3,037,055 United States Patent Office Patented May 29, 1962 s 2 ea or acetic anhydride constitutes from 10 to 90% by vol 3,037,055 ume, while the concentrated hydrohalic acid (preferably PREPARATION OF OXAMEDE hydrochloric acid) constitutes from 10 to 90% by vol William L. Fierce, Crystal Lake, Walter J. Sandner, Car ume. Water is present in a concentration of 5 to 50% pentersville, and Roger L. Weichnaan, Grayslake, Ill., by volume. The hydrolysis of cyanogen in this mixture assignors to The Pure Oil Company, Chicago, Ill., a is carried out at a temperature in the range from 0-75 corporation of Ohio C., which is high enough to increase the rate of reaction, No Drawing. Filed Apr. 28, 1960, Ser. No. 25,240 but not sufficient to promote the formation of oxalic acid 6 Clains. (C. 260-561) to a substantial degree. This invention relates to new and useful improvements O In carrying out this invention, a mixture of water, con in processes for the preparation of oxamide, and more centrated hydrochloric acid, and glacial acetic acid, or particularly to a process in which cyanogen is hydrolyzed acetic anhydride, are charged to a suitable gas-tight con to oxamide in a ternary mixture of water, concentrated tainer. In a static system, the reactants and solvents may hydrohalic acid, and acetic acid or acetic anhydride. be sealed in a glass vial and agitated occasionally. In a Oxamide is a well-known organic chemical which is 15 continuous system, the cyanogen may be continuously useful as an intermediate in the preparation of other bubbled through the mixture of water, hydrochloric acid, organic compounds and which has potential use as a and acetic acid. The hydrochloric acid (or other hydro fertilizer. Oxamide has a high nitrogen content and a halic acid, e.g., hydrobromic, or hydriodic acid) must low water solubility which provide a source of nitrogen be present in a molar excess over the cyanogen. The for the soil which is utilizable slowly over an extended 20 amount of water added to the mixture must constitute period of time. Oxamide, however, has not been used less than 50% by volume, i.e., the total volume of acetic commercially as a fertilizer due to its relatively high acid (or acetic anhydride) and hydrochloric acid must cost. While previous proposals have been made for the exceed the volume of the water in the mixture. The re manufacture of oxamide from cyanogen, they have not action may be carried out at a temperature in the range been carried out commercially due to the initial expense 25 from about 0 to 75° C. The reaction pressure may of the cyanogen and the infficiency of the process of hy vary from low subatmospheric pressures to very high drolysis of cyanogen to oxamide. superatmospheric pressures, depending only on the type The hydrolysis of cyanogen to oxamide has been previ of reactor used. At higher pressures, the rate of con ously reported in the literature. In 1860, von Liebig re version of cyanogen is higher due to the increased solu ported (Ann., 113, 246) that cyanogen could be treated 30 bility of cyanogen in the hydrolysis medium. While the with an aldehyde to produce oxamide. In 1867, Schmitt reaction proceeds satisfactorily at room temperature, the and Glutz (Ber., 1, p. 66), reported that when cyanogen reaction rate may be increased several-fold by an increase is contacted with aqueous concentrated hydrochloric acid, of the reaction temperature to about 50-75° C. oxamide forms as crystals which separate from the The following non-limiting examples are illustrative cyanogen-saturated acid. They also reported the forma 35 of the scope of this invention. tion of small quantities of ammonium oxalate. In 1916, EXAMPLE I Bucher, in U.S. Patent 1,194,354, disclosed an improved process for hydrolysis of cyanogen to oxamide using con In one experiment, 9.5 g. of cyanogen was contacted centrated hydrochloric acid. Bucher reported that it is with a mixture of 30 ml. of concentrated sulfuric acid, necessay to keep the hydrolysis reaction relatively cool, 40 30 cc. of water, and 25 cc. of glacial acetic acid for six since higher temperatures favor the formation of oxalic days at room temperature. The mixture was sealed in a acid, and that carrying out the hydrolysis of cyanogen glass vial and agitated occasionally. At the end of six linder higher pressure increased the formation of oxamide days, there was no precipitate of oxamide formed. When considerably, probably due to the increased solubility of cyanogen is contacted with glacial acetic acid, or with cyanogen at higher pressures. Bucher also reported that 45 aqueous solutions of acetic acid for a like period, there it was necessary to use hydrochloric acid of very high is no