K. SEWALL McMAHON' and KENNETH A. KOBE University of Texas, Austin, Tex.
Direct Mercuration of Benzene Data on process variables in the mercuration of benzene facilitate
b b b
planning for increasing yields improving products conserving raw materials
Aromatic mercury compounds have wide application as chemical intermediates, medicinals, antifouling agents in paints, and seed disinfectants. The mercurychemical industries and mercury supplies have been classified as essential b y the President's Materials Policy Commission.
different unit operations to be performed, the chemistry and reaction variables involved in the unit process of mercuration are very similar to those involved in alkylation, halogenation, sulfonation, and nitration. The present knowledge of industrial mercuration results is reported largely in the patent literature. T h e results are confused, because various analytical methods led to disagreement among the reported effects of reaction methods and process variables. The present work was limited to the uncatalyzed mercuration of benzene with mercuric acetate, with which most commercial applications are concerned. First, a standard analytical procedure was developed and checked for consistency and accuracy. This method can be used for the separation of the components on an industrial scale, as well as for analytical samples. Second, all important patented and published procedures for the mercuration of benzene were checked using the developed analytical method (4).
Tm
production of phenylmercuric salts is a sizable fraction of the total production of organic mercurials, yet previous reports on the effects of process variables on the mercuration of benzene have been a t considerable variance. Improved understanding of these effects is necessary to plan for increasing yields, improving products, or conserving raw materials. Mercuration as Unit Process
Direct mercuration is a substitutiontype reaction following the over-all equation : Aryl-H
+ HgX2=;t
aryl-Hg-X
+ H-X
Dimercuration may follow monomercuration by attack of the mercurating agent on the previously monomercurated product. Although the properties of the reactants and products require somewhat Present address, Wyatt C. Hedrick Engineering Corp., 5214 San Jacinto St., Houston, ?'ex.
42
Analytical Procedure
The standard analytical procedure involves the following steps : 1. Evaporate reaction mixtures rapidly and then chill quickly to minimize further reaction. Final volume contains about 0.083 mole of total mercury per
INDUSTRIAL AND ENGINEERINGCHEMISTRY
100 grams of solution. At higher final concentrations, dimercurate increases appreciably. 2. Precipitate dimercurate by seeding. A few drops of water added to the quiet solution causes a localized precipitation which spreads over the whole volume if dimercurate is present. The precipitate is filtered off, washed with a small amount of acetic acid, air-dried, and weighed as CsH4(HgCZH302)2. 3. Phenylmercuric chloride is precipitated by adding a 4 M aqueous solution of calcium chloride in 50y0 excess over the total mercury present, diluting 4 to 1 with hot water, and cooling to room temperature. The precipitate is filtered off, washed with water, airdried, and weighed as CeHsHgCl. 4. Unreacted mercury in the final filtrate can be determined by diluting an aliquot sample containing about 0.1 gram of mercury to 100 ml. and precipitating mercuric sulfide with hydrogen sulfide. 5. Mercurated acetic acid, if present, is precipitated with both the di- and monomercurate. I t can be extracted from the mercurated benzene with a solution of 5y0 sodium hydroxide and 10% sodium chloride in water, in which the mercurated acetic acid is soluble. Although some further reaction can occur during step 1, this is slight if the mercuration reactions have gone nearly to completion. This analyrical scheme is the only one presented that has determined all components present.
T h e accuracy of the above method is indicated by the over-all mercury balances of 99.1 =tO.lyoof mercury input. Phenylmercuric chloride analyzed 64.15 i 0.12y0 mercury (theoretical = 64.06y0); the melting point of the precipitated compound was 248-5OoC., and 249 .5-50' C. after two crystallizations from ethyl alcohol (literature value = 250' C.). Dimercurate from several runs analyzed 66.42 f o.13Y0 mercury [theoretical for CeH4(HgOzCzHa)z = 67.39% 1. Sartoretto ( 8 ) has indicated that for analytical size samples the sample should be drowned in water in step 1 before the removal of the benzene in order to prevent polymercuration during evaporation. Steps 3, 4, and 5 will isolate the remaining monomercurate and unreacted mercuric acetate. T h e mixed mercurials can be converted quantitatively to the corresponding bromobenzenes by merely agitating with bromine water a t room temperature. T h e bromobenzenes can be determined by infrared spectroscopy.
