2 process. In our process, a ketone cyanohydrin, such as ‘2,951,144 - acetone cyanohydrin or diethyl ketone cyanohydrin and METHOD OF PREPARING CYANOGEN cupric sulfate are dissolved in water. At this point little or no reaction occurs. Thena dilute aqueous alkaline William L. Fierce, Crystal Lake, and Walter J. Sandn'er, solution is slowly added. Immediately cyanogen is lib Carpentersville, Ill., assignors to The ‘Pure Oil Com erated as a gas and can be recovered by stripping the pany, Chicago, 111., a corporation of Ohio reaction solution with helium, nitrogen, or other inert No Drawing. Filed Nov. 10, ‘1958, Ser. No. 772,713 gas, preferably at elevated temperatures for most e?icient recovery. No polymerized cyanogen is produced and I 10 Claims. (Cl. 23-151) 10 none of the reactants are appreciably toxic. The following non-limiting examples are illustrative of This invention relates to new and useful improvements the scope of this invention. in processes for the preparation of cyanogen, and more particularly to a process in which a ketone cyanohydrin is EXAMPLE I reacted with a cupric salt in aqueous alkaline solution. 15 A one-liter, three-necked ?ask ?tted with a dropping Cyanogen (CN)2 is a well known compound which is funnel, a mercury-sealed stirrer, a condenser, and a useful as an intermediate in the preparation at a variety Glas-col electric heating mantle was charged with 63.8 g. of organic compounds. Classical methods of producing (0.4 mols) of cupric sulfate (a stoichiometric excess), cyanogen include (1) dehydration of ammonium oxalate, 250 ml. water and 45.7 ml. (0.5 mol) of acetone cyano (2) thermal decomposition of mercuric cyanide, and (3) 20 hydrin. A helium ?ow of 100 cc./min. was conducted reaction of sodium cyanide and copper sulfate solutions, through the mixture in the ?ask, through the condenser wherein part of the cyanogen is evolved as cyanogen gas to a gas-sampling tube, and ?nally through two bubblers and part remains as cuprous cyanide. Cyanogen is use in series, each containing 100 ml. of 2.0 N NaOH. From ful in the preparation of a variety of organic compounds, the dropping funnel 50 ml. of 5.0 N NaOH was added e.g., aliphatic nitriles, cyanic acid, and oxa'niide. 25 slowly, dropwise, over a period of 34 minutes. Five It is one object of this invention 'to' provide a new and minutes later heating was started and the solution was improved method for the production of cyanogen. brought to re?ux temperature, 84° C. During the run, Another object of this invention is to provide a method the gas-sampling tube and the ?rst bubbler were replaced for preparing cyanogen which does not involve the‘ twice for analysis. These changes took place after 20 handling of the highly toxic hydrogen ‘cyanide gas. 30 minutes and 69 minutes, respectively. The third gas A feature of this invention is the provision of an im sampling tube and bubbler were removed after 134 min , proved process for the preparation of cyahogen by reac utes. The contents of the bubblers were analyzed for tion of a ketone cyanohydrin with a cupric salt in alka cyanide ion ‘content by ‘titration with a standard silver line ‘solution at ambient temperatures in the range of nitrate solution (the Liebig method). This gave a. meas l5°—‘90° C. 35 tire of the total HCN and cyanogen in the gas stream. Other objects and features of this invention will be The gas samples in the sampling tubes were analyzed by come apparent from time to time throughout the spec means of a mass spectrometer to determine the relative i?cation and claims as hereinafter related. amounts of the HCN and (CN)2 in the gas stream. By This invention is based upon our discovery that cyano; combining these data, the cyanogen yields could be cal gen is produced in good yields by the reaction of a ketone 40 culated. In this run, a 31.8% yield of cyanogen was cyanohydrin and 1a cupric salt in aqueous‘ alkaline solu obtained, based on acetone cyanohydrin charged, and tion at moderate temperatures. assuming the reactions: The Jacquemin method for the preparation of cyano gen by the action of potassium cyanide (KCN) on cupric (1) CH3(OH) C(CN) CH3—> (CH3)2CO+HCN sulfate (CuSO4) has been in use for many years and is 45 (2) 6HCN+2CuSO4—-> (CN) 2+ . .. . now a standard laboratory method for preparing cyano EXAMPLE 11 gen. G. Hahn and W. Leopold described the method in In another experiment, using the apparatus described considerable detail in Ber., 68, 1974 (1935), B. Ricca in in Example I, the ?ask was charged with an aqueous