formation of oxamide. concentration, that diluting the acid reduced consider EXAMPLE II ably the formation of oxamide, and that sulfuric acid and nitric acid are ineffective for hydrolyzing cyanogen. In a series of experiments, cyanogen was hydrolyzed One object of this invention is to provide a new and 50 using various hydrolysis media. In one experiment, 9.7 improved process for the preparation of oxamide. g. of cyanogen was sealed in a 170-ml. vial with a mix Another object of this invention is to provide an im ture of 20 mi. of water and 80 ml. of concentrated hy proved process for the preparation of oxamide by the hy drochloric acid. The vial was sealed and held at room drolysis of cyanogen. temperature, with occasional inversion to mix the con A feature of this invention is the provision of an im 55 tents. After six days, the vial was opened and a precipi proved process for the hydrolysis of cyanogen to oxamide tate was recovered which consisted of an impure oxamide in a mixture of hydrohalic acid, glacial acetic acid (or (85% purity) representing a yield of 82%, based on the acetic anhydride), and water. cyanogen charged. In another experiment, 9.0 g. of A further feature of this invention is the provision of cyanogen was contacted for six days with a mixture an improved process for the hydrolysis of cyanogen to 60 consisting of 40 ml. of water and 60 mi. of concentrated oxamide using a ternary mixture of concentrated hydro hydrochloric acid. Oxamide of 93% purity was obtained halic acid, glacial acetic acid (or acetic anhydride), and in 90% yield. In a third experiment, 9.6 g. of cyanogen water, in which the hydrohalic acid is present in a molar was contacted with a mixture consisting of 60 ml of excess over the cyanogen, and water constitutes less than water and 40 ml. of concentrated hydrochloric acid for 50% by volume of the mixture. 65 a period of six days. Oxamide of 94% purity was ob Other objects and features of this invention will be tained in a yield of only 17%. In still another experi come apparent from time to time throughout the specifi ment, 9.6 g. of cyanogen was contacted with a mixture cation and claims as hereinafter related. of 80 ml. of water and 20 ml. of hydrochloric acid. At This invention is based upon our discovery that cyano the end of six days, no oxamide had formed. 70 gen can be hydrolyzed to oxamide in concentrated hydro EXAMPLE III chloric acid mixed with water and glacial acetic acid or acetic anhydride. In this mixture, the glacial acetic acid In another series of experiments, cyanogen was hy 3,037,055 3 4. drolyzed using a mixture of concentrated hydrochloric 5-50% by volume. The relative proportions of hydro acid, glacial acetic acid, and water. In the first experi chloric acid and glacial acetic acid are not critical within ment, 8.7 g. of cyanogen was sealed in a glass vial with the general ranges indicated. In fact, the principal re a mixture consisting of 50 ml. of water, 10 ml. of glacial quirement is that the hydrohalic acid must be present in acetic acid, and 40 ml. of hydrochloric acid at room tem a molar excess over the cyanogen, and that the volume of perature for six days with occasional agitation. At the water in the mixture must constitute less than 50% of end of this time, oxamide (95% purity) was found to the mixture. While the examples given above were car have formed in a yield of 61%, based on the cyanogen ried out at room temperature and atmospheric pressure, charged. From this experiment, it is seen that the sub it should be noted that the reaction proceeds well at sub stitution of 10 ml. of glacial acetic acid for a correspond O atmospheric and Superatmospheric pressures, and at tem ing amount of water caused a very substantial increase peratures in the range from about 0-75° C. At higher in the yield of oxamide over the previous experiment pressures, e.g., up to 5000 p.s.i.g., or higher, the reaction utilizing hydrochloric acid of the same concentration. In rate is higher due to increased solubility of the cyanogen a series of experiments, the relative amounts of concen in the reaction mixture. At temperatures of 50-75 C., trated hydrochloric acid, glacial acetic acid, and water the reaction rate is higher, although at the upper end of were varied and the effect on the production of oxamide the temperature range there is an increased tendency was determined. In these experiments, the reaction con toward formation of oxalic acid. ditions were the same as in the previous examples, except While we have described this invention fully and com for the variation in the relative amounts of acetic acid, pletely with special emphasis upon several preferred em water, and hydrochloric acid.