Table I. Effects of Process Variables on Mercuration of Benzene iMole Ratios t o Mercury PhH HOAc Hz0
A.
10 20 25 30 35 40 45
15
1.3
B.
40
Hours
oc.
Effects of Benzene 5 Reflux at 85
2
15 20 30
10
Time,
110
Yields, % ' of Hg Mono Di 54.4 56.2 57.1 57.2 56.7 56.9 57.0
2.5 1.6 1.5 1.5 0.8 0.9
87.6 90.4 92.8
6.9 5.2 3.4
1.8 4.8 4.8 4.3
1.8
Effects of Acetic Acid
15 20 25 30
1.3
1.6
54.4 59.0 59.6 59.8
loa
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
42.6 56.9 65.5 67.6 69.1 69.0 69.9 70.3
4.9
46.7 63.4 68.2 72.8 84.0 88.8 90.7 90.5 88.3 67.8
3.7 7.6 3.7 5.0 3.4 3.4. 2.1
15 20 25 30 35 40 45
5
1.4
Reflux at 85
0.8
2.3 4.3 5.3 3.6 7.9 3.6
Effect of Process Variables Process variables considered for this reaction are mole ratios of benzene and acetic acid to mercury, the presence of water or acetic anhydride, temperature, and time for the uncatalyzed reaction. T h e results are shown in Figures 1 to 5 and in Table I. Most of the data points shown are the average of several runs. Experiments at temperatures above the refluxing temperature of approximately 85' C. were conducted in a n autoclave made of a borosilicate glass pipe cap fitted with a stainless steel cover with pressure-tight fittings through which a thermometer and stirrer could be placed in the liquid (cf. 3 ) . Mole Ratio Benzene (Figure 1). T h e general effect of increasing the mole ratio of benzene to mercury is to favor monomercuration and retard dimercuration. Similar results were reported by Kobe and Leuth ( 3 ) and by Nenitzescu, Isacescu, and Gruescu (7). Mole Ratio Acetic Acid (Figure 2 ) . Increasing mole ratios of acetic acid to mercury favor increased yields of both mono- and dimercurated benzene at 85 ' C., though the effect was small above a mole ratio of 25. At 110" C., Kobe and Leuth ( 3 ) had found a decrease in yield with increasing mole ratio of acetic acid. Temperature (Figure 3). T h e effect of reaction temperature previously was not considered great and has not been reported. Higher temperatures appear to favor monomercuration over dimercuration, but yields from both reactions decrease above 110" C. a t the values of other reaction variables used.
C.
30
30
1.6
Effects of Temperature 3
79.6 84.6 87.4 89.9 94.8 99.8 104.7 109.9 119.9 140.0
1.3 ,
0 0
D. Effects of Water or Acetic Anhydride 30
30
20.1 15.1 10.1 5.1 1.58
3
110
0
2.0b 5.0b E.
10
15
1.3
30
1.6
0.5 0.4 0.6 0.4 1.3 0.7 0.1
24.0 35.7 43.6 51.8 54.4 61.0 60.1 68.7 76.2 79.3 83.5
0.1 0.6
88.8 90.0 91.0 90.5 88.2
3.4
1.6
Effects of Reaction Time 1
2 3 4 5 6 7 9 12 24 48 30
88.7 89.6 90.4 91.7 90.5 88.0 71.6 60.5
3 14 2 3 6.5
Reflux at 85
100 110
1.8
4.2 1.8
4.5 5. I 5.8 8.9 9.6 9.5 0.1
2.7 1.3 0
Amount of acetic acid insufiicient to dissolve all mercuric acetate. Acetic anhydride used instead of water.