Ann. Chim. Applicata, 16, 83 (1926), also discusses this 50 solution containing 0.40 mol of CuSO4. From the drop reaction, and the method is described in detail in “Inor ping funnel 1.09 mols of acetone cyanohydrin were added ganic Syntheses.” In this reaction, cyanogen is evolved slowly, dropwise, over a period of 40 minutes. No alkali spontaneously by the addition of a saturated aqueous was present during the reaction. Only a minute trace of KCN solution to a saturated aqueous CuSO4 solution. cyanogen was formed. The reaction is as follows: 55 EXAMPLE III In another experiment, using the apparatus of the pre We have found after several trials that this method is not ceding examples, 100 ml. of 4.0 N NaOH was added convenient as a general laboratory method for several slowly, dropwise, to an aqueous solution of 10 g. reasons. First, a large volume of highly toxic KCN CuSO4.5H2O and 10 ml. of acetone cyanohydrin. This solution must be added to the reaction solution from a 60 reaction mixture consisted of 0.04 mol CuSO4, 0.109 mol dropping funnel. The dangers in handling such toxic acetone cyanohydrin, and 0.40 mol NaOH. When the solutions are apparent. Second, during the addition of addition of the base was complete, the solution was re the aqueous KCN, there is a tendency for black, solid ?uxed ‘for 1.5 hours. No cyanogen was formed either material to be formed. This is apparently paracyanogen before, during, or after the re?uxing. 65 which forms in the presence of the alkaline KCN solu EXAMPLE IV tion. This reduces the yield and also causes difficulties in the experimental procedures, e.g., the dropping funnel Using the same apparatus as in the preceding example, tip and other restricted areas often become plugged with an‘ aqueous solution containing 0.40 mol cupric acetate this black solid. I . is charged to the ?ask together with 1.10 mol of ace We have found that these dif?‘culties can be avoided and 70 tone' cyanohydrin. From the dropping funnel 50 ml. of good cyanogen yields obtained by ‘our new and improved 5.0 N KOH is addedslowly, dropwise, over a period of 30 minutes.‘ The mixture is swept with helium at a 2,951,744. . " 3 4 ?ow of 100 cc./min. and analyzed for cyanogen content. addition of reactants is not critical. However, it is At room temperature, a small yield of cyanogen is ob preferred to mix the aqueous solution of cupric salt and tained. The reaction mixture is then brought to re?ux ketone cyanohydrin and add slowly thereto the dilute temperaturerand stripped with ‘helium for a period of aqueous alkali to initiate the reaction. This addition of alkali to the other reactants is preferably at room 1.5 hours. 7 A substantialryield of cyanogen is obtained temperature. After the alkali has been added, the from this reaction.‘ 7 > > ' EXAMPLE V solution should be stirred, stripped with helium, nitro gen, or other inert gas, and heated slowly to're?ux. In another experiment, using the apparatus of the Stripping is continued at re?ux until no more cyanogen preceding examples, an aqueous solution containing 0.60 10 is liberated. The solution is then cooled and su?icient mol of cupric bromide and 1.65 mols of diethyl ketone ketone cyanohydrin and cupric salt added to remake the cyanohydrin is charged to the ?ask. From the dropping original concentrations of reactants. Further addition funnel, 75 ml. of 4.0 N NH4OH is added, dropwise, over . of alkali with stirring,rsrtripping, and re?uxing, as previ a period of 50 minutes. The solution is heated to 60° ously described, produces further quantities of cyanogen, C. and swept with helium at a ?ow of 100 cc./min. A thus utilizing the unreacted ketone cyanohydrin from

substantial yield of cyanogen is obtained under these the initial reaction. ' ' ' ‘ ’ " . reaction conditions. While we have described our invention fully and completely as required by'the patent statutes,’inc1uding ‘EXAMPLE VI a full and complete description of What wenow consider In a series of experiments, using the apparatus of the 20 to be the best mode of carrying out our invention, we preceding examples, the relative proportions of acetone wish it to be understood that within the scope of the cyanohydrin and base were varied to determine optimum appended claims this invention may be practiced other.