Xylenol blue

Structural formula
General
Surname	Xylenol blue
other names	Xylenolsulfonphthalein 4- [3- (4-Hydroxy-2,5-dimethylphenyl) -1,1-dioxobenzo [ c ] oxathiol-3-yl] -2,5-dimethylphenol ( IUPAC )
Molecular formula	C 23 H 22 O 5 S
External identifiers / databases
CAS number 125-31-5 EC number 204-736-5 ECHA InfoCard 100.004.306 PubChem 67172 Wikidata Q1542346
properties
Molar mass	410.48 g mol −1
Physical state	firmly
Melting point	212 ° C (decomposition)
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Xylenol blue is a triphenylmethane dye and belongs to the group of sulfonphthaleins. It is used as a pH indicator . Its phthalein analogue is xylenolphthalein . The bromoxylenol blue can be represented by bromination .

properties

There are two areas of color change:

• pH 1.2-2.8: color change from red to yellow
• pH 8.0-9.8: color change from yellow to purple

Xylenol blue contains two hydroxyl groups and an unstable sultone ring . This ring is split in an aqueous medium, and after a rearrangement the quinoid yellow colored form of the dye is formed. In a strongly acidic environment (pH <1.2) the quinoid system is protonated, which causes the solution to turn red. In a basic environment (pH = 8.0-9.8) the hydroxyl group is deprotonated and the solution turns purple.

use

Xylenol blue is used as an indicator in acid-base titrations. In most cases, only the second transition range (pH = 8.0–9.8) is used for the indication.

Individual evidence

1. ↑ ^{a b c d} Xylenol Blue data sheet from Sigma-Aldrich , accessed on April 25, 2011 ( PDF ).