R.E. BENSON,T. L. CAIRNSAND G. M. WHITMAN
4202 [CONTRIBUTION No. 380
FROM THE
Vol. 78
CHEMICAL DEPARTMENT, EXPERIMENTAL STATION, E. 1. DU PONTDE NEMOURS ASI) COMPANY]
Synthesis of Hydroxylamine B Y RICHARD E. BENSON,THEODORE L. CAIRNS AND GERALD % \VI€ITXAN I. RECEIVED MARCH 7, 1936 The platinum-catalyzed hydrogenation of nitric oxide at atmospheric pressure in 10% hydrochloric acid has given 67-7370 yiclds of hydroxylamine at 73-77% conversions of nitric oxide. Optimum reaction conditions include t h e use of platinum catalyst, a pH less than 2.25, and nitric 0xide:hydrogen molar ratios of 1: 2 t o 1 :3.
The catalytic hydrogenation of nitric oxide to hydroxylamine has received relatively little attention since Cookel observed that mixtures of nitric oxide and hydrogen reacted over water in the presence of platinum catalyst to give hydroxylamine, nitrous oxide, ammonia and nitrogen. Jouve2 reported that the hydrogenation of nitric oxide a t 100-120° over platinum catalyst gave hydroxylamine (1-2% yield) and ammonia, and stated t h a t i t was necessary to use nitric oxide in excess of the stoichiometrically required amount to prevent destruction of the hydroxylamine formed. Butterworth and Partingtons reported t h a t hydruxylamine and ammonia were formed in small amounts when a 4 : l molar mixture of nitric oxide: hydrogen was brought into contact with platinized platinum in the presence of dilute hydrochloric acid. A special device was used by these authors in order that the platinum catalyst could be alternately wet by the acid and exposed to the synthesis gas mixture. In the present work hydroxylamine was obtained in 67--73Y0 yields a t 73-77y0 conversions of nitric oxide by the use of dilute hydrochloric acid medium, 10% platinum-on-carbon catalyst, nitric oxide : hydrogen molar ratios of 1 : 2 to 1:3 and temperatures of 0-5'. Ammonia in variable amounts (5-10yo yield) was also formed and presumably the remainder of the nitric oxide was converted to nitrogen or nitrous oxide. Evaporation of the filtered solution yielded hydroxylamine hydrochloride of purity up to %yo,and analyses indicated ammonium chloride to be essentially the only impurity. The yield of hydroxylamine realized was demonstrated to be dependent upon PH and nitric oxide: hydrogen gas ratios. Under conditions examined, the hydroxylamine yield was not significantly affected by the concentration of hydroxylamine hydrochloride or ammonium chloride formed in the reaction solution, nor by the presence of nitrogen or nitrous oxide in the synthesis gas. Furthermore, the catalyst appeared to suffer little loss in activity over a period of one week (the longest evaluation), and a continuous synthesis can be visualized through simultaneous withdrawal of the resulting hydroxylamine hydrochloride solution and addition of fresh acid. Although sulfuric and phosphoric acids were not investigated :is extensively as hydrochloric acid, they were found to be effective media for hydroxylamine formation, giving yields of 4t%370 of the ( 1 ) S Cooke, Pror Phrl S o c C l n r g o w , 18, 301 (1587) (2) A .IOU\e , Comfit r e n d , 128, 43.5 (1889). (3) A J Butterworth a n d J I< Partington, T r a n s F a r a d o y Soc , 2 6 , 144 (1930)
respective acid salts. A moderately acidic medium was necessary in this reaction since the synthesis gas converted hydroxylamine to other products a t pH values greater than 2.5. At lower pH values, hydroxylamine hydrochloride in aqueous solution was not reduced a t room temperature in the presence of platinum-on-carbon catalyst, even a t '73 atmospheres hydrogen pressure. In contrast, it was found that nitric oxide slowly converted hydroxylamine in acid solution to other products in the presence of platinum catalyst. This slow reaction of nitric oxide with hydroxylamine salts may account for the necessity of using hydrogen in excess of that stoichiometrically required in order to obtain good yields of hydroxylamine. For example, no hydroxylamine was obtained from an equimolar nitric oxide: hydrogen gas mixture, and only an 11% yield resulted from a 1 :1.5 molar nitric oxide: hydrogen mixture. The use of nitric 0xide:hydrogen gas mixtures of molar ratios 1:s to l : G did not result in significantly higher conversion of nitric oxide than that obtained from 1 : 2 to 1 :3 mixtures, probably because of inefficient gas contact with the catalyst in the simple laboratory apparatus that was used for this investigation. The presence of nitrogen and nitrous oxide in the synthesis gas, even in large amounts, had no effect on the production of hydroxylamine except to reduce the conversion of nitric oxide. While platinum was the most effective catalyst examined for the reduction of nitric oxide to hydroxylamine, palladium gave an 18% yield of hydroxylamine a t 53y0nitric oxide conversion using 10% hydrochloric acid medium. Under similar conditions, the use of iridium catalyst failed to yield hydroxylamine in detectable amount. DuParc4 has reported that the hydrogenation of nitric oxide with palladium or iridium catalyst yields nitrogen. The effcct of pressure on the platinum-catalyzctl reaction was investigated briefly. A t total pressures of 3.5 atmospheres gas mixtures containing 20-28 mole yo nitric oxide gave hydroxylamine in 6@'79y0 yields. In agreement with atmospheric pressure experiments, no hydroxylamine was obtained when gas mixtures containing more than 50 mole yonitric oxide were used.
