DE957388C - Process for the production of hexafluorophosphoric acid - Google Patents

Description

ISSUED JANUARY 31, 1957

N 5841 IVa / I2i

Amsterdam, Netherlands)

have been named as inventors

Up until now, hexafluorophosphoric acid was usually only obtained as a hydrate from gaseous phosphorus pentafluoride and a cooled aqueous solution of hydrogen fluoride. Attempts at representation the anhydrous acid from phosphorus pentafluoride and hydrogen fluoride at low temperatures resulted in such a long implementation time that this process is of no relevance to technology.

It has also been proposed to carry out the reaction in the presence of a non-reactive hydrogen-containing solvent, in particular ether, at higher temperatures. However, the use of ether has the disadvantage that complex compounds of hexafluorophosphoric acid and ether are formed. Although these can be ^{distilled off unchanged from the reaction mixture at about 114 0} , the preparation of anhydrous hexafluorophosphoric acid from the complex compounds is very difficult, since the ether from it cannot simply be extracted from it «? Distillation can be removed.

It has now been found that phosphorus pentafluoride and hydrogen fluoride are present in liquid sulfur dioxide can be reacted with each other. This procedure offers great advantages part that there are no complex compounds between the sulfur dioxide used and the hexafluorophosphoric acid are formed. As a result

The pure and anhydrous hexafluorophosphoric acid remains during the distillation of the reaction mixture back and can be made very easily in this way will.

A particularly suitable method for carrying out this reaction is that gaseous phosphorus pentafluoride is passed through a liquid mixture of hydrogen fluoride and sulphurous dioxide. The temperature used can vary within a wide range. The lower limit is the temperature at which the reaction mixture is just still liquid. Temperatures above room temperature are of little interest because of the decreasing stability of hexafluorophosphoric acid and the increasing vapor pressure with increasing temperature. In principle, however, the conversion can also be carried out ^{over 20 °.} Particularly suitable temperatures are between -30 and -15 °.

It is essential that sulfur dioxide be present in sufficient quantity. If the phosphorus pentafluoride is introduced at -20 ⁰ , suitable weight ratios of SO ₂ to HF are at and above 1: 1. At a lower temperature, a small amount of sulfur dioxide than corresponds to this ratio is sufficient. The higher the temperature, the more SO ₂ is required in relation to the amount of HF.

In order to check whether sufficient PF _{5 is} introduced to bind the HF, a wash bottle, which contains a very dilute solution of malachite green in water, can be switched on in series with the reaction apparatus after the reaction apparatus. When PF _{5 flows} through the reaction apparatus without being bound, the green color disappears. A small excess of PF ₅ in the reaction mixture can serve to prevent the occurrence of an excess of HF.

After the reaction has taken place, the sulfur dioxide can be distilled off. At atmospheric pressure, this distillation can take place at about 0 °. The hexafluorophosphoric acid remains in the form of an oily, colorless liquid. This liquid smokes heavily in the air; at room temperature it decomposes very quickly to form HF and PF ₅ .

In an experiment in which PF _{5 was introduced} into a mixture of HF and SO ₂ (weight ratio 1: 1) in an apparatus made of nickel chromium steel (V 2 A) at −20 °, and in which the distillation was carried out at ^{0 °,} was found by titration that 98% of the residue from HPF

HPF ₆ passed.

Considered publications:
German patent application ρ 38311 IVb / 12 i D (patent 812 247).

PF ₅ was made by heating calcium fluoride with phosphorus pentoxide in a chromium-nickel steel (V 2 A) retort. The calcium fluoride was previously made anhydrous by heating.

Instead of introducing PF ₅ into a solution of HF in SO ₂ , HF vapor can also be introduced into a solution of PF ₅ in SO ₂ , or liquid HF can be added to this solution. You can also add HF and PF ₅ at the same time.

Claims (4)

PATENT CLAIMS: 1. Process for the preparation of hexafluorophosphoric acid from hydrogen fluoride and phosphorus pentafluoride in the presence of a solvent, characterized in that liquid sulfur dioxide is used as the solvent will. 2. The method according to claim 1, characterized in that gaseous phosphorus pentafluoride is introduced into a liquid mixture of hydrogen fluoride and sulfur dioxide. 3. The method according to claim 1 or 2, characterized in that the reaction takes place at temperatures between -15 and -30 ⁰ . 4. The method according to claim 1 to 3, characterized in that the sulfur dioxide is added subsequently is distilled off from the reaction mixture. © 609 578/469 7.56 (609 777 I.57>