2.4- Dihydroxy-6- benzoic

Bromoresorcinol has been prepared by the monobromination of resorcinol monobenzoate and subsequent hydrolysis, from 2-bromo-5-aminophenol by the diazo reaction, by treating resorcinol with dichlorourea and potassium bromide, and by the bromination of 2,4-dihydroxy benzoic acid followed by decarboxylation. The above procedure is based particularly upon the observations of Rice. ... 

In this way, the operational range of the Kolbe-Schmitt synthesis using resorcinol with water as solvent to give 2,4-dihydroxy benzoic acid was extended by about 120°C to 220°C, as compared to a standard batch protocol under reflux conditions (100°C) [18], The yields were at best close to 40% (160°C 40 bar 500 ml h 56 s) at full conversion, which approaches good practice in a laboratory-scale flask. Compared to the latter, the 120°C-higher microreactor operation results in a 130-fold decrease in reaction time and a 440-fold increase in space-time yield. The use of still higher temperatures, however, is limited by the increasing decarboxylation of the product, which was monitored at various residence times (t). 

In less than one minute, half of the 2,4-dihydroxy benzoic acid is decomposed already at 160°C in the micro-reactor setup [18]. Thus, a study was conducted to find optimal process parameters for T and t to achieve efficient high p,T operation via discrimination between the desired electrophilic substitution and undesired decarboxylation routes. The best operation point was at (200°C 40 bar 2000 ml h" 16 s). 

A lot of features of MALDI are conveyed by its name it is a desorption ionization, produced by a laser beam, and assisted by a matrix (Figure 2.5). The analyte (1 pmol or less) is mixed with a suitable matrix in a 1 1000 or higher molar ratio. The matrix is composed of a compound with a strong absorption at the wavelength of the laser used. These two factors, matrix excess and its strong absorption, ensure that the energy from the laser pulse is absorbed by the matrix and not by the analyte, thus avoiding its decomposition. Nicotinic acid, sinapinic acid (SA), 2,5-dihydroxy benzoic acid (2,5-DHB) and 2-(4-hydroxyphenylazo)benzoic acid (HABA) are some of the most commonly used matrices for MALDI. 

Kricheldorf et al. have investigated several hyperbranched poly(ester-amide)s derived from combinations of 3,5-diaminobenzoic acids and 3,5-dihydroxy-benzoic acids and similar monomers [100-102]. The polymers exhibited values of Tg ranging from 160 to 250 °C and were highly soluble in various solvents. They employed diamines as star centers in order to control the molecular weight. 

Fig. 10.1. MALDI-TOF mass spectra of (a) porcine cytochrome C from 2,5-dihydroxy-benzoic acid matrix at 337 nm and (b) a monoclonal antibody from nicotinic acid matrix at 266 nm. Reproduced fromRef. [15] by permission. John Wiley Sons, 1991.

In a recent modification of the second synthesis (50S) effected for fluvibactin (45) an o-xylene protection group was proposed (reaction of 2,3-dihydroxy-benzoic acid methyl ester with 1,2-di(bromomethyl)benzene) which could be removed later by hydrogenolysis. The formation of the oxazoline ring from protected DHB-L-threonine methyl ester was achieved with Mo(VI) catalysts (e.g. (NH4)2Mo04) without affecting the chiral centers. Derivatization of the primary amino groups of norspermidine with the protected DHB methyl ester was catalyzed by Sb(OC2115)3. 

Figure 14.6 Structures of some commonly used MALDI matrices (a) 2,5-dihydroxy benzoic acid (DHB), (b) a-cyano-4-hydroxy-cinnamic acid, and (c) sinapinic acid (SA). Combination of these acidic MALDI matrices with organic bases leads to the formation of ionic liquid matrices.

Inorganic lead compounds such as PbO, Pb02, Pb304, PbS, lead molybdate and lead perchlorate 2) Lead salts of organic adds such as 2,4-dihydroxy benzoic add, salicylic add, acetyl salicylic add and methoxy propionic add i) Effective with propellants of cal. val. less than 900 cal. g 1 ii) Lead salts of aromatic adds are effective with propellants of higher cal. val. [237]. 

