2,991,311 Patented July 4, 1961

United States Patent Office 2 to be reacted, in form of a mixture, pass commonly up W 2,991,311 wardly through the phosphoric acid as a stream of gas METHOD OF ALKYLATING AM NES Matthias Thoma, Waldkraiburg, Upper Bavaria, Ger bubbles. The vaporous compounds leave the catalyst. many, assignor to Biller, Michaelis & Co., Berlin bed of phosphoric acid on top thereof and may there be Charlottenburg, Germany, a corporation of Germany separated from the catalyst without any difficulty. In this No Drawing. Filed Nov. 26, 1958, Ser. No. 776,431 manner, a continuous transformation is possible by in Claims priority, application Germany June 1, 1954 troducing the compounds to be reacted continuously into 3. Claims. (C. 260-577) phosphoric acid heated at high temperatures and with drawing the reaction products on top of this acid after This invention relates to a new and useful method of 10 having passed through the catalyst bed. alkylating amines and is a continuation-in-part of co It is preferred in carrying out the process to use the pending application Ser. No. 512,102, filed May 31, 1955, phosphoric acid in form of reaction columns which may now abandoned. be several meters in length, e.g. 4 to 8 meters or more. According to conventional methods, the alkylation of However, shorter reaction columns may be used depend amines is effected by transforming substances having 15 ing upon the efficiency desired of the conversion. Thus, alkyl groups, e.g. alcohols and amines, at higher tem it has been found, for example, that a considerable re perature in the presence of catalysts, e.g. hydrochloric action will also occur with a phosphoric acid column acid, phosphorous trichloride and oxylchloride. The re having a total height of as little as 5 centimeters so that, quired reaction temperature is between 180 and 220 C. e.g. with a height of 150 centimeters, the transformation, In view of this temperature and the low boiling point of 20 may be substantially completed after two passages only. one of the reaction components, i.e. the alcohol, the For full utilization of the existing catalyst column, it is . transformation takes place in a closed vessel. Owing to preferred to introduce the compounds to be converted the low boiling point of the alcohol this results in pres from below or into the lower section of this catalyst sures of 15 to 60 atmospheres gauge pressure, depend column. ing on the type of the alcohol. 25 If the compounds to be converted have not yet re The resulting product is a mixture, e.g. of ethyl ani acted satisfactorily when being withdrawn at the upper line, diethyl aniline, alcohol and ether. In general, the end, e.g., when using a short catalyst column, the re ratio of ethyl aniline to diethyl aniline is 1:3 to 1:5. action mixture may either be returned into the same, It is very difficult in this reaction to control the trans catalyst column or introduced into a second and, if de formation in such a way that only monoethyl aniline 30 sired, further reaction columns until the conversion has or only diethyl aniline is obtained. progressed to the extent desired. . . It has also been proposed to react highly negatively By passing the stream of vapor bubbles through the substituted aromatic amines with tertiary alcohols in the column of catalyst liquid, a large surface of contact is presence of phosphoric acid. In this process, the aro provided between the compounds to be reacted and the matic amines are substituted with cyano-, nitro- or car 35 catalyst so that the reaction between the reactants will boxyl groups in the ortho or para positions and these proceed easily and rapidly within the temperature range highly negativating substitutents loosen the hydrogen to be used in accordance with the invention. This per atoms on the amino nitrogen. Furthermore, highly re mits operation without the use of external pressure so actable tertiary alcohols are used and the reaction is that the process may be carried out at practically-at capable of being carried out in the temperature range 40 mospheric pressure. If desired, it is also possible to of between 20 and 100° C. This process, however, is not carry out the process while applying a subatmospheric applicable to the transformation of aromatic amines, the pressure to the reaction column. In this way, compounds reactivity of which is not influenced by highly negativat which are difficult to volatilize can be successfully con ing substituents, with primary alcohols, i.e. alcohols verted into the vapor phase within the temperature range which are relatively slow to react. used in accordance with the invention. The process of the invention relates to the alkylation 45 Particularly suited for the process of this invention are of mononuclear aromatic amines bearing at least one re aromatic amines having at least one reactive hydrogen placeable hydroegn atom on the amino nitrogen with atom on the amino nitrogen and boiling below about 220 primary alkanois. The process of the invention operates to 225 C. at atmospheric pressure. Suitable amines are at substantially atmospheric pressure and permits a fully especially aromatic amines such as aniline or anilines continuous conversion of the starting compounds to be 50 substituted with lower alkyl radicals, e.g. toluidine, xyli carried out in most simple manner. Furthermore, the dine, ethyl anilines and the like. The alkylating agents process of the invention permits the formation of the used for the process of the invention are lower primary alkylation products to be controlled in such a manner that alcohols or ethers thereof. Examples for these include both substantially monoalkylated amines and, if desired, methanol, ethanol and propanol-1. The lower limit of substantially dialkylated amines are obtained. 