On the mechanism of the ozonation of isopropyl alcohol: An experimental and density functional theoretical investigation. 17O NMR spectra of hydrogen trioxide (HOOOH) and the hydrotrioxide of isopropyl alcohol [17]

Full text of DOI:10.1021/ja981568z

J. Am. Chem. Soc. 1998, 120, 8005-8006
8005
Table 1. 17O NMR Chemical Shifts (δ) of the Hydrotrioxide of
On the Mechanism of the Ozonation of Isopropyl
Alcohol: An Experimental and Density Functional
Theoretical Investigation. 17O NMR Spectra of
Hydrogen Trioxide (HOOOH) and the Hydrotrioxide
of Isopropyl Alcohol
Isopropyl Alcohol (2) and Hydrogen Trioxide (HOOOH) in
Acetone-d6 at -10 °Ca-c
17O NMR
δO(1)
δO(2)
δO(3)
(H3C)2C(OH)(O1-O2-O3-H) 368 (840)d,e 445 (3470)d,e 305 (350)d,e
H-O1-O2-O3-H
305 (350)d-f 421 (3680)
306 (calcd)c 433 (calcd)
305 (350)
306 (calcd)
Bozˇo Plesnicˇar,* Janez Cerkovnik, Tomazˇ Tekavec, and
Jozˇe Koller*
H-O1-O2-H
187 (320)g
187 (320)
192 (calcd)c 192 (calcd)
Department of Chemistry
UniVersity of Ljubljana
P.O. Box 537, 1000 Ljubljana, SloVenia
a Values in parts per million downfield from the internal standard
H217O. b 17O NMR data were obtained on Varian Unity Inova-600
spectrometer operating at 81.37 MHz. c The calculated GIAO/MP2/6-
311++G** absolute shielding for H2O is 343.9 ppm. Experimental
values: H2O(g), 344 ppm; H2O(l), 307.9 ppm (Wasylishen, R. E.;
Mooibroek, S.; Macdonald, J. B. J. Chem. Phys. 1984, 81, 1057). d Area
ratio of peaks O(1):O(2):O(3) was 1:1:1 (2:1 for HOOOH). e Line
widths of the resonances at half-height (∆ν1/2), (5%. f Identical 17O
NMR chemical shifts were observed in the spectra of HOOOH,
generated by the ozonation of hydrazobenzene in acetone-d6 (see
footnote 8). g For a pioneering study, see: Olah, G. A.; Berrier, A. L.;
Prakash, G. K. S. J. Am. Chem. Soc. 1982, 104, 2373.
ReceiVed May 6, 1998
The mechanism of ozonation of the C-H bond of saturated
organic compounds (R-H) is still controversial.1 A concerted
1,3-dipolar insertion mechanism to form the corresponding
hydrotrioxide, ROOOH, has been proposed.2 The mechanistic
possibility involving hydrogen atom abstraction by ozone to form
the radical pair, [R• •OOOH], that collapses to ROOOH has also
been suggested.3 More recently, a hydride ion transfer to form a
carbenium ion and hydrotrioxide anion pair, [R+ -OOOH], has
been proposed.4 We now report that the hydrotrioxide of
isopropyl alcohol and hydrogen trioxide (HOOOH) are formed
in the low-temperature ozonation of the alcohol. Both polyoxides
were characterized for the first time by 17O NMR. These
observations, together with the results of a density functional
theoretical investigation of the ozonation of isopropyl alcohol,
support the “radical” mechanism of this reaction.
butyl methyl ether as solvents.8 2 and HOOOH were formed in
molar ratio of roughly 1:0.6 in all solvents investigated.
A detailed investigation of the products in the decomposition
mixture after warming up the ozonized solutions of 1 in tert-
butyl methyl ether by GC/MS and NMR revealed acetone (37 (
5%), peroxyacetic acid (11 ( 2%), acetic acid (39 ( 5%), formic
acid (7 ( 2%), hydrogen peroxide (11 ( 3%), water, isopro-
poxymethanol (H2C(OH)OCH(CH3)2) (5 ( 1%), and oxygen
(Σ3O2/∆1O26d). Peroxyacetic and formic acids, as well as iso-
propoxymethanol, were already present in the ozonized solutions
of 1 at -78 °C, and their concentrations did not change
significantly during the decomposition of 2/HOOOH.
