Patented June 9, 1942 2,285,843 UNITED STATES PATENT OFFICE 2,285,843 NTROGEN GENERATING CHEMICALS Wendell W. Smith, Nutley, N.J., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application December 13, 1939, Serial No. 308,957 5 Claims. (C1, 23-104) The present invention relates to chemicals, ingly has better ageing properties and lower wa suitable as chemical blowing or gassing agents ter absorption. for generating or liberating nitrogen gas, and The following examples are given to illustrate useful particularly for the making of gas-ex the invention: panded rubber products of both the cellular and 5 ECample A-Preparation of concentrated the Sponge types. aqueous solutions of ammonium nitrite: An object of the invention is to obtain concen The method comprises treating solid ammoni trated ammonium nitrite, in the fluid state as a um sulfate and solid sodium nitrite, in the ap concentrated aqueous solution, in the Solid State proximate ratio of 1 to 2 moles respectively, with as crystalline ammonium nitrite, and as the com O Water containing dissolved ammonia. The plex salt of zinc having the probable formula amount of Water may be regulated to give a so Zn(NH3)2(NO2)2. Other objects will be apparent lution of the desired concentration. When these from the following description. are mixed a double decomposition takes place, Ammonium nitrite has heretofore been ob and in the presence of only a limited amount of tained by evaporating and subliming in vacuo Water, two phases are present, a solid and a liq concentrated solutions of a mixture of ammo luid phase. The Solid phase is rich in Sodium Sull nium chloride and sodium or potassium nitrite fate and the liquid phase is rich in annonium ni (J. W. Mellor "A Comprehensive Treatise On In trite. Thus, by Separating the two phases, a so organic and Theoretical Chemistry' 1928; Long lution consisting of water, ammonia, ammonium mans, Green and Co., New York, vol. VIII, p. 20 nitrite and a Small amount of sodium sulfate is 470). This practice, involving interaction of the obtained. The ratio of sodium sulfate to ammo ammonium chloride and alkali metal nitrite to nium nitrite in the Solution is Small if a limited form annonium nitrite and alkali-metal chlo amount of Water is used in the preparation. Heat ride, is relatively costly and the yield of the con may be applied to the mixture before separating centrate somewhat limited, the ammonium ni the tWO phases in order to hasten the double de trite having a tendency to decompose as it is composition. formed, thereby requiring its preparation under A Specific example to illustrate this prepara definitely controlled conditions. tion is as follows (parts are by weight): It has now been found that by reacting am Mix: monium sulphate distinct advantages are Ob 30 Parts tainable over ammonium chloride. By utilizing Solid (NH4)2SO4------37 its greater solubility in an ammoniacal Solution Solid NaNO2------38.6 together with the lower solubility of sodium or Add 9% aqueous ammonia solution.------24.4 potassium sulphate formed therefrom (con Heat to 60 C. and maintain at this tempera pared to above sodium or potassium chloride), a 35 ture for one hour with occasional stirring. Sep more concentrated solution of ammonium nitrite arate the Solid phase (principally Na2SO4) from may be prepared and a better Separation of the the liquid phase by filtering. The liquid phase ammonium nitrite Solution from the other Salt So obtained, which is the product of interest, is (alkali-metal sulphate) produced in the double an ammoniacal water solution of ammonium ni decomposition reaction results. By using ammo 40 trite containing sodium sulfate as an impurity. nium sulphate, the ammonium nitrite Solution The ammonium nitrite concentration is between can be prepared sufficiently concentrated to per 50 and 60%, and the Sodium sulfate about 10%. mit crystallization of the ammonium nitrite from Eacample B.-Preparation of solid ammonium the solution by cooling with ice or other agency, nitrite (parts are by weight): as distinguished from crystallization by evapora 45 The method involves cooling an ammoniacal tion of the solution. The concentrated ammoni Water Solution of ammonium nitrite containing um nitrite solution also provides a means of more than 40% ammonium nitrite (such as that forming a new gassing agent useful for making described above) to a temperature low enough to gas-expanded rubber, and which is a Solid con 50 cause a Solid phase to form. This solid phase plex zinc diammonia nitrite. consists principally of ammonium nitrite and The present gassing agents liberate nitrogen may be separated from the liquid phase by any which is a most useful gas for making expanded suitable method such as filtering. The liquidi rubber products since it diffuses SO slowly phase may be used in preparation A in place of through rubber, compared with gases like car 55 the ammoniacal water Solution. bon dioxide and ammonia, thereby preventing A specific example which illustrates this meth collapse of the rubber which is an important item Od is as follows: 100 parts of an ammoniacal 57% in making cellular rubber. The new gassing Solution of ammonium nitrite containing Sodium agent, zinc diammonia nitrite, is associated with sulfate as an impurity (preparation described in little or no sodium Salts, and the rubber accord 60 Example A) is cooled to -2°C, to induce crystal 2 2,285,848 - lization, 41 parts of solid phase being this Each of the ammonium nitrite preparations of formed. The solid phase is 75% ammonium ni Examples A, B and C, above, evolves gases, prin trite and the remainder sodium sulfate. cipally nitrogen and water, when heated. There Eacample C.