Ozonolyses of Cyclopolyenes Adsorbed on Polyethylene

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RESULTS AND DISCUSSION

Ozonolysis of 8a and of 8b on polyethylene afforded the corresponding diozonides 11a and 11b in yields of ca. 21.2 and 26.3%. A small sample was extracted with CDCl3 and 1H NMR analysis of the extracted showed the presence of ozonides 11 and unreacted cyclopolyenes 8. There was no evidence for the formation of the corresponding monoozonides of type 10.

Ozonolysis of 9a and 9b on polyethylene afforded the corresponding monoozonides 12a and 12b and the corresponding diozonides 13a and 13b in yields of ca. 9.8, 8.7, 13.3, and 12.2%, respectively.

From these results it can be concluded that, in contrast to cyclopolyenes 8, the double bonds in aromatic compounds 9a and 9b are attacked stepwise by ozone to give equal amounts of mono- and diozonides.

Finally, ozonolyses of 9c on polyethylene afforded the corresponding monoozonide 12c in yield of ca. 14.9%.

The structures of all isolated ozonides were established by 1H and 13C NMR spectroscopy, and by their reduction with triphenylphosphine to give the expected dicarbaldehydes. Characteristic signals in 1H NMR spectra were those of the CH groups in the ozonide rings appearing in the range of 5.28-5.43 for ozonides 11a-b and in the range of δ 5.63-6.67 for ozonides 12a-b and 13a-b as singlet. In the 13C NMR spectra of all ozonides, the two carbon atoms in the ozonide ring exhibited signals in range of δ 99.33-106.63.

The results reported in this paper demonstrate that the ozonolysis of olefins on polyethylene is widely applicable for the preparation of ozonides that have not been accessible by the hitherto available preparation methods.

 

EXPERIMENTAL SECTION

Brucker AC-300 spectrometer in CDCl3 with TMS as internal reference. Chromatographic separations were carried out by flash chromatography on silica gel.

Procedure for Ozonolyses of Olefins on Polyethylene

(a) Pretreatment of Polyethylene.2 Polyethylene (Microethene FN 500 from Serva Feinbiochemica, Heidelberg, Germany; spherical particles, maximum size 20 μm) was continuously extracted with ether for 24 h to remove soluble components. Subsequently, it was dried at room temperature and 10−3 Torr for 24 h.

(b) Loading of the Olefin.2 The dried polyethylene was placed into a round-bottom flask and admixed with so much of a diethyl ether that the resulting suspension could be stirred. Then the olefin was added, the mixture was stirred for ca. 15 min., the solvent was removed by suction at room temperature, and the loaded polyethylene was transferred into an adsorption tower.

(c) Ozonolysis of the Olefin.3,4 The loaded adsorption tower was placed into a bath that had the desired temperature, and an O3/O2 stream (ca. 1 mmol of O3/L of gas) was passed through the tower at a rate of ca. 20 L/h. After completion of the ozonolysis, dried nitrogen was passed through the tower until residual ozone was removed, the tower was warmed up to room temperature, and the polyethylene was transferred into a round-bottom flask and repeatedly extracted with an appropriate solvent.

Reductions of Ozonides: A solution of 20-80 mg of an ozonide and an excess of triphenylphosphine in 0.6 mL of CDCl3was kept at room temperature for 24 hours. The products were analyzed by 1H NMR spectroscopy.

Ozonolysis of 1,3-cyclooctadiene (8a): Compound 8a (0.5 g, 4.62 mmol) was loaded on 40 g polyethylene and ozonized for 6 h at -78 ℃. The products were extracted with ether, and the combined extracts were distilled at room temperature and 15 Torr to leave 0.45 g of a peroxidic residue. From the residue, 200 mg (0.98 mmol, 21.2%) of ozonide 11a was isolated by column chromatography (silica gel, pentane / diethyl ether, 1 : 1).

1,3-Cyclooctadiene diozonide (11a): Colorless liquid; 1H NMR: δ 1.58-1.67 (m, 2H), 1.90-2.03(m, 6H), 5.33 (m, 4H); 13C NMR δ 20.45, 27.50, 100.05, 104.30. Anal. Calcd for C8H12O6(204): C, 47.05; H, 5.92. Found: C, 47.25; H, 6.04. Reduction of 11a with TPP gave hexanedial.

Ozonolysis of 1,5-cyclooctadiene (8b): Ozonolysis of 8b (0.5 g, 4.62 mmol) gave a peroxidic residue. From the liquid residue, 250 mg (1.22 mmol, 26.3%) of ozonide 11b was isolated by column chromatography (silica gel, pentane/diethyl ether, 1 : 2).

