US2781399A - Preparation of secondary amines - Google Patents

Description

ited States PREPARATION OF SECONDARY AMENES No Drawing. Application February 24, 1953, Serial No. 338,599

9 Claims. (Cl. 260-583) This invention relates to the preparation of secondary amines, and more particularly to the preparation of long chain dialiphatic secondary amines, such as dialkyl and dialkylene amines. The method of this invention can also be advantageously employed for the preparation of aromatic secondary amines such as dibenzylamine, or aromatic aliphatic secondary amines, such as alkylbenzylamines.

The catalytic hydrogenation of long chain aliphatic nitriles to the primary amines has been an industrial process for some time, but the direct production of secondary amines from aliphatic nitriles has not heretofore proven commercially feasible in spite of the demand for long chain aliphatic secondary amines as synthetic intermediates in the production of quaternary ammonium compounds. Aiso, the preparation of long chain aliphatic secondary amines from primary amines has not been a particularly desirable commercial process.

In the preparation of long chain aliphatic secondary amines, either from the corresponding aliphatic nitriles or primary amines, it has been difficult to obtain a high yield of the desired secondary amine product, and to have the product of good color and quality. Moreover, the reactions involved have been difficult to control, and the time required to compelte the reactions has been both variable and excessive. n the one hand, low temperatures with a correspondingly slower rate of reaction has been found desirable to minimize decomposition and side reactions, while on the other hand there has been a need for reducing the time required to carry out the reaction. In other Words, one of the problems involved is that of minimizing the reaction time while obtaining high yields of a good quality secondary amine product. Heretofore, the reaction conditions have not been sufficiently understood to permit "these results to be achieved.

It is therefore a general object of this invention to-provide an improved process for the production of secondary amines from aliphaticnitriles, which-can also be used to produce secondary amines from primary amines. Also, a more specific object of this invention is to provide a process of the character described which permits long chain dialiphatic secondary amines to be produced in high yields with a greatly decreased reaction time, While obtaining a product of good color and quality. Another object is to provide a process which permits reproducea'ole results to be obtained by the control of the important reaction variables so that the desired results can be consistently obtained in commercial-scale production. It is a "still further object of this invention to discover which factors or conditions are important in achieving high yields of a good quality secondary amine product, and to determine what the critical ranges are for each of the factors and conditions. Further objects and advantages will appear as the specification proceeds.

In practicing the method of this invention, aliphatic nitriles containing from -8 to .22 carbon atoms can be employed as the starting material. Because of their availability, aliphatic nitriles containing from 1 2 to 13 carbon ice atoms are preferred. For example, the 'alkyland alkylene nitriles derived fro'm'the fatty acids in common fats and oils are admirably suited for further processing in accordance with this invention. It is not necessary to separate the various chain lengths contained in naturalmixtures of such nitriles. In fact, nitriles derived from mixtures of tallow fatty acids (tallow nitril s) and nitriles derived from mixtures of coconut oil fatty acids (coco nitriles) are the preferred industrial materials. If desired, the process can-also be carried out with primary aliphatic amines containing from'8 to 22 carbon atoms, and preferably from 12 to 18 carbon atoms. Also, mixtures of such amines and nitriles of the character described can be employed.

In general, the process of this invention involves the catalytic hydrogenation of aliphatic nitriles. Any hydrogenation catalyst can be employed, although nickel catalyst, such as fresh Raney nickel are preferred. The proportion of nickel catalyst to the nitrile or aminehas been found to be critical for obtaining both high conversion and high yields. In general, and particularly with Raney nickel, the amount of catalyst employed should range from about .4 to 3% by weight based on the weight of nickel in the catalyst compared to the Weight of the nitrile or amine. With Raney nickel, best results are achieved when the proportion of catalyst to reactant is within the range from about .6 to 2% by weight basedon the nickel in the catalyst.

The yield of secondary amine has been' found to be sharply increased by rigidly maintaining anhydrous conditions during the reaction. Since water would ordinarily be present in the reaction mixture, special precau tions must be taken. For example, ordinaryiRaney nickel contains about 50% water, and both the nitrile and amine reactants will usually contain some moisture. Therefore, it is important to charge both the reactant and catalyst to the reaction vessel in a substantially anhydrous condition or alternatively, to dry the reaction mixture prior to the reaction. The drying of the reaction mixture can be carried out by heating the reaction mixture to a temperature above C. at atmospheric pressure, while bubbling a gas through the mixture. The temperature should be such as to vaporize the water, and suflicientgas should be admitted to completely sweep the vaporized water out of the reaction mixture. In practice, drying temperatures of from to C. have been found to be satisfactory, and either nitrogen or hydrogen can be used to sweep out the vaporized water with good results. it has also been found desirable to agitate the reaction mixture during the drying step. It will be understood, of course, that the reaction should be conducted throughout in such a way as to maintain anhydrous conditions. Even as little as 2% water has been found to be quite detrimental; therefore, the amount of water should be reduced below 1% by weight of the reaction mixture and preferably below .3% by weight. conditions should be as nearly anhydrous as possible.

