PATHWAYS FOR THE USE OF CERTAIN OXIDATION PRODUCTS OF PHENANTHRENE IN ORGANIC SYNTHESIS

L. P. Kulev

We have reported [1, 2] that, among the oxidation products of phenanthrene, 2-formyldiphenyl-2-carboxylic acid, 2,2-diphenic acid and its anhydride deserve particular attention; from these it is possible to obtain an entire series of derivatives of great practical interest.

Diphenic acid, being close in its chemical nature to phthalic acid, behaves analogously to the latter in many syntheses; however, the products obtained from it differ substantially in a number of respects from the corresponding products derived from phthalic acid. Thus, alkyd resins based on diphenic acid or its anhydride possess higher thermal stability and give a stronger film than glyptal resins [3]. Plasticizers from the same acid [4, 5] are characterized by higher dielectric properties in comparison with dialkyl phthalates, etc.

It may be expected that the structural features—above all the presence in the diphenic acid molecule of two benzene rings—will, to one degree or another, also have a favorable effect on the properties of other derivatives of this acid.

The investigation undertaken by us in this direction confirmed the assumption stated above.

From derivatives of diphenic acid we obtained a large series of complete and partial esters of aliphatic alcohols and phenols, aryl amides, and compounds with mixed functions, not described in the literature, of the following types:

\[ \begin{gathered} \text{[diphenyl]}-\mathrm{COOAlk};\quad \text{[diphenyl]}-\mathrm{COOAlk};\quad \text{[diphenyl]}-\mathrm{COOAlkX};\quad \text{[diphenyl]}-\mathrm{COOArX};\quad \text{[diphenyl]}-\mathrm{CONHArX};\\ \text{[diphenyl]}-\mathrm{COOAlk};\quad \text{[diphenyl]}-\mathrm{COOArX};\quad \text{[diphenyl]}-\mathrm{COOArX};\quad \text{[diphenyl]}-\mathrm{COOArX};\quad \text{[diphenyl]}-\mathrm{COOAlk}; \end{gathered} \]

\[ \begin{gathered} \text{[diphenyl]}-\mathrm{CONHArX};\quad \text{[diphenyl]}-\mathrm{CONHArX};\quad \text{[diphenyl]}-\mathrm{CO}> \mathrm{N{-}ArX};\\ \text{[diphenyl]}-\mathrm{COOAr};\quad \text{[diphenyl]}-\mathrm{CONHArX};\\ \mathrm{Ar}=\mathrm{C_6H_5};\ \mathrm{C_{10}H_7};\quad X=\mathrm{Cl};\ \mathrm{NO_2};\ \mathrm{CH_3}. \end{gathered} \]

The synthesis of these compounds was undertaken by analogy with the known derivatives of phthalic acid, with the aim of discovering new herbicides,

growth stimulants, insecticides, and plasticizers. Preliminary tests carried out under field conditions with respect to certain weeds (scentless chamomile, goosefoot, meadow grass) showed that the most active of them in their herbicidal action are the fully and partially chloro- and nitro-substituted arylamides of diphenic acid, for example:

\[ \begin{gathered} \text{bis(}p\text{-nitroanilide of diphenic acid)};\qquad \text{bis(}p\text{-chloroanilide of diphenic acid)};\\ \text{bis(}p\text{-toluidide of diphenic acid)};\qquad \text{diphenic acid imide with a naphthyl substituent} \end{gathered} \]

As contact-action insecticides, the chloro- and nitro-substituted arylalkyl esters of diphenic acid are apparently of the greatest interest.

Esters of higher fatty alcohols (heptyl, octyl, nonyl, and decyl), as well as isoamyl alcohol, exhibited good plasticizing properties for glyptal chloride, which is confirmed by the data in Table 1.

Table 1

Table 2

Esters of diphenic acid

Noteworthy are the high dielectric properties of plasticizers based on these esters, and the comparatively low frost resistance of some of them.

Recently, mixed arylalkyl esters of diphenic acid have also been obtained; their plasticizing properties are being tested at the Novosibirsk Branch of the Leningrad Institute of Polymer Plastics. Some properties of these esters are given in Table 2.

