657
Ind. Eng. Chem. Prod. Res. D ~ v 1086, . 25, 657-664
deamination reaction followed by a hydrogenation of butene(s) to give butane.
Acknowledgment This research was supported by the US.Department of Energy under Contract No. Ex-76-C-01-2233. Registry No. Butane, 106-97-8; butene, 25167-67-3; n-butylamine, 109-73-9.
Literature Cited Andreu, P.; Rosa-Brush, M.; Sanchez, C.; Nolier, H. Z. Naturforsch., 8 : Anorg. Chem., Org. Chem., Biochem., Biophys., Bo/. 1967, 228, 809. Brey, W. S.; Cobbledick, D. S. Ind. Eng. Chem. 1959, 51, 1031. Catfy, J. P.; Jungers, J. Ch. Bull. SOC.Chlm. Fr. 1964, 2317. Cocchetto, J. F.; Satterfield, C. N. Ind. Eng. Chem. Process Des. Dev. 1976, 15, 272. Giuskoter, H. J. Fuel 1965, 44, 285.
Hogan, P.; Pasek, J. Collect. Czech. Chem. Comm. 1973, 38, 1513. Hogan, P.; Pasek. J. Collect. Czech. Chem. Comm. 1974, 39. 3696. Katzer, J. R.; Sivasubramanian, R. Catal. Rev.-Sci. Eng. 1979, 2 0 , 155. Liu, K. H. D.; Hamrln, C. E., Jr. Ind. Eng. Chem. Process Des. Dev. 1983, 2 2 , 619. Liu, K. H. D.;Johannes, A. H.; Hamrin, C. E., Jr. Fuel 1984, 63, 18. Lycourghiotis, A.; Katsanos, N. A.; Vattis, D. J. Chem. SOC.,Faraday Trans. I 1979, 75,2481. McIivrled, H. 0. Ind. Eng. Chem, Process Des. Dev. 1971, 10, 125. Pasek. J. Collect. Czech. Chem. Comm. 1963, 2 8 , 1007. Pasek. J.; Tyrpeki, J.; Machova, M. Collect. Czech. Chem. Comm. 1966, 31, 410b. Sakata, Y.; Hamrln, C. E.. Jr. Fuel 1983, 62, 508. Satterfield, C. N.; Modell. M.; Hltes, R. A.; Declerck, C. J. Ind. Eng. Chem. Process Des. Dev. 1978, 17, 141. Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B. Prep.-Am. Chem. Soc., Div. Pet. Chem. 1977, 2 2 , 919.
Received for review June 5, 1985 Accepted July 18, 1986
Salting-Out Precipitation of Cocarboxylase Hydrochloride from Aqueous Solution by Addition of Acetone Jerzy Budz,+Plotr H. Karplirskl,' Jerzy Mydlarz,+ and Jaroslav Nqvltt Institute of Chemical Engineering and Heat Systems, Technlcai University of Wrociaw, Wrociaw, Poland, Department of Chemical Englneerlng, Worcester f%&technic Institute, Worcester, Massachusetts 0 7809, and Institute of Inorganic Chemistry, Czechoslovak Academy of Sciences, Prague, Czechoslovakia
Redpitation of cocarboxylase hydrochloride from aqueous solution induced by addition of acetone was investigated. The corrected separation density concept, bulk density, the results of screening, and the electron microscope observations have been used to study the effect of the acetone addition rate, initial concentration, the amount of seeds, and the intensity of mixing on the quality of precipitate agglomerates. A set of experimentally verified optimum conditions for the process yielding the product of desired quality was established.
