Thioindigo

• C. I. Vat Red 41
• C. I. 73300

Red to violet powder

Fixed

280 ° C

Insoluble in water, soluble in xylene with yellow in ethanol with brownish red in color

4170 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Thioindigo is a chemical compound from the group of organo-sulfur compounds, which is used as a dye. It is similar to the more familiar indigo, with its two imine groups are (NH ) are replaced by sulfur atoms.

Production and representation

Thioindigo was discovered in the early 20th century by Paul Friedlander and originally derived from the known Indigo by addition of sulfur (hence the Greek prefix " thio "). It is a quinacridone pigment. Today are known for the connection and its chlorinated derivatives, a number of processes. Generally it is carried out by oxidation of the corresponding 3- Hydroxythionaphthene. But it can also be obtained by S- alkylation of thiosalicylic acid with chloroacetic acid. The resulting thioether cyclized to 2- Hydroxythionaphthen, which dimerizes to Thioinigo.

Properties

Thioindigo is a red to violet powder. It is found in two different crystal structures. Thioindigo II case has a monoclinic crystal structure with space group P21 / n, while Thioindigo I has the space group P21 / c. In addition to the normal trans-form the isomeric cis form ( Isothioindigo ) occurs. In benzene solution an equilibrium between the cis and trans form is present.

Use

Thioindigo is used as a purple dye. After the discovery of the quinacridone pigment group around 1935 the DuPont Company established this in the 1960s as a synthetic pigments on the market. The related compound 4,7,4 ', 7'- tetrachlorothioindigo, also a commercially important dye can be obtained by chlorination of Thioindigo. The related compound Indanthrenbrillantrosa R (CI 73360 ) is a red Thioindiopigment. It is used in cosmetic products, such as toothpaste or in lipsticks, while it is prohibited by the Cosmetics Regulation in hair dyes.

There are other derivatives that result from accreted at the rings and remains a very good light and weather fastness, migration and solvent fastness have (this depends very much on the position of the substituents from ). The colors range from red-violet to this thioindigo Brown.