55 the temperature range used in accordance with the in-, In carrying out the alkylation process of the invention, vention is set by the conditions that the compounds to mononuclear aromatic amines with no interfering group be reacted are gaseous at the reaction pressure. Since. and having on their amino nitrogen at least one replace the lowest boiling aromatic amine, the aniline, boils at. atmospheric pressure in the range of between 180 and able hydrogen atom are introduced together with an 60 184 C., temperatures of about 180° C. may be regarded alkylating agent into concentrated phosphoric acid which as the lower limit for the temperature. The upper limit is maintained at practically atmospheric pressure and at for the temperature is set practically only by the condi a temperature which ranges above the boiling point of tion that no decomposition or undesirable side reactions. the amine to be converted at the reaction pressure but occur. Temperatures up to about 235. C. have been below about 235 C. The alkylating agents used are 65 found to be particularly suitable, a temperature of be lower primary alcohols or ethers thereof. tween 180 and 220 C. being most preferred for carry The compounds to be reacted may be introduced in ing out the process of the invention. the liquid or gaseous phase into the concentrated phos In choosing the compounds to be reacted, care shoul phoric acid. Due to the temperature of the phosphoric be taken that the reaction products formed are sufficiently acid, any liquid portions which may be present are 70 volatile within the temperature range of the phosphoric evaporated and, therefore, the vapors of the compounds acid column at the reaction pressure. It is not absolutely t 2,991,811 - - - 3 4. necessary for the reaction products to be already com once the catalyst had been heated to about 200 C., pro pletely evaporated, it being also possible to remove part ceeds without heating, maintaining the reaction tempera of the reaction products from the liquid column by means ture. of the other vaporous portions flowing through. At any Example 6 rate, the reaction products should be volatile without too 5 The alkylation with alcohol to mono- and diethyl ani much difficulty under the reaction conditions to ensure line proceeds in the same way if the process is carried that they are actually discharged from the reaction col out according to Example 1. It is possible by suitable umn in continuous operation of the process. An attempt choice of (a) the temperature and (b) the mixing ratio made to carry out the process at lower temperatures, e.g. between aniline and alcohol to determine whether es in the range of 80 to 120° C., shows that practically no O pecially monoethyl aniline with small amounts of aniline conversion occurs between the amines and the alkylating and diethyl aniline or, on the other hand, diethyl aniline agents. Moreover, at these low temperatures, the com with little mono-ethyl aniline and practically no aniline pounds introduced into the phosphoric acid are, of course, is to be obtained. not capable of being removed therefrom in gaseous state Example 7 so that a continuous conversion as it is possible in ac cordance with the invention is not capable of being carried 7.5 liters of phosphoric acid are filled into a cylindrical out at these low temperatures. tube of 150 cms. in length and 10 cms. in diameter and Owing to the specific control of the reaction condi equipped for electric heating. The temperature is slowly tions and of the particular amounts charged of com increased to 220° C. pounds to be reacted the process of the invention offers A mixture comprising 1 part by weight of o-toluidine the possibility of producing either substantially only and 3 parts by weight of ethanol is introduced into the monoalkylated products and only little dialkylated prod heated phosphoric acid at a rate sufficient to put through ucts or to form substantially dialkylated amines. In 3 kgs. per hour. The effluent gas mixture is condensed addition to the quantity of alcohol fed, reaction condi and the dilute alcohol is driven off from the alkylation tions essential to this end are the residence time in the mixture by simple distillation. catalyst bed, i.e. especially the height of the catalyst The alkylation mixture consists of: column, and the reaction temperature. 4 percent of unchanged toluidine, Example 1 35 percent of N-monoethyl toluidine, and 1000 kgs. of concentrated phosphoric acid are filled 30 61 percent of N-diethyl toluidine. into a reaction vessel of, for instance, 1 meter diameter Example 8 and 300 cms. height and heated, by a suitable heating coil, to a temperature of 180 to 220 C. A mixture of, 6 liters of phosphoric acid are saturated with 1.5 liters for instance, 1 part by weight of aniline and 2 parts by of Xylidine in the apparatus and under the conditions de weight of methanol is passed through the catalyst liquid Scribed in Example 7. Following this, the procedure de at a rate of 100 to 300 liters per hour. After passage scribed in Example 7, is followed, i.e., a mixture consist through the catalyst the reaction product, consisting of ing of 1 part by weight of xylidine and 3 parts by weight about 92 to 95 percent of dimethyl aniline and methanol of methanol is introduced. The effluent gas mixture is of about 75 percent strength, is passed, without cooling, condensed and substantially consists of alkylated xylidine into a fractionating column in which methanol of 98 to 40 and only a few percent of unchanged xylidine. 