Proton-fluoride contacts

Electrical Conduction by Proton Jumps. As mentioned in Sec. 24, a hydroxyl ion may be regarded as a doubly charged oxygen ion 0 , containing a proton inside the electronic cloud of the ion, which has the same number of electrons as a fluoride ion. The radius of the hydroxyl ion cannot be very different from that of the fluoride ion. But it will be seen from Table 2 that the mobility of the hydroxyl ion is about four times as great. This arises from the fact that a large part of the mobility is undoubtedly due to proton transfers.1 Consider a water molecule in contact with a hydroxyl ion. If a proton jumps from the molecule to the ion,... 

In the structure of [PSH][TFA] (Fig. 3) [50] the expected tetrahedral anion was confirmed. Not surprisingly, the F-Al-F bond angles were approximately 109°, with equivalent Al-F distances of around 1.62 A. The closest contact between the coordinated fluoride and the chelated proton of the cation was 2.77 A, which could be considered a long hydrogen bond. The crystal structures of [Ph4P][TFA], [Ph4As][TFA], and [n-Bu4N][TFA] (Fig. 4) have also been reported and are similar to that of [PSH][TFA] with discrete cations and anions [8]. 

Alkylation conditions are quite mild. Processes employing concentrated sulfuric acid operate at 2-12°C and 4.1—4.8 x lO N/m (4.1-4.8 atm), with a gas contact time of 5-30 min. Catalysis with anhydrous hydrogen fluoride requires slightly higher temperatures (25 5°C) and pressures than sulfuric acid, and contact times of 20-40 s. Both catalysts involve initial protonation of the double bond of an olefin. With isobutylene, for example, -butylcarbonium ion is formed. This can add to another isobutylene in the same manner as occurs during polymerization (Eq. 18.25). 

Another approach to evaluate the stability of the copolymer proposed by Carlson " ] was by hydrolytic stability. This method was comprised of measuring the amount of fluoride ions extracted from the copolymer by water. Acyl fluoride groups generate hydrofluoric acid upon contact with water, which ionizes to a proton and a fluoride ion. Typically, 10-20 g of copolymer was immersed in a 50/50% water/methanol mixture at a ratio of one part copolymer to one part liquid. Fluoride ion extracted into the water/methanol mixture was measured by a fluoride specific electrode after initial contact and after 18-24 hours of immersion. Untreated copolymer usually liberated twenty parts per million (ppm) by weight of fluoride ions compared to less than 1-5 ppm for the ammonia treated copolymer. 

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