With diphenic acid and diphenic anhydride, alkyd resins of the glyptal type have been obtained. A resin from diphenic anhydride and pentaerythritol, modified with oleic acid and maleic anhydride, has essentially the same properties as analogous resins based on phthalic anhydride, but differs from them in having a higher softening temperature and better qualities of the film prepared from it. Thus, diphenic acid should be regarded not only as a good substitute for phthalic acid, obtained from wastes of coke-chemical production, but to a much greater extent as a valuable starting material that may also have independent importance for industrial organic synthesis.

Alongside the search for new ways of using diphenic acid and its anhydride in the synthesis of various substances, work has been carried out on the preparation and use of 2-formyldiphenyl-2-carboxylic acid.

Of the methods described in the literature for preparing this acid [6, 7, 8], the method based on the ozonolysis of phenanthrene is of the greatest practical interest.

In simplified form, the scheme for obtaining 2-formyldiphenyl-2-carboxylic acid (V) by this method may be represented as follows:

\[ \ce{ phenanthrene ->[O3,\ CH3OH] II ->[{\Delta}] III ->[NaOH] IV ->[HCl] V } \]

where the intermediates and products shown in the scheme are:

\[ \ce{ II:\ o\text{-}C6H4(C6H4-CHO)(CHOOH)(OCH3) \qquad III:\ \text{dimethoxy peroxide} \qquad IV:\ o\text{-}C6H4(C6H4-CHO)(COONa) \qquad V:\ o\text{-}C6H4(C6H4-CHO)(COOH) } \]

This reaction was studied most fully by Bailey [8, 9, 10], who proposed a scheme for the ozonolysis of phenanthrene explaining the direction of the process as a function of the nature of the solvent. Thus, in the presence of methanol, an unstable methoxyhydroperoxide (II) is first formed; with an increase in temperature it passes into the more stable and less alcohol-soluble dimethoxy peroxide (III). The latter, by filtration, is freed from soluble impurities and is readily saponified with formation of the aldehydo acid (V). Bailey obtained this acid in a yield of up to 60% based on phenanthrene by hydrolysis of the pure dimethoxy peroxide in an aqueous-alcoholic medium.

Taking into account that 2-formyldiphenyl-2-carboxylic acid can be successfully used for the synthesis of various condensation products, we first of all set ourselves the goal of determining the possibility of obtaining it from inexpensive raw material, since in the methods described in the literature the authors proceeded from reagent-grade phenanthrene, i.e., from a product still scarcely available and expensive, which cannot serve as the basis for industrial production of the aldehydo acid.

For the experiments, crude anthracene from the Kemerovo Coke-Chemical Plant was taken, containing 17–19% phenanthrene. By means of the usual methods of isolating and purifying phenanthrene, namely by extracting it

solvents and distillation (the fraction boiling within the range 320–340° was collected), samples of technical phenanthrene with different contents of pure product in them were obtained.

Ozonation of the indicated samples was carried out in the same apparatus as the ozonation of pure phenanthrene [2], but using methanol alone as the solvent; in it, as it turned out, almost all the reaction products dissolve well, with the exception of dimethoxyperoxide. After separation and washing with methanol, the dimethoxyperoxide can be used to obtain 2′-formyldiphenyl-2-carboxylic acid without additional purification.

The results of the experiments are presented in Table 3.

Table 3

Consequently, the possibility of using technical low-grade phenanthrene for obtaining dimethoxyperoxide, and from it 2′-formyldiphenyl-2-carboxylic acid, may be considered proven. The economic advantage in this case is very substantial. According to our approximate estimates, the cost of chemically pure aldehydo acid obtained, for example, from 65% phenanthrene is 18–20 times lower than the cost of the same acid from pure phenanthrene. It should be noted that, taking into account all material costs, the processing specifically of 65% phenanthrene is the most advantageous, although the yield of ozonolysis products from purer phenanthrene is, naturally, higher. Experiments have been carried out with 2′-formyldiphenyl-2-carboxylic acid on the synthesis of dyes constructed according to the triarylmethane type, and also on obtaining unsaturated aromatic acids and weakly acidic cation exchangers of the wofatite C type [11].

The structures of all these substances are represented by formulas (see p. 8). The dyes (I, II, III), as was to be expected, possess very bright coloration characteristic of the corresponding triarylmethane dyes (malachite green and rhodamines), but differ advantageously from the latter in higher lightfastness. Dye (III), obtained by condensation of hexamethylenediamine with the leuco base of dye (I) with a free carboxyl group, has a considerably better affinity for synthetic fibers, in particular for capron, than the more simply constructed dyes of the same series.

