Xanthene, substituted

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

In general, the xanthenes are synthesized by the reaction of two moles of a nucleophilic / -substituted phenol (10) with an electrophilic carbonyl compound (11), the reaction occurring most readily with an acid catalyst at temperatures of 100—200°C. 

Aminohydroxy-substituted xanthenes ate of Httle commercial importance. They are synthesized by condensing one mole of y -diaLkylaminophenol with phthahc anhydride, and then condensing that product with an appropriately substituted phenol. For example. Mordant Red 77 [6528-43 ] (Cl45300) (45) is prepared by condensing m- dim ethyl am in opb en o1 with phthaUc anhydride, and then condensing the product with 2,4-dihydroxybenzenesulfonic acid. 

The reaction of methoxy-substituted 1,4-dihydroatomatic systems is a general one. Other condensed systems react ia a similar manner, for example, 3,6-dimethoxy-1,4,S,8-tetrahydronaphtha1ene and derivatives of anthracene (35) and xanthene (36) (74). The proposed method enables synthesis of the tri-and tetracarbocyanines where the whole chromophore is iategrated iato a rigidizing skeleton. Asymmetrical polymethines can also be obtained similarly. 

Various 10-substituted dibenz[/i,/]oxcpins 5 have been synthesized from 9-(hydroxymethyl)-xanthenes by treatment with dehydrating agents such phosphorus pentoxide.194,195... 

Dilithiated diphenyl ether reacts with heteroaiyl esters to give 9-substituted xanthen-9-ols, offering an alternative approach to pharmaceuticals containing a 9-xanthylidene unit <96TL5073>. 

Meisenbach M, Echner H, Voelter W. New methoxy-substituted 9-phenyl-xanthen-9-ylamine linkers for the solid phase phase synthesis of protected peptide amides. Chem Commun (Cambridge) 1997 849-850. 

Due to their longer wavelength fluorescence and photostability, rhodamine and its derivatives have often been employed for the labeling of probes tested in living cells. Like fluorescein, the chemical structure of rhodamine consists of an upper xanthene ring and a lower benzene ring. In this case, the xanthene ring is substituted... 

The most recent strategy to prepare [3]radialenes is the treatment of 1,1-dihaloalkenes with activated nickel. Thus, the aryl-substituted [3]radialenes (Z,E,E)-30 and (E,E,E) 30, 27 and 32 were obtained together with the corresponding butatrienes (29, 28, 31) from the 1,1-dibromo- or 1,1-dichloroalkenes with the help of nickel activated by ultrasound (Scheme 4)11. It is worth mentioning that the mixed-substituted radialene 33 was produced, when the nickel carbenoid derived from 9-(dichloromethylene)xanthene was generated in the presence of butatriene 2811. 

Xanthene dyes are used as colour formers. These so-called fluorans usually contain amino groups sited para and meta to the central carbon atom. Such a substitution pattern gives rise to broad absorption bands and leads to almost black colour production the lactone 6.200 is a typical example. This xanthene derivative finds use in direct thermal printing [36]. The chemistry of fluoran leuco dyes has been reviewed [78]. 

SNARF and SNAFL indicators are benzo[c]xanthene dyes that can be described as semi-naphthofluoresceins and semi-naphthorhodafluors, respectively, depending on whether the benzo[c]xanthene ring is substituted at the 10-position with oxygen or with nitrogen, respectively (Whitaker et al., 1991). These indicators, whose p K l values are in the physiological range, exhibit distinct emission bands for the pro-tonated and deprotonated forms so that emission ratio measurements are possible. In SNAFL, the acidic form is more fluorescent, whereas in SNARF, the basic form is more fluorescent. 

When highly fluorescent ionic fluorophores, such as acridinium or xanthene dyes, are linked to a flexible electron-donor-substituted aryl group, a low-lying intramolecu-... 

