PREPARATION OF PHENANTHRENE OXIDATION PRODUCTS BY OZONOLYSIS

L. P. KULEV, V. A. SAL’SKII, G. V. SHISHKIN

It is known that phenanthrene, which is present in considerable amounts in the anthracene fraction of coal tar, has not yet found advantageous routes of application. At the same time, the potential resources of phenanthrene in the Soviet Union are estimated at tens of thousands of tons per year, which may serve as a reliable basis for large-tonnage organic synthesis.

In recent years, much attention has been paid to the problem of the rational use of phenanthrene in the chemical industry. Of particular interest in this respect may be the oxidation products of phenanthrene: diphenic acid, its anhydride, and 2′-formyldiphenyl-2-carboxylic acid.

Diphenic acid has been recommended by a number of authors for the preparation from it of polymeric materials of the alkyd-resin type [1, 2] and of plasticizers [3]. Several methods for preparing diphenic acid have been described in the literature; among them, the most convenient should be considered those based on the oxidation of phenanthrene with 30–50% hydrogen peroxide in acetic acid [2, 4], or with ready-made peracetic acid. The maximum yield of diphenic acid by the indicated methods reaches 50–70% of theoretical.

Diphenic anhydride, which is required for the synthesis of many practically interesting derivatives of this acid, is usually obtained by treating it with acetic anhydride in glacial acetic acid, which considerably increases its cost.

Among the oxidation products of phenanthrene, the least studied is 2′-formyldiphenyl-2-carboxylic acid, for which, until recently, no sufficiently simple and convenient method of preparation had been developed. Owing to the presence of a free aldehyde group, this acid, as our preliminary experiments have shown, can be successfully used in the synthesis of dyes and polymeric materials.

2′-Formyldiphenyl-2-carboxylic acid was obtained by Cook and co-workers [6] by saponification of the benzosulfhydrazide of diphenic acid; Stephenson [7] gives a method for preparing the aldehyde acid by oxidation of diphenic acid hydrazide with sodium metaperiodate. A more convenient and promising method for preparing 2′-formyldiphenyl-2-carboxylic acid is the ozonolysis of phenanthrene.

The ozonation reaction of phenanthrene was first carried out by Harries and Weiss [8]. They obtained an explosive product, identified

them, according to elemental analysis, as diazonides; however, the authors were unable to determine the nature of the decomposition products of this compound.

Considerably later, Schmitt, Moriconi, and O’Connor [9] repeated this work and showed that in chloroform and in acetic acid 1 mole of phenanthrene reacts with only one mole of ozone, the addition taking place at the site of cleavage of the double bond in positions 9,10. We carried out work [10] on the hydrolysis of the products of ozonization of phenanthrene and on their oxidation to diphenic acid. The yield of diphenic acid in this case did not exceed 56%.

The mechanism of the ozonolysis of phenanthrene in chloroform, acetic acid, and methanol was studied in greater detail by Bailey and co-workers [11, 12, 13].

On the basis of Criegee’s work, whose investigations in the field of ozonization reactions are the most significant, and also on the basis of his own experimental data, Bailey proposed a scheme for the ozonolysis of phenanthrene explaining the direction of the reaction as a function of the nature of the solvent.

In the ozonolysis of phenanthrene in chloroform, it is not the monomeric ozonide I that is formed, as was found by Schmitt and co-workers [9], but a polymer of the bipolar ion II, the formation of which in the interaction of ozone with unsaturated compounds is a fundamental proposition of Criegee’s theory of ozonization [14].

The structure of the polymeric product of the ozonolysis of phenanthrene in chloroform probably corresponds to scheme III, where \(n\), depending on the experimental conditions, is equal to 1–4.

\[ \begin{array}{c} \text{I} \qquad \text{II} \qquad \text{III} \\ \text{[structural formulas of phenanthrene ozonolysis products I, II, and polymeric product III, as shown]} \end{array} \]

The structure of compound III was confirmed by analysis of its IR spectra, elemental analysis, analysis for active oxygen, and determination of molecular weight by the cryoscopic method in various solvents.

In the ozonolysis of phenanthrene in glacial acetic acid there is formed a mixture of polymeric ozonide III and acetoxy hydroperoxide IV.

\[ \text{IV: [structural formula of acetoxy hydroperoxide, as shown]} \]

When this same reaction is carried out in methanol at low temperatures, amphion II forms the slightly stable methoxy hydroperoxide V, which, with increasing temperature, is converted into the less soluble cyclic dimethoxy peroxide VI, precipitating from methanol. Under appropriate treatment, the latter can be converted into aldehyde ester VII or 2′-formyldiphenyl-2-carboxylic acid VIII.

\[ \text{V} \longrightarrow \text{VI} \longrightarrow \text{VII} \xrightarrow{\mathrm{NaOH}} \text{VIII} \]

\[ \begin{array}{c} \text{[structural formulas V, VI, VII, and VIII, as shown in the reaction scheme]} \end{array} \]

This acid was obtained by Bailey [11] by hydrolysis of pure dimethoxy peroxide VI with alkali in aqueous alcohol. The overall yield of the aldehyde acid from phenanthrene by the proposed procedure does not exceed 60%.

The aim of the present work was to find optimal conditions for the synthesis of 2′-formyldiphenyl-2-carboxylic acid by ozonolysis of phenanthrene and to develop a simple and economically advantageous method for obtaining diphenic anhydride from it.

