Ind. Eng. Chem. Res. 1991,30,1456-1461
1456
Palladium-Catalyzed Synthesis of N,N-Diphenylurea from Nitrobenzene, Aniline, and Carbon Monoxide Jae Seung Oh, Sang Moo Lee, and Jong Kee Yeo Lucky R 13D Center, Petrochemicals and Polymers, P.O. Box 10, Science Town, Daejeon, Korea
Chul Woo Lee and Jae Sung Lee* Department of Chemical Engineering, Pohang Institute of Science and Technology, P.O. Box 125, Pohang, Korea
N&’-Diphenylurea has been synthesized from nitrobenzene, aniline, and carbon monoxide in a batch reactor at 80-160 O C and 15-75 bar. Homogeneous catalyst systems consisting of a palladium(I1) salt, an onium salt, and triphenylphosphine dissolved in xylene or toluene were found to be highly efficient, giving isolated urea yields up to 98% a t 100% nitrobenzene conversion. The effects of catalyst composition and other reaction variables were studied. The reaction consumed more aniline than nitrobenzene on a molar basis, suggesting the existence of a new reaction path in addition to the well-known path of the reaction consuming equimolar nitrobenzene and aniline. The presence of excess aniline was essential in order to reuse the catalyst system for new batches without appreciable loss of activity.
Introduction Organic isocyanates such as toluene diisocyanate (TDI) and 4,4’-diisocyanatodiphenylmethane(MDI) are used commercially in the preparation of polyurethane foams and elastomers. The current commercial technology for the preparation of these isocyanates utilizes phosgene as a raw material, which is toxic, corrosive, expensive, and difficult to handle, It is thus natural that a great deal of recent research has been directed toward alternative routes to isocyanates without using phosgene. Most processes under development involves akoxycarbonylation of nitrobenzene with CO and a primary alcohol or of aniline with CO, Oz, and a primary alcohol to form alkyl phenylcarbamate in the presence of a homogeneous or heterogeneous catalyst system, mostly containing a noble metal. These efforts are in recent reviewe (Cenini, 19M, Ikariya, 1989). Summnnznd ’ In homogeneous catalyst systems, a great deal of difficulty has been experienced in separation of catalysts and the product alkyl phenylcarbamate by distillation due to the high boiling point of the product. To avoid this catalyst recovery problem, NJV-diphenylurea (DPU) has recently been proposed as a more convenient intermediate in the phosgene-free synthesis of MDI (Ikariya et al., 1987a). Since the urea is solid under usual synthesis conditions, it can be easily separated from reaction solution containing catalysts by filtration or centrifugation. Since the urea can then react readily with a primary alcohol to yield an alkyl phenylcarbamate (Ikariya et al., 1989; Giannoccaro, 19881, the scheme provides a two-step synthesis to the alkyl phenylcarbamate via the urea intermediate: PhNHCONHPh + ROH PhNHCOpR + PhNH, (1)
-
N,N’-Disubstituted ureas are usually prepared in small scales by stoichiometric reactions of isocyanates or phosgene with amines. More promising routes for a large-scale production involve oxidative carbonylation of aniline by nitrobenzene or dioxygen in the presence of a transitionmetal complex catalyst. Reported catalyst systems for the carbonylation include Pd (Dieck et al., 1975; Giannoccaro, 1987; Macho et al., 1975), P t (Teuji et al., 1985), Rh (Ikariya et al., 1987b), Ru (Ikariya et al., 1987a), Hg (Nefedov et al., 1973,19761,or Se (Kondo et al., 1972) as
* To whom correspondence should be addressed.
