PREPARATION OF POLY-GLYCOLAMINES G E O R G E P. SPERANZA, S H E R M A N
D. LESESNE, AND
E R N E S T L. Y E A K E Y
Jefferson Chemical Co., Inc., Austin, T e x .
Oxyethylene homologs of monoethanolamine, H ~ N ( C H Z C H ~ O ) , Hwere , prepared b y oxyethylation of Schiff base from modoethanolamine and ethyl amyl ketone, using sodium as catalyst. Heating 2 6 4 grams of monoethanolamine with 385 grams of ethyl amyl ketone and 100 ml. of benzene under reflux with water removal yieldbd 402 grams (78%) of Schiff base (boiling range, 1 2 4 - 5 " C./25 mm.). Addition of 3.9 grams of sodamide to 171 grams of Schiff base, with NH3 allowed to escape, followed b y reaction with 430 grams df ethylene oxide a t 90" C. and 50 p.s.i., yielded 4 3 0 grams of polyethyleneglycolamine-500,87% primary amine. Propylene oxide yielded a water-insoluble amine. Schiff bases from 2 - ( 2 -
hydroxyethoxy)ethylamine and ethyl amyl ketone were prepared, but on ethoxylation gave best results only with sodium among catalysts tested. Monoethanolamine with an equimolar quantity of N o and ethylene oxide yielded polyglycolamine with 75% primary amine content.
OXYETHYLENE homologs of monoethanolamine
(III), or polyglycolamines. are readily obtained by reaction of ethylene oxide with Schiff bases (I) prepared from monoethanolamine and selected ketones.
Experimental
Preparation of Schiff Base. A I-liter three-necked flask. equipped with a stirrer. a thermometer, and a vacuumjacketed distillation column 2.5 cm. in diameter filled to a 25-
I
I1
I H
I11
HyN(CHaCHz0) H n+'
+
R\ C=O -R,/
,-(
Hz0
R\ C=N(CH2CHZO) H
R !/
Sodium is a selective catalyst, as involvement of the tautomeric oxazolidine (11), reported to react preferentially under other conditions (3. 4 ) , is evidently slight. T h e preparation of polyglycolamines of higher molecular weight is of particular interest, the lower members of the series, n = 1, 2, being known (5. 6). Equally good results are obtained when propylene oxide is substituted for ethylene oxide. T h e Schiff base is prepared by heating monoethanolamine with the ketone and a n azeotroping agent to facilitate the removal of the water formed in condensation. Ethyl amyl ketone, a particularly good choice, reacts smoothly with the amine, and its low solttbility in water favors recovery in the final hydro!ysis step. The Schiff base is preferably distilled and used without prolonged storage. T h e sodium required for the ethoxylation step is conveniently introduced as sodamide, which reacts with the Schiff base with liberation of ammonia. Products with a satisfactory primary amine content as determined by Van Slyke analyris are obtained using 0.1 to 0.2 mole of catalyst per mole of Schiff base. 314
l&EC
PRODUCT RESEARCH A N D DEVELOPMENT
n+i
cm. height with stainless steel packing on which were mounted a Dean-Stark water trap and a condenser, was charged with 385 grams (3 moles) of ethyl amyl ketone (Shell Chemical Co.), 264 grams of monoethanolamine (4.3 moles). and 100 mi. of benzene. T h e charge was heated to boiling under reflux until collection of water in the trap slowed. Approximately 69 grams of aqueous layer containing some amine was obtained. Distillation was then continued ivith total distillate take-off until the temperature of the flask contents reached 182' C. After cooling to 90' C.. vacuum was applied cautiously until distillation a t 25 mm. of Hg \vas possible. A small forerun boilin a t 26' to 124' C. and containing 6 2 7 , Schiff base and 28# ketone was obtained, followed by 402 grams (78y0 yield) of the Schiff base at 124' to 125' C. The residue weighed 19 grams. Preparition of Polyethyleneglycolamine-500. A 1-liter, stainless steel stirred laboratorv autoclave (Autoclave Engineers. Inc., Easton, Pa.) was charged with 1'1 grams (1 muole) of distilled Schiff base. A total of 3.9 grams of sodamide was added in small portions while a stream of nitrogen was passed through the charge to purge the evolved ammonia. The autoclave was then closed and flushed twice by applying vacuum 'and admitting nitrogen. Finally, the pressure was reduced to 10 mm. of H g and the charge heated to 90" C. with stirring. Ethylene oxide was then introduced a s
Table 1.
Polyglycolamines from Schiff Base of Monoethanolamine and Ethyl Amyl Ketone
Mole
Schz'f Base
Equiualmt Weight Found Theory
Ethylene
0.5 0-2 0.1
535 1072 516
500 1000 500
98 96 88
0.9
1210 532 593
1000 500 500
99 85 76
Propylene
0.2 0,l
Table II.
5
Primary
Alkylene Oxide
~
~
%
Mole Catalyst/ Mole Schz'j Base
Catalyst j
~
~ , None BFa NaNH2
Polyglycolaminc Primary A mine Content, %a
14 23 93 98 63 91 46 89
0.01
0.1 0.4 0.04 0.2 0.01 0.1
NaH Na B y Van Slyke analysis.
