Patented Dec. 14, 1948 2,455,931

UNITED STATES PATENT OFFICE 2,455,931 METHOD OF MAKNG N-METHANNE Everett C. Hughes, Cleveland Heights, Ohio, as a signor to The Standard Oil Company, Cleve land, Ohio, a corporation of Ohio No Drawing. Application October 23, 1944, Serial No. 560,042 2 Claims, (C. 260-57) 2 . " This invention relates to a process for making In practicing the process of the invention, N-methyl antline. either a continuous or batch operation may be N-methyl aniline is a liquid having a relatively employed. A continuous operation will probably s high boiling point (195.5° C.). It is relatively be selected for a commercial embodiment, since insoluble in water. It is a valuable intermediate 5 it will permit more economic recovery and reuse in the manufacture of dyes and many other uses, of the catalyst and the unreacted ingredients. and has the desirable property of raising the This recovery and reuse of the catalyst and the anti-knock value of motor fuel. It could be used unreacted ingredients involves the employment in large quantities in producing aviation gaso of other inventions which are to be described in line of a high knock rating, for example, if a O other applications. For ease of description, there simple and inexpensive method were available for fore, the process of this invention will be de producing it in large quantities, free from in scribed primarily as applied to a batch operation, purities which are less effective in raising knock It may, however, be used in a continuous opera rating. tion, as is pointed out above. The production of N-methyl aniline has been s In carrying out the process, the mono-chloro accomplished heretofore, among other processes, benzene is placed in a reactor together with water by the methylation of aniline. This process also in which the methylamine and the cuprous chlo yields substantial amounts of di-methyl aniline, ride catalyst have been dissolved. The chloro and the mono and di-methylated products are benzene, being relatively insoluble, in the aqueous difficult to separate. For example, N-methyl an s solution, separates as a separate phase. The two line has been prepared by heating aniline with phases can be intimately admixed with any ap methyl alcohol and hydrochloric acid in an auto propriate agitating means. The reaction is con clave. tinued under temperature and pressure condi It is an object of my invention to produce N tions as indicated hereinafter, and is permitted methyl aniline by a simple and efficient process, 25 to proceed for the desired length of time to ob utilizing readily available raw materials to pro tain a good yield, as will be discussed herein duce high yields per pass and by means of which after. The reaction may be viewed substantially any unreacted component or the catalyst may be as follows: recovered and reused. N-CE Another object of the finvention is to produce 30 N-methyl aniline by a process which results in high yields with a minimum of secondary prod -- N-CHs in the presence -. HC ucts or by-products which require separation and sawa which decrease the value of the N-methyl andline of CC for raising the knock rating of motor fuel. Inasmuch as an excess of the methylamine pre Another object of the process is to produce ferably is employed, the hydrochloric acid N-methyl aniline under conditions which are formed as a by-product will react with such an readily obtainable in a commercial operation and excess, in accordance with the following reac readily available in industrial equipment. tion: I have discovered that N-methyl aniline can 40 be prepared by reacting mono-chlorobenzene with mono-methylamine in the presence of cop At the conclusion of the reaction, the agitation per chloride as a catalyst. The process is easy may be discontinued and the reaction mixture to operate, efficient and gives yields of 95 to 100% will separate in two phases. Inasmuch as the re per pass with a minimum of contaminates. 45 action is generally carried out at an elevated tem. , Chlorobenzene is readilly. available and can be perature and pressure, in order that it may pro prepared simply by chlorinating benzene. It is ceed to a good yield in a reasonable time, it is a liquid having a boiling point of 132.1 C. and convenient to cool the mixture before the separa is relatively insoluble in water. Methylamine is tion is accomplished. a gas having a boiling point of about -7°C. It is 50 One layer comprises the N-methyl andline and quite soluble in water and like all gases its solu any Small amount of unreacted chlorobenzene. bility can be increased under pressure. The pre This layer may be withdrawn and subjected to ferred catalyst, copper chloride, is soluble in the fractional distillation. Any unreacted chloro aqueous methyl amine, presumably forming a benzene will be readily separated from the N complex with the methylamine. 