Abstract:
A method of producing NF 4  PF 6  by a displacement reaction between NF 4  BF 4  and PF 5 .

Description:
The invention herein described was made in the course of or under a contract or subcontract thereunder, (or grant) with the United States Navy. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Ser. No. 732,275 filed Oct. 14, 1976, and abandoned Dec. 5, 1977, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to methods of producing compositions and is particularly directed to a method of producing NF 4  PF 6  by a displacement reaction between NF 4  BF 4  and PF 5 . 
     2. Description of the Prior Art 
     NF 4   +  salts are the key ingredients for solid propellant NF 3  --F 2  gas generators, such as that disclosed by D. Pilipovich in U.S. Pat. No. 3,963,542, for chemical HF-DF lasers. Whereas NF 4  SbF 6  and NF 4  AsF 6  can be prepared with relative ease, according to the methods taught by W. E. Tolberg et al, in U.S. Pat. No. 3,708,570, and K. O. Christe et al, in U.S. Pat. No. 3,503,719, these compounds suffer from the disadvantage of containing a relatively heavy anion, thus decreasing their performance in an NF 3  --F 2  gas generator. This disadvantage can be overcome by replacing the SbF 6   -  or AsF 6   -  anion by the lighter PF 6   -  anion. The existence of this salt has previously been claimed by Tolbert et al in U. S. Pat. No. 3,708,570, but their production process was so inefficient that they could not isolate an amount of material sufficient for its isolation, identification and characterization. 
     BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
     This problem of synthesizing NF 4  PF 6  is overcome by the present invention. The method of the present invention involves a displacement reaction between the readily available NF 4  BF 4  and PF 5  according to: 
     
         NF.sub.4 BF.sub.4 +PF.sub.5 →NF.sub.4 PF.sub.6 +BF.sub.3 
    
     applicants have found that the displacement reaction can be carried out at any temperature above the melting point of PF 5  (-94° C.) and below the decomposition temperature of NF 4  PF 6  (above 245° C.). Moreover, the pressure is not essential and is given by the reaction temperature (that is, the vapor pressure of PF 5 ). 
     This method provides NF 4  PF 6  of high purity. 
     Accordingly, it is an object of the present invention to provide an improved process for the production of NF 4  PF 6 . 
     This and other objects and features of the present invention will be apparent from the following examples. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a typical experiment, pure NF 4  BF 4  (2.07 mmol) was combined at -196° C. with an excess of PF 5  (40.01 mmol) in a 10-ml 316 stainless steel cylinder. The mixture was kept at 25° C. for 64 h. The volatile materials were removed in vacuo and separated by fractional condensation. They consisted of BF 3  (2.05 mmol) and unreacted PF 5  (37.93 mmol). The white solid residue had gained 120 mg in weight. Based on the above material balance, the conversion of NF 4  BF 4  to NF 4  PF 6  was essentially complete. This was further confirmed by vibrational spectroscopy which showed the solid to be NF 4  PF 6  containing no detectable amounts of NF 4  BF 4 . 
     The salt NF 4  PF 6  is a white, crystalline, hydroscopic solid, stable at room temperature, but rapidly decomposing at 245° C. Its characteristic x-ray diffraction powder pattern is listed in Table I. Its vibrational spectrum is listed in Table II and establishes the ionic nature of the salt, i.e. the presence of discrete NF 4   +  cations and PF 6   -  anions. This was further confirmed by  19  F nmr spectroscopy in HF solution which showed the triplet (J NF  =230 Hz at φ=-217) characteristic for NF 4   + . 
     
                       TABLE I______________________________________X-RAY POWDER DATA FOR NF.sub.4 PF.sub.6.sup.ad obsd      d calcd     Int       h k l______________________________________5.40        5.36        ms        1 1 04.55        4.53        s         1 0 13.91        3.89        vs        1 1 13.79        3.79        s         2 0 02.91        2.91        ms        2112.65        2.65        m         1 0 22.40        2.40        vw        3 1 02.307       2.305       m         3 0 12.204       2.205       vw        3 1 12.171       2.171       mw        2 1 21.882       1.883       ms        3 0 2,0 0 31.825       1.827       vw        3 1 2,1 0 31.784       1.785       w         3 3 01.747       1.747       mw        4 1 11.685       1.685       w         3 2 2,2 0 31.646       1.646       w         2 1 31.622       1.622       w         4 2 11.536       1.540       vw        4 1 21.485       1.486       vw        5 1 01.464       1.463       vw        5 0 11.437       1.437       w         5 1 11.408       1.407       vw        5 2 01.365       1.365       vw        5 2 1,1 1 41.333       1.335       w         5 0 21.318       1.319       vw        4 4 01.302       1.304       vw        2 1 41.259       1.259       w         4 2 31.214       1.216       w         6 1 1______________________________________ .sup.a Tetragonal, a = 7.577, c = 5.653A, Cu K.sub.α  radiation Ni filter 
    
     
                       TABLE II______________________________________VIBRATIONAL SPECTRUM OF NF.sub.4 PF.sub.6Obsd Frequency (cm.sup.-1)Ir           Raman      Assignments for NF.sub.4.sup.+ (T.sub.d)______________________________________2380 vw                   2ν.sub.3 (A.sub.1 + E + F.sub.2) = 23202320 w2005 w                  ν.sub.1 + ν.sub.3 (F.sub.2) = 20081765 w                  ν.sub.3 + ν.sub.4 (A.sub.1 + E + F.sub.2) =                   17691457 w                  ν.sub.1 + ν.sub.4 (F.sub.2) = 14571221 mw                 2ν.sub.4 (A.sub.1 + E + F.sub.2) = 12181166 vs        1168(1.5)  ν.sub.3 (F.sub.2)        1150(0.8)1135 vw1056 vw                 ν.sub.2 + ν.sub.4 (F.sub.1 + F.sub.2) =                   1049         880(0.2)  2ν.sub.2 (A.sub.1 +  A.sub.2 + E) = 880         849(8.2)  ν.sub.1 (A.sub.1) 611 m         609(7.4)  ν.sub.4 (F.sub.2) 608 m         441(2.9)  ν.sub.2 (E)______________________________________                   Assignments for PF.sub.6.sup.-  (O.sub.h)______________________________________1590 w                  ν.sub.1 + ν.sub.3 (F.sub.1u) = 15901414 w                  ν.sub.2 + ν.sub.3 (F.sub.1u + F.sub.2u) =                   14131308 vw                 ν.sub.1 + ν.sub.4 (F.sub.1u) = 1307 842 vs         838(1.5)  ν.sub.3 (F.sub.1u) 789 w 749 w        748(10)   ν.sub.1 (A.sub.1g)         571(0.8)  ν.sub.2 (E.sub.g) 559 s                  ν.sub.4 (F.sub.1u) 474 vw         469(1.2)  ν.sub.5 (F.sub.2g)______________________________________ 
    
     Obviously, numerous variations and modifications may be made without departing from the present invention. Accordingly, it should be clearly understood that the form of the present invention described above is illustrative only and is not intended to limit the scope of the present invention.