J
1 2 3 4
u;
Figure 1 .
I
t
REACTOR SECTIONS NH3 PREHEATER -STEAM REACTOR HOT WATER FINISHER -HOT WATER COOLER -COLD WATER
-
--
-
The process was studied in a reactor with interchangeable sections
EDWlN M. SMOLIN and L. CLAIR BEEGLE Research Division, American Cyanamid Co., Stamford, Conn.
Continuous High Pressure Synthesis 3-Aminopropionitrile Approximately 8OY0 yields of 3-aminopropionitrile can be obtained by using 50% aqueous ammonia in a mole ratio of 7 to 1 over acrylonitrile at 105" to 1 10" C. and a contact time of 1 to 2 minutes
PRODUCTS of the reaction of acrylonitrile with ammonia are 3,3'-iminodipropionitrile, 3-aminopropionitrile, and small amounts of nitrilotrispropionitrile. The proportions of the first two have been varied by selection of reaction conditions. The object of this investigation was to establish the conditions af-
fording a maximum yield of 3-aminopropionitrile by continuous high pressure ammoniation of acrylonitrile. Whitmore (72) examined the reaction of acrylonitrile with aqueous ammonia, and Hoffmann and Jacobi (8) patented the use of anhydrous ammonia. Buc (3, 4 ) studied the effect of mole ratio of ammonia to acrylonitrile on the relative amounts of 3-aminopropionitrile and 3,3 '-iminodipropionitrile, formed in the reaction; from 7 to 20 moles of ammonia per mole of acrylonitrile were required for 40'% yields of primary amine. The same result was obtained with a smaller excess of ammonia when the reaction mixture was not cooled. No temperatures were specifically investigated. Whitmore's data (12) implied that the
reaction of acrylonitrile was about 20 times faster with 3-aminopropionitrile than with ammonia, giving the secondary aminonitrile as the chief product. In another investigation (73) little of the tertiary compound, nitrilotrispropionitrile, was obtained. The reactions may be represented by Equations 1, 2, and 3 CH-CHCN
+ NH3 kl H ~ C H Z C H ~ C N +
(11
HzNCHzCHzCN
kz
+HN(CHzCHzCN)z CH-CHCN
4
HN(CHzCHzCN)z
+ CHFCHCN
k3
+
N(CHzCHzCN)s
VOL. 50, NO. 8
e
AUGUST 1958
(2)
(3)
1 1 15
O n the basis of this information, Ford, Buc, and Greiner ( 6 ) examined the effect of temperature in the range of 50' to 150' C. Yields of 3-aminopropionitrile were 60 to 80% when aqueous ammonia was preheated to 110' and acrylonitrile added rapidly below the surface of the solution. Reaction times were of the order of 2 to 5 minutes. Batch-type autoclaves were used, and the work was limited to use of aqueous 28% ammonia.
Table I. Increase in Mole Ratio of Ammonia to Acrylonitrile Gave Higher Yields of 3-Aminopropionitrile % Yield at Mole Contact Ratio of "3: Time, Temp., CH2=CHCNO c. 40 100 Min. 507, Ammonia
0.7
75 95 115 95 115
1.4
61 73" 75" 71a 77"
71 7 9" 8 1" 81'L 81a
7597, Ammonia
0.7
95 115 95 115
1.4
50a 57" 61" 61a
67"
70" 72"
745
Results used in statistical computation.
Table II.
Weijlard and Sullivan ( 7 7 ) claim that dilution with a tertiary alcohol reduces the proportion of ammonia required to obtain high yields of the primary aminonitrile. High temperatures-200' to 225' C.-have been used (5) to prepare @-alanine directly from aqueous ammonia and acrylonitrile. Russian workers (10) have studied the reversibility of Reactions 2 and 3 as a means to control the end product. They reported that self-polymerization of 3-aminopropionitrile occurs without evolution of ammonia. However, Whitmore (72) observed that pressure increased in closed containers of aqueous 3-aminopropionitrile.
Apparatus
A schematic block flow diagram is shown in Figure 1. The reactor sections consisted of spiral lengths of 3/8-inch pressure tubing welded into lengths o f 3-inch pipe, which served as the heating or cooling jackets. The sections had known, previously determined volumes, and were interchangeable. Thus residence time could be varied by substituting one section for another. U p to four sections could be used in series, one serving as the preheater for the ammonia solution,
Yield of 3-Aminopropionitrile W a s Greater When 50% Ammonia W a s Used
Mole Ratio of NHa:CI-Iz=CHChy
Temp., OC.
4:1
Contact Time, % Yield at 50% and 75% Ammonia
115
1O:l
0.7 1.4 0.7
50 % 73" 71a 75a
1.4
7 7"
0.7 0.7 1.4 0.7
71a 7 9a 81a
Min.