55 methyl aniline because of their wide difference, 2,455,981 3 4. in boiling point. The recovered chlorobenzene action time is from one-half to one hour. With can be recharged to the reaction Zone. increased amounts of catalyst, optimum pro The other layer comprises an aqueous phase portions and at the higher temperatures, the re containing the unreacted methylamine, the action time can be made very short. methylamine hydrochloride by-product and the The concentration of the methylamine in the copper chloride catalyst. This layer may be re aqueous phase is more or less critical and has an processed to neutralize the methylamine hydro important effect upon the yield of the N-methyl chloride and the recovered methylamine may be aniline, especially when the minimum reaction reused. The catalyst may also be recovered and time is used as it would be in a continuous com reused. O mercial operation. The preferred concentration In general the lower layer is the aqueous phase, is 40 to 75% methylamine based on the total but it is possible for the lower layer to be the non aqueous phase. It is interesting to note that aqueous phase in the case of low catalyst con at concentrations above 90%, the yields fall of centration and low conversion. markedly, contrary to what may be expected. : The temperature selected for the reaction pref 5 Similarly, concentrations below 20% result in erably should be such that the reaction proceeds markedly lower yields. The optimum concen ; at a rate so that good yields may be obtained in a tration appears to be about 60%, and the con reasonable time. In general, the temperature version per pass falls of on either side of this should be about 100 to 300° C.; the preferred figure unless much longer reaction times are range being about 150 to 250° C. and within this 20 used. It is very desirable to obtain optimum range a temperature of 215 to 235 C. seems to be conversion per pass in a minimum time as this optimum when the other variables are optimum. increases the net amount of the N-methyl aniline Too high temperatures are to be avoided as they that can be made with equipment of a given ca tend to introduce side reactions. pacity. This effect of the concentration of The pressure employed is sufficient to keep the 25 methylamine is quite unexpected since the litera material in the liquid phase at this temperature. ture states that the concentration of ammonia in Higher pressures may be used but with no ma the amination of chlorobenzene has no affect on terial advantage. This suggests the desirability the rate of the reaction when annonia is en of not employing any higher pressure than is ployed. This indicates that the use of methyl necessary to maintain a liquid phase operation. 30 amine presents special problems, and that it is Pressures within the range of 200 to 1500 pounds probably unique in interfering in some way with per square inch have been observed. the action of the particular catalyst employed in The proportion of the various ingredients for the aqueous phase in the process. optimum yields may vary considerably. The Operating under the conditions above described amount of the catalyst may be expressed con 35 yields of 75% or above are obtained and optimum veniently in relation to the methylamine since conditions give yields as high as 95%. these are both contained in the same aqueous As indicative of the yields that may be obtained phase. The ratio of the cuprous chloride cate in accordance with the invention, 450 parts by alyst to the methylamine may be from 0.01 to Weight of a 40% aqueous solution of methylamine ,0, expressed as copper (atomic)/methylamine 40 containing 92 parts by weight of cuprous chloride (no). With larger amounts of catalyst it is was charged into a stirred reactor. This amount possible to utilize somewhat lower temperatures to 0.16 no of catalyst (expressed as copper) per and shorter reaction times and this suggests the mol of methylamine; 30 parts by weight of use of a large amount. Generally, a ratio of 0. chlorobenzene was then charged to the reactor. to in over 0.4 is desirable, There is some evia 45 The nola ratio of methylamine to chlorobenzene dence that the conversion of chlorobenzene per is 5:1. These are within the ranges heretofore pass