March, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
A coating of pure starch propionate shrinks enough on drying to crack, although its hardness is comparable to any of the common fossil resins or to shellac. To eliminate this fault and to give flexibility to the films where it was desired, a few standard plasticizers were tried. Castor oil separated out on drying the film. Butyl stearate and butyl lactate did not accomplish the desired effect up to 50 per cent plasticizer (based on ester), since the resulting films were too brittle. Tributyl phosphate gave a film which was too soft and at the same time brittle. Triacetin and tributerin tended to dissolve out in water and leave the film brittle. Dimethyl phthalate was good for a while but slowly evaporated. Dibutyl phthalate, dibutyl Cellosolve phthalate, and tricresyl phosphate all gave good results. The films did not change after soaking in water, did not embrittle on aging, and were not sticky. Of these three, dibutyl phthalate seemed to be best and least of it was required for a good effect. Varying amounts had to be used, depending on the use to which the films were put. The films were not strong. Some of the thinner ones were so delicate that a special technique had to be used in their preparation: A thick solution of sugar, water, and a little soap (to aid spreading) was used to glue a sheet of unglazed paper to a glass plate. It was given a coating of the sugar solution and dried. The starch propionate solution was brushed on until enough coats were added to give the desired thickness. After drying, the paper and film were easily peeled from the glass plate. Soaking in water served to dissolve the sugar solution and release the film from the paper. For these thin or fragile films 35 per cent (ester basis) of dibutyl phthalate was used. This concentration was also used to make
309
coatings on cloth or any material where great flexibility was demanded. Although quite soft (rubbery), they did not stick together unless heated. For paper coatings where a reasonable amount of flexibility but no crumpling was involved, 20 per cent plasticizer was used. Nonflexible coatings of rigid materials, such as wood or metal, required only 5 per cent. ACKNOWLEDGMENT
The authors wish to thank the American Maize Company and the Tennessee Eastman Corporation for materials generously 'given. LITERATURE CITED (1) Goodman, A. H., private communication, April, 1941. (2) Higginbotham, R. S., and Richardson, W. A,, J. SOC.C h e m Ind., 57, 234-40 (1938).
(3) Niacet Chemicals Gorp., General Catalog, 9th ed., 1939. (4) Oil, Paint Drug Reptr., 139,No. 17 (April 28, 1941). . (5) Radley, J. A., "Starch and Its Derivatives", p. 155, New York, D. Van Nostrand Co., 1940. (6) Reich, W. S., and Damanski, A. F., Compt. rend., 196, 1610-13 (1933). (7) Sutra, R., Ibid., 196,1608-10 (1933). BABEDupon a thesis submitted by D. E. Mack to the faculty of Purdue University in partial fulfillment of the requirements for the degree of doctor of philosophy.
Monomercuration of Benzene enzene has been mercurated b y a method found t o produce exclusivelya monomercurated product. Optimum conditions have been established w h e r e b y a 92 p e r cent of crude phenyl mercuric chloride of high degree of purity has been obtained. The same method for direct mercuration has been incorporated w i t h the use of a high-boiling solvent to eliminate the use of a Fressure vessel. The crude product w a s found difficult t o purify. The solubility of mercuric acetate in glacial acetic acid from 25" t o 100' C. has been determined.
B
A
ROMATIC mercuration, a typical substitution reaction, was recently classified as a unit process by Kobe and Doumani (6), who reviewed the general importance of the aromatic mercury compounds. These compounds are important intermediates for organic syntheses because of the ease with which the mercury can be replaced by halogens and particularly by other metals, such as arsenic, tin, selenium, etc. The aromatic mercurials of type R-Hg-X, in which X represents a wide range of anions, possess useful properties as antiseptics, germicides, and fungicides, and are f
9
Present address, University of Texas, Austin, Texas. Present address, Union Oil Company, Wilmington, Calif.
