Patent GB-573154-A (GB)
Title: Improvements in or relating to n-substituted aspartic acid esters and methods of preparing same
Filed: 1943-06-15
Abstract: N-Substituted aspartic acid esters of the general formula <FORM:0573154/IV/1> in which R2 and R3 are alkyl or hydroxyalkyl radicals, being the same or different and R4 is an alkyl radical, are prepared by reacting a primary amine of the formula R4NH2 with at least a molecular equivalent of a maleic acid ester of the formula <FORM:0573154/IV/2> at a temperature not in excess of 100 DEG  C.  It is desirable that the reaction be carried out at a low temperature in the early stages, preferably less than 50 DEG  C. to secure formation of the N-substituted aspartic acid ester from the maleic acid ester whilst it remains as such in the reaction mixture, and then raise the temperature to expedite the reaction between the primary amine and the fumaric acid ester which has been formed from the unreacted maleic ester, to give the N-substituted aspartic acid ester.  The reaction may also be carried out by simply allowing the reaction mixture to stand at room temperature.  It is generally desirable to carry out the reaction in the presence of an organic solvent such as alcohol, mineral spirits, toluene, naphtha, or dioxane.  The reaction is exothermic, so it is generally advisable to add one of the reactants to the other slowly.  Use of high temperatures for a long time is to be avoided, as diketo-piperazines are then obtained, while excess amine gives rise to amide formation.  Specific examples of maleic acid esters are diamyl, dibutyl, dicapryl, di-(methyl amyl), di-(ethyl hexyl), di(n-hexyl)-, di-decyl-, hexyl octyl-, and diglycol-maleates.  Primary alkylamines specified are butylamine, amylamine, octylamine, dodecylamine and octadecylamine.  The products of relatively low molecular weight are easily soluble in water and aqueous acid solutions.  When R2 and R3 are radicals of low molecular weight, the compounds and their acid salts possess wetting, foaming, and detergent properties, but as the length of the substituent chain increases, water solubility decreases though they are soluble in aqueous acids, alcohols and mineral spirits.  In examples: (1) dimethyl maleate and octylamine are reacted to give dimethyl N-octadecyl aspartate; (2) diethyl maleate similarly gives diethyl N-octadecyl aspartate; (3) diglycol maleate and octadecylamine give diglycol N-octadecyl aspartate; (4) di-isopropyl maleate and octadecylamine give di-isopropyl N-octadecyl aspartate; (5) butylamine and di-octyl maleate are reacted and produce a light oil having foaming properties; (6) dimethyl maleate and octyl amine give dimethyl N-octyl aspartate and some dimethyl fumarate.  The Specification as open to inspection under Sect. 91 comprises also the preparation of N-alkoxy alkyl esters of aspartic acid. Thus, esters of the general formula <FORM:0573154/IV/3> wherein R1 represents hydrogen, or an alkyl or aryl radical, R2 is an alkylene or cycloalkylene radical of from 1 to 18 carbon atoms, R3 represents hydrogen, or hydroxyl, cycloalkyl, aryl, alkaryl, alkoxy and oxyalkylol radicals and R4 is an alkyl or alkoxy alkyl radical, and wherein R1, R2 and R3 may be the same or different, are prepared as above by reacting corresponding maleic acid esters with primary alkyl and alkoxy alkyl amines of formula R4NH2.  Additional maleic esters specified are di-hexyl-a -phenyl maleate, di-hexyl-citraconate, dicapryl pyrocinchonate, di-ethyl itaconate, dicyclohexyl maleate, di-(2-cyclohexyl ethyl) maleate, and dibenzyl maleate.  More generally R2 may be -C2H4-,-C8H16-, -C18H35-, <FORM:0573154/IV/4> , or cyclohexyl, and R3 may be <FORM:0573154/IV/5> -OC2H4OH, cyclohexyl, 4-methyl cyclohexyl, phenyl, and p-tolyl, radicals. Other suitable amines are methoxypropyl amine, ethoxypropyl amine, amoxypropyl amine and dodecoxypropylamine.  In a further example, ethoxypropylamine is reacted with diamyl maleate to yield diamyl N-ethoxypropyl aspartate.  This subject-matter does not appear in the Specification as accepted.