VOL. 49, NO. 1
JANUARY 1957
43
r
100
80
cr
W 60 a
14
I
60
I I
I
I
"
-
I
40
0
IO MOLE
Figure 1. 1. 2.
20 RATIO,
40
30
0
50
C,H,'/Hg
MOLE RATIO,
Effect of benzene on yields
Figure 2.
Mole ratio acetic acid 15, refluxed 5 hours a t 85' C. Mole ratio acetic acid 15. heated 2 hours a t 1 10' C.
Water and Acetic Anhydride (Figure 4). The acetic acid used as a solvent usually contains water, which also is formed if mercuric oxide is added to the reaction mixture to form mercuric acetate. Bake ( 7 ) and Memminger ( 6 ) have patented the use of acetic anhydride with the acetic acid to remove all water. The presence of even small amounts of acetic anhydride causes mercuration of the acetic acid. T h e presence of water in a 1 to 5 mole ratio retards this side reaction, as had been shown by March and Struthers (5) on acetic acid mercuration. As higher mole ratios of water, up to 20, show little effect on yields,
30
20
IO
1. 2.
40
5
HOAc/Hg
Effect of acetic acid on yields
Mole ratio benzene 10, refluxed 5 hours a t 85' C. Mole ratio benzene 40, refluxed 5 hours a t 8 5 O C.
a more dilute acetic acid than the glacial grade usually used may be useful in benzene mercuration. Reaction Time (Figure 5). Yields shown as a function of reaction time are for the uncatallzed reaction. From Figure 5 it is seen that although the yield of either mono- or dimercurate may reach an essentially constant value with time, the yield of the other product may still change with time. Thus, under reflux conditions the yield of dimercurate becomes constant, while the yield of monomercurate continues LO increase with time up to 48 hours. At higher temperatures yields of monomercurate
were essentially constant or decreased slightly with time, while the yields of dimercurate fell off rapidly \vith time. Because dimercurate yields were found to decrease as reaction periods werc increased a t the higher temperatures employed and also to decrease with increasing temperature a t constant time. there may exist an optimum reaction time for each temperature where the maximum conversion to monomercurate m ill occur and the yield of dimercurate will be a minimum lvith respect to the monomercurate. Mercuration reactions in homogeneous acetic acid solutions are strongly catalyzed by perchloric acid
IO0 3
IF I
80 I /"
I
I
MoNol
,'
60d
: I
40, 4'
4
IO
oo,,-:-a 80
90
100
110
TEMPERATURE Figure 3.
120 IN
Effect of temperature on yields
Mole ratio benzene 30, acetic acid 30, time 3 hours
44
INDUSTRIAL A N D ENGINEERING CHEMISTRY
130
-
DI "-
3
140
OC.
Figure 4.
Effect of water and acetic anhydride on yields
Mole ratio benzene 30, acetic acid 30, stirred 3 hours a i 1 10' C.
Table II. Reversibility of Mercuration Reactions at 85' C. Gram-Equivalents in Initial Reaction Mixtures Total Total Time, Yields, % of Total Hg Conversion, HgO Monoa Dib Ph-0Ac Hr. Mono Di HgS Other % 1.00 1.00
10.0 10.0 1.00 10.0 1.00 10.0 1.00 10.0 1.00 10.0 1.00 10.0 1.00 0.50 10.0 1.00 1.00 10.0 1 .oo 12.5 1.00 0.061 12.5 1.00 0.132 12.5 1 .oo 0.247 12.5 Purified PhHgOAc, 59.6% Hg
*
14.0 15.0 15.0 15.0 15.0 15.0 20.0 20.0 20.0 25.0 25.0 25.0 25.0
*.
