PATENT OFFICE 2,943.4 PRE PARATION of N-SUBSTITUTED ALKYO, AM NES Robert W
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Patented Mar. 19, 1940 2,194,314 UNITED STATES PATENT OFFICE 2,943.4 PRE PARATION OF N-SUBSTITUTED ALKYO, AM NES Robert W. Maxwell, Wilmington, Del, assignor to E. I. du Pont de Nemours & Company, Wil mington, Del, a corporation of Delaware Application July 16, 1938, No DrawingSeria No. 29,603 11 Claims. (CI. 260-584) sure of 2000 pounds per square inch, using 6% This invention relates to the manufacture of Raney nickel catalyst based on the weight of the N-alkyl-alkanolamines, and especially to the condensation product. The reaction required preparation of N-dialkyl alkanolamines. More about 20 minutes. The catalyst was filtered off, specifically the invention relates to the prepara the filtrate washed well with methanol, and the 5 tion of N-methyl ethanolamines. methanol removed by the addition of benzene and Heretofore Such compounds as, for example, distillation as a benzene-methanol binary boil N-methyl ethanolamine have been prepared by ing at about 56 C. The product was then dis reacting methyl amine with ethylene oxide at tilled. It consisted of approximately equimolar 40' to 60° C. in methanol solution. The disad proportions of N-methyl aminoethanol and 0 . O vantage of such a process is that the reaction . N-dimethyl aminoethanol. The yield of amino requires very careful control if the production of ethanols based on ethanolamine was approxi high molecular weight ether alcohols is to be mately 85%. avoided. The production of such high molecular If it is desired to make only N-dimethyl amino weight ether alcohols reduces the yield of desired ethanol, the N-methylaminoethanol can be con 5 s N-methyl ethanolamine and further increases costs by consumption of ethylene oxide in the densed with another mol of formaldehyde and production of undesired end products. hydrogenated. A more direct route to N-dimethyl This invention has as its object the preparation aminoethanol is described in Example 2. of N-alkyl alkanolamines by a new and improved Eacample 2 20 20 method. Another object is the preparation of Ninety parts of paraformaldehyde were added N-dialkyl alkanolamines by an improved process. in Small portions to 122 parts of monoethanol A further object is to provide a method which amine. Much heat was developed. The mixture. produces N-alkyl alkanolamine with minimum of Was then heated on the steam bath to complete side reaction products. Other objects will appear solution of the paraformaldehyde after which 100 25 25 hereinafter. parts of benzene Were added and the Water of These objects are accomplished by the use of condensation removed. This amounted to 54 the invention described herein, which invention part.S. The benzene was then distilled off and comprises condensing an aldehyde with an amino 30 more parts of paraformaldehyde added, and alcohol in which the amino nitrogen atom has at the mixture Warmed gently on a steam bath until 30 30 least one functional hydrogen atom attached clear. The mixture was then hydrogenated at thereto and Said nitrogen atom is attached to a 70° C. under 2000 pounds per square inch pres carbon atom other than a carbon to which a sure, using 6% Raney nickel catalyst based on hydroxyl group is attached, and catalytically the weight of the condensation product. The re hydrogenating the condensation product to give action required three hours. The product, which 35 an N-alkyl alkanolamine. was a blue-green solution, was filtered to re In Order to illustrate Specifically the invention, move catalyst and the filtrate Washed well with the following examples are given. These ex methanol. Fifty parts of benzene were then amples, however, are merely for the purpose of added and the methanol removed as a benzene illustration and do not in any way limit said in methanol binary, followed by distillation of the 40 40 Wention. Water formed in the reaction which amounted to Eacample 1 approximately 18 parts by weight. The product Three mols of paraformaldehyde were con was then distilled and was found to consist almost densed with two mols of monoethanolamine by completely of N-dimethyl aminoethanol, the yield adding the formaldehyde with the amine in small being approximately 85%. 