I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2366
ACKNOWLEDGMENT
(5)
The author wishes to express his appreciation to the Firestone Tire & Rubber Co. for permission to publish this work and to F. W. Stavely for his continued interest in the problem. LITERATURE CITED
(1) Rock, W. (to I. G. Farbenindustrie), Ger. Patent 737,276 (July 9, 1943). (2) Chern. Inds., 67, 29 (July 1950). (3) collins, A. M, (to E. 1. du Pant de Nemours and Co,, Inc,j, u.8 , Patent 2,264,173 (Nov. 25, 1942). (4)Craig, D. (to B. F. Goodrich co.1, Ihid., 2,362,052 (Nor-. 7 , 1944).
J
Vol. 43, No. 10
Dillon, J. H., Prettyman, I. B., and Hall, G. L., J . A p p l i e d Phys.,
15,309-23 (1944). (6) Du Pont de Nemours and Co., Inc., E. I., Rubber Chemicals Div., Bull. BL223 (April 15, 1948). (7) Harrison, S. A., and Meincke, E. R.. Anal. Cheni., 20, 47-8 (1948). (8) Houston, R. J.,Ibid., 20,49-51 (1948). Liska3J' w ' 2 IND' 36140-6 (1y44)' (10) Mochel, W.E., Salisbury, L. F., Barney, A. L., Coffman, I).D., and Mighton, C. J., Ibid., 40,2285-9 (1948). (11) Wilder, F. N. (to E. I. du Pont de Nemours and C o . , Iuc.), Brit. Patent 587,804 (May 6, 1947). RECEIVED March 2, 1931. Presented before the Division of Rubber Chemist r y of the AMENICAN CHESIICAL SOCIETY.Washington, D. C., 1951.
rolvsis of J
0
ERNEST G. LONG' AND KENNETH A. KOBE University of Texas, Austin, Tex.
T h e hydrolysis of mercuric acetate makes impossible a simple solution of this salt in watei. The minimum concentration of acetic acid necessary to prevent precipitation of mercuric oxide has never been determined. The extent of hydrolysis of mercuric acetate has been determined for concentrations up to saturation over the temperature range -1.5" to 100" C. Pure mercuric acetate can be prepared from solutions containing more acetic acid than the amount formed dn hydrolysis. In mercuration processes i t is necessary to exceed this concentration.
acetic acid, and water may be in equilibrium with (a) aohd mercuric acetate, as along a simple solubility curve, or ( b ) solid mercuric oxide, formed under conditions of hydrolysis, or (c) with mercuric acetate and mercuric oxide, as a t the intersection of solubility and hydrolysis curves. Thus the hydrolysis-solubility curve of mercuric acetate represents one branch of the ternary solubility isotherm for which the solid phase is mercuric oxide. The aceti6 acid concentration in the equilibrium hydrolysis solution represents the minimum acetic acid concentration possible in the ternary system for any specified temperature and concentration of mercuric acetate. EXPERIMEIYTAL
0
RGANIC mercurials are of considerable interest because of their properties as bactericides and fungicides as well as their properties as chemical intermediates. An extensive literature exists concerning their preparation, properties, and reactions (1). However, there are few data relative to the medium which is almost invariably used in mercuration processes. Data on this mercurating medium (the system, mercuric acetateacetic acid-water) are needed if the study of the reactions is to be put on a fundamental basis. In addition, data on this system are needed in the general study of salt solubility for a system in which considerable hydrolysis of the salt occurs. For this particular salt, these data are required for proper control of the crystallization process by which a salt of high purity can be produced. The usual mercurating agent for organic compounds is mercuric acetate which is normally introduced as an aqueous acetic acid solution. Although there are several references to the water solubility of mercuric acetate without mention of hydrolysis ( 2 , S ) , mercuric acetate does not dissolve in water to form a simple binary solution. When pure mercuric acetate is dissolved in water, hydrolysis occurs, producing acetic acid and precipitating mercuric oxide according to Equation 1. Hg(0Ac)z
+ HzO
2HOAc
+ HgO(s)
(1)
The reaction is reversible, and the equilibrium is affected by temperature and concentration. At temperatures above the freezing point of acetic acid, the solution of mercuric acetate, 1
Present address, Johns-bhnville Research Center, RIanville, N. J
Determination of Mercury. Mercuric ion wm determined by precipitating mercuric sulfide Kith hydrogen sulfide in a dilutc aliquot. Standard laboratory procedure was used. Check analyses shoxed accuracy of 1 part in 2000. Determination of Acetic Acid. The hydrolysis of the mercuric acetate prevented a direct deterinination of the acetic acid by titration. Instead, it was necessary to determine the total acetate present and, by subtracting the acetate equivalent to the mercuric ion as mercuric acetate, t o calculate the acetic acid acetate by difference. A simple direct titration with standard sodium hydroxide (0.08-0.20 A') using phenolphthalein as an indicator gave accurate results, and this method was used at all times. Addition of excess base and back-titration with hydrochloric acid gave the same results as a direct titration with base. At the end point the solution is one of sodium acetate in water. The solubility of the mercuric oxide, 0.000237 gram-mole per liter (4),is negligible. Determination of Water. Water was calculated by subtracting the percentage of mercuric acet,ate and acetic acid from 100%.
