Patented Mar. 16, 1948 2,438,091 UNITED STATES PATENT OFFICE 2,438,091 ASPARTICAC DSTERS AND TER PRE PABATON Kathryn L. Lynch, Stamford, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application September 6, 1943, Serial No. 50117 5 Claims, (C. 260-482) 2 This invention relates to N-substituted aspartic phobic properties sufficiently strong to Orient the acid esters and to their preparation. The inven molecule at an oil-water interface. In order that tion includes the new compounds themselves, the this condition may be met the total number of novel method by which they are prepared and carbon atoms in R2, R3 and R4 should be at least also compositions containing them. twelve. I have found that primary alkyl and primary The compounds vary in physical character from alkoxyalkyl amines may be caused to react with oily liquids to hard wax-like materials. The con certain maleic acid esters to be hereinafter de pounds are in general colorless but some are pale scribed to yield N-alkyl and N-alkoxyalkyl sub yellow to light brown in color. Those compounds stituted aspartic acid esters having the gen O of low molecular weight are soluble in water and eral formula: very readily soluble in aqueous solutions of acids. R. O. As the length of the substituent chains increases, however, the compounds become more difficultly soluble in water but may be dissolved in aqueous 5 acids, mineral spirits, alcohols, and other organic h k, ) Solvents. Although it would be expected in a reaction in in which R and R1 are members of the group con volving a maleic acid ester with a primary amine sisting of hydrogen and alkyl radicals of from 1 that the ester groups would be hydrolyzed with the to 3 carbon atoms, R2 and R3 are alkyl radicals of 20 formation of amides, I have found that by fol from 1 to 18 carbon atoms and R4 is a member of lowing the procedure to be described hereinafter the group consisting of alkyl and alkoxyalkyl rad the primary amine may be caused to react at the icals. The alkyl radicals, R2 and R3, may be in double bond of the maleic acid ester to form N terrupted, terminated or substituted with various substituted aspartic acid esters directly in sub types and kinds of substituent groups. 25 stantially quantitative yield. As a result of my . Many of the compounds of this class, particu studies of the reaction I have discovered that when larly those which have in the R2, R3 and R4 posi a primary amine is mixed with a maleic acid tions a long chain hydrophobe group and a short ester of the type described hereinafter a number chain group are cationically surface active in the of different reactions may occur simultaneously form of their acid salts and possess wetting, foam 30 at different rates depending upon the temperature ing and detergent properties. The hydrophobe of the reaction mass and the relative proportions group may be a long chain alkyl or alkoxyalkyl of the reactants. At temperatures within the group of about six or more carbon atoms and may range of 10-100° C. the principal reaction in be positioned at any of R2, R3 or R4 in the general volves the addition of the primary amine at the formula above. 35 double bond of the maleic acid ester with the Although the compounds of the present inven formation of N-substituted aspartic acid esters. tion may be used in the form of their acid salts A second and concurrent reaction involves the as surface active agents, they are of greatest conversion of unreacted maleic acid ester to the value as intermediates in the preparation of a corresponding fumaric acid ester. The third, a class of Superior Wetting agents and detergents 40 much slower reaction, involves the reaction of the described and claimed in my copending applica primary amine with the fumaric acid ester. A tion, Serial No. 501,851, filed September 10, 1943. fourth reaction involves the reaction of the as When used as intermediates in this process at partic acid ester with itself to form undesirable least one of the groupS R2, R3 or R4 should be a by-products such as diketo piperazine derivatives. hydrophobe alkyl or alkoxyalkyl radical having 5 This latter reaction occurs principally at ele four or more carbon atoms. Of course, One or two wated temperatures and upon heating the reac of the groups R2, R3 or R4 may be a short chain tion mixture for long periods of time. alkyl or alkoxyalkyl radical provided that the During the early stages of the reaction the addi requisite number of carbon atoms is present in the tion of the primary amine to the maleic acid ester molecule to give a portion thereof having hydro- 50 is rapid, an approximately 