CAS number 92-84-2 YesY
ChemSpider 21106365 YesY
KEGG D02601 YesY
Jmol-3D images Image 1
Molecular formula C12H9NS
Molar mass 199.27 g/mol
Appearance yellow rhombic leaflets or

diamond-shaped plates

Melting point

185 °C, 458 K, 365 °F

Boiling point

371 °C, 644 K, 700 °F

Solubility in water 0.00051 g/L (20 °C)[1]
Solubility in other solvents benzene, ether, petroleum ether, chloroform, hot acetic acid, ethanol (slightly), mineral oil (slightly)
Acidity (pKa) approx 23 in DMSO
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phenothiazine is an organic compound that occurs in various antipsychotic and antihistaminic drugs. It has the formula S(C6H4)2NH. This yellow tricyclic compound is soluble in acetic acid, benzene, and ether. The compound is related to the thiazine-class of heterocyclic compounds. Derivatives of the parent compound find wide use as drugs.



The compound was originally prepared by Bernthsen in 1883 via the reaction of diphenylamine with sulfur, but more recent syntheses rely on the cyclization of 2-substituted diphenylsulfide. The pharmaceutically significant derivatives of phenothiazine are not prepared from phenothiazine.[2]

Non-drug applications

The synthetic dye methylene blue, containing the structure, was described in 1876. Phenothiazine itself was introduced by DuPont as an insecticide in 1935.[3] It is sometimes used as an antihelminthic in livestock.

In the manufacture of monomers, Phenothiazine is used as a chemical stabilizer or inhibitor to prolong storage and shelf life of products like acryloyl chloride.[4]

Many water soluble phenothiazine derivatives such as methylene blue, methylene green, thionine, and others are able to be electropolymerized into conductive polymers that are used as electrocatalysts for NADH oxidation in enzymatic biosensors and biofuel cells. [5],[6],[7]

Phenothiazine-derived drugs

The phenothiazine structure occurs in various neuroleptic drugs, e.g. chlorpromazine, and antihistaminic drugs, e.g. promethazine. The term "phenothiazines" describes the largest of the five main classes of neuroleptic antipsychotic drugs. These drugs have antipsychotic and, often, antiemetic properties, although they may also cause severe side effects such as extrapyramidal symptoms (including akathisia and tardive dyskinesia), hyperprolactinaemia, and the rare but potentially fatal neuroleptic malignant syndrome as well as substantial weight gain.

Phenothiazines are used as inodilators in congestive heart failure, acting upon the type I calcium/calmodulin dependent phosphodiesterase.[8][citation needed]

Phenothiazine antipsychotics are classified into three groups that differ with respect to the substituent on nitrogen: the aliphatic compounds (bearing acyclic groups), the "piperidines" (bearing piperidine-derived groups), and the piperazine (bearing piperazine-derived substituents).

Group Autonomic Example Sedative Extrapyramidal side-effect
Aliphatic compounds
moderate Chlorpromazine (marketed as Thorazine, Chlor-PZ, Klorazine, Promachlor, Promapar, Sonazine, Chlorprom, Chlor-Promanyl, Largactil) strong moderate
Promazine (trade name Sparine) moderate moderate
Triflupromazine (trade names Stelazine, Clinazine, Novaflurazine, Pentazine, Terfluzine, Triflurin, Vesprin) strong moderate/strong
Levomepromazine in Germany and Methotrimeprazine in America (trade names Nozinan, Levoprome) extremely strong low
Piperidines strong Mesoridazine (trade name Serentil) strong weak
Thioridazine (trade names Mellaril, Novoridazine, Thioril) strong weak
Piperazines weak Fluphenazine (trade names Prolixin, Permitil, Modecate, Moditen) weak/moderate strong
Perphenazine (sold as Trilafon, Etrafon, Triavil, Phenazine) weak/moderate strong
Prochlorperazine (trade names Compazine, Stemetil)
Trifluoperazine (trade name Stelazine) moderate strong

Appendix: tradenames for phenothiazine

Like many commercially significant compounds, phenothiazine has numerous trade names including AFI-Tiazin; Agrazine; Antiverm; Biverm; Dibenzothiazine; Orimon; Lethelmin; Souframine; Nemazene; Vermitin; Padophene; Fenoverm; Fentiazine; Contaverm; Fenothiazine; Phenovarm; Ieeno; ENT 38; Helmetina; Helmetine, Penthazine; XL-50; Wurm-thional; Phenegic; Phenovis; Phenoxur; Reconox.[9]


Further reading