Barium bis(dihydrogenorthophosphate)

Boiling point

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

boiling point

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is a solid which decomposes before boiling

Reference 2

Endpoint:

boiling point

Type of information:

other: Expert statement based on the experimental tests

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

Differential thermal analysis as well as thermogravimeric analysis were preformed. In addition a sample was determined by XRD at 300 °C to confirm the condensation of orthophosphate to pyrophosphate.

GLP compliance:

no

Type of method:

differential thermal analysis

Remarks:

as well as thermogravimeric analysis

Based on the company experience on this type of phosphate substances, the melting point measured for barium bis(dihydrogen orthophosphate) (study no. 108281180) is not really the melting point of substance itself. Because along with the condensation reaction, the water is obtained in the test matrix and barium bis(dihydrogen orthophosphate) dissolved in the water at once. Therefore it seems that the substance melts and becomes liquid. However this stage exists only in a short period. When more barium pyrophosphate is formed the substance becomes again an insoluble solid. And during further the polymerization reaction the metaphosphate obtained is more insoluble, and it has a melting point over 1560 °C.

The process of these transitions begins with two phosphate units coming together in a condensation reaction shown as following:

Ba(H₂PO₄)₂    – H₂O    -> BaH₂P₂O₇    – H₂O ->    Ba(PO₃)₂

 

In order to confirm the observation and assumption, the differential thermal analysis as well as thermogravimeric analysis internally. The thermogram shows two mass changes: in the temperature range of 240 – 280 °C and 350 – 400 °C. The first change has a mass loss of 7.02%, which indicates clearly a transition of dihydrogen orthophosphate to pyrophosphate (BaH2P2O7). Afterwards barium pyrophosphate polymerizes sequently to metaphosphate [Ba(PO3)2] at 350 – 400 °C with a mass loss of 3.60%.

Also the registrant has characterized the substance at 300 °C by means of X-Ray powder diffraction. Comparing with the standard diffractogram of barium bis(dihydrogen orthophosphate), barium pyrophosphate and barium metaphosphate, it shows that the test substance changes completely at 300 °C and condenses to barium pyrophosphate or barium metaphosphate.

Therefore it can be concluded that the substance barium bis(dihydrogen orthophosphate) decomposes before melting and boiling. The condensation reaction followed by polymerization happens along with increasing temperature.

Description of key information

not applicable

Additional information

The test substance decomposes before melting and boiling. The condensation reaction followed by polymerization happens along with increasing temperature (DTA and TGA). The substance becomes barium pyrophosphate or barium metaphosphate, which are confirmed by XRD.