ETHYLATION AND HYDROXYLATION As Simultaneous Operations HARRY MCCORMACK, Armour Institute of Technology, G . J. STOCKMAN, Wurster and Sanger, Chicago, 111.
HE experimental work discussed in this paper had its inception in a desire to find commercial uses for p-nitrochlorobenzene, described in a previous paper ( 3 ) . A seemingly promising compound which could be derived from p-nitrochlorobenzene was p-nitrophenetole. I n preparing compounds of this type it has long been common practice to effect condensation of an alcohol, alkali metal alcoholate, or similar alkoxy compound, with a halogenated nitroaryl compound, in the presence of a caustic alkali condensing agent, such as sodium or potassium hydroxide; the reaction is conducted with the aid of moderate heating, usually in the absence of a substantial proportion of water. In order to suppress side reactions of a reducing nature tending to produce azo or azoxy compounds, it is also customary to conduct the reaction under pressure in the presence of a gaseous or other suitable oxidizing agent. Because of the strong tendency for side reactions to occur, resulting in the formation of various unwanted products which not only materially lower the yield of the product sought but must also be separated from it by appropriate treatment involving more or less tedious and expensive manipulative operations, the need for a more efficient and economical manufacturing process has long been recognized. A review of prior work disclosed the practicability of forming the desired end product by treating the p-nitrochlorobenzene with sodium hydroxide and ethyl alcohol; it also disclosed some of the difficulties to be encountered in carrying the reaction to a conclusion which would be satisfactory from a commercial viewpoint. The technical literature, other than patents, is almost barren as to suggested processes which might offer commercial possibilities; the reaction times were long, the required reagents were expensive, the yields of product were low, or the purity of product left much t o be desired. The patents consulted disclosed methods of a more promising nature than any of those described in the technical literature. Lewcock ( 2 ) obtained a patent for a process using sodium or sodium hydroxide as the alkaline reagent in an aqueous alcoholic solution containing 85 per cent alcohol. To avoid reduction, p-nitrochlorobenzene was used in concentrations not exceeding 5 per cent. By heating in an autoclave lined with either enamel, nickel, or silver for 24 hours a t 95-120" C., a high yield of p-nitrophenetole was claimed with p-nitrophenol as the only other organic byproduct along with some unchanged nitrochlorobenzene. I n 1924 Cruikshank (1) patented a process, carried out at atmospheric pressure, in which reduction was prevented by feeding the alkali to the reaction chamber gradually. This was done by allowing the condensed vapors from the boiling alcoholic solution to pass through solid alkali before they were returned to the hot solution; thus fresh alkali was brought into the reaction. The same principle was applied to the production of o-nitroanisole. An almost quantitative yield of p-nitrophenetole is claimed (6) by heating a mixture of glycerol, sodium hydroxide, alcohol, and p-nitrochlorobenzene under pressure a t 100' C. in
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the presence of cuprous chloride or copper sulfate. This process appears to be expensive, since the glycerin used must be recovered. One obstacle to efficient production of a high yield of the desired condensation products in a satisfactorily high state of purity consists in the necessity for employing a large excess of the caustic alkali in order that the reaction may reasonably approximate completion. Rapid progress of the condensing reaction is favored by high concentration of strong alkali in free or active form, and by relatively high reacting temperatures, and hence it is essential in practice to use much more alkali than theory requires ; but under these conditions the accompanying side reactions tend to cut down the yield of desired product and to contaminate it excessively with impurities. To remedy this, it has been proposed to operate with a relatively substantial proportion of water in the reaction mixture ( Y ) , or to hold the reaction temperature down to a relatively low maximum (6). Such expedients have the disadvantage of slowing down the reaction undesirably. Moreover, whatever may be the alkali concentration initially, it becomes progressively lower as the reaction goes on, thus slowing down the reaction and greatly delaying its completion, besides rendering it nonuniform. Another proposal (4) involves the initial use of only a portion of the total required quantity of alkali. The remainder is later introduced into the reaction mixture in separate proportions a t successive stages of the reaction; and between each stage it is necessary to cool the mixture and release the autoclave pressure. The time required to complete the operation is therefore not shortened, nor is uniformity of reaction attained. I n addition, the procedure is thereby complicated materially.