Experimental Hydrogenation of Nitric Oxide6 (Procedure A).-A fournecked, 500-ml., creased flask was equipped with a sealed stirrer, a sintered-glass gas dispersing tube, a thermometer a n d a gas exit tube w1iic.h w is :ittached to a wet t e i t meter (4) L. DuParc, e t af.,I l e l v . C k i m . A d a , 11, 337 (10281, C. A . . 2 2 , 1880 (1828). ( 5 ) R. E. Beuson, U.S . P a t e n t 2,G?6,880 (February 18, 1953).
SYNTHESIS OF HYDROXYLAMINE
Sept. 5 , 19.36
4203
TABLE I PLATIEUM-C.4TALI'ZED
Procedure
Expt.
1
A
Approximate NO/Hz ratio
1/2.0
I-IYDROGENATION O F NITRIC OXIDE ----Rate, NO
Medium
10% HCl
37-39.5
AT
ATMOSPHERIC PRESSURE NH20H, % yield
ml /min.--
H1
7;-8 1
7iO %
ronversion
77
67.5 ( 5 . 1 % NHa)
2
A
1/2.6
10% HCl
32.5-33
3
c
1/2.3
10% HCI
26 5-28
73.6 (10% A X ? ) 01 .s
85-89 150 then 59 5 6 3 . 5 197-205 190-200 1c;0-200
73 I
i l
64 5 4 B 10% HC1 28-29 1/7.1 60 68 (i 10% HCl plus 1 % NHdCl 25-28 5 B 1p.4 69 10% HC1 PIUS NH20H.HCI' 71 6 B 24 5 2 7 13 1/7.0 10% HCl 0 8 7 A 1/0.88 31-33 5 27-28 5 11.1 1/1,5 l o ~ .€IC1 32-31 29' 8 A 45-50 1/5.5 52.5 si; 1,51)-1iO 9 B 10% rwo4 23- 35 49 3 10% HlPOd 10 B 1/6.7 26-28 175-185 08 45 11 B 1/10 32-35 37 10% HSO1 295-350 10 12 13 l/fi.4 10% CHaCOOH 26-27 164-187 82 b 13 B 1/6.6 10% H S O j 2527.5 170- 175 89 0 14 A 1/3.5 H20 137- 141 39 5-41 3i 1/5.1 8% S a O H 26-28 5 135-140 0 52 15 A a Initial concentration of NH20H was 15.9%; final concentration, 16.9% "*OH. On cooling, h"20H.HCl separated Conversion fell from solution. * Yield not determined, but qualitative test for hydroxylamine was strongly positive. from 83 t o 8% in 6 hours. joined t o a large drying tower containing calcium chloride. A manometer was connected t o the system in front of the gas dispersing tube t o indicate the positive pressure on the system. The aqueous medium (usually 300 nil.) was placed in the flask, 1.0 g. of 10% platinum-on-carbon catalyst was added, vigorous stirring was beguu and the gas dispersing tube was adjusted so as t o extend as far as possible below the surface of the liquid. After the system had been flushed x i t h nitrogen, hydrogen was metered into the vessel a t approximately 100 rnl./minute. T h e contents of the flask were warmed t o 35-50' for 20 minutes and then cooled t o 0-5", and t h e hydrogen flow was adjusted t o the desired rate. The wet test meter for nitric oxide was flushed with t h a t gas, the r a t e was adjusted and nitric oxide was introduced into the hydrogen stream. After one-half hour, the hydrogen, nitric oxide and exit gas rates were determined (10 minute reading), and a gas bottle was attached t o the exit line connected t o the drying tower. After one-half hour the gas bottle was removed and the nitric oxide concentration determined by photometric analysis. This procedure was repeated each hour. After six hours, the nitric oxide valve was closed, the wet test meter for nitric oxide was read and t h e system was flushed with hydrogen for 15 minutes, and finally with nitrogen. T h e reaction solution was filtered and the filtrate was analyzed for hydroxylamine a n d , in some instances, ammonia. The results of Experiment I, Table I, are detailed below. T h e aqueous medium was 300 ml. of 10% hydrochloric acid, and 13.61 1. of nitric oxide was introduced at a positive pressure of 60 mm. on the system a t a barometric pressure of 758 mm.
