2-Methylpropane fluorination

Fluorination of aliphatic hydrocarbons with cobalt trifluoride gives complex mixtures Isobutane (2-methylpropane) fluorinated at 140-200 °C affords a mixture of 30 products of different degrees of fluorination and of isobutane as well as butane skeletons. The tertiary hydrogen is replaced preferentially Products containing 5-10 atoms of fluorine including a small amount of perfluoroisobutane were isolated [10]. 

The products from the partial fluorinations of butane32 and 2-methylpropane33 over cobalt(lll) fluoride are even more complex, 51 and 27 compounds, respectively, being identified. Most are C4F H10 n isomers which retained the original carbon skeletons, but up to 2% in each case has the carbon skeleton of the isomer (i.e., 2-methylpropane fluorination yields ca. 2% of products with the butane skeleton). From butane, at 140-230 C, only two compounds are present as more than 10% of the reaction product, 1 //,3//-octafluorobutane (11%) and 1 //,27f,4//-heptafluorobutane (14%). 2-Methylpropane is similar, at 140- 200°C only four compounds are present as over 10% of the product 2-(difluoromethyl)-l,1,1,2,3-pentafluoro-propane (14%), 2-(difluoromethyl)-l,l,2,3,3-pentafluoropropane (16%), 1,1,2,3,3-pentafluo-ro-2-(fluoromethyl)propane (24%), and l,l,2,3-tetrafluoro-2-(fluoromethyl)propane (15%). 

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]... 

Interaction of propane, butane or 2-methylpropane with fluorine and oxygen produces peroxides. Appropriate reaction conditions are necessary to prevent explosions. 

Pozzi and co-workers have also reported a fluorous soluble cobalt complex, which is active in the aerobic epoxidation of alkenes in a fluorous biphasic system (FBS).[50] The ligand used in this complex was a fluorinated tetraarylporphyrin, with eight perfluorooctyl chains shown in Figure 6.13. The cobalt complex was dissolved in perfluorohexane and added to a solution of the alkene with 2-methylpropanal (aldehyde substrate — 2 1) at room temperature. 

Perfluoro-tert-butyl hypofluorite [perfluoro(2-fluoroxy-2-methylpropane), 14], readily prepared by the low-temperature fluorination of potassium or sodium perfluoro-/cr/-butoxide,812 reacts with hexafluoropropenc at low temperature to give 15 with more than 95 % regiosclcctivity, which may be explained by electrophilic attack and the formation of a fluorocarbeniuni ion, whose intervention is suggested in order to explain the production of perfluoro(l-/m-butoxy-propane) (15).12... 

Cobalt tetraarylporphyrins with fluorine-containing substituents were active in epoxidation of alkenes using fluorous catalysis in the presence of oxygen and 2-methylpropanal [167,170-171]. Manganese and cobalt complexes of perfluorinated tetraazocyclonone catalyzed allylic oxidation of alkenes with r-BuOOH/Oa [172]. The complex with the salen ligand 57 was active in alkene epoxidation under Mikayama s conditions, and indene was epoxidated at a high stereospecificity [173]. 

A detailed mechanistic study of the carbon-chain isomerization during the electrochemical fluorination of two short-chain 1-sulfonyl fluorides, 2-methylpropane- and 2-methylethane-l-sulfonyl fluoride has been reported. This study gives insight into the complexity of this process and the... 

The boiling points of fluoroalkanes are comparable to those of hydrocarbons of similar molecular weight. Compare, for example, the boiling points of hexane (MW 86.2, bp 69°C) and 1-fluoropentane (MW 90.1, bp 63°C) and the boiling points of 2-methylpropane (MW 58.1, bp -1°C) and 2-fluoropropane (MW 62.1, bp -11°C). This low boiling point is attributable to the small size of fluorine, the tightness with which its electrons are held, and their particularly low polarizability. 

---