Thiazine dyes

Preparation 393.—Methylene Blue (Tetramethylthioninc Chloride) (Hydrated zinc double chloride). 

Thiosulphonic Add and Dye.—Before entering on this stage of the preparation the following solutions are prepared — 

If zinc-free methylene blue is desired, the filtrate from the chromium hydroxide is heated to 80°, 15 gms. of common salt added for each 100 c.cs. of solution, also 10 c.cs. of cone, hydrochloric acid. On cooling, the zinc-free methylene blue separates in fine crystals. 

Methylene blue is of a very pure shade, and is much used for dyeing tannined cotton the zinc-free dye is used for medicinal purposes, and also for the production of discharge effects in silk printing. 

—About 25 gms. Used in conjunction with iron-mordanted logwood, or with tin phosphate for dyeing black on silk, also for cotton and calico printing. (E.P., 8992 (1886).) 

Source Reprinted from Ref. 36 with permission of copyright owner, John Wiley Sons, Inc. aPaper T coated with a solution consisting of O.Olg of dye, l.Og of PVA, and 10ml of water. 

As can be seen from Table 9.12, photochromism is also strongly affected by humidity. It is well known that thiazine and its derivatives undergo photoreduction smoothly in the presence of such activated surfaces as silica gel and alumina with water molecules,37 and that methylene blue is also photochemically reduced in acid solution, even with only available water as the reducing agent38 Therefore the water present in polymer films must produce a thionine-water hydration system, which accelerates the rate of the photoreduction of thionine, as well as promoting the contact of reductants by a plasticizer effect. PVA, used as the matrix, can also play the role of reductant, but its extent may be minor as compared with the added reductant. The effect of water is supported by the fact that a less hydrophilic polymer matrix such as poly(methyl methacrylate) does not exhibit photochromism even though the system contains an appreciable amount of reductants. 

---

Thiazine dyes Thiazines Thiazole dyes Thiazole ring Thiazoles Thiazolidine... 

Azine, oxazine, and thiazine dyes were among the earliest of synthetic dyes. The names are derived from the 6-member heterocycHc ring system present in... 

Azine, oxazine, and thiazine dyes were historically more important than they are at present. However, at least one example of each, introduced more than 100 years ago, is still offered commercially today (1,2). Azo and anthraquinone dyes have largely displaced them in commercial appHcation. Azo dyes (qv) offer better fastness and broader shade ranges at more economical prices. 

Methylene Blue [61-73-4] CI Basic Blue 9 (CI 52015), (26), is the classic thiazine dye still in use today. This dye was first reported in 1876 (1). 

There have been approximately 60 references to thiazine dyes in the past 15 years of Chemical Jibstracts. Although most of these references are to titration indicators, photophysical evaluation, and spectral properties, a few refer to stmctures for use as dyes (13). 

Synthesis. The method of synthesis for Methylene Blue described in reference 14 is stiU the stepwise method of choice for thiazine dyes. /V,/V-Dimethy1-y-pheny1ene diamine [99-98-9], CgH22N2, reacts with sodium thiosulfate [7772-98-7] to form the thiosulfonic acid which condenses with /V, /V-dimetby1 ani1 ine [121 -69-7], CgH N, in the presence of sodium dichromate [10588-01-9] to the indamine, then with copper sulfate [18939-61 -2] and sodium dichromate to Methylene Blue (26). 

When Methylene Blue is reduced, the yellowish leuco cannot be isolated due to instant air oxidation. Benzoylation of the leuco form provides stabilization. There are also leuco thiazine dyes stable enough to be isolated without the need for aroylation. 

There are cationic thiazine dyes (3 to 5) and neutral thiazinone dyes exemplified by Methylene Violet (6). Like leuco Methylene Blue, leuco Methylene Violet is too air sensitive to be isolated and therefore requires acylation. 

