REARRANGEMENT OF A "LONG-LIVED" CARBOCATION ON A SOLID SUPPORT

G. I. Borodkin~ Sh. M. Nagi, UDC 541.124:542o952.1:547.537.26-128 M. Mo Shakirov, and B. G. Shubin

To the best of our knowledge, there have been no reports concerning rearrangements of "long-lived" carbocations on solid supports although such processes are considered key steps in the isomerization of organic compounds on solid acid catalysts [i].

The labeled atom method was used to discover and study the rearrangement of l,l,2,3,4,5,6-heptamethylbenzenonium tetrachloroaluminate (I) deposited on a neutral alumina surface (grade ii activicy) (160-200 mesh)

CH 3 CI~ 3 ~13C~C~3

CHR 2 (D

R = H , D

which had been s u b j e c t e d to p r i o r h e a t i n g a t 500~ f o r 6 h i n vacuum. The amount o f o r g a n i c s a l t d e p o s i t e d was 7o4%. The ~3C N~R s p e c t r u m of ( I ) on a lumina a t 24~ (~, ppm from TMS): 18.26 (CH~), 59 (C:), 143 (C~,5), 194, 200 (Ca, s , C ~) [2].

The rate of the degenerate rearrangement of (I) on alumina at from--70 ~ to --20~ which apparently proceeds through i,2-shift of a methyl group [2], is significantly higher than in the crystalline state (kAlaO~/kcryst from 4.6 to 41) and even in solution in CHaCI2 (kAI203/kCH2Ci~ from 2.6 to 1.2) o The values for E a (15.0 +_ 0.2 kcal/mole) and log A (10.3 + 0.2)* are intermediate between the corresponding values for the crystalline state and solution [2]. The lower Ea relative to solution may be a result of an interaction of the partial positive charge of the migrating group with the nucleophilic sites of alumina and the AICI~ anion, while the decrease in log A is apparently a consequent of restrictions to the motion of the cation atoms upon reaching the transition state [2] o

2.

LITERATURE CITED

Yu. M. Zhorov, The Chemistry and Technology of Hydrocarbon Isomerization [in Russian]~ Izd. Khimiya, Moscow (1983). G. I. Borodkin~ Sh, M~ Nagi (So M~ Nagy), V. I~ Mamatyuk, and Vo Go Shubin, Chem. Commun., 1533 (1983)o

*Taking account of the statistical factor taken to be 4.

Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSRo Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, Noo 7, p. 1691, Julyt 1985. Original article submitted March 4, 1985.

0568-5230/85/3407-1551509.50 �9 1986 Plenum Publishing Corporation 1551