Kenneth A. Kobe' and Paul
F. Lueth, Jr.*
University of Washington, Seattle,
Wash.
incorporated in pharmaceutical and industrial preparations. The direct mercuration of benzene has been difficult, and the development of a rapid industrial process which gives high yields of monomercurated benzene is essential for the development of processes based on this compound as an intermediate. The direct mercuration of benzene has been studied by numerous investigators. I n general, benzene is heated with the mercuric salt, usually either the oxide or the acetate, in the presence of glacial acetic acid or acetic anhydride. Because relative amounts of these constituents, as well as time and temperature, are important variables, the yields of monomercurated product reported have varied widely. Critical data on the direct mercuration of benzene by previous workers are summarized in Table I. I n all cases the reactants were intimately mixed together a t the beginning and allowed to remain in contact for the requisite length of time. Under these conditions it was generally found that the yield of monomercurated product was decreased by the formation of varying quantities of the dimercurated product, or by the reduction of the original mercuric acetate to mercurous acetate or metallic mercury. Certain modifications were employed in some cases. Maynard (6) used ethanol in the reaction mixture to esterify
310
Vol. 34, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY OF PREVIOUS WORK TABLE I. SUMMARY
Components of Mixture (Other Than Benzene) blercuric acetate, glacial acetic acid , Mercuric acetate, ethanol Mercuric oxide, glacial acetic acid Mercuric acetate, nitrobenzeneb Ncrcuric acetate, 1 2-dichlorobensen eb Mercuric oxide, glabial acetin acid hIercuric oxide, glacial acetic acid Mercuric oxide, acetic anhydride Mercuric oxide, acetic anhydride Mercuric acetate, glacial acetic acid Mercuric acetate glacial acetic acid a
-Mole RatiosCeHe CHsCOOH T,emp., Hg salt Hg salt C.
-~ 7.17 19.2 20.6 9.16 7.18 3.0 13.0 9.7 13.0 16.0 3.50
5.57
... . ..
66.9 2:o
100
%.p.
90-95 130-5 128-30 120
1.5 120 2.0 120 2.0 120 5.32 100 19.9 Water bath
Time, Yielda, CltaHr. yo tion 5 55
..
80
..
2-3 3 1 7
SO
7 7 2 9
72
2
Monomercurated product.
b Used as a solvent f o r the reactants
the acetic acid formed in the primary reaction and thus permit this reaction to proceed further to completion. Taube (11) dissolved the reactants in a high-boiling solvent so that the required temperature could be attained at atmospheric pressure, and the use of a pressure vessel was not necessary. I n the preparation of mercury compounds by direct mercuration, it is desirable t o obtain a monomercurated product exclusively. Polymercurated compounds are sometimes relatively valueless because they are frequently insoluble in organic solvents, and they consume large quantities of mercury. A new modification for direct mercuration, which gives only monomercurated products, has been successful with p-cymene (3). This method consists of adding the mercurating agent (mercuric acetate in glacial acetic acid) to the hydrocarbon at a controlled temperature and at such a rate that the mercuric acetate is constantly utilized to form a monomercurated product. The object of this work was to employ the same general procedure in the mercuration of benzene to obtain a monomercurated product. Optimum conditions of operation were to be established by the proper adjustment of the important variables.
..
24 7s
SO
73 92
IB Figure
1.
