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HYDROGENATION OF HALOAROMATIC NITRO COMPOUNDS
CATALYSIS IN ORGANIC SYNTHESES
HYDROGENATION OF HALOAROMATIC NITRO COMPOUNDS
J. R. Kosak
INTRODUCTION
Hydrogenation of haloaromatic nitro compounds to the corresponding haloaromatic amines is always accompanied by some hydrogenolysis of the carbon-halogen bond. Depending on the halogen"'" and its position relative to nitro in the aromatic system, dehalogenation can vary from negligible to 100%. The more reactive the aromatic halogen the greater the loss. During the past twenty years, a substantial amount of technology has been developed to preferentially reduce the nitro group and minimize the dehalogenation reaction. A previous paper (1) reviewed the state of the art up to 1969. Since then, a number of processes have been developed which are, essentially, variations on that technology. Three of the more effective procedures for hydrogenating haloaromatic nitro compounds with minimum dehalogenation are those using triphenylphosphite/platinum catalyst (2), sulfided platinum catalyst (3), and morpholine/platinum catalyst (4). Table I shows a comparison of these processes for the hydrogenation of 3,4-dichloronitrobenzene under the same temperature and pressure conditions. Triphenylphosphite/platinum catalyst is the most effective of these in minimizing dehalogenation but also gave the lowest purity because of other by-product formation. The sulfided platinum catalyst yielded the highest purity product but had the lowest reduction activity of these three systems. The morpholine/platinum catalyst system is accompanied by slightly 7 Halogen here and throughout this presentation represents fluorine chlorine, bromine and iodine. f
107
Copyright © 1980 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-389050-0
J O H N R. KOSAK
TABLE I.
Effectiveness of Procedures for Minimizing Dehalogenation 1)
Reduction Rate Relative
3
Inhibitor (Wt. %)
Catalyst (ppm Pt)
Tr iphenyl phosphite (0.05) None
5% Pt/ carbon (20) 5% Pt/ carbon sulfided (20) 5% Pt/ carbon (20)
Morpholine (1^0)
1.0
0. 09
19.3
Dehalogenation %
Product^ Purity %
<0. 01
98.52
0.09
99.82
0. 18
99.50
a
Basis - Moles H consumed per gram platinum per minute. ^ GLC, area percent 2
more dehalogenation but yields product of excellent purity and exhibits the best reduction rate. A new inhibitor has been found which minimizes the dehalogenation reaction during reduction of the nitro group. This is phosphorous acid, H3PO3. It is effective with both platinum and palladium catalysts. Reduction temperatures to 140 C can be used successfully with some haloaromatic nitro compounds without significant dehalogenation. Hydrogen pressures of 100-1500 psig have been used successfully. This procedure is applicable to all the halogens. In a typical example, p-chloronitrobenzene was hydrogenated to p-chloroaniline essentially
109
PREPARATION O F H A L O A R O M A T I C A M I N E S
quantitatively with only 0.02% dehalogenation 5 ) .
5% Pt/C 0.1% H P 0 3
H
2
3
Temp. 100-115 C Press. - 500 psig
CI Purity - 99.6% Dehalogenation 0.02%
Inhibitor To determine whether phosphorous acid is unique in its capacity to inhibit dehalogenation or whether it represents a class of compounds useful as inhibitors, it was proposed that the basic structure required for inhibition is 0 it
X-P-X' H wherein X and X' might be H, OH, or aryl. To test this hypothesis, the compounds shown in Table II were evaluated using the hydrogenation of o-chloronitrobenzene as the model system. Although it is evident that diphenylphosphinic acid shows a limited inhibiting effect, these results indicate that the structure most effective for inhibiting dehalogenation is 0 it
X-P-OH H where X = H, OH, or aryl. 1 Standard laboratory hydrogenation conditions were: 2 moles haloaromatic nitro compound, 0.05-0.1 wt. % phosphorous acid, 20 ppm platinum (as 5% Pt/C) at 110-115°C and 500 psig hydrogen pressure. Parr Autoclave-Titanium. RPM-900.