TABLE I. EFFECTO F MERCURIC OXIDE ON ACETATETITRATION Bample x-1 2-2
2-3 x-4 2-5 37-6 2-7
Mercuric Oxide None None Small amount all dissolved Twice x-3 all 'dissolved 3 times 5-5, all dissolved 4 times 2-3,some excess HgO 6 times 2-3,some excess HgO
A-&OH, RI1. 14.73 14.74 14.78 14.74 14.74 14.74 14 74
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1951
RIC
0.5
07
I.o
2
MOLES
Figure 1.
3
MERCURIC
4
5
7
2367
ACETATE
IO
20
30
40
50
ACETATE PER 100 MOLES WATER
Effect of Temperature and Concentration on Hydrolysis of Mercuric Acetate 0 Solid phase is mercuric oxide and mercuric aaetate
0 Solid phase is mercuric oxide
Checkirig Analytical Method. To ensure that the precipitating mercuric oxide had no effect on the titration of the total acetate, the following test was made: A solution of acetic acid was prepared and equal portions were titrated in the presence of varying amounts of mercuric oxide. This varied the ratio of mercuric acetate to acetic acid while maintaining a constant total acetate concentration. The results, given in Table I, indicate that the dissolved mercuric acetate or precipitated mercuric oxide has no detectable effect on the titration of the acetate. To determine the effect of the ratio of acetic acid to mercuric acetate on the acetate titration, the following tests were made: Measured volumes of standardized acetic acid and standardized mercuric acetate were mixed and then titrated with standard sodium hydroxide. The results, given in Table 11, indicate, as does Table I, that the titration is accurate in varying ratios of mercuric acetate to acetic acid. From the data of Tables I and I1 and because of the consistent accuracy of the analyses shown in the subsequent section of this work, the method is considered accurate and reliable. Sample Preparation and Treatment. Equilibrium concentrations were measured in samples of approximately 40 ml. For temperatures above 40" C., glass-sealed tubes were used; for temperatures below 40' C., glass-stoppered tubes were sufficient. The samples were prepared by mixing reboiled distilled water and mercuric acetate in the desired proportions and then allowing them to come to equilibrium in a constant-temperature bath. At low temperatures, where the hydrolysis is small, it was first necessary to wash the mercuric acetate with cold water to remove the excess acetic acid. At high temperatures where the hydroly-
sis is extensive, a small amount of acetic acid was sometimes added to reduce the amount of mercuric oxide formed. The equilibria were not affected by this addition of acetic acid. For 20' C. and less, the samples were rotated in a+constanttemperature bath for 36 hours. Twenty-four hours were allowed for temperatures of 20" to 60" C. and 12 hours for 60" to 100' C. Experiments indicated that such times were ample for equilibrium. When sufficient time for equilibrium had elapsed, the sample tube was fastened in an upright position, and the solid phase or phases were allowed to settle for 24 hours or more. Samples were then withdrawn in Rspecially constructed weightpipets. The samples of approximately 10 ml. (10 to 22 grams)
TABLE 11. EFFECTOF RATIOOF MERCURIC ACETATETO ACETICACIDON .ACETATE TITRATION Sample No. x-8
Titration of H O A C / H ~ ( O A ) C )Mixtureb ~ Mole Ratio
Titration of Component Solutionsc
Hg(OAc)za HOAc" 1.26 7.94 1.30 7.76 x-9 2.62 7.94 r-10 2.60 x-11 7.76 4.30 x-12 15.80 5.06 2-13 15.88 15.52 5.18 2-14 11.29 10.70 2-18 13.17 2-16 20.14 Columns 2 and 3 are expressed as equivalent ml. of the titrating sodium hydroxide solution (0.1 N ) . b Column 6 is aatual number of ml. of sodium hydroxide required for the titration of the mixture of 2 and 3. C Column 6 is calculated value for titration assuming t h a t titration of the mixture requires the sum of the titrations for the components.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2368
Vol. 43, No. 10
DETWRXIIXATIOSS OF HYDROLYSIS OF MERCURIC ACET~TE TABLE 111. EXPERIMENTAL Composition, W t . % Rg(0Ac)z HOAc HzO
Mole Fraction Hydrolysis Constant, K,h, io3
Mole Ratio Hg(Ohc)2/100 ks0
Composition, W t . Hg(0dc)z HOAc
9%
Temperature, 100' C. 16.38 30.06 40.59 51.12 62.37 78.74 85.20 86.32Sa
2.67 3.14 3.16 3 .OO 2.79 2.08 1.51
17.87 30.08 45.42 54.01 67.42 70.40 79.63 80.40s
2.40 2.68 2.71 2.72 2.42 2.20 1.78 1.77
77.08 77.40 S
1.75 1.79
8.42 27.16 27.92 50.91 66.98 70.52 '72.43 s
1.58 2.56 2.44 2.55 2.18 2.03 2.00
Temperature, 90' C. 1.27 2.53 4.96 7.06 12.67 14.53 24.2 25.5 Temperature, 85' 21.17 20.81
0.525 2.19 2.26 6.19 12.28 14.30 16.0 Temperature, 75' C.
