1 ,l-Dichloro-2,2-difluoroethylene

The combination zinc dust-methanol serves for dechlorination of tetrachloro-difluoroethane (Genetron-131, m.p. 38-40°, Gen. Chem. Div., Allied Chem. and Dye Corp.) to 1, l-dichloro-2,2-difluoroethylene a small amount of zinc chloride apparently functions as catalyst. ... 

Poly( 1, l-dichloro-2,2-difluoroethylene) 240 20% black involatile residue 80% monomer 22... 

Nonfluonnated allenes also readily react with fluoroalkenes to give diverse fluonnated alkylidenecyclobutanes [727, 12S, 129, 130] (equations 55 and 56), except for tetramelhylallene, which rearranges to 2,4-dimethyl 1,3-pentadiene under the reaction conditions prior to cycloaddition (equation 57) Systematic studies of l,l-dichloro-2,2-difluoroethylene additions to alkyl-substituted allenes establish a two-step, diradical process for alkylidenecyclobutane formation [131, 132, 133]... 

The attack at the CFZ group of l,l-dichloro-2,2-difluoroethylene by EtMgBr (Tarrant and Warner, 1954), the attack at the CF2 group of phenoxytrifluoroethylene by phenoxide ion (England et al., 1960) and the replacement of the 1-fluorine of 1-diethylaminotrifluoroethylene with water (Yakubovich et al., 1966) are in line with predictions based on the carbanionic theory. On the other hand, the attack of triethyl phosphite at the terminal difluoro group of w-iodoperfluoro-1-olefins (Knunyants and Pervova, 1962) could be explained by steric control. 

Bartlett et al. found that in sealed tubes at 80° with excess l,l-dichloro-2,2-difluoroethylene and a polymerization inhibitor, butadiene, cM-piperylene, and rru/ii-piperylene each yielded a single 1,2-addition product. Wherever the structures have been established they conform to type 1 and not II. 

In the 1,2-cycloaddition of the trans-trans, trans-cis, and cis-cis isomers of 2,4-hexadiene to l,l-dichloro-2,2-difluoroethylene, under conditions of stereochemical stability of reactants and products, it has been ascertained that there is cis-trans isomerisation at the site of addition, and retention of configuration only on the side chain . An equilibrium composition of the product is approached but not attained, proving that in the open-chain (diradical) intermediate there is competition between ring closure and internal rotation around the C-C bond at the reaction site, the latter process being about 10 times faster than the former, at 80°C . 

When a diene is involved, there is often competition between ring closure to 1,2- and 1,4-cycloadduct (see also Section 4.2). For instance, the photo-sensitised reactions of l,l-dichloro-2,2-difluoroethylene, 1,1-dichloroethylene and tetrachloroethylene with cyclopentadiene at 0°C give the following products ... 

Organolithiums add onto tetrafluoroethylene and eject lithium fluoride far more effectively than Grignard reagents do (Scheme 1-120). With chlorotrifluoro-ethylene and l,l-dichloro-2,2-difluoroethylene as the substrates, the new carbon-carbon bond is established at the chlorine-remote end of the double bond. The element-specific orientation rules out any S v2-like direct substitution (that inevitably would displace the heavier halogen) and argues in favor of an addition/elimination mechanism passing through the ephemeral species 166 (Scheme 1-120). 

With CF3C=CCF3 or olefins with an internal double bond such as cis- or fraras-F-2-pentene, F-cyclobutene, or l,2-dichloro-l,2-difluoro-ethylene, or with a geminally disubstituted olefin such as 1,1-dichloro-2,2-difluoroethylene, only fully fluorinated products were obtained, likely through a nucleophilic fluorination mechanism. This fact, plus the necessity for a Lewis acid catalyst for addition to proceed, is evidence for an electrophilic addition mechanism. Others have suggested polar addition of BF3 to the olefin with RfBF2 as a reactive intermediate (294). 

Ethereal n-butyllithium added to a stirred ice-cooled ethereal soln. of thiophene, refluxed 0.5 hr., added at -30 to -20° during 0.5 hr. to an ethereal soln. of 1,1-dichloro-2,2-difluoroethylene, and refluxed 4 hrs. 2-(2,2-dichloro-l-fluoro-... 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

Finally, both difluoromethylenecyclopropane (456) (Table 41, entry 5) and its isomer 2,2-difluoro-methylenecyclopropane (5) (Scheme 73) gave a [2 + 2] cycloaddition with l,l-dichloro-2,2-difluoroethylene (520), but the latter required more drastic conditions. Compound 5 reacted with dienes similarly to perfluoromethylenecyclopropane, affording exclusively [4 + 2] cycloadducts (see Sect. 2.1.1) [9],... 

Methoxyflurane Methoxyflurane, 2,2-dichloro-l,l-difluoroethylmethyl ether (1.1.10), is synthesized from l,l-difIuoro-2,2,2-trichIoroethane, which undergoes dehydrochlorina-tion by potassium hydroxide to give l,l-dichloro-2,2-difluoroethylene (1.1.9) to which methanol is added in the presence of potassium hydroxide [8]. 

Halogen (X2) can be removed thermally or by use of metals (Fe, Mg, Zn, Al). E.g., 1,2-dichloroethylene is obtained industrially from 1,1,2,2-tetrachloroethane by means of iron turnings and steam,140 and l,2-dichloro-l,2-difluoroethylene from l,2-difluoro-l,l,2,2-tetra-chloroethane by means of Zn dust in ethanol.342,343... 

Further details have been published of the cycloadditions of alkenylidenecyclo-propanes with 1-phenyl-1,3,5-triazoline-2,5-dione, which were discussed in detail in an earlier Report. The stereospecificity observed with chiral alkenylidenecyclo-propanes supports the proposal of a cycloaddition pathway involving an eight-electron (i.e. Mobius) transition state, [( +, 2 -I- 2) -I-, 2]. Partial or complete loss of stereochemistry, depending on temperature, is observed with chlorosulphonyl isocyanate, implying a dipolar intermediate, and l,l-dichloro-2,2-difluoroethylene appears to add via biradicals. ... 

Vinylidene fluoride (1,1-difluoroethylene) n, H2C=CF2. a colorless, nearly odorless gas prepared by the dehydrohalogenation of 1-chlorol,l-difluoroethane, or by the dehalo-genation of l,2-dichloro-l,l-difluorethane. It polymerizes readily in the presence of free-radical initiators to produce the homopolymer polyvinylidene fluoride, and is also co-polymerized with olefins and other fluorocarbon monomers to make fluorocarbon elastomers. (See image). 

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