110
J O H N R. KOSAK
TABLE II.
Effect of Inhibitor in Control 1ing Dehalogenation
20 ppm Pt 0. 1% Inhibitor Temp. 110° + 5°C Press. - 500 psig
Inhibitor Phosphorous Acid
Inhibitor Concentration Wt. %
Dechloroination
Prod. Purity %
0. 1
0.02
98.3
0. 1
0.02
95.2
0. 1
1.2
92.8
0 H0-P-0H H
Hypophosphorous Acid
0 H-P-OH H
Phenylphosphinic Acid
0 Ph-P-OH H
Diphenylphosphinic Acid
0. 1
30
66. 0
50
40.0
0
Ph-P-Ph H None GLC, area percent.
PREPARATION O F H A L O A R O M A T I C A M I N E S
111
Inhibitor concentrations beyond the established minimum do not enhance control of the dehalogenation reaction. However, hydrogenation activity does vary significantly with concentration (Figure 1 ) . Control of the dehalogenation reaction remains essentially the same between 0.05 and 0.4 wt. percent phosphorous acid. Below 0.05 wt. percent, a slight decrease in control is detectable. Reduction rate remains constant between 0.2 and 0.4 wt. percent phosphorous acid and begins to increase below 0.2 wt. percent.
Catalysts A definite sensitivity is exhibited by different catalyst metals toward phosphorous acid. The order of hydrogenation activity with the tested catalyst metals was found to be Pd > Pt >> Ni Though palladium is more active than platinum, it causes more dehalogenation. In a direct comparison using 2,5-dichloronitrobenzene as the model compound, the palladium catalyst (as 5% Pd on carbon) was 2.6 times faster but yielded 3 times more dehalogenation than the platinum catalyst (as 5% Pt on carbon) (Table III).
TABLE III. Precious Metal
Comparison of Palladium vs. Platinum Catalyst Rel. Reaction Rate
Dechloroination %
Purity' %
Palladium 2.6 1.1 96.4 Platinum 1.0 0.37 98.4 Basis: Reduction of 2 5-dichloronitrobenzene using 0.1 wt. % H^P0 20 ppm precious metal, 95-100°C 500 psig hydrogen pressure. f
V
GLC
?
area percent.
t
112
J O H N R. KOSAK
EFFECT OF INHIBITOR CONCENTRATION BASIS- HYDROGENATION OF 3,4-DICHLORONITROBENZENE-20 ppm 2
Pt
PRESSURE.
0EHAL0GENATION
0.01
0.06
]
b
0.02
%
1—•
*
b
0.05
7
1
0.07
1
0.04
r
1
0.03 '00 1
^HYDROGEN• g. Pf'-min"
1
II0-II5°C, 500 psig H
0
5.0 I 0.1
0.2 WT.
0.3
0.4
0.5
H 3 P O 3
FIGURE 1
Varying platinum concentration in the hydrogenation of 3,4-dichloronitrobenzene from 10-100 ppm influences reduction time (the more catalyst the shorter the time) but the effect on dehalogenation was inconsequential varying from 0.01% to 0.04%.
Temperature Effect The effect of reduction temperature will vary with the halogen substituent present and its position relative to the nitro group. A number of haloaromatic nitro compounds, (e.g., 3,4-dichloronitrobenzene, p-chloronitrobenzene, 6-chloro-2nitrotoluene) can be hydrogenated at temperatures up to 140°C without incurring any substantial amount of dehalogenation. The effect of temperature on rate and dehalogenation in the hydrogenation of 3,4-dichloronitrobenzene is shown in Figure 2. The increase in reaction rate with increasing temperature was found to be relatively small under these
113
PREPARATION O F H A L O A R O M A T I C A M I N E S
E F F E C T OF TEMPERATURE ON DEHALOGENATION AND REDUCTION RATE B A S I S : HYDROGENATION OF 3 , 4 - D I C H L O R O N I T R O B E N Z E N E O.IV. H P 0 , 2 0 p p m P t , 5 0 0 p s i g H PRESSURE 3
2
°/o DEHALOGENATION
MHYDROGEN'g. Pt'^min
1
3
100
110 120 130 140 TEMPERATURE ( ° C )
150
FIGURE 2
experimental conditions. There is very little change in the amount of dehalogenation up to 125°C Between 125°C and 140°C, dehalogenation becomes significantly greater but still very low.
