6105. Methyl Orange

Nomenclature

CAS number: 547-58-0
4-[2-[4-(Dimethylamino)phenyl]diazenyl]benzenesulfonic acid sodium salt (1:1); 4-[[(4-dimethylamino)phenyl]azo]benzenesulfonic acid sodium salt; sodium p-dimethylaminoazobenzenesulfonate; helianthine B; C.I. Acid Orange 52; C.I. 13025; Orange III; Gold Orange; Tropaeolin D.
C14H14N3NaO3S; mol wt 327.33.
C 51.37%, H 4.31%, N 12.84%, Na 7.02%, O 14.66%, S 9.80%.

Description and references

Monoazo dye. Prepn from sulfanilic acid sodium nitrite + dimethylaniline: L. Gattermann, Die Praxis des Organischen Chemikers (de Gruyter, Berlin, 40th ed., 1961) pp 260-261. See also Colour Index vol. 4 (3rd ed., 1971) p 4043. Chromoisomerism studies: W. M. Dehn, L. McBride, J. Am. Chem. Soc. 39, 1348 (1917).

Chemical structure

Properties

Orange-yellow powder or cryst scales. Sol in 500 parts water; more sol in hot water. Practically insol in alcohol.

Use

As indicator in 0.1% aq soln. pH: 3.1 red, 4.4 yellow. Employed for titrating most mineral acids, strong bases, estimating alkalinity of waters; useless for organic acids. In assays for bromide ions, oxalic acid, and malonic acid. In dyeing and printing of textiles. In film dosimeters.