a major component and some promoters. In the case of N,”-diphenylurea synthesis from aniline, nitrobenzene, and carbon monoxide, the reaction has been presumed to occur according to the following stoichiometry (Dieck et al., 1975): PhNHz + PhNOz + 3CO PhNHCONHPh + 2C02
-
(2)
Recently, we discovered that a catalyst system comprising a palladium(I1) complex, an onium salt, and triphenylphosphine dissolved in toluene or xylene gives excellent yields of N,”-diphenylurea from aniline, nitrobenzene, and carbon monoxide (Lee et al., 1989). This paper covers a detailed account of the work. The catalyst system works in relatively mild conditions and is one of the most selective systems reported so far. Furthermore, it is demonstrated that the catalysts are readily recovered after the reaction and are recycled for further works without significant loss of their original performance. An interesting feature of our catalyst system is that the reaction proceeds according t~ a stoichiometry different from that indicated by eq 2, especially when aniline was used in excess. It is proposed that the following reaction might take place simultaneously with reaction 2: PhNOz + 5PhNH2 + 3CO 3PhNHCONHPh + 2H20 (3)
-
Experimental Section A 300-cm3high-pressure stirred autoclave with an SS 316 wall (Autoclave Engineering) was employed as a batch
reactor. The reactor was enclosed in an electric furnace regulated by a proportional-integral-differential temperature controller. A local thermocouple monitored the temperature of the reaction solution during the reaction. In a typical experiment, 300 mmol of aniline, 0.67 mmol of a palladium salt, 2 g of a halogen promoter, 3.8 mmol of triphenylphosphine (PPh8),and 60 g of xylene were charged into the reactor. While this stirred, the gas phase in the reactor was flushed with carbon monoxide (Airco, 99.2%) several times and then pressurized to a desired pressure. The reactor was then heated to the reaction temperature. When temperature w a stabilized, ~ 50 mmol of nitrobenzene was rapidly pumped into the reactor. The time required for the pumping was less than 1 min, and
0888-5885f 91f 2630-1456$02.50f 0 0 1991 American Chemical Society
Ind. Eng. Chem. Res., Vol. 30,No. 7, 1991 1467 Table I. Synthesis of NJV-Diphenylurea from Aniline, Nitrobenzene, and Carbon Monoxiden urea Pd salt Pd(CH&OO)Z Pd(CHsCOO)2 Pd(CH&OO)2 Pd(CH&00)2 Pd(CH&00)2 Pd(CFSC00)Z PdCl2 Pd(acac1, Pd metalb
T, P, time, nitrobenzene yield, convn, W ‘C a b h w cocatalyst NEt4Cl BGPBr KCI CUCl, none NEt4Cl NEt4CI NEt4Cl NEt4CI
120 40 120 40 120 40 100 55 100 57 100 60 120 40 120 40 100 50
2 4 5.5 5 6 7 6 2 5.5
100
92.8 55.5
98 92 49
nf 11.1 97.2 88.9
11 94 87
‘a
the instant that the pumping was completed was assumed to be the start (time = 0) of the reaction. This procedure will eliminate confusion due to the reaction during heating of the reactor when nitrobenzene was charged together with other components. In a separate experiment, it was confirmed that a reaction mixture containing all components but nitrobenzene did not undergo any change for an extended period of time under the otherwise same reaction conditions. The reaction mixture was sampled during the reaction for analysis by gas chromatography (GC). After the reaction, the reactor was cooled and the solid products were isolated and identified by GC-MS and NMR analyses. Quantitative analysis of the liquid phase was carried out by a GC (HP 5890) equipped with a flame-ionized detector and a cross-linked 5 % poly(diphenyldimethylsi1oxane) capillary column (Ultra 21, with tert-butylbenzene as an internal standard. Solid products were analyzed by an HPLC (Waters 990) with a pBondapak C18 column. A 50/50/1 mixture by volume of methanol, water, and acetic acid was employed as an eluant.
