Indigo-group

From his synthesis of indol from orthonitrocinnamic Baeyer ascribed to it the constitutional formula  

Kekule had already (1869) [53] published an opinion that isatin is an inner anhydride of orthoamidophenylglyoxylic acid, and accordingly suggested the structural formula  

Claisen and Shadwell proved that isatic acid is orthoamidophenylglyoxylic acid, and that isatin is its inner anhydride by a direct synthesis [26]. However, various properties of isatin noted by Baeyer speak for the presence of an hydroxyl group according to the formula  

Oxindol is, from its synthetic production, an inner anhydride of orthoamidophenylacetic acid, and has the formula  

The formation of oxindol and dioxindol by reduction of isatin is, however, more in favour of the following constitution for these compounds — 

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Indol, CgH N, is the mother substance of the indigo group of compounds. It exists in various essential oils including neroli oil and oil of jasmin flowers. It is a crystalline compound, melting at 52° and boiling at 253° to 254°. Its odour is powerful and disagreeable, being distinctly faecal in character. Its constitution is as follows —... 

Five membered monoheterocyclic compounds. The indigo group , Sainsbury, M., in Campbell, N., Rodd s Chemistry of Carbon Compounds, Vol IVB, Ch. 14, 1977 and Supplement, Ch. 14, 1985. 

Topics which have formed the subjects of reviews this year include photoinduced organic synthesis, photoisomerisations involving super-cyclophanes, regioselec-tive and stereoselective [2+2] photocycloadditions, position- and stereoselective photocyclisation, the photochemistry of indoles, five-membered heterocyclic compounds of the indigo group, pyrazoles and isothiazoles, and heterocyclic N-oxides, photochromic reactions of naphthopyran derivatives, photodegradation reactions of photochromic spirooxazines and 2H-chromenes, ° and chiral photo-chromic compounds. ... 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

In the same paper Baeyer concluded that isatin and indoxyl must first be converted into isomeric compounds before they can form members of the true indigo group. The isomers are known only in compounds, in the free state they pass back spontaneously into the original form. Their instability depends on the mobility of the hydrogen atom . He called the labile forms pseudocompounds and introduced the names lactam and lactim for the two forms ... 

Hydroxyindole (181) represents a well known example of a compound in which the hydroxyl group is to the ring heteroatom. The equilibrium mixture again contains mainly the carbonyl form (182), indoxyl. Deprotonation gives a reactive ambident anion which can be methylated either on oxygen or C-2 (Scheme 73). Indoxyl is easily oxidized to indigo (184), which may be formed by dimerization of the radical (183) produced by electron loss from the anion. 

Tile basic chromophors of indigo and of some tetraazafulvalenes are very similar and therefore the frontier orbitals are comparable (90JPC949). PPP calculations on the 1,3,5,7-tetraazafulvalene 90 (R = Me) showed a good agreement with its UV/VIS spectrum. Tlie substitution of both methyl-sulfanyl groups in 90 by diethylamino/piperidino moieties led to a hypso-chromic shift of about 45 nm. 

WD-50 s two bartenders wore raw-indigo blue jeans and dark cherry shirts. The arriving clientele, with their flattened hair, small bowling-bag purses and mini trench coats, could have stepped out of a dressing trailer parked on Clinton Street and walked into the restaurant as a group. 

Indigo (57), the parent system of this group of colorants, is one of the oldest known natural dyes (see Chapter 1). The naturally occurring... 

Yellow to brown compounds are obtained when one or more nitro groups are conjugated with electron-donor substituents such as hydroxy or, of more importance, amino groups. Such dyes are relatively cheap. Picric acid, 2,4,6-trinitrophenol, can be regarded as the oldest synthetic dye it was produced in 1771 by Woulfe by treating indigo with nitric acid. 

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