Labelled aluminum alkyls

Determination of the number of labeled alkyl groups bound to the polymer chains (end groups) of polymers obtained with catalysts prepared in the presence of " C-labeled aluminum alkyls [268,279]. 

Ti—13Cp 40.1 ppm), and only weak signals of 13C-labeled alkyl groups at the aluminium were observed (see Fig. 6). These results indicate that an insertion of ethylene takes place into a titanium-carbon bond of a titanium-aluminum complex and no alkyl exchange between the bonds of titanium-alkyl and aluminum-alkyl occurs. 

This is the Verdrangungsreaktion with the monomer, and it is catalyzed by the Ziegler catalyst or its consecutive products. Using aluminum alkyls and 14C-labeled ethylene, under conditions not causing any insertion or hydride formation and in the presence of a dead catalyst, an equilibrium distribution of labeled ethylene between the gas phase and the alkyl is reached (33). It has been possible in certain cases to use this effect to reduce molecular weight from over l million to some hundreds by increasing the temperature from 25 to 100°C without any loss in efficiency (34). 

Fia. 23. Specific radioactivity (and corresponding values of —CjHs mol. per mol. of polymerized CsHj) of the atactic polypropylene fraction, as function of the square root of the alkyl-aluminum concentration. (Tests performed with C-labeled Al(CjH()s at t = 70°, pc H, = 450 mm. Hg, grounda-TiCU sample A). 

Preparation of the C-labelled compound 65 was accomplished in a manner analogous to Scheme 14. Friedel-Crafts acylation of 44 was conducted with [2- C]-chloroacetyl chloride under aluminum trichloride catalysis to give the radiolabelled intermediate 64 (48 mCi/mmol). The carbonyl group of 64 was reduced with triethylsilane and the resulting alkyl chloride was reacted with piperazine 40 to provide C-labelled ziprasidone (65). The HCI salt of 65 was formed resulting m a final compound with a specific activity of 9.6 mCi/mmol. 

Studies by Nakane et al. also support the two-step mechanism when alkylation is carried out with alkyl halides under substantially nonionizing conditions. It was further shown that in nonpolar organic solvents carbocations rather than the polarized complexes participate directly in the formation of the first n complex. BF3—H20 catalyzes ethylation,130 isopropylation,131 and benzylation132 through the corresponding carbocations. Accordingly, ethylbenzene equally labeled in both a and p positions was obtained when [2-14C]-ethyl halides were reacted in hexane solution in the presence of boron trifluoride, BF3—H20, or aluminum... 

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