2.4- Dihydroxybenzaldehyde, reaction with

Sahcylaldehyde is readily oxidized, however, to sahcyhc acid by reaction with solutions of potassium permanganate, or aqueous silver oxide suspension. 4-Hydroxybenzaldehyde can be oxidized to 4-hydroxybenzoic acid with aqueous silver nitrate (44). Organic peracids, in basic organic solvents, can also be used for these transformations into benzoic acids (45). Another type of oxidation is the reaction of sahcylaldehyde with alkaline potassium persulfate, which yields 2,5-dihydroxybenzaldehyde (46). 

A similar reaction is the methylenation of 3,4-dihydroxybenzaldehyde in the presence of a phase-transfer catalyst on a benign calcium carbonate surface [26]. Presumably, bonding of the vicinal hydroxyl groups is low thereby enhancing the reaction with the alkylating agent under the action of solvent-free microwave irradiation (Eq. 15). 

Norepinephrine Norepinephrine, L-l-(3,4-dihydroxyphenyl)-2-aminoethanol (11.1.4), is synthesized by two methods starting from 3,4-dihydroxybenzaldehyde. According to the first method, the indicated aldehyde is transformed into the cyanohydrin (11.1.3) by reaction with hydrogen cyanide, which is then reduced into norepinephrine (11.1.5) [11,12]. 

From Catechol. Several routes have recently been developed for the synthesis of heliotropin from catechol. In one such route, catechol is converted into 3,4-dihydroxymandelic acid with glyoxylic acid in an alkaline medium in the presence of aluminum oxide. 3,4-Dihydroxymandelic acid is oxidized to the corresponding keto acid (e.g. with copper-(II) oxide), which is decarboxylated to 3,4-dihydroxybenzaldehyde [176]. The latter product is converted into heliotropin, for example, by reaction with methylene chloride in the presence of quaternary ammonium salts [177]. 

The studies on the methylation of dihydroxybenzaldehyde and the earlier studies on the decarboxylation of oxaloacetic acid illustrate a hypothesis about metal-catalyzed enzymes that is not proved but has been substantiated in a number of instances in which it has been tried. The hypothesis is that, if a metal constitutes the active site of an enzyme, it should be possible to carry out the reaction with metal ions alone in the absence of the enzyme. The rates of non-enzymatic reactions may be much lower, and the metal ions may be more active metal ions than those that activate the enzyme, for the reasons already discussed. This hypothesis is the basis for much of the work on metal catalytic reactions that are models for enzyme systems. 

Periodate can be determined by its redox reaction with o-dianisidine [35], benzhydrazide [36], or 2,2 -azinodi(3-ethylbenzothiazolesulphonic acid) [37] and phthalimide-bisthiosemicarbazone (e = 2.8-10 ) [38]. Cyclohexane-1,3-dione bis-thiosemicarbazone [39], 3,4-dihydroxybenzaldehyde guanylhydrazone [40], salicylaldehyde guanylhydrazone [41], and amyloride hydrochloride [42] allow IO4 to be determined in the presence of 103". 

A more specific route (ref.46) to osthenol from which racemic meranzin, isomeranzin and auraptenol were obtained commenced with 2,4-dihydroxybenzaldehyde. By its reaction with 2-methylbut-3-en-2-ol in the... 

Mercapto pyrimidines 82 were synthesized from acetoacetanilide, dihydroxybenzaldehyde, and thiourea, which were readily alkylated with benzyl chloride to afford 2-benzylthio derivatives 83 (Scheme 32). 83 when reacted with different amines in acetic acid furnished 2-amino derivatives 84 (R = Ar), whereas upon reaction with hydrazine hydrate 83 afforded 2-hydrazinyl derivative 84 (R = NH2), which with different aldehydes gave hydrazones 85 (R = 2-furyl, 2-thienyl). Arylidene thiazolidinone 86 was obtained from 84 with carbon disulfide, monochloroacetic acid, and aryl aldehydes, while 84 with ethyl acetoacetate and different aromatic aldehydes provided pyrazoles 87 (Scheme 32) (10MI9). Such tetrasubstituted pyrimidines act as cyclin-dependent kinase (CDK2) inhibitors. 

Other o-quinone derivatives have also shown a drastic increase of the reaction with NADH in the presence of Ca " " or Mg " ". Electrodeposited 3,4-dihydroxybenzaldehyde on GC was shown to have a pAIa of around 7 [190]. At pHs higher than the pAIa value, the predominant form of the reduced form of the mediator is then QH , whereas below the pAIa. it is QH2. Additions of Mg + or Ca + were shown to increase the reaction rate with NADH only at pHs above the pX a, reflecting the binding of the divalent ion only for the QH but not for the QH2 form of the mediator. 

SYNTHESIS (from protocateehualdehyde) A solution of 18 g commercial protocatechualdehyde (3,4-dihydroxybenzaldehyde) in 200 mL warm acetic acid was filtered free of any insolubles, to provide a very dark but clear solution. With good stirring there was then added 20 g elemental bromine. The reaction spontaneously heated to about 30 °C and solids appeared in about 5 min. Stirring was continued for 1 h, and then the light gray solids that had formed were removed by filtration and lightly washed with acetic acid. 