Introduction Salting-out precipitation of organic compounds from aqueous solutions by addition of an organic solvent (alcohols, acetone) is widely used in chemical and pharmaceutical industries. The major advantage lies in that the precipitation can be carried out a t ambient temperature and that the crystals of precipitate are usually of high purity. The organic solvent should be chosen on the basis of the following criteria (Mullin, 1972): (1) that it be miscible with water, (2) that the solubility of the solute in it be limited, and (3) that it be economically separable from water (e.g., by distillation). In spite of the wide use of the process (Gee et al., 1947; Hoppe, 1968),data concerning it are not easily accessible and only limited attention has been paid to describe its theoretical side (Karpiiiski and N*lt, 1983; N*lt, 1983). The scope of this paper is to point out typical operational parameters that influence the salting-out batch precipitation and to provide an experimentally optimized set of these parameters for the case of crystallization of cocarboxylase hydrochloride from ita aqueous solution
* Addreas correspondence to this author (formerly at Worcester Polytechnic Institute) a t Research Laboratories, Building 59, Eastman Kodak Co., Rochester, NY 14650. f Technical University of Wroclaw. t Czechoslovak Academy of Sciences. 0196-4321I861 1225-0657$01.50/0
induced by addition of acetone. The cocarboxylase is a coenzyme (ClzH,gC1N40,PzS.Hz0)that is a pyrophosphate of thiamine and is important in metabolic reactions (as decarboxylation in the Krebs cycle). Utilitarian rather than theoretical aspects of the problem will be emphasized. An aqueous solution of the cocarboxylase hydrochloride (hereafter CX.HC1) to be used for medical purposes must be freshly prepared to be effective. Therefore, this substance is distributed in a crystalline form rather than as a solution. The crystals of CX.HC1 are automatically distributed into open glass ampules that are subsequently sealed by a gas burner. It is of the utmost importance to avoid the carbonization of CX.HC1 during the sealing operation. The carbonization, however, may occur when small particles of CX.HC1 stick to the walls of the ampule. This undesired case becomes unavoidable when the crystallization product contains a significant fraction of fines. Therefore, the major requirement imposed on the commercial CX.HC1 product, aside from its high purity, is that fines must not be present.
Experimental Section Equilibria. The knowledge of the solubility of a given substance is a prerequisite to investigate the crystallization. The solubility for the system CX-HC1-water-acetone a t 15 "C was determined in the following simple experiment. An acid solution of CX-HC1and water of a known composition was placed in an Erlenmeyer flask, and a known 0 1986 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
658
321
I
!
I \
t
1
3 L
s
--,
Figure 1. Solubility of cocarboxylase hydrochloride in acetonesmoothed water mixture at 288 K: (*) experimental points; (0) values, eq 1.
volume of acetone was added. The contents of the flask were mixed by a magnetic stirrer for 4 h (this time interval has been experimentally proven to be sufficient for the solution to attain equilibrium). The CX.HC1 precipitated was filtered, dried at 40 "C, and weighed. Figure 1shows the equilibrium curve. The solubility (wt 7%) of CXOHCl is plotted vs. S, the ratio between the cumulative volume of the acetone added and the volume of the initial solution that did not contain any acetone. The solubility equation, valid for the descending part of the solubility curve where S < 2.0, can be expressed as (Karpifiski and N@lt, 1983) log
~ 1 , e q=
log WlO,eq - K12S - K122S2
(1)
where w ~ is ,the~ solubility ~ (wt % ) of CX.HC1 in the ternary system and wlO,e, K12, and Klzz are solubility constants. The values of tiese constants, found by means of the least-squares method, are wlO,eg= 0.167, K12= 1.237, and K122= -0.384. As can be clearly seen from Figure 1, the concentration of CX.HC1 remains practically unaltered for S > 2.0. Therefore, the twofold excess of acetone has been used in the precipitation process. Characterization of the Product Quality. As has been previously emphasized, the ease of CX-HC1 distribution into glass ampules is the basic requirement (aside from the purity) placed on the crystallization product. Such a requirement, however, is difficult to express in a quantitative way. Nevertheless, the generally accepted properties of granular materials, such as bulk density, the results of screening, and direct microscopic observation of the product seemed to assure the necessary level of objectivity. Measurements carried out on different samples of the crystalline CXeHCl have revealed that products with bulk density exceeding Pb = 300 kg/m3 do not stick to the walls when poured into the glass tubes. The results of screening analysis were interpreted by means of the standard RRS (Rosin, Rammler, Sperling) graphs based on a known (Bennet, 1936) empirical equation of the form log (log[lOO/M(L)]) = -0.3623 - y log La,
+ 7 log L
(2)
where L, denotes that sue of crystal for which the oversize fraction M(L) is approximately 36.8%. The two parameters of the RRS size distribution, such as the average particle size, La,, and the uniformity coefficient, y, have been used to characterize the product quality. In addition, the electron microscope (Stereosca 180, Cambridge Instruments) has been used to analyze the