Nitroderivotives of Dihydroxy benzoic Acid Mononitrodihydroxybenzoic Acid,... 

The resorcinol and phloroglucinol derivatives (Table IV) all precipitated rather completely as expected except for 3,5- and 2,4-dihydroxy-benzoic acids. Their precipitation was enhanced if phloroglucinol was added this indicates that formaldehyde substitution occurred but the products were too soluble and too polar to precipitate until crosslinked with phloroglucinol. It had been shown previously that phenols which did not react with formaldehyde were not appreciably entrained in the precipitate formed with those which did (21) (see Table X). Hydro-quinone derivatives, except for one which is also a resorcinol derivative, did not precipitate with formaldehyde (Table V). 

Reaction XXIX. (e) Condensation of Meta-hydroxy- and di-meta-dihydroxy-benzoic Acids with themselves and with Benzoic Acid under the action of hot Sulphuric Acid. (B., 18, 2147.)—The products of this action are hydroxyanthraquinones like the above. 

Owen RW, Wimonwatwatee T, Spiegelhalder B, Bartsch H (1996) A high performance liquid chromatography system for quantification of hydroxyl radical formation by determination of dihydroxy benzoic acids. Eur J Cancer Prevention 5 233-240 Pan X-M, Bastian E, von Sonntag C (1988) The reactions of hydroxyl radicals with 1,4- and 1,3-cyclohexadiene in aqueous solution. A pulse radiolysis and product study. Z Naturforsch 43b 1201—1205... 

Groger, D., D. Erge and G-H. Floss On the biosynthesis of 2,3-dihydroxy-benzoic acid in submerged cultures of Claviceps paspali Stevens et Hall. Z. Naturforsch. 20 (b), 856 (1965). 

Dihydroxy benzoic acid trinexapac Di-isobutylamine butylate Di-isopropanol amine fenpropimorph Di-isopropylamine diallate, triallate Di-isopropylaniline diafenthiuron... 

Dihydroxy benzoic acid Benzoic acid + H2S04 - 3.5 disulfonic benzoic acid followed by alkali fusion... 

In order for proper description of the acidic analyte retention versus the mobile-phase pH, the pH shift of the aqueous portion of the mobile phase must be taken into account. Plot of the retention factor of 2-4dihydroxyben-zoic acid versus two different pH scales [ pH (Figure 4-34, line A) and pH (Figure 4-34, line B)] is shown in Figure 4-34. A theoretical curve (Figure 4-34, line C) of the retention dependence versus pH of the mobile phase was constructed for 2,4-dihydroxy benzoic acid, based on its potentiometric pKa of... 

More recently benzoic acid derivatives (MW 122-170) have also been shown to be astringent (17). The most astringent compounds, salicylic (2-hydroxy benzoic acid) and gentisic (2,5 dihydroxy benzoic acid) acids, were ortho substituted, but neither had vicinal hydroxyl groups. Both derivatives had lower pHs than the non-ortho substituted ones, which may have contributed not only to sourness but also to astringency. McManus et al (1981) (18) proposed previously that simple phenols which contain 1,2 dihydroxy or 1,2,3 trihydroxy groups (such as epicatechin or catechin) may cross link and thereby precipitate proteins. It could be speculated that ortho substitution conveys some kind of binding capability similar to that of flavan-3-ols or polyphenolics of hi er MW. 

The solvent isotope effect in the decarboxylation of 2,4-dihydroxy-benzoic acid is ( atcoohJhjO /( ArcooD)D,o = 6.25. The solvent isotope effect on the acid ionization constant of 2,4-dihydroxybenzoic acid has been determined separately, by potentiometric methods ... 

The increase in acid strength due to hydrogen bonding of this type is even more marked in 2,6-dihydroxy benzoic acid 5 x 10 ) in which the... 

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