A SPECTROPHOTOMETRIC STUDY OF COMPLEX FORMATION BY IRON(III) AND 2,3-DIMERCAPTO-1-PROPANOL IN ALKALINE SOLUTIONS

Iron(III) and 2,3-dimercapto-1-propanol (DMP) react in alkaline solutions to form the red complex FeDMPOH. The formation constant of this species is 5 X 10(+30) as determined by competition with EDTA at 25 degrees in 0.10 M ammonium chloride. The complex FeDMP(NH(4))OH with a formation constant of about 7 X 10(+31) is also formed in ammoniacal solutions. In the more alkaline of those solutions studied in the present investigation (up to pH 11.00), the +3 valence state of iron is stable in the DMP systems. This is in contrast to the cysteinate and mercaptoacetate systems where reduction to iron(II) is accompanied by oxidation of the mercaptan to disulfide. With bidentate ligands steric factors seem to limit to two the number of sulfur atoms coordinated to an iron(III) nucleus.