PRODUCTION OF 2,2’,6,6’-BIPHENY
LTETRACARBOXYLIC ACID
AND ITS DIANHYDRIDE R .
H.
CALLIGHAN
AND
P .
MASCIANTONIO
X .
Applied Research Laboratory, Chemicals Division, United States Steel Corp., Monroeuille, Pa. 15146 M . J.
GRUBBER’
AND
M . S .
MORGAN
Mellon Institute, Carnegie-Mellon University, Pittsburgh, Pa.
15213
2,2’,6,6’-Biphenyltetracarboxylic acid may be produced by treating an ethyl acetate solution of technical-grade pyrene at 0’ to 5 O C . with 2.5 equivalents of rnoist ozone, decomposing the ozonide with a stoichiometric amount of pyridine, ancl oxidizing the intermediates with hydrogen peroxide. A good-quality tetraacid is obtained in 91% yield. If necessary, the product may be purified by crystallization from a dimethylformamide-acetic acid mixture. The tetraacid dissolves in hot acetic anhydride to form a mixed anhydride, which can be vacuum-sublimed to yield the dianhydride.
IN recent
years, conisiderable interest has developed in the synthesis of multifunctional chemical compounds to be used in polymer synthesis. One such compound, 2,2’6,6’-biphenyltetracarboxylicacid, can be obtained by ozonolysis of pyrene, lbut this acid is not readily available or easily prepared. A3 part of a general exploratory program on the upgrading and utilization of high-boiling coaltar fractions, the Applied Research Laboratory of U. s. Steel has developed a process for preparing this tetraacid from technical 90% pyrene. It is believed that this process is superior to any that has previously been published. That 2,2’,6,6’-biphenyltetracarboxylic acid can be made by ozonolysis of pyrene was mentioned in the literature (Vollman et al., 193‘7) as early as 1937. This fact was verified, and a simple method of isolating the product in high yield was developed. Pyrene, dissolved in ethyl acetate, is treated a t 0” to 5°C. with 2.5 equivalents of moist ozone. An excess of ozone is required because ozone absorption is not quantitative and some unreacted ozone escapes during the reaction. Ethyl acetate is classified as an inert solvent, and, if moist ozone is not used, an ozonide may partially precipitate from the solution. Since most ozonides are unstable and may often be explosive, ozonide precipitation is not desirable. I t has been reported (Cromwell, 1960) that as little as 1% water in the reactants will markedly reduce the hazard of Rame and explosion in the ozonolysis of fatty acids. After the required amount of ozone has been added, the ozonide is cautiously decomposed by the addition of 2 equivalents of pyridine (Kerur, 1960). The solvent is removed under reduced pressure, and the residue treated with aqueous hydrogen peroxide and refluxed overnight. On acidification of the solution, tetraacid precipitates and is filtered and dried. We believe that this method for the laboratory preparation of 2,2’,6,6’-biphenyltetracarboxylicacid represents an improved procedure. Prior methods can be summarized ’Present address, S. C. Johnson & Son, Inc., 1525 Howe St., Racine, Wis. 53403
as requiring many steps, giving low over-all yield, and/ or requiring the use of costly reagents or elaborate and special reaction techniques. The dianhydride is prepared by first dissolving the tetraacid in acetic anhydride by warming. The product formed in the first step is a mixed anhydride (Goins and Van Deusen, 1968) and is recovered by evaporation of the excess acetic anhydride. The solids thus obtained are then subjected t o vacuum sublimation, and the sublimate consists of practically pure dianhydride of 2,2‘,6,6’biphenyltetracarboxylic acid. Although a Czech patent (Arient et al., 1964) claimed that this dianhydride can be prepared by the vapor-phase oxidation of 4,5,9,10tetrahydropyrene, no physical properties were given. Reaction Mechanism
The mechanism of the reaction has not been studied. Following Criegee as detailed in a review article (Bailey, 1958), the authors postulate the following reaction scheme:
HOOC8
HooC
~
0
(CH3COIz 0HEAT ~ 0 -
0
I
0.8 275.C mm /Hg
0 ($!-O-!-CH3
8
0
.
