March 21, 1950 R. H. HARTIGAN 2,500,946 PROCESS FOR MAKING CYANDE Filed Sept. 19, 1946

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Patented Mar. 21, 1950 2,500,946

UNITED STATES PATENT OFFICE 2,500,946 PROCESS FOR MAKING BROMINE CYANDE Raymond H. Hartigan, Pittsburgh, Pa., assignor to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application September 19, 1946, Serial No. 69,956 5 Claims. (C. 23-19) 2 This invention relates to bromide. From Equations 1, 2 and 3 above it will be seen More particularly the invention relates to the that the bromine which is not combined with manufacture of by the bromi the cyanogen radical as cyanogen bromide ap nation of Sodium . pears as inorganic bromides, such as HBr, NaBr Cyanogen bromide is a solid at ordinary at 5 and NH4Br, and the yield of cyanogen bromide mospheric temperatures having a formed in the reaction is substantially reduced. of 52° C. and a boiling point of 61.2° C. This The reaction of Equation 2 is catalyzed by acid. solid material, therefore, may be advantageously The reaction of Equation 3 takes place in a neu handled and used for the manufacture of cyanuric tral Solution. Accordingly when the synthesis of bromide and melamine. O Cyanogen bronide is conducted in a sulphuric In Volume XI, “Organic Synthesis' (1931) page acid solution the reactions shown in Equations 3 30, Hartman and Dreger describe a process for and 4 are avoided. Furthermore, it is found that the bromination of directly With the reaction in Equation 5 is insignificant with a elemental bromine. The yields of cyanogen bro dilute acid solution, mide obtained by their process vary from 73% to The presence of acid during the reaction forms 85% of the theoretical cyanogen bromide avail an important part of the present invention, able. Furthermore, it has been found that the strength The primary object of the present invention is of acid in the reaction mixture is very important to provide a process of brominating Sodium cy in obtaining the most efficient reaction and the anide to obtain a substantially theoretical yield maximum yield. Experiments have shown that of cyanogen bromide. Substantially theoretical yields may be obtained Another object of the invention is to provide With 0.5 to 8.0 normal sulphuric acid present in a process by which Sodium cyanide may be easily the reaction mixture. Expressed in another way, brominated without the loss of products to obtain the distillation residue should have a 0.3 to 4.3 a high quality cyanogen bromide. 2 5 normal Sulphuric acid acidity. With these and other objects in view, the in In the absence of acid (preferably a mineral vention consists in the process of producing acid) it is probable that sodium cyanide and cyanogen bromide as hereinafter described and cyanogen bromide react to consume the cyanogen particularly defined in the claims. bromide. Furthermore in the absence of acid In the bromination of sodium cyanide with ele 30 and with an excess of sodium cyanide, the sodium mental bromine some or all of the following re Cyanide reacts with the cyanogen bromide to give actions occur: a quantitative destruction of the cyanogen bro i. Br2--NaCN=BrCN--NaBr mide. To carry out the process in accordance with A part of the cyanogen bromide prepared as in the preferred form of the invention the materials Equation, 1 may be decomposed by to are reacted in the following proportions: one mol ammonium bromide in accordance. With the foll of bronine is added to 150 ml. of 2 normal sul lowing equation: phuric acid solution which is preferably placed within a mixer that may be provided with a cool Further cyanogen bromide may have a metathleti O ing coil or a cooling jacket. The bromine mix cal reaction with sodium cyanide in accordance ture is cooled to a temperature of approximately with the following equation: 20 C. and to it is added 52-54 grams of sodium Cyanide (95% pure) dissolved in 100 ml. of water. 3. BrCN--NaCN=NaBr- (CN)2 The Sodium cyanide solution is slowly added to Some of the cyanogen formed by Equation 3 may, 45 the bromine mixture and the reactants are mixed in turn, hydrolyze to azulinic acid and other prod and cooled to maintain the temperature below ucts in accordance With equation: 23 C. At the end of the reaction a clear solu tion of Sodium bromide is formed in which a 4. X(CN)2--Y(H2O) = azulmic acid--NH3-- major portion of the cyanogen bromide is pre HCOOH-- (COOH)2--HCN--CO (NH2)2 50 cipitated as White crystalline cyanogen bromide. Furthermore sodium cyanide may react with Wa When the reaction is completed the cyanogen ter to produce a formate in accordance with the bromide may be directly distilled out of the re equation: action mixture. ... The reaction mixture contains a large amount of water and it is important to 5. NaCN-2H2O=HCOONa--NH3 55 exclude Water from the cyanogen bromide if a. 2,500,946 3 4 pure product is desired. The water may be re The data of Table III show that an excess of moved from the cyanogen bromide vapors dis 30% sodium cyanide in run 2, a practically quan tilled out of the reaction mixture by passing the titative amount of cyanogen bromide is destroyed. vapors through calcium chloride or other suitable In run 1 when using the 30% excess of Sodium dehydrating agent which is located in the frac cyanide sufficient sulphuric acid is present