Halogenated fluorinated solid phases

Halogenation. Fluorination, chlorination, and bromination of alkanes catalyzed by superacids have been reported.1,2 Reactions may be carried out in the liquid phase, or in the gas phase over solid superacids or supported noble metal catalysts. High selectivity and relatively mild reaction conditions are the main features of these transformations. 

Halogenation The fluorination of carbon nanotubes is an important primary functionalization because it may be conducted even as heterogeneous process between gaseous and solid phase. The reaction of fluorine with SWNT, for example, can be performed in a tube furnace at about 150°C. It yields perfluori-nated nanotubes with a degree of fluorination of up to 100%. 

Carbon-halogen groups are well known to exist for fluorine, chlorine and bromine. These groups can be attached by redox reactions involving the halogen elements cither in aqueous solution or in the gas phase. At elevated temperatures bulk reactions occur under intercalation and eventually under formation of bulk covalent carbon-halogen materials (CF1.1 solid, CCU... 

Halogens Group 17 Halogens (salt formers) have seven valence electrons and form ions with a charge of 1-. The halogens exist in three phases at room temperature. Fluorine is a pale-yellow gas, chlorine is a green gas, bromine is a brown-orange liquid, and iodine is a purple solid. 

Calculations and experimental data (in solid, liquid, and gas phases) show that the tendency of different halogens to give strong halogen bondings is I>Br>Cl>F, namely, opposite to the sequence of their electronega-tivies. Due to this, reports on short contacts having fluorine as the acceptor site are rare, and they were never encountered in the solid state. 

Carbonyl and formyl halides CF O, CCIFO, and CCljO are stable gases and are commercially available. CBr O is a liquid and is prepared by the reaction of tetra-bromomethane with concentrated sulfuric acid. The replacement of a halogen atom by hydrogen decreases the molecular stability. Formyl fluoride, CHFO, is usually generated, as needed, by the fluorination of dry formic acid with NaF. CHClO is unstable, and must be prepared in a flow system. The procedure is to pass formic acid vapor over solid PClj immediately before it is to be used. The bromine compound, CHBrO, is very short lived. It has been prepared in the vapor phase by the photolysis of a bromine-formaldehyde mixture. 

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