March 18, 1969 E. A. LAWTON ETAL 3,433,595 METHOD OF PREPARING DIFLUORAMINE AND PREPARING TETRAFLUOROHYDRAZINE THEREFROM Original Filed Sept. 15, 1959

4. F 2 (X) O 2 seesR C/N FLUORINE HF Q> FLOWMETER REACTOR 15 ABSORPTION , -X 17 VACUUM PUMP N M OUTLET I6 WASTE 2 22 AUXILARY SULPHURIC FUORINE HF TRAPACID ABSORPTION ABSORPTION 2O IS

FIG. I.

REACTOR LIQUID

INVENTORS EMI. A. LAWTON By JOHN Q. WEBER 622 - 4-at ATTORNEY 3,433,595 United States Patent Office Patented Mar. 18, 1969 1. 2 3,433,595 FIG. 3 is an apparatus for the preparation and re METHOD OF PREPARNG DFLUORAMINE covery of tetrafluorohydrazine. AND PREPARING TETRAFLUOROHYDRA Basically, the preparation of difluoramine involves the ZINE THEREFROM steps of fluorinating a nitrogen compound containing Emil A. Lawton, Woodland Hills, and John Q. Weber, amide and imide linkages such as urea, biurea, biuret, Topanga, Calif., assignors to North American Rockwell aminoguanidine, diaminourea, or 5 - aminotetrazole by Corporation, a corporation of Delaware Original application Sept. 15, 1959, Ser. No. 804,066, now gaseous fluorine source such as fluorine gas diluted with Patent No. 3,294,495. Divided and this application an inert gas such as nitrogen and both liquid and gaseous Aug. 29, 1963, Ser. No. 308,614 products are obtained which contain NF bonds. In heat U.S. C. 23-205 2 Clains 0. ing the liquid products difluoramine is obtained along with nt. C. CO1b 21/18 other gases and can be purified by low temperature frac tional condensation. The tetrafluorohydrazine is in turn prepared from difluoramine by a decomposition process ABSTRACT OF THE DISCLOSURE entailing the treatment of difluoramine in the presence of 5 certain solid materials an example of which is the solid A fluorinating process for preparing difluoramine and residue from the above distillation of fluorinated urea. a catalytic process for preparing tetrafluorohydrazine from The process of formation of difluoramine may be illus the difluoramine. trated by the following equation: -amirumumw (1) O 20 | This application is a division of application Serial 4F -- NH-C-NH2 - 2NHF - COF2 -- 2HF No. 804,066, filed September 15, 1959, and now U.S. Alternatively, the reaction may be written as shown in Patent No. 3,294,495. w Equation 2 since the bulk of the fluorine used was found The present invention is directed to a novel method of in the initial liquid product. preparing difluoramine and preparing tetrafluorohydrazine therefrom. More particularly, the invention is directed to 25 (2) a fluorination process of preparing difluoramine and a H2N-C-NH2 -- 2F2 - H2N-C-F -- FNH -- HF catalytic process of preparing tetrafluorohydrazine from The Equation 3 for the decomposition of difluoramine the prepared difluoramine. to tetrafluorohydrazine is: The products of the processes herein described find use 30 (3) cat. as storable oxidizers and monopropellants for use in 2HNF2 - NF4 -- He rocket engine applications and, further, are useful in pre FIGURE 1 is a flow diagram of the method of making paring intermediates useful in the preparation of other difluoramine and shows the entry of the hereinafter de compounds containing a nitrogen-fluorine bond. The scribed amounts of fluorine gas and nitrogen gas which process herein disclosed is cheaper than the only known are metered by valves 10 and 11 into a glass or Pyrex prior art process due to the fact that the methods are flow meter 12 which measures the rate of flow of the gases carried out at ambient temperatures and pressures and into a reactor 14. The solid to be fluorinated is placed the fact that better yields are obtainable. on a grid 9 in a reactor 14 which is preferably of stain Tetrafluorohydrazine which is made by the herein de less steel and arranged so that any liquid formed drops scribed method has recently been reported in the Journal 40 below the grid and collects in the bottom of the reactor of the American Chemical Society, volume 80, at page adjacent to the gas inlet tube. Prior to the commencement 5004 (1958). It was prepared by the reaction of NF with of actual fluorination the system shown in FIG. 1 is metals at temperatures of 350° to 450° C. in the presence flushed with nitrogen and cooling baths employed where of such metals as copper and arsenic. One particular necessary. The reactor 14 may be cooled with low tem species of the concerned method of making tetrafluoro perature water. Measured flows of fluorine and nitrogen hydrazine uses as a catalyst certain solid residues from the are passed into the reactor 14 forming the reactor liquid distillation of fluorinated urea formed during the making containing difluoramine and the exit gas passed into hy of difluoramine by the herein disclosed process. drogen fluoride absorbers 15 and 16 which contain sodium An object of this invention is to provide a method of fluoride as the absorbing agent. The gases then pass making difluoramine. through a cooled U-trap 19 in which gaseous by-products A further object of this invention is to provide a method are condensed, which may contain some residual di of making tetrafluorohydrazine from difluoramine. fluoramine, a fluorine absorber 20 containing potassium A still further object of this invention is to provide a or sodium chloride and a sulfuric acid trap 21. Residual satisfactory process of fluorinating urea and other nitro gases from the trap 21 are passed to waste through line gen compounds to form difluoramine. 22. The trap 19 is detachable from the overall system. An additional object of this invention is to provide a Three-way valve 18 is suitably positioned when removing method of reacting difluoramine in the presence of a suit able catalyst such as a catalyst formed in the fluorination trap 19 from the system so that vacuum pump outlet 17 of urea, to form tetrafluorohydrazine. may remove gases being formed in reactor 14. A further object of this invention is to provide a 60 It has been found that the preferred temperature with method of making monopropellants having a nitrogen in the reactor 14 is approximately 0° C. The temperature fluorine bond. may range, however, from approximately -30° C. to A still further object of this invention is to provide a --40 C. for satisfactory results. The pressure in the process of making difluoramine and tetrafluorohydrazine reactor 14 is generally atmospheric although it has been oxidizers which are useful as rocket propellants. 65 determined that a pressure range of from about one-half Further objects to this invention will be apparent from atmosphere to two atmospheres is a preferable pressure the following description taken in conjunction with the range usable in the described fluorination process. The accompanying drawing, in which: particular time of fluorination is dependent upon the size FIG. 1 is a flow diagram of the process of making of the sample, the gas flow rate and the particular par difluoramine; 70 ticle size and shape of the starting material. FIG. 2 is a typical trap apparatus for isolating quantities The ratio of the mole of fluorine to mols of urea, which of difluoramine; and is a preferred starting material, is in the range of from