Table I. Characterization of Samples of the Crystalline Cocarboxylase Hydrochloride maker figure La,, mm y Pb, kg/m3 class this paper 2A 0.130 4.3 520 I Merck 2B 0.140 2.4 660 I1 JZF Polfa first class 2C 0.255 2.9 510 I11 this paper 2D 0.230 2.8 290 IV JZF Polfa second class 2E 0.275 2.6 410 V
product samples. Table I summarizes the results of the tests aiming to characterize the crystalline CX-HC1,and Figure 2 presents pictures of representative product samples taken at X3200 magnification. A detailed analysis of photographic data distinguishes the following five classes of the product: Class I (Figure 2A). This is, basically, an ideal product. The crystalline agglomerates are well developed and formed of large individual crystals. The latter have a lensed shape and grow jointly in the radial direction advancing from the center of the agglomerate. The amount of fines is negligible. Class I1 (Figure 2B). The product is less uniform, although the agglomerates are still compact. More fine particles are present. Class I11 (Figure 2C). The product is composed of smaller and less structurally coordinated agglomerates. More fine particles that have a tendency to stick to the larger crystal's surfaces are present. Class IV (Figure 2D). The product has loose small agglomerates of a random structure and a considerable amount of fines. A large surface area may intensify the occurrence of surface phenomena. Class V (Figure 2E). The product shows an excessive amount of fines and is composed of loose agglomerates of a random structure. It is very likely the product has been formed a t a high supersaturation level under conditions giving an elevated nucleation rate. As follows from the comparison of Figure 2 and the average crystal size of Table I, the results of the screen analysis contradict the fact that the agglomerates shown in parts A and B of Figure 2 are clearly larger than the others. The results of the screen analysis, however, for the agglomerates of the "ramified" structure (classes IV and V, in particular) are apparently shifted toward the higher particle sizes because of the observed tendency of such agglomerates to stick and gather together during the screening. The values of the uniformity factor, y, seem to be less affected by this phenomenon. Although the results of screening tests are presented in this paper for all runs, only those for classes I, 11, and, partially, I11 can be considered reliable. The others should be treated as less certain measures of the product quality. Generally, the products falling into classes 1-111 can be considered as acceptable, whereas those of classes IV and V are below the required standard. The presence of undesirable fines was relatively easy to detect by evaluating the sedimentation rate of the crystallizer's content after the mixer was stopped. Two easily differentiable cases, as characterized below, were observed. Sedimentation A. Most of the crystals sediment quickly, but the upper part of the solution contains fines that sediment very slowly. Sedimentation B. All the crystallization product sediments a t the same time. The solution is clear and free of fines. Salting-Out Experiments. The apparatus shown in Figure 3 consists of a cylindrical glass crystallizer (1) with a volume of 0.0015 m3 provided with a paddle stirrer and a precise thermometer (8). The revolutions of the stirrer
Ind. Eng. Chem. Prod. Res. De"., VoI. 25, No. 4, 1986
A
B
E Figure 2. CX.HCI samples at X3200 magnification; cf. Table I and the t e x t for details.
659
660
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986 3
2
4
6
e
423
Figure 3. Apparatus for investigations of CX.HC1 precipitation from aqueous solution by addition of acetone: (1)crystallizer; (2) motor; (3) stirrer; (4) water bath; (5)thermostat; (6) precise piston metering pump; ( 7 ) graduated cylinder; (8) precise thermometer.
were controlled over a wide range by using a motor (2) equipped with a control system (not shown here). The crystallizer was placed in a water bath (4) controlled by a thermostat (5). The acetone was added to the crystallizer by a precise piston metering pump (6) fed from a graduated cylinder (7). The experimental procedure was as follows. A volume of 200 cm3of the 32 wt % aqueous solution of the CXaHCl and 26 cm3of concentrated hydrochloric acid was filtered and placed in the crystallizer at 15 "C and 100 rpm. The redistilled commercial acetone was used as a salting-out agent and added at a constant flow rate until its cumulative volume reached 400 cm3. Some experiments were run with a diluted (15 wt %) initial solution (cumulative volume of acetone, 800 cm3) and/or by using commercial acetone. The seeds were prepared by pestling the crystals of CX-HCl in a mortar and introduced to the crystallizer as a mixture with water and acetone (at the ratio 1:l). After the completion of the process of adding acetone, the crystalline product was filtered, rinsed with the mother liquor, and dried first at ambient temperature and subsequently at 40 "C. Samples of all the products were subject to screen analysis. The results of the screening were interpreted by means of the RRS standardized graph paper.