95
75 95 115
75% 50Q 61Q 575 61a 69 67" 72a
8l a 8 la
1.4
70a
746
Results used in statistical computation.
Table 111.
Maximum Yields of 3-Aminopropionitrile Lie within Upper Middle Portion of Temperature Range Mole Ratio of Contact % Yield at Various Temperatures NHa :CH2= Time, CHCN Min. 75" C. 85'C. 95'C. l05OC. 115°C. 125OC: 5070 NHa
4:l
7.7:1 10:1
0.7
1.4 1.05 0.7
1.4 4:1
0.7 1.4
10:1
0.7
1.4 a
62
..
.. .. .. ..
..
69
..
...
... 7Za ... ...
...
79" 8Ia
75% NHa
... ... ... ...
Results used in statistical computations.
1 1 16
73.
71a
INDUSTRIAL AND ENGINEERING CHEMISTRY
50" 61a 67" 72a
...
755
...
77"
...
81C
74n
...
... ... ...
...
...
81a
5 7a 61a 70a
74"
...
...
75"
... ...
... ... ... ...
Procedure Ammonia of the desired concentration was prepared by weighing water into the ammonia feed tank and adding anhydrous ammonia in portions, with circulation and cooling, to bring the total volume to mark. Acrylonitrile was charged to the ocher feed tank. The pumps (Milton-Roy, high pressure type) were primed and set for the desired delivery rates. The ammonia pump \\'as started first, to avoid high concentrations of acrylonitrile, which might cause polymerization in the reactor sections. Temperatures were controlled by Powers mixers which proportioned steam and water to the jackets of the individual reactor sections. These were brought to temperature and the acrylonitrile flow was started. A cold water cooler was placed after the last reactor section ; thereafter the product mixture was vented through a Gismo pressure control valve, w-hich maintained constant pressure of about 1600 p.s.i.g. on the system. Excess ammonia was allowed to flash from the solution which was then collected and analyzed.
Analysis Essentially all of the acrylonitrile was converted to the three reaction products. The crude product was further deammoniated a t reduced pressure in the cold. Residual ammonia was removed by codistillation with benzene or acetonitrile. Primary and secondary amines were determined (7) b>- differential nonaqueous titration with perchloric acid; tertiary amine ( g ) , by difference in titration after acetylation; Tvater, by the Karl Fischer method; residual acrylonitrile in the product mixture ( 7 ) , by dodecyl mercaptan titration. Tables I through V show yields of 3aminopropionitrile, calculated on a 10070 dry, ammonia-free basis, corrected for the small (0.5 to 1.5%) amount of nitrilotrispropionitrile.
Effect of Operating Conditions
Mole Ratio. Under comparable conditions, yields of 3-aminopropionitrile were always higher when the mole ratio of ammonia to acrylonitrile was increased (Table I). This was expected on the basis of BUC'S results (4, and the present work has provided a more quantitative correlation. Because ammonia is a reactant in the first reaction and not in the second, one way to maximize the yield of primary amine is to use large excesses over the amount required to react &ith one mole of acrylonitrile. In deciding on an upper limit for excess ammonia, three considerations apply : ease of product recovery, economy, and the point beyond
AMlNOPROPlONlTRlLE SYNTHESIS which further yield improvement becomes negligible. Ammonia Concentration. The effect of 50 and 75y0aqueous ammonia on the yield of 3-aminopropionitrile is shown in Table I1 for two mole ratios of ammonia to acrylonitrile, and for different temperatures and contact times. Yields with 82y0 and 93% ammonia a t a mole ratio of 4 to 1 are comparable with those in Table 11. Contact times are not critical. The advantage of working with 50% ammonia is apparent. The yield of primary amine fell off even more markedly when the ammonia concentration in the feed was raised to 82% and then to 93y0. The higher the ammonia concentration, the slower was the reaction. Longer minimal residence times of some runs a t 93% were needed to ensure complete utilization of acrylonitrile within the reactor.
Temp., O
yo Yield of Ammonia Concentration
Contact Time,
c.
Min. 1.05 2.0 3.0
115
130
82YO
93%
36
36 15 21
ammonia (Equation 5) and, finally, loss + ofa proton by the-NHa group (Equation 6). OH /
H
H&CH*GHCN + [H&CH&HzCN] OH- (5)
+
& H ~ C H ~ C H ~ C N OHI Ft HzNCH2CHzCN f HzO
HNH
-
H
H ~ ~ C H Z C H C N HsN+CHzCHCN A B At high ammonia concentrations, ammonia, rather than water, must supply, to a greater extent, the proton required in Equation 5. It will be more difficult to break the N-H bond than the 0-H bond if transition ,states A and B are considered. Accordingly, a longer reaction time or more drastic conditions will be needed when less
Highest Yields of 3-Aminopropionitrile Were Obtained at Contact Times of 0.7 to 1.4 Minutes
Mole Ratio of NHa:CHz= CHCN
YoYield of Various Contact Times, Min.a
Temp., C.