With regard to the unsaturated acids (IV, V), it can so far be said that after decarboxylation, carried out under conditions analogous to the decarboxylation of cinnamic acid derivatives (12), 2′-vinyldiphenyl-2-carboxylic acid (V) is obtained, which under more severe conditions is converted into 1-phenylstyrene, capable of polymerizing. The properties of the polymer obtained have not yet been studied.

The examples we have given by no means exhaust all the possibilities for the rational use of diphenic acid, diphenic anhydride, and 2′-formyldiphenyl-2-carboxylic acid in organic synthesis.

\[ \begin{gathered} \text{(I)}\quad \text{methyl ester of a diphenylcarboxylic-acid derivative containing two } N,N\text{-dimethylamino groups and chlorine} \\[4pt] \text{(II)}\quad \text{analogous }N,N\text{-dimethylamino oxonium/imine chloride derivative} \\[4pt] \text{(III)}\quad \text{bis-dimethylamino derivative joined through } \mathrm{CONH-(CH_2)_6-NH-CO} \end{gathered} \]

\[ \begin{gathered} \text{(IV)}\quad \mathrm{C_6H_4{-}C_6H_4} \begin{matrix} {-}\mathrm{CH{=}CH{-}COOH}\\ {-}\mathrm{COOH} \end{matrix} \;\xrightarrow{-\,\mathrm{CO_2}}\; \text{(V)}\quad \mathrm{C_6H_4{-}C_6H_4} \begin{matrix} {-}\mathrm{CH{=}CH_2}\\ {-}\mathrm{COOH} \end{matrix} \;\xrightarrow{-\,\mathrm{CO_2}}\; \text{(VI)}\quad \mathrm{C_6H_4{-}C_6H_4{-}CH{=}CH_2} \;\longrightarrow\; \text{polymer} \end{gathered} \]

\[ \text{fluorenonecarboxylic acid: } \mathrm{ \begin{matrix} & \mathrm{COOH}\\ & |\\ \text{fluorenone nucleus} \end{matrix}} \]

The exploratory investigations begun by us will receive broader development in the direction of the synthesis of certain medicinal preparations, fragrant substances, dyes of various classes, new polymeric materials, and other products.

The range of a large part of these substances can also be considerably expanded through fluorenonecarboxylic acid, which is readily obtained from diphenic acid upon heating with sulfur \([14]\). We have synthesized esters, substituted amides, and amide oximes of fluorenonecarboxylic acid, which are undergoing preliminary tests with respect to their insecticidal activity.

A considerable reduction in the cost of 2′-formyldiphenyl-2-carboxylic acid as a result of replacing pure phenanthrene with technical-grade, low-percentage phenanthrene opens quite real prospects for the industrial production of many of the above-mentioned substances specifically on the basis of this acid.

The significance of 2′-formyldiphenyl-2-carboxylic acid as the principal starting material for a number of syntheses is further confirmed by the fact that

from it, diphenic anhydride can be obtained very readily and in good yield according to the scheme:

\[ \begin{array}{c} \text{2'-carboxybiphenyl-2-carboxaldehyde} \end{array} \ \xrightarrow{\mathrm{Cl_2}}\ \begin{array}{c} \text{2'-carboxybiphenyl-2-carbonyl chloride} \end{array} \ \xrightarrow{-\mathrm{HCl}}\ \begin{array}{c} \text{diphenic anhydride} \end{array} \]

The method of oxidative chlorination of the aldehyde acid developed by us [15] has undoubted advantages over the known methods used in laboratory practice for preparing diphenic anhydride [16], and considerably broadens the prospects for using the ozonolysis products of phenanthrene in the chemical industry.

At present our efforts are directed toward further improving the method of ozonolysis of phenanthrene, with the aim of bringing it as close as possible to production conditions, and also toward the detailed development of syntheses of the substances of greatest practical interest.

REFERENCES

1. L. P. Kulev, Abstracts of Reports at the All-Union Interuniversity Conference on the Chemistry and Technology of Monomers, MITKhT, 93, 1960.
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15. L. P. Kulev, V. A. Salskii, Author’s Certificate 127656, 1960.
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