To gain mechanistic insight and to accommodate the above
observations, ab initio density functional calculations at the
B3LYP/6-31G* + ZPE level9,10 were used to fully optimize the
stationary points on the singlet potential energy surface of the
title reaction.11 Upon going from the reactants to the product,
ROOOH, two stationary points were calculated which were found
Ozonation of isopropyl alcohol (1) (1 M) with ozone-oxygen
or ozone-nitrogen mixtures in acetone-d6 at -78 °C produced
the corresponding hydrotrioxide, Me2C(OH)(OOOH) (2), char-
acterized by the OOOH 1H NMR absorption at 12.9 ppm (δ CH3,
1.44) and 13C NMR absorptions at 25.7 (δ CH3) and 104.3 (δ C)
ppm downfield from Me4Si (-10 °C) in yields of 40-50%. Still,
another OOOH absorption at 13.1 ppm, belonging to another
polyoxide species with exchangeable protons (fast exchange with
CH3OD at -60 °C), was, on the basis of 17O NMR of the species,
highly enriched with 17O,5 assigned to HOOOH.6 This assignment
was confirmed by GIAO/MP2/6-311++G** calculations7 of 17
O
(7) (a) GIAO/MP2/6-311++G** 17O NMR chemical shifts were calculated
by using ACESII package of programs (Stanton, J. F.; Gauss, J.; Watts, J. D.;
Lauderdale, W. J. Bartlett, R. J. Quantum Theory Project, University of Florida,
Gainesville, 1994). For some relevant references, see: Gauss, J. Chem. Phys.
Lett. 1992, 191, 614 (GIAO/MP2). Raghavachari, K.; Trucks, G. W.; Pople,
J. A.; Head-Gordon, M. Chem. Phys. Lett. 1989, 157, 479. Bartlett, R. J.;
Watts, J. D.; Kucharski, S. A.; Noga, J. Chem. Phys. Lett. 1990, 165, 513
(CCSD(T)). (b) HOOOH, MP2/6-311++G** (CCSD(T)/6-311++G**, for
comparison): R(H-O) ) 0.969 Å (0.969), R(O-O) ) 1.421 Å (1.433),
HOO ) 101.4°(101.3), OOO ) 107.2°(107.1), HOOO ) 80.4°(81.7).
(8) HOOOH, generated in this way, decomposed somewhat faster than 2
in all solvents investigated, thus enabling unambiguous 17O NMR assignments.
For example, kinetic and activation parameters for the decomposition of the
polyoxides obtained by following the decay of the OOOH (CH3) absorption(s)
in tert-butyl methyl ether are: 2, k1 ) 1.2 × 10-4 s-1 (-10 °C), Ea ) 25.6 (
1.0 kcal/mol, log A ) 17.3 ( 0.5 (-15 to +5 °C); HOOOH, k1 ) 2.9 × 10-4
s-1 (-15 °C), Ea ) 16.7 ( 1.0 kcal/mol, log A ) 10.2 ( 1.0. The values for
HOOOH are in good agreement with those for the decomposition of HOOOH,
generated by the ozonation of hydrazobenzene (Ea ) 15.3 ( 1.0 kcal/mol,
log A ) 8.3 ( 1.0 (-10 to +25 °C). The latter procedure yields solutions of
HOOOH without the interfering presence of other hydrotrioxides.6f,g
(9) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.;
Ortiz, J. V.; Foresman, J. B.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M.
W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;
Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-Gordon, M.;
Gonzalez, C.; Pople, J. A. GAUSSIAN 94, ReVision B.3; Gaussian, Inc.:
Pittsburgh, PA, 1995.
NMR chemical shifts for this species, which are in excellent
agreement with the experimentally obtained values (Table 1).
Similar observations were also made in methyl acetate and tert-
(1) For reviews, see: (a) Bailey, P. S. Ozonation in Organic Chemistry;
Academic Press: New York, 1982; Vol. II, Chapter 9. (b) For a review on
polyoxides, see: Plesnicˇar, B. In Organic Peroxides; Ando, W., Ed.; Wiley:
New York, 1992; Chapter 10. (c) Olah, G. A.; Molnar, A. Hydrocarbon
Chemistry; Wiley: New York, 1995; Chapter 8.
(2) (a) Tal, D.; Keinan, E.; Mazur, Y. J. Am. Chem. Soc. 1979, 101, 502.
(b) Bailey, P. S.; Lerdal, D. A. J. Am. Chem. Soc. 1978, 100, 5820. (c) Teillefer,
R. J.; Thomas, S. E.; Nadeau, Y.; Fliszar, S.; Henry, H. Can. J. Chem. 1980,
58, 1138. (d) Giamalva, D. H.; Church, D. F.; Pryor, W. A. J. Org. Chem.
1988, 53, 3429.