-Zinc diammonia nitrite (parts fore, each may be used in rubber as the gas-pro are by weight): ducing substance in forming expanded rubber A concentrated solution of ammonium nitrite articles (soft, elastic or hard), either of the such as that described in Example A is treated closed-cell type (cellular rubber) or of the inter with an amount of zinc oxide in excess of that connecting cell type (sponge). The substance necessary for the maintenance of a Solid phase in is incorporated into the rubber along with the equilibrium with the solution. A reaction takes O other necessary and desirable compounding in place forming a new solid, zinc diammonia ni gredients, and the rubber mix is subjected to the trite, the composition of which is expressed by usual control treatments to produce cellular rub the formula, believed to be as follows: ber or sponge. The rubber may be natural rub ber or artificial rubber that has substantially 5 the physical properties of natural rubber. Too large a quantity of zinc oxide is to be avoid The present gaSSing agents may also be used, ed as it would only contaminate the solid product. as chemical reagents, to introduce nitrogen into The maximum quantity of Zinc oxide which can other chemicals. be used without such contamination is deter Having thus described my invention, what I mined by the original ammonium nitrite content 20 claim and desire to protect by Letters Patent is: of the solution and by the composition of the So 1. A process which comprises mixing ammo lution which is in equilibrium with the two solid nium sulphate with alkali metal nitrite in the phases, zinc diammonia nitrite and zinc oxide. ratio of approximately one molecular proportion This latter composition is a function both of of the Sulphate to approximately two molecular temperature and of the initial free annonia con 25 proportions of the nitrite in ammoniacal Water tent. solution containing an annount of Water only suf A specific example which illustrates this prep ficient to maintain in Solution most of the am aration is as follows: To 100 parts of an ammo monium nitrite formed in the ensuing reaction niacal 45% ammonium nitrite solution contain but insufficient to maintain in Solution the alka ing approximately 4.2% of free ammonia, pre 30 li-metal sulfate formed, and heating the mixture pared as in Example A add 22.5 parts of zinc to cause the reaction to take place. oxide. Stir for one hour to break up lumps of 2. A process as Set forth in claim 1 in which, zinc oxide and thus bring about complete re after heating the mix and allowing the solid action. This produces 39 parts of the complex phase of alkali-metal sulfate to precipitate out, salt, zinc diammonia, nitrite, as a Solid phase 35 the ammoniacal solution of ammonium nitrite which may be separated from the liquid phase is separated from said Solid phase, and cooled to by filtering. The liquid phase from this treat a temperature sufficiently low to precipitate out ment contains about 29% ammonium nitrite. It the annonium nitrite, and Segregating Said pre can be enriched with respect to ammonium ni cipitate of ammonium nitrite from the mother trite by using it in place of the annoniacal So AO) liquor. ution in preparation. Example A and the cycle 3. A process which comprises mixing ammo repeated. nium sulphate with alkali metal nitrite in the By starting with an ammonia solution as in ratio of approximately one molecular proportion Example. A not substantially greater than 9%, of the sulphate to approximately two molecular very little ammonia is lost in preparing the an 45 proportions of the nitrite in ammoniacal water monium nitrite solution, and the annonia, CO solution containing an amount of Water only centration of the resulting solution is such that sufficient to maintain in solution most of the am a good yield of the product is obtained on the monium nitrite formed in the ensuing reaction addition of the Zinc oxide. but insufficient to maintain in solution the alka Chemical analysis of a sample of the Zinc di 50 li-metal sulfate formed, and heating the mix ammonia nitrite gives the following results: ture to cause the reaction to take place, with for mation of ammonium nitrite in Solution, and rer Theoretical acting the ammoniacal solution containing the Analysis based on formula ammonium nitrite in solution With Zinc oxide to 55 form a solid complex zinc diammonia, nitrite. Percent Percent 4. A process which compriseS reacting an an Zinc oxide------47 42.3 moniacal solution of ammonium nitrite With Zinc Total nitrogen.------28.5 29.3 oxide, the amount of zinc oxide being in exceSS Ammonia. ------1.0 17.8 of that necessary for maintaining a solid phase in 60 equilibrium with the Solution. The actual analysis lies between the compo 5. The compound, zinc diammonia dinitrite sitions expressed by the formulaS having an analysis; zinc as oxide approximately 42.3 percent; total nitrogen approximately 29.3 percent; ammonia approximately 7.8 percent 65 but nearer the former. WENOELL. W. SMITH,