and Ni in benzene oxides of nitrogen were also generated and were probably due to the catalyzed reaction of residual atmospheric gases. Conclusions From the results of the present investigation, the following conclusions can be drawn. 1. Metal powders cannot be comminuted in organic or inorganic liquids without becoming contaminated with the elements making up the milling liquid. I t is surmised that the same holds true for milling in gases. 2. The results reported herein should make it possible to select milling liquids that produce either low levels of contamination or contaminants which may be removable by simple reduction procedures.
3. Reactions of bare metal surfaces, whether produced by milling or otherwise, with organic and inorganic compounds should prove useful in the synthesis of other chemical compounds. Literature Cited Arias, A,, NASA TN D-4862 (1968). Bevington. J. C.. "Polyethers". Part 1, pp 9-81. N. G. Gaylord. Ed., Wiley, New York, N.Y.. 1963. Morrison, R. T.. Boyd, R. N., "Organic Chemistry". 2d ed, Allyn and Bacon, Boston, Mass.. 1968. Quatinetz, M., Schafer, R . J.. Smeal, C. R., "Ultrafine Particles", W. E. Kuhn, Ed., pp 271-296, Wiley, New York, N.Y.. 1963. Wicks, C. E., Block, F. E., U . S . Bur. Mines Bul. 605, (1963).
Receiued for review October 17, 1975 Accepted March 2,1976
Nitric Acid Oxidation of Dixylylethane to Benzophenone Tetracarboxylic Acid Johann G. D. Schulz' and Anatoli Onopchenko Chemicals Division, Gulf Research and Development Company, Pittsburgh, Pennsylvania 15230
Oxidation of 1,l-dixylylethane (DXE) to 3,4,3',4'-benzophenone tetracarboxylic acid (BTA) with nitric acid proceeds via the benzophenone intermediate. There are two pathways to this ketone. The first involves direct formation of benzophenone from alcohol and is favored with dilute nitric acid. The second pathway proceeds through olefinic intermediates with concentrated nitric acid which are then oxidized to benzophenone at temperatures above 120'. All intermediates including ketone, alcohol, olefin, mononitro-, and dinitroolefins are converted to BTA on further reaction with nitric acid under typical DXE conditions. With the exception of ketone and depending on conditions, the intermediates can undergo substantial degradation to trimellitic acid by-product (up to about 15-20%). To maximize BTA yields, conditions must therefore be chosen which will tend to minimize nitroolefin formation. They involve initially gradual addition of nitric acid of low concentration until essentially all of the ethylidene bridge has been oxidized to a carbonyl.
Introduction 3,4,3',4'-Benzophenone tetracarboxylic dianhydride (BTDA) (McCracken and Schulz, 1963) has found commercial use in the production of polyimide and epoxy resins. BTDA is best prepared from o-xylene and acetaldehyde in three steps involving alkylation, nitric acid oxidation, and dehydration with overall yield of about 70%. (11
(DXEI
Recent papers of Russian workers describe bench-scale results which are in general agreement with our earlier findings for each of the above reactions (Farberov e t al., 1968a; Akhmetov et al., 1971; Mironov et al., 1972; Faberov et al., 152
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 2, 1976
1968b). One reference mentions preparation of BTA by oxiwith nitric acid and dizing l,l-di(3,4-dimethylphenyl)ethylene potassium permanganate (Korshak et al., 1962), but details are lacking. While overall eq 2 is deceptively simple, it conceals some rather interesting and complex chemistry. In this paper mechanistics vital to the development of a successful BTDA process are reported in detail. Results Although the alkylation and dehydration reactions involved (eq 1 and 3) are well documented (McCracken and Schulz, 1963; Farberov et al., 1968a; Akhmetov et al., 1971; Mironov e t al., 1972; Farberov et al., 1968b; Sturrock et al., 1948),oxidation with nitric acid (eq 2), except when carried out under exhaustive oxidation conditions, has not been reported. In this paper, we present details of the nitric acid oxidation of DXE under a variety of conditions. Commercially, the reaction is carried out in a pressure vessel employing -20% nitric acid as oxidant. It is started a t 130' (1 h) to convert the alkane bridge largely to carbonyl in a highly exothermic step. The temperature is then raised to 175' for 2 h. Solid benzophenone tetracarboxylic acid (70%yield) is obtained from the solution on cooling. The minimum nitric
