polyphosphoric acid experiences ?

[psyloxy]

Uhhm, this may seem a bit pathetical, but my great interest in the subject gently forces me to post this nonetheless:

I want to hear peoples voices on failed and/or successful attempts or some detailed 2nd hand writeups on preparations of the title compound (best without using P₂O₅) cause it is another important puzzle-piece in the picture showing the clandestine way to EtNO₂ / propiophenones. 

Post 377568

(FriendlyFinger: "I want to make proipiophenone", Methods Discourse)

Post 463377

(psyloxy: "alpha-bromopropanoic acid - a final word ?", Chemistry Discourse)

Notes for it's preparation can be found in

Post 398338

(Aurelius: "repost", Methods Discourse)

Post 412338

(Aurelius: "Ulmann's Polyphosphoric acid", Methods Discourse)

Post 362697 (missing)

(starlight: "not sure as yet", Newbee Forum).

I know there's lot's of refs that I could all read myself but I simply don't have easy access to them, thanks for your undestanding.

--psyloxy--

[roger2003]

From Merck 13th:

Literature References:  May be prepd by heating H3PO4 with sufficient phosphoric anhydride to give the resulting product an 82-85% P2O5 content:  Bell, Ind. Eng. Chem. 40, 1464 (1949); Van Wazer, Holst, J. Am. Chem. Soc. 72, 639 (1950); Kennard, Org. Chem. Bull. 29, no. 1 (1957).  Consists of about 55% tripolyphosphoric acid, the remainder being H3PO4 and other polyphosphoric acids.  Typical analysis:  83.0% P2O5; ortho equivalent 115.0%.

[Rhodium]

Structure and Properties of the Condensed Phosphates. I. Some General Considerations about Phosphoric Acids
John R. Van Wazer, Karl A. Holst

J. Am. Chem. Soc. 72, 639-644 (1950)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/polyphosphoric.acid.pdf)

May be prepd by heating H₃PO₄ with sufficient {P₂O₅} to give the resulting product an 82-85% P₂O₅ content

For calculating the needed amounts, assume that 85% H₃PO₄ is a mixture of 15 wt% H₂O and 85 wt% of a 19:81 mixture of H₂O/P₂O₅ - This as phosphorous pentoxide and water reacts to form phosphoric acid as follows:

3 H₂O (18g/mol) + 2 P₂O₅ (142 g/mol) 2 H₃PO₄ (169 g/mol)

We can then calculate that 85% H₃PO₄ is equal to a mixture of 15 + (0.85 * 19) = 31.15 wt% H₂O and 0.85 * 81 = 68.85% P₂O₅

Now simply add enough P₂O₅ to make a 82-85% solution and heat as in the article linked above.