OZONOLYSIS OF TECHNICAL LOW-PERCENTAGE PHENANTHRENE

Communication II. Study of the ozonation reaction of various samples of low-percentage technical phenanthrenes

A. K. LEBEDEV

(Presented by the scientific-methodological seminar of the Chemical-Technological Faculty)

The solution of questions concerning the rational utilization of large-tonnage industrial wastes is of great economic importance.

One such waste is phenanthrene, contained in the anthracene fraction of coal tar; its potential resources amount to 180–200 thousand tons per year, which would fully provide a raw-material base for the production of large-tonnage products of organic synthesis.

The most advantageous route appears to be the conversion of phenanthrene into its oxidation products—2,2′-diphenic acid, its anhydride, and 2′-formyldiphenyl-2-carboxylic acid—which may find wide application in industrial organic synthesis [1–7].

As Bailey showed [8, 9, 10], on ozonizing phenanthrene (I) in methyl alcohol, a stable cyclic dimethoxy peroxide is formed, [3,8-dimethoxy-4, 5, 6, 7-dibenzo-1, 2-dioxacyclooctane] (II), which precipitates.

\[ \begin{gathered} \mathrm{I} \ \xrightarrow[\ ]{\mathrm{O_3,\ CH_3OH}}\ \mathrm{II} \ \longrightarrow\ \mathrm{III} \\[4pt] \text{a) } R=H;\quad R'=OH.\\ \text{b) } R=R'=OH.\\ \text{c) } R=H;\quad R'=OCH_3.\\ \text{d) } R=R'=H. \end{gathered} \]

From the dimethoxy peroxide (II), under definite conditions, 2′-formyldiphenyl-2-carboxylic acid (aldehyde acid) (IIIa), 2,2′-diphenic acid (IIIb), aldehyde ester (IIIc), and dialdehyde (IIId) may be obtained.

However, Bailey obtained these compounds starting from pure phenanthrene, which to the present time remains a very expensive product [11] and cannot be taken as the basis for the production of the indicated compounds.

L. P. Kulev and co-workers [12, 13] found that technical phenanthrene can be ozonized instead of pure phenanthrene. From crude anthracene from the Kemerovo Coke-Chemical Plant, samples of a technical product with different percentage contents of phenanthrene were obtained,

during the ozonization of which dimethoxy peroxide was obtained in 70% yield.

Continuing the study of the ozonolysis process of technical phenanthrene in order to determine the optimal conditions for obtaining dimethoxy peroxide, we found that samples of the technical product with a phenanthrene content of not less than 60% may be of practical interest.

The work was begun with an attempt to ozonize crude anthracene in order to obtain dimethoxy peroxide; however, this did not lead to the desired results, since crude anthracene contains considerable quantities of oils, which strongly contaminate the dimethoxy peroxide and hinder its isolation in crystalline form. Moreover, from an economic standpoint it is hardly expedient to ozonize crude anthracene without separating the main mass of carbazole and anthracene. In addition, the ozone consumption increases greatly, and the separation of the resulting products presents great difficulties.

In the ozonization of a technical product with a phenanthrene content from 42 to 60%, it is possible to obtain highly contaminated dimethoxy peroxide in a yield of 40 to 70%, with a melting point 10–20° lower than that of the pure substance.

Table 1 gives data on the ozonolysis of samples of technical phenanthrene with different percentage contents of phenanthrene.

Table 1

All known schemes for separating crude anthracene lead to the production of a phenanthrene fraction containing from 60 to 70 percent phenanthrene [14, 15, 16, 17].

Therefore, all subsequent experiments, in order to develop the optimal conditions for obtaining dimethoxy peroxide, were carried out with technical phenanthrene containing 60–70 percent phenanthrene.

Bailey ozonized pure phenanthrene in absolute methyl alcohol in a phenanthrene:alcohol ratio of 1:25 at a temperature from −20 to 0°. We found that an essential condition for carrying out the reaction is the use of a strictly definite amount of alcohol, since decreasing or increasing the latter leads to a decrease in the yield of dimethoxy peroxide. Decreasing or increasing the reaction time also lowers the yield of dimethoxy peroxide. The use of methyl alcohol containing several percent of water has no substantial effect on the yield and quality of dimethoxy peroxide; in addition, it was found that raising the temperature of the reaction medium from −20 to +20° does not noticeably affect the process.

The work was carried out on a scaled-up laboratory ozonator unit, constructed according to the type described in the literature [18], which, under certain conditions, gave from 4 to 7% ozone by weight.