In a 40-mL Pyrex tube, 1.38 g (10 mmol) of 3,4-dihydroxybenzaldehyde 1 were mixed together with 1.12 g (20 mmol) of powdered KOH, 2.8 g (20 mmol) of anhydrous K2CO3, 0.32 g (1 mmol) of TBAB and 22 mmol of the appropriate alkyl halide. The reaction mixture was introduced into the microwave reactor and irradiated for 10 min at 130 °C under stirring (maintaining the temperature by power modulation from 15 to 300 W). After cooling to room temperature, the organic... 

The standard reaction mixture contained 0.3 fig of mushroom tyrosinase in 300 fiL of 0.05 M Mops buffer (pH 6.5) and 3.6 /tmol of 3,4-dihydroxybenzaldehyde dissolved in 300 fiL of the same buffer. The reaction mixture was incubated at 30°C, and aliquots were withdrawn at various times up to 10 minutes, with each added to an equal volume of ice-cold 0.2 M perchloric acid. After centrifugation, 2 to 5 fiL was analyzed by HPLC. For single time-point determinations, the reaction volume was reduced to 50 fiL. Product formation was linear with time to 10 minutes and with the amount of protein added. 

Dihydroxybenzaldehyde 5 9 0 A reaction flask (500-ml capacity) is fitted with an efficient stirrer, a reflux condenser, and a wide gas-inlet tube the end of the condenser is connected to, successively, a wash-bottle containing sulfuric acid, an empty safety flask, and a tube that passes over the surface of a sodium hydroxide solution. Resorcinol (20 g) and anhydrous ether (150-200 ml) are placed in the reaction flask, and anhydrous zinc cyanide (1.5 equivalents) is added. Then a rapid stream of dry gaseous hydrogen chloride is passed in. The zinc cyanide disappears as a milky mixture is formed and as the hydrogen chloride dissolves, the imide hydrochloride condensation product separates as a thick oil which solidifies in 10-30 min. The ether is usually saturated in 1.5 h, after which hydrogen chloride is passed in slowly for a further 0.5 h. Then the ether is decanted, water (100 ml) is added to the imide hydrochloride, and the solution is heated to the boiling point, filtered and allowed to cool. About half the aldehyde separates. After this has been collected the remainder of the aldehyde crystallizes in 10-15 h. The total yield is about 95 %, and the m.p. is 135-136° after recrystallization with charcoal from water. 

By related reactions racemic haematoxylin was synthesised (ref. 116) by first formation of 7, 8-dihydroxychromanone from reaction of 3-chloropropionic acid with pyrogallol in the presence of hydrofluoric acid. Claisen condensation with 3, 4-dihydroxybenzaldehyde in ethanol... 

Erbstatin was chemically synthesized by several groups. One of the effective syntheses includes the reaction of diethyl (isocyanomethyl)phosphonate with dihydroxybenzaldehyde by a modified Schollkopf s procedure (3). This procedure was used for preparation of various erbstatin analogues (3). 

Although Vilsmeier and Haack in 1927 were the first who recognized the general applicability of this method, Dimroth and Zoeppritz in 1902 had obtained dihydroxybenzaldehyde from resorcinol, formanilide, and phosphorus oxychloride. The modern mechanistic interpretation of this reaction was advanced by Arnold and Sorm Jutz and Bosshard and Zollinger (, 43 example, when a suitable substrate, such as N,N-dimethylaniline, is treated with the phosphorus oxychloride complex of a N,N-disubstituted formamide, the intermediate iminium chloride... 

The similar treatment in the presence of chlorogenic acid produced the modified chitosan soluble imder both acidic and basic conditions (311). On the other hand, the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenylethylamine (dopamine) provided water-resistant adhesive properties to chitosan (312). A chitosan derivative modified with hydroxy or dihydroxybenzaldehyde was cross-linked by tyrosinase to give stable and self-sustaining gels (313). Phenolic moiety of a synthetic polymer, poly(p-hydroxystyrene), was also subjected to tyrosinase-catalyzed oxidation (314). 

Based on AA oxidation to dehydroascorbic acid in acidic medium using iodine-iodide solution as oxidizing reagent. The iodine amount consumed in the redox reaction was detected Electrocatalysis of AA on a glassy carbon electrode chemically modified with polyaniline films AA was determined at a vitreous C electrode modified with 3,4-dihydroxybenzaldehyde AA was determined with a chemically modified with methylene green (electron mediator) carbon paste electrode... 

Lastly, norbelladine (top of Scheme 1.7) is issued from the reductive amination of 3,4-dihydroxybenzaldehyde (derived from phenylalanine) with tyramine (derived from tyrosine) and constitutes a biosynthetic node leading to Amaryllidaceae alkaloids such as galantamine, crinine, or lycorine depending on the topology of phenolic couplings. In all these biosynthetic routes, radical phenolic couplings are key reactions for C—C and C—O bond formations and rearrangements [30, 31]. 

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