, nmr analysis of mixtures can be made down to the 0.1% level.

Hexafluoroacetone hydrazone chemistry

Abstract Hexafluoroacetone hydrazone condenses with ketones and aldehydes to give azines. β-Diketones give either azino-enols or hydrazino-ketones depending on the substrate. Aldehydes capable of aldol condensation and some α, β-unsaturated carbonyl compounds give pyrazoles. Isocyanates yield semicarbazones and acid chlorides give hydrazides. Variable-temperature NMR processes in hexafluoroacetone azines are consistent with consecutive nitrogen inversions and intermediate rotation about the nitrogen-nitrogen single bond. Resonance effects lower the barriers in the fluorinated azines.

Synthesis and aromatization of 2+2 cycloadducts of butadienes and tetrafluoroethylene

Abstract Passing tetrafluoroethylene (TFE) and hydrocarbon dienes down a hot tube at 600 °C with a contact time of a few seconds produces substituted fluorobenzenes. Specifically, tetrafluoroethylene and butadiene form 1,2-difluorobenzene. The aromatics produced by the pyrolysis of TFE and methyl-substituted butadienes do not necessarily result from eliminating HF from the 2+4 adducts of the starting materials. Solid-acids such as alumina or silica/alumina accelerate the ring-expansion elimination of the 2+2 cycloadducts. Aromatic products result from the preformed 2+2 cycloadducts at temperatures 200 °C lower than the corresponding thermal reaction. The solid-acids can also influence product regiochemistry.

PREPARATION OF A FLUORINATED SHIKIMIC ACID

Abstract The reaction of dialkylaminosulfur trifluoride with shikimic acid (1) gives a single isomer of a product 2 in which two hydroxy groups have been replaced by fluorine.

(Perfluoroalkyl)polyfluoroarenes by copper-promoted cross-coupling of perfluoroalkyl halides and polyfluoroarenes

Abstract Group 11 and 12 metals act as halogen acceptors to promote a selective cross-coupling between perfluoroalkyl halides and polyfluoroarenes to give (perfluoroalkyl)polyfluoroarenes. This reaction is a non-catalytic, fluorine analog of Friedel-Crafts alkylation in hydrocarbon chemistry.

Fluorine nuclear magnetic resonance parameters for hydrochlorofluoropropanes with one terminal hydrogen atom and all possible combinations of fluorine and chlorine atoms in the other positions

Abstract This paper presents the 19 F nuclear magnetic resonance chemical shifts and couplingconstants for all saturated compounds with three carbon atoms at least one fluorineatom, one terminal hydrogen atom and all possible combinations of fluorine and chlorineatoms in the remaining six positions.

Aromatization of 2+2 cycloadducts of butadienes and fluoroolefins other than tetrafluoroethylene

Abstract The 2+2 cycloadducts of fluorinated olefins other than tetrafluoroethylene and hydrocarbon dienes also ring-expand and eliminate two moles of hydrogen halide to form aromatic products. The hydrogen halide eliminated from chlorofluoroolefin adducts depends on the solid present during the aromatization. Alumina and other accelerators favor elimination of HF, while HCl evolves in the presence of inert solids such as SiC. The aromatics derived from hexafluoropropene adducts generally have the more sterically hindered regiochemistry. Alumina promotes extrusion of difluorocarbene from trifluoromethylcyclobutanes leading to fluorobenzenes rather than benzotrifluorides. Carbon accelerates these aromatizations without difluorocarbene extrusion.

Interaction of perfluorocarbons with carbon

Abstract Activated carbon is an effective stoichiometric fluorine acceptor which defluorinates perfluoroalkanes with the partial structure (Rf)2CFCF(Rf)2 to alkenes and perfluoroalkenes to dienes. Carbon catalyzes double-bond shifts, as well as cis/trans and ring-chain perfluoro-olefin isomerizations. Carbon effectively catalyzes TFE and HFP dimerizations. Less effectively, carbon catalyzes further oligomerization of TFE to give low yields of linear, internal olefins. Free radicals may be the key surface intermediates.