Results Results of DPU synthesis from aniline, nitrobenzene, and carbon monoxide in the presence of various palladium salts and halogen promoters are summarized in Table I. Reaction proceeded smoothly, producing solid products confirmed by GC-MS and NMR analyses to be the desired N,”-diphenylurea (Tsuji et al., 1985). The conversion of nitrobenzene or aniline was calculated by a GC analysis of filtrate after reaction. The DPU yield was obtained by comparing the weight of isolated solid products and the amount of consumed nitrobenzene and aniline. In the most favorable case with Pd(CH3C00)2and NEt4Cl,the conversion of nitrobenzene was 100% and DPU yield was 98%. No other byproducts were detected by HPLC analysis of solid products. Hence, the remaining 2% in yield should be due to the loss during product handling, and the reaction itself appears to proceed almost quantitatively. Palladium salts such as Pd(CF3C00)2and PdC12 were slightly less effective, and Pd(acacI2 and Pd metal were inactive under the same reaction conditions. The presence of PPh3 and a halogen promoter was essential for the catalyst system to show a good activity. Without PPh3, palladium seemed to precipitate as metal. As a halogen promoter, onium salts such as NEt4Cl and Bu4PBr were more effective than KC1. CuC12, which is known to be an effective promoter for PdC12 in many carbonylation reactions (Tsuji, 1980), was found to be inactive in the present system. Hence, the present catalyst system does not represent the Wacker-type chemistry involving a redox cycle between Pd(I1) and Pd(0) with Cu(I1) serving as a reoxidant of Pd(0) to active Pd(I1) species.
h 0
‘i
nr nr
OAniline, 300 mmol; nitrobenzene, 50 mmol; Pd salt, 0.67 mmol; PPh8,3.8 mmol; cocatalyst, 2 g; xylene, 60 g. Prepared by alcoholysis of Pd(CHSCOO)l. No reaction.
100
00
Aniline Nitrobenzene
Reaction 1 ‘Time (hr) 2
Figure 1. Typical change in millimoles of aniline and nitrobenzene with reaction time. Reaction conditions: 120 “C; 40 bar; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH3C00)2,0.67 mmol; PPhS, 3.8 mmol; NEt4C1,2 g; xylene, 60 g. Initial AnillnelNilrobenzene (moth”)
0
1
3
2
4
5
Reaction Time (hr)
Figure 2. Change with reaction time in reacted mole ratio of aniline to nitrobenzene at different initial aniline-to-nitrobenzenecharge ratios. Reaction conditions: 120 OC; 40 bar; nitrobenzene,50 mmol; Pd(CHSC00)2,0.67 mmol; PPh3, 3.8 mmol; NEt,Cl, 2 g; xylene, 60 g.
Table 11. Effect of Different Initial Charge of Aniline (AN) and Nitrobenzene (NB) in N,”-Diphenylurea Synthesis at 120 OC and 40 bar initial charge,” amt reacted, mmol mmol AN NB reaction time, h AN NB 50 50 4.0 49 43 100 150
300
50 50 50
6.0 4.5
2.5
98 121 144
49 50
50
oPd(CH3C00)z,0.67 mmol; PPh3,3.8 mmol; NEt4Cl,2 g; xylene, 60 g.
One of the reasons for the inability of these inorganic halides to promote the reaction efficiently may be due to their limited solubility into the reaction mixture. The disappearance of aniline and nitrobenzene with time was followed by analyzing samples taken during the reaction by GC. A typical example is shown in Figure 1for an initial charge containing 300 mmol of aniline and 50 mmol of nitrobenzene. It is evident that greater amounts of aniline disappear than those of nitrobenzene. The mole ratios of aniline to nitrobenzene that had been reacted away were calculated, and the results are shown in Figure 2 for different aniline-to-nitrobenzene mole ratios initially charged in the reaction mixture. In all cases, more aniline was consumed than nitrobenzene, especially for high an-
1458 Ind. Eng. Chem. Res., Vol. 30, No. 7, 1991
f
(mmol)
Pd(0Ac)
40
n 0.45 0.67 0.89
2of 0
0
L 4
0
1
2
n 5.0 5.1
0
n
3
0
1
Reaction Time (hr)
1
4
3
Reaction Time (hr)