1,5-Cyclooctadiene diozonide (11b): Colorless liquid; 1H NMR: 1.96-2.07 (m, 8H), 5.37 (t, J=3 Hz, 4H), 13C NMR δ 25.01, 101.99. Anal. Calcd for C8H12O6(204): C, 47.05; H, 5.92. Found: C, 46.88; H, 5.98.

Reduction of 11b with TPP gave butanedial [1H NMR δ 2.67, 9.69].

Ozonolysis of pyrene (9a): Compound 9a (0.5 g, 2.47 mmol) was loaded on 40 g polyethylene and ozonized for 4 h at -78 ℃. The products were extracted with ether, and the combined extracts were distilled at room temperature and 15 Torr to leave 0.45 g of a peroxidic residue. From the residue, 60 mg (0.24 mmol, 9.8%) of monoozonide 12a and 100 mg (0.34 mmol, 13.3%) of diozonide 13a were isolated by column chromatography (silica gel, pentane / diethyl ether, 1 : 1).

Pyrene monoozonide (12a): Colorless crystals; mp 162-164 ℃ (Lit. 8, 163~165 ℃); 1H NMR: δ 6.67 (s, 2H), 7.57-8.05 (m, 8H), 13C NMR: δ 106.63, 125.36, 126.20, 126.51, 127.81, 128.20, 129.18, 131.56, 135.06. The data are identical to those reported.8

Reduction of 12a with TPP gave phenanthrene-4,5-dicarbaldehyde [1H NMR: δ 7.41-8.14(m), 10.03].

Pyrene diozonide (13a): Colorless crystals; mp 71 ℃; 1H NMR: δ 6.40 (s, 4H), 7.47 (m, 6H), 13C NMR: δ 105.73, 128.36, 132.85, 132.96, 138.20. Anal. Calcd for C16H10O6(298): C, 64.44; H, 3.38. Found: C, 64.66; H, 3.42.

Reduction of 13a with TPP gave biphenyl-2,2',6,6'-tetracarbaldehyde [1H NMR δ 7.20-8.21 (m), 9.69].

Ozonolysis of naphthalene (9b): Ozonolysis of 9b (0.5 g, 3.08 mmol) gave a peroxidic residue. From the residue, 60 mg (0.34 mmol, 8.7%) of monoozonide 12b and 110 mg (0.49 mmol, 12.2%) of diozonide 13b were isolated by column chromatography (silica gel, pentane / diethyl ether, 1 : 1).

Naphthalene monoozonide (12b): Colorles liquid; 1H NMR δ 6.37 (s, 2H), 7.71-7.95 (m, 6H); 13C NMR 98.25, 102.74, 123.67, 123.81, 124.43, 125.83, 127.60, 129.78, 131.17, 134.78. Anal. Calcd for C10H8O3(176): C, 68.17; H, 4.58. Found: C, 68.26; H, 4.64.

Naphthalene diozonide (13b): Colorless liquid; 1H NMR δ 5.63 (s, 2H), 6.11 (s, 2H), 7.44 (m, 4H), 13C NMR δ 99.33, 105.53, 131.42, 132.32, 133.30. Anal. Calcd for C10H8O6(224): C, 53.57; H, 3.60. Found: C, 53.32; H, 3.48.

Reduction of 13b with TPP gave benzene-1,2-dicarbaldehyde [1H NMR δ 7.21-7.69, 10.51].

Ozonolysis of 1,2-dihydronaphthalene (9c): Ozonolysis of 9c (0.5 g, 3.84 mmol) gave a peroxidic residue. From the residue, 100 mg (0.56 mmol, 14.9%) of ozonide 12c was isolated by column chromatography (silica gel, pentane / diethyl ether, 1 : 1).

1,2-Dihydronaphthalene monoozonide(12c): Yellow crystal; mp 123~124 ℃; 1H NMR δ 2.04-2.16 (m, 2H), 2.71-2.77 (m, 1H), 3.53 (m, 2H), 5.91 (s, 1H), 6.15 (s, 1H), 7.20-7.30 (m, 5H); 13C NMR δ 30.11, 33.03, 103.93, 105.96, 126.68, 128.81, 130.13, 130.89, 136.82, 141.02. Anal. Calcd for C10H10O3(178): C, 67.40; H, 5.66. Found: C, 67.55; H, 5.55.

Reduction of 12c with TPP gave o-(2-formylethyl) benzaldehyde [1H NMR δ 2.72, 3.31, 9.75, 10.10].