Formation of Carcinogenic Aromatic Amines from Azo Dyes

Azo dyes represent the major class of dyestuffs. Azo colorants are the most important class of synthetic dyes and pigments, representing 60 – 80% of all organic colorants. They are used widely in substrates such as textile fibres, leather, plastics, papers, hair, mineral oils, waxes, foodstuffs and cosmetics.Henceazo colorants are part of our everyday colorful life, they are all around us and we could not do without them because It allows colors with outstanding colorfastness and wide range of spectrum of colors.

Some of these dyes have the capacity to release certain aromatic amines which pose cancer risk. For that reason the European union has laid down legislation to prevent exposure to these hazardous amines. This implies that azo dyes containing aromatic amines can no longer be used to dye textile product that may come into contact with the skin. European union legislation specifically prohibits the use of 22 aromatic amines in a concentrate above the limit of 30 ppm.

Why do azo dyes contain amines?

Azo dyes contain one or more nitrogen-nitrogen double bonds called azo groups in

their chemical structure, see Fig. 1.

-N=N –

Fig. Azo group

Under reductive conditions using sodium dithionite these azo groups can be cleaved

to form 2 amines, which can be schematically shown as in Fig. 2.



Fig. Reductive cleavage of the azo dye to form amines

A small number of the aromatic amines are classified as being carcinogenic or potentially carcinogenic to humans. Only those few azo dyes that can release these amines upon reductive cleavage are affected.

Testing methods:

- General Textiles: EN 14362-1:2003

- Polyester : EN 14362-2:2003

It should be noted that if there are several color in the fabric, all the different color need to be tested.

Sl. No.	Substance Name	CAS Number
01	Biphenyl-4-ylamin 4-aminobifenyl Xenylamine	92-67-1
02	Benzidine	92-87-5
03	4-chloro-o-toluidine	95-69-2
04	2-naphthylamine	91-59-8
05	o-aminoazotoluene4-amino-2’,3-dimethylazobenzene4-o-tolylazo-o-toluidine	97-56-3
06	5-nitro-o-toluidine	99-55-8
07	4-chloroaniline	106-47-8
08	4-methoxy-m-phenylenediamine	615-05-4
09	4,4′-methylenedianiline4,4′-diaminodiphenylmethane	101-77-9
10	3,3′-dichlorobenzidine3,3′-dichlorobiphenyl-4,4′-ylenediamine	91-94-1
11	3,3′-dimethoxybenzidineo-dianisidine	119-90-4
12	3,3′-dimethylbenzidine4,4′-bi-o-toluidine	119-93-7
13	4,4′-methylenedi-o-toluidine	838-88-0
14	6-methoxy-m-toluidinep-cresidine	120-71-8
15	4,4′-methylene-bis- (2-chloro-aniline)2,2′-dichloro-4,4′-methylenedianiline	101-14-4
16	4,4′-oxydianiline	101-80-4
17	4,4′-thiodianiline	139-65-1
18	o-toluidine2-aminotoluene	95-53-4
19	4-methyl-m-phenylenediamine	95-80-7
20	2,4,5-trimethylaniline	137-17-7
21	o-anisidine2-methoxyaniline	90-04-0
22	4-amino azobenzene	60-09-3

All the several colors should comply with this limit.

False positive result:

For certain dyed Fabrics a listed amine is detected under the conditions of the analytical test even though no banned azo dye is present in the garments. In our BUTex lab they commercially tested AZO Group. The Test result of BUTex lab are very reliable to Some international buyer like Marks & Spencer. They evaluated our campus so specially even they prefer the BUTEX Lab than other ISO accredited LAB such as ITS, SGS, BUREAU VERITAS etc in case of AZO testing. But our testing equipment is not so updated. That conventional equipment detect the AZO group when it finds any nitrogen bond. It creates a confusion in the test result of BUTex lab and others. we expect more precision testing from the authority of BUTEX Lab in future.