(3) (a) Hellman, T. M.; Hamilton, G. A. J. Am. Chem. Soc. 1974, 96, 1530.
(b) Whiting, M. C.; Bolt, A. J. N.; Parish, J. H. AdV. Chem. Ser. 1968, 77, 4.
(c) Deslongchamps, P. Stereoelectronic Effects in Organic Chemistry;
Pergamon: Oxford, 1983; Chapter 2.
(4) (a) Nangia, P. S.; Benson, S. W. J. Am. Chem. Soc. 1980, 102, 3105.
(b) For the thermochemistry of polyoxides, see: Benson, S. W.; Cohen, N.
In Peroxyl Radicals; Alfassi, Z., Ed.; Wiley: New York, 1997; Chapter 4.
(5) 17O-enriched ozone was generated by flowing 17O-enriched oxygen (58%
17O2, ISOTEC) through an ozonator.
(6) For the previous studies on HOOOH, see: (a) Giguere, P. A.; Herman,
K. Can. J. Chem. 1970, 48, 3473. (b) Bielski, B. H. J.; Schwartz, H. A. J.
Phys. Chem. 1968, 72, 3836. (c) Cremer, D. J. Chem. Phys. 1978, 69, 4456.
(d) Plesnicˇar, B.; Cerkovnik, J.; Koller, J.; Kovacˇ, F. J. Am. Chem. Soc. 1991,
113, 4946. (e) Jackels, C. F. J. Chem. Phys. 1993, 99, 5768. (f) Cerkovnik,
J.; Plesnicˇar, B. J. Am. Chem. Soc. 1993, 115, 12169. (g) Koller, J.; Plesnicˇar,
B. J. Am. Chem. Soc. 1996, 118, 2470. (h) Speranza, M. Inorg. Chem. 1996,
35, 6140. (i) Fujii, T.; Yashiro, M.; Tokiwa, H. J. Am. Chem. Soc. 1997, 119,
12280. (j) Mckay, D. J.; Wright, J. S. J. Am. Chem. Soc. 1998, 120, 1003.
(10) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. Lee, C.; Yang, W.;
Parr, R. G. Phys. ReV. B 1988, 37, 785. (b) Hehre, W. J.; Radom, L.; Schleyer,
P. v. R.; Pople, J. A. Ab Initio Molecular Orbital Theory; Wiley: New York,
1986.
S0002-7863(98)01568-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/28/1998

8006 J. Am. Chem. Soc., Vol. 120, No. 31, 1998
Communications to the Editor
Scheme 1
are 3.3 and 127.3 kcal/mol, respectively, above the energy of the
isolated reactants. However, solvation of these species (particu-
larly ions) could dramatically lower the endothermicity of these
reactions.4,13 Overall, the ozonation of 1 to form the intramo-
lecularly hydrogen-bonded ROOOH (2) is exothermic by 55.8
kcal/mol, while the adduct, 2-hydroxypropen-HOOOH, is 33.3
kcal/mol below the energy of the isolated reactants.
The Mulliken population analysis indicates that the migrating
hydrogen does not behave as a hydride ion in this reaction. Also,
the geometry of the TS resembles that of the forming hydrotri-
oxide radical more than does that of the hydrotrioxide anion.6j,14
The extraordinary long HO-OO bond in the anion calculated in
the present study (1.73 Å) is in accord with the calculations on
this species at higher levels of sophistication.6g,14 Therefore, it
seems unlikely (but not impossible) that such a loosely bound
species could exist as a distinguished molecular entity in solutions
of organic solvents containing water (decomposition into HO-
and O2) and undergo the above-mentioned reactions.
In summary, the present calculations have clarified the transi-
tion structure for the ozonation of isopropyl alcohol and have,
together with the formation of HOOOH (and some other
products15), indicated the involvement of radical intermediates
in the reaction (Scheme 1). The origin of the experimentally
observed rate acceleration of the formation of ROOOH16 (and
HOOOH as well) in polar aprotic solvents, could be attributed to
the enhanced polarization of the TS relative to the reactants (1,
µ ) 1.56 D; O3, 0.61 D; C, 1.15 D; TS, 4.50 D). The increased
reactivity of the alcohol, compared to that of simple hydrocarbons,
might be due to the additional stabilization of the TS by hydrogen
bonding between the forming OOOH radical and the OH group
(O-H‚‚‚O).
Figure 1. Relevant geometrical parameters for the fully optimized
structures (B3LYP/6-31G*) of isopropyl alcohol and ozone (A), the
complex (B), the transition state (C), and the hydrotrioxide of isopropyl
alcohol (D).
to be an intermediate complex and a transition state (TS) (Figure
1). A complex is formed in a fairly early stage of the reaction
and is held together by a stabilization energy of 3.1 kcal/mol.
