polyphosphoric acid refs?

[FriendlyFinger]

Hi there,
I know there's lot here about making polyphophoric acid so I will wait till TFSE is back, but in the mean time is anyone aware of references about the dehydration/vacuum method?

Thanks,
FF

[Nicodem]

The preparation of polyphosphoric acid by heating phosphoric acid under vacuum is described in Organikum in the reagents section. A rough translation:

"The water from the 85% H3PO4 is distilled out under the vacuum of a vater jet pump and the rest is heated for 6 hours at 150°C in the same vacuum. The remaining phosphoric acid crystalises out."