Condensation of diphenic acid with o-aminophenol
Abstract Generated abstract
This study reports the synthesis of previously undescribed benzoxazole derivatives as part of a search for potentially biologically active compounds in this class. Diphenic acid was condensed with o-aminophenol under melt conditions in a carbon dioxide stream to obtain 2,2′-bis-(2-benzoxazolyl)-diphenyl and 2-(2-benzoxazolyl)diphenyl-2′-carboxylic acid, followed by purification and isolation from acidic or alkaline media. The products were characterized by melting points, elemental analysis, functional group determination, and UV absorption spectra, with reported yields of approximately 20 to 30%.
Full Text
CONDENSATION OF DIPHENIC ACID WITH o-AMINOPHENOL
O. F. Malyushchitskaya, A. N. Novikov
(Presented by the scientific seminar of the departments and laboratories of organic synthesis, KhTF)
With the aim of searching for new biologically active preparations among benzoxazole derivatives, individual representatives of which exhibit therapeutic action [1], the previously undescribed 2-(2-benzoxazolyl)-diphenyl-2′-carboxylic acid and 2,2′-bis-(2-benzoxazolyl)-diphenyl were synthesized. A known method for obtaining this series of substances was used, based on the condensation reaction of o-aminophenol with carboxylic acid derivatives [2]. The structure of the compounds obtained, as follows from the method of their synthesis, was confirmed by UV absorption spectra, the results of quantitative elemental analysis, and determination of functional groups.
Experimental Part
Synthesis of 2,2′-bis-(2-benzoxazolyl)-diphenyl
\[ \text{diphenic acid} + 2\,\textit{o}\text{-aminophenol} \longrightarrow \text{2,2′-bis-(2-benzoxazolyl)-diphenyl} \]
A mixture of 10.9 g of o-aminophenol and 15.0 g of diphenic acid, placed in a flask equipped with a tube for introducing carbon dioxide, was fused in a metal bath at a temperature of 100°C. In a stream of carbon dioxide the temperature was raised to 195°C (with evolution of water being observed) and maintained for two hours. The temperature was then brought to 200–205°C, and the reaction was continued for 10 hours. After completion of the synthesis the flask was cooled to 130°C, the melt was poured into cold water, and the insoluble portion was filtered off, ground, and dissolved in boiling concentrated hydrochloric acid. The solution was filtered and treated with activated carbon until it became pale blue. From the acidic extract, dilution with water precipitated a curdy blue precipitate of 2,2′-bis-(2-benzoxazolyl)-diphenyl. The product was purified by crystallization from n-heptane. Yield 25–30%, mp 130–131°C. Found, %: C 79.82; H 4.63; N 7.12. C₂₄H₁₆N₂O₂. Calculated, %: C 80.38; H 4.16; N 7.21.
Preparation of 2-(2-benzoxazolyl)diphenyl-2′-carboxylic acid. The amounts of the starting materials were: 5.45 g of o-aminophenol and 15.0 g of diphenic acid. The synthesis was carried out under the conditions described above. The reaction product was treated, with heating, with a solution of soda; from this, after filtration, 2-(2-benzoxazolyl)diphenyl-2-carboxylic acid was precipitated with hydrochloric acid.
Fig. 1. UV spectra. 1—2-phenylbenzoxazole; 2—2-(2-benzoxazolyl)diphenylcarboxylic acid; 3—2,2′-bis-(2-benzoxazolyl)diphenyl.
Yield 20–25%, m.p. 140–141°C (from n-heptane). Found, %: C 76.65; H 4.12; N 4.80. $\mathrm{C}_{19}\mathrm{H}_{13}\mathrm{NO}_3$. Calculated, %: C 76.18; H 4.15; N 4.44.
Conclusions
- Benzoxazole derivatives not described in the literature have been synthesized: 2-bis-(2-benzoxazolyl)diphenyl-2′-carboxylic acid and 2,2′-bis-(2-benzoxazolyl)diphenyl.
Literature
- Heterocyclic Compounds. Moscow, IL, p. 365, 1961.
- Ibid., p. 341.