Experimental Part

Optimal conditions for obtaining 3,8-dimethoxy-4, 5, 6, 7-dibenzo-1, 2-dioxocyclooctane (dimethoxy peroxide). 30 g of technical 70% phenanthrene were placed in a round-bottom flask equipped with a reflux condenser; 300 ml of methanol were added, and the mixture was heated on a water bath until complete dissolution. The solution was then rapidly cooled with cold water to obtain a fine suspension, and the mixture was transferred into a glass reaction vessel for ozonation, through the porous bottom of which a stream of ozone–oxygen mixture containing 4–7% ozone by weight was passed. The ozonation reaction was conducted at −10 to +20°C for 60 minutes. Toward the end of the reaction almost the entire solid phase passed into solution, which became light yellow in color. After this the ozonator was switched off and, in order to remove excess ozone, pure oxygen was blown through the reaction mixture for 2 minutes. The reaction mixture was then immediately filtered through a No. 2 glass filter. A small light-yellow precipitate on the filter was separated and dried. To the filtrate were added 10–15 drops of concentrated hydrochloric acid. Crystals of dimethoxy peroxide immediately began to separate; this was completed when the solution stood for 6–8 hours. The separated crystals of dimethoxy peroxide were filtered off on a No. 2 glass filter, washed with 75–100 ml of methanol, and dried at a temperature of 60–80° (not higher) for one hour.

26.65 g of dimethoxy peroxide were obtained. Melting point 175–177°.

The yield, calculated from the theoretical amount based on the pure phenanthrene contained in the technical product, was 83.3%. The light-yellow precipitate obtained after filtration of the reaction mixture was identified as anthraquinone.

The weight of the precipitate was 0.9–1.0 g, m.p. 256–263°, which corresponds to an anthraquinone yield from the anthracene contained in the technical phenanthrene of about 32%.

The filtrate obtained after separation of the dimethoxy peroxide was placed in a flask equipped with a packed column and a straight condenser, and the methanol was distilled off on a water bath; in this way not less than 95 percent of the methanol is regenerated and returned again to the cycle. The still residue after distillation of the methanol, containing various compounds, is, in appearance, a resinous black product. The results of a preliminary investigation of the still residue will be discussed below.

Samples of the technical product obtained from crude anthracene from the Kemerovo coke-chemical plant, which contained 69–70% phenanthrene, 9–10% anthracene, and 10–12% carbazole, were subjected to ozonation. The average dependence of the yield of dimethoxy peroxide on the reaction time, from three determinations for each time interval, is presented in Fig. 1.

The same dependence, obtained by us for pure phenanthrene, is presented in Fig. 2.

It is known [8–9] that 1.1–1.2 moles of ozone are consumed for the ozonolysis of 1 mole of pure phenanthrene. But since technical phenanthrene contains 30–40% impurities, for the ozonation of which ...

ozone, the necessary amount of ozone, or the optimal ozonation time for technical phenanthrene, has to be found experimentally.

Knowing the ozone output of the ozonizer and the amount of ozone required for ozonation of one mole of phenanthrene contained in the technical product, it is easy to calculate the time required to obtain the maximum yield of dimethoxy peroxide.

To determine the possibility of applying the ozonolysis method to technical phenanthrenes obtained from other coals and at other coke-chemical plants, we ozonized, according to the procedure described above, floated phenanthrene from the Dnepropetrovsk Coke-Chemical Plant, containing 67–70% phenanthrene, 9–11% anthracene, and 10–12% carbazole, and technical phenanthrene obtained at the Nizhne-Tagil Metallurgical Combine, containing 70–72% phenanthrene.

The results obtained are presented in Tables 2 and 3.

Table 2

Dependence of the yield of dimethoxy peroxide on the ozonation time
(Dnepropetrovsk technical phenanthrene)

Table 3

Dependence of the yield of dimethoxy peroxide on the ozonation time
(technical phenanthrene of the Nizhne-Tagil MC)

*) DMP—dimethoxy peroxide.

From the data in Tables 1–3 and Fig. 1 it is evident that, in the ozonolysis of technical phenanthrene, samples containing not less than 60 percent phenanthrene may be of practical interest and economically expedient. In the ozonolysis of 70% phenanthrene isolated from crude anthracene or anthracene oil from the Kemerovo and Dnepropetrovsk coke-chemical plants or the Nizhnii Tagil Metallurgical Combine, dimethoxy peroxide is obtained in the same yield. It is obvious that the various samples of technical phenanthrenes obtained from different coals and at different coke-chemical plants contain no impurities that can interfere with the preparation of dimethoxy peroxide; moreover, the yield and quality of the resulting dimethoxy peroxide are not inferior to the yield and quality of the latter obtained from pure phenanthrene.

Fig. 1.

Fig. 2.

Thus, it may be considered proven that the ozonolysis method for technical phenanthrene can be applied to samples of the technical product obtained from different coals and at different coke-chemical plants.

