Ind. Eng. Chem. Prod. Res. Dev. 1982, 27. 599-600
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Reaction of Dimethylurea and Glyoxal John G. Frlck, Jr.,' and Robert J. Harper, Jr. Southern Regional Research Center,' Post Offlce Box 19687, New Orleans, Louisiana 70179
The reaction of 1,3dimethylurea and glyoxal to form the formaldehyde-freefinishing agent 4,5-dihydroxy-l,3-dimethyl-24midazolidinone was studied using liquid chromatography. Conversion of 70-80 YO was reached in 6 days at 23 "C or in 3.5 h at 59 "C. The reaction was slightly faster and more complete at pH 8 than at lower pH. No other products were noted. Dihydroxydimethylimidazolidinonewas stable under the reaction conditions, but interconversion of isomers did occur.
Introduction The reaction of 1,3-dimethylurea and glyoxal in the absence of strong acid produces 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone(1,3-dimethyl-4,5-dihydroxyethyleneurea) (Figure 1). This product is used as a formaldehyde-free cross-linking agent in textile finishing (Vail and Murphy, 1963; Beachem, 1967). As such there is interest in the reaction to maximize yield and to avoid byproducts that would adversely affect a finishing formulation if not separated from the reaction product. In this work, reaction mixtures of l,&dimethylurea and glyoxal were examined by liquid chromatography to determine the nature of the reaction, optimum conditions, and the number of byproducts. Experimental Section 1,3-Dimethylurea and glyoxal as a 40% solution were reagent grade chemicals obtained from Aldrich Chemical Co. and Kodak Laboratory Chemicals. 4,BDihydroxy1,3-dimethyl-2-imidazolidinonewas prepared in the trans and cis forms (Vail et al., 1965). The trans isomer, mp 135 "C, was prepared by reaction of dimethylurea and glyoxal in concentrated solution for 24 hours at room temperature and recrystallization from ethanol. The cis isomer, mp 125-127 "C, was prepared by reaction for 4 h at room temperature and was used as crystallized from the reaction mixture. Reaction mixtures were prepared as follows. The dimethylurea was dissolved in water to give a 40% (w/w) solution. An equimolar amount of glyoxal in 40% solution was added, and the mixture was adjusted to the desired pH with 10% sodium hydroxide solution. Reactions were allowed to proceed under room conditions (23 "C) with samples removed periodically for testing, or they were run in a water bath at 59 "C for 3.5 h. A t 23 "C, the pH was checked frequently the first day and daily thereafter and readjusted if necessary. A t 59 "C, the pH was checked every half hour. For chromatography, samples from reaction mixtures and 40% solutions of isolated 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone were diluted 1to 10 to give 4% total solute. The diluted samples were filtered through a Millipore 0.45-pm filter before injecting into the chromatograph. The chromatograph was a Waters Associates liquid chromatograph equipped with a pBondapak C18 column and a differential refractive index detector. Chromatograms were made using 10-pL injections of the 4% solutions, water as the mobile phase, 1.0 mL/min flow 'One of the facilities of the Southern Region, Agricultural Research Service, U.S.Department of Agriculture.
rate, and 1 cm/min recorder chart speed.
Results The chromatogram obtained from the reaction mixture of 1,3-dimethylurea and glyoxal after 3.5 hours at 59" and pH 5 is shown in Figure 2. It is typical of the chromatograms obtained. Identification of peaks was made from chromatography of the reagents and dihydroxydimethylimidazolidinone and is as follows: 3.0 min, retention time, glyoxal; 5.0 min, dihydroxydimethylimidazolidinone;6.4 min, dimethylurea; and 7.6 min, dihydroxydimethylimidazolidinone. The two peaks from dihydroxydimethylimidazolidinone were ascribed to the cis and trans isomers from positions of the hydroxy groups (Vail et al., 1965; Frick and Harper, 1982). A freshly prepared solution of trans-dihydroxydimethylimidazolidinonegave a chromatogram with a high peak of 5.0 min retention time and only a trace of a peak at 7.6 min retention time. The peak at 5.0 min retention time, therefore, was ascribed to the trans isomer and the peak at 7.6 min to the cis isomer. As the solution of trans isomer aged, the peak at 5.0 min retention time decreased and the peak at 7.6 min increased. After several days at room temperature, the solution gave chromatograms in which peak heights for the 5.0 and 7.6 min peaks approached a ratio of 10 to 1. A freshly prepared solution of cis-dihydroxydimethylimidazolidinone gave peaks at 5.0 and 7.2 min retention times. Ratio of peak heights was one to 8.3. As this solution aged, the height of the first peak increased, and the height of the second peak decreased. These changes in the chromatograms resulted from solutions of dihydroxydimethylimidazolidinone going toward an equilibrium mixture of cis-trans isomers in which the trans isomer predominated. The sum of peak heights for the peaks at 5.0 and 7.6 min retention times was taken as a measure of dihydroxydimethylimidazolidinone concentration, and the sum in the chromatogram from a solution of the compound that stood 3.5 h at room temperature was taken to represent 100%. Then, the indicated conversion to dihydroxydimethylimidazolidinone in the reaction mixture after 3.5 h at 59 "C was 73% at pH 8 and 71% at pH 5. These values for conversion are essentially identical although less reagents seemed left at pH 5. No peaks for any other product appeared at either pH. The small peaks trailing the signal from glyoxal and the larger peak from dihydroxydimethylimidazolidinone are unexplained but occurred in the chromatogams from the glyoxal reagent alone and from the isolated dihydroxydimethylimidazolidinone. They remained in near constant ratio to the primary peaks and seemed to be artifacts. The glyoxal peak appeared at or
This article not subject to US. Copyright. Published 1982 by the American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 4, 1982
0 It CH,N/'\N I HOCH
CH,
-
I HCOH
Figure 1. 4,5-Dihydroxy-1,3-dimethyl-2-imidazolidinone.