‘ reaction conditions. In these runs the mass spectrometer wise than as speci?cally described. was not used for analysis. The ef?uent gases were passed What is claimed is: ' through a bubbler containing acidi?ed silver nitrate to 26 1. A method of preparing cyanogen which comprises remove HCN. Then the gas stream was bubbled through reacting a ketone cyanohydrin with a cupric salt in aque-' dilute NaOH to convert the cyanogen into cyanide ion, ous alkaline solution containing alkali in the amount of which was analyzed by silver nitrate titration according 0.05—l.0 mol per mol of the ketone cyanohydrin. ' to the Liebig method. The results of these experiments 2. A method in accordance with claim 1 in. which the are shown in the following table: 30 reaction temperature is in the range frompabout 15° to Table 90° C. . ' 3. A method in accordance with claim 1 in ,which the ketone cyanohydrin is acetone cyanohydrin. - Mols of Reactants 7 (ON); Yield 1 4. A method in accordance wih claim 1 in which Run No. per pass, 85 Acetone percent the ketone cyanohydrin is diethyl ketone cyanohydrin. CuSOr cyano- NaOH 5. A method in accordance with claim 1 in which the hydrin ketone cyanohydrin and cupric salt are mixed in an aqueous solution and aqueous. alkali slowly added thereto. 0. 40 0.50 0.25 22. 7 0. 40 0. 50 0. 40 32. 3 ‘6. A method in accordance with claim 1 in which the 0. 40 0. 50 0.50 21.0 40 alkaline solution is an aqueous solution of an alkali metal

hydroxide. ' ' 1 Yields based on acetone cyanohydrin charged, assuming reactions 7. A method in accordance with claim 6 in which the set forth in Example I. ketone cyanohydrin and cupric salt are mixed ' in an From these and other experiments, we have found that aqueous ‘solution, aqueous alkali metal hydroxide is any ketone cyanohydrin is useful in the production of 45 addedto said solution at room temperature, the reaction‘ cyanogen according to this invention. In carrying out mixture is stripped with an inert gas, and slowly heated our process, ‘a ketone cyanohydrin and a cupric salt are to re?ux temperature. ' " mixed and a‘small amount of alkali added thereto. Any 8. A method in accordance with claim 1 in which the _ ketone cyanohydrin may be used, whether alkyl, aryl, or cupric salt is selected from the group consisting of mixed alkyl-aryl, and vwhether symmetrical or unsym 50 CuSO4, Cu(NO3)2, CuOlz, CuBrZ, and Cu(CH3CO‘2)2. metrical. Ketone \cyanohydrins which may be used 9. A method of preparing cyanogen which comprises include acetone cyanohydrin, diethyl ketone cyanohydrin, reacting acetonecyanohydrin with cupric sulfate in aque-. methyl ethyl ketone cyanohydrin, dibutyl ketone cyano out solution containing 0.05—1.0 mol of an alkali metal hydrin, dioctyl ketone cyanohydrin, ethyl propyl ketone hydroxide per mol of acetone cyanohydrin at a tem cyanohydrin, ethyl octyl ketone cyanohydrin, dinaph 55 perature of about 15°-90° C. thyl ketone cyanohydrin, benzophenone cyanohydrin, 10. A method of preparing cyanogen which comprises and acetophenone cyanohydrin. I mixing acetone cyanohydrin with an aqueous solution of Cupric salts which may be used include any water ' cupric sulfate, slowly adding to the mixture at room soluble cupric salt, such as the sulfate, acetate, bromide, temperaturean aqueous solution containing 0.05—l.0 mol chloride, and nitrate. Any aqueous alkali, preferably 60 of an alkali metal hydroxide per mol of acetone cyano an alkali metal hydroxide or ammonium hydroxide, may hydrin, stripping the reaction mixture with an inert gas, be used to effect the reaction between the cyanohydrin slowly increasing the temperature of the reaction mixture and the cupric salt to generate cyanogen. The alkali is to the re?ux temperature, re?uxing the mixture with con required to be present in the amount of of 0.05-1.0 mol tinued stripping, and recovering the cyanogen stripped per mol of the ketone cyanohydrin.‘ Amounts of alkali from the reaction mixture. - less than 0.05 mol pervmol of ketone cyanohydrin are ine?ective in this reaction, while amounts substantially in References Cited in the ?le of this patent’ excess of 1 mol per mol of ketone cyanohydrin appar UNITED STATES PATENTS _ ently decompose the cyanohydrin without generating 2,841,472 - ‘Fierce etal ______~______Ju1y1,19ss cyanogen. Preferably, the ketone cyanohydrin'should 70 be present in a slight molar excess over the base, e.g., :OTHER REFERENCES 0.8-1.0 mol of‘ base per mol of ketone cyanohydrin. The reaction may be carried out‘at any temperature in AqueousYates etSolution,” al.: “The Journal Dissociation of the Americanof Lactonitrile Chemical the range from about 15° to 90° C. but is preferably carried out at a temperature of’ 60-850 C. _. The-order of 75 Society, vol. 74, 1952, pp. 4153-4155. ’ -