History on Para Red

In the 1940's severe methemoglobinemia poisioning occured in children who ate crayons, some resulted in death (1). Hemolytic anemia is a condition in which there are not enough red blood cells in the blood, due to the premature destruction of red blood cells. The color studied was Para Red which was originally produced by
coupling diazotized paranitraniline with ,8-naphthol. The dye was discovered in 1880 by von Gallois and Ullrich, and was the first azo dye (1). In a study, Para Red was added to stomach fluid of pH 1.1 to 8.15, shaken in a Waring Blendor, incubated for twenty-four hours at body temperature, and shaken again. After filtering, the fluid did not contain Para Red. This means the body absorbed a dye that was originally thought not to. The same results were obtained with chlorinated Para Red. Four different brands of wax crayons of red-orange, orange, yellow, and violet color have also effects. They have found Para Red in red-orange and orange crayons. An analysis of yellow crayons by the Food and Drug Administration2 has shown benzidine yellow YB. Both dyes are derived from methemoglobin- forming compounds-paranitraniline and benzidine. This is just another example of a dye that was passed as harmless, later to be proved as poisonous.

From Wikipedia: In the United Kingdom, the dye is not permitted in food because it could be a genotoxic carcinogen. On 21 April 2005, the FSA announced that some batches of Old El Paso dinner kits had been contaminated with the dye, and issued an alert. Also, reported on the 5 May 2005, the dye was found in 35 products which have now been taken off supermarket shelves. The products were mainly cooking sauces, though some are also spices.

According to Wikipedia, azo dyes derived from benzidine are carcinogens so have been discontinued in the 1980's.

Google books (2) has in depth info on current dyes containing this. Other names for para red are: 1-((4-Nitrophenyl)azo)-2-naphthalenol, 1-((4-nitrophenyl)azo)-2-naphthol, 1-((p-nitrophenyl)azo)-2-naphthalenol, 1-((p-nitrophenyl)azo)-2-naphthol, paranitraniline red, Pigment Red 1, C.I. 12070, Recolite Para Red B, Carnelio Para Red BS. The chemical make up is: diazotisation of para-nitroaniline at ice-cold temperatures, followed by coupling with β-naphthol

1. http://en.wikipedia.org/wiki/Para_red
2. http://www.ajph.org/cgi/reprint/39/8/1023.pdf.
3. http://books.google.com/books?id=bkQAAAAAYAAJ&pg=PA789&lpg=PA789&dq=diazotized+paranitraniline+with+,8-naphthol.&source=bl&ots=2jlgYBpEXV&sig=g-EMEqVuvjw-C7hKahu0H9DHPTA&hl=en&ei=ND2ZStCILIXCNvz9sacF&sa=X&oi=book_result&ct=result&resnum=2#v=onepage&q=diazotized%20paranitraniline%20with%20%2C8-naphthol.&f=false