C O M M U N I C A T I O N S
Table 2. Kinetic and Activation Parameters for the Decomposition of the Hemiortho Ester 2a and the Hydrotrioxide 3a in Various Solventsa
R−OH (2a)
R−OOOH (3a)
k × 104,b s-1
k × 104,b s-1
d
e
solvent
T, °C
δ, ppm
OH
CH
3
E , kcal/mol
a
log A
δ, ppm
OOOH
CH
3
E , kcal/mol
a
log A
acetone-d6
-15
15
-15
15
-15
15
5.84
3.15
11.74
0.82
3.23
12.5 ( 1.2c,d
14.5 ( 1.3d
14.8 ( 1.5d
7.2 ( 0.8
13.11
12.58
12.67
12.33
12.80
12.60
3.73
5.54
1.40
3.83
5.34
17.5 ( 1.6c,e
19.0 ( 1.5e
24.7 ( 1.7e
9.9 ( 1.1
11.2 ( 1.1
15.0 ( 1.2
methyl
acetate
tert-butyl
methyl ether
5.32
5.51
11.27
9.5 ( 1.0
8.4 ( 1.1
a 2a ) (0.08 ( 0.02)M. b Standard deviations e(10%. c 2b:acetone-d6, Ea ) 13.1 ( 1.1 kcal/mol, log A ) 8.1 ( 0.9. 3b: acetone-d6, Ea ) 20.0 ( 1.5
kcal/mol, log A ) 12.5 ( 1.1. d Following decay of the OH absorption. e Following decay of the OOOH absorption.
Scheme 1
(6) Deslongchamps, P.; Moreau, C. Can. J. Chem. 1971, 49, 2465. (b)
Deslongchamps, P.; Atlani, P.; Frehel, D.; Malaval, A.; Moreau, C. Can.
J. Chem. 1974, 52, 3651. (c) Li, S.; Deslongchamps, P. Tetrahedron Lett.
1993, 34, 7759 and references therein.
(7) Deslongchamps, P. Stereoelectronic Effects in Organic Chemistry; Per-
gamon: Oxford, 1983; pp 41-47. (b) Kirby, A. J. Stereoelectronic Effects;
Oxford University Press: Oxford, 2000, pp 70-71. (c) Perrin, C. L. Acc.
Chem. Res. 2002, 35, 28.
(8) Kovacˇ, F.; Plesnicˇar, B. J. Am. Chem. Soc. 1979, 101, 2677.
(9) Taillefer, R. J.; Thomas, S. E.; Nadeau, Y.; Fliszar, S.; Henry H. Can. J.
Chem. 1980, 58, 1138.
(10) Nangia, P. S.; Benson, S. W. J. Am. Chem. Soc. 1980, 102, 3105.
suggesting a HOδ-‚‚O2δ- structure with a relatively large negative
charge at position O1 and a smaller one at O3.
(11) Pryor et al. have suggested that transition states for the ozonation of C-H
bonds in saturated systems might have contributions ranging from radical
to ionic resonance forms, depending on the substrate and the conditions
used. (Giamalva, D. H.; Church, D. F.; Pryor, W. A. J. Am. Chem. Soc.
1986, 108, 7678. Giamalva, D. H.; Church, D. F.; Pryor, W. A. J. Org.
Chem. 1988, 53, 3429.)
(12) The hemiortho ester 2a (2-hydroxy-2-methyl-1,3-dioxolane) was character-
ized before in the hydronium ion-catalyzed hydration of 2-methylene-
1,3-dioxolane (Capon, B.; Ghosh, A. K. J. Am. Chem. Soc. 1981, 103,
1765). (b) For a review on tetrahedral intermediates, see: McClelland,
R. A.; Santry, L. J. Acc. Chem. Res. 1983, 16, 394.
(13) A radical inhibitor, i.e., 2,6-di-tert-butyl-4-methylphenol has a relatively
small effect on the rates and the activation parameters for the decomposi-
tion of 3a and 3b. This, together with relatively low yields of H2O2 formed
in these reactions, supports an “in cage” reaction as the predominant
reaction pathway. (b) The formation of ∆1O2 in the decomposition of the
hydrotrioxide of 2-propyl-1,3-dioxolane has been confirmed by chemi-
luminescence measurements. (Khurshan, S. L.; Khalizov, A. F.; Avzy-
anova, E. V.; Yakupov, M. Z.; Shereshovets, V. V. Russ. J. Phys. Chem.
