Rearrangement of Cyclopropylcarbinyl Chloride Over Protonic Zeolites: Formation of Carbocations and Behavior as Solid Solvents
- 16 Downloads
The rearrangement of cyclopropylcarbinyl chloride was studied over protonic zeolites and K-10 Montmorillonite. The energy of activation is lower on zeolites, with K-10 showing almost the same value for the rearrangement in 80% aqueous ethanol solution. HUSY showed the lowest energy of activation, whereas HZSM-5 and HYD [dealuminated with (NH4)2SiF6] presented similar energy of activation. This difference may be due to the presence of extra-framework aluminum species. On the other hand, the entropy of activation is significantly less negative on ZSM-5 and may be associated with the narrower pore structure, providing ionization of the substrate without losing many degrees of freedom. Kinetic isotope effects indicated that ionization is assisted by hydrogen bonding of the zeolite OH groups with the leaving halide, similar to the push–pull mechanism proposed for solution chemistry. Hence, zeolites behave as solid solvents, providing a polar microscopic environment for ionic reactions to take place, and solvating the transition state and the ions formed.
KeywordsZeolites Carbocation Acid catalysis Rearrangement
Authors thank financial support from CNPq and FAPERJ.
- 11.Olah GA, Schlosberg RH (1968) Chemistry in super acids. I. Hydrogen exchange and polycondensation of methane and alkanes in FSO3H-SbF5 (“magic acid”) solution. Protonation of alkanes and the intermediacy of CH5 + and related hydrocarbon ions. The high chemical reactivity of “paraffins” in ionic solution reactions. J Am Chem Soc 90:2726–2727CrossRefGoogle Scholar
- 14.Olah GA, Prakash GKS, Williams RE, Field LD, Wade K (1987) Hypercarbon chemistry. Wiley, New YorkGoogle Scholar
- 27.Franco M, Rosenbach N Jr, Ferreira GB, Guerra ACO, Kover WB, Turci CC, Mota CJA (2008) Rearrangement, nucleophilic substitution and halogen switch reactions of alkyl halides over NaY zeolite: formation of the bicyclobutonium cation inside the zeolite cavity. J Am Chem Soc 130:1592–1600CrossRefGoogle Scholar
- 35.van Bokhoven JA, Roest AL, Koningsberger DC, Miller JT, Nachtegaal GH, Kentgens APM (2000) Changes in structural and electronic properties of the zeolite framework induced by extraframework Al and La in H-USY and La(x)NaY: A 29Si and 27Al MAS NMR and 27Al MQ MAS NMR study. J Phys Chem B 104:6743–6754CrossRefGoogle Scholar
- 49.Lowry TH, Richardson KS (1981) Theory and mechanism in organic chemistry. Harper and Row, New YorkGoogle Scholar