Results and Discussion The results, summarized in Table 11, were calculated by taking 1.0 m3 of the initial solution as a base. Thus, the acetone dosage rate, V, is expressed in cubic meters of acetone per cubic meter of initial solution per second, and the seeds' concentration is expressed in kilograms of seeds per cubic meter of the initial solution. The corrected separation density, defined as the following relation between the crystal size and the precipitation/crystallization rate (Njlvlt, 1982) CSI = Lavm,l13
(3)
can be rewritten in terms of the acetone dosage rate to yield CSI = 6.7La,p13
(4)
where La, is in millimeters and V is in cubic meters of acetone per cubic meter of initial solution per hour. The precoefficient in eq 4 was obtained on the basis of the fact that the mass of crystals precipitated was approximately 60 gj200 cm3 or m, = 300V. This simplified parameter ought to be treated with caution, and it was introduced because of the lack of any alternative design-oriented ap-
L
0
2
4
6
10
8 VXl
12
14
16
I
06 (s-")
Figure 4. Effect of the acetone dosage rate on properties of the product obtained without seeding: C, = 32 wt '70; 0 , = 15 "C, n, = 100 rpm.
proach. Its physical meaning is that the interrelation between the average particle size and the acetone dosage rate should be the same regardless of the scale of a batch operation occurring at well-mixed conditions. Altogether, 46 individual measurements on 9 experimental series have been performed as outlined in Table 11. Several measurements (1.6-1.8, 9.2, and 9.4) were performed without the routine filtration of the solution prior to the experiment. Such solutions were turbid, and organic particles forming the sediment might have been formed of particular crystallographic forms of the cocarboxylase hydrate. As a rule, the freshly prepared solutions were not turbid. By contrast, the solutions left for some 2 or 3 days always featured an increasing turbidity with time and the presence of sediment. The effects studied and/or observed are separately discussed below. The decision as to the optimum precipitation conditions was made on the basis of the bulk density of the crystalline product and its examination under a microscope. The results of the screening and the sedimentation observation have been treated as auxiliary tests of the product quality. Reproducibility of the measurements was checked in the first series of experiments (runs 1.1-1.8). The reproducibility for clear, turbid, and seeded solutions was found acceptable (cf. Table 11). Effect of the Salting-Out Rate. The effect of the acetone dosage rate on the particular parameters characterizing the products obtained without seeding is illustrated in Figure 4. The dosage rates have been changed over the interval from 1.67 X m3/m3s to 16.7 X 10" m3/m3s. The corresponding dosage time for 400 cm3 of the acetone covered the range 1.2 X lo3 s through 1.2 x 104 s. As follows from Figure 4, the optimum dosage rate at which the product attained the maximum bulk density was 4.16 X lo-* m3/m3 s. The average size of the product's agglomerates,La,, as well as the unformity coefficients, y, fell into the intermediate group of all the values obtained. All the post-crystallization slurries exhibited the A type sedimentation behavior. Almost all the products, however, were classified as the third quality class. In other words, the products may be easily poured into glass ampules.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986 661 Table 11. Operating Data and Results of Principal Experiments" mo, V x io4, run Cot % turbidity kg/m3 m3/m3s n,, rpm L,, mm y Pb, kg/m3 419 4.16 100 0.300 3.15 none 0 1.1 32 410 0.300 3.15 0 100 4.16 1.2 32 none 419 100 4.16 0.300 3.15 0 1.3 32 none 372 100 8.35 0.195 6.3 0.54 none 1.4 32 382 0.210 5.0 100 0.54 8.35 1.5 32 none 0.170 3.5 623 100 0 5.56 1.6 32 yes 565 100 0.185 3.4 5.56 0 1.7 32 Yes 590 0.175 3.0 0 100 5.56 1.8 32 Yes
