Neutral Red
Title: Neutral Red
CAS Registry Number: 553-24-2; 366-13-2 (free base)
CAS Name: N8,N8,3-Trimethyl-2,8-phenazinediamine monohydrochloride
Additional Names: C.I. Basic Red 5; 3-amino-7-dimethylamino-2-methylphenazine hydrochloride; toluylene red; neutral red chloride; nuclear fast red (basic dye); aminodimethylaminotoluaminozine hydrochloride; C.I. 50040
Trademarks: Kernechtrot; Michrome no. 226
Molecular Formula: C15H17ClN4
Molecular Weight: 288.78
Percent Composition: C 62.39%, H 5.93%, Cl 12.28%, N 19.40%
Literature References: Prepn from N,N-dimethyl-p-nitrosoaniline hydrochloride + toluene-2,4-diamine: Witt, Ber. 12, 931 (1879); DE 15272 (1880), Frdl. 1, 274; Bernthsen, Schweitzer, Ann. 236, 332 (1886); Pokorny, J. Soc. Dyers Colour. 42, 347 (1926). Toxicity data: F. Stolarsky, T. J. Haley, Fed. Proc. 10, 337 (1951). Brief review: H. J. Conn's Biological Stains, R. D. Lillie, Ed. (Williams & Wilkins, Baltimore, 9th ed., 1977) pp 377-380, 596. See also: Colour Index vol. 4 (3rd ed., 1971) p 4446.
Properties: Dark green powder. Absorption max (50% alc): 533 nm. pKa 6.7. Soluble in water or alcohol with red color. Soly in water 4.0%, in abs alcohol 1.8%, in Cellosolve 3.75%, in ethylene glycol 3.0%. Practically insol in xylene. LD50 in mice, rats, rabbits (mg/kg): 142, 112, 97 i.v. (Stolarsky, Haley).
pKa: pKa 6.7
Absorption maximum: Absorption max (50% alc): 533 nm
Toxicity data: LD50 in mice, rats, rabbits (mg/kg): 142, 112, 97 i.v. (Stolarsky, Haley)
NOTE: Not to be confused with Nuclear Fast Red (acid dye) which is C.I. 60760.
Use: As indicator (0.1% in 60% alcohol) for alkalinity of water, urea, nitrite, etc. pH: 6.8 red; 8.0 yellow. Also used for preparing neutral-red paper. As biological stain (study of the Golgi apparatus in cells).

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