In contrast to Bailey’s method, the ozonolysis of phenanthrene was carried out by us not in pure methanol, but in a mixture of dichloroethane or carbon tetrachloride with methanol (1 : 1) at a higher temperature (−5°C—+5°C). Hydrolysis of the ozonolysis products is effected with a 5% NaOH solution without isolating them from the reaction mixture, with simultaneous distillation of the solvent. The aldehyde acid was precipitated from the reaction mixture with dilute hydrochloric acid and purified under vacuum. The aldehyde acid thus obtained in the form of a yellowish glassy mass was precipitated from its sodium carbonate solution with simultaneous recrystallization from weak acetic acid; for this purpose, before adding hydrochloric acid, a small amount of sodium acetate was introduced into the sodium carbonate solution of the aldehyde acid.

Under these conditions the volume of the reaction mixture during ozonolysis is reduced by half, the danger of explosion is eliminated, and the yield of aldehyde acid is considerably increased (by 15–17%).

Fig. 1.

The IR spectrum obtained by us for 2′-formyldiphenyl-2-carboxylic acid (Fig. 1) shows the presence of a carbonyl absorption band in the region 1660–1700 cm⁻¹, typical of aldehydes and carboxylic acids, and a broad associated band in the region 1200–1300 cm⁻¹, characteristic of the aldehyde group.

The UV spectrum of the aldehyde acid in hexane (Fig. 2) has two absorption bands with maxima at 226–289. The first of these is probably due to absorption by the carbonyl of the aldehyde group, and the second to selective absorption by the carboxyl.

With concentrated sulfuric acid, the aldehyde acid gives an intense green coloration ($\varepsilon = 3000$), which can be used for its identification (Fig. 3).

Diphenic anhydride was obtained by oxidative chlorination of the aldehyde acid under definite temperature conditions according to the scheme (see p. 26).

In the work an ozonizer of the usual type [15] was used, giving 4% ozone by weight at an oxygen flow rate of 80 l/hr and a voltage of 15 kV. The end of the reaction was determined by the cessation of absorption of ozone by the reaction mixture (test with neutral KI solution).

\[ \text{2′-formyldiphenyl-2-carboxylic acid} \xrightarrow[\,-\mathrm{HCl}\,]{\mathrm{Cl_2}} \text{acid chloride} \xrightarrow{\,-\mathrm{HCl}\,} \text{cyclic anhydride} \]

In the ozonolysis experiments, reagent-grade phenanthrene from the Kharkov Coke-Chemical Plant, with m.p. \(99.5^\circ\mathrm{C}\), was used.

Fig. 2.

Fig. 3.

The IR spectrum was obtained on a modernized IKS-11 spectrometer [16]. Formyldiphenyl-2-carboxylic acid was taken as a melt in a thin layer between two KBr plates. The UV spectrum was obtained on an SF-4 spectrophotometer; the absorption spectrum of the aldehydo acid in sulfuric acid was recorded on an SF-2 spectrophotometer.

Experimental Part

Preparation of 2′-formyldiphenyl-2-carboxylic acid

Into an ice-cooled cylindrical vessel with a porous plate at the bottom was placed a suspension of \(5.34\ \mathrm{g}\) (\(0.03\ \mathrm{mol}\)) of phenanthrene in \(25\ \mathrm{ml}\) of anhydrous methanol and \(25\ \mathrm{ml}\) of dichloroethane or carbon tetrachloride, and a stream of ozonized oxygen was passed into the lower part of the vessel. After completion of the reaction, the mixture was poured into a flask and allowed to stand at room temperature until complete precipitation of dimethoxy peroxide from the solution; this can be accelerated by adding a drop of concentrated hydrochloric acid. Then \(50\ \mathrm{ml}\) of a \(5\%\) NaOH solution was poured into the mixture and the solvents were distilled off on a steam bath using an efficient column. Toward the end of the hydrolysis, the test for active oxygen [17] should be negative. Otherwise the column was replaced by a reflux condenser and heating was continued for another 1 hour. Then \(0.5\ \mathrm{g}\) of activated carbon was added, the mixture was boiled for 10 minutes, cooled, filtered, and the aldehydo acid was precipitated from the filtrate with \(10\%\) HCl as a thick oil that solidified on standing. After distillation in vacuo (\(225–230^\circ\) at \(15\ \mathrm{mm}\)) and repeated slow precipitation from \(50\ \mathrm{ml}\) of soda solution with hydrochloric acid, with preliminary add-

with 1 g of sodium acetate. Yield of the aldehyde acid 5.4 g (80% of theoretical), mp 132° (6, 7, 11).

Preparation of Diphenic Anhydride

6.78 g (0.03 M) of 2′-formyldiphenyl-2-carboxylic acid was heated in a sulfuric-acid bath to 140°, and a stream of dry chlorine was passed through the melt until the product began to solidify. The temperature was then gradually raised to 220°C, and chlorine was passed through until the liquid had completely changed into the crystalline state. The duration of chlorine passage from the start of the experiment was about 40 min. The yellowish-colored product was recrystallized twice from dichloroethane. Yield of diphenic anhydride with mp 216–217° [18]: 90% of theoretical (calculated on the aldehyde acid).

Conclusions

1. By ozonolysis of phenanthrene in a mixture of methanol with dichloroethane or carbon tetrachloride, 2′-formyldiphenyl-2-carboxylic acid was obtained in yields up to 80%. The IR and UV absorption spectra of the aldehyde acid and the absorption spectrum of its solution in concentrated acid were obtained.

2. A method has been developed for preparing diphenic anhydride from 2′-formyldiphenyl-2-carboxylic acid in 90% yield by oxidative chlorination of it under specified temperature conditions.

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