2,826,613 United States Patent Office Patiented Mar. 11, 1958 smacawakawa 1. 2 Other objects and advantages of the present invention. will be apparent from a further reading of the specifica 2,826,613 tion and of the appended claims. RECOVERY OF SOLD GUANDINE CARBONATE With the above objects in view, the present invention 5 mainly consists in a process of obtaining solid guanidine Otto Grosskinsky, Eifriede thirauf, Water Klempt, and carbonate from Solutions containing the same, compris Her at Umbach, Dortmund-Eving, Germany ing the steps of adding ammonia to a solution com No Drawing. Application July 8, 1954 prising gilanidine carbonate and a solvent therefor, there Serial No. 442,206 by lowering the solubility of the guanidine carbonate in 0. the solvent and causing precipitation of the same from Claims priority, application Germany July 11, 1953 the Solution, and recovering the thus precipitated solid guanidine carbonate. 9 Claims. (CI. 260-564) The present invention is based on our discovery that the Solubility of guanidine carbonate in water or in a The present invention relates to new, useful improve 15 suitable organic solvent therefor is greatly lowered by ments in the recovery of solid guanidine carbonate and the presence of a sufficient amount of free ammonia in Incre particularly to the recovery of solid guanidine car troduced into the solution. This discovery offers the bonate from liquids containing the same in dissolved possibility of recovering solid guanidine carbonate from condition. - its solutions without either the necessity of special vacuum Guanidine carbonate is very readily soluble in water. operating devices or the risk of losses by decomposition. It might therefore appear at first glance that it would be The precipitation of the solid guanidine carbonate from possible to recover the solid salts from solutions con the solutions containing the same by the addition of am taining the same in dissolved condition merely by evapo monia to the solution without any danger of decomposi rating the solution, allowing the salt to crystallize, and tion of the guanidine carbonate is enhanced by cooling recovering the same by filtration. However, this method 25 the solution, preferably during the addition of the am is not practicable with guanidine carbonate because monia thereto, to relatively low temperatures of 10° C. guanidine carbonate is decomposed to form ammonia and or lower and preferably to a temperature of about 0° C. urea when an aqueous solution containing the same is Moreover, the reduced solubility of guanidine car heated to the boiling point. Evaporating under vacuum bonate by the presence of free ammonia considerably im is circumventive and expensive and moreover although 30 proves the yield of the solid salt precipitated when re it somewhat lowers the risk of decomposition, it does acting a guanidine salt with a soluble carbonate, e.g. as not completely avoid it. " in the above equation. In this connection, the precipita In addition, the high water solubility of guanidine car tion of the formed guanidine carbonate moves the equi bonate is very troublesome in preparing the salts accord librium of the equation to the right so that not only is ing to the known methods by converting soluble guanidine 35 the guanidine carbonate easily obtained in solid form, but salts such as guanidine chloride with suitable soluble car the yield of guanidine carbonate is higher. bonates such as potassium carbonate, in an aqueous Therefore it is a preferred embodiment of the present medium. When guanidine chloride is reacted with po invention to produce guanidine carbonate by the reaction tassium carbonate for example according to the following of a soluble guanidine salt such as guanidine sulfate, equation: 40 guanidine chloride, guanidine thiocyanate, etc., with a water-soluble carbonate, and particularly with the alkali 2CHNC1--K2CO3e (CHN). CO3--KCl metal salt carbonates and ammonium carbonate in the the amount of precipitated solid guanidine carbonate ob presence of free ammonia, whereby the formed guanidine tained is rather small, as will be later shown. In addi carbonate is precipitated from the solution due to the tion, the valuable potassium carbonate is converted dur 45 presence of the ammonia. This precipitation may be en ing the process to potassium chloride which has a much hanced by cooling the solution. The reaction may be lower value. Similar conditions prevail when processing carried out in any suitable solvent, but is of course most other guanidine salts such as guanidine thiocyanate preferably carried out in water. (CHNSCN), as starting material. - - Furthermore, the presence of excess free ammonia It is therefore a primary object of the present inven 50 offers a method of preparing solid guanidine carbonate tion to provide a process of obtaining solid guanidine by reacting a guanidine salt with a carbonate of am carbonate from solutions containing the same without monium selected from the group consisting of ammonium any danger of decomposition of the guanidine carbonate. carbonate and ammonium bicarbonate. When substitut It is another object of the present invention to provide ing e. g. in the above equation the potassium carbonate a process of recovering solid guanidine carbonate in high by an ammonium carbonate, no precipitation of solid yield from aqueous solutions containing the same. guanidine carbonate takes place at all. On the contrary, It is still another object of the present invention to when preparing an aqueous solution containing guanidine provide a process of producing guanidine carbonate in carbonate and ammonium chloride and heating the same solution and obtaining the formed guanidine carbonate to an only moderate temperature, the reaction takes from the solution. 