EXPERIMENT 1 Nitric oxide analysis InterVal, hr.
7'0
NO
NO
Hourly % NO conver-
18.6 18.5 19.3 18.9 16.7 1G.9 11.3 10.9 11.2 11.5 11.9 11.9
18.5
BG.8
19.1
64.0
16.8
83.4
70
Gas rates, Transml./rnin. Sample, mis- hfm. NO 1 1 2 Exit mm. sion' NO
1
38
78
95
2
39.5
78
80
3
37
81
39
4
..
,.
..
5
38.5
77
45
6
37.5
80
52
145 127 155 135 141 151 128 141.5 129 144 130 151.5
11 14 9 12 14 12 27 25 27 23 25 21
27 23.5 30 25.5 23.5 25.5 14.6 15.5 14.5 16.5 15.5 18
( G ) See photometric analysis of nitric oxide.
?G
Av.
sion
11.1
(8Best)
11.3
87.7
11.9
84.5
The hourly Conversion values were calculated in the following manner nil. NO (introduced)/rnin. = rate X pressure
+ barometer reading 700
ml. YO (in exit gas)/min. = rate X barometer reading __ 760
x
%YO
The difference in the corrected rates is the nil. XO/min. converted, and this value divided by the corrected iiitrvduction rate gives the % N O conversion. For the first hour 60 755 KO (introduced) = 38 X -r-= 40.8 nil. S O / m i n .
+
60
i
NO (vented)
= 95 X
758
760 X 0.185 = 17.6ml.
KO/min.
23.2 ml. NO/niin. x 100 = 56.873 40 8 ml. KO/min. An over-all conversion value of 77.070 was obtained by averaging the hourly conversion figures. Conversion
= - __---
mole NO converted
=
+
758 273 760 298 1 _ _X 0.77 = 0 . 4 2 mole 22,4
60
13.61 X ___
Analysis of the reaction solution (310 g.) indicated 0.0332 g. of S&OH/g. solution. Thus, 10.3 g. of h~-droxylamine was formed (67.5% yield). Analysis of the re:iction s d u t i o n indicated 0.0013 g. of KH3/g. solution, corresporitling to 5.14y0 yield of ammonia.' Procedure B.-The equipment and procedure descritetl in A were the same, except t h a t the reaction was begun a t room temperature without preactivating the catalyst with hydrogen. After 30 minutes, the temperature of tlie reaction medium had risen several degrees, and the mixture was cooled t o 0-5'' for the remainder of the run. Procedure C.-The procedure described in B was modified slightly, in t h a t after the temperature rise was noted, the hydrogen flow was adjusted t o a lower rate before cooling the flask contents t o 0-5". Effect of pH on Synthesis of Hydroxylamine.-Procedure B was used, and tlie reaction flask was equipped with a Y ~~
(7) T h e a u t h o r s art. indebted t o Dr W. H. Taylor and M r . I;. J. Friel of t h e Physical and Analytical Division for t h e ammonia analyses.
tube t o provide for a sintered glass filter stick extending below the surf'tce of the liquid. The medium mas 1,'; ml. of ciilicentrated I~ydrochli~ric acid diluted t o 350 rnl. S:irnplrs (I,? ~ 2 nil.) 0 were remnved through the filter stick b y v,iruiin~ filtration without interrupting the reactioii . I n calculating the appareilt hydroxylamine yields no correction WJS applied for the samples removed. The result5 are sumninrized in Tahle 11.