quality class
I11 I11 I11 I
sedimentation
remarks, CSI
A A A B B A A A
2.30 2.30 2.30 1.89 2.03 1.44 1.56 1.48
A A+B B B B B
2.30 1.80 1.07 1.19 1.15 1.00 0
A A B A+B B
B B B B
2.30 crust, scalingb scaling, 2.30 1.80 1.92 1.07 scaling, 1.82 1.15 scaling, 1.95
A A A A A A A A A
1.02 1.01 2.30 2.70 2.62 3.53 scaling,b 1.92 scaling,c 2.34 scaling, 2.21 1.04 1.89 optimum, 1.89 1.99 scaling, 1.96 scaling, 1.92 scaling, 2.33 scaling, 2.88
2.1 2.2 2.3 2.4 2.5 2.6 2.7
32 32 32 32 32 32 32
none none none none none none none
0 0.25 0.50 0.535 1.105 2.50 40.0
4.16 4.16 4.16 4.16 4.16 4.16 4.16
100 100 100 100 100 100 100
0.300 0.235 0.140 0.155 0.150 0.130 fine
3.15 5.2 5.2 5.3 2.55 3.0
419 442 337 332 281 298
I I11 I1 I I11 I I I I1 I1
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9
32 15 15 32 15 32 15 32 15
none none none none none none none none none
0 0 0.05 0.25 0.25 0.50 0.50 1.105 1.0
4.16 4.16 4.16 4.16 4.16 4.16 4.16 4.16 4.16
100 130 130 100 130 100 130 100 130
0.300 crust 0.285 0.235 0.250 0.140 0.238 0.150 0.255
3.15
419
I11
3.4 5.2 3.9 5.2 4.5 2.55 6.0
394 442 392 337 360 287 315
I1
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
32 32 32 32 32 32 15 15 15
none none none none none none none none none
0 0 0
100 100 100
0 0 0 0 0
1.67 2.84 4.16 5.56 10.00 16.67 2.83 4.41 10.00
100 100 130 130 130
0.180 0.150 0.300 0.320 0.255 0.290 0.285 0.300 0.215
3.4 3.1 3.15 3.25 3.35 4.1 3.4 4.4 3.1
342 360 419 360 359 336 436 352 235
5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8
32 32 32 32 15 15 15 15
none none none none none none none none
0.515 0.54 0.25 0.50 0.25 0.25 0.25 0.25
2.50 8.35 8.35 12.50 2.83 4.16 6.65 10.00
100 100 130 100 130 130 130 130
0.160 0.195 0.175 0.180 0.290 0.250 0.260 0.280
4.0 6.3 6.8 3.5 4.9 3.9 5.1 4.5
289 372 400 330 306 392 314 315
I I I I1 I I I1
I11
A+B B B B B B B B
6.1 6.2
32 32
Yes Yes
1.25 1.30
4.16 4.16
100 100
0.180 0.210
3.4 5.3
261 329
I1 I
A A
heteroseeds-monoester, 1.38 heteroseeds-CX hydrate, 1.61
7.1 7.2 7.3 7.4
32 32 32 32
none none none none
0 0 0 0
4.16 4.16 5.56 5.56
100 100 100 100
0.300 0.180 0.210 0.295
3.15 5.8 4.2 3.1
419 340 300 414
I11 I1 I11 I11
A A A A
2.30 commercial acetone, 1.38 mixing disturbances, 1.77 commercial acetone, 2.49
8.1 8.2 8.3
32 32 32
none none none
0.54 0.54 0.54
4.16 4.16 4.16
60 100 200
0.255 0.155 0.130
3.5 5.3 2.8
360 332 245
IV I
A+B B B
scaling,b 1.95 1.19 1.00
9.1 9.2 9.3 9.4 9.5 9.6
32 32 32 32 32 32
none Yes none Yes none yes
0 0 0 0 0 0
2.88 2.88 4.16 4.16 5.56 5.56
100 100 100 100 100 100
0.150 0.135 0.300 0.175 0.320 0.170
3.1 4.5 3.15 4.7 3.25 3.5
360 607 419 566 360 623
A A A A A A
1.01 0.92 2.30 1.34 2.10 1.44
0
100
I I I
I I1
I I11 IV I11 I11 I11 I1 I1 I11 V
I IV I I11 I I11 I11
a Initial solution volume: 200 cm3. Cumulative volume of acetone: 800 cm3 for Co = 15 wt % and 400 cm3 for Co = 32 wt %. Working temperature: 0, = 15 bC. bExtensive scaling. 'Moderate scaling.