Hydrogen Pressure
Hydrogen pressure has little or no effect on the extent of halogen displacement during hydrogenation. It does influence the rate of hydrogenation - the higher the pressure the greater the rate. Pressures of 100-1500 psig can be used successfully. 7
Reaction rate does not increase with increased agitation but does increase with increased catalyst concentration and/or hydrogen pressure. It is proposed that a 1iguid-solid mass transfer 1 imitation is operative. Private communication K. F. Cossaboon E. I. Du Pont de Nemours £ Company, Deepwater, N. J. r
114
J O H N R. KOSAK
Halogen Sensitivity
As is known, the order of susceptibility to hydrogenolysis for isomeric chloroaromatic nitro compounds during hydrogenaation is ortho > para > meta The phosphorous acid inhibitors do not affect this proclivity. In a direct comparison of morpholine and phosphorous acid inhibitors in the hydrogenation of the chloronitrobenzene isomers, the expected ortho, para, meta order of susceptibility is observed, and the superiority of phosphorous acid to morpholine in controlling dehalogenation is demonstrated (Figure 3 ) . In addition to isomer position sensitivity, the various halogens also exhibit varying susceptibility to displacement by hydrogen. The order is as expected with iodine most sensitive and fluorine least sensitive. I > Br > CI > F In spite of the greater sensitivity of bromo and iodo substituted nitrobenzenes, it is possible to produce some of the % DEHALOGENATION VS. ISOMER POSITION B A S I S : HYDROGENATION OF CHLORONITROBENZENE ISOMERS
10 0.9 N0I1VN3901VH3Q %
0.8
E 2 M 0 R P H 0 L I N E - 2 0 p p m Pt I WGT. % , REDUCTION AT 95-IOO°C AND 500 psig H Wm PHOSPHOROUS A C I D - 2 0 ppm Pt 0.1 WGT. % , REDUCTION AT I I 0 - I I 5 ° C AND
0.4 0.3 0.2 0.1 0
ORTHO
PARA
META
CHLORONITROBENZENE ISOMERS
FIGURE 3
2
115
PREPARATION O F H A L O A R O M A T I C A M I N E S
corresponding haloanilines in very good to excellent yields using phosphorous acid as the dehalogenation inhibitor (Table IV). It is interesting to note that reduction of m-iodonitrobenzene was affected successfully in the presence of iodide ion which is a potent catalyst poison (6).
Safety The potential exists for a destructive runaway reaction in the batch hydrogenation of aromatic nitro compounds. This potential stems from possible accumulation of the corresponding hydroxylamine during the course of the hydrogenation and subsequent energetic disproportionation of the hydroxylamine 2 R-NHOH
> R-NO + RNH^ + H 0 2
Two incidents have been documented in the literature recently. One occurred in a production scale hydrogenation reactor (7) and the other in laboratory scale equipment (8). These experiences may be pertinent to others studying or operating similar processes. It should be noted that accumulation of arylhydroxylamines can be influenced by numerous factors. Thus, each process must be examined individually to ascertain the hazard potential.
Summary A new class of inhibitors has been found for minimizing dehalogenation during the hydrogenation of haloaromatic nitro compounds. It is based on the general structure 0 ft
X-P-OH H and is effective for all the halogens. Both platinum and palladium catalysts are effective with these inhibitors platinum being the preferred catalyst.
J O H N R. KOSAK
116
TABLE IV.