TABLE I\'
TABLE I1 KFFPCT n F p11 ny SYNTIIESIS nr I€YDROXYI,AMINE Apparent
Time, ,Sample i n i n
0
0
1
120
2
liiT,
8
195
4 5 c,
240 260 30.5
1Ivle NO convrrteil
!!lOII
#TI
yield,
..!i!rcl
0.81)
0
.06,43 ,122 , 144 ,199 ,219
0.90 1.12 1.30 2.25 5.55 9 20
000203 .00490 ,00700 0.0049 ,0102 .0007 ,00814 .000
34
40 4fi 46.6
32 0
Catalyst Life.-Procedure B was used and t h e reaction flask was equipped with a Y-tube to provide for a sintered glass filter stick extending below the surface of the liquid. The main portion of the reaction solution was removed d d y by filtration through the filter stick, and fresh acid without interrupting t h e reaction. T h e hydr yield, averaged about 8iy0 over a six-day period. Tlie iiitric oxide conversion value for the se determined, b u t the conversion t o hydro Since the nitric oxide conversions iiver'i tlie first six days of this experiment, it i, evident that there wits no serious loss in catalyst activity. Effect of Added Gases on Hydrogenation of Nitric Oxide. -The various gases were introducetl iiito the Iiytlrogeii neans of a Y-tube. Procetlurr B was f o l l o ~ v d . Tlic~rriults are siinini:trizciI i t i T:ihlc I I I . 'rAI3I.E
EFFECT O F
ADDED G A S E S
111
OX II\.I)R(K:IiYATIOV
OF I\TITRIC
OXIDE
Approx. NO/LI*/ Added gas Rxpt. gas ratio 1 S? 1,'ti 2'5.G '2 3 !
S?
?-?Oa S?O
1 '12/10 1 '7/0.75
l!tLl'O.Q4
N0
xn*- ' ' 2 Rates, ml./min
SO
Hz
20-30 6-17
150-IF0 335-145 220-230 18.5-195
27-37 31
Gas 136-145 110-117 20-28 24-34
OH,
LZ
yield
74 53.6 AG..ja 56
version 31 >5 ,5l 49
(1
Hydrogenation of Nitric Oxide Under Pressure .-The effect of pressure o n the cLttalytic hydrogenation of nitric oxide W:E investigated briefly uiing a Parr catalytic sliaker.s T h e g;is reservoir was removed and mounted on a mechanical shaker so t h a t nitric oxide/hydrogen gas mixtures could he agitated in the presence of water t o assure mixing of the gases. The equipment was located behind a barricade since the gas mixtures were within the explosive range. T h e reserviiir containing 500 ml. of distilled water wa5 evacuated t o 4.5 m m . and nitric oxide was added to a de>ired pressure followed by hydrogen t o a total pressure of ,50 Ib./sq. in. The catalyst and acid medium were placed in t!ie reaction bottle, hydrogen was added, and the mixture WAS heated briefly t o activate the catalyst. During this time the reservoir w i s agitated t o mix t h e gases. After 15 ~niriutes,the hydrogen in the bottle was released, the bottle was evacuated, and a gas sample was removed from the reservoir and analyzed for nitric oxide. T h e reservoir was opened t o the reaction bottle and shaking begun. .4t the end of the reaction time a sample of t h e reservoir gas was analyzed again for nitric oxide. There appeared t o be no - conversion t o cyclohexanone oxime. Yields of liydrou~-l:tmitie werc determined b y the nnalyticd procedure of Rascliig" niotiilied by the addition OF the Zinimermann-Reinhardt reagciit to prevent interference by chloride ion when hytirochloric acid was used as the hydrogenation medium. Determination of Ammonia.-The acidic reaction solution 11as treated with excess permanganate t o destroy the hydroxylamine present. Excess base was added and the aininonin mas removed by diitillation and determined b y adsorption in stanchrd acid :ind back-titration wit11 st:intlartl base.' Isolation of Hydroxylamine Hydrochloride.--A portioii of the reaction solution from expt. 1, Table I, was evaporated t o dryness a t reduced pressure to yield a white, crystalline product. Analyses of tlie solid indicated it t o be a mixture of hydroxylamine hydrochloride (05.870) and : t ~ n m o ~ ~ i i ~ n i chloride (4.2yo). SimiLtrIj-, the product obtained froin expt. 2, Table I , contained 88.270 hydro. chloride and 11.;yo ammonium chloride. Action of Hydrogen on Hydroxylamine Hydrochloride .A liydrocliloric acid solution of hydroxylamine (0.0118 g . / g . (9) R . E , Benson, U . S. P a t e n t 2,628,SRR (February 18, 19.53). ( I O ) I:. F e i p l , "Qualitative Analysis by S p o t T e s t - , " Rlsevier PIIII
sii," . - ~ l l i l?