2 .oo
30.56
3.32
1.48 2.03 2.34 2.40 2.39 2.12
89.08 78.81 59.60 57.43 47.65 35.30
1.74 1.74 1.79
49.53 49.49 49.43
8.81 19.29 30.44 37.29 39.11 44.87s 44.905 44.94s
1.05 1.51 1.63 1.67 1.71 1.65 1.65 1.62
90.14 79.20 67.93 61.04 39.18 53.48 53.45 53.44
41.14s
1.53
57.33
10.47 20.31 30.28 37.79s 37.81 8 37.83s 37.95 9 37.97 s
1.01 1,25 1,35 1.36 1.34 1.40 1.37 1.39
34.86s 34.92 S
1.20 1.23
63.94 63.83
31.978
1.08
66.95
4.21 4.37 3.81 3.96 3.82 3.24
29.63 S 29.63s 30.158
0.93 0.89 0.67
69.44 69.48 69.18
58.355
2.04
4.31 10.35 13.66 17.35 18.40 21.62 22.52 25.24 28.95 29.17 37.80 41.07 44.77 48.06 48.57 53.16s 53.17s 53.19s 53.19s 53.61 9 54.489
0.88 1.32 1 45 1.60 1.67 1.76 1.79 1.85 1.90 1.90 1.99 1.97 1.98 1.95 1.95 1 90 1.88 1.92 1.86 1.33 0.85
2.88
27.60s 27.84s
0 74 0.72
71 .66 71 44
25.58s 25.57s
0.59 0.62
73.83 73 81
23.909 24.288
0.42 0.22
75.68 75.50
22.41 8
0.26
77.33
20.59s 20.849
0 44 0 28
78 97 78 88
5 56 5.57 5.57
2.25 2.37 2.07 1.97 2.02 1.82 1.82 1.74
0.554
1.37 2.53 3.45 3.74 4.47 4.47 4.73
Temperature, 45' C.
1,j 7
4.06
0.61 1.38 3.62 3.95 5.93 10.01
0.67 1.47 2.51 3.31 3.51 3.52 3.53 3.54 Temperature, 35' C. 1.02 1,09
3.08 3.09
Temperature. 30' C. 0 . a70
2.71
Temperature, 25' C. 0.666 0.599 Metastable
2.41 2.41
Temperature, 20' C.
Temperature, 65' C. 39.61
2.00 2.00 2.12
Temperatore, 50' C.
12.49
Temperature, 70' C. 9.44 19.16 38.06 40.17 49.96 62.588
Mole Ratio, Hg(OAc)r/100 f i e 0
Temperature, 40' C. 20.6 21.0
Temperature, 80' C
67.44s
48.73s 48.77s 48.785
C
3 .OO 3.17
&h.lOB
Temperature, 55O C. 1.14 2 , ,i3 4.08 6.30 10.14 23.2 36.3 40.1
1.50
€€EO
Mole Fraction Hydrolysis Const,ant.
8 33
Temperature, GO0 C.
0.435 0.429
2.17 2.20
Temperature, 15' C. 0.26 0.66 0.90 1.21 1.30 1.60 1.68 1.96 2.36 2.40 3.55 4.08 4.75 6.44 5.65 6.69 6.69 6.70 6.69
0.282 0,333
1.96 1.96
Temperature, 10' C. 0.149 Netastable
1 79
Temperature, 5' C.