Benzo[l,2-fl]-8-methyl-9-azaphenothiazinone (14) was reduced to a leuco form 15 which was too unstable to be isolable.10 The leucos 16 and 18 obtained from thionation of iV,iV-diphenyl-p-phenylenediamine and j9,//-dianilinodiphenylamine, respectively, are also air sensitive. 11 They are oxidized to thiazine dyes 17 and 19 which are reported to absorb in the near infrared. 

The thiazine dyes used in the preparation of this type of leuco are obtained through oxidative coupling of phenothiazine with an active methylene compound or an aniline. The reduction of the dye 23 with zinc powder in acetic acid is straightforward.9 Treatment of the leuco 24 with acetic anhydride at 40°C yields a more air stable leuco 25.9 Addition of arylsulfinic acid to thiazine dyes such as 26 produces directly leuco dyes such as 27.Sb... 

The decolorization potential of immobilized P. chrysosporium MTCC 787 for azo dyes Acid Orange, Acid Red 114, triphenylmethane dye Methyl Violet, diazoic dye Congo Red, vat dye Vat Magenta, thiazine dye Methylene Blue, and anthraqui-none Acid Green was demonstrated by Radha et al. [53]. Decolorization experiments were carried out with immobilized calcium alginate (Ca-ALG) beads of different sizes (2-6 mm). 

Conventional singlet oxygen sensitizers such as Thiazine dyes, 2 and 3, have been reported to promote Wagnerova Class II electron-transfer photooxygenations.60 For example, the participation of singlet oxygen in the reaction depicted in Fig. 9... 

Thermal decomposition reactions, of IV-acyloxy-lV-alkoxyamides, 90-96 free radical decomposition, 91-93 HERON reactions, 93-96 Thiazine dyes, 233... 

Stockert JC, Juarranz A, Villanueva A, Canete M (1996) Photodynamic damage to HeLa cell microtubules induced by thiazine dyes. Cancer Chemother Pharmacol 39 167-169. 

Many complex dye molecules form triplet states which undergo facile reduction. Thiazine dyes such as thionine, 49, and methylene blue are photoreduced by a variety of oxidizing agents, including ferrous ion.475... 

Blue dyes are derived from anthraquinone, phthalocyanine, or metallized formazan. See also Anthraquinone (Figs. I and 2). There are also oxazine and thiazine dyes reported (Fig. 2). 

Classes Of Sensitization, a. Photoreducible Dye Sensitization. In 1954 Oster (7) reported the first documentation of a dye-sensitized photoredox system. During the course of his work, Oster identified several classes of effective dyes, termed by him "photoreducible." These included examples of the classes of acridine, xanthine, and thiazine dyes. Figure 3 illustrates an example of each class, chosen in such a manner that the entire visible spectrum is covered by their absorption spectra. In Oster s work, identification of suitable activators (reduc-tants) to use in conjunction with the dyes was empirically determined. 

Oxazine, azine and thiazine dyes are named for the characteristic heterocyclic ring systems 1,4-oxazine, 1,4-diazine, and 1,4-thiazine. The dyes are generally cationic (basic) or acid dyes. They also can be reduced to colorless forms, then oxidized back to the dye, as in vat dyeing. The dyes also have been used to a limited extent in disperse and fiber reactive applications. They are used as titration indicators and may be applied to acrylic fibers and leather. 

In Systems 29 and 30 suggested by Sudo and Toda [82-84] no intermediate acceptor At was added. Instead of A1 the photosensitizer itself which is able to penetrate through a lipid bilayer both in oxidized and reduced states, performs electron transfer across the membrane. System 30 allows one to accumulate and store the products of electron transfer from the reversible donor, Fe2+, to the reversible acceptor, Fe(CN)g Note that in homogeneous solution it is impossible to accumulate and store the products of this reaction. It is well known that back recombination of the products formed upon PET from Fe2+ to thiazine dyes... 

MB belongs to the group of thiazine dyes and is widely used as a redox indicator in analytical chemistry and as a staining dye in biology. In aqueous solutions, which are intensely blue due to the strong light absorbance, MB forms monomers and dimers. The reduced form of MB, called Leuco Methylene blue (LMB), is colorless. 

---