Xylenol orange metallochromic indicator

Selenium, bis(diethyldithiocarbamato)-stereochemistry, 60 Selenium, bis(dithiofurancarbamato)-stereochemistry, 60 Selenium(II) complexes bis(dithiochelate), 60 Selenocyanate complexes linkage isomers, 186 Selenonium ions, trifluoro-stereochemistry, 37 Self-exchange reactions, 333 electron transfer rate constants, 347-353, 366 rate constants calculation, 348 rate constants, 362 Semicarbazide, 1,4-diphenylthio-ruthenium determination, 546 Semi-glycinecresol red metallochromic indicator, 557 Semi-xylenol orange metallochromic indicator, 557 Seven-coordinate compounds stereochemistry, 69-83 Sidgwick, Nevil Vincent, 16 Silicon, tris(acetylacetone)-configuration, 195... 

Xanthocobalt—see Cobalt, nitropentaammine-Xenon, pentafluoro-lone electron pair structure, 50 Xenon, trifluoro-structure, 45 Xenon(IV) complexes six-coordinate compounds structure, 53 Xenon hexafluoride geometry, 37 stereochemistry, 74 X-ray diffraction cobalt ammines, 13 configuration, 16 crystal structure, 15 Xylenol orange metallochromic indicator, 557... 

A large number of metallochromic indicators have been proposed for the detection of the equivalence point for the titration of the rare earths with EDTA and other polydentate ligands. These include Alizarin Red, Arsenazo I, Xylenol Orange, Eriochrome Black T, and Murexide to name only a few. The structure, conditions under which these indicators can be used, possible interferences, and references to the original papers are summarized by Aladjem (1970), p. 287. 

There are now many metallochromic indicators which may be used in complexometric titrations. For successful end-point indication the pK value of the metal-dye complex should be at least 4 units less than that of the metal-EDTA complex which is formed during the titration if the difference is less than 4 units the titrant is unable to compete satisfactorily with the indicator dye and a sluggish end-point results. The indicators which are most widely used in the methods described in this book are solochrome black (for titrations carried out in ammoniacal solution), xylenol orange (for titrations carried out between pH 4 and 7) and catechol violet (for titration in mineral acid solution at pH 1 to 2). Table 63 lists the various indicators called for in methods in the monographs. Discussion of the merits of different indicators for specific purposes will be found in various parts of the book. 

A number of valuable metallochromic reagents are based on the triphenylmethane structure. A typical example is Pyrocatechol violet which is an acid-base indicator, as well as forming coloured (usually blue) chelates with a wide range of metal ions. Compounds such as Xylenol orange are also based on this structure, with the addition of two iminodiacetic acid groups. 

---