Thymol blue

• Thymolsulfonphthalein
• 4 - [3 - (4- hydroxy-2- methyl-5- propan-2- ylphenyl ) - 1,1- dioxobenzo [c] oxathiol -3-yl ] - 5-methyl -2- propan-2- ylphenol ( IUPAC)

Green solid with phenolartigem odor

Fixed

221 ° C

Insoluble in water, poor in ethanol

Template: Infobox chemical / molecular formula search available

Thymol blue is a triphenylmethane dye and is a member of the sulfonphthaleins. It is used as a pH indicator. His phthalein analogue is the thymolphthalein. By bromination of the bromothymol blue can be represented.

Properties

There are two points ahead of color change:

• PH 1.2-2.8: color change from violet- brownish yellow after
• PH 8.0 to 9.6: color change from greenish yellow to blue

Thymol contains two hydroxyl groups and a little stable sultone. In aqueous medium, this ring is cleaved, and after a relocation arises the quinoid form of the colored yellow dye. In a strongly acidic medium (pH <1.2 ) the quinoid system is protonated, the solution is violet-red by it. In basic medium (pH = 8.0 to 9.6 ), the hydroxy group is deprotonated and the solution turns blue.

Use

Thymol is used for acid-base titrations, as indicator. It usually only the second envelope region ( pH = 8.0 to 9.6 ) used for indication.