April, 1930
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NOTES AND CORRESPONDENCE Methylation of Phenol b y Dimethyl Sulfate Editor oi Industrial and Engineering Chemistry: The article under this title by Lewis, Shaffer, Trieschmann, and Cogan contains the surprising statement : Under some conditions as much as 90 per cent of the avaliable methyl groups has been converted into anisole. This is contrary to common experience with dimethyl sulfate and checks more nearly with t f i e action of diethyl sulfate (1). The reference is t o Cade, Chem. Met. Eng., 29, 319 (1923), who, a t least in my opinion, has shown all the criteria for using alkyl sulfates in a manner which produces yields of high chemical efficiency. He shows that for the utilization of the second alkyl group, the most important factors are (1) stirring and (2) minimization of the water content of the reaction mass. Both of these, it seems t o me, ha* been overlooked; hence the discrepancy between the actions of the two alkyl sulfates quoted above. For, while Cade worked with diethyl sulfate, in my experience dimethyl sulfate may be handled in an exactly analogous manner, always bearing in mind that dimethyl sulfate is more reactive than diethyl sulfate-that is, where the latter may require the application of heat, the former will react a t room temperature. Cade states (Ibid, p. 321) : Thorough mixing to prevent occlusion of particles and to permit thoroughness of reaction by intimate contact between reacting particles is very essential, When dry reagents are used in the above manner, good yields are obtained. Furthermore, it has been found that an improvement in the above process is accomplished by the use of nonaqueous solvent. When such foreign solvents as benzene, toluene, etc., are used, difficulties arise such as that of separating the solvent from the desired ethylated product and that of possible fire hazards. The principal difficulty in carrying out Cade’s method is mechanical-that is, to keep the reaction mass sufficiently mobile or mixable. Cade provides for this by adding a t the start a quantity of the liquid reaction product; thus in the production of ethyl benzoate he provides a quantity of ethyl benzoate (Cade uses the word “preformed”) sufficient t o permit stirring of the sodium benzoate with which the diethyl sulfate introduced is t o react. Similarly in the case of anisole, a quantity of anisole might be first provided to allow easy stirring of the solid caustic soda. In this connection flake caustic soda is found to be the physical form which least interferes with mixing by stirring. Or a quantity of an inert hydrocarbon might be provided. However, in the case of anisole no extraneous liquid is needed because in the early stages of the reaction sufficient liquid phenol is present, and in the latter stages sufficient anisole is present to keep the reaction mass stirrable, although it may be very thick. Of course, in this event metal apparatus has the advantage of greater mechanical strength than glass. Unless one deals with anhydrous sodium phenolate, where extraneous liquid must be provided, the minimum of water present, analogous to Cade, is two bulk molecules per bulk molecule of dimethyl sulfate. As two bulk molecules of phenol and caustic soda each must be provided per bulk molecule of dimethyl sulfate, these react to give two bulk molecules of both sodium phenolate and water. However, it is possible to manipulate the course of the reaction so that less than two bulk molecules of water are present in the reaction mass until the final stage; that is, by keeping solid unreacted caustic soda present, the formation of water apparently is restricted until just the mo-
ment when sodium phenolate is needed to react with the dimethyl sulfate. Under these conditions, despite the high reaction velocity of dimethyl sulfate and water, the reaction velocity between dimethyl sulfate and sodium phenolate appears fromathe results to be higher. Of course, the ratio of actual individual water molecules to individual dimethyl sulfate or sodium methyl sulfate molecules present in the reaction mass a t any moment may be very high. Fortunately, owing possibly to the higher net heat of reaction, the dimethyl sulfate or sodium methyl sulfate molecule prefers t o react with the sodium salt rather than with the sodium hydroxide or the water molecule. This same point is illustrated by the course of the reaction in the presence of alcohols, where the preference is toward producing a mixed alkyl ether above an alkaryl ether and both are preferred above simple hydrolysis, a t least as far as the reaction of the first alkyl group. It is pleasing to see this heretofore neglected or obscure action of alkyl sulfates on absolute alcohol so well demonstrated by Lewis and his confreres. Cade mentions only the formation of diethyl ether The first six entries in Lewis’s table show the effects of stirring and of varying quantities of water present. While no stirring is mentioned, the reacting mass not even being agitated by boiling, it can be assumed that some convection currents caused agitation a t 100” C. Remembering that stirring would be expected to increase the yield, and water present would decrease the yield, let us consider the plot of results where per cent yield is shown as the ordinate and mols of water present as the abscissa. All experiments were with 0.1 M (12.6 grams) dimethyl sulfate, 0.2 M (18.8 grams) phenol, 0.3 X (12 grams) sodium hydroxide,