Pratt and Weltz Process The process as described by Pratt and Weltz (4) was thought to be far the best of those found. It was therefore made the basis of study for the development of modifications which might improve the process. The description of their process, as disclosed in the cited patent, is quoted: PREPARATION OF ~-XITROPHENETOLE, Three to six parts of 90-100 per cent ethyl alcohol are heated in an autoclave with 0.3 part of 100 per cent caustic until solution is effected. The mass is cooled down and 1 part of p-nitrochlorobenzene is added. Oxygen is then introduced into a freeboard space of 25-50 per cent of the autoclave capacity, from a high pressure cylinder until a pressure of 100-150 pounds is reached. The temperature is then raised in 3-5 hours t o 100' C. and maintained 1 hour. During the course of the reaction, the pressure is maintained at about 150 pounds by passing in more oxygen. The charge is then cooled down t o 30-40", the pressure is released, and an additional 0.096 part of fine dry 100 per cent caustic soda is added. Oxygen is then led in until the above pressure conditions are re-established, the charge is again heated to 100" in 2-3 hours and held for one hour, the temperature is again lowered, and a second additional charge of 0.096 part of caustic soda is charged in, oxygen is recharged into the autoclave, and the mass is again heated t o 100" C. in a similar manner. This time the temperature is held at 100' C. until the maximum condensation, as indicated by control tests, has taken place. Maximum condensation takes place in 2-8 hours. When the reaction is complete,
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the product may be obtained after distilling off the alcohol, or it may be isolated by crystallizing from the mother liquor solution. A yield of 85-95 per cent of the theoretical amount of p nitrophenetole is obtained. In the above example there may ordinarily be used any quantity of caustic soda between 0.35 and 0.50 part for each 4 parts of ethyl alcohol, although we prefer t o use a total of 0.492 part in the manner described above.
A critical study of this disclosure reveals the following pertinent facts: The operation is interrupted three times while the autoclave with its charge is cooled, the pressure is released, sodium hydroxide and oxygen are added, and the heating is resumed. The minimum elapsed time for the operation is 9 hours and may be as long as 18 hours. The indicated niaximum temperature is 100" C. Oxygen, in excess of that actually required, is wasted on account of the necessity of releasing pressure when the second and third additions of sodium hydroxide are made. This study indicated the desirability of initiating such changes in operating conditions as would permit continuous operation, a higher operating temperature, a use of less oxygen, and a shorter operating time without any sacrifice in completeness of reaction, yield of product, or purity of product. The change which appeared to be most likely to accomplish the desired result was some method for maintaining reasonably constant hydrogen-ion concentration during the entire progress of the reaction. The reaction was attempted by adding sodium hydroxide, in alcoholic solution, from an auxiliary chamber connecting with the autoclave and maintained under the same pressure as the latter. This was accompanied with many difficulties and was soon abandoned. The feasibility of adding t o the charge some chemical compound which would hydrolyze and yield free sodium ion during the progress of the reaction was considered, and this procedure was finally adopted. Several compounds of the character mentioned were experimented with; the one giving most satisfactory results was sodium metasilicate.
there is present during the reaction an oxidizing agent, preferably in comparatively high concentration, as, for example, gaseous oxygen under pressure, which may advantageously be from 75 to 175 pounds per square inch." Our experimental work soon disclosed that still further shortening of the reaction period, together with other economies in operation, may be accomplished by adding a certain amount of sodium metasilicate t o the reacting materials and, after cooling the charge from one condensation, separating the crystallized p-nitrophenetole and re-using the mother liquor as component parts of another charge.
Operating Conditions The opemting details, as well as the utility of using sodium metasilicate, are illustrated by the operating data and results obtained in the five experiments (Table I). Runs 1 to 3, inclusive, were conducted re-using the mother liquor from the preceding experiment, made up to the indicated composition by the addition of the required reagents. Experiments 4 and 5 were direct comparisons, with and without the presence of sodium metasilicate. A direct comparison of these operating conditions and results with those described by Pratt and Weltz is as follows:
Material per 100 lb. p-nitrochlorobenaene: p-Nitrochlorobenzene Ethyl alcohol, 90-100% Sodium hydroxide Sodium hydroxjde Sodium hydroxide Sodium silicate Temperature, C: Time t o attain this temp., hours Cooled and reheated Total elapsed time, hours Yield of product, %
Pratt and Welta
-Stockman-Expt. Expt. 1, 2, 3 4
10 30-60 3.0 0.96 0.96
10 37 3.18
...
