5. Operating Cost. Table IV shows the comparison of raw materials and energy consumption of the membrane process, modern asbestos diaphragm process, and modern mercury Drocess. 6. Product Quality. The quality of products of the membrane process is equivalent to that of the mercury process and superior to that of the asbestos diaphragm process.
Literature Cited Connolly, D. J.. Gresham, W. F., (to E. I.du Pont de Nemours and Co.)U.S.Patent 3 282 875 ( b v 1,1966). Japan Soda Association, "Soda Handbook-1975".
Received for review M a r c h 31, 1976 Accepted June 12,1976
A New Anhydride. 3,4,3', 4Wenzhydroltetracarboxylic Dianhydride Johann G. D. Schulz' and Anatoli Onopchenko Gulf Research and Development Company, Catalyst and Chemicals Research, Pittsburgh, Pennsylvania 15230
A hydrogenation procedure was developed for the direct and selective conversion of 3,4,3',4'-benzophenonetetracarboxylic dianhydride (BTDA) to the corresponding benzhydroltetracarboxylic dianhydride (BHDA) over a Ni catalyst. Ester solvents are unique in this procedure, allowing facile recovery of solid BHDA, mp 167-170 OC. With ethers such as pdioxane and tetrahydrofuran, only the solvated product is formed. The new anhydride shows enhanced solubility in most organic solvents compared to the rather insoluble BTDA. This property alone makes BHDA particularly attractive for applications in epoxy coatings and laminating resins.
Introduction 3,4,3',4'-Benzophenonetetracarboxylic dianhydride occupies a unique position among dianhydrides presently available in commercial quantities for the manufacture of high-temperature stable polyimide and epoxy resins. Polymers based on BTDA, for example, possess high mechanical strength over a wide temperature range. They do not lose their electroinsulating properties in the presence of radiation, and are stable toward chemicals and moisture. One difficulty in the early use of BTDA was its relatively poor solubility in common solvents. For many applications new technology for using BTDA as a solid rather than in solution had to be developed (Barie and Franke, 1969; Dine-Hart, 1965). For some applications, however, even these techniques do not suffice and only a more soluble anhydride will solve the problem.
As the high melting point of BTDA (225-226 'C) and its poor solubility appear to be a function of the rigid benzophenone structure, conversion of the keto function into alcohol was expected to lead to a derivative with improved solubility characteristics. In this paper, we report on the direct hydrogenation of benzophenonetetracarboxylic dianhydride to the corresponding benzhydrol structure.
Results and Discussion Initial attempts to prepare benzhydroltetracarboxylic dianhydride (BHDA) were made by us during the 1960's (McCracken et al., 1966). Procedures involved hydrogenation of either the tetrasodium salt or the tetramethyl ester of benzophenonetetracarboxylic acid over nickel or copper chromite catalysts, followed by dehydration of the benzhydroltetracarboxylic acid (Chart I). This last step proved to be
Chart I. Attempted Synthesis of BHDA
B
C
N a O O C a NaOOC
tiooc
H
00
HOOC
B C
COONa HCI
1 u
COOH
,MeOH
I MeOOCQ
P
MeOOC
a
COOMe
COOMe
H2
NaoH/ M e O O C oY G C O O M e MeOOC
0
u 292
COONa
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15. No. 4, 1976
H
COOMe
0
poor as dehydration competes with esterification, while salt formation with nickel catalyst presents additional complications. The complexity of our problem in achieving exclusive hydrogenation of keto carbonyl to alcohol is illustrated by the
work of Adkins et al. (1933), who showed that anhydride functions are readily converted over nickel catalyst to phthalides under conditions commonly employed for the reduction of keto functions to alcohols (Chart 11). Austin et al.