0.35
95 115 105 95 115
... 73 ... ...
... 79
95 115 95 115
... ... ... ...
75% NHs 50 57 67 70
0.7 50%
4: 1 7.7:l 1O:l
4: 1
10:1
1.05
1.4
... 74 ... ...
71 77
"8
73 75
9 . .
I
81
.
.
...
73 ... ...
... 81
...
81
... ... ...
... ... ... ...
61 61 72 74
...
1.75
Results used in statistical computations.
-
N
CHFCHCN
(6)
OH
H
Table IV.
In the only run where a direct comparison is possible, there was an apparent decrease in yield with 29% ammonia (Table V). The reason is not certain. The effect of water on the course of the reaction was unexpected. This anomalous behavior may be explained if it is assumed that acrylonitrile and ammonia are immiscible even a t 75' to 130° C. and that the reaction occurs mainly in the acrylonitrile phase. If these assumptions are correct, addition of water could increase the yield of primary amine by increasing the mole ratio of ammonia to acrylonitrile in the acrylonitrile phase. There are no solubility us. temperature data available on the acrylonitrile water ammonia system. Acrylonitrile is only slightly soluble in cold aqueous ammonia and the reaction products are completely soluble. Because the reaction is so fast, it was not possible to distinguish experimentally between acrylonitrile solubilized by increased temperature and by reaction. The slower rate observed at higher ammonia concentrations suggests a possible mechanism. It may be assumed that reaction begins with lone pair addition to acrylonitrile.
water is present. Thus the effect of higher ammonia concentration may be explained by attributing the change in product ratio to a physical cause and the change in reaction rate to a chemical consideration. Temperature. The effect of temperature on the distribution of products is illustrated in Table 111. The area for maximum yields of 3-aminopropionitrile lies within the upper middle portion of the temperature range examined. Only below 95' does the yield markedly decrease. The specific region of temperature for maximum yields cannot be easily defined by inspection, but is revealed by statistical methods. Contact Time. An attempt to correlate yields of 3-aminopropionitrile with contact or holding time is presented in Table IV. The only perceptible relationship from these data is that highest yield figures were obtained at contact times of 0.7 to 1.4 minutes. Here again, statistical evaluation of the results was required to derive a more distinct picture.
~f
Table V. Miscellaneous Syntheses of 3-Aminopropionitrile Mole Ratio Contact NHa:CHs= Temp., Time, % Yield at Five Ammonia Concentrations CHCN c. Min. 29% 50% 64% 75% 82% O
4.0:l
5.5:l 7.0: 1 7.7:l
105 115 85 105
N
+CHz=CHC=N-
1O:l
:NHa + -+H~NCHEHCN (4) Equation 4 may be followed by abstraction of a proton from either water or
75 115
12.2:l a
105 115 125 40 115 105
0.7 1.05 2.6 5.0
...
2.1
1.05 0.35 1.05 1.75 0.7 1.05 0.7 1.4 1.05
...
69 67 72
81a
... ...
... ... ... ... ... ... ... ...
61
... ... ... ... ... 72a 73" 74a 73a 77 75a 41
...
76"
... 70 ... ... ... 69
... ... ... ...
...
... ... ... ...
... ... ... ... ... ... ... ... ... ... ... ... ... ... I . .
...
36.
... ... ... ... ... ...
... ... ... ... ... 70 ...
Results used in statistical computation.
VOL. 50, NO. 8
AUGUST I958
1 1 17
I
I
I
I
I
I
1
I
I
2. ( I
MOLE RATIO, "3
: GH2 = CHCN = 8.5 : I )
/
/
i'
I.!
or frothing was observed. Distillation residues from the nitrile mixture have polymerized in about 1 hour at 120' to 130" without violence. The polymer is water-soluble, and forms a cloudy, opalescent solution. Available evidence suggests that a polyamidine is formed under essentially anhydrous conditions, which reacts with water to give a polyamide and ammonia. Equations 7 and 8 describe the polymerization :
+
HzNCHzCHzCN HzNCHzCH2CN -+ HzNCHzCHzC(=XH)NHCH2CH zCN, etc. (7)
1.1
HzNCHzCHzC(=NH)NHCHzCHKN HzO
REACTION TEMPERATURE, I
I
I
I
I
I
+
OC.
