Methyl red

Description

A reddish-violet powder that was formerly used as an acid-base indicator. Methyl red is a monoazo dye that was discovered by E. Rupp and R. Loose in 1908. When mixed as a 0.1% alcoholic solution, methyl red has a red color below pH 4.4 and yellow above pH 6.2. It has been used for titrating ammonia and weak organic bases, but it is not suitable for titrating acids. Currently, methyl red is rarely used because it is easily reduced to a colorless form.

Synonyms and Related Terms

Acid Red 2; CI 13020; 2-[[(4-dimethylamino)phenyl]-azo]benzoic acid; 4'-dimethylaminoazobenzene-2-carboxylic acid; rojo de metilo (Esp.); rouge méthyle (Fr.); vermelho de metilo (Port.)

Chemical structure

Other Properties

Soluble in ethanol and acetic acid. Insoluble in water.

Composition	(CH3)2NC6H4NNC6H4COOH
CAS	493-52-7
Melting Point	181-182
Molecular Weight	mol. wt. = 269.29

Hazards and Safety

Toxic by ingestion and inhalation. Contact may cause irritation

Potential carcinogen.

Flammable. Flash point = 12 C

Fisher Scientific: MSDS

Sources Checked for Data in Record

• G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 184

• Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993

• Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997

• The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 6199

• S.R.Trotman, E.R. Trotman, Textile Analysis, J.B. Lippincott Company, Philadelphia, 1932

• Colour Index International online at www.colour-index.org