Comparison of Morpholine and Phosphorus Acid Inhibitor % Dehalogenation vs. Specific Halogen
Halonitrobenzene p-Fluoro p-Chloro p-Bromo m-Iodo
Morpholine Inhibitor
Dehalogenation Phosphorous Acid Inhib itor
0. 1 > w
Trace 0.02 1.6° 2.5
d
-
e
1 wt. % morpholine, 20 ppm Pt as 5% Pt/C, 95-100°C, 500 psig H . a
2
0. 1 wt. % H PQ , 20 ppm Pt as 5% Pt/C, 110-115°C, 500 psig H . b
°Methanol solvent, 0.175 wt. % H^PO
y
20 ppm Pt as 5%
Pt/C, 70-80°C, 500 psig H . Methanol solvent, 1 wt. % morpholine, 100 ppm Pt as 5% Pt/C, 70-80°C, 500 psig H . Low product purity. Methanol solvent, 0.31% phosphorous acid, 200 ppm Pt, 50-55°C, 500 psig H pressure. Product purity - 93%.
REFERENCES
1.
2. 3.
4. 5. 6. 7.
Kosak, J. R., "Catalytic Hydrogenation of Aromatic Halonitro Compounds", Ann. New York Acad. Sci. 172, p p . 174-185 (1970) . Craig, W. C , G. J. Davis & P. 0. Shull, U.S. Patent No. 3,474, 144 (1969). Greenfield, H., "Platinum Metal Sulfides in Catalytic Hydrogenation", Ann. New York Acad. Sci., 145, p p . 108-115 (1967) . Kosak, J. R. , U.S. Patent No. 3, 145,231 (1964). Kosak, J. R., U.S. Patent 4,020,107 (1977). Rylander, P. N., "Catalytic Hydrogenation over Platinum Metal Catalysts", Academic Press, N.Y., pp. 17-18 (1967). Tong, W. R., Seagraves, R. L., Wiederhorn, R., 3,4-Dichloroaniline Autoclave Incident, Chemical Engineering Progress, Loss Prevention, Vol. II, pp. 71-75 (1977).
PREPARATION O F H A L O A R O M A T I C A M I N E S
8.
117
Rondestvedt, C. S., and Johnson, T. A., "Explosion of an Arylhydroxylamine During Preparation of 2-Chloro-5-methylaniline", Synthesis, p. 851, December 1977-
HYDROGENATION OF HALOAROMATIC NITRO COMPOUNDS
J. R. Kosak
INTRODUCTION
Hydrogenation of haloaromatic nitro compounds to the corresponding haloaromatic amines is always accompanied by some hydrogenolysis of the carbon-halogen bond. Depending on the halogen"'" and its position relative to nitro in the aromatic system, dehalogenation can vary from negligible to 100%. The more reactive the aromatic halogen the greater the loss. During the past twenty years, a substantial amount of technology has been developed to preferentially reduce the nitro group and minimize the dehalogenation reaction. A previous paper (1) reviewed the state of the art up to 1969. Since then, a number of processes have been developed which are, essentially, variations on that technology. Three of the more effective procedures for hydrogenating haloaromatic nitro compounds with minimum dehalogenation are those using triphenylphosphite/platinum catalyst (2), sulfided platinum catalyst (3), and morpholine/platinum catalyst (4). Table I shows a comparison of these processes for the hydrogenation of 3,4-dichloronitrobenzene under the same temperature and pressure conditions. Triphenylphosphite/platinum catalyst is the most effective of these in minimizing dehalogenation but also gave the lowest purity because of other by-product formation. The sulfided platinum catalyst yielded the highest purity product but had the lowest reduction activity of these three systems. The morpholine/platinum catalyst system is accompanied by slightly 7 Halogen here and throughout this presentation represents fluorine chlorine, bromine and iodine. f
107
Copyright © 1980 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-389050-0
J O H N R. KOSAK
TABLE I.