Diagram
OF
Apparatus
DESIGN OF APPARATUS A special apparatus permitted the dropwise addition of the mercurating agent to a heated pressure vessel containing the benzene. The equipment is shown in Fi ures 1, 2, and 3. A small stainless-steel autoclave, A , is fabricated from a 6-inch length of 3-inch-diameter stainless steel pipe, the upper flange and bottom being welded to the ipe section. The machined surfaces of the &nge and the cover are sealed by a thin, oil-proof gasket of vegetable fiber composition and held securely by six S/s-inch cap screws threaded into the flange. The liquid contents are agitated with a stainless steel stirrer, B, operating through a packing gland, E, in the cover. This stirrer is attached to a gearhead motor through a flexible coupling and turned at 100 r. p. m. A hot solution of mercuric acetate in glacial acetic acid is admitted to the autoclave through a 1 2 inch, stainless steel, semineedle valve, C. hhe valve handle is equipped with a lever to provide for its manipulation when submerged in the oil bath. This mechanism provides a sensitive means of control over the rate at which the mercuric acetate solution is added to the benzene. The mercuric acetate solution is contained in a 16-mm. glass tube, D, attached t o the valve through a packing gland, E. Pressure is applied t o the top of the glass column from a nitrogen cylinder through an u per packing gland, a special stainless steel ltting, and a coil of l/r-inch Imperial copper tubing. To prevent the mercuric acetate from crystallizing from the acetic acid while it is being added, the solution is heated by wrapping the glass column with a Nicbrome electric element. The autoclave and its contents are heated by immersion in a lagged oil bath, F , as shown in Figure 1. The oil is thoroughly agitated by a motor-driven stirrer, H , to ensure uniform Courtesy, The Edwal Laboratories, Inc. temperature throughout. Its temperature, as recorded on thermometer I sus ended in V i g o r o u s A g i t a t i o n of the Mercuration M i x t u r e Is Essential the bath, is manually controlled by t f e voltage
March, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
31 1
required for the addition of 35 ml. of solution. Then the valve was closed and the column opened to the atmosphere so that it could be rinsed with 10 ml. of hot glacial acetic acid. Pressure was again applied to the column, and the valve was opened. Any residual mercuric acetate held in the column or in the valve was thereby flushed into the autoclave. The valve between the dispensing column and the autoclave was closed tight, and the heating and stirring of the autoclave were continued for an additional hour. During this period the temperature of the oil bath was maintained a t lloo The autoclave was removed from the oil bath and allowed to cool. After venting through the valve and removing the cover, the contents were transferred to a 250ml. beaker. The transfer was made complete by rinsing the autoclave with 5-10 ml. of glacial acetic acid; these rinsings were added to the bulk of the solution. At this point the solution appeared faintly orange in color. In
c.
Courtesz/, The Edwal Laboratories, Inc.
Drying of Phenyl M e r c u r i c Salts
Is
a Batch O p e r a t i o n
applied through a variable transformer to a 500-watt electrical immersion heater, G. EXPERIMENTAL PROCEDURE
