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Spectral and Chemical Properties of Dimethyldioxirane As Determined by Experiment and Ab Initio Calculations

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Spectral and Chemical Properties of Dimethyldioxirane As Determined by Experiment and Ab Initio Calculations 2800 J. Org. Chem. 1987,52, 2800-2803 Spectral and Chemical Properties of Dimethyldioxirane as Determined by Experiment and ab Initio Calculations Waldemar Adam,*+ Yuk-Yee Chan,tJ Dieter Cremer,! Jiirgen Gauss,s Dieter Scheutzow,+ and Michael Schindler" Institut fur Organische Chemie, Uniuersitat Wurzburg, Am Hubland, 0-8700 Wurzburg, West Germany, Institute of Photography Chemistry, Academia Sinica, Beijing, China, Lehrstuhl fur Theoretische Chemie, Uniuersitat Koln, 0-5000Koln 41, West Germany, and Lehrstuhl fur Theoretische Chemie, Ruhr- Universitat Bochum, 0-4630 Bochum, West Germany Received November 26, 1986 Dimethyldioxirane (2b), prepared by the reaction of potassium monoperoxy sulfate with acetone under buffered conditions as a yellow acetone solution, exhibits a 13C resonance at 102.30 ppm. Ab initio calculations are in good agreement with this experimental value. At room temperature the dioxirane 2b persists for ca. 7 h. The unexpected stability of this most strained cyclic peroxide is rationalized in terms of gem-dimethyl substitution, imparting thermodynamic as well as kinetic stabilization, as suggested by ab initio calculations. Oxygen transfer by dioxirane 2b to thianthrene 5-oxide (SSO) reveals a dominating nucleophilic character, causing mainly oxidation of the sulfoxide sulfur. Among the reaction intermediates, the carbonyl oxides It seemed to us, therefore, advisable to check our previous 1 and the dioxiranes 2 have received much attention from oxygen-transfer results' with the thianthrene 5-oxide (SSO) + probe by employing the recently isolated6 dimethyl- dioxirane (2b). We used this opportunity to reinvestigate the spectroscopic properties of 2b and to compare these with the results of ab initio calculations carried out for 1, 2a,b, and appropriate reference compounds. I 2a, R=H b. R=CH3 Results and Discussion the experimental and theoretical point of view, especially We found it convenient and advantageous to simplify during the last few years.'-3 Although carbonyl oxides have been invoked some 35 years ago as key species in the the published6" procedure. For large-scale preparations (more than mL 0.1 solutions of in acetone), mechanism of ozonolysis,4 only recently was it possible to 300 of M 2b provide spectral data on these elusive entities by means best results were obtained when vigorous mechanical of matrix isolation.' Dioxiranes, on the other hand, have stirring was used, a carrier gas (argon or nitrogen), mod- erately reduced pressure (ca. 150-200 Torr; water aspira- a much later history, the parent system 2a having been tor), an efficient double-jacketed spiral condenser, a re- spectroscopically detected in the gas phase.5 In fact, the action temperature of ca. 20 OC, and addition of the po- relatively stable dimethyldioxirane (2b) was recently iso- tassium monoperoxy sulfate in ca. 100-g portions over a lated in acetone solution and number of oxygen-transfer a period