VI I
I
I
I
0 2 04
08
/6
32
M Wuier Added with varying quantities of water as plotted, heated for 1 hour. The 54.5 per cent yield, where no water was added and probably not all of the 0.2 M of water possible from reaction between phenol and sodium hydroxide was present, is as low as it is because practically no stirring could take place, and is as high as it is because but little water was present. The next yield of 70.0 per cent shows that the 0.2 M of water added (giving 0.4 M or 7.2 cc. of water really present) was sufficient t o effect some stirring by convection and insufficient to cause a great deal of hydrolysis. The third result of 64.5 per cent shows that the 0.4 M of water added (giving 0.6 M or 10.8 cc. of water present) was sufficient to effect more hydrolysis of dimethyl sulfate or more likely sodium methyl sulfate, despite the greater stirring effect, and so on out to 3.2 or better 3.4 M of water present. I n short, more water does not favor more stirring and does favor hydrolysis in the higher ranges Note that the formation of sodium hydroxide monohydrate might reduce the quantity of free water present, but the low
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melting point of this substance (64” C.) casts a doubt on its ability to remove water from the liquid reaction phase. Further in the first four experiments recorded, where time and water are varied (water was in these four case5 1.6 M), the yield is practically constant over a range of time from 10 minutes to 3 hours. This leads me to believe that the entire reaction was complete in less than 10 minutes and the 54 to 55 per cent yield shows that the first methyl group reacted completely and the second methyl group to the extent of, say, 10 per cent. If it were assured that all sodium methyl sulfate had reacted-and it is quite possible that considerable proportion remains unreacted-to form sodium sulfate and anisoie or methanol after 10 minutes-and this should not be difficult t o determine by titrating excess sodium hydroxide with the proper indicator-it might be concluded that the reaction forming anisole is but one-tenth as fast as the hydrolysis reaction velocity. This conclusion, however, is not warranted in view of present insufficient experimental data. There are other interesting relations between various magnitudes of yield, the discussion of which could become very extended. It is sufficient t o say that all these depend on competing reaction velocities, the investigation of which would be pertinent. Even the order of the methylation reaction, whether mono-, di-, or tri-molecular, is unknown. In 1924 I had occasion to prepare anisole in commercial quantities by a method which, in view of its strict analogy t o Cade’s work, I had not heretofore considered to be of sufficient novelty t o warrant publication. The equipment was a clean, dry, steam-jacketed Duriron kettle provided with a condenser and reflux condenser, interchangeable a t will by a three-way cock at the base of the reflux, a solids charging port, a deep liquids charging line, an anchor type stirrer (30 r. p. m.), and deep and shallow thermometer wells. Through the solids port two molecular parts plus 2 per cent of molten phenol and two molecular parts plus 5 per cent of flake caustic soda were introduced. As soon as the charging port was closed, the careful introduction of one molecular part of dimethyl sulfate was begun a t a rate to keep the temperature of the reaction mass above 45“ C. Cooling water was applied to the jacket t o keep the temperature below 60’ C. as indicated by the thermometer in the deep well, while the dimethyl sulfate was introduced as rapidly as consistent with this limitation. The introduction of dimethyl sulfate generally required about half an hour. Steam was then applied t o the jacket quickly raising the temperature of the reaction mass to 100-105” C., whereupon some refluxing Of water with a little anisole occurred. Gentle refluxing was maintained for a half-hour to an hour, depending on the magnitude of the reaction mass. Then, stopping the refluxing momentarily, the vapor was diverted to a condenser by the three-way cock and live steam was blown into the reaction mass through the liquids charging line. The anisole was rapidly steamdistilled out of the kettle, The aqueous layer of the distillate was separated and, while the anisole might be further purified by distillation, the steam-distilled material when properly dried was of satisfactory quality for use as a raw material for further reactions. The excess of phenol, if of sufficient quantity, could be recovered by acidifying the reaction residue with sulfuric acid and steam-distilling. The chemical efficiency of the reaction calculated on both methyl groups of dimethyl sulfate was always better than 90 per cent, generally 95 per cent, and occasionally as high as 97 per cent, I believe that, with stirring and minimization of water content of the reaction mass, similar high yields result when dimethyl sulfate is replaced by sodium methyl sulfate. The publication of Professor Lewis’s studies on methylation of phenol with sodium methyl sulfate is anticipated with interest. INDUSTRIAL R E S E A R C H E. YEAKLEWOLFORD AND
ENGINEERING COMPANY
PITTSBURGH,
PA.