100 3-6
Twice 10-16 8595
6.0 120 2 No 6 85
10
37 3.18
.. .. ..
6.0 150 1.5 K O
4 87
TABLEI. OPERATINGDATAAND RESULTS Run No. p-Nitrochlorobenaene: Grams M1. 95y0 ethyl alcohol, liters Sodium metasilicate, grams Sodium hydroxide, grams Normality of soln. b y analysis Max. temD.. C. Time opeiaied a t max. temp., hours Total operating time, hours Yield expressed in terms of total crystallizable material, grams Yield expressed i n grams pure product, % Purity ( i e t d . b y setting point), C.
1
2
550
550
276 2.0 300
175 2.2 120 3.5 6
275 2.0 300 150 1.9 120
4 6
3
4
550 275 2.0 300 150
600
120
550 275 2.0 300 175 2.2 150
4
2.5
3
1.9
6
5
300
2.0 None 190 2.1 150
4
4
472
425
602=
510
80
72
85b
87
57.2
57.0
56.5
56.5
480 1
60-66
a Setting point for pure material, 57.8' C. b These figures were taken a t the end of the cycle so t h a t the, 85 per cent is the average of the three runs. The crystals from run 5 were estimated t o contain about 60 per cent p,p'-dichloroaaoxybenzene.
The experimental work reported here deals solely with the results obtained, when it was used as one of the reacting materials. Pratt and Weltz (4.) state: "We have discovered that a remarkable saving in time may be effected by conducting the condensation under a comparatively high temperature, and that undesirable side reactions are almost entirely avoided, with a consequent increase in yield and purity of product, if MARCH, 1939
Experiments 2 and 3 were operated using the mother liquor from experiment 1, from which the product had been crystallized and separated and the solution re-used by adding p-nitrochlorobenzene in same quantity as was initially employed; the p H was adjusted by adding sodium hydroxide and repeating the process. Operating conditions during run 4 show the following divergencies from the Pratt and Weltz process : temperature, 50" C. higher; time elapsed in attaining this temperature, 0.3 to 0.5 of Pratt and Weltz's; cooling and reheating, none; total elapsed time, 0.25 to 0.4 that necessary in the Pratt and Weltz process; yield of product, approximately as great; and purity of product, the same. These changes indicate a marked decrease in the cost of producing pnitrophenetole. The process developed materially shortens the time required, operates with a more concentrated solution, secures approximately the same yield of high-purity product, and avoids the necessity of distilling off the alcohol to obtain the product desired. The process finally adopted is as follows: 550 grams p-nitrochlorobenzene, 200-300 grams sodium metasilicate, 150 grams sodium hydroxide, and 2.0 liters of 95 per cent ethyl alcohol were charged into a n alloy steel autoclave. The pressure was raised to 150-200 pounds per square inch with oxygen, and heat was applied at a rate t o reach the
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final temperature of 150" C. in 2-2.5 hours. This temperature was held for 3 hours, and the autoclave was then cooled rapidly to"70-75" C. At this point the mass in the autoclave is still liquid and should be blown into a steam-heated filter press and filtered to remove any free silica and sodium metasilicate remaining. Instead of carrying this step out in the laboratory, the autoclave was cooled down as far as possible with water, and the product was then filtered; the alcoholic solution was recovered and made up to the original volume with fresh alcohol, and a new charge was added to start the cycle again. The product obtained requires washing with water a t about 30-40" C. to remove the nitrophenol. The over-all yield obtained by this method varies between 83 and 87 per cent of the theoretical, the remainder being recovered as nitrophenol. The purity of the product obtained varies, as estimated from the setting point, between 87 and 95 per cent.
