Acid red

Thymol blue, thymol-sulfonphthalein (indicator) dissolve 0.1 g in 10.75 mL 0.02ANaOH and dilute with water to 250 mL or dissolve 0.1 g in 20 mL warm alcohol and dilute with water to 100 mL pH range (acid) red 1.2-2.8 yellow, and (alkaline) yellow 8.0-9.6 blue. 

Another group of halogenated fluorescein dyes is prepared by condensing chloro derivatives of phthalic anhydride with resorcinol, followed by bromination or iodination. Thus Phloxine B /78472-87-2] (Acid Red 92, Cl45410) (42) is prepared by condensing tetrachlorophthaUc anhydride with resorcinol followed by tetrabromination. Phloxine B undergoes ethylation to yield the yellowish ted acid dye Cyanosine B [6441-80-1] (43). 

Lead Tetroxide. Lead tetroxide (red lead minium lead orthoplumbite), Pb O, is a brilliant orange-red pigment which accounted for U.S. shipments of 17,780 t ia 1977, mainly to the ceramics and storage battery iadustries (40). U.S. shipments ia 1993 amounted to approximately 12,000 t. The decrease ia usage siace 1973 (19,000 t) is attributable to discontinued use ia the paint and coatings (qv) iadustry, and alterations ia mbber and ceramics (qv) markets. It is iasoluble ia water and alcohol, and dissolves ia acetic acid or hot hydrochloric acid. Red lead is manufactured by heating lead monoxide ia a reverberatory furnace ia the preseace of air at 450—500°C uatil the desired oxidative composition is obtaiaed. 

An example of an a2o dyestuff in which y-acid is the coupling component is Acid Red 337 (19), which is obtained through the reaction of dia2oti2ed -trifluoromethylaniline and y-acid (52). 

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