3,433,595 5 6 -112 C. and -142 C. The -45° C. condensate was For a further example lithium hydride (1.00 mmol) mainly a very slightly volatile liquid with a small amount and difluoramine (21.4 cc.; 0.96 mmol) were combined of gas whose infrared spectrum showed only a band at and stored exactly as in the previous experiment. After 2.9. The infrared spectrum of the -112 C. condensate, standing 17 hours without apparent change, the reaction 3.9 cc, showed bands at 4.6, 8.0, 8.6, 8.8, 9.7 (SiF) products were examined as before. Data are summarized and 11.0a. The -142 C. condensate, 51.7 cc. was di 5 in Table V. fluoramine, with a trace of silicon tetrafluoride and car TABLE W.-REACTION PRODUCTS FROMIDIFLUORAMINE bon dioxide. The material, noncondensible at -142° C., WITH LITHIUM HYDRIDE was refractionated several times to yield mixtures of sili Prod- Quantity, How Isolated Method of con tetrafluoride and carbon dioxide with traces of di 10 uct cc. S.T.P. Identification fluoramine and 6.2 cc. gas, whose infrared spectrum N2------3.5 Noncondensible------Mass spectrum. indicated chiefly silicon tetrafluoride and tetrafluoro H2------11.0 -----do------Do.