tetrahydrofuran (THF) showed more promise and were therefore used during initial experimentation. Using these solvents, recovery of BHDA was first attempted by concentrating the catalyst-free filtrate, followed by cooling to induce crystallization. This approach failed and after evaporation of solvent the product was obtained as a pale yellow, tacky, semi-solid. Analysis showed that it was associated with one to two moles of solvent. Attempts to remove the bound solvent by freeze-drying, vacuum techniques, and other conventional procedures proved unsuccessful. With time, the product changed into a glass-like material (appearance of 1725-cm-1 band). Using ether solvents, BHDA can thus be prepared and used in solution, but its shelf life appears short. Hydrolysis of BHDA.2THF afforded the corresponding tetraacid along
Chart 11. (Adkins, 1933) 0
Ni 150'
E
o
Is
+
b
'gH1l
N(CH3)2
(1937) improved on this procedure and suggested the intermediacy of hemiacetal-like structures of anhydride (Chart 111). On this basis, BTDA could potentially be converted into
Chart 111. (Austin, 1937) Nl
0
/
C
H 3 COOH
+
(
y
3
COOH
s
H2 (34%)
n
O
-50%
dianhydrides o benzhydrol or diphenylmethane, to a mixture of half-anhydrides, half-phthalides, or to a mixture of full phthalides of benzophenone, benzhydrol, and diphenylmethane, assuming that no ring reduction occurs. Optimum conditions developed for the selective reduction of BTDA to BHDA include temperatures of 125-140 "C, hydrogen pressures of 75-100 atm, reaction times of 30-60 min, and BTDA concentrations of %lo% (by wt) in the solvent. Reaction a t 180 "C led to the formation of diarylmethane in varying amounts (4.2 ppm, singlet, ArCHZAr) and phthalide (5.35 ppm, singlet, CH2) structures. Use of higher concentrations of BTDA, even a t 140 "C, additionally produced considerable amounts of ester by-product, arising from interaction of alcoholic hydroxyl with anhydride. The choice of solvent for the hydrogenation was important since it had to be recoverable and also inert toward catalyst, substrate, and hydrogen. This excludes ketones, carboxylic acids, alcohols, and water. Reactions in hydrocarbon solvents-cyclohexane, methylcyclohexane, and benzene-at temperatures up to 220 "C gave no evidence of any reaction as anhydride remained unreacted due to its poor solubility in nonpolar solvents. An acetal, 2,2-dimethoxypropane, decomposed into methanol and acetone under reaction conditions, the latter being reduced to 2-propanol. Reaction in dimethylformamide was also unsuccessful. p-Dioxane and
(36%)
(23%)
with THF, noted by its odor. The isolated acid is a white solid which already undergoes chemical transformations at temperatures as low as 100 "C. It became imperative therefore to find a solvent which would not solvate. This solvent should have sufficient solvent power for BTDA to enable the reaction to occur, but it should also have poor solvent power for BHDA produced, allowing its recovery through crystallization. Several esters were found to meet all of these requirements. While ethyl acetate is the solvent of choice, methyl acetate, amyl acetate, and dimethyl malonate all gave equally good results. Nickel 0104P catalyst as received did not perform well a t 140 "C, leaving a considerable amount of BTDA unconverted. Good results, however, were obtained if the catalyst was first activated. Indiscriminate activation of nickel in ethyl acetate produced a superactive and nonselective catalyst which even at 140 "C led to a complex mixture of products. Activation of nickel in THF, however, was found to impart a moderating effect on catalyst activity with selective formation of BHDA in ester solvents. How T H F imparts the desired characteristics to the catalyst is not clear at this time. The shelf life of solid BHDA has not been determined. Various samples