Figure 3. Effect of Pd(CH&OO)2 concentration on the conversion of nitrobenzene. Reaction conditions: 120 OC; 40 bar; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH8C00)2,0.67 mmol; PPh,, 3.8 mmol; NEt4CI, 2 g; xylene, 60 g. 100
2
Figure 5. Effect of NEt,C1/Pd(CH&00)2 mole ratio on the conversion of nitrobenzene. Reaction conditions: 120 OC; 40 bar; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH&OO),, 0.67 mmol; PPhS, 3.8 mmol. xylene, 60 g. 100
s==
-ep
80
C
.-
E e
60
f Li
Pressure (bar)
40
I
a 5 m 9 0 13 18
0 15
n 21
g
0 40
20
62
Y-
0
1
2
3
4
0
1
iline/nitrobenzene charge ratios. The reacted aniline/ nitrobenzene ratio was slightly higher in the early stage of the reaction. As shown in Table 11,the conversion of nitrobenzene is almost complete when the aniline/nitrobenzene mole ratio is above 2. Hence net results of charging more aniline is increase in urea production for the same amount of reacted nitrobenzene. Furthermore, it is evident in Table I1 that the conversion of both nitrobenzene and aniline is more rapid for higher aniline/ nitrobenzene charge ratios. Some efforts have been devoted to find an optimal catalyst composition and the results are presented as curves of nitrobenzene conversion vs time in Figures 3-5. As expected, the reaction rate increased as the concentration of Pd(CHSC00)2increased. However, the effect was levelled off above Pd concentration of 0.7 "01. Since all nitrobenzene was converted to urea, Pd should have turned over at least 70 catalytic cycles during the run at this Pd concentration. The initial rate of turnover could be calculated to be 75-113 h-l from the first datum points of Figure 3. The reaction rate was strongly dependent on the amount of triphenylphosphine (Figure 4) and NEt4C1 (Figure 5 ) below critical concentrations. However, the effects were flattened out above the concentrations. It is interesting to note that the insufficient amount of NEtlCl lowers not only the rate but also the final nitrobenzene conversion as indicated in Figure 5 by the plateaus of
4
Reaction Time (hr)
Reaction Time (hr)
Figure 4. Effect of PPha/Pd(CH&OO)z ratio on the conversion of nitrobenzene. Reaction conditions: 120 O C ; 40 bar; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH8C00)z,0.67 mmol; NEt,Cl, 2 g; xylene, 60 g.
3
2
Figure 6. Effect of pressure on the conversion of nitrobenzene. Reaction conditions: 120 "C; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH3C00)2,0.67 mmol; PPh,, 3.8 mmol; NEt4C1, 2 g; xylene, 60 g. 100
10
pc
t I
'O
Temperature
U
II
h
'O
0
80
30
0
2
4
6
8
10
Rencllon T h e (hr)
Figure 7. Effect of reaction temperature on the conversion of nitrobenzene. Reaction conditions: 40 bar; nitrobenzene, 50 mmol; aniline, 300 mmol; Pd(CH&OO),, 0.67 mmol; PPhS, 3.8 mmol; NEt4C1,2 g; xylene, 60 g.
nitrobenzene conversion below 100%. On the other hand, low concentrations of triphenylphosphine retard the rates but do not affect the final nitrobenzene conversion. The effect of pressure was small (Figure 6) as fax as CO waa supplied in more than a stoichiometric amount, which, in our reaction system, corresponded to ca. 10 bar. Even apparent inhibition of the reaction rate by CO is observed
Ind. Eng. Chem. Res., Vol. 30, NO. 7, 1991 1459 Table 111. Effwt of Solvent" solvent xylene toluene anilineb methanol acetone
temp, OC 120 120 120 120 100
press., bar 40 40 40 40 55
reaction nitrobenzene time, h convn, % 2 100 2.5 100 1.5 100 4 23.3 6 21.1
aPd(CH&00)2, 0.67 mmol; PPh3, 3.8 mmol; NEt,Cl, 2 g; solvent, 60 g; aniline, 300 mmol; nitrobenzene, 50 mmol. *Aniline, 1.25 mol. Table IV. Longevity Test of the Catalyst Systema nitrobenzene convn, % DPU yield? % batch AN/NB = 2 AN/NB = 6 AN/NB = 2 AN/NB = 6 1 92 100 90 97 2 28 100 26 98 100 98 3 100 98 4 Other conditions are the same as given in Table I. 2 X moles of isolated N,"-diphenylurea/moles of reacted aniline and nitrobenzene.
