MONOMERCURATION OF AROMATIC HYDROCARBONS Toluene
1
Process conditions have been developed whereby toluene i s exclusively monomercurated with a yield of 98%. The orientation is approximately in the ratio ortho:meta:para = 43:13:44.
H E successful monomercuration of benzene (7) in an autoclave a t a temperature above the normal boiling point made i t desirable to study the mercuration of toluene under similar conditions a t atmospheric presaure. Kobe and Doumani (6) reviewed the many useful reactions and pharmaceutical properties of the monomercurated compounds. Toluene can be mercurated directly; thus, Dimroth @), Steinkopf (IO), and Coffey (1) prepared tolylmercuric acetate by refluxing together toluene and solid mercuric acetate. Sharp (9) added acetic acid and water to the reaction mixture and obtained essentially polymercurated compounds. Table I lists these procedures. For the experiments reported here, toluene was purified from the commercial 3" toluene by shaking in a mechanical shaker with seven separate portions of concentrated sulfuric acid, equal to 2% by volume of the toluene, once with 10% sodium hydroxide solution, and twice with water. The product was dried with calcium chloride and fractionated through a twenty-plate laboratory column. The fraction distilling at 110.8' C. (762.0 mm.) was used. If the toluene was purified in a n identical manner, except that it was shaken only three fimes with sulfuric acid, part of the mercuric,acetate used for mercuration was reduced to mercurous acetate, and the reaction solution and.fina1 product had a slight yellow color, The acetic acid was a C.P. glacial grade. The mercuric oxide was the yellow U.S.P. grade, 99.5% HgO. Figure 1 shows the apparatus used. The dropping funnel is of special design (4) and is totally enclosed in a steam jacket. A standardized mercuratton procedure was adopted to determine the optimum ratios of reactants: Ten grams of mercuric oxide a r e d i s solved i n , 25 g r a m s of h o t acetic acid and introduced into the sCeam-heated dropping funnel. Over a period of 90
T
d
1 Present address, Tide Water-Associated O i l Company, Assooiated, Calif. * Present address, University of Texas, Austin, Texas.
Figure 1. Diagram of Apparatus
Allen J. Barduhn' and Kenneth A. Kobe* UNIVERSITY OF WASHINGTON, SEATTLE, WASH.
minutes this solution is added dropwise to 75 ml. of boiling toluene (mole ratio HgO: HOAc :C,HS = 1:9: 15). The initial boiling point is 111" and the final is 97" C . After all the solution is added, the dropping funnel is washed out with two 5-ml. portions of hot acetic acid, the washings being added t o the reaction mixture. The total solution is then boiled for one hour, cooled, and filtered. If the solution is not colorless a t this point, impurities were present in the toluene. The material filtered from the solution is 0.005 gram and contains no mercury, mercurous acetate, OP polymercurated compounds; it appears to be foreign matter from the mercuric oxide. The filtrate is steamdistilled t o remove excess toluene. While the solution of tolylmercuric acetate in acetic acid and water is still hot, 2.6 grams of calcium chloride in concentrated solution are added, the solution is cooled in ice water and filtered, and the precipitate is washed well with cold water and dried a t 50" C. The yield is 14.30 grams or 95.0%. Analysis of C?H,HgCl: calculated for Hg, 61.3%; found, 61.4%. The procedure of Tabern and Shelberg (11) was followed exactly in analyzing for mercury. Modifying their method by oxidizing undecomposed hydrogen peroxide with permanganate was not successful since the presence of manganese sulfate gave high results, as pointed out by Fenimore and Wagner (3). Elemental sulfur was washed from the precipitate with carbon disulfide in an extraction apparatus similar t o that shown by Scott (8). To study the effect of the ratios of reactants on the yield of monomercurated toluene, the mole ratio of each reactant was varied. Table I1 and Figure 2 give the results. The optimum conditions for monomercuration are taken to be a t mole ratios, HgO :HOAC:C7Hs = 1:9:15. With less acetic acid the mercuric acetate added does not 100 remain in solution. The increase in yield with in95 creased toluene is only slight. Higher yields are 90 5 IO I5 20 25 30 35 obtained by preMOL RATIO HOAC/H~O cipitating the bromide or iodide, Figure 9. Effect of Ratio of Reactants rather than the on Yield of Monomercurated Toulene
INDUSTRIAL AND ENGINEERING CHEMISTRY
248
TABLE 1. A~ERCI.RATION Mercurating Mixture
Mole Ratio, Tzmp., C?He/HgO C.
Toluene, Hg(0Ac)n Toluene, Hg(0Ac)s Toluene HgO, H O A ~H?O Toluene ‘ H g ( 0 A c ) ~ H0.4:
17.3 17.3
B.P. R.P.
OF
Time, Hours
... 5-6
0 5
85-7
12
i.0
B.P.