falls of somewhat if the amount of the described. catalyst is too large. Since the recovery and The reaction mixture is agitated for 30 minutes reuse of the catalyst presents certain problems, while the temperature is maintained at 215 to this also suggests the use of a minimum amount, 50 225 C. The reaction is in a closed vessel and The amount to be selected in a commercial en under the pressure developed at this temperature bodiment will be within the above ranges and which keeps the ingredients in the liquid phase. will be related argely to the other variables of At the end of this reaction time, the mixture was the process and the facilities for recovering and rapidly forced out of the reactor and discharged Freusing the Catalyst. - 55 through an efficient condenser where it was cooled The ratio of the methylamine to the chloroa and then sent to a stratifying vessel. The non benzene is such as to have a substantial excess aqueous layer was drawn off and upon analysis of the methylamine, since this removes the hya it was found to contain 7% unreacted chloroben drochloric acid by-product, the formation of zene and 93% N-methyl aniline. Although in this which slows the reaction. Stoichiometric con 60 example the methylamine concentration was less siderations indicate that at least 2 mols of than the optimum value for economic reasons, methylamine should be used for each mol of nevertheless the yield was exceptionally high. chlorobenzene. There is probably no upper limit As illustrative of an additional example in except the objection to recycling the excess. An which the methylamine concentration was main upper limit of 10 mols is reasonable in a com tained at the optimum value but the amount of mercial operation. In a continuous process, there catalyst was exceptionally small in order to min is no particular objection to having the large ex inize the problems incident to the recovery there cess, since this can be recycled and does not no of, 5 mols of a 60% aqueous solution of methyl volve any economic loss, amine containing 0.04 mol of Cu2Cl2 per mol of The reaction time should be adjusted with ref 70 methylamine was reacted for one-half hour at a erence to the other variables and should be such temperature of 200 to 230 C, with 1 mol of chlo as to obtain as high a yield as possible. Under robenzene. The procedure in general was that the optimum conditions of the other variables described in the previous example and the con good yields can be obtained in a reaction time version of cholorobenzene to N-methyl aniline was as small as 10 minutes, but preferably the re 75 75% per pass. 465,08 fn the above description a preference for cop dients in the liquid phase, continuing the réad per chloride as the catalyst has been indicated. tion for not over 1 hour, cooling the reaction mix This may be either CuCl2 or CuCl2 which are ture, separating the aqueous and non-aqueous about of equal effectiveness as starting materials. phases, and separating the N-methyl aniline from The copper chloride may shift from the cuprous is the non-aqueous phase, whereby an at least 75% to the cupric state and vice versa depending on conversion of the chlorobenzene to N-methyl ani the conditions of the reaction, line is obtained. It is obvious that my invention may be prac EVERETT C. HUGHES, ticed by variations in the conditions and other factors indicated heretofore and intend all of 0. REFERENCEs CITED the same to be included within the invention, as The following references are of record in the fled within the scope of the following claims. file of this patent: claim: 1. The method of making N-methyl antine UNITED STATES PATENTS which comprises agitating mono-chlorobenzene Number Name Date with an aqueous phase containing 40 to 75% 1921,726 Britton ------Aug. 8, 1933 mono-methylamine and a catalyst comprising a 1932,518 Hale ------Oct. 31, 1933 copper chloride. 1,935,515. Mills ------Nov. 14, 1933 2. The method of making N-methyl andline 2,212,825 Daudt ------Aug. 27, 1940 which comprises agitating an aqueous phase Con 20 taining about 60% mono-methylamine and a cat OTHER REFERENCES alyst comprising copper chloride with a non Marcinkow et al., “Roczniki Chemie,' vol. 16, aqueous phase comprising a mono-chlorobenzene pages 395-402 (1936). in an amount to provide not more than one-half Chem. Abstracts, vol. 3 (1937), page 1776. mol of mono-chlorobenzene per mol of monon 25 Groggins: "Unit Processes in Organic Synthe methylamine, at a temperature of 150 to 250 C. sis” (1938), p. 299. and a pressure to maintain the reaction ingre