R. Martinez-Utrilla

Singlet oxygen photogeneration by ionized and un-ionized derivatives of Rose Bengal and Eosin Y in diluted solutions

Abstract Quantum yields of singlet oxygen photogeneration (relative to commercial Rose Bengal) were determined for the pure dye, Eosin Y, their corresponding methyl, benzyl, and p-isopropylbenzyl esters, and the product of Rose Bengal decarboxylation, all in solution in basic methanol (in order to assure total ionization). The similar values found for each series of salts indicate a low influence, if any, of the different C-2′ groups on their behaviour as sensitizers. As expected, the monodehalogenated parent dyes showed in the same medium somewhat lower yields. Slightly lower values were also found for the un-ionized forms of the methyl esters and for the non-ionizable methyl ether of Rose Bengal methyl ester in acidic dioxane as medium. In order to avoid the formation of dye aggregates and the quenching of the triplets of the sensitizer by the acceptor, all the yields were determined using solutions of 10−5 M sensitizer and 10−4 M or 10−5 M acceptor. The methodology, including the spectrophotometric procedure used to determine relative β values, is also reported.

Synthesis and Spectroscopic Properties of New Rose Bengal and Eosin Y Derivatives

Abstract Selective esterification of purified Rose Bengal and Eosin Y have been carried out by reaction with methyl iodide, benzyl chloride or p-isopropylbemyl chloride. The lactonic form of each dye reacts with diazomethane producing mixtures of the monomethyl ether and the dimethyl ether of the lactone, and the methyl ether of the methyl ester of the tautomeric quinonoid form. On heating, Rose Bengal decarboxylates in dimethylformamide solution, while Eosin Y loses a bromine atom in dimethylsulphoxide. The structures of all the products obtained have been studied by the usual Spectroscopic techniques. HPLC data are also reported.

Polycyclic hydroxyquinones—VIII: Preparation of acetylhydroxynaphthazarins by photo-fries rearrangement. A convenient synthesis of spinochrome A

Abstract Several synthetic routes to mono- and dihydroxynaphthazarins bearing an acetyl side-chain have been explored. Methoxynaphthazarin 1 has always been the starting material. Acylation is brought about via a photo-Fries rearrangement of various adequately substituted acetoxynaphthalenes prepared in several steps from 1 . Further steps including oxidative demethylation, hydrolysis and ether cleavage reactions, led to the desired mono- and dihydroxysubstituted acetylnaphthazarins. A new synthesis of Spinochrome A 24 , a natural occurring pigment representative of this kind of naphthazarin derivatives, is described.

Cyclic acetals as carbonyl blocking groups in the photo-Fries rearrangement of acyl substituted aryl esters

The ethylene acetals of o and p-acetoxyacetophenone 3a,b, prepared from the corresponding hydroxyacetophenones by treatment with acetic anhydride in pyridine and subsequently with ethylene glycol and p-toluenesulphonic acid, give upon irradiation the expected photo-Fries products 4a,b (from 3a) or 6 (from 3b). These compounds are converted in part into diacetylphenols 5a,b as a consequence of a deacetalization, occurring to some extent during the irradiation and further in the chromatographic workup. The yields of the photoproducts and the ortho/para ratio (in the case of 3a) are very similar to those given in the literature for phenyl acetate. By contrast, the acetoxyacetophenones 2a,b do not undergo any appreciable change upon irradiation,showing the deactivating effect of the acetyl side chain. Therefore, it is concluded that cyclic acetals are suitable carbonyl blocking groups in order to circumvent the deactivating effect of acyl substituents on the photo-Fries rearrangement of aryl esters.

Photocyclization of enol acetates of o-acetoxyacetophenones to chromones

Abstract Enol acetates of o-acetoxyacetophenones give chromones upon irradiation with uv-light.

Direct and dye-sensitized aqueous photo-oxidation of 3-indoleacetic acid, methyl-3-indoleacetate and 1-methyl-3-indoleacetic acid. I: Analysis of products

Abstract The products obtained in the direct and riboflavin- or Rose-Bengal-sensitized photo-oxidation of 3-indoleacetic acid ( 1a ), methyl-3-indoleacetate ( 1b ) and 1-methyl-3-indoleacetic acid ( 1c ) in aqueous buffer (pH 5 or pH 8) containing 10% methanol have been analysed. Both the direct and riboflavin-sensitized irradiations give essentially the same products. At pH 5 the main products are 3-oxindolemethanols ( 2 ), 3-indolemethanols ( 6 ) and 3-acylindoles ( 8 ), all resulting from the oxidation of the 3-methylene group, and a polymeric material which probably has the same origin. As primary intermediates, radicals I or II , formed by hydrogen abstraction from the 3-methylene group, are proposed. At pH 8 the breakdown of the 2,3-double bond of the starting indole predominates in both types of photo-oxidation, producing o -formamidobenzoyl derivatives ( 9 ), probably through the corresponding intermediate dioxetanes ( V ). At pH 5 and pH 8 the ring rupture is enhanced when Rose Bengal is used instead of riboflavin. The formation of other compounds can be explained by secondary thermal reactions.

Quantitative evaluation of polymeric photosensitizers

SummaryThe xanthene dye Rose Bengal (disodium salt of 3′, 4′, 5′, 6′-tetrachloro-2, 4, 5, 7-tetraiodofluorescein) has been covalently bound to a linear (soluble) copoly styrene-vinyl benzyl chloride. The chemical union takes place through alkylation of the carboxylate anion of the dye by one of the chloromethyl groups grafted on the polymer. The quantum yield of singlet oxygen generation results equal to that of the free dye and the photostability seems to be improved.

Indirect hydroquinone succinoylation via a photo-fries rearrangement. Application to the synthesis of enol lactones.

Abstract A photo-Fries rearrangement of hydroquinone succinates is the key step that allows the preparation of some γ-aryl enol lactones by dehydration of the corresponding aroyl propionic acids.

Photochemical versus aluminium chloride-catalyzed fries rearrangement of aryl hydrogen succinates. synthesis of 2(3H)-furanones

SummaryThe photochemical and aluminium chloride-catalyzed Fries rearrangement of a series of aryl hydrogen succinates3 a–f to the corresponding 4-oxoacids1 a–f are compared. Both approaches are complementary: the photochemical process is more general and becomes the method of choice for the succinoylation of phenols supporting alkoxy or hydroxy substituents, while the classical rearrangement is superior in the presence of alkyl or halogen substituents. These results are applied to the preparation of the 2(3H)-furanones2 a–f.ZusammenfassungDie photochemische und AlCl3-katalysierte Friessche Umlagerung einer Reihe von Bernsteinsäuremonoarylestern3 a–f zu den entsprechenden 4-Oxosäuren1 a–f werden verglichen. Beide Methoden ergänzen einander: Der photochemische Prozeß ist breiter anwendbar und wird bei Phenolen mit Alkoxy- oder Hydroxy-Substituenten bevorzugt, während die klassische Umlagerung in Gegenwart von Alkyl- oder Halogen-Substituenten vorteilhafter ist. Diese Ergebnisse werden für die Synthese der 2(3H)-Furanone2 a–f angewendet.

Thermal decarboxylation of rose bengal dye

Abstract The xanthene dye rose bengal undergoes decarboxylation when heated in dimethylformamide or cyclohexanone.