Cyclopropylcarbinyl chloride

Carbocations on Surfaces Formation of Bicyclobutonium Cation via Ionization of Cyclopropylcarbinyl Chloride over NaY Zeolite... 

Recent progress in preparation and study of alkylated fullerene cations RC6o+ and RC o+ as long-lived species are examined by T. Kitagawa in Chapter 12. Chapter 13 by C. J. A. Mota and co-workers examines the formation of the bicyclobutonium cation via cyclopropylcarbinyl chloride over solid acid catalysts. 

Cyclopropylcarbinyl chloride rearranges to cyclobutyl and allylcarbinyl chlorides over NaY zeolite at room temperature. This result is consistent with ionization of the... 

The rearrangement of the cyclopropylcarbinyl chloride in solution is well known in the literature (//). In polar solvents three products, arisen from the nucleophilic substitution of the solvent to the chloride, are usually detected, which are formed via nucleophilic substitution of chloride by solvent. This chemistry can be explained by the formation of the bicyclobutonium cation (C4H7+), which acts as a tridentated ion, generating the three products shown in scheme 3. 

There are no reported studies of this rearrangement on the zeolite surface and we argued that it could give some clues to the alkyl-aluminumsilyl oxonium ion/carbocation equilibrium. In this work we show experimental and theoretical results on the rearrangement of the cyclopropylcarbinyl chloride over NaY zeolite, aiming at demonstrating the equilibrium between the carbocation and the alkyl-aluminumsilyl oxonium ion. 

When a gaseous flow of cyclopropylcarbinyl chloride is passed over NaY zeolite at room temperature, formation of cyclobutyl chloride and allylcarbinyl chloride was observed (scheme 4), as well as cyclopropylcarbinyl chloride (product and unreacted starting material). These data are consistent with formation of the C4H7+ cation with internal return of the chloride ion. 

These results are consistent with ionization of the cyclopropylcarbinyl chloride on the zeolite, with formation of the C4H7+ cation. Attack of the chloride ion (internal return) might then occur at the three possible positions, giving the rearranged alkyl chlorides. This hypothesis was supported by the data obtained with impregnation of the NaBr on the NaY zeolite. The observation of the three alkylbromides is consistent with a mechanism involving ionization and attack of the external bromide nucleophile. 

Scheme 5 Product distribution from reaction of cyclopropylcarbinyl chloride on NaY impregnated with 15% of NaBr.

Scheme 6 Possible mechanistic scheme for cyclopropylcarbinyl chloride rearrangement over NaY/NaBr zeolite.

Table 2 Effect of NaBr impregnated on NaY on the distribution of alkyl bromides formed upon ionization of cyclopropylcarbinyl chloride... 

Rearrangement of the cyclopropylcarbinyl chloride takes place over NaY zeolite, indicative of the formation of the bicyclobutonium cation. Theoretical calculations show that the bicyclobutonium is an intermediate on the zeolite surface and might be in equilibrium with the alkyl-aluminumsilyl oxonium ion. 

The results of cyclopropylcarbinyl chloride rearrangement over NaY impregnated with NaBr suggest that there is an equilibrium between the bicyclobutonium cation and the alkyl-aluminumsilyl oxonium ion, explaining the preferred formation of the allylcarbinyl bromide in the rearranged products. It also suggests that zeolites may act as solid solvents, providing unsymmetrical solvation for the ions inside the cavities. 

Cyclobutyl- or cyclopropylcarbinyl chloride or the corresponding alcohols react with SbFj to give stable ion solutions with identical H- and C-nmr spectra. These spectra indicate either an ion with three-fold symmetry, the tricyclobutonium ion [32], or a set of rapidly equilibrating, less symmetrical ions with the same effective averaged symmetry. These include cyclopropylcarbinyl cation [33], bicyclobutonium ion [34] or bent cyclobutyl cations [35]. Theoretical calculations predict similar energies for [33]-[35], but indicate that [32] is less likely (Hehre and Hiberty, 1974 Hehre, 1975). Isotopic perturbation studies by Saunders and Siehl (1980) indicate that the... 

Cyclopentylidenecyclopentanol, 294 Cyclopentyllithium, 205 Cyclophanes, 187 Cyclopropanecarbaldehyde, 64 Cyclopropanecarboxylic acid fluoride, 346 Cyclopropanemethanol, 64 Cyclopropanes, 172, 196 Cyclopropanols, 118, 119 Cyclopropanone, 104 Cyclopropenone, 424 Cyclopropylcarbinyl chloride, 463 Cyclopropylidenecycloxhexane, 96 Cyclopropyltriphenylphosphonium bromide, 95-96... 

Roberts and Mazur1 reported that treatment of a mixture of cyclopropylcarbinyl chloride and cyclobutyl chloride (approximately 2 1) with zinc chloride in coned, hydrochloric acid (Lucas reagent2) gave allylcarbinyl chloride in 46% yield. They also isomerized the corresponding bromides with zinc bromide in 48% hydrobromic acid. 

It has just been reported that two different C4H ions can be generated in the gas phase from cyclobutyl and cyclopropylcarbinyl chlorides. When sampled shortly ca. 10 s) after their formation and in the absence of excitation, they display different patterns of reactivity, quite consistent with the structures given above for 14 and 15. 

Caserio M. C., W. El. Graham, and J. D. Roberts. 1960. Small-ring compounds—XXEX. A reinvestigation of the solvolysis of cyclopropylcarbinyl chloride in aqueous ethanol. Isomerization of cyclopropylcarbinol. Tetrahedron 11 171-182. 

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