The reaction can be carried out at temperatures ranging from to 210 C, although greatly improved results are obtained Within thespecific temperature range of from to 198 C. If desired, the reaction can be carried out in two-stages, with the initial stage at temperature of from 130 to 160 C., and the final stage at the temperatures just specified. However, excellent results have been obtained by carrying out both stages of the reaction within the range from 180 to 198 C.

In one embodiment of this invention, the reaction is carried out in two stages with the reaction mixture being heated in the first stage at a temperature of from 130 to 210 C., and in the second stage at a temperature of from 170 to 210 C. However, the more specific temperature ranges set out above are preferred. in the first stage of in other words, the

6 the reaction, it is preferred to hold the ammonia formed in the reaction within the reaction zone while maintaining the reaction zone under an elevated pressure. In the second stage of the reaction, it is preferred to remove the ammonia formed in the reaction from the reaction zone and to maintain a substantially atmospheric pressure in the reaction zone. More specifically, in the first stage of the reaction pressures of from l to 500 p. s. i. g. are satisfactory, while in the second stage of the reaction a pressure below p. s. i. g. is desirable. In practicing the invention in accordance with this two-stage process, the reactant and catalyst are charged to a pressure reaction vessel, and if water is present, they are subjected to a preliminary drying step as described above. Thereafter hydrogen is introduced without venting ammonia and an elevated pressure is maintained during the first stage of the reaction. Samples of the reaction mixture are Withdrawn periodically and analyzed for the total amine content, that is, the combined percent by weight of primary and secondary amines. When the total amine content has reached a substantially constant value, the pressure is reduced and ammonia is continuously removed from the reaction zone. The reaction can also be carried out by employing alternate cycles of venting and hydrogenation after the amine content has reached a constant value.

It has been discovered that the presence of hydroxides in the reaction mixture is undesirable and tends to decrease the yield. The presence of metallic soaps is also undesirable for this reason. Therefore, the reaction mixture should be maintained substantially free of hydroxides and metallic soaps. Since the nitrile and amine reactants will usually contain a small percentage of free fatty acids, the introduction of an alkali or alkaline earth metal hydroxide is doubly undesirable, because not only does it introduce a hydroxide but also forms soaps by the reaction of the hydroxide with the free fatty acids.

It has also been discovered that the color of the secondary amine product can be greatly improved by bleaching it in situ during the course of the reaction. Furthermore, this bleaching cannot be accomplished after the reaction has been completed. Therefore, it is preferred to incorporate a small amount of an inert bleaching adsorbent in the reaction mixture, such as activated carbon or an adsorbent clay. In practice, from 1 to 3% of such adsorbent has been found to be satisfactory.

This invention is further illustrated by the following specific examples.

Example 1 11,000 pounds of coconitrile was charged to an agitated hydrogenation converter along with 150 pounds of Raney nickel catalyst (50% nickel). The reaction was heated in a slow stream of hydrogen to 130 C. and held there for one hour to drive oil moisture. The hydrogen pressure was then raised to l75185 pounds and the temperature was not allowed to exceed 136 C. until the total amine had reached 80%. After this time the temperature was allowed to go around 178 C. Alternate cycles of venting and hydrogenation were made until the end of the reaction. The reaction was terminated at the end of fourteen hours with a product that analyzed as 93% secondary amine and 4.8% primary amine.

Example II 11,000 pounds of tallow nitrile and 150 pounds of Raney nickel catalyst (50% nickel) were charged to a hydrogenation autoclave equipped with an agitator. The reaction was then heated to 130 C. accompanied by agitation and a slow stream of hydrogen to help in driving off moisture. At the end of one hour the hydrogen pressure was raised to 200 and the temperature held at 130 C. maximum until the total amine had reached 90% (two hours). At this time the temperature was allowed to rise to ISO-185 C. As in Example I, alternate cycles of hydrogenation and venting were made throughout the run are 1,399

until the reaction was complete. The final product analyzed 91% secondary tuning and 2.6% primary amine.

Example 111 11,000 pounds of tallow nitrile and catalyst were charged to the hydrogenator and dried as in Example II. At the end of the drying period the reaction was heated to 195 C. as soon as possible instead of holding it below 140 C. until the total amine reached -85% as in Examples I and II. The reaction was continued with alternate cycles of hydrogenation and venting as previously. The final product had an analysis of 90.6% secondary amine and 3.9% primary amine.

Example IV The hydrogenation unit was charged with 11,000 pounds of tallow nitrile and 150 pounds of 50% Raney nickel catalyst. The reaction was conducted as in Example III. The product analyzed 92.2% secondary amine and 3.9% primary amine.

Example V The hydrogenation unit was charged with 11,000 pounds of coconitrile and 150 pounds of Raney nickel catalyst (50% nickel). The reaction was carried out as in Example HI. The product analyzed 92.2% secondary amine and 3.9% primary amine.

