p-Phenylenediamine

p-Phenylenediamine
File:P-phenylenediamine.png
IUPAC name 1,4-diaminobenzene
Other names paraphenylenediamine, 1,4-diaminobenzene, 1,4-phenylenediamine
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	106-50-3 Y
SMILES
InChI
style="background: #F8EABA; text-align: center;" colspan="2" | 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
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
R-phrases	R23 R24 R25 R36 R37 R38 R40 R42 R43
S-phrases	S26 S36 S37 S39
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

p-Phenylenediamine (PPD) is an organic compound with the formula C₆H₄(NH₂)₂. This derivative of aniline is a colorless solid when pure, but typically samples are partially oxidized and appear yellowish. It is mainly used as a component of engineering polymers and composites. It is an ingredient used in some hair dyes, though it may be a contact allergen.

Production

PPD is produced via three routes. Most commonly 4-nitrochlorobenzene is treated with ammonia and the resulting 4-aminonitrobenzene is then hydrogenated:

ClC₆H₄NO₂ + 2 NH₃ → H₂NC₆H₄NO₂ + NH₄Cl

H₂NC₆H₄NO₂ + 3 H₂ → H₂NC₆H₄NH₂ + 2 H₂O

In the DuPont route, aniline is converted to diphenyltriazine, which is converted by acid-catalysis to 4-aminoazobenzene. Hydrogenation of the latter affords PPD.

Uses

Precursor to polymers

PPD is a precursor to aramid plastics and fibers such as Kevlar. 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.

Other uses

PPD is easily oxidized, and for this reason PPD is used as antiozonants in production of rubber products. 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.

Dyeing

This compound is used in almost every hair dye on the market, regardless of brand. The darker the colour, usually, the higher the concentrations. Some of the so-called "natural" and "herbal" hair colours, while ammonia-free, contain PPD. Some products sold as henna also contain PPD added, particularly so-called "black henna." In many cases, PPD causes allergic reaction, and can cause scarring in some people. PPD should never be applied directly to the skin in its pure form or mixed with anything else.

Safety

The aquatic LD50 of PPD is 0.028 mg/L. The U.S. Environmental Protection Agency reported that in rats and mice chronically exposed to PPD in their diet, it simply depressed body weights, but there were no other clinical signs of toxicity, as were observed in several studies. Between 1992 and 2005, thirty-one articles were published a causal association between PPD and cancer. Associations between personal hair dye use and non-Hodgkin's lymphoma, multiple myeloma, acute leukemia, and bladder cancer were observed in at least one well-designed study with detailed exposure assessment, but were not consistently observed across studies. However, the EPA has not classified PPD as a carcinogen. Therefore, no warnings of toxicity have been printed on boxes of hair dye.

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. 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.

External links

• Du Pont technical data sheet and sales policy for p-Phenylenediamine (PPD)de:Phenylendiamine

pt:P-fenilenodiamina