Effectiveness of Procedures for Minimizing Dehalogenation 1)
Reduction Rate Relative
3
Inhibitor (Wt. %)
Catalyst (ppm Pt)
Tr iphenyl phosphite (0.05) None
5% Pt/ carbon (20) 5% Pt/ carbon sulfided (20) 5% Pt/ carbon (20)
Morpholine (1^0)
1.0
0. 09
19.3
Dehalogenation %
Product^ Purity %
<0. 01
98.52
0.09
99.82
0. 18
99.50
a
Basis - Moles H consumed per gram platinum per minute. ^ GLC, area percent 2
more dehalogenation but yields product of excellent purity and exhibits the best reduction rate. A new inhibitor has been found which minimizes the dehalogenation reaction during reduction of the nitro group. This is phosphorous acid, H3PO3. It is effective with both platinum and palladium catalysts. Reduction temperatures to 140 C can be used successfully with some haloaromatic nitro compounds without significant dehalogenation. Hydrogen pressures of 100-1500 psig have been used successfully. This procedure is applicable to all the halogens. In a typical example, p-chloronitrobenzene was hydrogenated to p-chloroaniline essentially
109
PREPARATION O F H A L O A R O M A T I C A M I N E S
quantitatively with only 0.02% dehalogenation 5 ) .
5% Pt/C 0.1% H P 0 3
H
2
3
Temp. 100-115 C Press. - 500 psig
CI Purity - 99.6% Dehalogenation 0.02%
Inhibitor To determine whether phosphorous acid is unique in its capacity to inhibit dehalogenation or whether it represents a class of compounds useful as inhibitors, it was proposed that the basic structure required for inhibition is 0 it
X-P-X' H wherein X and X' might be H, OH, or aryl. To test this hypothesis, the compounds shown in Table II were evaluated using the hydrogenation of o-chloronitrobenzene as the model system. Although it is evident that diphenylphosphinic acid shows a limited inhibiting effect, these results indicate that the structure most effective for inhibiting dehalogenation is 0 it
X-P-OH H where X = H, OH, or aryl. 1 Standard laboratory hydrogenation conditions were: 2 moles haloaromatic nitro compound, 0.05-0.1 wt. % phosphorous acid, 20 ppm platinum (as 5% Pt/C) at 110-115°C and 500 psig hydrogen pressure. Parr Autoclave-Titanium. RPM-900.
110
J O H N R. KOSAK
TABLE II.
Effect of Inhibitor in Control 1ing Dehalogenation
20 ppm Pt 0. 1% Inhibitor Temp. 110° + 5°C Press. - 500 psig
Inhibitor Phosphorous Acid
Inhibitor Concentration Wt. %
Dechloroination
Prod. Purity %
0. 1
0.02
98.3
0. 1
0.02
95.2
0. 1
1.2
92.8
0 H0-P-0H H
Hypophosphorous Acid
0 H-P-OH H
Phenylphosphinic Acid
0 Ph-P-OH H
Diphenylphosphinic Acid
0. 1
30
66. 0
50
40.0
0
Ph-P-Ph H None GLC, area percent.
PREPARATION O F H A L O A R O M A T I C A M I N E S
111
Inhibitor concentrations beyond the established minimum do not enhance control of the dehalogenation reaction. However, hydrogenation activity does vary significantly with concentration (Figure 1 ) . Control of the dehalogenation reaction remains essentially the same between 0.05 and 0.4 wt. percent phosphorous acid. Below 0.05 wt. percent, a slight decrease in control is detectable. Reduction rate remains constant between 0.2 and 0.4 wt. percent phosphorous acid and begins to increase below 0.2 wt. percent.
Catalysts A definite sensitivity is exhibited by different catalyst metals toward phosphorous acid. The order of hydrogenation activity with the tested catalyst metals was found to be Pd > Pt >> Ni Though palladium is more active than platinum, it causes more dehalogenation. In a direct comparison using 2,5-dichloronitrobenzene as the model compound, the palladium catalyst (as 5% Pd on carbon) was 2.6 times faster but yielded 3 times more dehalogenation than the platinum catalyst (as 5% Pt on carbon) (Table III).