I
I
I
Miscellaneous Experiments
A number of interrelated experiments, not comparable with the runs reported in 'Tables I to IV, were carried out to extend the scope of the investigation and provide a statistically significant number of runs (Table V). Statistical Analysis of Results
A number of the runs in Tables I to V were part of a statistical study, made to determine the effect of reaction temperature, ammonia concentration, mole ratio, and contact time on the yield of primary amine. Preliminary inferences from the statistical analysis pointed to an overwhelming preference for an ammonia concentration of 5oY0 as opposed to 75%. Comparative averages of eight runs showed a 77.2y0 yield for the 50% concentration of ammonia us. 64.0% for the 75% concentration. The ammonia concentration was then fixed at 50% and the reaction conditions were further varied, disclosing a maximum yield of 8070 at a contact time of 1.12 minutes, a mole ratio of 11.6 moles of ammonia per mole of acrylonitrile, and a temperature of 105' C. However, very little advantage in yield of primary amine can be shown for a mole ratio higher than the more practical level of 8.5 to 1, where maximum yields of 7970 were obtained at a contact time of 1.07 minutes and 109" C. The yield of primary amine has been
Acknowledgment
plotted as a function of contact time and reaction temperature in Figure 2 by the method of Box and Wilson (2) to give an ellipsoidal surface.
The authors thank H. C. Brown for his suggestions on a proposed mechanism, E. L. Carpenter, A. G. Houpt, and other staff members for their reviews of the manuscript, members of the Research Service Department of the Stamford Research Laboratories for analytical work, and Ernest Bianco for the statistical portion of the work.
Stability of 3-Aminopropionitrile
Literature Cited
Figure 2. Maximum yields were obtained a t contact time of 1.07 minutes a t 109' C.
1 1 18
+
HzNCH2CHzC(=O) NHCH2CHnCN NHI (8)
A low molecular weight is indicated by the water solubility. Not enough work has been done to be sure of the mechanism, but it is probably ionic, either acid- or base-catalyzed, and may require the presence of traces of water even in the first step.
O.!
(
-+
Pure, dry 3-aminopropionitrile appears to be stable below 5" C. (for over 3 years). I n the presence of more than traces of water or at higher temperatures, it undergoes polymerization. Below 12O0, the polymerization has never assumed violent proportions, but pressure may develop if wet samples are shipped or stored in closed vessels. Whitmore has mentioned (72) the polymerization of 3-aminopropionitrile and postulated beta elimination of ammonia, regenerating free acrylonitrile which polymerized. Russian workers proved this concept to be in error (10); the composition of the polymer was the same as that of the monomer. Polymerization occurs without evolution of ammonia when moisture is absent (70). Buc ( 3 ) found that the moist nitrile is unstable at room temperature and that pressure was developed in stoppered bottles of the dry nitrile stored in the ice chest. In these laboratories, about six of over 50 samples containing 3-aminopropionitrile, 3,3 '-iminodipropionitrile, 1% ammonia, and 20 to 7070 water polymerized after storage in the ice chest for 6 to 8 weeks. Although ammonia was evolved, it was sufficiently soluble so that no pressure increase, heat,
INDUSTRIAL AND ENGINEERING CHEMISTRY
(1) Bessing, D.W., Tyler, W. P., Kurtz, D. M., Harrison, S.A., Anal. Chem. 21, 1073 (1949). (2) Box, G. E. P., Wilson, K. B., J . Roy. Stat. Soc., Series B, 13, 1-45 (1951). (3) Buc, S. R., Org. Syntheses 27, 3-5 (1945). (4) Buc, S. R., Ford, J. H., Wise, E. C., J . Am. Chem. SOC.67,92-4 (1945). (5) Carlson, G. H., Hotchkiss, C. N.
(to Lederle Laboratories, Inc.), U. S. Patent 2,377,401 (June 5, 1945).
S. R., Greiner, J. W., J . Am. Chem. SOC.69, 844-6 (1947). (7) Fr?;G53jJ S., Anal. Chem. 25, 407 ( 6 ) Ford, J. H., Buc,
(8) Hoffman;, U., Jacobi, B. (to I. G. Farbenindustrie), U. S. Patent 1,992,615 (Feb. 20, 1935). (9) Siggia, S., Hanna, J. G., Kervinski, I. R., Anal. Chem. 22, 1295 (1950). (10) Terentyev, A. P., Chursina, K. I., Kost,A. N., J . Gen. Chem. (U.S.S.R). (Eng. trans) 20,1115-20 (1950). (11) Weijlard, J., Sullivan, A. P. (to Merck & Co.), U. S. Patent 2,742,491 (April 17, 1945). (12) Whitmore, F. C., Mosher, H. S., Adams, R. R., Taylor, R. B., Chapin, E. C., Weisel, C., Yanko, W., J . Am. Chem. SOC.66, 725-31 11944). (13) Wikdeman, 0. F., Montgomery, W. H., Zbid., 67, 1994-6 (1945).
RECEIVED for review November 1, 1957 ACCEPTEDFebruary 12, 1958