It is evident that the objectives established at the inception of the research were accomplished, Acknowledgment The process developed is covered by a U. S. patent application assigned to the Yorth Shore Coke and Chemical Company, by whose courtesy this paper is presented. Literature Cited (1) Cruikshank, H. G. (to National Aniline & Chemical Co.) , British Patent 239,320 (July 15, 1924). (2) Lewcock, W. (to Gas, Light & Coke Co., London), Ibid., 204,594 (Oct. 4, 1923). (3) McCormack, Harry, IND.ENQ.CHEY.,29, 1333 (1937). (4) Pratt and Weltz, U. S. Patent 1,619,368 (March 1, 1927). (5) Tschechoslowakii, French Patent 602,977 (June 4 , 1926). (6) Weiland and Stallman, U. S. Patent 2,038,620 (April 28, 1936). (7) Weltz, Ibid., 1,578,943 (March 30, 1926). RECEIVED November 2, 1938.
ACID CATALYSIS IN LIQUID AMMONIA Ammonolysis of Fatty Oils V. F. BALATY, L. L. FELLINGER, AND L. F. AUDRIETH University of Illinois, Urbana, Ill.
The ammonolysis of natural oils and fats by the action of liquid ammonia to produce mixtures of the corresponding fatty acid amides is catalyzed by the presence of ammonium salts. Solvolytic reactions of this type represent a special case of acid catalysis in a nonaqueous solvent. Amide mixtures were prepared from olive, cottonseed, maize, soybean, castor, linseed, perilla, and tung oils, and from pork lard. The nitrogen contents and iodine numbers of all ammonolyzates were determined.
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H E ready availability of liquid ammonia as a solvent and reaction medium, together with the fact that it possesses unusual and distinctive chemical properties, has led to its extended use as an ammonolytic agent. Reactions of ammonolysis are analogous to those of hydrolysis. Just as hydrolysis of esters leads to the corresponding acids, so ammonolysis of esters results in the formation of the acid amides (ammono acids from the Franklin point of view, 5). Parallel Equations 1 and 2 serve to bring out this analogy. Hydrolysis: RCOOR' Ammonolysis: RCOOR'
+ HOH-RCOOH + R'OH (1) + HNHz+RCONHZ + R'OH (2)
I n the widespread attempt t o utilize easily available raw materials and those which might be made more available through assured demand, the chemical industry has focused increasing attention upon the naturally occurring fats and 280
oils. Ammonolysis of these materials yields the amides of the long-chain fatty acids. Technically (4) the preparation of fatty acid amides is carried out a t higher temperatures either under pressure or in the vapor phase. Operation at moderate temperatures is impractical, because of the slowness of the reaction between the oils and ammonia. Even a t 150" C. the reaction between anhydrous ammonia and various glycerides is apparently quite slow. This is to be inferred from the fact that Oda (5) investigated for their possible catalytic effect a large and varied number of materials such as zinc chloride, calcium chloride, activated carbon, precipitated silica, benzene, ethanol, and ethyl ether. None of these mas found to accelerate the ammonolytic reaction. From the established fact that acids catalyze the hydrolysis of esters, and from the fact that ammonium salts are known to behave as acids in liquid ammonia (S), it was to have been expected that ammono acids would catalyze the ammonolysis of esters in liquid ammonia. That ammonium salts do catalyze ammonolytic reactions has been demonstrated both qualitatively and quantitatively by various investigators. Pinck and Hilbert (6) showed that the ammonolysis of fluorenone ani1 takes place readily in the presence of ammonium chloride. Blair (1) showed that urea could be converted into guanidine by heating it with liquid ammonia and ammonium chloride. Franklin (3) cites numerous instances where ammonium salts act as acid catalysts in liquid ammonia. Shatenshtein (7) made a series of quantitative studies to determine the effect of equivalent concentrations of ammonium salts on the rate of ammonolysis of santonin. Experimental studies in this laboratory have demonstrated that the rates of ammonolysis by liquid ammonia of diethyl malonate at -33" and 0" C. ( 8 , 9 ) and of ethyl benzoate a t 0" and 25" C. ( 2 ) are markedly accelerated by the addition of various am-
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