3 ,4 -dihydroxyphenols

The Reaction has the following limitations (i) a compound that can liberate nitrous acid in acid solution is required (e.g., a metallic nitrite or a nitroso-amine, p. 204). (2) Nitrophenols and />-substituted phenols do not give the test. (3) Among the dihydroxyphenols. only resorcinol gives a satisfactory positive test. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The system has been used as an analytical tool (4), because the complex formed shows greater conductivity than the sum of the conductivities of the boric acid and the diol compound. Favorably situated diols have a pronounced effect in increasing the conductivity. cis-l,2-Diols fixed in position by molecular structure—e.g., o-dihydroxyphenols and cis-dicyclic polyols—are favorable structures. The reaction is depicted in Figure 2. 

Oxidation of phenols.1 The reagent oxidizes 1,2- and 1,4-dihydroxyphenols to the quinones in almost quantitative yield at 25° in methanol. 4-Alkylphenols are oxidized to 4-alkyl-4-methoxycyclohexadienones (mixed quinone ketals) in >90% yield. Monohydric phenols can be oxidized to p-quinone diketals on oxidation with 2 equiv. of the reagent in CH,OH at 25°. 

Data for the metabolites in plasma are generally for the unbound forms, but there is ample evidence that PPT bind noncovalently to proteins. Most studies on PPT-protein interaction have focused on protein utilization or astringency but a few studies have addressed binding to plasma proteins and lipoproteins. " " Strongest binding has been associated with 1,2-dihydroxyphenols and proline-rich proteins such as those character-istic of human saliva and structure-activity relationships have been reported. 

In apple, the glycoside phloridzin (1.27) and its aglycone phloretin are thought to inhibit the apple scab fungus Venturia inaequalis. Phloridzin is also an ort/20-dihydroxyphenolic compound, and, like chlorogenic acid, can also be easily converted to a reactive quinone upon attack by a pathogen. Raa (1968) demonstrated that oxidation products of phloridzin inhibit fungal... 

SYNS BENZENE-s-TRIOL BENZENE-1,3,5-TRIOL 1,3,5-BENZENETRIOL 3,5-DIHYDROXYPHENOL DILOSPAN S 5-OXYRESORCINOL PHLORO-GLUCIN s-TRIHYDROXYBENZENE sym-TRI-HYDROXYBENZENE 1,3,5-TRIHYDROXYBENZENE 1,3,5-TRIHYDROXYCYCLOHEXATRIENE... 

DIHYDROXYPHENOL see PGROOO DIHYDROXY-l-PHENYL LANINE see DNA200... 

Quinones are cyclic unsaturated diketones in which the carbon atoms are derived from the oxidation of an aromatic system. Although the underlying reactivity of quinones is that of unsaturated ketones (cyclohexadi-enediones), it is tempered by this relationship to aromatic compounds and in particular by their reduction to dihydroxyphenols (quinols). 

Dihydroxyphenols—see also Trihydroxybenzenes mass spectra of 305 photooxidation of 1084, 1085... 

Trihydroxyanthraquinones, chemical shifts for, isotope effects on 345 Trihydroxybenzenes—see also Dihydroxyphenols... 

Cotton tissues also may contain 1-3% flavonoid glucosides, most of which contain ortho-dihydroxyphenolic groups ( ). Additional quantities of flavonoid glucosides are formed Tn response to infection. These compounds are important in constitutive defense against insects, but their importance in the resistance of cotton to... 

L-ascorbic acid (AA) and its isomer D-erythorbic acid (EA) (also called D-isoascorbic acid) have been used as inhibitors of enzymatic browning in fruit and vegetable products for at least 50 years, (15-17). These compounds prevent quinone accumulation and subsequent pigment formation by reducing the 0-quinones generated from the phenolic substrates of PPO back to O-dihydroxyphenolic compounds (17-18). AA also can act as a PPO inhibitor (19-20). AA and EA are used interchangeably although there are indications that AA is more effective in some systems (21-22). 

Photochemical oxidation of phenol in aqueous solution produces dimers, HOCftH fiH OH, and dihydroxyphenols [221], It is suggested that these products are formed by reactions of phenoxyl radicals. 

Methylenation of catechols. Bashah and Collins have converted various <3-dihydroxyphenols into the methylenedioxy derivative by addition of a solution of the phenol in aqueous NaOH to a mixture of dibromomethane, water, and this phase-transfer catalyst. Reported yields are 76-86%. Classical methods require anhydrous conditions and aprotic solvents. 

Diffee, J.T. The spectrophotometric determination of total ortho-dihydroxyphenolic compounds in tobacco RDM, 1973, No. 32, December 11, see www.ijrtdocs. com 500606307-6317. 

H. A. Smith University of Tennessee) Gilman and Cohn indicate that the peculiar kinetic behavior of the dihydroxyphenols is unexplained (Lecture 74). The explanation probably lies in the fact that the hydrogenation of such compounds proceeds by a two-step mechanism with ketone intermediates, and this leads to complex kinetic behavior. 

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