above 40 bar. The effect of reaction temperature is shown in Figure 7. The rate increased with increasing temperature up to 120 "C and decreased at higher temperatures. The unusual behavior at high temperatures strongly suggests that catalytic species may be unstable above 140 "C. Indeed, usually yellow reaction products became darker when the reaction temperature was higher than 140 "C. The Pd(CH3C00)z itself is known to decompose at 194-206 OC. As shown in Table 111, nonpolar solvents such as xylene, toluene, and aniline showed much better performance than polar ones. The Pd(CH,COO), is unstable in polar solvents and is believed to decompose to form inactive Pd metal particles. Xylene and toluene are desirable because they dissolve reactants but not the product and thus help the reaction proceed to completion and allows easy separation of the product and catalysts. When aniline was used as a solvent, the reaction mixture became viscous, which may cause some processing problem in practical applications. The longevity of the present catalyst system was tested by repeated uses of the same catalyst mixture for new batches of reactants. After the first batch of the reaction, solid products were filtered and washed with fresh aniline. This aniline and the filtrate were charged into the reactor, and a new batch of nitrobenzene was added for another run. The results are summarized in Table IV, Without adding any catalytic component between runs,the catalytic system did not show any deterioration in performance up to four batches. When the amount of aniline is reduced below 6-fold of nitrobenzene, however, the catalyst system showed substantial loas of its activity starting from second batches.
Discussion The catalyst system employed in the present study was found to be exceptionally efficient in N,IV'-diphenylurea synthesis from aniline, nitrobenzene,and carbon monoxide. Almost quantitative yields are obtained under relatively mild reaction conditions. Since the reaction gives solid products and catalysts remain in solution, they can be easily separated, for example, by filtration for catalyst recycle. These attributes of the catalyst system are of paramount importance when a large-scale application is considered. The present catalyst system may appear to be similar to the one proposed by Dieck et al. (1975). At 90 OC and
atmospheric pressure and with the 1:l.l mole ratio of aniline to nitrobenzene in the feed, Dieck et al. reported a DPU yield of 64% with a catalyst system consisting of Pd(CH3C00)2,NEt4C1, tri-n-butylamine (n-Bu3N),and PPh3. Compared to our catalyst system, their system contained the n-Bu3N in addition. They reported that the presence of a basic tertiary amine was essential to achieve reasonable yields. However, the role of n-Bu3N, if added to our catalyst system, appears only to enhance the solubility of palladium salts. No significant improvement in yield was observed if the reaction condition was chosen such that all palladium salt was dissolved in the reaction mixture. Use of excess aniline may have helped enhance the solubility of palladium salts and have made the amine component dispensable. Noting the fact that metallic Pd is inactive (Table I), the solubility of palladium must be important for activity and longevity of our catalyst system. The catalyst system would lose some of its initial activity in the second run if solid Pd were formed and stayed with the solid products during filtration. This appears to be the case when the amount of aniline was less than 6-fold of nitrobenzene. The other factor that contributed to much higher DPU yields of our system than observed by Dieck et al. appears to be higher carbon monoxide pressure emplyed in our work. Indeed, the amount of carbon monoxide used in their experiments corresponded only to 88% of theory. If the reaction follows eq 2, nitrobenzene and aniline will be consumed on equimolar basis. This is the stoichiometry reported so far in metal-catalyzed DPU synthesis from nitrobenzene, aniline, and CO. However, with our catalyst system, much more aniline was consumed than nitrobenzene, especially when high aniline/nitrobenzene charge ratios were employed. Most studies on DPU synthesis reported so far have employed near-equimolar reaction mixtures of aniline and nitrobenzene. Hence, it is not clear whether this different stiochiometry is a unique characteristics of our catalyst system or other catalyst systems would followed the same stoichiometry if excess aniline were used. The consumption of more aniline cannot be due to a reaction between aniline themselves since no reaction takes place without nitrobenzene. There must be a reaction that consumes more aniline than