acid requirements are based on the following stoichiometry (11.3mol of HNOs/DXE), although in practice about a 15% excess of acid is used to ensure good quality BTA. -CH,
-
2HN0,
+
/
3CH,CH + 1 0 H N 0 ,
\
+
- C O O H + 2 N 0 + 2H,O
\ 3C=O /
+ 3C0, + 10NO + 11H,O
The residual filtrate contains nitric acid and 8-10% by weight of solids (residual BTA, 20%; mono-, di-, and tricarboxylic acids of tetramethylbenzophenone, 30%; trimellitic acid, 35%; phthalic acid, 8%; and miscellaneous other byproducts, 7%). By-products isolated or detected are shown in Chart I. Chart I. By-products Formed During DXE OxidationQ C39H
-@
COOH
Il%*hi03
OXE
coo*
+
NO
+
acoon
mccoH
&COOH
coo*
COOH
COOH 92N
on
BALICIL
c
P
"CIO
IO0,
CRIC
Discussion Oxidation of DXE with nitric acid is readily carried out with acid concentrations of 3-30%. Acid concentrations in excess of 30% are conducive to ring nitration and lead to overoxidations and severe corrosion of equipment. Concentrations below 3% require operations a t temperatures well above 100' to obtain practical rates. Nitric acid of 70-90% or in combination with sulfuric acid is known to be an effective ring nitrating reagent for dixylylethanes, without promoting oxidation of the ethylidene bridge (Schulz and Seekircher, 1972; Kropa and Roemer, 1951). Oxidation of DXE with nitric acid initially involves the tertiary-benzylic hydrogen as expected from a known reactivity sequence for cumene > ethylbenzene > toluene toward nitric acid a t 90' (Tadao et al., 1970).Products formed suggest two major pathways, reflecting different mechanisms. Under one set of conditions ketone formation predominates, while under different conditions mono and dinitroolefins are formed. The latter are also converted to ketone, but only a t higher temperatures (>l2Oo). At these temperatures methyl group oxidation competes with oxidation of the bridge portion of the molecule. A general reaction sequence is shown in Scheme I.
7%
4 Cl3 IP'.
0
probably involves both ketone and nitroolefin intermediates to an approximately equal extent.
874
% distribution of solids in the filtrate.
T o determine the nature of intermediates, oxidation reactions were carried out under mild conditions, and its products were characterized (Table I). Data for C18H18N204 compound was consistent with the product being I or 11,although a sharp single peak on the chromatogram indicated a single compound, favoring 11.
Scheme I. General Reaction Sequence (DXE
BTA)
.
(OXEI
C=CHNOZ
-f
NITROOLEFIN
POoH
OR
I
n
To differentiate between I and 11, the product in question was oxidized with 33% nitric acid (170', 2 h), resulting in the recovery of BTA in 85% selectivity. Simple heating of this olefinic compound in the presence of water (200', 2 h) afforded benzophenone through oxidative hydrolysis. On the other hand, structure I should have produced the corresponding nitrogen-containing products. Existence of a nitro-nitrite isomer of I1 is still a third possibility; we have, however, no evidence from ir or 13C nmr spectra to support such possibility. Runs made under mild conditions are summarized in Tables 11-IV. Both methyl group oxidation and ring nitration are practically negligible in this case. Data indicate that selective ketone (TMB) formation is favored by low nitric acid concentration and low nitric acid to DXE ratios. The use of high nitric acid concentrations and high nitric acid to DXE ratios at low temperatures (