HNF--- 10.3 Condensible at -142 C------Infrared spectrum. hydrazine. The nearly pure difluoramine, 51.7 cc., was re N2F4---- 3.7 Noncondensible at -142 C--- Do. fractionated through -127 C. and -142° C. The LiH----- 13.7 Solid------H2 Evolution. -142 C. condensate, 1.9 cc., was pure difluoramine, and LiF----- 14.7 ----- do------Chemical analysis. the gas noncondensible at -142 C, 5.4 cc., was nearly all silicon tetrafluoride and carbon dioxide. Noteworthy in this experiment is the smooth formation In a further example a major amount of difluoramine of 3.7 cc. tetrafluorohydrazine from 11.9 cc. di condensed out in a -126 C. trap. Difluoramine can be fluoramine. This represents a 67 percent yield. recovered in traps within the range of from about -120° For a still further example, 2 cc. of difluoramine C. to about -150° C. The particular temperatures de 20 were stored in a stainless steel ampoule at room tem pend on the particular pressures employed. perature. After several days it was found that about two FIGURE 3 shows an apparatus for obtaining tetra thirds of the difluoramine had been converted into tetra fluorohydrazine from difluoramine. It comprises a flask fluorohydrazine. Results of this are seen in Table VI. 41, stoppered at 42 and containing a frozen ring 43 of TABLE WI difluoramine which was formed in the -152 C. or Quantity Storage Quantity Quantity Test HNF Duration, HNF NF thereabouts cold trap above described. Contained in the No. Introduced, days Recovered, Formed, bottom of the flask 41 is a catalyst material 44 which CC CC C. may be the insoluble solid refractory material from the i------2.0 6 ca. 10------ca. 0.5. -80 C. or thereabouts fractional condensation trap 30 2------3.8 23 ca. 1.5------ca. 1.0. above described (believed to be HCNO polymers), or solid lithium hydride, or type 304 stainless steel or Although the invention has been described and illus gaseous perchloryl fluoride FCIO or gaseous HCl. The trated in detail, it is to be clearly understood that the amounts of these latter gases is not critical. A 4:1 ratio same is by way of illustration and example only and is of difluoramine to FCIO is preferred. As the frozen ring 35 not to be taken by way of limitation, the spirit and scope or slug 43 is melted the gas formed contacts the catalyst of this invention being limited only by the terms of the material 44 forming NFA gas 45 within the flask. Yields appended claims. as high as 67% have been obtained. Liquification of this We claim: N2F4 gas makes the material useful in the aforesaid 1. The catalytic method of preparing tetrafluoro rocket propellant field. 40 hydrazine from difluoramine comprising contacting di A specific example of the practice of this process is: fluoramine with a catalyst selected from the group con 14.5 cc. of difluoramine was introduced into an ampoule sisting of steel and the compound prepared by fluorinat containing lithium hydride (4.1 mg.) in such a manner ing urea with fluorine, fractionally condensing at a tem that the difluoramine formed a solid ring above the perature of about -80 C. gaseous products formed by hydride. The ampoule was then stored in a Dewar con said fluorinating step, thereby forming gaseous products taining a small amount of liquid nitrogen so that the and a solid residue and contacting difluoramine with the reactance would warm slowly to room temperature. solid residue formed in said condensing step. After 60 hours at room temperature, the gaseous prod 2. The method of claim 1 wherein the initial ratio ucts were removed and separated in the vacuum line. The of moles of fluorine to moles of urea is in the range solid product was tested with aqueous hydriodic acid 50 of from about 0.5:1 to about 3:1. and gave a negative test for oxidants. The composition of the gaseous product mixture is described in Table IV. References Cited TABLE IV.--GASEOUS PRODUCTS FROMIDIFLUORAMINE UNITED STATES PATENTS AND LITHIUM HYDRIDE 3,077,377 2/1963 Lawton et al. ------23-356 Product Quantity, cc. Method of Identification Nitrogen 55 Content 3,220,799 11/1965 Colburn ------23-205 (as N2), cc. 3,220,800 11/1965 Martin ------23-205 Ni------1.2 Mass spectrograph------2 3,346,347 10/1967 Schmall ------23-205 H2------8.0 ----- 0------NF4------2.5 Infrared spectrum------2.5 OSCAR R. VERTIZ, Primary Examiner. HNF------4.4 -----do------2.2 Other------None ------60 G. O. PETERS, Assistant Examiner. Total nitrogen in products (as N2): 5.9 cc. U.S. C1, X.R. Total nitrogen in reactants (as Ns): 7.2 cc. 23-356