Hydroxyaromatic acids

Several caffeic acid esters of hydroxyacids (90,91,92,93) are known in ferns. Chicoric acid (90) is present in many ferns (54). o-Coumaric acid (70) and its P-D-glucoside, melilotoside (72) have been isolated together with coumarin (120) from Polystichum gemmiferum and Phy mat odes scolopendria (55). 

Chlorogenic acid Chart 3. Hydroxyaromatic acids found in the filicopsida 

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Goodman, I. and Nesbitt, B. R, Polyesters from aromatic and hydroxyaromatic acids. Polymer, 1, 384, 1960. 

Among new methods of fonning polyesters is a preparation of completely aromatic polyesters by direct condensation of hydroxyaromatic acids (like hydroxybenzoic) with the aid of triphenyl-phosphorus compounds or dichlorophenylphosphine. ... 

Diterpenoids (7-oxo-dehydroabietic and 15-hydroxy-7-oxo-dehydroabietic acid) triterpenoids (isomasticadienonic, masticadienonic, moronic and oleanonic acids) alkanes (C25-C33), wax esters (C o-Cso), hydroxy wax esters (C42-CS4) hydroxyaromatic acids fatty adds steranes and hopanes... 

Partenheimer W. The aerobic oxidative cleavage of lignin to produce hydroxyaromatic benzaldehydes and carboxylic acids via metal/bromide catalysts in acetic acid/water mixtures. Adv Synth Catal. 2009 351 456-66. 

Diazooxides react with hydroxyaromatic coupling components in the same manner as diazoniiun salts, giving dihydroxysubstituted azo compounds. An interesting feature of this reaction is the fact that the reaction rate incr with medium acidity, reaches a maximum (between 50-80% HjSO in reactions with resorcinol, depending on the diazooxide under study) and then decreases... 

Katritzky AR, Singh SK, Cai C, Bobrov S. Direct synthesis of esters and amides from unprotected hydroxyaromatic and -aliphatic carboxyhc acids. J. Org. Chem. 2006 71 3364-3374. 

H -tetramethylbenzidine in anionic-cationic mixed micelles has been studied in detail by ESR . The photochemistry of the semi-oxidised forms of eosin Y and rose bengal have been investigated in colloidal solutions. Relevant to the fluorescence of proteins is a study of fluorescence quenching of indolic compounds by amino-acids in SOS, CTAB, and CTAC micelles O Rate constants for proton transfer of several hydroxyaromatic compounds have been measured in a variety of surfactant solutions. Photoprotolytic dissociation does not require exit of the reactant molecules from the micelles. Micellar solutions can be used to improve the fluorescence determination of 2-naphthol by inhibiting proton transfer or proton inducing reactions z2. jpe decay of the radical pair composed of diphenylphosphonyl and 2,4,6-trimethyl benzoyl radicals in SDS is affected by magnetic... 

Ramaswamy, S., M. Malalyandi, and G.W. Buchanan. 1985. Phase-transfer-catalyzed methylation of hydroxyaromatic adds, hydroxyaromatic aldehydes, and aromatic polycarboxylic acids. Environ. Sci. Technol. 19 507-512. 

The carboxylation of hydroxyaromatic compounds in the form of alkaline salts (the Kolbe Schmitt reaction) is well known and applied in the synthesis of acids such as salicylic acid, para-hydroxybenzoic acid and orf/to-cresotinic acid. 

In this reaction, the course of condensation and the type of products formed depend on several factors, such as the nature of hydroxyaromatic compounds, amines, aldehydes, and the actual ratio of the components in the reaction system. For examples, besides the initial ammonia, this reaction has been extended successfully to both primary amines and secondary amines and among the secondary amines, the reaction particularly works for dimethylamine, diethylamine, and piperidine. In addition, when one of the secondary amines exists in large excess or when dimethylamine or ammonia is removed from the reaction system via vaporization, good yields of pure products are often achievable. Besides the commonly used -naphthol, many other hydroxyaromatic compounds are suitable for this reaction as well, such as phenols, and quinolinols. " It is found that among kojic acid, 8-quinolinol, and 8-hydroxquinaldine, kojic acid is the most reactive compound for the Betti reaction, which reacts with benzylideneaniline in less than 1 day... 

The existence of ion pairs of hydroxy aromatic anions with polar groups of cationic micelles was proposed by Zaitsev et al. [66] to explain the effective charge of anions close to zero, observed in acid-base photoreactions of hydroxyaromatics in CTAB solutions. Such a value for the effective charge was found by simulation of the values of the diffusion rate constants of hydrogen ions to excited anions of hydroxyaromatics to make the calculated diffusion-controlled protonation reaction of the excited anions rate constants close to experimentally observed ones. In aqueous solution, the excited anions are protonated with diffusional values of the rate constant with some nonsignificant steric factor [67,68]. The three-phase model can help to interpret the reactivity of polar and charged substances in micellar solutions. 

Photoprotolytic reactions in micellar solutions were systematically studied by the authors of the present review with coworkers [15, 16, 66, 120-122]. Effective dissociation rate constants ki for a set of hydroxyaromatic compounds in anionic, cationic and uncharged micelles were determined from the dependence of fluorescence quantum yields on the concentration of micelles [Eq. (22)] or on the concentration of acid [Eq. (49)]. The latter method was also used for determining the effective equilibrium constants and effective rate constants of the reverse protonation reaction [Eq. (49)]. The data obtained are presented in Table 3. 

Now we shall analyze the regularities in rate constants of protolytic photodissociation of hydroxyaromatic compounds in the micellar phase and in the membranes of vesicles ( Tables 1 and 5 ). For one and the same compounds in cationic micelles the acidity constants are usually greater than in the aqueous solution ( pA decreases ), and dissociation rate... 

Enhanced Acidity of Hydroxyaromatic Compounds in the Excited Singlet State. .. 39-2... 

The excited state properties of hydroxyaromatic compounds (phenols, naphthols, etc) are of interest to a wide audience in chemistry, including those interested in the environmental decomposition of phenols, chemical physicists interested in the very fast dynamics of excited-state proton transfer (ESPT) and excited-state intramolecular proton transfer (ESIPT), physical chemists interested in photoionization and the photochemical pathways for phenoxyl radical formation, and organic photochemists interested in the mechanisms of phenol and hydroxyarene photochemistry. Due to space limitations, this review is restricted to molecular photochemistry of hydroxyaromatic compounds reported during the last three decades that are of primary interest to organic photochemists. It also includes a brief section on the phenomenon of enhanced acidity of phenols and other hydroxyaromatics because this is central to hydroxyarene photochemistry and forms the basis of much of the mechanistic photochemistry to be discussed later on. Several reviews that offer related coverage to this work have also appeared recently. This review does not cover aspects of electron photoejection from phenols or phenolate ions (and related compounds such as tyrosine) or phenol OH homolysis induced photochemically, as shown in Eq. (39.1), as these are adequately covered elsewhere ... 

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