1 BO TIME (HOURS)
I 120
I 160
Figure 3. Conversion of reagents to dihydroxydimethylimidazolidinone at 23 "C.
E E T E N T I O N TIME ( m l n )
Figure 2. Chromatogram of dimethylurea-glyoxal reaction mixture after 3.5 h at 59 "C.
near the retention time for an unretained substance. This peak contained all forms of glyoxal in the aqueous solution and, in the chromatograms of reaction mixtures, may include a small peak from a product that has a similar small retention time. Dihydroxydimethylimidazolidinonewas stable under the reaction conditions. A 40% solution of the compound was heated to 59 "C for 3.5 h and gave only the same two peaks. Sum of peak heights changed less than 3% on heating. Reactions at 23 "C and pH 5,7, and 8 also gave only the same four peaks. The relationships of conversion and reaction time at 23% are shown in Figure 3. Conversion was calculated again by comparison with a chromatogram from a dihydroxydimethylimidazolidinone solution of 40 % initial concentration. Conversion reached 70-8070 in 6 days, but there was little change after 3 days. The reaction between glyoxal and dimethylurea was not reaching an equilibrium because dihydroxydimethylimidazolidinone, in a separate experiment, remained stable in solution. This stability persisted in the presence of added dimethylurea and glyoxal; chromatograms from dihydroxydimethylimidazolidinone solution with small amounts of dimethylurea and glyoxal showed no decrease in dihydroxydimethylimidazolidinone or increase in dimethylurea or glyoxal concentrations on standing for 2 days. The reason for termination or drastic retardation of the reaction is not known. Possibly the remaining glyoxal was in an unreactive or only slightly reactive form (Union Carbide, 1967). Reaction at pH 8 was slightly faster and more complete than at pH 5 or 7. Extending the reaction to higher pH is an unlikely possibility because glyoxal can tolerate little
more than pH 8 without undergoing internal oxidationreduction (Union Carbide, 1967). Below pH 5, the reaction would likely lead to condensates such 1,3,4,6-tetramethyltetrahydroimidazo[4,5-d ]imidazole-2,5(1H,3H)dione (Nematollahiand Ketcham, 1963). It was noted that the reaction mixture at pH 8 tended to develop more color than those at lower pH. Also, constant adjustment was needed to maintain pH 8 while little adjustment was needed to maintain lower pH values. Summary In following the reaction of 1,3-dimethylureaand glyoxal by liquid chromatography, it was found that conversion to 4,5-dihydroxy-1,3-dimethyl-2-imidaolidinone reached 70-8070 in 3 to 6 days at 23 "C or in 3.5 h at 59 "C. Reaction was slightly faster and more complete above pH 7. The reaction was not reversible although reagents remained after 6 days at 23 "C. It probably continued very slowly. Dihydroxydimethylimidazolidinone was stable under the reaction conditions although interconversion of isomers did occur. No other product was noted. Acknowledgment The authors thank J. E. Helffrich for assistance in the experimental procedures and G. I. Pittman for drawings of the figures. Mention of companies or commerical products does not imply recommendation or endorsement by the US.Department of Agriculture over others not mentioned. Literature Cited Beachem, M. T. US. Patent 3304312, 1967. Flick. J. G., Jr.; Harper, R. J., Jr. Ind. Eng. Chem. Prod. Res. Dev. 1962, 21, 1-4. Nematollahi, J.; Ketcham, R. J. Or#. Chem. 1963, 28, 2378-2380. Union Carbide Corporation "General Chemistry of Olyoxal"; New York, NY, 1967. Vail. S. L.; Barker, R. H.; Mennitt, P. G. J . Org. Chem. 1965, 30, 2179-2182. Vail. S. L.: Murphy, P. J., Jr. U.S. Patent 3 112 156, 1963.
Received for review January 18, 1982 Accepted June 7, 1982
