Perylene leuco form

The third reaction stage is the most important and complex in the sequence, and is an alkaline fusion reaction. This is the synthesis stage in which the perylene chromophore is chemically formed, as well as the step in which many of the important physical properties of perylene tetracarboxylic acid diimide (PTCI) are determined. In the fusion reaction, (4) is fused with itself via a bimolecular nucleophilic substitution in the presence of molten alkali at temperatures in excess of 200 C. The resulting alkaline mass is then precipitated by slowly mixing into water. The subsequent slurry contains perylene in its reduced (leuco) form or salt. One of the several possible isomers of the lenco form is represented with the general formula (5). 

Vatting is a process where the perylene crude is reduced in an aqueous alkaline dithionite solution to a (colorless) leuco form, then filtered and washed to remove impurities. It is then oxidized by air or peroxide to give purified and recrystallized perylene pigmentl" . Since this type of processing purifies the pigment, higher chroma and specific hue shifts can often be obtained as a result. 

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See also in sourсe #XX -- [ ]

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