CATALYTIC REDVCTIOK O F KITRO-ORGASIC COMPOUKDS I N T H E LIQUID SYSTEAf BY 0 . T. BROWN, G. ETZEL AXD C . 0. HEKKE
Introduction In this investigation a study of the catalytic reduction of nitro-compounds in the liquid phase was undertaken. The compounds reduced were: nitrobenzene, a-nitronaphthalene, p-nitrotoluene, o-nitrophenol, p-nitrophenol and di-nitro toluene. The reductions were carried out with a nickel catalyst, in a hydrogen atmosphere under a pressure of zoo to 700 pounds per square G -.E
E
S
*P'
I
P-
c
FIG.I A-Autoclave proper, capacity 80 cc., tested for 3000 lbs. per B-Six in. piece f in. rigid hydraulic iron pipe. C-Vnion. -Eight ft. piece f in. flexible copper hydraulic pipe. -ne-half in. elbow. G-Support t o attach apparatus to the ceiling of the room. H-One-fourth in. steel wire. I--Four ft. piece f in. hydraulic iron pipe.
SQ.
in.
G"T".
M-One-half in. nipple 3 in. long. N-One-half in. nipple one foot long. K-One-half in. hydraulic iron pipe one f t . long. M n e - h a l f in. adaptor carrying lefbhanded female threads. P-Small hydrogen tank 4 in. in diameter and 25 in. in height. Q-Hydrogen tank, zoo cu. ft. capacity. R-Hydrogen pressure gauge.
inch ( 1 s t to 473 atmospheres). In order to insure intimate contact between hydrogen, catalyst, and nitro compound, the mixture was agitated
632
0 . W. BROWN, G . ETZEL h S D C . 0 . HEX'KE
vigorously by shaking. The variable factors studied were : temperature, pressure, amount of catalyst, time of reduction and kind of solvent used. Borchet' states that he has carried out the reduction of some nitro-organic compounds in the liquid phase with a nickel catalyst. A. N.Parret and A. L o w 2 have studied the catalytic reduction of a-nitronaphthalene with hydrogen under pressure in presence of a nickel catalyst.
Apparatus The apparatus used in this investigation was designed by 0. W. Brown and C. 0. Henke. Fig. I shows the apparatus. The autoclave was shaken by means of an eccentric arm which had a stroke of two in. and was driven by a 1:'6 horse power electric motor. Pipe B was threaded to the upper part of the autoclave. The autoclave proper was connected to the autoclave cover by means of six bolts,+ hindiameter, S.A.E. threads. The flexible copper pipe D was looped once at S. This loop takes care of the backward and forward movement caused by the eccentric arm. The junction between the cover and the autoclave was sealed by means of a lead gasket. Heating Element The heating element consisted of an electric heating jacket. It was made by wrapping asbestos paper around a strong tin can. Then about six turns of No. 18 chrome1 wire were wrapped around the paper, and the whole covered with more asbestos paper. The ends of the wire were doubled and twisted tightly in order to insure greater strength. Method of Procedure Known weights of organic compound and of reduced nickel catalyst were placed in the autoclave, and a definite amount of solvent added. A slow current of hydrogen was passed thru the pipes to wash out all air while the autoclave was being bolted to its cover. The bolts were then tightened and the hydrogen pressure was turned from the large tank until the required pressure was reached. The large tank was then closed. The autoclave was then immersed in water to test for leakage. The purpose of the small tank was to act as a reservoir and to insure an uniform pressure during the reduction period. The heating jacket was placed in position around the autoclave and connected to a source of current ( I I O volt). The temperature of the reaction mixture was determined by means of a thermocouple which was inserted into a hole drilled into the wall of the autoclave. This hole was a in. in diameter bore from one side to the center of the bottom of autoclave. The point a t which the temperature was taken was in. above the outer bottom surface of the autoclave and about one in. below the reacting chamber. An iron collar was used to hook the eccentric
+
+
Brochet: Bull., (4) 13, 197 (1913);15, 554 (1914). J. Am. Chem. SOC.,4d, 778-782 (1926).