g - 0 - p
\
Historical Background
The compound 2,2’,6,6’-biphenyltetracarboxylic acid was apparently first prepared by Vollman et al. (1937) by ozonolysis of a suspension of pyrene in glacial acetic VOL. 8 NO. 4 DECEMBER 1969
427
acid. The initial product was 4-formyl-5-phenanthrenecarboxylic acid in 20 to 34% yield. This phenanthrene aldehyde-acid was then further oxidized with alkaline potassium permanganate to give the tetraacid in about 33% yield. In 1938, Vollman and Becker obtained a U.S. patent on polycyclic aromatic aldehydes and carboxylic acids and a process for preparing them (1938). Depending on the extent of ozonolysis, a suspension of pyrene in glacial acetic acid was converted into 4-formyl-5phenanthrenecarboxylic acid or 2,2',6,6'-biphenyltetracarboxylic acid. The yield of tetraacid was not given, and the amount of ozone used was not stated. Kerur, by ozonolysis of pyrene, obtained only 17 to 20% yields of 2,2',6,6'-biphenyltetracarboxylic acid by using acetic acid as the solvent and hydrogen peroxide to oxidize the intermediate. I n a recent British patent, Copeland (1965) claimed a 61% yield of 2,2',6,6'-biphenyltetracarboxylic acid by the ozonolysis of pyrene in an inert solvent a t low temperature, isolation of the ozonide, decomposition of the ozonide with 50% aqueous pyridine, and then oxidation of the intermediate with potassium permanganate. The crude product was crystallized from 10% hydrochloric acid. I t was stated that oxidation with hydrogen peroxide normally gives much lower yields of acid. The most recently published procedure is in an Air Force Materials Laboratory Technical Report (Blake et al., 1967). A suspension of pyrene in methanol (0" to -5' C.) was treated with a 20% excess of ozone, the solution oxidized with alkaline hydrogen peroxide, charcoaled, and filtered. Acidification gave a 75% yield of crude product that was reoxidized with permanganate and purified to give a 53% yield of the tetraacid. Experimental
Preparation of 2,2',6,6'-Biphenyltetracarboxylic Acid. A solution was prepared by dissolving 101.0 grams of technical 90% pyrene (0.45 mole) in 200 ml. of ethyl acetate, filtering to remove undissolved solids, and cooling to 5" C. (ice-H20 bath). A finely dispersed stream of an ozoneoxygen mixture containing about 3 weight % ozone was passed into the solution with good stirring until 60 grams (1.25 moles) of ozone had been added (6 hours). Moist ozone was used by first passing the ozone-oxygen gas stream through a wash bottle containing water and then into the solution of pyrene. The ozone absorption was not quantitative and a light-yellow solution resulted. The diozonide was then decomposed by adding pyridine (100 ml., 1.2 moles) and allowing the mixture to warm with stirring for 2 hours (exotherm t o 43°C.). The ethyl acetate was then removed by distillation, and the red, oily residue treated with 200 ml. of water and 250 ml. (2.2 moles) of 30% hydrogen peroxide. T h e mixture was then refluxed (100" C.) for 18 hours. Upon cooling to room temperature, crystallization occurred. The mixture was then acidified
428
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
with 250 ml. of cold concentrated hydrochloric acid. The solids were collected by filtration, washed well with cold water, and dried. The yield was 135.7 grams (91.2% yield) of light-tan 2,2',6,6'-biphenyltetracarboxylic acid that had a neutral equivalent of 85.8 (theory = 82.5). Purification was accomplished by crystallization from dimethylformamide-acetic acid (1 to 3) to yield a white product (77'; recovery, 70% yield) that melted a t about 394" C. (by differential thermal analysis) and had a neutral equivlent of 82.8. ANALYSIS. Calculated for C16Hlo08: C, 58.20; H , 3.05. Found: C , 58.42; H, 2.97. Preparation of Dianhydride. In a 500-ml. flask were placed 10.0 grams (0.03 mole) of 2,2',6,6'-biphenyltetracarboxylic acid and 60 ml. of acetic anhydride. The solids were dissolved by warming on a steam bath for about 1 hour. The excess anhydride was removed by flash evaporation, and the solid residue subjected to vacuum sublimation a t 275°C. and 0.8 mm. of mercury pressure for 4 hours. The sublimed product weighed 7.2 grams (80.7% yield) and had a neutral equivalent of 73.2 (theory = 73.5). The nuclear magnetic resonance spectrum (in pyridine) showed only aromatic protons. The product had a melting point of 268" C. (by differential thermal analysis). The analytical sample, obtained by crystallization from chloroform, melted a t 269-71" C. ANALYSIS.Calculated for C16H60fi:C, 65.31; H , 2.06. Found: C, 65.41; H, 2.22. Safety. Ozone is extremely toxic. The ozonolysis should be conducted in such a way that no one has to breathe an atmosphere containing more than 0.1 p.p.m. of ozone (Stokinger, 1959). Literature Cited
Arient, J., Norad, Z., Habada, M., Czech. Patent 111,551 (July 15, 1964). Bailey, P. S.,Chem. Rev.58, 927 (1958). Blake, E. S., DeBrunner, R . E., Webster, J. A., "Chemistry and Synthesis of Multifunctional Chemical Compounds," Air Force Materials Laboratory Technical Report, April 1967. Copeland, P. G. (to Coal Tar Research Association), Brit. Patent 1,007,012(Oct. 13, 1965). Cromwell, W. F., Ind. Erg. Chem. 52, 245 (1960). Goins, 0. K., Van Deusen, R. L., Polymer Letters 6 (ll), 821 (1968). Kerur, D. R., Ph.D. dissertation, University of Texas, 1960; University Microfilms, Ann Arbor, Mich., Publ. 64-3017(1964). Stokinger, H. E., Aduan. Chem. Ser. No. 21, 363 (1959). Vollman, H., Becker, H. (to General Aniline Works), U. S. Patent 2,127,096 (Aug. 16, 1938). Vollman, H., Becker, H., Corell, M., Streeck, H., Ann. 531, 1 (1937). RECEIVED for review June 10, 1969 ACCEPTED August 25, 1969