The results of the series of experiments with seeds, performed with a constant amount of seeds of 0.5 kg/m3 (runs 1.4,1.5, 2.3,5.1,and 5.4), are shown in Figure 5. The optimum dosage rate was found at 8.35 X m3/m3 s, i.e., twofold the value found without the seeds (cf. Figure 4). Effect of Seeding. The seeding of a solution to be crystallized is in industrial practice frequently considered as a means of stabilizing the crystallization process. Both mass and size of the seeds have appeared to be very im-
portant. In the case of strongly soluble inorganic salts the situation is quite simple. To obtain the uniform product the mass and the size of seeds is set in such a way that growth of the seeds is allowed only while the supersaturation level is maintained well below that at which a more extensive nucleation is a possibility. The case under consideration, however, is more complex. The crystals of CX-HC1form agglomerates, and thus the crystal size and the crystals' surface area are difficult to evaluate. Aside, however, from the true mechanism of the process, it can
662
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
e
, C 16 4
6
.
:IC
f
A - SCOEFFICIENT 0 - AVERAGE SIZE
0
?
q VXlO'
8
:
- 00 12
10
:
i
Is- I
Figure 5. Effect of the acetone dosage rate on properties of the product obtained by using a constant mass of seeds at 0.5 kg/m3: Co = 32 w t 70;8, = 15 "C; n, = 100 rpm.
Figure 6. Effect of the mass of seeds on properties of the product obtained a t a constant dosage rate of acetone at 4.16 X m3/m3s: Co = 32 wt %; 8, = 15 O C ; n, = 100 rpm.
be predicted that the presence of the seeding crystals affects nucleation phenomena and/or formation of agglomerates from the very beginning of the process. The tentative run 2.8 revealed that the mass of seeds applied (18 wt 7% of that of the product) was too big, and as a result very fine product agglomerates were obtained. The results of the empirical search for the optimum mass of seeds (seeds prepared by pestling were estimated to be of uniform size) carried out at the optimum dosage rate of the acetone (0.0416 m3/m3s) are presented in Figure 6. The bulk density of the product increased with a seeds' mass increase (and so did the uniformity factor and the average particle size), whereas a smaller amount of seeds used resulted in an elevated fines content (type A sedimentation). The optimum mass of the seeds was assumed at m0 = 0.25 mg/m3, i.e., 0.12 wt % of the mass of the product (run 2.2). This optimum mass of seeds should be a t the same time considered as a minimum allowable amount if the product quality is to be improved in comparison with that achievable with no seeds. Most likely, the overall surface area of the seeds used in run 2.2 was not sufficient to reduce appropriately supersaturation in the course of the experiment. The effect described has not been observed for the twofold higher mass of the seeds (run 2.3). More seeds in the system caused a gradual deterioration of the product quality. This fact can be explained as follows. The amount of solute that may be recovered from the solution is constant, and it is more or less uniformly distributed among the seeds during their growth. The mass of solute to be deposited on an individual seed is inversely proportional to the number (or the mass) of the seeds: therefore, the more seeds in the solution the smaller the incremental growth of a given seed. On the other hand, the crystal size increment is proportional only to the power of of the mass increment, and with the increasing mass (and thus the number) of the seeds the size of the product tends to approach the average seed's size. Intensity of Mixing. The effect of the mixer speed can be clearly seen from the results of series 8 performed a t the constant mass of the seeds mo = 0.54 kg/m3. At n, = 60 rpm, extensive scaling on the walls and the bottom of the crystallizer was observed. The crystals sedimented
very quickly, and nucleation was observed throughout the bulk of the solution. The overall product fell into class IV. Too intense mixing should be avoided as well (run 8.3 at n, = 200 rpm) because it leads to a much less uniform product (y = 2.8) of low bulk density. The reason for getting such a product is obvious: the intense mixing facilitates the occurrence of secondary nucleation and inhibits the agglomeration, thus producing the undesirable fines. The optimum mixer speed for the overall conditions of the test performed was found to be 130 rpm, close enough to the initially adopted value of 100 rpm. Precipitation from Diluted Solution. The salting-out process usually produces extremely high supersaturation that in turn by an excessive nucleation may totally suppress any other effort undertaken to control it. There are two ways of preventing the production of excessive supersaturation: use of a secondary solvent diluted with a primary solvent (here, acetone diluted with water) or carrying out the operation from a diluted solution. The former approach to the problem has been recently studied by N*lt (1983); therefore, the latter approach was applied in this study. The initial solution concentration was chosen to be approximately one-half of that previously investigated, i.e., 15 wt 7%. The influence of the amount of the seeds and of the acetone dosage rate was studied at the optimum mixing conditions (n, = 130 rpm). The results of the experiments (described in detail in Table 11, runs 3.1-5.8, and illustrated in Figures 7-9) may be summarized as follows. The experiments without the seeds (runs 4.7-4.9) revealed that extensive scaling at the walls of the crystallizer had occurred, particularly at the lower acetone dosage rate (Figure 7). In such circumstances, the seeding seemed to be an appropriate solution. The experiments conducted at constant dosage rate and variable mass of seeds (Figure 8) and vice versa (Figure 9) have shown that the optimum conditions were mo = 0.25 kg/m3 and V = 3.33 X m3/m3 s. In general, the uniformity of the product obtained was remarkable, and the results indicated that salting-out precipitation can be successfully carried out from a diluted solution. Effect of Solution Aging. The precipitation products
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986 863
310-
230
-
SCALE INTENSITY
A-PCOEFFICIENT -028
5-
-025
a.
