SYNTHESIS OF GUANIDINE FROM UREA, AMMONIUM BENZENESULPHONATE, AND AMMONIUM SULPHAMATE1

Transcription

1 SYNTHESIS OF GUANIDINE FROM UREA, AMMONIUM BENZENESULPHONATE, AND AMMONIUM SULPHAMATE1 ABSTRACT Guanidine benzenesulphonate has becn obtained in yiclds exceeding 70% by heati!lg urea, anlmonium sulphamate, and an~rnonium benzencsulphonate in respecti\-? nlo!ar ratlos of 1: 1: The effects of temperature, proportion of reactants, and reactlo11 tlme were studied batchwise. Then the process was operated on a continuous I~asis in a four-flask cascacle reactor at tetnperatures between 240' and 260" C. The fusion of urea with ammonium sulphamate gives rise to guanidine sulphamate in relatively low yield, and even a large excess of ammonium sulpharllate does not effect the transformation in yields higher than 80% (3). Moreover, the fusion is hampered by the formation of ammonium sulphate coming out of the melt at high temperature. The presence of this insoluble salt in the fusion mixture maices a contin~ious process impossible. A search has been made for a g~ianidine salt \vhich would be stable up to 300' C. in the fused state and could be readily transformed into either guanidine nitrate or nitroguanidine. Sulphonic acids appeared to be suitable since they are stable and, unlilre sulphamic acid, are not readily hydrolyzed. Guanidine benzenesulphonate melts at 212' C. and can be fused at 300' C. without decomposition or appearance of melamine (2). hlioreover, guanidine benzenesulphonate is less soluble in water than guanidine nitrate and can be crystallized from it. Guanidine benzenesulphonate can be obtained by the reaction between urea, ammonium sulphamate, and ammonium benzenesulphonate. The fusion of urea and ammoilium sulphamate gives cyanamide and ammonium sulphate (1); cyanamide then reacts with ammonium benzenesulphonate to yield guanidine benzenesulphonate according to the following equations: NHZSOJVH, + NHZCONH, -+ NHICN + (SH,)zSOI, NH?CN + I\IH,SO~CBI-IE + NHZC(NH)NH* HS03C'Hj. A study of the effect of temperature, molar ratio of reactants, and reaction time was made batchwise by heating the mixture in a flask, and on a continuous basis in a fourflaslr cascade reactor. It was observed that the addition of ammonium sulphate to the urea - ammonium benzenesulphonate - ammonium sulphamate mixture did not appreciably change the fluidity of the melt at the synthesis temperature, because of its relative solubility in the fused mixture. The crude guanidine benzenesulphonate thus formed was isolated by crystallization from water and melted at 212' C. A mixed melting point determination with an authentic sample was not depressed. EXPERlMENTr\L AND RESULTS Preparation of Guanidine Benzenesulphonate Batch Process The preliminary experiments were directed to the study of the effect of temperature, molar ratio of reactants, and time of the reaction on the yield. The reaction was carried IhIanuscript received October 25, Contribzlt~on from Canadian Armament Research and Development Esta~lishnze?zt, Valcartier, Quebec. Can. J. Clrem. Vol. 36 (1868) 378

2 BOlVIN AND TREMBLAY: GUANIDINE SYNTHESIS 379 out in a three-necked flask equipped with a stirrer, a thermometer, and gas inlet. Heating was accomplished by means of a heating mantle. The mixture of ammollium sulphamate, ammonium benzenesulphonate, and urea melted at about 100" C., and at " C. an exothermic reaction took place with evolution of gases and the formation of a sublimate. The melt was heated to the desired temperature for a period of 15 to 90 minutes. The liquid was then poured into a beaker, allowed to cool, dissolved in water, and diluted to 500 cc. in a volumetric flasl;. The solution was analyzed for guanidine with a solutioil saturated with ammonium picrate and guanidine picrate. Efect of reaction temperatz~re.-table I shows the results obtained at different temperatures. The maximum yield of guanidine benzenesulphonate was obtained at 240' C. after a 1-hour period of heating. TABLE I EFFECT OF TEMPERATURE Urea: 15 g. (0.25 mole); am~lioniurn sulphamate: 28.5 g. (0.25 mole); ammonium benzenesulphonate: 57.4 g. (0.25 mole) Temp., Time, Yiel fro r e, /( lemp., Time, Yieltl from urea, " C. min. % C. min. 7; Effect of molar ratio of reactants.--results are summarized in Table 11. Yields increased with excess of urea, but much decomposition occurred giving rise to a material insoluble in water. Yields increased also with the amount of ammonium sulphamate and remained practically constant as the proportion of benzenesulphonate was increased. - TABLE I1 EFFECT OF MOLAR RATIO OF REACTANTS Temperature: 240" C.; time: 1 hour Ammonium i\rnmonium Urea sulphamate be~ize~lesulphonate Yield -- from urea. 0' ~, g. mole g. mole g. mole /o

