What is the acid dissociation constant of cacodylic acid?
I found this article (TW. Shin, K. Kim, IJ. Lee, J. Solution Chem. 1997, 26, 379. doi: 10.1007/BF02767677) with precise analysis of the pKa of cacodylic acid - it says that in 25&nbsp;&deg;C it's estimated to be 6.27. Values lower than 6 are wrong, but found often. Sometimes it's said to be a diprotic (which it isn't) with first pKa 1.57 and second 6.27 - pubchem says 1.57 citing Lide, D.R. (ed.). CRC Handbook of Chemistry and Physics. 76th ed. Boca Raton, FL: CRC Press Inc., 1995-1996., p. 8-45 - it might be one of the sources of problem.