- 0 24 - 0 22
4-
A- TCOEFFICIENT
3r
0- AVERAGE SIZE
E
2E J
\
2
4
8
6
2 0
10
02
04
06
06
10
12
vxio4 (54)
m,(Wm3)
Figure 7. Effect of the acetone dosage rate on properties of the product obtained without seeding: Co = 15 wt %; 8, = 15 O C ; n, = 130 rpm.
Figure 9. Effect of the acetone dosage rate on properties of the product obtained by using a constant mass of seeds at 0.25 kg/m3: Co = 15 wt %; 8, = 15 O C ; n, = 130 rpm.
process appeared also to be influenced by the purity of the acetone precipitant (cf. series 7). An industrial application of the aging effect does not seem to be immediate. The only conclusion is that the possible aging effect may, at the most, improve the product quality and should not be considered to be detrimental in CX.HC1 technology.
\*
A - TCOEFFICIENT
0 - AVERAGE SIZE
3.51
{
0.30
10.24
Vxl 0‘
(S’)
Figure 8. Effect of the mass of seeds on properties of the product obtained at a constant dosage rate of acetone at 4.16 X lo4 m3/m3a: Co = 15 wt %; Ow = 15 “C;n, = 130 rpm.
obtained from the “aged” solutioq-series 9-had surprisingly good properties. The bulk density exceeded 550 kg/m3, all the products fell into classes 1-111, and the product uniformity coefficients were within acceptable limits. All the solutions after aging were turbid due to, most likely, the presence of fine crystals of cocarboxylase hydrates and/or its monoesters. Tentative runs 6.1 and 6.2 with the above compounds used as seeds resulted in a different product quality than that obtained without seeding (runs 1.1-1.3). The presence of such “foreign” crystals can induce heterogeneous nucleation at much lower supersaturation levels and also at lower rates than those characterizing pseudohomogeneous nucleation, and as a result a more coarse product can be formed. Extremely small particles causing the solution turbidity probably act as heteroseeds. The CX.HC1 precipitation
Conclusions The process of the salting-out precipitation of cocarboxylase hydrochloride from its aqueous solution by addition of acetone may be remarkably improved if the following operating parameters are carefully selected: the size and amount of seeds (0.25 kg/m3 of the seeds obtained by pestling in a mortar), the mixer speed (a paddle stirrer, 130 rpm), and the acetone dosage rate (4 X lo4 and 8 X m3/m3 s for the operation without and with seeds, respectively). The results of run 5.3 seem to corroborate fully the above set of optimum operating parameters. An application of the corrected separation density (CSI) provided a useful guideline for design purposes. CX-HC1precipitation can be successfully conducted by the me of diluted rather than concentrated intial solutions. Acknowledgment The research grant from Pharmaceutical Works JZF “Polfa”, Jelenia Gora, Poland, is gratefully acknowledged.
