3,6-Dichlorochromotropic acid

Solutions of chromotropic acid darken on standing in contact with atmospheric oxygen. A related reagent, 2,7-dichlorochromotropic acid, is resistant to oxidation. It gives a coloured complex with titanium at pH 2. The complex has max 490 nm (e = 1.12-10 ). A (1 1 1) complex is formed in the presence of DAM in 0.8-2 M HCl [23]. 

Both the Fe and the FeOH " pathways appear to be important in the reaction of iron(III) with 5-chloro-, 5-nitro-, 6-hydroxy-, and 3,5-dinitrosalicylic acid but, it is suggested, only the latter features in the reactions with mandelic acid, tiron, 2,7-dichlorochromotropic acid, and citric and tartaric acids. Mechanistic analyses have also been given of the reaction of iron(III) with pyridoxamine and pyridoxal, and with thiocyanate in DMSO-water mixtures. ... 

Dichloro-l, 8-dihydroxynaphthalene-3,6-disulfonic acid (2,7-dichlorochromotropic acid) (C QH OgCl2S2)... 

Dichlorochromotropic acid was used for determining Ti in the presence of excess of uranium [93] and beryllium [94], in aluminium alloys [95], and in minerals and rocks [96]. 

Dichlorochromotropic acid can be used for the detection of titanium instead of chromotropic acid since it is more stable and its solution is colorless. It forms colored compounds with Ti v (crimson), Fe i (green), U i (brown), Mo i(yellow) and W i (yellow). It gives no color with Ag, Al, Ba, Bi, Ca, Cd, Co, Cr , Cu, Fe or Ga. The procedure is the same as that using chromotropic acid. 

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