Study of the still residue from the ozonolysis reaction of technical phenanthrenes

We observed that, on standing, a solid crystalline product precipitates from the still residue. To separate the crystalline product, a sample of resin (still residue) of 500 g, after the lumps had been ground, was stirred with methyl alcohol at room temperature (16–20°) in resin:alcohol ratios of 1:2, 1:3, and 1:4. The resulting mixture was filtered on a Büchner funnel. The precipitate on the filter was washed with a small amount of methanol and dried (the wash alcohol is included in the above resin:alcohol ratios). 150–180 g of crystalline product was obtained. Methanol was distilled off from the filtrate and returned to the cycle. Still residue II (resin II) was distilled under vacuum.

The results of isolation and analysis of the crystalline product are presented in Table 4.

Table 4

The best conditions for isolating the crystalline product are those of experiments 2 and 3. The average yield of product is 34% of the resin.

From resin (II), at 110–120°, the water formed in the ozonolysis reaction of phenanthrene and passing into the still residue was distilled off.

The dehydrated resin II was distilled under vacuum at a residual pressure of 5 mm Hg; fractions were collected at specified temperatures.

The results obtained are presented in Table 5.

Table 5

In each of the fractions obtained, a solid precipitate separates. The precipitate was filtered on a no. 2 glass filter and washed with a small amount of methanol. A very white crystalline substance was obtained. Under the microscope these were colorless crystals in the form of plates.

From each fraction of experiment no. 1, white crystals were isolated:

In all, 25.37 g of white crystals were obtained.

Elemental analysis of the white product. Found: C = 92.1%; H = 6.35%.

Nitrogen was not found. The qualitative test for sulfur was negative.

Upon recrystallization of this product from methanol, crystals with m.p. 104–114° and 100–109° were obtained; from n-hexane, with m.p. 131–149 and 90–93°.

From the foregoing it may be concluded that the white crystalline product isolated from resin II is a mixture of polycyclic hydrocarbons, the identification of which requires further investigation. The filtrate (142 g) obtained from the vacuum distillation fraction of resin II, after separation of the white crystalline product

is a transparent, readily mobile oil of cherry color, the composition and properties of which have not yet been studied.

Conclusions

1. The optimal conditions have been found for obtaining dimethoxy peroxide by the ozonolysis reaction of low-percentage technical phenanthrenes.

2. The possibility has been demonstrated of applying the ozonolysis method to various samples of low-percentage technical phenanthrenes isolated from anthracene fractions of various coal-tar pitches; in this case, dimethoxy peroxide is obtained in the same yield.

3. A procedure has been developed for isolating anthraquinone, obtained as a by-product in the ozonation of technical phenanthrenes.

4. Preliminary studies have been carried out on the still residue from the ozonation reaction of technical phenanthrenes.

Literature

1. A. A. Snedze. Bull. United Paint and Varnish Industry 8, 17, 1939.

2. R. E. Dean, E. N. White, D. McNeil. J. Appl. Chem. 3, 469, 1953.

3. L. P. Kulev. Abstracts of reports at the All-Union Interinstitutional Conference on the Chemistry and Technology of Polymers, MITKhT, 93, 1960.

4. U. S. P. 2,631,248; C. A. 47, No. 7825, 1953.

5. P. Z. Li, Z. V. Mikhailova, P. P. Sedov. Plast. Massy No. 3, 14, 1959.

6. U. S. P. 2,785,076. 1957; RZh Khim. 9262, 1959.

7. N. D. Rusyanova et al. Abstracts of reports at the conference on polymeric materials based on chemical products of coal coking, p. 82. Dnepropetrovsk, 1964.

8. P. S. Bailey. J. Am. Chem. Soc. 78, 3811, 1956.

9. P. S. Bailey, S. B. Mainthia. J. Org. Chem. 21, 1335, 1956.

10. P. S. Bailey, S. B. Mainthia. J. Org. Chem. 23, 1089, 1953.

11. Price list 05-11 of wholesale prices for chemical reagents and preparations, p. 103, Moscow, 1962.

12. L. P. Kulev, V. A. Salskii. Author’s Certificate 137926, 1961.

13. L. P. Kulev, V. A. Salskii, A. K. Lebedev, V. P. Shabrov. Journal of the All-Union Chemical Society, vol. VII, No. 5, 599, 1962.

14. L. D. Gluzman, M. A. Krasovitskaya. POKh 4, No. 19, 353, 1937.

15. L. D. Gluzman. Coke and Chemistry, No. 2, 39, 1959.

16. N. D. Rusyanova et al. Coke and Chemistry, No. 7, 48, 1961.

17. See 7, I. E. Ruzhina et al., p. 86.

18. Syntheses of Organic Preparations, collection 4, p. 382, 1949.

19. W. J. Schmitt et al. J. Am. Chem. Soc. 77, 5640, 1955.