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ii'atented Oct. 20,, 1953 2,656,253 .Pnrnnrr :QEELGE 1 "52,656,253 ' ' PREPARATION orgoxl'linld?i'nn .. Nd’D'fawing. , Application. Noyemben 23,4951, *seralr No. ‘257371 4 Claims. (Cl. 23-190) 1 2 The present invention relates to the prepara ucts), the heat is removed from the tube, and tion‘of cyanamide, HzNCN, and more particu the tube is allowed to cool. The cyanamide can larly to the preparation of cyanamide from mel ' be recovered from the upper part of the tube by amine or its deamination products. various means well known in the art. If it is It is an object of the invention to heat mel not essential that the cyanamide be pure, it can amine,‘ melam, melem, or melon, or mixtures simply be scraped from the tube. If a pure prod thereof, at a temperature su?iciently high to uct is desired, it can be separated from melamine “crack” the triazine molecule into cyanamide contamination by leaching the entire solid con vapor. A further object of the invention is to tents of the tube with ether, followed by evapo pyrolyze melamine at red heat to form cyan ration to produce pure crystalline cyanamide. amide, thereafter cooling the cyanamide rapidly ‘to prevent its dimerization or trimerization. Ad-v Example 2 ditional objects will be apparent from the dis The melamine decomposition product obtained cussion hereinafter. as a residue after boiling away all the melamine It is well known in the art that cyanamide 15 used in Example 1 was analyzed and found to can be heated to form melamine. It has always consist largely of melam, with smaller amounts been assumed, however, that this transforma of melem and melon. This mixture was placed tion was irreversible. For example, if melamine in another cracking tube similar to that used in is boiled, at say 500° C., and the resultant vapors Example 1 and heated to a temperature of about chilled, no cyanamide is detectable either in the 620° C. by means of one laboratory burner. This residue or the sublimate. It has now been dis was the only heat applied to the cracking tube. covered that if melamine, melam, melem, or The mixture was observed to fume. In a region melon, is heatedat red heat, e. g. at 610° C. about five inches from the sealed end of the tube. and up, a fair yield of cyanamide is obtained on a clear product deposited in a well de?ned an cooling the vapor e?luent. 25 nulus. When the mass of melam, melem, and _ The following examples illustrate without melon began to char, the heating was discon— limiting the invention. tinued, and the annular condensate was analyzed and found to be substantially pure cyanamide. Example 1 Example 3 The apparatus consists of a piece of heat re 30 sistant glass tubing about 1/2" in diameter and A quartz tube 24 inches long by 21/2 inches about 20" long, sealed at one end. 10 g. of inner diameter is heated in a horizontal electric melamine is placed in the bottom of the tube. furnace to a temperature of 635° C. The feed The tube is supported at a slight upward tilt end of the tube extends about 8 inches from the from horizontal, and is then ready for heating. furnace. In this end is placed a combustion boat The heating is conveniently done by means of containing 9 g. of melamine. The feed end of four laboratory gas burners. Three burners are the tube is ?tted with a port to receive nitrogen placed under the tube to heat the portion of gas and a thermometer to measure the temper ature over the boat. After the furnace is brought the tube beginning at a point about four inches to cracking temperature, the portion of the tube from the sealed end up to a point‘about twelve 40 inches from the sealed end, thus providing a hot around the boat is heated to about 360° 0., while “cracking” zone about eight inches long. After simultaneously passing nitrogen through the sys this portion of the tube becomes red hot, as evi tem. Nitrogen serves the function of minimizing denced by the usual red glow, the fourth burner ‘the decomposition of melamine to its deamina is applied at the sealed end of the tube, under tion products such as melam. The exit vapors 45 are bubbled slowly into a water scrubbing ?ask the melamine. After a few moments, the mel amine begins to boil. The melamine vapor to at room temperature to recover cyanamide as an gether with some extremely ?ne particles of aqueous solution thereof. melamine sublimate pass rapidly through the The process is not limited to atmospheric pres sure, but can be conducted either at sub-atmos “cracking” zone, where they are converted in 50 pheric or super-atmospheric pressures. The part to free cyanamide. The cyanamide passes temperature can vary widely, but should be sub on into the cooler part of the tube, where it con stantially over 600° in order to “crack” the tri denses. Some melamine also condenses with it. _ azine molecule. The preferred temperature is After the melamine ceases to boil (indicating about 625-675° C., but higher temperatures, e. g, formation of stable residue of deamination prod 55 700° C., and even higher can be used. 2,656,253 > 3 4 While the invention has been described with 3. The method according to claim 2 in which particular reference to speci?c embodiments, it the heating is carried out at atmospheric pres is to be understood that it is not to be limited sure. thereto but is to be construed broadly and re 4. The method of preparing cyanamide which stricted solely by the scope of the appended comprises heating melamine vapor at a temper claims. ature of at least 610° C. followed by condensing Iclaim: the resultant vapor mixture of cyanamide and 1. The method of preparing cyanamide which melamine by cooling su?iciently rapidly to in comprises heating a member of the group con hibit polymerization of the cyanamide and re sisting of melamine, melam, melem and melon 10' covering the cyanamide. to a temperature of at least 610° C. to form a JOHNSTONE S. MACKAY. vapor e?luent containing cyanamide, followed by condensing the vapor e?iuent by cooling su?i References Cited-in the ?le of this patent ciently rapidly to inhibit polymerization of the “Cyanogen Compounds,” by H. E. Williams, cyanamide and thereafter recovering the cyan 15 second ed. (1948), pp. 29, 35; Edward Arnold amide. and Co., London, publishers; ?rst ed. (1915), 2. The method according'tc claim 1 in which page 24, J. and A. Churchill (30., London. melamine vapor is heated at a temperature with- ‘ in the range SID-700° C. 20 .

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