The method developed for the direct mercuration of benzene is best illustrated by an explanation of the laboratory procedure for the optimum production of the monomercurated compound. The mercuric oxide was U. S. P. grade, 99.5 per cent pure; Figure 2. Stainless Steel the glacial acetic acid and thiophene-free benzene were Autoclave for Benzene Baker's c. P. grade. Ninety-nine milliliters (1.12 moles) of Mercuration benzene and 12.5 ml. (0.218 mole) of glacial acetic acid were charged to the stainless steel autoclave, the cover was attached, and the valve to the dispensing tube was closed. The autoclave was submerged in the oil bath maintained TABLE 11. RESULTS OF MERCURATIONS at 110' * 1' C., and the stirring mechanism Mole Ratios Yieldsb was set in operation. Under these condiMerourio Oxide Benzene Acetic Acid4 CeHa HOAs Per tions the time required for the temperature Crams Moles M1. Moles M1. Moles HgO ' HgO Grams oent 10.0 0.0462 of the contents of the autoclave to reach A31: 82 35 0.923 92 1.61 20 11.0 76.2 10.0 0.0462 S6b 82 0.923 79 1.38 20 30 12.1 83.7 that of the oil bath (110' C.) was 30 minutes, A30: 10.0 0.0462 82 0 , 9 2 3 66 1.156 20 25 12.35 85.5 A26 10.0 0.0462 82 0.923 50 0.875 20 18.9 13.2 91.4 as determined by preliminary experiment. A23 10.0 0.0462 82 0.923 50 0.875 20 18.9 13.0 90.0 The electric heating element around the glass 13.3 0.0614 109 S5C 1.227 61 1.068 20 17.5 17.7 92.2 S4b 13.3 0.0614 109 1.068 20 17.5 1.227 61 15.5 80.8 dispensing column was turned on, before the S6 12.0 0.0555 99 0.831 20 15 47.5 1.115 16.4 94.2 column W L ~ Bfilled with a solution of 12 grams S13cvd 12.0 0.0555 99 1.115 47.5 0.831 20 15 16.0 92.0 812 12.0 0.0555 99 15 1.115 47.5 0.831 20 15.8 90.8 (0.0555 mole) of mercuric oxide in 35 ml. 52 12.0 0.0555 99 47.5 0.831 15 1.115 20 15.1 86.8 (0.613 mole) of hot glacial acetic acid. The A27 12.0 0.0555 99 1.115 47.5 0.0831 20 15 15.0 86.3 copper tubing from the nitrogen cylinder S4a 13.3 0.0614 109 1.227 44 0.770 20 12.5 17.0 88.5 S30 13.3 0.0614 109 1.227 35 0.612 20 10 17.8 92.7 was joined tight to the fitting at the top of 0.0785 140 1.575 45 0.787 20 10 22.5 91.5 A2: 17.0 97 13.3 0.0614 109 1.227 5 17.5 0.306 20 14.6 76.1 the dispensing tube, and pressure was apS l l b d 12.0 0.0555 74 0.832 0.831 15 47.5 15 15.6 89.6 plied to the column so that, when the valve 88 12.0 0.0555 74 0.832 47.5 0.831 15 15 14.4 82.8 was opened, the liquid in the column S9bd 1 2 . 0 0.0555 61.6 0.692 47.5 0.831 1 2 . 5 15 14.8 85.1 89 12.0 0.0555 4 9 . 3 0.555 47.5 0.831 10 15 14.0 80.5 could be forced into the autoclave withSlla 12.0 0.0555 49.3 0.555 47.5 0.831 10 15 14.0 80.5 S10a 12.0 0.0555 24.7 0.278 47.5 0.831 5 15 13.3 76.5 out the escape of vapors from the space Slob 12.0 0.0555 24.7 0.278 47.5 0.831 5 15 13.0 74.8 below. S13bd 12.0 0.0555 148 1.662 47.5 0.0831 30 15 15.7 90.2 After the 30-minute preheating period, 0 The quantity of glacial acetic acid used for rinsing is not included in any of the volume or molal quantitres. or ratios involving acetic acid, which appear jn the tables or curves. the valve was opened and adjusted so b Crude monomercurated product obtained as phenyl mercuric ohloridc, based on mercuric oxide introduced. that the hot mercuric acetate soluC Plotted in the curve of Figure 4. tion was added to the benzene at 0.47 to d Plotted in the curve of Figure 5. 0.58 ml. per minute; 60 to 75 minutes were
312
INDUSTRIAL AND ENGINEERING CHEMISTRY
no case was metallic mercury or decomposed mercuric acetate found in the reaction mass. The solution was heated on the steam bath to evaporate the excess, cooled, and filtered. Any polymercurated benzene compounds which may have been formed were thereby removed, according to the method of Rentschler (8). The solids removed in this
Vol. 34, No. 3
tained constant as described in the procedure. The data are illustrated in Figure 4. Under the conditions of these experiments the optimum yield of crude phenyl mercuric chloride was obtained when the ratio of acetic acid t o mercuric oxide was 12 to 18 moles, but economy dictates the lower amount. Another series was run to determine the effect of varying the quantity of benzene. The mole ratio of benzene t o mercuric oxide was varied from 5 to 30; the ratio of acetic acid to mercuric oxide was constant at 15 moles. Here again all othcr conditions were maintained as previously described. Figure 5 shows the relation between the percentage yield of the crude phenyl mercuric chloride and the amount of benzene used. Increasing the amount of benzene resulted in a n increase in the yield of crude monomercurated product. However, beyond a mole ratio (benzene to mercuric oxide) of 20, the increase in yield was negligibly small DIRECT M E R C U R A T I O N OF BENZENE A T A T M O S P H E R I C PRESSURE