60 place, proceeding from the right to the left side of the It is yet another object of the present invention to pro above equation (in which KCO is to be assumed as vide a process of precipitating guanidine carbonate from substituted by (NH4)2CO3); the ammonium carbonate is solutions containing the same and being formed by re decomposed to form NH8 and CO2 which escape, and acting a guanidine salt with a soluble carbonate such as guanidine chloride is formed again almost quantitatively. an alkali metal or ammonium carbonate. 65 However, when preparing a mixture of guanidine chlo It is a further object of the present invention to pro ride (or guanidine thiocyanate) and ammonium car vide a continuous method of producing guanidine car bonate (or bicarbonate) dissolved in water, and intro bonate by the thermal treatment of ammonium thyo ducing ammonia into said solution, preferably under cyanate to form guanidine thiocyanate and the conver cooling to about 0. C., appreciable amounts of guani sion of the guanidine thiocyanate to guanidine carbonate 70 dine carbonate are precipitated. In this way an am in aqueous solution and the recovery of the guanidine monium carbonate may be used as a cheap and useful carbonate in solid form from the aqueous solution. reactant. 2,826,618 3 4. In addition, the possibility of employing a carbonate ing the yield accordingly. As a rule, cooling to about 0. of ammonium offers a further important advantage: to 10° C. will be satisfactory, but lower temperatures are When starting from guanidine thiocyanate (obtained e.g. suitable also. In all events, cooling should take place by thermal treatment of ammonium thiocyanate accord whenever introducing gaseous ammonia, on account of ing to patent application Serial No. 302,786, filed August the high absorption heat of ammonia when dissolved. 5, 1952, now Patent No. 2,700,056) and converting said The mother liquors separated from the solid guanidine guanidine thiocyanate with ammonium carbonate in the carbonate contain, more or less, large amounts of free presence of Sufficient free ammonia according to the ammonia which is recovered by distillation under vac present invention, ammonium thiocyanate is reobtained uum. During this procedure, the temperature of the as a by-product (in lieu of potassium thiocyanate), this O liquids is strongly lowered, said liquids thus being very being a valuable starting material for preparing new suitable cooling agent for other reaction mixtures, fairly guanidine thiocyanate. Thus, when considering the pres paying the expenses of the aforesaid vacuum distillation, ent invention as a continuation of the aforesaid produc the respective distillation apparatus incidentally acting tion of guanidine thiocyanate, the entire manufacturing as a refrigerator. process, i. e. the method starting from ammotium thio 5 in general, water is the most important medium for the cyanate to the production of guanidine carbonate, pro process of the present invention. It should be noted, ceeds Substantially without obtaining out-of-the-way by however, that organic solvent liquids may be employed products which might not be utilizable. also, according to the conditions of solubility of the salts The amount of ammonia to be added to the solution employed and produced. Such solvents are e.g. alcohols, in order to cause precipitation of the guanidine carbonate 20 such as methanol, ethanol, cyclohexanol; etheralcohols, therefrom will vary greatly depending upon various con Such as methoxyethanol; ketones, such as acetones, buta ditions such as the concentration of the solution, the none, cyclohexanone; lower esters, such as methyl ace particular solvent, the temperature to which the solution tate; organic bases, such as pyridine, etc. is cooled, etc. The particular amount may be easily The invention will be further illustrated but is not in determined by anyone skilled in the art by simple pre 25 tended to be limited by the following examples in which testing of a sample of the solution, so that specific the parts stated are parts by weight: amounts of ammonia which would be necessary need not be given. In general, an amount of ammonia which Example I is 25% by weight of the weight of the solvent will be 100 parts of a crude guanidine carbonate containing 4 Sufficient.