to tionating tower. The cyanogen bromide is a take care of the entire excess of sodium cyanide, product which may be readily polymerized to and therefore a substantially quantitative yield produce cyanuric bromide. of cyanogen bromide is secured. It is important, In Table I is shown the effect of the presence therefore, to have present in the reaction mixture of different strengths of sulphuric acid which O sufficient acid to react with the excess Sodium may be used in the bromination of Sodium cyanide in order to obtain the maximum yield cyanide. of cyanogen bromide. A large number of tests TABLE have been made using stoichiometric proportions of bromine and Sodium cyanide. It has been The preparation of cyanogen bromide from bro 15 found that in such runs the yield of cyanogen mine and sodium cyanide in a Sulphuric acid bromide is between four and five percent lower medium than when sulphuric acid is present. It is de Effect of high acidity on the yield. sirable when obtaining the maximum yields of cyanogen bromide to use slight excess of sodium Normality 20 cyanide and have sufficient acid present in the ISO Total BrCN, Size, Run, Moles Solution Mo. Percent reaction to take care of the excess Sodium cyanide. Charged The graphs shown in the drawings are curves which are plotted from the data of Tables I and 2 98.4 II. Figure i is made from the data, of Table 4. 98.5 6 98.4 25 and Figure 2 is made from the data of Table II. 8 98.2 9 96.7 These graphs show the yield of cyanogen bromide 96.2 produced by reactions taking place in different 93.0 strengths of sulphuric acid. These curves illus 90.2 trate clearly the fact that the use of 0.5 to 8 30 normal sulphuric acid gives an important and in In Table II are shown the yields of Cyanogen creased yield of product. bromide which are produced by the bromination A large number of experiments have shown of sodium cyanide when the strength of Sulphuric that in the absence of the Sulphuric acid in the re acid is normal or less than normal. action mixture approximately 31% of the bro TABLE II 35 mine is not recovered as cyanogen bromide when an excess of 30% sodium cyanide is used. The preparation of cyanogen bromide from bro Experiments have also shown that if the re mine and Sodium cyanide in a dilute Sulphuric action takes place in the presence of an alkali acid medium. the cyanogen bromide is destroyed quantitatively. Effect of low acidity on the yield. The preferred form of the invention having been thus described, what is claimed as new is: 1. A process of making cyanogen bromide con Normality Total BrCN, HSO Mol, Per Cent sisting in slowly reacting sodium cyanide with Charged bromine Water in the presence of an added re 45 agent consisting of Sulphuric acid having a con centration of 0.5 to 8.0 normal. 2. The process of making cyanogen bromide consisting in cooling bromine water to a tempera ture of approximately 20° C., slowly adding a 50 Water Solution of Sodium cyanide while main In Table III is illustrated the effect of 30% taining a temperature below 23° C. in the presence excess of Sodium cyanide on the yield of cyanogen of an added reagent consisting of sulphuric acid bromide obtained when directly brominating having a concentration between 0.5 and 8.0 Sodium cyanide with elemental bromine without normal. acid present and the bromination of the same 55 3. The process defined in claim 2 in which the Sulphuric acid concentration in the residue mix amount of Sodium cyanide under the same con ture is 0.3 to 4.3 normal. ditions when having 4-normal H2SO4 present. 4. A process of making cyanogen bromide TABLE II while avoiding an oxidation reaction consisting Preparation of cyanogen bromide from bromine 80 in: Cooling a mixture of bromine and Sulphuric and 30% eaccess Sodium cyanide acid having a concentration between 0.5 and 8.0 Run 1-67 g. NaCN dissolved in 1i0 in). HO; 51.8 ml. Bra; 150 ml. normal to a temperature of approximately 20° C., 4-NH2SO. slowly adding a reagent consisting of a Water Hin 2-67 g. NaCN dissolved in 110 ml. HO; 51.8 ml. Br; 150 ml. Solution of sodium cyanide while maintaining the U. 65 temperature of the reaction mixture below 23° C., thereafter distilling the reaction mixture and re Run sizep?. Run, NormalitySC. TESN, moving cyanogen bromide through a fractionat Moles SolutionCharged cent e ing tower containing a drying agent to recover a dry cyanogen bromide. 1------4.0 98.8 70 5. The process of making cyanogen bromide 2------O 69.0 consisting in: cooling bromine water to a tem perature of approximately 20° C., slowly adding a These runs illustrate clearly the advantage of Water Solution of sodium cyanide while main the presence of sulphuric acid in the reaction taining a temperature below 23° C. in the pres mixture. - 5 ence of an added reagent consisting of sulphuric

2,500,946 S 6 acid having a concentration between 0.5 and 8 FOREIGN PATENTS normal, and distilling cyanogen bromide Out of the reaction mixture. Number Country Date RAYMOND H. HARTIGAN. 9,710 Great Britain ------of 1900 REFERENCES CTE) 3) OTHER REFERENCES The follo eferences are of record in the "Cyanogen Compounds,'s by Williams;s J. & A. file of E. eleCe e Churchill, London (1915), pages 6 and 7. UNITED STATES PATENTS 10 Number Name Date 666,135 Goepner et al. ------Jan. 15, 1901 1938,324 Dieterle ------Dec. 5, 1933