Properties of Schiff Bases from Diglycolamine and Monoethanolamine
Amine
Ca~bonylCompound
B.P., ' C . / M m . Hg
DGA DG.4 DGA DGA DGA MEA ME.4
Diethyl ketone Methyl isobutyl ketone Ethyl amyl ketone Isobutyraldehyde 2-Ethylhexaldehyde Ethyl amyl ketone Diethyl ketone
113/5 121/5 115/0.5 99/5 138/5 84/3 76/30
Molar refraction.
Table 111. Preparation of Polyethyleneglycolamine-506 Using Schiff Base from Diglycolamine and Ethyl A m y l Ketone
MrD4
DZi 0.9637 0,9657 0.9366 0.9636 0.9215 0.9040 0.9380
For Scht'f-base structure; values used: H = 1. I , C = 2.42, N =
liquid from a charge tank through a flowmeter. The flow was regulated so as not to exceed a pressure of 50 p.s.i. while the temperature was maintained a t 90' to 100' C. by cooling. Addition of the ethylene oxide (430 grams, 9.8 moles) required 2 . 5 hours and heating a t 100' C. was continued for an additional 45 minutes. After the charge had been cooled to 40' C., vacuum was applied and held a t 10 mm. of Hg for 30 minutes while the charge was stirred to remove any unreacted ethylene oxide. The catalyst was then neutralized by adding 5 grams of sulfuric acid in 300 ml. of water. The contents of the autoclave were finally discharged and transferred to a 1-liter stirred flask equipped for distillation. O n heating, water and ethyl amyl ketone codistilled. When the temperature of the charge reached 140' C., the pressure was reduced to 5 mm. of Hg to remove remaining water. The product was then filtered while hot. The yield was 430 grams. Estimated equivalent weight from titration of amine with standard acid was 516, the corrected hydroxyl number was 125, and the primary amine content was 1.75 meq. per gram (calculated, 2.0). Substitution of propylene oxide for ethylene oxide yielded a similar but water-insoluble polyglycolamine.
Discussion of Results
Table I summarizes the preparation of a group of polyglycolamines by the procedure described, using varying amounts of catalyst. The primary amine content rose with increased amounts of sodamide used. Product color ranged from light yellow to amber. While protection of the amino group of monoethanolamine by forming the Schiff base is preferable, the polyglycolamines can be prepared directly from monoethanolamine, but nearly molar equivalent amounts of sodium catalyst must be used. Using 1 mole of sodium, 1 mole of monoethanolamine, and diethylene glycol dimethyl ether (DIGLYME) as solvent, ethoxylation typically yielded a polyglycolamine with 75y0 primary amine content. With less sodium, secondary and tertiary amine content increased greatly.
0 bsd. 49.27 54.25 63.68 44,79 63.56 51.90 36.84
ni0
1 ,4625 1.4601 1 ,4636 1 ,4548 1 ,4563 1 ,4600 1 ,4475 4.10, 4 = 1.53.
Calcd.
49.83 54,45 63.69 45.22 63,70 53.05 39,07
Schiff bases from monoethanolamine have been shown to be largely in the oxazolidine form ( 7 ) . It was of interest to use 2-(2-hydroxyethoxy)ethylamine, or diglycolamine, in preparing polyglycolamines. Schiff bases derived from this amine would not exist in the cyclic tautomeric form. Ethyl amyl ketone and other ketones condensed readily with diglycolamine, and distilled Schiff bases were obtained in 70 to 85% yields. Agreement of the observed and calculated molar refractions supported the single assumed structure (Table 11). NH absorption in the near-infrared, typical of oxazolidines, was absent. Surprisingly, the results obtained on ethoxylation of the Schiff base indicated little advantage. The primary amine content of the polyglycolamine was high when liberal amounts of catalyst were used, but drifted lower when catalyst was decreased (Table 111). Several catalysts were employed and the general selectivity of sodium in various forms is apparent. The low molecular weight polyethyleneglycolamines are of interest for simultaneous sweetening and dehydration of natural or refinery gas streams (2). Removal of carbon dioxide and hydrogen sulfide is reported to be highly efficient, and regeneration losses are low because of the high boiling points of the amines. The polypropyleneglycolamines become increasingly less soluble in water above a molecular weight of 400. The higher polyethyleneglycolamines are all water-soluble. Both types are useful for synthesizing surface active agents. literature Cited (1) Bergmann: E. D., Gil-Av: E., Pinchas, S., J . A m . Chem. Soc.
75. 358 11953). (2) Bloom,' C. L., Riesenfeld. F. C. (to Fluor Corp.), E. S. Patent 2,712,978 (July 12, 1955). (3) Carnes, J. (to American Cyanamid Co.), Ibtd.. 2,571,985
(Oct. 16. 1951).
(4) Ibzd.. 2,629,740 (Feb. 24, 1953). (5) Dickey. J. B., McNally, J . G. (to Tennessee Eastman Co.). Zbzd.. 2,412,209 (Dec. 10. 1946). (6) Lange, R., Wahl, H., Bull. Soc. Chtm. France 1951, p. 340. RECEIVED for review July 27, 1964 ACCEPTEDOctober 5, 1964
VOL: 3
NO:
4 DECEMBER 1964
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