TABLE III. Precious Metal
Comparison of Palladium vs. Platinum Catalyst Rel. Reaction Rate
Dechloroination %
Purity' %
Palladium 2.6 1.1 96.4 Platinum 1.0 0.37 98.4 Basis: Reduction of 2 5-dichloronitrobenzene using 0.1 wt. % H^P0 20 ppm precious metal, 95-100°C 500 psig hydrogen pressure. f
V
GLC
?
area percent.
t
112
J O H N R. KOSAK
EFFECT OF INHIBITOR CONCENTRATION BASIS- HYDROGENATION OF 3,4-DICHLORONITROBENZENE-20 ppm 2
Pt
PRESSURE.
0EHAL0GENATION
0.01
0.06
]
b
0.02
%
1—•
*
b
0.05
7
1
0.07
1
0.04
r
1
0.03 '00 1
^HYDROGEN• g. Pf'-min"
1
II0-II5°C, 500 psig H
0
5.0 I 0.1
0.2 WT.
0.3
0.4
0.5
H 3 P O 3
FIGURE 1
Varying platinum concentration in the hydrogenation of 3,4-dichloronitrobenzene from 10-100 ppm influences reduction time (the more catalyst the shorter the time) but the effect on dehalogenation was inconsequential varying from 0.01% to 0.04%.
Temperature Effect The effect of reduction temperature will vary with the halogen substituent present and its position relative to the nitro group. A number of haloaromatic nitro compounds, (e.g., 3,4-dichloronitrobenzene, p-chloronitrobenzene, 6-chloro-2nitrotoluene) can be hydrogenated at temperatures up to 140°C without incurring any substantial amount of dehalogenation. The effect of temperature on rate and dehalogenation in the hydrogenation of 3,4-dichloronitrobenzene is shown in Figure 2. The increase in reaction rate with increasing temperature was found to be relatively small under these
113
PREPARATION O F H A L O A R O M A T I C A M I N E S
E F F E C T OF TEMPERATURE ON DEHALOGENATION AND REDUCTION RATE B A S I S : HYDROGENATION OF 3 , 4 - D I C H L O R O N I T R O B E N Z E N E O.IV. H P 0 , 2 0 p p m P t , 5 0 0 p s i g H PRESSURE 3
2
°/o DEHALOGENATION
MHYDROGEN'g. Pt'^min
1
3
100
110 120 130 140 TEMPERATURE ( ° C )
150
FIGURE 2
experimental conditions. There is very little change in the amount of dehalogenation up to 125°C Between 125°C and 140°C, dehalogenation becomes significantly greater but still very low.
Hydrogen Pressure
Hydrogen pressure has little or no effect on the extent of halogen displacement during hydrogenation. It does influence the rate of hydrogenation - the higher the pressure the greater the rate. Pressures of 100-1500 psig can be used successfully. 7
Reaction rate does not increase with increased agitation but does increase with increased catalyst concentration and/or hydrogen pressure. It is proposed that a 1iguid-solid mass transfer 1 imitation is operative. Private communication K. F. Cossaboon E. I. Du Pont de Nemours £ Company, Deepwater, N. J. r
114
J O H N R. KOSAK
Halogen Sensitivity
As is known, the order of susceptibility to hydrogenolysis for isomeric chloroaromatic nitro compounds during hydrogenaation is ortho > para > meta The phosphorous acid inhibitors do not affect this proclivity. In a direct comparison of morpholine and phosphorous acid inhibitors in the hydrogenation of the chloronitrobenzene isomers, the expected ortho, para, meta order of susceptibility is observed, and the superiority of phosphorous acid to morpholine in controlling dehalogenation is demonstrated (Figure 3 ) . In addition to isomer position sensitivity, the various halogens also exhibit varying susceptibility to displacement by hydrogen. The order is as expected with iodine most sensitive and fluorine least sensitive. I > Br > CI > F In spite of the greater sensitivity of bromo and iodo substituted nitrobenzenes, it is possible to produce some of the % DEHALOGENATION VS. ISOMER POSITION B A S I S : HYDROGENATION OF CHLORONITROBENZENE ISOMERS
10 0.9 N0I1VN3901VH3Q %
0.8
E 2 M 0 R P H 0 L I N E - 2 0 p p m Pt I WGT. % , REDUCTION AT 95-IOO°C AND 500 psig H Wm PHOSPHOROUS A C I D - 2 0 ppm Pt 0.1 WGT. % , REDUCTION AT I I 0 - I I 5 ° C AND
0.4 0.3 0.2 0.1 0
ORTHO
PARA
META
CHLORONITROBENZENE ISOMERS
FIGURE 3
2
115
PREPARATION O F H A L O A R O M A T I C A M I N E S
corresponding haloanilines in very good to excellent yields using phosphorous acid as the dehalogenation inhibitor (Table IV). It is interesting to note that reduction of m-iodonitrobenzene was affected successfully in the presence of iodide ion which is a potent catalyst poison (6).