24 48 12 24 48 852 5 5 5
79.3 9.6 83.5 9.5 5.6 97.4 0.1 2.0 96.2 0.2 3.3 94.0 0.0 5.7 30.5 Trace 18.2 51' 59.0 5.3 69.0 11.9 l;:7 67.4 19.6 12.2 5 67.1 5.8 25.7 5 65.9 8.6 24.2 5 65.1 11.9 21.2 5 60.6 16.5 21.7 (59.6% theo.), m.p. 249.5-50' C. Ph(Hg0Ac)n from mercuration runs, unpurified, 66.4% Hg (67.4% theo.).
94.4 total 98.0 total 96.7 total 94.3 total
....
59.0 to mono 35.7 to monod 17.4 to monod +5.8 to die 4-2.9 to die +0.2 to die -3.3 to die
Mercurated acetic acid, sealed tube reaction. Increase in gram-equivalents of mono divided by total gram-equivalents of mercury initially present. e Percentage of original total mercury which reacts to produce di.
but no information is available on the dimercuration reaction. Table I1 gives data for mercuration reactions in which mercuric acetate, phenyl mercuric acetate, and phenylene dimercuric diacetate were used in the reaction mixtures. I n 48 hours, the same yield of mercuric
( 9 ) . No work was done on acid catalysis of the mono- and dimercuration reactions. Mercuration Reactions T h e reversibility of the monomercufation reaction has been reported (2, 9 ) ,
sulfide can be obtained from the reaction mixture starting with either mercuric acetate or phenyl mercuric acetate. With the latter, no dimercurate is formed. Extended reaction periods (as 852 hours) gave lower yields of phenyl mercuric acetate and relatively large quantities of mercuric sulfide and mercurated acetic acid. T h e latter compound failed to mercurate benzene under these reaction conditions. T h e dimercuration reaction is reversible and can be inhibited by adding dimercurate to the initial reaction mixtures. From Table I1 (last four experiments) it is seen that reaction mixtures that contained less than 13 equivalents of dimercurate per 100 equivalents of mercuric acetate produced some new dimercurate, the mixtures initially containing more than 13 equivalents showed a conversion of dimercurate to monomercurate. Essentially the same amount of mercuric acetate reacted in each experiment independently of the amount of dimercurate charged, and the amount of monomercurate is increased by the conversion. T h e recycling of dimercurate in the reaction mixture is similar to industrial practice of recycling diethylbenzene in the manufacture of ethylbenzene in order to improve the utilization of raw materials. However, in the case of mercuration, conditions have been shown under which the amount of dimercurate formed may not be detrimental for the industrial use of the product.
literature Cited
TIME Figure 5.
IN
HOURS
Effect of reaction time on yields Mole Ratio
Acetic Benzene
acid
1
10
2
30 30
15 30 30
Curve 3
O
c.
85 (refluxed) 100 (stirred) 1 10 (stirred)
(1) Bake, L. S . , U. S. Patent 2,075,951 (April 6, 1937). ( 2 ) Brown, H. C., McGary, C. W., Jr., J.Am. Chem. Sac. 77,2300-12 (1955). ( 3 ) Kobe, K. A., Leuth, P. F., Jr., IND. ENC.CHEM.34, 309 (1942). (4) Kobe, K. A., McMahon, K. S., Drug Standards 25, in press. ( 5 ) March, J. E., Struthers, R. J. F., J . Chem. SOC.1927, 2658. ( 6 ) Memminger, K., French Patent 843,092 (June 29, 1938); Ger. Patent 699, 773 (Dec. 5, 1940). (7) Nenitzescu, C. D., Isacescu, D. A., Gruescu, D., Bul. SOC.Chim. Romania 20A, 135 (1938). (8) Sartoretto, P. A,, personal communication, May 11, 1956. (9) Schramm, R. M., Klaproth, W., Westheimer, F. H., J. Phys. Chem. 843-60 (1951). RECEIVED for review October 24, 1955 ACCEPTED October 4, 1956 Division of Industrial and Engineering Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955. VOL. 49, NO. 1
JANUARY 1957
45