Figure 3. Assembled Apparatus for Laboratory Mercuration of Benzene
Taube ( 1 1 ) heated benzene with mercuric acetate in the presence of nitrobenzene and obtained a n 80 per cent yield of mercurated benzene. The nitrobenzene in this case served as a n inert, high-boiling solvent. Thus the reactants may be heatcd to the required temperature a t atmospheric pressure, and direct mercuration may be accomplished without the use of a pressure vessel. However, it was found that a slight increase in the yield of mercurated benzene could be realized by incorporating the dropwise addition of the mercurating agent Tvith this general method for heating: Fourteen grams (0.0645 mole) of mercuric oxide were dissolved in 40 ml. (0.700 mole) of glacial acetic acid, and this solution Tyas transferred to a heated dropping funnel 80 that it could be added dropwise to a refluxing mixture of 60 ml. (0.675 mole) of benzene, 15 ml. (0.263 mole) of glacial acetic acid, and 200 ml. of nitrobenzene. This mixture will reflux a t a n internal (liquid) temperature of 118-122" C. The liquid in the dropping funnel was heated to prevent the mercuric acetate from crystallizing from the acetic acid. This was accomplished by surrounding it n-ith a hot water funnel and maintaining the temperature of the mater at 95-100" C. Mercuric acetate solution was added a t 0.53 to 0.67 ml. per minute, and 60 to 75 minutes were required for the addition of 40 ml The dropping funnel was rinsed with 5 nil. of hot glacial acetic acid, and the resulting solution was refluxed for an additional hour. The solution was allowed to cool and then filtered. The filtrate was treated with a solution of 10 grams of calcium chloride in 50 ml. of 95 per cent ethanol, which converted the phenyl mercuric acetate to the insoluble chloride. The
operation were negligible in almost every instance. The filtrate was treated with a solution Of 10 grams of calcium chloride in 50 ml. of 95 per cent ethanol. The precipitate of phenyl mercuric chloride was filtered and air-dried, and the yield of crude phenyl mercuric chloride was 16.0 grams or 92 per cent. This product, without further purification, was almost white and exhibited a melting point range of 246-249" C. After two recrystallizations from 95 per cent ethanol, a melting point of 249-250' C. was obtained, using a Brothcom total immersion thermometer graduated in degreef. The melting point of phenyl mercuric chloride was previously reported as 249" C. ( 7 ) , and as 251' C. ( I S ) . The recrystallized product was analyzed for mercury by precipitation as the sulfide according t o the method of Tabern and Shelberg (IO): Calculated for CeHSHgC1: Hg = 64.06 per cent; found: Hg = 64.12 per cent. A series of mercurations was made by this general procedure in which the quantities of benzene and acetic acid, relative to the mercuric oxide, were varied. Data are given in Table 11. The time and temperature conditions were niaiiitainecl as described in the experimental procedure. Bake showed previously ( 1 ) that increases of temperature 100 and time do not increase the total mercuration, but do increase the yield of dimercurated compound. 9 90 w T h e e f f e c t of v a r y i n g t h e quantity of glacial acetic acid was 'Wz 80 studied; the mole ratio of benzene Y to rnercuric oxide wa'ab kept con::70 stant, and the mole ratio of glacial acetic acid to mercuric oxide was MOL RATIO. CHaCOOH/HgO varied from 35 t o 5. In each instance the temperature, time of Figure 4. Y i e l d Variation w i t h addition of mercurating agent, and other conditions were mainA c e t i c A c i d Increase
MOL RATIO'
Figure
5.