which have been in storage for several months, however, showed no apparent deterioration (mp, spectral data, reactions). Work describing the preparation and properties of polyimide and epoxy resins based on BHDA will be published separately. Conclusion Selective hydrogenation of BTDA to BHDA appears to be a function of catalyst activity. Highly active nickel is nonselective even at relatively low temperatures, leadingto simultaneous reduction of anhydride carbonyl. Low activity nickel, on the other hand, affords only partial conversion of BTDA, favoring undesirable side reactions. Activation of nickel catalyst in T H F produces a sufficiently attenuated but still active catalyst, ideally suited for the selective reduction of keto carbonyl to alcohol. The use of ester solvents is equally critical in the recovery of solid BHDA. Experimental Section Hydrogenations were carried out in a 1-l., 316 stainless steel, magnetically stirred autoclave (Autoclave Engineers Inc., Erie, Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 4, 1976
293
/ j r
A RoM RINGAT
c/
#f
R
O 0
*
Y
'0
(EXCHANGE ABLE)
mp167-170'
t
ACETONE - d 6
Me4 SI
p m
Figure 1. NMR spectrum of BHDA. Pa.), which was equipped with a heater and cooling coils. Nickel catalyst was purchased from the Harshaw Chemical Co. as Ni 0104P and activated in T H F solvent prior to hydrogenation (190 OC, 70 atm of Hz, 30 min for a 20-25-g batch of nickel in 500 ml of THF; 100-150-g batches required 1.5-2 h of activation). The hydrolyzed products were analyzed by glc as the trimethylsilyl derivatives on a Hewlett-Packard 5710A gas chromatograph employing a 20 X 0.125-in. 10% UCW 982 packed column on 80-100 WAW DUCS 885 support (150-300 "C at 8O/min). The nmr spectra were determined on a Varian T-60 spectrometer. The chemical shifts are quoted in 6 units (ppm). The ir spectra were recorded on a Perkin-Elmer 237B spectrometer. The melting points were taken in capillary tubes and are uncorrected. In a typical experiment, 40 g of BTDA in 500 ml of ethyl acetate was reduced over 20 g of Ni 0104P catalyst (140 OC, 115 atm of Hz, 30 min). The reaction mixture was filtered to recover the catalyst, and the pale yellow filtrate was concentrated to a volume of -100 ml in a rotary evaporator. After standing overnight, the pale yellow solids that formed were filtered and air-dried to give 38 g (94% yield) of BHDA mp 167-170 OC, neut equiv 82,84 (theor. 81). This procedure was used for the preparation of sample quantities of product with good reproducibility. Anal. Calcd for CI7H807: C, 62.98; H, 2.47; 0,34.55. Found: C, 63.04; H, 2.68; 0,34.28 (by diff.). Ir (Nujol): 3448 cm-I, OH; 1848,1776 cm-', anhydride bands;
294
Ind. Eng. Cham., Prod. Res. Dav., Vol. 15, No. 4, 1976
and absence of 1675 cm-l benzophenone band. Hydrolyzed product, glc: 98% benzhydrol tetracarboxylic acid; 2% benzophenone tetracarboxylic acid. neut equiv: 92, 95 (theor. 90). Solubility data, gh. (25')
BTDA
BHDA
N-Methyl-2-pyrrolidone N,NDimethylacetamide Dimethylformamide Dimethyl sulfoxide Acetone
334 242 210 89
982 964 964 998 131
25
Note Added in Proof. A recent paper by N. Finch et al. ( J . Org. Chem., 41,2510 (1976)) reports on the hydrogenation of BTDA in ethanol-acetic acid over Pd/C to give 3,3'-dimethyl-4,4'-dicarboxydiphenylmethaneexclusively. Literature Cited Adkins, H., Wojcik, B., Covert, L. W., J. Am. Chem. Soc., 55, 1669 (1933). Austin, P. R.. Bousquet, E. W., Lazier, W. A.. J. Am. Chem. SOC., 59, 864 (1937). Barie, W. P., Franke, N. W., Ind. Eng. Chem., Prod. Res. Dev., 8, 72 (1969). Dine-Hart, R. A., The Preparation and Fabrication of Aromatic Polyimides, Royal Aircraft Establishment, Tech. Report No. 65 228, 1965. McCracken, J. H., Schulz. J. G. D., Whitaker, A. C., U S . Patent 3 293 267 (1966).
Received f o r review March 29, 1976 Accepted July 18, 1976