nitrobenzene. A possible candidate is reaction 3, which consumes 5 mol of aniline/ mol of nitrobenzene. Tsuji et al. (1985) proposed that both reactions 2 and 3 might take place with a catalyst system of PtC12(PPh3)z-SnC14-EbN. However, no experimental results were provided indicating the importance of reaction 3. They proposed that reaction 3 might involve a carbamoyl complex, PhNHCO[Pt]H, as an intermediate, while reaction 2 might involve a phenylisocyanate complex PhNCO[Pt], formed by reductive carbonylation of nitrobenzene. There have been many precedents in literature for these types of intermediate proposed for other catalyst systems in carbonylation of nitrobenzene and aniline (Cenini, 1984; Ikariya, 1989). Similar intermediates could have been involved in our palladium system as well. Employing these intermediates to our Pd system and to account for the stiochiometry given by reactions 2 and 3, the schemes shown in Figure 8 could be considered. Here, [Pd] represents a catalytically active Pd complex, probably containing, among others, PPh3 as a ligand. Possible structures of this Pd complex under similar conditions have been discussed (Hidai et al., 1973). As mentioned, this Pd complex does not undergo a redox cycle and maintains the same oxidation state throughout the catalytic cycle. As indicated in Scheme 1, the phenyliso-
Figure 8. Possible reaction schemes of N,”-diphenylurea Synthesis from nitrobenzene, aniline, and CO in the presence of Pd catalyet.
cyanate complex PhNCO[Pd] is known to be formed by carbonylation of a nitrene complex, PhN[Pd], which in turn has been generated from the stepwise deoxygenation of nitrobenzene by CO. The phenylimyanate complex can react with aniline to give the desired N,”-diphenylurea. This catalytic cycle requires same moles of nitrobenzene and aniline. In Scheme 2, the carbamoyl complex PhNHCO[Pd]H is formed from the reaction between aniline and CO (Tkatchenko, 1982). It reacts with aniline in the presence of nitrobenzene to give the urea. Here, nitrobenzene serves as an oxidizing reagent by removing hydrogen from the carbamoyl intermediate. Since a mole of nitrobenzene can oxidize 6 mol of aniline or the carbamoyl complex and itself is reduced to aniline, 5 net mol of aniline is consumed per mole of nitrobenzene as eq 3 indicates. Another interesting aspect of the reaction 3 is that HzO is a coproduct instead of COz, and thus less CO is consumed per mole of the urea. Indeed, from an analysis by a gas chromatography of a reaction mixture before and after the reaction, it was established that water was formed during the reaction. When aniline is present in excess, in particular, the reaction 3 becomes more important as seen in Table 11. During the review of this work, a referee suggested another possible scheme for the reaction as outlined in eqs 4 and 5. It is the condensation of amine with COz genPhNOz + CO PhNO + Cop (4) 2PhNH2 + COZ PhNHCONHPh + HzO ( 5 ) erated by nitrobenzene oxidation of CO. However, this scheme was diecarded because the reaction between aniline and COB(equation 5 ) under otherwise similar conditions did not proceed at all. The promoting effect of NEt4C1is not well understood. As shown in Table I, the reaction did not proceed beyond 11%of nitrobenzene conversion without an onium salt in agreement with the report of Dieck et al. (1975). When an insufficient amount of NEt4Cl was added, the nitrobenzene conversion stopped at a certain level as indicated in Figure 4. These findinge are consistent with the original suggestion of Dieck et al., who assumed that an onium salt maintained Pd solubility by forming a complex such as (Ph3P)zPdC13--NR4+. However, Han et al. (1989)demonstrated that halides dramatically enhanced the rates of both the formation of the nitrene complex from the reaction between nitrosobenzene and R U & C O )and ~ ~ its carbonylation to the phenylisocyanate complex. The role
--
of NEt4C1in our system has yet to be proved. Conclusions The reaction conditions and catalyst system employed in the present study were found to be exceptionally efficient in N,”-diphenylurea synthesis from aniline, nitrobenzene, and carbon monoxide. The system also allows facile product separation and catalyst recovery. Also, the study presented some experimental evidence that exhibited a new stoichiometry of the reaction which, to the best of our knowledge, has not been observed previously. Acknowledgment We thank Lucky R & D Center for the permission to publish this work. Registry No. Pd(CH3C02)2, 3375-31-3;Pd(C12),7647-10-1; Pd(CFSC02)2, 42196-31-6;NEt4C1,56-34-8Bu,PBr, 3115-68-2; KCl, 7447-40-7;CO, 630.080;NJV-diphenylurea, 102-07-8; aniline, 62-53-3;nitrobenzene, 630-08-0.