The TS, calculated to be 7.4 kcal/mol less stable than that of the
isolated reactants and 10.6 kcal/mol12 less stable than that of the
complex, apparently does not involve synchronous C-O and
O-H bond formation to form ROOOH. Rather, a highly
asymmetric TS with considerable O-H bond (but not C-O bond)
formation is indicated.
Acknowledgment. We dedicate this work to the memory of Professor
Glen A. Russell. Financial support for this project by the U.S.-Slovene
Joint Fund (NSF No. 95-455) is gratefully acknowledged. We also thank
Dr. J. Plavec (National Institute of Chemistry, Ljubljana) for rerunning
17O NMR (Bruker Avance 300 DPX) spectra on the 600 MHz Varian
NMR spectrometer.
A concerted insertion mechanism involving a transition state
with the O-H bond formation preceding C-O bond formation
has already been proposed for ozonations of C-H bonds.2d
However, it is unclear how the calculated TS could accommodate
the formation of HOOOH in terms of a concerted 1,3-dipolar
insertion mechanism. Therefore, we were left with two remaining
mechanistic possibilities. (1) The radical pair at a sufficiently
large separation was formed after the transition state of the rate-
limiting step, thus allowing both the collapse (with less than unit
efficiency) of the pair to ROOOH3a,b and the abstraction of the
hydrogen atom from the 2-hydroxy-2-propyl radical to form the
enol, i.e., 2-hydroxypropen,3b and HOOOH. (2) The ion pair3,4
that produces the same products was formed along the reaction
path. The energies of the radical and ion pair at infinite separation
Supporting Information Available: B3LYP/6-31G*-optimized ge-
ometries and energies (B3LYP/6-31G* + ZPE) of the structures reported
(4 pages, print/PDF). See any current masthead page for ordering
information and Web access instructions.
JA981568Z
(13) By using known heats of formation for the radicals and molecules, as
taken from Benson and Cohen,4 ∆rH(g) ) 21 ( 1.5 kcal/mol, and ∆rH(l) )
13 ( 2.0 kcal/mol were calculated for the reaction: O3 + Me2CHOH f HO3
+ Me2COH. The ∆rH(l) value is now close to the estimated 9 kcal/mol for
the experimental activation energy to make the hydrogen atom abstraction
plausible. We thank one of the reviewers for this information.
(14) HOOO•: UB3LYP/6-31G*, R(H-O1) ) 0.981 Å, R(O1-O2) ) 1.503
Å, R(O2-O3) ) 1.262 Å, HO1O2 ) 98.8°, O1O2O3 ) 112.2°, HO1O2O3
) 0°. E ) -226.035 175 au. HOOO-, B3LYP/6-31G* (CCSD(T)/6-
311++G**), R(H-O1) ) 0.972 Å (0.966), R(O1-O2) ) 1.734 Å (1.882),
R(O2-O3) ) 1.336 Å (1.315), H1O1O2 ) 87.6°(85.1), O1O2O3 ) 108.5°
(110.1), HO1O2O3 ) 0° (-43.7). E ) -226.058 174 au (-225.682 552 au).
(15) Peroxyacetic and formic acids are presumably formed by the ozonolysis
of the enol.1a,3b The initially formed formaldehyde is oxidized further (O3/
O2), and also reacts with isopropyl alcohol to form isopropoxymethanol.
(16) Kovacˇ, F.; Plesnicˇar, B. J. Am. Chem. Soc. 1979, 101, 2677. Pryor,
W. A.; Ohto, N.; Church, D. F. J. Am. Chem. Soc. 1983, 105, 3614. Zarth,
M.; de Meijere, A. Chem. Ber. 1985, 118, 2429. Plesnicˇar, B.; Kovacˇ, F.;
Schara, M. J. Am. Chem. Soc. 1988, 110, 214.
(11) The ozone molecule is best described as a diradical with two unpaired
electrons on the terminal oxygens in orbitals, pointing out of the plane of the
molecule (π direction), that are weakly coupled in a singlet pair (Meredith,
C.; Quelch, G. E.; Schaefer, H. F. J. Am. Chem. Soc. 1991, 113, 1186, and
references therein.).
(12) For example, the activation parameters for the ozonation of isopropyl
ether in CCl4 are: Ea ) 10.0 kcal/mol, log A ) 7.9. (Giamalva, D. H.; Church,
D. F.; Pryor, W. A. J. Am. Chem. Soc. 1986, 108, 7678.).