Perfluoro-2-methylbutane

Primary alkyl chlorides are fairly stable to fluorine displacement. When fluorinated, 1-chloropropane is converted to 1-chloroheptafluoropropane and 1-chloto-2-methylbutane produces 39% l-chlorononafluoro-2-methylbutane and 19% perfluoro-2-methylbutane. Secondary and tertiary alkyl chlorides can undergo 1,2-chlorine shifts to afford perfluonnated primary alkyl chlorides 2-Chloro-2-methylpropane gives l-chlorononafluoro-2-methylpropane, and three products are obtained by the fluorination of 3-chloropentane [7] (equation 1). Aerosol fluorina-tion of dichloromethane produces dichlorodifluoromethane which is isolated in 98% purity [4 (equation 2). If the molecule contains only carbon and halogens, the picture is different. Molecular beam analysis has shown that the reaction of fluorine with carbon tetrachlonde, lodotrichloromethane, or bromotrichloromethane proceeds first by abstraction of halogen to form a trichloromethyl radical [5]... 

Pentafluorocthyl iodide is of practical interest, particularly as a precursor of higher perfluoroal-kyl iodides. There are several patents for the preparation of the key compound from tetra-fluoroethene, iodine pentafluoride and iodine at 75-80 C in the presence of catalysts anti-mony(III) fluoride, titanium(lV) chloride, boron trifluoride, vanadium(V) fluoride, niobium(V) fluoride, and molybdenum(Vl) fluoride.11-13 The agents iodine monofluoride" and bromine monofluoride" can add to branched pcrfluoroalkcnes, e.g. perfluoro-2-methylbut-2-ene gives perfluoro-2-iodo-2-methylbutane.1415... 

Using cobalt(III) fluoride at 150 , pyridine gives94 mainly perfluoro(l-methylpyrrolidine) and its 3H derivative, together with a small quantity of an open-chain compound. With potassium tetrafluorocobaltate(III),94 95 open-chain compounds predominate, the main ones being perfluoro(A-methylbutan-l-imine) and 2//,3//-heptafluoro(Af-methylbut-2-en-l-imine). Also formed are smaller amounts of polyfluorinated 1-methylpyrrolidines (ca. 5 % of the product mixture) and polyfluoropyridines (ca. 10%). 4-Methylpyridine gives95 only open-chain products, akin to those formed from pyridine, over potassium tetrafluorocobaltate(III) at 200-220 CC. 

The yields decrease with increasing chain length of the carboxylic acid and the results are best for the sodium salts. Nevertheless, the yields are 60-98%. This reaction is also possible with branched molecules, such as perfluoro(3-melhylhexanedioic acid) which gives l//,4//-per-fluoro(2-methylbutane)... 

Alkanes span a wide range of SPP values (e.g., 0.214 for perfluoro-n-hexane, 0.479 for 2-methylbutane and 0.601 for decalin). 

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