2001, 75, 1225.). See also ref 8.
(14) Plesnicˇar, B.; Cerkovnik, J.; Tekavec, T.; Koller, J. J. Am. Chem. Soc.
1998, 120, 8005. (b) Plesnicˇar, B.; Cerkovnik, J.; Tekavec, T.; Koller, J.
Chem.-Eur. J. 2000, 6, 809. (c) Cerkovnik, J.; Erzˇen, E.; Koller, J.;
Plesnicˇar, B. J. Am. Chem. Soc. 2002, 124, 404. (d) For reviews of earlier
literature, see: Plesnicˇar, B. In Organic Peroxides; Ando, W., Ed.;
Wiley: New York, 1992; p 479. (e) Shereshovets, V. V.; Khursan, S. L.;
Komissarov, V. D.; Tolstikov, G. A. Russ. Chem. ReV. 2001, 70, 105.
Hydrotrioxide 3a decomposes to RO• and HOO• radicals in an
endergonic process (∆RG ) 19.2 kcal/mol in acetone solution). The
RO• radical can easily abstract an H atom to form 2a. This, together
with considerably greater kinetic stability of 3a, as opposed to that
of 2a (see Table 2), suggests that the hemiortho ester 2a is
-
preferentially formed by ion pair recombination involving the HO3
anion rather than via hydrotrioxide 3a.21
Finally, the hydrogen trioxide (HOOOH), observed recently in
the low-temperature ozonation of isopropyl alcohol, isopropyl
methyl ether, and various hydrocarbons,14a-c was not detected in
the ozonized solutions of acetals under investigation. This corre-
sponds to the fact that H-atom abstraction by ozone to form HOOO•
radicals (and subsequently HOOOH) is energetically disfavored
when dioxolanes are dissolved in acetone, thus underlining the
-
important role of the HO3 anion in ozone reactions22 involving
substrates with the potential of forming relatively stable carbenium
ions in solution.
(15) Water was always present in the reaction mixture in small but sufficient
amounts to participate in the reaction (molar ratio 2a:H2O ) 1:2 in
acetone-d6 (by 1H NMR)). Also, the addition of water (4 ( 1 vol %) to
acetone-d6 solutions (-60 °C) did not change significantly the kinetic
and activation parameters of the decomposition of either 2a or 3a.
(16) Somewhat smaller activation parameters for the decomposition of 3a and
3b in acetone-d6 and methyl acetate as compared to values in tert-butyl
methyl ether might reflect the fact that the decomposition is proceeding
by several simultaneous first-order processes involving radical (predomi-
nant) and nonradical pathways. Among the latter, water-assisted decom-
position might be more important in acetone than in tert-butyl methyl
ether (different solubility of water in these solvents).14b
Acknowledgment. This work was supported by the Ministry
of Education, Science, and Sport of the Republic of Slovenia, and
by the Swedish Natural Science Research Council (NFR). Calcula-
tions were done on the supercomputers of the Nationellt Superda-
torcentrum (NSC), Linko¨ping, Sweden.
Supporting Information Available: Details of calculations and
structures and complete kinetic data for the decomposition of 2 and 3
(PDF). This material is available free of charge via the Internet at http://
pubs.acs.org.
(17) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Becke, A. D. Phys. ReV.
A 1988, 38, 3098. (c) Lee, C.; Yang, W.; Parr, R. P. Phys. ReV. B 1988,
37, 785.
References
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(20) CRC Handbook of Chemistry and Physics on CD-ROM, 2000 Version;
Lide, D. R., Ed.; CRC Press LLC: Boca Raton, FL, 2000.
(21) 2a was found to be enriched with 17O in the OH group as indicated by its
17O NMR spectrum, which appears to indicate the reaction of the
carbenium ion with HOOO- anion in the solvent cage.
(3) Bailey, P. S. Ozonation in Organic Chemistry; Academic Press: New
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(4) Wentworth Jr., P.; Jones, L. H.; Wentworth, A. D.; Zhu, X.; Larsen, N.
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(22) Supporting the hydride abstraction mechanism is the observation that ethyl
diethoxy acetate is inert toward O3 and that electron-withdrawing groups
in benzaldehyde acetal6b and 2-phenyl-1,3-dioxolane9 retard the ozonolysis
of these substrates.
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