99 percent concentration is separated and the reaction Example 9 product, i.e., in this case dimethyl aniline and water, is 6 kilograms of phosphoric acid and 6 kilograms of o continuously removed from the still. On separation of toluidine are placed into the apparatus described in Exam the water in a separating vessel, there results a dimethyl ple 7. Upon heating to 220-230° C., alcohol is intro aniline containing 92 to 95 percent of dimethyl aniline, 45 duced into the tube from below. A column mounted on 7 to 4 percent of monomethyl aniline and 1 to 2 percent top of the apparatus takes care that only the excess alco of aniline. hol diluted with water distils. The process is discon Example 2 tinued as desired depending upon the product intended to The process is carried out as in Example 1 except that be recovered, i.e., the desired mono-diethyl toluidine or the reaction mixture before the separation of methanol 50 Substantially only diethyl toluidine. The introduction of is passed once more, with addition of one further part alcohol is stopped and the diethyl toluidine is distilled by weight of methanol, through a second, smaller reaction off after having shut off the dephelgmator arranged in the vessel which is also filled with phosphoric acid, thus ob column. Fresh toluidine may be immediately introduced taining a dimethyl aniline with a purity above 99 to 99.5 into the remaining catalyst and the process may be con percent. tinued as described above. A yield of 99 to 100 percent Example 3 of mono- or diethyl toluidine is obtained. In the examples given above it has been found that the The process is carried out as in Example 1 except that catalyst is durable almost without a limit, but at least en the aqueous methanol is separated after the first passage, Sures a 40 to 50-fold conversion or transformation, based about 1 part by weight of methanol is added to the 60 resultant dimethyl aniline of 90 to 95 percent strength on the weight of the catalyst. For the rest, in case of a and the mixture is put through a second similar reaction deterioration of the catalyst, the same can be regenerated unit or alternately through the first one, thus also ob in a simple manner and thus be made ready for renewed SC. taining a product of a purity of at least 99 to 99.5 percent. It will be appreciated that alkylations of any kind can Example 4 65 be carried out by the novel method. Practically no Instead of methanol, dimethyl ether or a mixture of Waste gases or other decomposition products are formed. dimethyl ether and methanol is passed through the re The continuous process hereinbefore described offers actor in the manner described in Example 1, thus ob a substantial advantage over the known methods, since taining a product containing 90 to 95 percent of dimethyl 70 the reaction products are brought together in their origi aniline. nal form in the presence of catalysts, without pressure, Example 5 and the desired product is obtained in commercial purity, The process is carried out as described in Example 1 practically without losses of the reactants. except that the aniline-methanol mixture fed is heated to While the invention has been described in detail with 100-200° C. In this way it is achieved that the reaction, respect to certain now preferred examples and embodi

2,991,811 5 6 ments of the invention it will be understood by those body is maintained at a temperature between about 180 skilled in the art after understanding the invention that and 220 C. various changes and modifications may be made without 3. A process according to claim 1 in which said liquid departing from the spirit and scope of the invention and body is a body of a height of at least 4 meters and in it is intended, therefore, to cover all such changes and which said amine and alkylating agent are introduced modifiactions in the appended claims. into the lower portion of said body to bubble upwardly I claim: therethrough. 1. Process for alkylating amines which comprises main taining a liquid body of concentrated phosphoric acid at References Cited in the file of this patent a temperature ranging from above the boiling point of the O amine to be alkylated to 235 C. and a pressure not sub UNITED STATES PATENTS stantially in excess of atmospheric, introducing an amine 2,073,671. Andrew ------Mar. 16, 1937 selected from the group consisting of aniline and aniline 2,391,139 Dickey et al. ------Dec. 18, 1945 substituted with a lower alkyl radical at the nucleus and 2,766,277 Gleim ------Oct. 9, 1956 an alkylating agent selected from the group consisting of 5 FOREIGN PATENTS lower primary alkanols and their lower alkyl ethers into said liquid body to bubble through said body in contact 492,022 Canada ------Apr. 14, 1953 and separating the gaseous reaction products containing OTHER REFERENCES the alkylated amine. Perry: "Chemical Engineers Handbook,” 3rd ed., pp. 2. Process according to claim 1 in which said liquid 20 1216-1217, McGraw-Hill, New York (1950).