Literature Cited Cenini, S. Carbonylation of Nitroaromatics. In Industrial Applications of Homogeneous Catalysis and Related Topics; Universita di Milano: Milano, 19M,p 135. Dieck, H. A.; Laine, R.M.; Heck,R.F. A Low-Preeaure, PalladiumCatalyzed N,”-Diphenylurea Synthesis from Nitro Compounds, Amines, and Carbon Monoxide. J. Org. Chem. 1975, 40, 2819-2822. Giannoccaro, P. Palladium-CatalyzedN,N’-disubstitutedUrea Synthesis by Oxidative Carbonylation of Amines Under Carbon Monoxide and Oxygen at Atmospheric Pressure. J . Organomet. Chem. 1987,336,271-278. Giannoccaro, P. Palladium-Catalyzed Conversion of N,”-Diphenylurea into Carbamate Esters. Inorg. Chim. Acta 1988,142, 81-84. Han, S.H.; Song, J. S.; Macklin, P. D.; Nguyen, S. T.; Geoffroy, G. L. Organometallics 1989,8, 2127-2138. Hidai, M.; Kokura, M.; Uchida, Y. Reactions of Palladium(I1)Compounds with Carbon Monoxide in Alcohol Amine Systems: A New Route to Palladium Carbonyl and Carboalkoxy-palladium(I1) Complexes. J . Organomet. Chem. 1973,52,431-436. Ikariya, T. Carbonylation Reaction of N-containing Aromatics. Shokubai (Catalysis) 1989,31,271-278. Ikariya, T.; Itagaki, M.; Mizuguchi, M.; Sakai. I.; Tajima, 0. Ureas. J m . Kokai Tokkvo Koho JP 62-69 263. 1987a: Chem. Abstr. l987a,107,96447;. Ikariya, T.;Itagaki, M.; Mizuguchi, M.; Sakai, I.; Tajima, 0. Aromatic Urethanes. Jpn. Kokai Tokkyo Koho J p 62-59261,1987h Chem. Abstr. 1987b,107, 96448d. Ikariya, T.;Itagaki, M.; Shmoyama, I.; Mizuguchi,M.; Hachiya, T. Preparation of Arylcarbamatea. Eur. Pat. Appl. EP 310,907,1989; Chem. Abstr. 1989,111,232337d.
