United States Patent (19) (11 3,959,371 Gavlin et al. (45) May 25, 1976

54 PROCESS FOR THE PURIFICATION OF 2,953,503 9/1960 Freure ...... 203/69X N,N-DIMETHYLACETAMIDE 75 Inventors: Gilbert Gavlin, Lincolnwood; Abid Primary Examiner-James H. Tayman, Jr. Hashim Bengali, Chicago, both of Attorney, Agent, or Firm-John L. Hutchinson II. 57 ABSTRACT (73) Assignee: Custom Organics, Inc., Chicago, Ill. The present invention relates to the recovery of N,N- dimethylacetamide from a mixture containing N,N- (22 Filed: Oct. 8, 1974 dimethylacetamide and . Potassium hydrox 21 Appl. No.: 513,106 ide is added to the mixture to neutralize the acetic acid and form potassium acetate having a low solubil 52 U.S. Cl...... 260/561 R; 203/67; ity in N,N-dimethylacetamide and a high affinity for 203/69; 260/561 R; 203/37 water. The water concentration is adjusted to a de (51) Int. Cl.’...... B01D 3/34; C07C 102/04; sired range and a water non- such as benzene is CO7C 103/34 added to effect separation of an aqueous solution of 58 Field of Search...... 203/36, 69; 260/561 R potassium acetate from the dimethylacetamide as two distinct phases. The phases are then separated and the (56) References Cited dimethylacetamide removed from the solvent phase by UNITED STATES PATENTS distillation. 2, 156,642 5/1939 Slagh ...... 260/561 A 5 Claims, No Drawings 3,959,371 2 not one that is readily suitable for commercial produc PROCESS FOR THE PURIFICATION OF tion. The solubility of sodium acetate trihydrate in dimethylacetamide remains high, of the order of 13 N,N-DIMETHYLACETAMIDE 15 percent, even in the presence of a large quantity of DESCRIPTION OF THE INVENTION the non-solvent. From relatively dry solutions Sodium Several methods for the production of N,N-dime acetate in excess of this quantity will precipitate as the thylacetamide involve the reaction of in crystalline trihydrate and must be filtered with accom the presence of water with acetic acid or methyl or panying loss of dimethylacetamide. If excess water is ethylacetates. Such methods result in mixtures contain added with the non-solvent, a two phase system is es ing relatively large quantities of acetic acid. Due to O tablished, however, no separation of dimethylacetam what has been termed “the hydrogen bonding effect' ide from sodium acetate and water is effected. The acetic acid and N,N-dimethylacetamide form a mixture lower layer will be found to be the principal layer and which cannot be readily separated. In the presence of to contain all of the water, all of the sodium acetate and acetic acid, N,N-dimethylacetamide acts as a base ex about 90% of the dimethylacetamide. The upper layer erting a strong attraction for the acid. As a result of the 15 is virtually entirely xylene and will contain about 10% above phenomenon, the acid and the form a high of the dimethylacetamide. The net result of such a boiling azeotrope containing about 21.1 percent acetic process is that it fails completely in the separation of acid and having a boiling point at 170.3C. dimethylacetamide from sodium acetate and all of the Low boiling azeotropes are frequently used in frac original problems persist. tionation procedures to separate liquid mixtures. Such 20 It has been discovered that the use of potassium hy azeotropic distillation has found little application how droxide to neutralize the acetic acid in a mixture of ever for splitting the N,N-dimethylacetamide-acetic acetic acid and N,N-dimethylacetamide produces a acid complex. The equilibrium constant for dissocia completely different result as compared to the use of tion of the complex does not provide sufficient free . More particularly, potassium ace acetic acid over a wide range in temperature to permit 25 tate has a low solubility in dimethylacetamide, does not efficient separation in the form of a lower boiling acetic form a trihydrate and has a high affinity for water. acid azeotrope. When this procedure is attempted, it is In the presence of water and even in the absence of a observed that as acetic acid is removed the remaining water non-solvent such as xylene, potassium acetate acetic acid is more tightly bound in the complex and has been found to have a pronounced tendency to increasingly more difficult to separate. Furthermore, if 30 separate from dimethylacetamide as a second layer of any basic impurities are present such as dimethylamine concentrated aqueous solution. If a water non-solvent they are more difficult to separate by distillation in the is present, this separation will be found to be more presence of acetic acid. marked. Formation of a cleanly defined aqueous layer One solution to the separation of the N,N-dime in this manner offers a great advantage in the separa thylacetamide and acetic acid is proposed in the patent 35 tion process and improved