1
To~usr;~;
TABLE11. SUMMARY OF MERCURATIOXS
Type of Alercuration Citation M o n b ’ & poly
(2, 10) (f)
Poly
(0)
86% mono
(6)
1
G. HgO Used 10
6
10 10 10 10 10 10
Expt. No. 2 3 4 5
A9
chloride, possibly as a result of their decreased solubility in the acetic acid-water solution from which they are precipitated. A mercury balance was made on experiment 15: Input, 20 grams U.S.P. HgO (99 5 % ) Output, grams 33.25 CiHiHgBr 0 . 3 2 HaS (mt. from s o h ) Unacooint&i for, gram
Giams HgO 19 90
Vol. 38, No. 3
Pel Cent 100
The tolylmercuric acetate can be obtained in a relatively pure state by evaporating the toluene-acetic acid solution to dryness under vacuum and extracting the small amount of uiireacted mercuric acetate with cold water. Coffey ( 1 ) studied the orientation of the mercuiation reaction. His mercuration process produced about 15y0polymercurated toluene, and the yields in the transformation to bromobenzoic acids is hardly quantitative. He reported that the ratio of 0rtho:meta:para was 43: 13: 44. The mixture of tolylmercuric bromides produced in experiment 19 was converted quantitatively to the corresponding bromotoluenes by treatment with bromine in chloroform solution. No separation of the isomeric bromides could be made by fractionation through a 55-plate packed column. Lines of constant refractive index and constant density plotted on a ternary diagram proved to be practically parallel. Lines for these two properties a t the values ob-
10 11 12 13 14 15 IS 17 19 l8
10
10 10
-Mole RatiosC?Ha/HgO HO.lo/HgO 20 20 20 9 20 15 20 25 20 30.5 35 20 35.3 20 20 5 10 15
10 10 10 10 20 20 20 20 40
25 30 35 15 15 15 15 15 I5
i:20
20 20 9 9 9 9 9 9
Product CiHiHgCl HiCrEIgCl CiHiHgCl CiHiHgCl CrHiHgCl CrHiHgCl CiHyHgCI CiHiHgC1 C7H7HgCI CiHiHgCl CiHiHgCl CiHiEIgCl CiHiHgCI GHiHgCl CrH7HgBr C7HiHgI C7H7HgBr CiHiHgI ClH7HgBr
-YieldGrams 14.05 14.35 14.25 13.90 13.75 13.80 13.65
13.55 14.10 14.15 14.25 14.30 14.40 14.30 33.25 37.60 32.95 37 30 67.0
vc 93 95 4 94 7 92 4 91 3 91 8 90 7 90 0. 93 7 91 94 I 95 0 95 6 95 0 97 5 97 8 96.5 97.0 98.1
2
tained for the bromotoluenes from the tolyl mercuric bromide= passed quite close to the point representing the composition found by Coffey; this indicates that it probably does riot differ greatly from the true orientation. LITERATURE CITED
Coffey, J . Chem. Soc., 127, 1029-32 (1925). Dimroth, Ber., 32, 761 (1899). Fenimore and R‘agner, J. Am. Chem. SOC.,53, 2455 (1931). Kobe, IND.ENG.CHEM.,ANAL.ED.,16, 641 (1944). Kobe and Doumani, IKD.ENG.CHEM.,33, 170-6 (1941). Kobe and Doumani, U. S. Patent 2,353,312 (July 11, 1944). Kobe and Lueth, IND. ENG.CHEM.,34, 309-13 (1942). Scott, “Standard Methods of Chemical Analysis”, 5th ed.. Vol. I, p. 577, New York, D. Van Nostrand Co., 1939. Sharp, Brit. Patent 406,725 (March 5, 1934). Steinkopf, Ann., 413, 329 (1916). Tabern and Shelberg, IND.EKG. CHmr., AX.^. ED., 4, 401-3
(1932).
1
Exclusively monomercurated products can b e obtained from p-cymene in high yield.
Paracymene
A new method of separating the 2- and 3-isomers is given. The bactericidal properties of some cymyl derivations are compared with basic phenylmercuric nitrate (Merphenyl).
ARACYhIENE (l-meth~-1-4-isopropylbenzenc~ has long been an aromatic hydrocarbon for which a more extensive chemical utilization has been sought. A by-product of the sulfite pulping of the eastern spruce, it is known as spruce turpentine and can be produced in large quantities. The naval stores industry uses dipentene to produce p-cymene and pmenthane. The petroleum industry is a potential producer from toluene or cumene. The mercuration of p-cymene was studied by Kewstrom and Kobe ( I S ) , who obtained a yield of 647, monomercurated products and 137, polymercurated products by heating, with stirring, a mixture of mercuric acetate with ethanol, acetic acid, and p-cymene for 8-10 hours. The monomercurated product was separated into two fractions, the 2substituted and the 3-substituted compounds in the ratio GO l o 40. The mercuration process with p-cymene is unique in that it produced far more 3-substituted product than does any other substitution reaction with this compound. The reactions and utilization of aromatic mercurated compounds were discussed previously (9). The work reported in this paper was conducted to develop a mercuration process which would eliminate as far as possible the formation of polymercurated compounds (IO, 11). As in the
P
1 9
Present address, Union Oil Company, Wilmington, Calif. Present address, University of Texas, Austin, Texas.
Thomas
F.
Doumani‘ and Kenneth A. Kobe*
UNIVERSITY OF WASHINGTON, SEATTLE, WASH.
mercuration of benzene ( I I ) , gradual addition of a glacial acetic acid solution of mercuric acetate to a boiling p-cymene-acetic acid solution materially increased the yield of monomercurated products and reduced the yield of polymercurated products 01)tained when the reactants were simply mixed together and heateti. Because of the structural relation of these compounds to thymol (3-1iydroxy-p-cymene), the bactericidal properties of varioua derivations of the mercurated compounds were tested. In the direct mercuration of p-cymene the merbnrg atom can wbstitute in either the 2- or the 3-position. h-ewstrom and Kobe found that the mixture of p-cymylmercuric chlorides was heparated into 2-p-cymylmercurie chloride and a minimunimelting eutectic of the two isomers. The eutectic could be separated by conversion to the di-p-cymylmercury compounds and by crystallization of the latter. An improved method of separation has been developed in which the bromides are used rather than the chlorides and benzene is the solvent. p-Cymene was obtained from Newport Industries, h e . , and boiled at 176.6-176.8” C. a t 753.5 mm. Two liters of p-cymene were shaken with six 100-ml. portions of concentrated sulfuric
