Flavanthrone

In 1901, mercury cataly2ed a-sulfonation of anthraquinone was discovered, and this led to the development of the chemistry of a-substituted anthraquinone derivatives (a-amino, a-chloro, a-hydroxy, and a,a -dihydroxyanthraquinones). In the same year R. Bohn discovered indanthrone. Afterward flavanthrone, pyranthrone, and ben2anthrone, etc, were synthesi2ed, and anthraquinone vat dyes such as ben2oylaniinoanthraquinone, anthrimides, and anthrimidocarba2oles were also invented. These anthraquinone derivatives were widely used to dye cotton with excellent fastness, and formed the basis of the anthraquinone vat dye industry. 

Flavanthrone. Flavanthrone [475-71-8] (177) (Cl 70600) has exceUent dyeiag properties, which ate due to the stabUity of the leuco form, but its fastness is not satisfactory. Only the unsubstituted flavanthrone is used as a vat dye, ie. Cl Vat YeUow 1 (177). It is mainly used as a pigment, ie. Cl Pigment YeUow 24. Synthetic routes ate iUustrated ia Figure 10. 

The syntheses of three polycyclic anthraquinones, indanthrone (53), pyranthrone (55a) and flavanthrone (55b), are illustrated in Scheme 4.7. In spite of the structural complexity of the products, the syntheses of these types of compound are often quite straightforward, involving, for... 

Scheme 4.7 Syntheses of the polycyclic anthraquinones indanthrone (53), pyranthrone (55a) and flavanthrone f55b)...

A number of vat dyes developed originally for textile applications are suitable, after conversion into an appropriate pigmentary physical form, for use in many paint and plastics applications. Examples of these so-called vat pigments include the anthraquinones, Indanthrone Blue (215, C. I. Pigment Blue 60) and Flavanthrone Yellow (216, C. I. Pigment... 

Flat plate, flow parallel to, 15 7191 Flat-screen printing, 26 398 Flat wall paint, 7 137-139 Flavanthrone dye, 9 336 Flavanthrone Yellow, pigment for plastics, 7 366t... 

The times of half-reduction of five typical vat dyes are listed in Table 3.3. Most of the commercially important products give values within the range 25-500 seconds. Few dyes are as slow to reduce as Cl Vat Red 1 and even fewer are reduced as quickly as flavanthrone. In fact, when these times were measured the average particle size of the sample of flavanthrone under test was greater than that of the Cl Vat Green 1 sample, which was reduced at least ten times more slowly [26]. 

The formation of indanthrone and flavanthrone, as well as alizarin, during the alkali fusion of 2-aminoanthraquinone can be explained mechanistically on the basis of the initial loss of a proton. The resulting anionic species can be represented as a resonance hybrid and is also tautomeric (Scheme 6.12). Primary 1-hydroxylation of 2-aminoanthraquinone is probably the first step in the formation of the alizarin by-product (compare Scheme 6.8). Such an attack may initiate the formation of flavanthrone [31 ]. It is also possible to envisage the formation of all three species by a radical mechanism [32]. 

Flavanthrone Yellow, the only commercially used flavanthrone, is a moderately brilliant reddish yellow. Excellent lightfastness and weatherfastness, combined with good solvent and migration resistance, make this pigment an attractive supplement to Anthrapyrimidine Yellow, mainly in the automotive finish industry. 

P.Y.179, an isoindolinone/cobalt complex pigment, was introduced to the market only few years ago but the production has recently been discontinued. It was recommended for use in paints, especially in automotive finishes. The pigment produces a reddish yellow shade. High lightfastness and excellent weatherfastness are an asset in pastel colors. Besides, good transparency made P.Y.179 a suitable product for metallic finishes. Yet, it is not quite as weatherfast as the equally reddish yellow P.Y.24, a flavanthrone pigment. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

Most pigments derived from vat dyes are structurally based on anthraquinone derivatives such as indanthrone, flavanthrone, pyranthrone, or dibromoan-thanthrone. There are other polycyclic pigments which may be used directly in the form in which they are manufactured. This includes derivatives of naphthalene and perylene tetracarboxylic acid, dioxazine (Carbazole Violet), and tetrachloro-thioindigo. Quinacridone pigments, which were first introduced in 1958, and recently DPP pigments have been added to the series. 

In 1901, R. Bohn synthesized indanthrone and flavanthrone. Both compounds are thus among the oldest synthetic vat dyes known. 

Flavanthrone has also been used for a long time as a vat dye. It gained recognition as a pigment when more and more lightfast and durable paints were required. 

Flavanthrone, like indanthrone, must be extremely pure in order to develop useful pigment properties. Subsequent finishing converts the thus prepared material into an appropriate product for use in paints or plastics. 

Converting the crude product into its leuco form, separating the intermediate, and reoxidizing the compound to form pure flavanthrone. 

The crude pigment may also be treated with an aromatic sulfonic acid (such as toluene sulfonic acid, xylene sulfonic acids, m-nitrobenzene sulfonic acid) in sulfuric acid or with nitric acid at 80°C to yield a somewhat redder yellow transparent modification of flavanthrone [22],... 

Flavanthrone Yellow, together with its chemical structure, is listed in the Colour Index under Constitution No. 70600. It was temporarily known as Pigment Yellow 112, but now it is exclusively referred to as Pigment Yellow 24. Since some time sales products of P.Y.24 are not listed anymore in the catalogues of the manufacturers, but the grades are still available on the market. 

High transparency makes P.Y.24 a valuable pigment for metallic finishes. It is used in relatively light shades, typically at a ratio of one part of color pigment to three parts of aluminum pigment. Thus prepared systems demonstrate excellent weatherfastness. Flavanthrone Yellow, like P.Y.108, tends to seed (Sec. 3.7.3.1). The pigment is heat stable up to 200°C and thus satisfies all possible heat stability requirements in this area. Flavanthrone Yellow is used in various industrial paints, especially in automobile O.E.M. finishes and in automotive refinishes. 

Pyranthrone pigments are related to the pyranthrone structure (99), which is formally derived from flavanthrone (Sec. 3.7.3.2) in that the nitrogen atoms are replaced by CH groups. 

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