I n d . Eng. Chem. Res. 1991,30, 1461-1468 Kondo, K.; Sonoda, N.; Tsutaumi, S. New Selenium-triethylamine Catalyzed Synthesis of Arylureaa from Carbon Monoxide and Aromatic Amines. J. C h " SOC.,Chem. Commun. 1972,307-308. Lee, S. M.; Lee, C. W.; Lee, J. S. Manufacture of N,N'-substituted Ureas. Korean Patent Application 89-15880, 1989. Macho, V.; Hudec, J.; Polievka, M.; Filadelfyova, M. One-Step Synthesis of N,N'-diphenyl Urea. Chem. h u m . 1975,25, 140-144. Nefedov, B. K.; Sergeeva, N. S.;Eidus, Ya. T. CarbonylationReactions. 9. Carbonylation of Amines by Carbon Monoxide in the Presence of Mercury(I1) Acetate. Zzu. Akad. Nauk SSSR, Ser. Khim. 1973,807-808. Nefedov, B. K.; Sergeeva, N. S.; Eidus, Ya. T. CarbonylationReactions. 21. Synthesis of N,N'-substituted Urea by Carbonylation
1461
of Amines by Carbon Monoxide at Atmospheric Pressure. Izu. Akad. Nauk SSSR, Ser. Khim. 1976,349-353. Tkatchenko, I. In Comprehensive Organometallic Chemiatry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, p 173. Tsuii, J. Organic Synthesis with Palladium Compounds:. Swingerverlag: Berlin, i9aO; p 81. Tsuji, Y.; Takeuchi, Y.; Watanabe, Y. Platinum Complex Catalyzed Synthesis of Urea Derivatives from Nitroarena and Amiiea under C-arbon Monoxide. J. Organomet. Chem. 1981, 290, 249-255.
Receiued for reuiew July 30, 1990 Accepted January 3,1991
Kinetic Study of NH3-CatalyzedImage Reversal in Positive Photoresist Gary L. Wolk* and David H. Ziger AT&T Bell Laboratories, P.O. Box 900,Princeton, New Jersey 08540 Ammonia-catalyzed image reversal of a positive photoresist was studied by investigating the kinetics of thermal reactions, in air and NH3 ambients, by using in situ UV/vis and FTIR spectroscopic techniques. Kinetic data indicate that the photoactive compound, a substituted 1,Bnapthoquinone diazide, decomposes three times faster in ammonia than in air and that an azo compound is formed during thermal treatment in NH3. Activation energies for thermal decomposition in air- and ammonia-catalyzed azo dye formation are calculated to be 32 f 1and 29.7 f 3.6 kcal/mol, respectively. FTIR data obtained before and after treatment with amine indicate that rapid decarboxylation is observed a t temperatures lower than typically used for ammonia-catalyzed image reversal. This discrepancy is attributed to either ammonia mass transport limitations or other, as yet undefined, secondary reactions that may be important to the reversal process. 1. Introduction
Advances in microelectronic circuit fabrication have been accelerated by the availability of photopolymer materials used for submicron pattern definition. Positiveworking photoresists, materials that faithfully reproduce an object pattern upon exposure and development, have been the mainstay of the semiconductor industry for some time (Bowden, 1984). This type of resist consists of a photolabile material, typically a substituted 1,2-napthoquinone diazide (I),
additional photoactive moieties tied to a benzophenone backbone. The lithographic utility of this combination of materials depends on the solubility, in basic aqueous developer, of irradiated material: the photoactive compound I (hereafter PAC) inhibits the base solubility of the acidic novolac resin I1 (hereafter NOV). Photolysis of the PAC leads to the formation of an indenecarboxylic acid 111, which is base soluble (Pacanksy and Lyerla, 1979) 0
0
I
R
R
and a phenolic (novolac) polymer backbone (11) (Willson, 1983): OH
OH
I
R
I11
I
r
c
1
I1
Commercial photoresists oftan employ poly(diazoquinone) compounds with the R group in I possessing two or more 0888-5885191/ 2630-1461$02.50/0
thereby allowing the exposed material to be removed with a basic developer. Numerous methods (Burggraff, 1987) have been proposed to extend the lithographic resolution of these materials, including amine-catalyzed image reversal (Moritz and Pall, 1978; Moritz, 1986; Takahashi et al., 1980). While image reversal adds processing steps to the simple positive process, it can extend the resolution of an exposure tool by 30% (Alling and Stauffer, 1986; Ziger and Reightler, 1988b). The image reversal process involves heating a photoresist film, in which a latent image has been created, in the presence of base. The base can be part of the photoresist formulation (the monazoline process) (MacDonald et al., 1982) or may be supplied as a gaseous amine such as anhydrous ammonia or ammonium hydroxide vapors (MacDonald et al., 1982; Long and Newman, 1984; Kloee et al.,
ca 1991 American Chemical Society