50% yield of diethyl 2,488,091 3 4. N-Octadecyl aspartate being obtained in 30 min perature of the reaction mixture. The reaction . utes upon reacting octadecyl amine with diethy mixture is then allowed to stand until the reaction maleate at 20° C. At higher temperatures the is substantially complete. Towards the end of the reaction proceeds even faster. The conversion of reaction period the reactants may be heated up the maleate ester to the fumarate ester is also to about 100° C. for a short time to hasten con fairly rapid during the early stages of the reac pletion of the reaction. As stated before, how tion. Since as stated before the reaction of the ever, use of high temperatures for extended pe primary amine with the fumarate ester is quite riods of time is to be avoided if a product of high slow, it will be scen that the evenual completion purity is to be obtained. of the reaction to form N-substituted aspartic O The maleic acid esters which may be employed acid esters depends to a considerable extent upon in the reaction described herein are those having - the amount of fumarate ester formed. As high the general formula: temperatures favor the conversion of the maleic acid ester to the fumaric acid ester more than they favor the reaction of the primary amine with 15 maleic acid ester it is desirable that the reaction be conducted at low temperatures, preferably less than about 50 C., in the early stages of the re in which R and R1 are members of the group action. This is desirable in order to secure the consisting of hydrogen and alkyl radicals of from formation of N-substituted aspartic acid esters 20 from the maleic acid ester in as high yields as 1 to 3 carbon atoms, R2 and R3 are alkyl radicals possible, while the maleic acid ester remains as of from 1 to 18 carbon atoms. The alkyl radicals, Such in the reaction mixture. After holding the R2 and Ra, may be interrupted, terminated or sub reaction mixture at relatively low temperatures stituted with various types and kinds of substit until the maleic acid ester has either reacted with 25 uent groupS. Specific examples of the maleic acid the primary amine or has been converted to the esters that may be employed in my invention are corresponding fumaric acid ester, the tempera diethyl maleate, diamyl maleate, dibutyl maleate, ture may be raised thereby allowing the reaction dicapryl maleate, di (methyl amyl) maleate, di of the primary amine and the fumaric acid ester (ethyl hexyl) maleate, di-n-hexyl maleate, di to proceed more rapidly with the formation of 30 decyl maleate, dioctyl ethyl maleate, di-hexyl N-Substituted aspartic acid esters. citraconate, dicapryl pyrocinchonate, di-ethyl Another important factor which enables me to itaconate, hexyl octyl maleate, diglycol maleate, obtain N-Substituted aspartates of high purity dicyclohexyl maleate, di (2 cyclohexyl ethyl) and in good yield relates to the proportions of maleate, and the like. reactants used. I have found that the use of 35 Primary alkyl and primary alkoxyalkyl amines more than the theoretical quantity of primary which may be employed in my process include alkyl or primary alkoxyalkyl amine necessary to those such as butyl amine, amyl amine, octyl react with the maleic acid esters at the double amine, dodecyl amine, Octadecyl amine, methoxy bond position results in the formation of amides propyl amine, ethoxypropyl amine, amoxypropyl through replacement of the ester groups. Ac 40 amine, dodecoxypropyl amine and others of sim cordingly I employ an equal molecular propor ilar character. tion of the maleic acid ester or a slight excess The invention will now be illustrated in greater thereof with each mole of primary amine. detail by means of the following specific examples. From the foregoing it will be seen that my new It should be understood that although these ex method comprises the steps of reacting a primary 45 amples may describe in detail some of the more alkyl amine or a primary alkoxyalkyl amine with specific features of the present invention they are at least a stoichiometric proportion of maleic given primarily by Way of illustration and the acid ester at temperatures not in excess of about invention in its broader aspects in not to be lim 100° C. Preferably I carry out the first phase of ited thereto. the reaction at temperatures not in excess of 50 EXAMPLE about 50° C. until substantially all of the maleic 145 g. (1 mol) dimethyl maleate was added acid ester has reacted with the primary amine to slowly with stirring to a solution of 265 g. (1 mol) yield the corresponding N-substituted aspartic of octadecyl amine in 500 cc.