Thianthrene radical ion(l+) perchlorate was employed to effect one-electron oxidation of Cu(TPP) (TPP, tetraphenylporphyrinate) to [Cu (Tpp )]+[sbcy (82JA6791). It was also used to dehydrogenate thio-xanthene (44)(R = H), forming perchlorate 43 or, in the presence of an electron-rich aromatic, the 9-Ar-substituted-thioxanthene 44 (R = Ar) (80MI4 82MI4) or, in the presence of a phosphine, phosphonium salts 44 (R = P-"R (81MI7). 

The literature of the xanthenes provides many examples of compounds with various substituted aromatic nuclei at C-9, and other examples with different substituents on the xanthene ring. The basic skeleton, however, has not been modified in recent years. It is apparent that the crowded aromatic subunit will slow reactions involving the formation of intermediates involving reaction at C-9 and may retard the subsequent reactions of the intermediates as well. This observation predicts slower rates of electron transfer, for example, and subsequent photoreduction than would be expected for unsubstituted xanthenes. Our interest was to synthesize a new series of dyes without substituents at that position and to investigate the effect of C-9 substitution on photochemical and photophysical properties. 

Comparison of these new compounds with the common xanthene dyes reveals that substitution of H at C-9 has only a minor influence in the absorption and emission spectra. Table 15 summarizes the spectral properties of HF, TBHF, and TIHF as well as the acid dissociation constants and electrochemical potentials. The color, fluorescence quantum yield, ap-... 

TABLE 15 Properties of Novel Xanthene Dyes Derivatives H-Substituted Compounds"... 

Xanthene itself results from the dehydration of 2,2 -dihydroxydiphenylmethane (43JOC316), and this route provides access to the important derivative, 3,6-bis(dimethyl-amino)xanthene (192). The reactive m -dimethylaminophenol condenses readily with formaldehyde and subsequent cyclization occurs in sulfuric acid (Scheme 37) (1896JPR(54)217). Other aldehydes behave in a similar manner to yield 9-substituted xanthenes (12LA(391)308). 

Many other types of polymer have been prepared which exhibit semiconductivity. All obey the equation a = a0exp — E/kT. These include xanthene polymers (109, 110), polymerized phthalocyanines (111, 112), epoxides and polydiketones (86, 113), polypentadienes (114), polydicyanoacetylenes (115), polyvinylferrocene and substituted ferrocene (116, 117, 118, 119), polymeric complexes of tetracyanoethylene and metals (120), poly(vinyl chloride) and poly(vinylidene chloride) (121), polyvinylene and polyphenylene (122) and poly(Schiff s bases) (123, 124). 

Hydroxyl Derivatives. The building block of most hydroxyl-substituted xanthenes, or fluorones, is fluorescein (2). The sodium or potassium salt of fluorescein, commonly called uranine (Cl 45350). is used for dyeing wool and silk brilliant yellow shades. However, the principal use of fluorescein is as an intermediate for more highly substituted hydroxyxanthenes. 

Aminohydroxy-suhstituted xanthenes are of little commercial importance. They are synthesized by condensing one mole of m-dialkylaminophenol w ith phthalic anhydride, and then condensing that product with an appropriately substituted phenol... 

The rhodamines are economically the most important amino-substituted xanthene dyes. The total sales of Rhodamine B in the United States in 1980 were over 107. The total domestic market for fluorescein and uranine was estimated to be over 0.5 x 106 /yr. 

The alkylidene dimethone (2) upon boiling with glacial acetic acid, acetic anhydride, hydrochloric acid and other reagents frequently loses water and passes into the anhydride, or dimethone anhydride (3) (a substituted octahydro-xanthene) which often serves as another derivative. The derivatives (2) are soluble in dilute alkali and the resulting solutions give colorations with ferric chloride solution on the other hand, the anhydrides (3) are insoluble in dilute alkali and hence can easily be distinguished from the alkylidene dimethones (2). 

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