recovery of the dimethylac to Freure 2,953,503, dated Sept. 20, 1960. According etamide. Also, since potassium acetate has little ten to the patent disclosure, separation may be accom dency to be retained by dimethylacetamide the separa plished by heating a mixture of the dimethylacetamide tion process can be completed without interference and acid in the presence of a non-polar solvent, such as from precipitating solid salts. a substituted benzene, to a temperature sufficient to 40 In the purification process sufficient potassium hy vaporize the acetic acid and solvent. The dimethylacet droxide should be added to a mixture of acetic acid and amide is recovered in the residue. Suggested as addi N,N-dimethylacetamide to completely neutralize the tional non-polar are chlorobenzene and the acetic acid present. The neutralization temperature lower alkylbenzenes, such as toluene, ethylbenzene and should be maintained below 50° C. and, preferably the xylenes. 45 between about 25°C. to 40 C. to avoid possible hydro One of the problems encountered in a process of the lysis of the dimethylacetamide. Either before or after type proposed in the above patent relates to the fact neutralization, the water content of the mixture should that the solvents should be used in quantities amount be adjusted so that the final potassium acetate to water ing to from about 100 - 500% of the mixture whose ratio covers a range of from about 111 to about 3/1 by components are to be separated. Distillation of such 50 weight, with a preferred ratio of about 2/1. If too much large quantities of solvent is not considered economi water is present, the dimethylacetamide will tend to cal. Further, in view of the fact that the most efficient dissolve in the water layer whereas, if too little water is solvents boil relatively close to N,N-dimethylaceta used, the overall separation process will be appreciably mide, separation by fractional distillation must be care slowed. fully controlled. 55 In addition, an organic non-polar water non-solvent Sodium hydroxide has been proposed for use in neu is preferably added which also is a strong solvent for tralizing the acetic acid in a mixture with N,N-dime the dimethylacetamide, as distinguished from a com thylacetamide and permit the latter to be distilled off. pound which may be merely miscible with the dimeth However, this process has not been used extensively ylacetamide. In general, such a solvent is added in the outside of the laboratory for several reasons. First, 60 ratio of about 25% to 50% by volume of the dimethyl sodium acetate and its hydrate are very soluble in di . Exemplary solvents are benzene and the methylacetamide making separation difficult. Second, lower alkyl substituted benzenes, such as toluene, eth as the dimethylacetamide is distilled, accumulation of ylbenzene and the xylenes. solid sodium acetate prevents good heat transfer and Following adjustment of the water content and addi also creates handling difficulties that result in losses of 65 tion of the organic solvent, separation of two indepen the dimethylacetamide. Further, if a sodium acetate dent phases is clearly established, the water phase con non-solvent, such as xylene, is added to the separation taining substantially all of the potassium acetate and process, it is possible to obtain a partial separation but the organic solvent or nonaqueous phase containing 3,959,371 3 4 substantially all of the N,N-dimethylacetamide. The water layer is washed with an equal volume of benzene water phase will be the lower layer and may then be and the dimethylacetamide is taken up completely. The removed by either gravity separation or automatic de dimethylacetamide-benzene solutions are combined cantation. In some instances, it may be necessary to and are stripped of benzene by distillation during which wash the water phase with the solvent to remove a time the remaining water is also stripped. The benzene portion of the dimethylacetamide which may have dis with a boiling point of 80° C. is readily fractionated solved in the aqueous layer. cleanly from dimethylacetamide having a boiling point The solvent phase may then be subjected to frac of 166°C. The residue is essentially pure dry dimethyl tional distillation to remove the solvent and any water acetamide. Distillation of this residue yields 8 g. of remaining leaving bottoms that are essentially pure 10 dimethylacetamide and leaves a semi-solid residue of N,N-dimethylacetamide. A final distillation may be 1-2 g. employed to remove color impurities. Overall, the recovery of dimethylacetamide is about In general, it has been found that recovery of dimeth 95 percent based on the continued dimethylacetamide ylacetamide by the process of the present invention in the starting sample. results in yields of