* A. Pi. Parret and A. Lowry:
CATALYTIC REDUCTIOS OF NITRO-ORGANIC COMPOCNDB
633
arm to the autoclave. A hole was left in the heating jacket for the insertion of the eccentric arm. The temperature required was obtained by adjusting an external resistance. When the desired temperature was reached the motor was started and the apparatus shaken for a definite period of time, usually two hours, a t 150 R.P. M. At the end of this time the heating jacket was removed, the small tank closed, and the autoclave cooled by surrounding with cold water. The hydrogen pressure in the autoclave was allowed to escape thru the gauge. The autoclave was then opened, the contents examined as to color and odor. It was poured into a two-liter beaker containing 50 cc. of concentrated hydrochloric acid. The autoclave and the lower end of the pipes were carefully washed with alcohol. The hydrochloric acid solution was diluted to two liters, mixed, and portions titrated against a standard solution of sodium nitrite. Preparation of Catalyst The nickel catalyst was prepared by igniting the nitrate and then reducing the oxide in hydrogen. The nitrate, with a small addition of nitric acid was ignited in a small porcelain evaporating dish in an electrically heated muffle. The temperature of ignition was measured by a copper constantan thermocouple, the junction being in the dish just above the nickel oxide. The nickel oxide, after cooling, was powdered and put in the furnace as described by Brown and Henke.' The temperature of ignition of the nitrate was 560°C. The oxide was reduced a t a temperature of 378°C with the rate of flow of hydrogen 14 liters per hour. Material Used Xitrobenzene used was purified by shaking it with sodium carbonate solution and then steam-distilling it. The distillate was dried with calcium chloride and then redistilled twice. The hydrogen used for reduction was commercial hydrogen. The a-nitronaphthalene used was a C.P. product from Eastman Kodak Co. Experimental Part A series of experiments was first made to ascertain the best temperature and pressure. The amount of nitrobenzene used in each experiment was 4.7354g. The amount of benzol, which was used as a solvent, was 8 cc. Results obtained are given in Table I. TABLE I Amount of reduced nickel catalyst 2 . 5 g. Time of reaction 2 hrs. Temperature Pressure.lbs. Amine of C per sq. in. theory
I90
5 00
215
500
2 53 282
500
5 00
99.05 100.03 95.54 52.53
Brown and Henke: J. Phys. Chem., 26,
Temperature Pressure lbs. C per sq. In. 215
2 00
215
300
Amine % ' of theory
25.04 67.45
215
500
100.03
215
700
100.
161-190 (1922).
0. A ' .'
634
BROWN, G. ETZEL AND C. 0 . HENKE
The experiments of Table I indicate that 215°C is the best temperature for the reduction when a pressure of 500 lbs. is used. By changing the temperature 2o°C above or below 215°C the yields vary slightly, while by a constant increase they suddenly drop. By varying the pressure and keeping the other factors constant we notice that as the pressure increases the yields increase, joo lbs. per sq. in. giving a quantitative reduction. Table I1 gives the results of a study of t h e variation of the amount of catalyst and time of reaction. TABLE 11 Temperature 215°C Pressure joo lbs. 8 cc. Solvent Benzol .amount of Catalyst g.
Time of Reaction minutes
.Amine % of theory
3.96 93.21 99.21
I5
30
60
100.3
120
43 42 16.06
120
1.
.I
'
I20
Experiments described in Table I1 show that the maximum yields were obtained when the reaction was allowed to take place for the period of two hours, although a good yield was obtained when the period was one hour. Two and one half grams of catalyst for 4.73j4 g. of nitrobenzene gave the best results. The yields decreased quite rapidly with a decrease in the amount of catalyst. Effects of different solvents on reduction of nitrobenzene were tried. The results are shown in Table 111. TABLE I11 Temperature 2 1 j" c Pressure joo lbs. Amount of Catalyst 2 . 5 €5 Time of Reaction z hrs. Solvent Used
None Benzol Absolute Alcohol
Amount of Solvent cc.
-
Amine % of theory
8 8
99.94 100.03 99.78
It is seen from Table I11 that quantitative yields were obtained with or without solvent. A few experiments were carried out on the reduction of a-nitronaphthalene to a-naphthylamine a t a pressure of 500 lbs. A. N. Parret and A. Lowyl reduced this same compound using a pressure of jo to I O O lbs. and ob1
A. N. Parret and A. L o w : J. Am. Chem. SOC., 48, 778-782 (1926).
CATALYTIC REDUCTION OF NITRO-ORGANIC COMPOUNDS
63 5
tained with nickel catalyst a maximum yield of 70%. The results obtained by the writers are given in Table IV.
TABLEIV Temperature Pressure Amount of catalyst Amount of a-nitronaphthalene Time of reaction Solvent
21
2.5
g.
4 €5 2
Amount of Solvent cc.
Benzol Ethylene Glycol Ethyl Alcohol
5°C
joo lbs.
8 IO IO
hrs.
Amine '% of Theory
99.55 89.78 98.31
Better yields were obtained with benzol as solvent than with either ethyl alcohol or glycol. The latter was the poorest. Brown, Henke and 0. C. Criswell reduced in this laboratory p-nitrotoluene, with a pressure of j o o lbs. per sq. in. and 2i 5°C.. A quantitative reduction was obtained. 0-nitrophenol pnitrophenol and di-nitrotoluene were also quantitatively reduced. The conditions were as follows: temperature 226"C, pressure j o o lbs. per sq. in., solvent used absolute alcohol, catalyst nickel made by reducing nickel carbonate a t 378°C. Conclusions I. Experiments were conducted showing that liquid nitrocompounds and nitrocompounds in suitable solvents can be reduced quantitatively to amines, with hydrogen under pressure, and with a nickel catalyst. 2. Quantitative reduction of nitrobenzene, a-nitronaphthalene, p-nitrotoluene, o-nitrophenol, and di-nitrotoluene was obtained a t 2 1 j°C and a t a pressure of 500 lbs. per sq. in. 3 . For the best results 0. j z g. of nickel catalyst was required for each gram of nitrocompound reduced. 4. Benzol and ethyl alcohol were solvents that permitted quantitative reduction of nitrocompounds studied. Labmatory of Physical Chemistry Indiana Unauersify, Bloomington
