Trityl hexafluoroantimonate

Rooney has recently revived work on this monomer in an investigation of its polymerisation by trityl hexafluoroantimonate - He used a spectroscopic stop-flow apparatus to follow initiation and an adiabatic calorimeter to measure rates of polymerisation. Propagation was shown to compete effectively with initiation to the point that some initiator was often present at the end of the polymerisations. These observations cast some doubts on the assumption made in the paper by the Liverpool school discussed above. A kinetic analysis of the initiation reaction showed it to be bimolecular, with a rate constant of about 130 sec at 20°C. The determination of the propagation rate constant was less strai tforward despite the fact that further monomer-addition experiments seemed to rule out any appreciable termination. The kp values fluctuated considerably as the initial catalyst concentration was varied, a fact which induced Rooney to propose that the empirical constant was a composite function of kp and kp. Experiments with a common-anion salt supported this proposal and their kinetic treatment led to the individual values of kp = 6 x 10 sec and kp = 5 x 10 sec. It is difficult to assess the reliability of these values in view of the following statement by the author the reaction at a 5 x 10 M concentration of initiator, thought to proceed exclusively through paired ions. .. . This statement is certainly incorrect as far as the initiator is concerned for which the proportion of ion pairs for a concentration 5 x 10 M at 20°C is only about 20% in methylene chloride However, the experiments... 

The second part of Johnson and Pearce s investigation dealt with trityl hexafluoroantimonate. This initiator was found to be extremely active for the polymerisation of styrene, as already reported by Pepper and coworkers ). Monomer conversions reached 100% before complete bleaching of the trityl salt, and as polymerisations proceeded the... 

We can summarise the situation with styrene by a few observations. Obviously this monomer is not easily attacked by the trityl ion and the most favourable case encountered is that in which trityl hexafluoroantimonate it used. Termination reactions seem to plague most of these polymerisations and we believe that halogen-ion transfer from the anion to the growing species soon after initiation is responsible for the loss of activity of these systems. Again, the SbF counterion is an exception in that it does not seem to undergo this termination reaction. Except for the last study discussed, little reliable evidence is available to date to elucidate these difficult problems. Much fundamental information could be obtained by continuing on the line followed by Johnson and Pearce. 

Trityl hexafluoroantimonate, (CeHsljC SbF ", and trityl hexafluorophosphate, (C5ll5)3C Pf4", can be prepared in the same way using anhydrous fluoroantimonic acid and the ether complex of hexalluorophosphoric acid, respectively. 

Synthesis of aldehydes and ketones.1 Trityl ethers2 disproportionate to triphenyl-methane and aldehydes or ketones in the presence of small amounts of trityl salts trityl hexafluorophosphate, trityl hexafluoroantimonate, (C6H5)3C+AbF6 , or trityl hexafluoroarsenate, (C6H5)3C+AsF6. ... 

Organosilicon hydride reductions of preformed stable carbocations such as triphenylmethyl (trityl) tetrafluoroborate and hexafluoroantimonate salts are rapid... 

At low temperatures in inert solvents (such as methylene dichloride) a controlled polymerization can be effected using various acids and alkylating agents. These initiators include boron trifluoride etherate, triethylaluminum, trityl hexachloroantimonate, triethylam-monium hexachloroantimonate, diethyloxonium hexafluoroantimonate, p-toluenesulfonic acid and diethylzinc or cadmium-1,2-dioI complexes. Crystalline, high molecular weight... 

WhUe this nomomer cannot be polymerised either by trityl or by tropylium salts, Plesdi and Pask were able to promote its polymerisation by using diphenylethylium hexafluoroantimonate. This recent discovery opens up new interesting potentials in the field of carbenium-salt initiated polymerisatkm of aliphatic olefins. 

Acetylation Acetic anhydride. N-Acetoxyphthalimide. 2- and 3-Acetoxypyridine. Acetyl chloride. N-Acetylimidazole. Boron trifluoride. Catalysts (see Acetic anhydride). Ketene. Magnesium. Methyl oxocarbonium hexafluoroantimonate. Perchloric acid. Phenyl acetate. Pyridine. Sodium acetate. Tetraelhylammonium acetate. p-Toluenesulfonic acid. Tri-n-hexylethyl ammonium hydroxide. 2,4,6-Triisopropylbenzenesulfonyl chloride. Trityl-sodium. Zinc chloride. 

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