of 15 min. Under these operations, besides the dry reactions reported.6 ice cooled receiving flask, only one additional trap was In the interest of differentiating the nucleophilic char- necessary. The pale yellow dioxirane solution could be acter of these distinct chemical species in their oxygen concentrated maximally to ca. 0.10 by means of frac- transfer (epoxidation, sulfoxidation, etc.), we developed M thianthrene 5-oxide (SSO) as a convenient mechanistic probe.' Indeed, the carbonyl oxides 1 with their nucleo- (1) (a) Bell, G. A.; Dunkin, I. R. J. Chem. SOC.,Chem. Commun. 1983, 0 0 1213-1215. (b) Chapman, 0. L.; Hess, T. C. J. Am. Chem. SOC.1984,106, 1842-1843. (c) Dunkin, I. R.; Bell, G. A. Tetrahedron 1985,41,339-347. (d) Ganzer, G.A.; Sheridan, R. S.; Liu, M. T. H. J. Am. Chem. SOC.1986, 108,1517-1520. (e) Sander, W. Angew. Chem. 1986,98,255-256; Angew. Chem., Znt. Ed. Engl. 1986,25, 255-257. (2) (a) Talbott, R. I.; Thompson, P. G. US.Pat. 3632606, 1972. (b) Montgomery, R. E. J. Am. Chem. SOC.1974,96,7820-7821. (c) Gallopo, sso /I ss02 A. R.; Edwards, J. 0. J. Org. Chem. 1981,46,1684-1688. (d) Cicala, G.; 0 Curci, R.; Fiorentino, M.; Laricchiuta, 0. J. Org. Chem. 1982, 47, soso 2670-2673. (e) Jeyaraman, R.; Murray, R. W. J. Am. Chem. SOC.1984, 106, 2462-2463. philic pendant oxygen produced proportionally more (3) (a) Cremer, D. J. Am. Chem. SOC.1979, 101, 7199-7205. (b) Cremer, D. J. Am. Chem. SOC. 1981, 103, 3619-3626, 3627-3632, sulfone SSOz than disulfoxide SOSO compared to the 3633-3638. (c) Yamaguchi, K. J. Mol. Struct. 1983,103, 101-120. (d) dioxiranes 2. However, in those experiments7 the di- Cremer, D.; Schindler, M. Chem. Phys. Lett. 1987, 133, 293. methyldioxirane (2b) was prepared in situ from acetone (4) Criegee, R. Angew. Chem. 1975,87, 765-771. (5) (a) Lovas, F. J.; Suenram, R. D. Chem. Phys. Lett. 1977, 51, and potassium monoperoxy sulfate, and the possibility that 453-456. (b) Suenram, R. D.; Lovas, F. J. J. Am. Chem. SOC.1978,100, the "true" electronic character of the dioxirane could be 51 17-5122. obscured by oxygen transfer from unknown intermediary (6) (a) Murray, R. W.; Jeyaraman, R. J. Org. Chem. 1985, 50, 2847-2853. (b) Murray, R. W.; Jeyaraman, R.; Mohan, L. Tetrahedron oxidants in that reaction could not be rigorously excluded. Lett. 1986,27,2335-2336. (c) Murray, R. W.; Jeyaraman, R.; Mohan, L. J. Am. Chem. SOC.1986,108,2470-2472. (d) Murray, R. W.; Jeyaraman, R.; Krishna Pillay, M. J. Org. Chem. 1987,52, 746-748. (e) Cassidei, L.; + Universitat Wurzburg. Fiorentino, M.; Mello, R.; Sciacovelli, 0.;Curci, R. J. Org. Chem. 1987, 1 Academia Sinica; deceased, February 1987. 52, 699-700. f Universitat Koln. (7) Adam, W.; Hass, W.; Sieker, G. J. Am. Chem. SOC.1984, 106, I1 Ruhr-Universitat Bochum. 5020-5022. 