February 13, 1930
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Vol. 22, KO.4
Editor of Industrial and Engineering Chemistry: I quite agree with Mr. Wolford in his implication that the data necessary for an improved technic in the use of dimethyl sulfate as a methylating agent are to be found by analogy in the paper of Cade, as referred to above. In spite of this, the use of dimethyl sulfate as a methylating agent, as outlined even in the recent literature, is following the older procedures of Dumas and Peligot (Centralblatt, 1835, 279) and Ullmann and Wenner ZBer., 33, 2476 (1900)j. For this reason the data presented in our paper call attention to the relative influence of varying amounts of sodium hydroxide, sodium phenolate, dimethyl sulfate, and water on the course of the reaction and on the yield of anisol. I n the latest volume of “Organic Syntheses” [Vol. IX, p. 12 (1929) J there is outlined a preparation of anisole in which the relatively large quantities of water present cut down the yield of anisole to the extent of 15 per cent. This in itself justifies the presentation of our data. The method for making anisole outlined by hlr. Wolford is a valuable addition to the literature of the subject and should be used in place of the above method as given in “Organic Syntheses.” The questions raised by Mr. Wolford in regard to the relative reactions of hydrolysis and methylation, the influence of stirring by convection, etc., are debatable. On the basis of past experience [Lewis, Mason, and Morgan, IND.ENG.CHEM.,16, 811 (1924)], it appears that reactions or hydrolysis are favored by relatively smaller concentrations of water, rather than the opposite. HARRY F. LEWIS OHIO WESLEYAN UNIVERSITY DELAWARE, OHIO
March 4, 193C
Mothproofing Editor uj Industria2 and Engineering Chemistry: I n the recent article under this title by Minaeff and Wright, IND.ENG.CHEM., 21, 1187 (1929), statements are made regarding the application of cinchona alkaloids for mothproofing that are at variance with observations made by the writer and ENG.CHEM.,19, 1175 (1927). Helen E. Wassell, IND. From the inception of the work that led t o the publication of our original paper on the application of the cinchona alkaloids in mothproofing textile products, our constant aim has been t o obtain dependable and confirmable results. Methods for testing the mothproofing properties of substances had to be devised. Then, too, the development of suitable criteria for judging the relative mothproofing values of various materials required considerable time. The final result of this study was that, instead of depending upon one single method, six different procedures were evolved by us in reaching our definite conclusions. In brief, these methods are as follows: (1) Exposure of treated pieces of wool in a cupboard containing wool materials infested with moths. (2) Exposure of treated and untreated pieces in Petri dishes to twenty-five full-grown larvae. (3) Exposure of treated pieces in Petri dishes, with no other choice of food, t o twenty-five full-grown larvae. (4) Observation of moth-infested pieces of wool clothing that have been treated and hung in closed cupboards, with and without reinfesting the garments with m x e clothes moths. ( 5 ) Exposure of treated pieces of wool in Petri dishes to six to twelve moth flies, followed by incubation. (6) Treatment of moth-infested furniture, rugs, and clothing in homes under actual conditions as they occur in everyday life. When treated pieces of wool withstood the attack of moths in the preliminary test (l), then similarly treated pieces were tested by as many of the other methods as the progressive results of the observations indicated t o be desirable. When continued test
