User:Wildvineyard/Diarylide yellow

Diarylide yellow, also called ‘’’benzidine yellow’’’ is a group of synthetic organic yellow pigments of the group of benzidine pigments. The diarylide yellows are the most common yellow pigments used in printing as well as a wide variety of other applications including paints, plastics, textile printing, and paper. Their color can range from yellow to green. One of the most common diarlyide yellow pigments is ‘’’Yellow 12’’’. Its CAS number is. Other diarylide yellow pigments include ‘’’yellow 13’’’, ‘’’yellow 17’’’  and ‘’’yellow 83’’’. These pigments share the same backbone and vary in color depending on substitution of the benzene rings. Their chemical formulas range from C32H26Cl2N6O4 (yellow 12) to C36H34Cl2N6O4 (yellow 13) to C34H32Cl2N6O6 (yellow 17) to C36H32Cl4N6O8 (yellow 83).

Properties, chemistry and production
The diarylide yellows are a benzidine pigments. The diarylide yellow backbone is highly thermally stable. The formation of azo pigments involves the reaction of diazotized aromatic amines with appropriate coupling component. Diarylide yellow pigments are a series of disazoacetoacetanilides, synthesized by azo coupling of a tetrazotised benzidine derivative, most commonly 3,3’-dichlorobenzidine, with an acetoacetanilide coupling component. Worldwide production of color organic pigments was estimated to be about 250,000 metric tons (t) in 2006, with about 25%, or 62,500 t, being diarylide yellows.

Uses
Due to their stability, diarylide yellows are used in inks, coatings, and many plastics. The pigment is insoluble. It is a standard pigment used in printing ink and packaging industry. The diarylide yellow pigment Yellow 12 is one of the three main colored pigments used in the four color process of color printing. As such, its use is ubiquitous in printing both in commercial applications and in home color printers, as well as in textile printing.

Toxicity and Hazards
One of the main feedstock chemicals for diarylide yellow pigments is 3,3’-Dichlorobenzidine, which is considered a carcinogen and is listed in the US EPA’s Toxics Release Inventory. This chemical is structurally similar to benzidine. Diarylide yellow pigments using 3,3’-dichlorobenzidine were developed to avoid the toxicity issues of benzidine-based pigments. 3,3’-dichlorobenzidine is structurally similar to one of the polychlorinated biphenyl congeners, PCB 11 (3,3’-dichlorobiphenyl), and there is some evidence that the use of diarylide yellow pigments introduces PCB 11 to the environment. Other pigments may contain PCBs as well. Because the diarlyide yellows can contain PCBs, some sources warn against their use by artists, especially those that are pregnant. In the US, the Toxic Substances Control Act contains a specific exemption for the inadvertent production of PCBs in pigments, and allows PCBs to be present in them at a maximum concentration of 50 ppm with the average no higher than 25 ppm. However, for the purposes of calculating the concentration of PCBs, monochloro PCB congeners are discounted by dividing their concentration by a factor of 50, and dichloro PCB congeners, a class which includes PCB 11, are discounted by a factor of 5. In the European Union, Council Directive 89/677/EEC set a limit of 50 ppm for the sum of PCBs in pigments and other manufactured or imported goods that may contain inadvertently produced PCBs, with no discounting factors. The Stockholm Convention on Persistent Organic Pollutants contains similar provisions, such that most of the global economy is governed by some restriction on PCBs in pigments. However, in 2013 the Japanese Ministry of Economy, Trade and Industry tested batches of manufactured and imported pigments, and found PCB concentrations as high as 2,000 ppm.