0022-3263/87/1952-2800$01.50/0 0 1987 American Chemical Society Dimethyldioxirane J. Org. Chem., Vol. 52, No. 13, 1987 2801 Table I. lacNMR Chemical Shifts of Dimethyldioxirane Table 11. Ab Initio NMR Chemical Shifts" (2b) and Appropriate Reference Compounds Relative to 13c 'H Me&% molecule 170 molecule carbon ppm ref dioxirane (2a) CH2 82.6 CH2 4.32 250 dimethyldioxirane (2b) C 99.2 Hi 0.31 330 dimethyldioxirane (2b) CH3 22.69 this work, CH3 17.0 H, 0.73 C 102.30 and 6d, e dioxetane CH2 65.5 CHp 3.82 268 1,2-dioxetane CH2 76.14 9 acetone CO 23.5 Hi 1.16 680 acetone CH3 30.71 this work CHB 209.7 H, 1.01 co 206.52 cyclopropane CHZ -6.2 a "All values in ppm relative to MelSi (13C, 'H) or H20 (170). oxirane CH2 37.4 a Subscripts i and o denote in-plane and out-of-plane protons with n-propane CH2 12.5 a the reference plane given by the positions of the three C atoms. dimethoxymethane CH2 109.9 b MP2/6-31G* geometries have been used for 2a3aand 2b (see Fig- 1,3-dioxane C(0-)p 94.8 b ure 1). Dioxetane geometry: Schmidt, T.; Cremer, D.; unpub- 1,l-dimethylcyclopropane C(CH3)2 11.3 b lished results. Acetone geometry: ref 3d. tetramethyl-1,2,4,5-tetroxane C(CH& 106 6d "Breitmaier, E.; Voelter, W. 13C NMR Spectroscopy, 2nd ed.; Table 111. Isodesmic Stabilization Enthalpies (cf. eq 1)" Verlag Chemie: Weinheim, West Germany, 1978. * Kalinowski, molecule H2CXY AAH(1) molecule HzCXY AAH(1) H.-0.; Berger, S.; Braun, S. 13C NMR Spektroskopie; Thieme Ver- n-propane 8.5 cyclopropane 10.0* lag: Stuttgart, West Germany, 1984. dimethoxymethane 13.9 oxirane 16c ethene 12.0 oxirane (0-protonated) 25c tional distillation (bath temperature ca. 0 "C and ca. 35 formaldehyde 21.2 dioxirane 21.4d Torr). Either the dioxirane 2b and acetone form an azeotrope at this concentration or the dioxirane decom- uAAH(l) in kcal/mol. AHf0(298)values from Cox and Pilcher [Cox, J. D.; Pilcher, G. Thermochemistry of Organic and Organo- poses about at the same rate as it is being concentrated. metallic Compounds; Academic Press: New York, 19701. bAHfOof The yellow acetone solutions of 2b could be stored in 1,l-dimethylcyclopropanefrom Fuchs et al. [Fuchs, R.; Hallman, J. the freezer (ca. -20 "C) for weeks, but at room temperature H.; Perlman, M. 0. Can. J. Chem. 1982, 60, 1832-18351. (ca. 22 "C) the dioxirane content was consumed within ca. cEstimated from ab initio reaction energies AE(1). Cremer, D.; 7 h, as monitored by UV spectrometry. Its decomposition Kraka, E. J. Am. Chem. SOC.1985,107,3800-3810. dMP2/6-316* kinetics was not first order as expected but exhibited a value of AAE(1). pronounced inhibition period. For small-scale preparation of dioxirane 2b (ca. 10-15 known 13C shift values are listed that provide a basis to mL of ca. 0.10 M solutions), we found it more practical to estimate the position of this signal. Extrapolating the 13C use efficient magnetic stirring, no external carrier gas shift values for cyclopropane and oxirane to the one of 2a, (sufficient oxygen gas is self-produced during the reaction), a shift value of ca. 80 ppm can be predicted. A somewhat and to add the potassium monoperoxy sulfate all at once, higher value is obtained when comparing 13C(H2)shifts for propane, dimethoxymethane, and 1,3-dioxane (Table I). but to maintain otherwise the same reaction conditions as in the large-scale preparation. The difference in the 13C absorptions of cyclopropane and For the quantitative determination of the dioxirane 2b 1,l-dimethylcyclopropane(Table I) suggests that geminal in these acetone solutions, three methods were utilized. methyl groups lead to a downfield shift of ca. 20 ppm for These consisted of iodometric titration for peroxide con- a substituted ring carbon.
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