Safety The potential exists for a destructive runaway reaction in the batch hydrogenation of aromatic nitro compounds. This potential stems from possible accumulation of the corresponding hydroxylamine during the course of the hydrogenation and subsequent energetic disproportionation of the hydroxylamine 2 R-NHOH
> R-NO + RNH^ + H 0 2
Two incidents have been documented in the literature recently. One occurred in a production scale hydrogenation reactor (7) and the other in laboratory scale equipment (8). These experiences may be pertinent to others studying or operating similar processes. It should be noted that accumulation of arylhydroxylamines can be influenced by numerous factors. Thus, each process must be examined individually to ascertain the hazard potential.
Summary A new class of inhibitors has been found for minimizing dehalogenation during the hydrogenation of haloaromatic nitro compounds. It is based on the general structure 0 ft
X-P-OH H and is effective for all the halogens. Both platinum and palladium catalysts are effective with these inhibitors platinum being the preferred catalyst.
J O H N R. KOSAK
116
TABLE IV.
Comparison of Morpholine and Phosphorus Acid Inhibitor % Dehalogenation vs. Specific Halogen
Halonitrobenzene p-Fluoro p-Chloro p-Bromo m-Iodo
Morpholine Inhibitor
Dehalogenation Phosphorous Acid Inhib itor
0. 1 > w
Trace 0.02 1.6° 2.5
d
-
e
1 wt. % morpholine, 20 ppm Pt as 5% Pt/C, 95-100°C, 500 psig H . a
2
0. 1 wt. % H PQ , 20 ppm Pt as 5% Pt/C, 110-115°C, 500 psig H . b
°Methanol solvent, 0.175 wt. % H^PO
y
20 ppm Pt as 5%
Pt/C, 70-80°C, 500 psig H . Methanol solvent, 1 wt. % morpholine, 100 ppm Pt as 5% Pt/C, 70-80°C, 500 psig H . Low product purity. Methanol solvent, 0.31% phosphorous acid, 200 ppm Pt, 50-55°C, 500 psig H pressure. Product purity - 93%.
REFERENCES
1.
2. 3.
4. 5. 6. 7.
Kosak, J. R., "Catalytic Hydrogenation of Aromatic Halonitro Compounds", Ann. New York Acad. Sci. 172, p p . 174-185 (1970) . Craig, W. C , G. J. Davis & P. 0. Shull, U.S. Patent No. 3,474, 144 (1969). Greenfield, H., "Platinum Metal Sulfides in Catalytic Hydrogenation", Ann. New York Acad. Sci., 145, p p . 108-115 (1967) . Kosak, J. R. , U.S. Patent No. 3, 145,231 (1964). Kosak, J. R., U.S. Patent 4,020,107 (1977). Rylander, P. N., "Catalytic Hydrogenation over Platinum Metal Catalysts", Academic Press, N.Y., pp. 17-18 (1967). Tong, W. R., Seagraves, R. L., Wiederhorn, R., 3,4-Dichloroaniline Autoclave Incident, Chemical Engineering Progress, Loss Prevention, Vol. II, pp. 71-75 (1977).
PREPARATION O F H A L O A R O M A T I C A M I N E S
8.
117
Rondestvedt, C. S., and Johnson, T. A., "Explosion of an Arylhydroxylamine During Preparation of 2-Chloro-5-methylaniline", Synthesis, p. 851, December 1977-