0.062
1.64
Temperature, 0' C.
a S =
iSot hydrolyzed Not hydrolysed
saturated solution. ~
were diluted to 120 to 500 ml., and aliquots were taken for analysis. Reagents used were of the highest quality obtainable; all laboratory apparatus was carefully calibrated; and temperature control and measurement were to 0.01 " C. DISCUSSION
The hydrolysis of mercuric acetate was determined over the temperature range 0" to 100" C. and from a minimum mercuric acetate concentration of 4.31% by weight to a maximum of 86.32%. The hydrolysis from dilute t o saturated solutions was determined a t 10" C. intervals and for saturated solutions at 5" C. intervals. The results, expressed as weight per cent composi-
tions and as mole per cent hydrolysis constants, are given in Table 111. In considering the components of the system of Equation I it is realized that all are either slightly ionized or insoluble. Hence a hydrolysis constant calculated from molar quantities might be reasonably constant or might vary in a uniform manner so that it could be used to interpolate and rectify the data. A hydrolysis constant was calculated from Ksh
= [Mole
yo HOAc] % [Uole Hg(OBc)t] [Uole % HzO]
(2)
The usual molar hydrolysis constant is based on volumetric units and is a constant over a limited range of concentrations. How-
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1951
2369
30
0
0.4
I.2
0.8 ACETIC
Figure 2.
ACID
-
MOLE
1.6 2.o PER C E N T
2.4
2.8
3.0
Hydrolysis of Mercuric Acetate
ever, densities of many of the solutions analyzed were not kno’wn accurately, and the gravimetric hydrolysis eonstant, ( K 3 J , using mole fractions (or mole percentages), was calculated and used to interpolate and extrapolate the data. The solutions tested were not dilute solutions in the physical-chemical sense; the extreme case was the saturated hydrolysis equilibrium a t 100’ C. with 86.32% mercuric acetate, l.5070 acetic acid, and only 12.18% water. In view of the extremely high salt concentrations, it was surprising to find that the calculated hydrolysis constant was not more depressed at the high concentrations. In Figure 1, the hydrolysis constant approaches a limiting value in dilute solutions. In solutions of less than 1 mole of mercuric acetate per 100 moles of water (about 15% by weight of mercuric acetate), the value is essentially a constant within the limits of error of the method of analysis. A t a concentration of about 2 moles of mercuric acetate per 100 moles of water the hydrolysis constant is noticeably depressed, and it steadily decreases as the concentration increases. The hydrolysis constant has been plotted in Figure 1 on a loglog diagram as a function of the mole ratio of mercuric acetate to water. As the relation of these two variables is the most predictable, such a plot allows reliable interpolation and extrapolation of the data. Figure 2 presents the smoothed hydrolysis data in a conventional composition plot. Normally the hydrolysis reaction is initiated quickly in the concentrations investigated and proceeds smoothly. However, a few cases of inhibited or retarded hydrolysis were observed; no visible sign of hydrolysis (precipitation of mercuric oxide) was produced although sufficient time had been allowed for equilibrium. It occurred only four times in several hundred determinations.
Extrapolation of the data to temperatures below 0” C. indicates that, within the accuracy of the data, no hydrolysis occurs a t -1.5’ C., which corresponds to the eutectic of mercuric acetate and water at 20.7% mercuric acetate. Figure 2 shows that dilution with water of an equilibrium solution will cause further hydrolysis of the mercuric acetate. I n dilute solutions (less than 1yo mercuric acetate) the hydrolysis produces a thin film of yellow mercuric oxide on the bottom of the vessel. Over a period of weeks, this film gradually turns orange and finally changes into one or two large crystals of red mercuric oxide. A t elevated temperatures the transformation from yellow to red mercuric oxide is much more rapid. SUMMARY
The hydrolysis of mercuric acetate to mercuric oxide and acetic acid has been determined from the eutectic of mercuric acetate and water a t -1.5’ to 100’ C. A t 100’ C. it is necessary t o have 11.0% acetic acid in the solvent to prevent hydrolysis. The solubility of mercuric acetate at 100’ C. in this solution is 86.32 weight %. LITERATURE CITED
(1) Kobe, K. A., and Doumani, T. F,, IND. ENQ.CHEM.,33, 170-6 (1941). (2) Mameli, E., and Cocconi, G., Gazz. chim. ital., 47, I, 160 (1917). (3) Merck & Co., Rahway, N. J., “Merck Index,” 5th ed., p. 1027, (4)
1940. Seidell, A., “Solubilities of Inorganic and Metal Organic Compounds,” p. 650, New York, D. Van Nostrand Co., 1940.
RECEIVED Ootober 23, 1950.
