| p-Phenylenediamine | |
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1,4-diaminobenzene |
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Other names
paraphenylenediamine, 1,4-diaminobenzene, 1,4-phenylenediamine |
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| Identifiers | |
| CAS number | 106-50-3 |
| UNII | U770QIT64J |
| KEGG | C19499 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C6H8N2 |
| Molar mass | 108.1 |
| Appearance | white (tan when impure) |
| Melting point |
143-145 °C |
| Boiling point |
267 °C, 540 K, 513 °F |
| Solubility in water | 10% at 40°C, 87% at 107 C, 100% at 140 C [1] |
| Hazards | |
| R-phrases | R23 R24 R25 R36 R37 R38 R40 R42 R43 |
| S-phrases | S26 S36 S37 S39 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
p-Phenylenediamine (PPD) is an organic compound with the formula C6H4(NH2)2. This derivative of aniline is a colorless solid, but typically samples can contain yellowish impurities arising from oxidation. It is mainly used as a component of engineering polymers and composites. It is also an ingredient in hair dyes.
Contents |
PPD is produced via three routes. Most commonly, 4-nitrochlorobenzene is treated with ammonia and the resulting 4-nitroaniline is then hydrogenated:
In the DuPont route, aniline is converted to diphenyltriazine, which is converted by acid-catalysis to 4-aminoazobenzene. Hydrogenation of the latter affords PPD.[2]
PPD is a precursor to aramid plastics and fibers such as Kevlar. These applications exploit PPD's difunctionality, i.e. the presence of two amines which allow the molecules to be strung together. This polymer arises from the reaction of PPD and terephthaloyl chloride. The reaction of PPD with phosgene gives the diisocyanate, a precursor to urethane polymers.[2]
This compound is a common hair dye. Its use is being supplanted by other aniline analogues and derivatives such as 2,5-diamino(hydroxyethylbenzene and 2,5-diaminotoluene. Other popular derivatives include tetraaminopyrimidine and indoanilines and indophenols. Derivatives of diaminopyrazole give red and violet colours.[3] In these applications, the nearly colourless dye precursor oxidizes to the dye.
PPD is easily oxidized, and for this reason derivatives of PPD are used as antiozonants in production of rubber products. The substituents, naphthyl, isopropyl etc affect the effectiveness of their antioxidant roles as well as their properties as skin irritants.[4]
PPD is also used as a developing agent in the C-41 color photographic film development process, reacting with the silver grains in the film and creating the colored dyes that form the image.
The aquatic LD50 of PPD is 0.028 mg/L.[2] The U.S. Environmental Protection Agency reported that in rats and mice chronically exposed to PPD in their diet, it simply depressed body weights, and no other clinical signs of toxicity were observed in several studies.[5] One review of 31 English-language articles published between January 1992 and February 2005 that investigated the association between personal hair dye use and cancer as identified through the PubMed search engine found "at least one well-designed study with detailed exposure assessment" that observed associations between personal hair dye use and non-Hodgkin's lymphoma, multiple myeloma, acute leukemia, and bladder cancer,[6] but those associations were not consistently observed across studies. A formal meta-analysis was not possible due to the heterogeneity of the exposure assessment across the studies.
The CDC lists PPD as being a contact allergen. Exposure routes are through inhalation, skin absorption, ingestion, and skin and/or eye contact; symptoms of exposure include throat irritation (pharynx and larynx), bronchial asthma, and sensitization dermatitis.[7][8] Sensitization is a lifelong issue, which may lead to active sensitization to products including, but not limited to black clothing, various inks, hair dye, dyed fur, dyed leather, and certain photographic products. It was voted Allergen of the Year in 2006 by the American Contact Dermatitis Society.
Poisoning by PPD "is rare in western countries."[9]