45 45 portions. Benzene was then added and the water In carrying out the preparation of N-dimethyl of condensation distilled off. Three mols of water aminoethanol in one step, it has been found were obtained. Thus it was concluded that the necessary to use low temperatures in the hydro product probably had the following composition: genation reaction; i. e., below 80° C., and to re move all Water of condensation in order to obtain 50 CH-CH2 CH-CH N /. good yields. Where the temperature is allowed N-CH-N to rise above 80, large proportions of tar are / N formed and the yield is low. Likewise, where 2 O-CF CH-O mols of paraformaldehyde are mixed with one The remaining benzene was then distilled off and 55 the residue hydrogenated at 80° C. under a pres of monoethanolamine followed by hydrogenation 2 Y 2,194,814 without water removal, yields are low and the a definite advance over the art, since it makes proportion of tar formed is high. it possible to synthesize this important class of Carple 3 compounds from low cost, readily available re Two mols of paraformaldehyde were mixed agents. with two mols of diethanolamine. Very little The hydrogenated product, after removal of heat was given off due to the condensation, and the catalyst, is isolated usually by distillation. it was necessary to heat the mixture upon the In forming the aldehydeamine condensation steam bath in order completely to dissolve the product, it is usually sufficient to mix the amine paraformaldehyde. The mixture was then treat with the aldehyde in the desired molar portions. ed with about one-third of its weight of benzene Condensation generally takes place Spontaneous O and the water of condensation distilled out. This ly. If it is desired, small amounts of alkaline amounted to slightly more than two molds (the catalysts may be used, but their use does not in excess probably being due to water present in the general have any particular advantage. The s reagent). The mixture was then hydrogenated crude condensation mixture can then be hydro at 85° under 2500 pounds per square inch pressure genated. However, it is preferable that the water using 6%. Raney nickel catalyst, based on the of condensation be first removed. This is easily weight of the condensation product. The reac accomplished by distillation with a water-immis tion proceeded smoothly and rapidly. The reac cible liquid, such as benzene or toluene. This tion mixture which was blue-green in color was water-immiscible liquid may be added prior to or filtered to remove catalyst and then distilled. during condensation or it may be added after 20 The yield of N-methyl diethanolamine was 93%. the condensation reaction has taken place. Fol In general, it has been found that reactions a lowing the removal of the water, the condensa involving diethanolamine go more Smoothly than tion product may be further purified by distilla tion or other suitable means; however, Such ad those in which monoethanolamine is used. ditional purification is by no means necessary. Eacample 4 The amines which can be used may be any One mol of isobutyraldehyde was mixed with primary or secondary amine containing a hydrox one mol of diethanolamine. Practically no heat yl group attached to a carbon atom which is di was generated. An equivalent weight of benzene rectly linked to the carbon atom to which the was then added and the water of condensation amino nitrogen is attached. Such compounds, 30 distilled out as a binary with the benzene. The for example, are monoethanolamine, diethanola remaining benzene was then removed and the mine, monopropanolamine, dipropanolamine, N mixture hydrogenated using 4%. Raney nickel methyl ethanolamine, N-methyl propanolamine, 35 catalyst, based on the weight of condensation N-decyl ethanolamine, N-methyl isobutanola product, at a pressure of 2500 pounds per Square mine, cyclohexanolamine, N-acetyl aminoethanol, 35 inch, and a temperature of 90°. The catalyst N-stearyl aminopropanol, etc. In general, how was filtered off, and the product distilled. The ever, the ethanolamines are most satisfactory for yield was 90% of N-isobutyl-diethanolamine. the reaction, because of the great ease with which A particularly good way of making N-dimethyl they condense with aldehydes. aminoethanol consists in condensing one mol of The term 'alkanolamine' is intended to in formaldehyde with one mol of monoethanola elude alkanolamines in which the hydroxyl is mine, followed by removal of water and catalytic attached to a carbon atom which is at least one hydrogenation in the usual manner. The crude carbon removed from the carbon atom to which reaction mixture contains approximately equi the amino nitrogen is attached. The term is molar proportions of monoethanolamine, N also intended to include those alkanolamines in monomethyl-ethanolamine, and N - dimethyl which one, but not both, of the amino hydrogens 45 ethanolamine. Using these proportions, tar for is replaced by methyl, ethyl, phenyl, acyl groups, mation is at a minimum and yields are especially etc. high. In the practice of this invention a preformed The exact mechanism of the reactions involved oxazolidine condensation product derived from in the alkylation of alkanolamines by the process a wide range of aldehydes may be used. Broad described herein is not definitely known but it is ly, oxazolidine derivatives made from all alde believed, that since in the reaction between for hydes are suitable. However, oxazolidine com SS maldehyde and the alkanolamine water is split pounds derived from aliphatic aldehydes are off, that the condensation involves the formation preferred, particularly those derived from simple of cyclic compounds of the oxazolidine type which aldehydes such as isobutyraldehyde and formal in the hydrogenation step open to form the de dehyde.