Tetrafluoroethylene with olefins

In contrast to the telomerisation of tetrafluoroethylene with perfluoroalkyl iodides (RFI), the addition of these telogens to this olefin has not been quite investigated. This may be explained by the fact that the RF(CF2CFCl)nI telomers produced are more efficient telogens than the starting RFI transfer agents as it can be seen in the previous section. Table 13 sums up the results of the literature. 

The development of these elastomers was based on the pioneering work of the inventor of du Font s Teflon, Plunkett (1941). However, in order to obtain rubbery polymers, it was necessary to modify this tough plastic, and this was first done in 1949 by Hanford and Roland (du Pont), who oopolymerized tetrafluoroethylene (TFE) with olefins, and by Schroeder ... 

Fluorinated alkenes have been reported to give cyclobutane derivatives by thermal additions to other alkenes. Olefins in their ground electronic states have not been observed to give stereospecific cycloaddition one with another whereas a carbon-carbon double bond which is part of an allene or keten will undergo stereospecific concerted cycloadditions. The separate reactions of tetrafluoroethylene with cis- and trans-[l,2- H2]ethylene, which should not be subject to an adverse steric effect, have been studied to establish whether these reactions are stereospecific. Identical mixtures of products were obtained from both reactions, as expected if they proceed through the... 

A -Halogenated compounds such as iV-chlorotnfluoroacetamide, A -chloro-imidosulfuryl fluonde and N N dichlorotnfluoromethylamine add across C=C bonds to form saturated amides [14] tmidosulfury I fluorides [15] and amines [16], respectively Allylic halogenation also occurs with the use of A-bromo- or A-chIo roperfluoroamides The primary amine A,A-dichlorotrifluororaethylamine selectively affords 11 or 2 1 adducts with either tetrafluoroethylene or chlorotrifluoroethylene [16] (equation 7) The reaction mechanism is believed to involve thermal free radicals, with control achieved principally by reaction temperature The 1 1 adduct is formed even in the presence of a large excess of olefin... 

A new thermal preparation ot fluorinated species is copyrolysis Copyrolysis of fluorinated compounds like perfluorobenzene, fluorinated aromatic anhydndes, and fluorinated heteroaromatics with tetrafluoroethylene or other fluonnated olefins is a useful method of preparing fluorinated olefins [88 89], functionalized fluoroaromatics [90 91 92, 93, 94, 95], fluonnated benzocycloalkanes [80, 96, 97, 98, 99, 700], fluorinated heterocycles [80, 93, 101, 102, 103], and fluonnated polycyclic compounds [104] (equations 19 and 20)... 

The first [2 + 2] cycloaddition of methylenecyclopropane which has been reported involves the use of tetrafluoroethylene (482) (Table 38, entry 1) [131], an olefin having a high tendency to give cycloadditions in a [2 + 2] fashion, which are considered to occur in a two-step process involving diradical intermediates. In the same article, the author reports unsuccessful attempts to react methylenecyclopropane with maleic anhydride or acrylonitrile [131]. 

Compounds with Metal-Metal Bonds. There is one clear example of the addition of a compound with a metal-metal bond to an olefin. Cobalt octacarbonyl reacts with tetrafluoroethylene to form a symmetrical adduct (102). 

One complex with a metal—metal bond that has been added to an olefin is cobalt octacarbonyl. It reacts with tetrafluoroethylene and it seems reasonable that this is an insertion reaction but again it has not been proved. 

The photochemical addition of simple olefins to a,/ -unsaturated ketones is a reaction of great current interest.113 The steroidal A16-20-ketone system is especially prone to cycloaddition under mild conditions. Sunder-Plassmann et al114,115 irradiated 3/ -acetoxypregna-5,16-dien-20-one (67) in the presence of tetrafluoroethylene and obtained a 2 1 mixture of the a- and / -face adducts (68) and (69) together with a third adduct which has been characterized as (70) by X-ray crystallographic analysis.1153... 