Notation initial concentration of CX.HC1, wt 70 average crystal size from the RRS graph paper, mm precipitation rate, kg (m3 of solution)-s m c mass of seeds, kg/(m of solution).s $L) oversize fraction, w t % mixer speed, rpm ratio between cumulative volume of acetone added and acetone-free initial solution acetone dosage rate, m3 (acetone)/m3(solution)-s 0 W mass fraction, wt % uniformity coefficient from the RRS graph paper Y ow working temperature, “C Pb bulk density, kg/m3 Registry No. CX.HC1, 23883-45-6; Me2C0,67-64-1.
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Ind. Eng. Chem. Prod. Res. Dev.
664
Literature Cited Bennet, R. C. J. Inst. Fuel 1936, 10, 12. Gee,E. A,: Cunninghem, W. K.; Heindl, R. A. Ind. fng. Chem. 1847, 3 9 , 1178. Hoppe, H. Chem. Process Eng. (London) 1868, 49, 61. KarpiRski, P. H.; Njhlt, J. Cryst. Res. Techno/. 1983, 18, 959. Mullin. J. W. Crysfallissfion,2nd ed.: Butterworths: London, 1972: p 265
1986,2 5 , 664-665
N W , J. Industrial Cwstal/lzaflon. The State of the Art. 2nd ed.: Chemie Verlag: Weinhem,. 1982. Njwlt, J. Chem. R u m . 1883, 33, 402.
Received for review April 2 , 1985 Revised manuscript received April 14, 1986 Accepted June 9, 1986
Long-Acting Androgens: Esters of Testosterone with Bile Acids Josef E. Hew' and Jesus Sandoval+ Department of Chemistry, CIEA-IPN, and Department of Biotechnology, Institute for Biomedical Research, UNAM, Apartado Postal 70228, Mexico, D.F. 045 10, Mexico
Long-acting androgens are potentlaliy useful as male contraceptives and to maintain libido and potency under certain pathological conditions. This paper describes the synthesis of esters of testosterone with four bile acids as part of a World Health Organization Program for the synthesis and screening of potential longacting contraceptive agents. Two methods of esterification were fwnd to give optimum resutts of yield and purity of the final product: (a) reaction of the acid chloride with the thallium(1) salt of the steroidal alcohol and (b) reaction of the free acid with testosterone in the presence of 4-(dimethylamino)pyridineand dicyclohexylcarbodiimide.
Introduction Until recently there has been much less research conducted on the development of male contraceptives than on those intended for women. In the male, the need to maintain libido and potency is of greatest importance, and the close morphological and functional relationship of spermatogenic and androgenic functions makes many methods unacceptable. The control of male fertility could theoretically be achieved by interference in three major areas: (a) spermatogenesis, (b) spermmaturation, and (c) spermtransport (Harper and Sanford, 1980). The most promising approach to reversible interference with spermatogenesis by suppression of gonadotropin secretion has been in studies using various combinations of steroid hormones: progestin-androgen (Ulstein et al., 1975), estrogen-androgen (Briggs and Briggs, 1974),or a long-acting androgen alone (Steinberger et al., 1978). The greatest difficulty facing these approaches has been the lack of long-acting androgen. The desired characteristic for a long-acting testosterone ester would be to maintain a uniform level without an inital peak so as not to stimulate the prostate. Such a preparation would be useful not only in male fertility control alone or in combination with a long-acting progestin but also for the control of infertility and in gerontology (WHO Program, 1982). In 1975, the World Health Organization initiated a program for the synthesis and screening of potential long-acting contraceptive agents, and as part of this project a number of bile acid esters of testosterone were synthesized The biological activities of these compounds are reported elsewhere. Chemical Synthesis The testosterone esters described in this paper were prepared by two previously described methods: Method A, reacting the thallium salt of testosterone with the acid chloride (Herz et al., 1977), and Method B, reacting testosterone with free acid in the presence of dicyclohexyl-
carbodiimide (DCC) and 4-(dimethylamino)pyridine (4DMAP) according to Neises and Steglich (1978). The acid chlorides were prepared as described in our previous publication (Herz and Sandoval, 1983), according to the method of Wissner and Grudzinskas (1978).
Experimental Section Testosterone ester of 3a-(formyloxy)-5@-cholan-24oic acid (I) was crystallized from methanol: mp 159-161 "C; [a]25D + 89' (CHCI,); UV max 238 nm ( 6 12420, cy-
I.
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Present address: Department of Chemistry, University of Puebla, Puebla, Mexico. 0196-4321/86/1225-0664$01.50/0
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0 1986 American Chemical Society
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