about 85-95 percent and at consid 5 By way of further illustrating the advantages of this erable economic and time savings over prior art pro invention, the following example is presented of a pro C2SSS. cess using sodium hydroxide. As further illustrating the invention, the following examples are presented. EXAMPLE 3 20 One hundred cc. of dry N,N-dimethylacetamide solu EXAMPLE I tion containing 20 percent acetic acid is neutralized One hundred cc. of dry N,N-dimethylacetamide solu with commercial 50 percent sodium hydroxide. Ap tion containing 9.5 percent by weight of acetic acid is proximately 31 g. (21 cc.) is required containing 15 g. neutralized with 13.4 cc. of commercial liquid potash of water. At this point, a dense gel sets up that would be (45% of 90% potassium hydroxide flake). The temper 25 substantially unmanageable in a commercial size reac ature during neutralization is maintained at about 35 tor. The gel is eliminated by blending in an additional C. A homogenous solution is formed of potassium ace 3-4 percent of water. To cause separation of the so tate and dimethylacetamide. To this solution is added dium acetate, 50 cc. of xylene is added to the solution. 35 cc. of xylene solvent, whereupon an aqueous layer Approximately 31 g of sodium acetate trihydrate crys comprising 26 cc. separates containing the following 30 tallizes out. On filtration, there is a loss of about 30 g. component percentages by weight: of dimethylacetamide as holdup with the crystals. Frac potassium acetate 48% tional distillation of xylene will leave a solution of so water 30% dium acetate in dimethylacetamide of about 65 cc. On dimethylacetamide 22% 35 stripping this solution to dryness, approximately 40 cc. The lower aqueous layer is separated by draining of dimethylacetamide is recovered leaving a residue of from a separatory funnel and then is washed twice with 14 g. of sodium acetate and 10 g. of dimethylacetam two 22 cc. portions of xylene to reduce the dimethylac ide. etamide content to 5%, Overall, the recovery of dimethylacetamide is about The xylene washings and the solvent phase are com- 40 50-60 percent based on the contained dimethylacet bined and subjected to fractional distillation to effect amide in the starting sample. separation of xylene, boiling at 143°C. from N,N-dime Having described the invention and certain exem thylacetamide boiling at 166 C. at atmosphere pres plary embodiments, the same is only intended to be sure. 80 cc. of N,N-dimethylacetamide are recovered limited by the scope of the following claims. comprising about 88% of the initial quantity in admix We claim: ture with acetic acid. The distillate from a laboratory 1. A process for the separation of N,N-dime helix packed column having ten trays included an inter thylacetamide from a mixture of N,N-dimethylaceta mediate fraction of 21 cc. containing xylene and ap mide and acetic acid which comprises neutralizing the proximately 50% dimethylacetamide. This intermedi acetic acid with potassium hydroxide, adjusting the ate fraction may be used in subsequent dimethylacet- so water content of the mixture whereby the water to amide recovery processes, in which case such subse potassium acetate ratio is between about 1/1 to 3/1 by quent recoveries are within the 90-95 percent range. weight, adding a non-polar water non-solvent and per The dimethylacetamide distillate residue contained no mitting the formation of an aqueous phase containing salt and was subject to simple distillation to make it potassium acetate and a separate non-aqueous phase, water white. 55 separating the aqueous phase from the non-aqueous phase and subjecting the non-aqueous phase to distilla EXAMPLE 2 tion to remove the solvent. One hundred cc. of dry N,N-dimethylacetamide solu 2. A process as described in claim 1 wherein the tion containing 15 percent acetic acid is neutralized water nonsolvent is member of the class consisting of with 15.5 g. of commercial flake caustic potash (potas- so benzene and the lower alkyl substituted benzenes. sium hydroxide) at a temperature of 40 C. There is 3. A process as described in claim 2 wherein the some tendency toward gel formation which is dispelled solvent is benzene. with the addition of 5 cc. of water. With this amount of 4. A process as described in claim 2 wherein the water there is produced a small amount of a second water to potassium acetate ratio is about 2/1 by weight. liquid layer. On addition of 27 cc. of benzene, a water is 5. A process as described in claim 2 wherein the layer of 27 cc. separates cleanly from the dimethylacet water non-solvent is added in a ratio of about 25% to amide solution. This water layer comprises 24 g. potas 50% by volume of the N,N-dimethylacetamide. sium acetate, 10 g. water, 3 g. dimethylacetamide. The ck ck ck k sk