P-Phenylenediamine
The phenylenediamines (also diaminobenzenes ) are chemical compounds selected from the group consisting of aromatic diamines and important starting materials for many organic compounds. They consist of a benzene ring having two amino groups (-NH2). 1,2- phenylenediamine (ortho -phenylenediamine ), 1,3 -phenylene (meta -phenylene ) and 1,4- phenylenediamine ( p- phenylenediamine ) by different arrangements of the groups are three structural isomers result.
Production and representation
The phenylenediamines are prepared by reduction of the nitro aniline with hydrogen in toluene as solvent in the presence of a catalyst purified by distillation. Reduction of m- dinitrobenzene with Fe / HCl leads to m- phenylenediamine.
Properties
The phenylenediamines form colorless to pale red crystals, which oxidize in the air quickly and thereby brown color (o- phenylenediamine: formation of o- quinone diimine and further 2,3- diaminophenazine ). Therefore, the stable dihydrochlorides of the compounds are often used. o-phenylenediamine is condensed with ketones or aldehydes to Schiff's bases. This reaction allows the synthesis of substituted benzimidazoles. Quinoxalinedione can be prepared by condensation of o -phenylenediamine with dimethyl oxalate.
The phenylenediamines are crystalline solids. Their melting points are significantly different. p-phenylenediamine, which has the highest symmetry, has the highest melting point.
Water is not very suitable as a solvent. In many organic solvents, however, they dissolve well.
Use
O-phenylenediamine is used as a starting material or intermediate for the synthesis of heterocyclic compounds, particularly of benzotriazole and phenazine. Further o-phenylenediamine is used in the manufacture
- Of benzotriazoles, which are used for preparing photographic chemicals and plastics, as well as corrosion inhibitors for copper
- Of plant protection products (such as benzimidazole, phenylenediamine Thioharnstoffcarbamat and quinoxaline ), dyes and pigments
- Of benzimidazole derivatives of UV absorbers in cosmetics, thermostable polymers and pharmaceuticals ( virucides and anthelmintics used in veterinary )
- Of 2-mercaptobenzimidazole ( rubber antioxidant )
- As a substrate in the ELISA reagent in biotechnological laboratories
Certain compounds derived from o- phenylenediamine may be used in cosmetics and are probably the cause of many allergic symptoms in hairdressers.
The plastics industry produces p- phenylenediamine in large quantities for the preparation of aromatic polyamides. It is there along with terephthalic acid essential part of aramids. p-phenylene diamine is obtained in the preparation of azo dyes of the intermediate. The synthetic routes of some pharmaceuticals and photographic chemicals run as often through this connection. Coloring because of its properties are p-phenylenediamine and some of its derivatives in cosmetics use. Presumably based many allergic reactions among hairdressers on the contact with this dye. In some photographic developers, the alkaline solution of p-phenylenediamine is an active component.
Safety
O- phenylenediamine is classified as carcinogenic, category 3B and a skin sensitizer. The vapor of o- phenylenediamine forms an explosive mixture with air. p- phenylenediamine is counted to allergens, since it can result in skin irritation and contact sensitization. Furthermore, this chemical is used in some resorts also as fixing of henna tattoos.