General method for the synthesis of diazonium salt

(f) Towns AD., Synthesis and coloration properties of novel hetero-cyclic azo dyes.


. A small group of 17 azo pigments formed, like the diarylides, of two coupled arylide molecules: but these are joined in condensation with a bifunctional hydrocarbon molecule — hence the name. An industrially economical process to do this was discovered in 1951 by M. Schmid at CIBA, but use in artists' paints has been very limited. Available hues range from yellow (PY93, PY95, PY128, PY166), orange (PO31), red (PR144, PR166, , PR220, PR221, , PR248, PR262), and brown (PBr23, , PBr42). The few available as watercolor paints are semitransparent, have high tinting strength, and are typically very lightfast (more lightfast than analogous monoazo pigments, though also more expensive).


. An important group of about 20 azo pigments with a broad range of hues, from yellow (, , , , PY180, PY181, PY194), through orange (, , PO60, , PO72) and red (, , , PR185, PR208) to a maroon of fair lightfastness (), and a delicious brown (). Developed and patented by Hoechst in 1960, the benzimidazolones were first used as watercolor pigments in the late 1970's. They are relatively expensive, but are also among the most durable pigments used in artists' paints. (Winsor & Newton, for example, has chosen a benzimidazolone pigment for their "winsor yellow" and "winsor orange.")

The structure of PY151 is representative: a base structure very similar to the arylides, but with a charactertistic triangle of two nitrogen atoms and a carbon atom attached to the righthand carbon ring. Variations in hue arise from different arrangements of atoms attached to the lefthand (and sometimes the righthand) benzine rings. As a group the benzimidazolones are nontoxic, saturated, semitransparent and nonstaining, provide beautifully clear if somewhat bland colors (on all counts, cadmium pigments provide a revealing standard for comparison). For lightfastness alone the benzimidazolones should usually be preferred to comparable arylide or diarylide pigments in artists' colors (although there are a few benzimidazolones with only good lightfastness, such as ). The widest range of benzimidazolone colors are available in watercolor paints made by Winsor & Newton, Rembrandt and Daniel Smith. Curiously, "benzimidazolone" is also the pigment name most often replaced by "permanent," "winsor," "azo" or some other marketing moniker (I especially like DaVinci's "benzimida" as a nickname). To my ear, "benzimidazolone" is no harder to say (or remember) than "Benji, my dad's alone!" and everyone seems to be getting along just fine with the label "quinacridone" ... but marketing prejudices about artists die hard — very hard.

Synthesis of azo pyridone dyes - Open Access Library

The structure of PY3 is characteristic: a pair of carbon rings, joined by nitrogen to a central cluster of four carbon atoms (note the double nitrogen atoms just left of center). Variations in the hue arise from additional atoms hung asymmetrically off the outer carbon rings. About 5 different monoazo pigments are commercially available in watercolor paints. In general the monoazos are serviceable and relatively inexpensive colorants, semitransparent with good tinting strength. Unfortunately they have only moderately good lightfastness in artists' materials. They work very well as student paints, but always should be tested carefully for lightfastness before using in a major work. (The are also sometimes classified as monoazo pigments, for example by the Colour Index International.)

Synthesis and spectroscopic properties of new azo …

The schematic for PY153 shows the basic organization: two hydrocarbons symmetrically attached to a single metallic atom (in this case, nickel). First developed around 1920, many metal complex pigments did not come on the market until the late 1940's, but these compounds have proven to be unique, highly durable and reasonably lightfast artists' paints. Most azomethines reflect a significant amount of green light, making them wonderful choices to mix muted, natural greens with the phthalocyanines (, and ) and iron blue (). They are nontoxic but may (depending on the metal atom used) irritate the skin, particularly after prolonged contact with the raw pigment powder.

Synthesis and properties of bis(hetaryl)azo dyes

. These are specialized forms of disazomethine pigments, in the azo group, first described in 1946 and first offered commercially in the 1960's. Less than a dozen are available, in colors that range from yellow (PY109, , , PY173, PY185) to orange (PO61, PO66, ) and red ().

Microscale Chemistry - The microscale synthesis of azo dyes

. A family of about 30 azo pigments, identified by the term providing almost exclusively yellow hues. Many (, , PY73, PY74, and PY98) are commonly marketed under the trademark name first introduced in 1909. The two orange (PO1 and PO6) and red (PR211) monoazos are not used as artists' pigments.