Example VI The hydrogenation unit was charged with 11,000 pounds of coconitrile and 150 pounds of Raney nickel catalyst (50% nickel). The reaction was carried out as in Example III. The product analyzed 87.3% secondary amine and 3.4% primary amine.

In the preceding examples, the primary reactions occurring to produce the desired products can be represented by the following two equations, wherein R is a hydrocarbon chain:

While in the foregoing specification this invention has been described by setting forth specific details of preferred embodiments thereof, it will be apparent to those skilled in the art that many of the specific details and embodiments set forth can be varied considerably without departing from the broad idea of the invention.

I claim:

1. A process for the production of secondary ahphatic hydrocarbon amines which comprises preheating a mixture of a reactant selected from the group consisting of aliphatic hydrocarbon nitriles and amines having from 8 to 22 carbon atoms and mixtures of said nitriles and amines, and a hydrogenation catalyst to remove substantially all of the water therefrom; contacting said mixture under elevated pressure with hydrogen while maintaining within the hydrogenation zone the ammonia formed until the total amine content becomes substantially constant; venting the ammonia formed from the hydrogenation zone; and thereafter continuing said hydrogenation reaction to substantial completion.

2. A process according to claim 1 wherein the reactants are coco nitriles.

3. A process according to claim 1 wherein the reactants are tallow nitriles.

4. A process for the production of secondary aliphatic hydrocarbon amines which comprises preheating to a temperature in the range of to C. a mixture of an aliphatic hydrocarbon nitrile containing from 8 to 22 carbon atoms and a hydrogenation catalyst while bubbling a gas therethrough selected from the group consisting of inert gases andhydrogen, to remove substantially all of the moisture from said mixture; contacting said mixture at a pressure in the range of 100 to 500 p. s. i. g. and a temperature in the range of 130 to 160 C. with hydrogen while maintaining within the hydrogenation zone the ammonia formed until the total amine content becomes substantially constant; venting the ammonia formed from the hydrogenation zone; and thereafter continuing said hydrogenation reaction to substantial completion.

5. A process for the production of secondary aliphatic hydrocarbon amines which comprises preheating to a temperature in the range of 120 to 150 C. a mixture of an aliphatic hydrocarbon nitrile containing from 8 to 22 carbon atoms and a Raney nickel catalyst in an amount ranging from 0.4 to 3 weight percent based on the weight of nickel in said catalyst compared to the total Weight of nitrile, while bubbling hydrogen therethrough to remove substantially all of the moisture from said mixture; further contacting said mixture at a pressure in the range of 100 to 500 p. s. i. g. and at a temperature of 130 to 160 C. with hydrogen while maintaining within the hydrogenation zone the ammonia formed until the total amine content becomes substantially constant within the range of 75 to 90%; venting the ammonia formed from the hydrogenation zone; and thereafter continuing said hydrogenation reaction by alternate hydrogenation and venting until the reaction is substantially complete.

6. A process for the production of secondary aliphatic hydrocarbon amines which comprises preheating a mixture of an aliphatic hydrocarbon nitrile containing from 8 to 22 carbon atoms and a Raney nickel catalyst in an amount ranging from 0.4 to 3 weight percent based on the weight of nickel in said catalyst compared to the total weight of nitrile, while bubbling hydrogen therethrough to remove substantially all of the moisture therefrom; further contacting said mixture with hydrogen at a pressure in the range of 175 to 190 p. s. i. g. and a temperature of about 135 C. while maintaining within the hydrogenation zone the ammonia formed until the total amine content becomes substantially constant at about to venting the ammonia formed from the hydrogenation zone; and thereafter continuing said hydrogenation reaction at a temperature in the range of to 198 C., alternately hydrogenating and venting, until said reaction is substantially complete.

7. A process according to claim 6 wherein there is incorporated into the reaction mixture an inert bleaching agent.

8. A process according to claim 7 wherein there is incorporated into the reaction mixture from 1 to 3 weight percent of finely divided activated charcoal.

9. A process according to claim 7 wherein there is incorporated into the reaction mixture from 1 to 3 weight percent of an adsorbent clay.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF SECONDARY ALIPHATIC HYDROCARBON AMINES WHICH COMPRISES PREHEATING A MIXTURE OF A REACTANT SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC HYDROCARBON NITRILES AND AMINES HAVING FROM 8 TO 22 CARBON ATOMS AND MIXTURES OF SAID NITRILES AND AMINES, AND A HYDROGENATION CATALYST TO REMOVE SUBSTANTIALLY ALL OF THE WATER THEREFROM; CONTACTING SAID MIXTURE UNDER ELEVATED PRESSURE WITH HYDROGEN WHILE MAINTAINING WITHIN THE HYDROGENATION ZONE THE AMMONIA FORMED UNTIL THE TOTAL AMINE CONTENT BECOMES SUBSTANTIALLY CONSTANT; VENTING THE AMMONIA FORMED FROM THE HYDROGENATION ZONE; AND THEREAFTER CONTINUING SAID HYDROGENATION REACTION TO SUBSTANTIAL COMPLETION.