Phenol red

Structural formula
General
Surname	Phenol red
other names	Phenolsulfonphthalein 4,4- (3 H -2,1-benzoxathiol-3-ylidene) bisphenol-1,1-dioxide
Molecular formula	C 19 H 14 O 5 S
Brief description	red solid with a faint odor
External identifiers / databases
CAS number 143-74-8 EC number 205-609-7 ECHA InfoCard 100.005.100 PubChem 4766 Wikidata Q418719
properties
Molar mass	354.38 g mol −1
Physical state	firmly
Melting point	> 300 ° C
solubility	very bad in water (0.77 g l −1 at 100 ° C)
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Phenol red is a triphenylmethane dye and forms the basic compound of the sulfonphthalein family . It is used as a pH indicator and has two transition areas. At pH  ≈ 0.9 the color changes from red to yellow and at pH ≈ 6.4–8.2 from yellow to red-violet.

presentation

In a Friedel-Crafts acylation , two equivalents of phenol and one equivalent of 2-sulfobenzoic anhydride are reacted in the presence of small amounts of concentrated sulfuric acid or zinc chloride.

properties

Phenol red is a red solid with a faint odor.

Phenol red in powder form

Phenol red 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. This quinoid system can be protonated in a strongly acidic environment (pH <1), causing the solution to turn red. In a neutral environment (pH = 6.4-8.3) the hydroxyl group is deprotonated and the solution turns red-violet. In the strongly basic range (pH> 14) an addition of an OH group takes place with the formation of a triphenylmethanol structure. Phenol red is then present as a colorless trianion.

The structures of the phenol red

species	H 2 In	In -	In 2−
structure
pH	<1	1-7.3	> 7.3
colour	red	yellow	Red-violet

use

Phenol red (40 µm) in cell culture medium, pH 6.0 - 8.0

Phenol red is used as an indicator in acid-base titrations , with a transition range between pH 6.4 and 8.2. The color changes from red-violet in the basic to yellow in the acidic. Since phenol red dissolves very poorly in water, the ready-to-use solution is prepared either by

• Dissolve 0.1 g in 100 ml of 20 percent ethanol or through
• Dissolve 0.04 g in 1.13 ml sodium hydroxide solution (0.1 mol / l) and then make up to 100 ml with water.

Phenol red serves as a pH indicator for cell culture media .

Individual evidence

1. ↑ ^{a b c d e f} data sheet phenol red (PDF) from Merck , accessed on January 3, 2013.
2. ↑ ^{a b} Udo R. Kunze: Fundamentals of quantitative analysis. 3. Edition. Georg Thieme Verlag, Stuttgart 1990, p. 96.
3. ↑ Markus Weinmann, Max Planck Institute: Sulfonphtaleine - Phenolrot ( Memento from July 8, 2007 in the Internet Archive )
4. ↑ K. Yamaguchi, Z. Tamura, M. Maeda: Molecular Structure of the Zwitterionic Form of Phenolsulfonphthalein. In: Analytical Sciences . 1997, 13 (3). Pp. 521-522. doi: 10.2116 / analsci.13.521
5. ↑ BDSoft: Phenol red
6. ↑ chemie-master.de: Phenol red

literature

• Z. Tamura, M. Maeda: Differences between phthaleins and sulfonphthaleins. In: Yakugaku Zasshi. 1997, 117 (10-11), pp. 764-770. (jap.); PMID 9414589

Web links

Commons : Phenol Red  - Collection of images, videos, and audio files

• Website with 3D model of the molecule