Thioindigo dyes

Photodegradation as well as fluorescence quenching has been observed in chlorophyll monolayers [302,316]. Whitten [317] observed a substantial decrease in the area of mixed films of tripalmitin and a ci5-thioindigo dye as isomerization to the trti 5-thioindigo dye occurred on irradiation with UV light. 

Free Electron Molecular Orbital method colour and constitution, 1, 342 Freelingyne occurrence, 4, 706 Free radical processes in photography, 1, 387-389 Friedlander synthesis quinolines, 2, 443 thioindigo dyes, 4, 910 Fries rearrangement chroman-4-one synthesis from, 3, 850 Fructose, 1-deoxy- C NMR, 4, 575 Frusemide as diuretic, 1, 174 metabolism, 1, 245 FS-32 — see 1/f-Indazole, l-[3-... 

Thioindigo [522-75-8] M 296.2, m >280 . Adsorbed on silica gel from CCl4/ benzene (3 1), eluted with benzene, crystd from CHCI3 and dried at 60-65°. [Wyman and Erode J Am Chem Soc 73 1487 1951.] This paper also gives details of purification of other thioindigo dyes. 

Absorption spectra of some thioindigo dyes in benzene and chloroform solutions are reversible and reproducible functions of the wavelength... 

The symmetrical thioindigo dyes have the structure (355), where R = Cl, Br, Me, NH2, OMe, OEt or SEt located at the 4-, 5-, 6- or 7-position of the benzo[6 jthiophene parent compound, or combinations of two or three of these substituents. The original Friedlander synthesis involved mild oxidation of a 3-hydroxybenzo[6 jthiophene, but numerous methods, many patented, have been used. The 2,3 -bithioindigos, also known as thioindirubins (356), by analogy with the indigo isomer, indirubin, are also dyes of some interest. 

However, it was not until 1939 that the correct structure of indophenine was established as (359). Other ortho -quinones also condense with thiophene in the presence of acid to form dyes having the general structure (360). Although the indophenine dyes were not as commercially important as the thioindigo dyes, many compounds were prepared and evaluated (54HC(7)l). 

Thioindoxyls are readily oxidized to thioindigo dyes.584 They may be reduced to benzo[6]thiophenes (Table XI) with zinc (Clemmensen reduction) or tin and acid (method a) (use of mossy zinc is preferred for the reduction of halothioindoxyls and also minimizes reduction of the thiophene ring),315 sodium borohydride (method b),222,424,432 or... 

Beside indigo itself, the indigoid colorant thioindigo and its derivatives are also important vat dyes, but because of the low affinity of vatted thioindigo dyes for the fiber, these dyes are used mainly in textile printing. 

The structure of 2,2,5,5-tetramethyl-2,3,5,6-tetrahydrothieno[3,2-6]thiophene-3,6-dione (see equations 64, 73), the first compound containing the basic chromophoric system of the thioindigo dyes, was also determined with the aid of X-ray analysis (77CB1421). 

In addition, sulfur monochloride (37) will react with p-chloroarylamines, like (45) in the presence of sodium hydroxide to give the sodium thiophenolate (46) this is the Herz reaction (Scheme 31) used in the synthesis of o-aminothiophenols, which are useful in the manufacture of thioindigo dyes (see Chapter 11, p. 221). 

In liquid solutions in the absence of a sensitizer, T-T absorption has hitherto been observed predominantly with nitro-substituted frans-arylethy-lenes (Tables 16c-e) such as nitrostilbenes [31,200], nitroazastilbenes [172,416], and nitrostyrenes [417], Apparently, the nitro group enhances strongly direct excitation conditions at room temperature [96,200] because the triplet yield is too small (see Section 1V.B.6). 

Plazek and Sucharda29 and Colonna3 prepared thioindigo dyes from 2-pyridylacetic acids it may be assumed that 3-hydroxythieno[2,3-6]-pyridines were intermediates, but they were not isolated. An improvement in yield of hydroxythienopyridines in the cyclization of carboxy-pyridylthioacetic acids with acetic anhydride is achieved if the intermediate acetoxy compound is isolated20 (Scheme 7). 

Evidence has been obtained for the intermediacy of the triplet state in the direct photoisomerization of thioindigo dyes,228 a long-lived intermediate has been detected in the flash photolysis of 4-thiouridine in aqueous solution,224 and the p values of the lumiflavin triplet state have been determined by flash photolysis.225 ... 

Several compounds which are known as thioindigo dyes are derived fromm benzo[Z>]thiophene. Thio-indigo 6 itself is made from 2-sulfanylbenzoic acid via benzo[fe]thiophen-3(2//)-one 5 (thioindoxyl) by the following steps (Friedlander 1905) ... 

Thioindigo, a vat dye, forms red needles and its vat is bright yellow. As a dye, it has a blue-red colour. Thioindigo dyes were produced in large quantities until the fifties, but since then they have become less important. 

G. M. Wyman, W. R. Brode, The relation between the absorption spectra and the chemical constitution of dyes, XXII. Cis-trans isomerism in thioindigo dyes, J. Am. Chem. Soc. 73(1951) 1487. 

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