The Use of Hydrogen Fluoride in Preparing Organo-silicon Fluorides

Abstract

The replacement of chlorine by fluorine in a molecule is usually accomplished with the aid of metallic fluorides as reagents or catalysts.' If, however, the chlorine is sufficiently 'labile, the use of anhydrous hydrogen fluoride alone is possible. Because of side reactions induced by the metals, yields in the absence of catalysts are generally better, and the purification of the products is simplified. Chlorine attached to silicon enters readily into reactions such as hydrolysis or ammonolysis. We have found the corresponding reaction with hydrogen fluoride to proceed a t room temperature or below, producing the fluorides in good yield.The previous literature on fluorosilanes is limited, with one exception, to the trisubstituted monofluoro compounds. Triethylmonofluorosilane was made from the reaction of ammonium fluoride on a sulfuric acid solution of di-triethylsilyl ether.3 The addition of SiF4 to an ether solution of a suitable Grignard reagent resulted in the formation of the corresponding trialkyl and triaryl fluorosilane~.~J The preparation of the di-and tri-fluorosilanes of ethyl and phenyl from the action of zinc fluoride on the corresponding chlorides and by a modification of the procedure used by Flood3 employing the hydrolyzed polymer is reported in a recent paper.6In the present work the reaction of hydrogen fluoride on the chlorosilanes proceeded rapidly without the addition of any metallic catalyst. Neither silicon tetrafluoride nor hydrocarbons were detected in the reaction products, indicating the complete stability of the carbonsilicon bond to hydrogen fluoride at room temperature.The chlorosilanes were prepared by the usual procedure' from 'the diethyl ether solution of the appropriate Grignard reagent and silicon tetrachloride. In most cases the mixed chlorosilanes were distilled to obtain the individual chlorides. The methyl compounds, whose boiling points are too similar for convenient separation, and the phenyl compounds, whose boiling points are high, were converted before separation. In all cases the final products were purified by careful fractional distillation.Since the procedure for conversion was essen-(1) For a recent review see

The Power of the Proton: From Superacidic Media to Superelectrophile Catalysis

“…In analogy to the carbenium ion formation, Olah and co-workers attempted the generation of silylium ions in superacidic media from alkoxysilanes (Scheme A, with X = OR). − Using magic acid (HSO 3 F·SbF 5 ), the protonation of alkoxysilanes such as trimethyl­methoxysilane was indeed detected by low temperature NMR spectroscopy, but the corresponding silyl fluoride was obtained as the final product ( 8 → 9 , Scheme , top). The same outcome is observed when alkoxy- as well as chlorosilanes (Scheme A, with X = Cl) are exposed to hydrogen fluoride , or fluorosulfonic acid alone. Likewise, the treatment of chlorosilanes with triflic acid − results in quenching of the incipient silyl cation by the triflate anion ( 10 → 11 , Scheme , bottom).…”

The Present State of Organosilicon Chemistry.

“…Even dibutyldifluorosilane can be heated in a glass tube to 300°C. without apparent decomposition (268).…”

“…Organochlorosilanes are not only solvolyzed by water and liquid ammonia, but also by anhydrous hydrogen fluoride (268). When the alkylchlorosilanes are added to anhydrous hydrogen fluoride, hydrogen chloride is evolved.…”

Black “Soap” Films of Fatty Acids in Sulfuric Acid

“…Experimental Sodium 1-Dodecanesulfinate.-This salt was prepared by the method of Allen. 4 The crude salt showed at least 74% sulfinate content on potentiometric titration in acetic acid with sodium nitrite.5'6 An anhydrous sample of the salt was also prepared and analyzed both for the elements and for sulfinate content.…”