C&/H~O
Y i e l d Variation w i t h Benzene Increase
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1942
Figure 6. Solubility of M e r c u r i c Acetate i n Glacial A c e t i c A c i d
nitrobenzene was then removed from the mixture by steam distillation, and the crude phenyl mercuric chloride was filtered and air-dried. The yield of crude product was 16.7 grams or 83 per cent. The melting point was 241-248” C., and the mass had a yellow tinge, indicative of contamination from residual nitrobenzene. This contamination p e r sisted, and the improvement in purity after two recrystallizations from 95 per cent ethnno1 was slight.
313
solution. Furthermore, the equilibria were always approached from the unsaturated state. Reagent-grade chemicals were used, and the equilibrium mixtures were contained in special test tubes with ground-glass stoppers a t the lower temperatures and in sealed-glass tubes a t the higher. Samples were withdrawn and weighed in a specially designed weight pipet ( 1 2 ) . Mercury was determined by the potassium thiocyanate titration method. The mercury was calculated as mercuric acetate, and the solubility was expressed as grams of mercuric acetate per 100 grams of glacial acetic acid. The results are given in Table I11 and Figure 6. It was found that the van’t Hoff equation, expressing the variation of equilibrium constant with temperature, could be applied to this system: d l n S - AH dT RP‘Z
TABLE111. SOLUBILITY OF MERCURIC ACETATEIN GLACIAL ACETICACID t
Temperature 0 c. T 0 K. 25 298 40 313 60 333 80 353 101 374
SOLUBILITY
I / T x 104 33.6 32.0 30.0 28.4 26.8
Grams Hg(CzHaOdd100 Grams CHsCOOH 7.73 15.0 32.7 64.3 125
OF MERCURIC ACETATE IN G L A C I A L ACETIC A C I D
Because the method employed for direct mercuration involves the use of a solution of mercuric acetate in glacial acetic acid, it was important to determine the solubility curve for this system. The composition of the liquid phase only was of interest, so no investigation was made of the composition of the solid phase in equilibrium with the saturated
Figure
7. Log S vs. I / T Plot of Solubility
Integration of this equation results in an expression in which the logarithm of solubility, S,is directly proportional to the reciprocal of the absolute temperature, T,assuming that the heat of solution in a saturated solution, A H , remains constant over the range of temperature in question. Thus a straight line is obtained in Figure 7, a semilogarithmic plot of solubility us. the reciprocal of the absolute temperature. LITERATURE CITED (1) (2) (3) (4)
(5) (6) (7)
(8) (9)
(10) (11) Courtesy, The Edwat Laboratories, Inc.
M e r c u r a t i o n of Benzene Is an Autoclave Reaction
(12) (13)
Bake, L. S.,U. S. Patent 2,075,971 (April 6, 1937). Carpmael, A., Brit. Patent 325,846 (Nov. 30, 1928). Doumani, T. F., and Kobe, K. A., J . Am. Chem. SOC.,to appear. Grave, T. B., Harris, S.E., and Christiansen, W. G., J . Am, Pharm. Assoc., 25, 752 (1938). Kobe, K. A., and Doumani, T. F., IND.ENG.CHEM.,33, 170-6 (1941). Maynard, J. L., J . Am. Chem. SOC.,46, 1510 (1924). Nenitzescu, C. D., Isacescu, D. A., and Gruescu, Carol, Bul. 800. chim. Romania, 20A, 135 (1938). Rentschler, M. J., U. S.Patent 2,050,018 (Aug. 4, 1936). Roeder, C., and Blasi, N., Ber., 47, 2748 (1914). ENG.CHEM.,ANAL.ED., Tabern, D. L., and Shelberg, E. F., IND. 4, 401 (1932). Taube, C., U. 8. Patent 1,786,094 (Dec. 23, 1930); German Patent 548,902 (Aug. 28, 1928). Toribara, T. Y., Univ. Wash., thesis, 1939. Whitmore, F. C., “Organic Compounds of Mercury”, New York, Chemical Catalog Co., 1921.