3 380 CANADIAS JOLTRXAL OF CI-IEMISTRY. VOL Eifect of reaction time.-the results are shown in Table 111. At low temperature (240" C.) yields were practically the same, but a 30-minute period of heating was sufficient. With longer heating times some solid separated from the melt and impaired the stirring. Higher temperatures (260" C.) required shorter times. TABLE I11 EFFECT OF REACTION TIME AT 240, 250, AND 260' C. Ammonium benzenesulphonate: 57.4 g. (0.25 mole); urea: 18 g. (0.3 mole); arnnioni~~m sulphamate: 57 g. (0.5 mole) Temp., Time, Yield from ammonium " C. hr. benzcnesulphonate, O/b I." Continuous Process The main object of this work was to produce guanidine benzenesulphonate on a continuous basis. A cascade reactor consisting of four 500-m1. flasks was built in such a way that molten material overflows from flaslc 1 to flask 4 by gravity. A stream of anhydrous ammonia was introduced at the bottom of each flask to stir the molten solid while the flasks were heated by mantles. Runs were made by adding urea, ammonium sulphamate, and ammoni~~m benzenesulphoilate in respective molar ratios of 1: These molar ratios were co~lsidered to be the optimum proportions to give maximum melt fluidity. The reduced molar ratio of ammonium benzenesulphonate was sufficient to form the salt of the guanidine produced in the reaction. The residence time in the reaction flasks varied from 15 to 120 minutes at the rates of feed of 20 to 5 grams per minute respectively. The mixture was first added manually at a constant rate of 5 to 15 grams per minute. Attempts were made to introduce the same mixture by means of a screw feeder to obtain a constant rate of addition but this mixture absorbed water rapidly and became tacky, causing plugging of the screw feeder. It was found that the mixture became hygroscopic owing to the presence of urea. Two screw feeders were then used to introduce respectively urea and the mixture of ammonium sulphamate and ammonium benzenesulphonate. With this arrangement two 8-hour runs were made successfully using 10 pounds of mixture each. The mixture was melted at " C. in the first flask and allowed to overflow to the second flask where the temperature reached " C. The reaction in the second flaslc was exothermic with evolution of ammonia. The liquid flowed through two more flasks to complete the reaction and mas finally collected in a beaker where it solidified. After solidification, a weighed sample was dissolved in the minimum of water and analyzed for guanidine. The guanidine benzenesulphonate was also crystallized, weighed, and its purity determined. Yields of about 60 to SOY0 were obtained depending on the rate of feed. The results given in Table IV show that the yields obtained by adding the mixture at a constant rate from 10 to 13 grams per minute were 66 to 71% by crystallization, the product obtained being about 97Y0 pure. -

4 BOIVIN.\ND TKEAMBL;\\'. GI'-\XIDINIS SYNTHESIS COXTIXUOUS PUSIOSS 'I'emperature of flask 1: " C. Temperature of flasks 2, 3, and 1: 250" C. Molar ratio of urea, ammonium sulphamate, and anlmoni~~m benzerlesulphonate: 1: 1 : 0.9 Yield of guanidine Estimated residence fro111 urea, % time of reaction, Rate of feed, min. g./min. By analysis By cryst. * Usins two screw feeders. ta mired n~eltirag Poitzt with an authetatic sample of gz~araidilie bensenesulpho7zate (?iz.p.,212" C.) was tzot depressed. RECOVERY OF UNIiEACTED I\MIMO?JIUM SULPHAUIATE To make the synthesis more attractive, the unreacted ammonium sulphamate should be recovered. The melt obtained from the continuous reactor was dissolved in water and fractiollally crystallized. Results given in Table V show that guanidine bellzenesulphonate crystallized first, then on further concentration ammonium sulphate was obtained, and fillally ammonium sulphamate. The separation is not very clear-cut and a more practical procedure is required to reclaim the ammo~liurn sulphamate on a production scale. TABLE V FIIACTIONAL CRYSTALLIZATION or PCSION PKODL~CT Weight of melt ~~scd: 5-10 g. Co~nposition of solid Volume of Weight of Amnioniun~ Ammonil1111 Guariidine ben- Crop of solution, solid, sulphate, sulphamate, ~enes~~lphonate, crystals ml. g. '70 %I O/o DISCUSSIOS The results obtained by the fusion of urea, ammo~~ium sulphamate, and ammonium benzenesulphonate are promising. The fusion stage is sufficiently exothermic to preclude an). use of exter~lal heating and the conversion of urea into guanidine is high using a stoichio~netric ratio of reactants. It has been shown that the proportion of ammonium benzenesulphonate could be reduced below the stoichiometric amount with equally good results. The use of ammonium be~lzenesulphonate stabilizes the guanidine formecl and preve~lts its transformatio~~ into melamine; this stabilizing effect could otherwise be

5 3 82 CAN.&DI:\N JOURNAL OF CHEMISTRY. VOL accomplished by the use of a large excess of ammo~lium sulphamate. The presence of ammo~lium benzenesulphonate in the fusion mixture also increases the fluidity of the melt and prevents the separation of ammonium sulphate. The presence of guanidine as its benzenesulphonate salt makes possible a colltinuous process which has been demonstrated in a laboratory system. Guanidine benzenesulphonate was separated easily from the salts present in the fusion mixture. However, the high stability of this salt made difficult its transformation into guanidine nitrate directly by means of ammonium nitrate or nitric acid. This fusion has the advantage of being made at atmospheric pressure. A reactor will be easily constructed from conve~ltional materials. No difficult heat transfer problem will arise since the reaction is self-sustaining. REFERENCES 1. BOIVIN, J. L. and LOVECY, A. L. Can. J. Chem. 33, 1222 (1955). 2. I~ARRER, P. and EPPRECHT, J. Helv. Chim. Acta, 24, 310 (1941). 3. PIac~ca~, J. U.S. Patent Yo. 2,464,247 (1949) to American Cyanamid Co.