[rgal]

I have been trying to find data on the heat of reaction for Sodium Thiophosphate, sometimes called Sodium Dithiophosphate or Nokes (Na3PO2S2).  There is nothing that I can find in literature or on the internet on this.  So I have resorted to trying to use delta Hf estimates to calculate.  Some compounds I have been able to find data for.  But P2S5 and Na3PO2S2 data are just not out there.  So I have tried estimating these from bond enthalpies.  The reaction and data I have come up with are below.

P2S5 + 6Na OH ==> 2Na3PO2S2 + H2S + 2H2O
H2S + NaOH ==> NaHS + H2O

P2S5 = -509 KJ/Mol (estimated from reaction 2PH3 + S8 ==> P2S5 + 3H2S)
Na3PO2S2 = -1340 KJ/Mol (estimated from bond energy)
H2S = -20 KJ/Mol
H20 = -286 KJ/Mol
NaOH = -427 KJ/Mol

I got the last three from published tables.  I have used Hess' Law to do calculations.  I calculated -201 KJ/Mol but I don't have much confidence in my numbers due to the estimations I made.

Could someone please help me with this?