The rates and orientation of free radical additions to fluoroalkenes depend upon the nature of the attacking radical and the alkene, but polar effects again are important For instance, methyl radical adds 9 5 times faster to tetrafluoroethylene than to ethylene at 164 °C, but the tnfluoromethyl radical adds 10 times taster to ethylene [7551 The more favorable polar transition states combine the nucleophilic radical with the electron deficient olefin 17 and vice versa (18) These polar effects account for the tendency of perfluoroalkenes and alkenes to produce highly regular, alternating copolymers (see Chapter starting on page 1101)... 

The first free radical initiated copolymerization was described by Brubakerl) in a patent. A variety of peroxides and hydroperoxides, as well as, 02, were used as initiators. Olefins that were copolymerized with CO included ethylene, propylene, butadiene, CH2=CHX (X—Cl, OAc, CN) and tetrafluoroethylene. A similar procedure was also used to form terpolymers which incorporated CO, C2H4 and a second olefin such as propylene, isobutylene, butadiene, vinyl acetate, tetrafluoroethylene and diethyl maleate. In a subsequent paper, Brubaker 2), Coffman and Hoehn described in detail their procedure for the free radical initiated copolymerization of CO and C2H4. Di(tert-butyl)peroxide was the typical initiator. Combined gas pressures of up to 103 MPa (= 15,000 psi) and reaction temperatures of 120—165 °C were employed. Copolymers of molecular weight up to 8000 were obtained. The percentage of CO present in the C2H4—CO copolymer was dependent on several factors which included reaction temperature, pressure and composition of reaction mixture. Close to 50 mol % incorporation of CO in the copolymer may be achieved by using a monomer mixture that is >70 mol% CO. Other related procedures for the free radical... 

Terpolymers made from two different olefins and CO are known. They were first described in Brubaker s initial patent and involved the free radical initiated terpolymerization of CO and C2H with another olefin such as propylene, isobutylene, butadiene, vinyl acetate, diethyl maleate or tetrafluoroethylene More recently, in another patent, Hammer has described the free radical initiated terpolymerization of CO and C2H with vinyl esters, vinyl ethers or methyl methacrylate 26Reaction temperatures of 180-200 °C and a combined pressure of 186 MPa were employed. Typically a CO QH4 olefin molar ratio of 10 65 25 was observed in the terpolymers. In other patents, Hammer 27,28) has described the formation of copolymers with pendant epoxy groups by the free radical initiated polymerization of CO, QH4, vinyl acetate and glycidyl methacrylate. Reaction conditions similar to those stated above were employed, and a typical CO C2H vinyl acetate glycidyl methacrylate molar ratio of 10 65 20 5 was observed in the product polymer. 

Table 12 there is a marked increase in the orientation ratio as the attacking radical becomes more bulky. With vinylidene fluoride the orientation ratio for perfluoro-t-butyl radicals is too large to measure. Even with perfluoro-isopropyl the orientation ratio (kjk is 103. In the other tables the orientation ratios for addition to vinyl fluoride and trifluoroethylene vary only slightly, but in Table 12 there is a marked increase as the radical becomes more branched. Perhaps the most striking feature of the table is that the increase in orientation ratio is almost entirely due to a reduction in the rate of addition to the most substituted end of the olefin. The relative rates of attack at the unsubstituted ends of vinyl fluoride and vinylidene fluoride vary only slightly across the table. In other words, the high orientation ratio is almost entirely due to the difficulty of addition at the substituted end of the olefin, a conclusion supported by the great variation in the relative rate of addition to tetrafluoroethylene (i.e. where both ends are fully substituted). 

In this case, a mixture of cis- and ra s-perfluoro-4,5-dihydro-2,3,4,5-tetramethyl-4-ethylfurans is obtained. This is a general reaction, which also works with other perfluoroolefins and alcohols. For example, when the tetrafluoroethylene pentamer reacts with allyl alcohol in the presence of bases, the initial reaction is nucleophilic addition at the multiple bond, forming olefin 44, followed by the formation of perfluoro-4-ethyl-2,3,4,5-tetramethyl-4,5-dihydrofuran 45 in the presence of KF (87ASCC31). 

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