A general synthesis of 2'-hydroxychalcones from bromomagnesium phenoxides and cinnamic aldehydes

A highly selective synthetic route of general utility was devised for the preparation of 2'-hydroxychalcones 4. The procedure involves the regiochemical controlled reaction between bromomagnesium salts of mono and dihydric phenols 1 and variously substituted cinnamaldehydes 2 in aprotic apolar media and in the presence of a suitable basic additive. Application of this procedure to some naturally occurring chalcones is reported. The crucial role of the additive is also emphasized.     

Inhibitory effects of catechol derivatives on arachidonic acid-induced aggregation of rabbit platelets

Pyrocatechol and other non-substituted dihydric phenols, which have strong redox power, inhibited arachidonic acid-induced aggregation of rabbit platelets at much lower concentrations than those at which these phenols inhibited stable prostaglandin endoperoxide, U46619-induced aggregation. Among non-substituted dihydric phenols, pyrocatechol was most potent. In order to clarify the physicochemical properties of the phenolic compounds which control the inhibitory potencies of dihydric phenols, we observed the inhibitory effects of 3- and 4-substituents of pyrocatechol on arachidonic acid-induced platelet aggregation. Among seven derivatives tested, the inhibitory effect of 4-C6H5-substituent was strongest and 4-COOH-substituent was weakest. Inhibitory effects of the catechol derivatives were well correlated with the quotients of their hydrophobicities and oxidation-reduction potentials. Inhibitory effects of hydroquinone and resorcinol were also on the same correlation line. These results suggest that the inhibitory effects of catechol derivatives and other dihydric phenols are controlled by two physicochemical properties: oxidation-reduction potential and hydrophobicity.     

Empirical procedure for the calculation of ionization constants of organic compounds in water from their molecular volume

An empirical procedure was used to calculate 278 ionization constants of 271 organic compounds, including phenols, NH acids, benzoic acid derivatives, and mono- and dihydric carboxylic acids, in water. The examined compounds were divided into 11 structural groups. The ionization constants for compounds belonging to a single group were calculated from constant empirical coefficients, molecular volumes, and formulas with an average error of less than 3.5%, the maximal error not exceeding 9.9%.     

Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols

A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C₃N₄ catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C₃N₄-OH) has been prepared from graphitic carbon nitride (g-C₃N₄) scaffold by converting the residual –NH₂ and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C₃N₄-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N₂ adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C₃N₄-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C₃N₄-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%).     

A coulometric method for the assay of some easily oxidized organic substances with iodine as an oxidizing agent

A coulometric method for the assay of easily oxidized organic substances, using iodine as an oxidizing agent, has been developed. The principle of the method is to oxidize the substance with an excess of iodine in a water-acetic acid medium and then titrate the iodide formed, with anodically generated silver ion. The titration is followed by dead-stop indication using two platinum electrodes. The method has been applied to the assay of dihydric phenols with hydroxyl groups in the ortho or para positions and to the determination of ascorbic acid in various pharmaceutical preparations. The absolute relative error varied between 0.2 and 2.8% for the 8 phenols investigated and the relative standard deviation between 0.2 and 1%. For standard solutions of ascorbic acid the absolute relative error was 0.9% and for the 6 pharmaceutical preparations investigated the relative standard deviation lay in the range 0.3-0.9%. The method is easy to apply and has a number of advantages over current iodimetric methods.     

Coulometric titration of acids in non-aqueous solvents

Coulometric titrations of mineral acids, sulphonic acids, carboxylic acids, enols, imides and phenols have been carried out in t-butanol or in acetone with electrically generated tetrabutylammonium hydroxide. Either a potentiometric titration or a visual indicator end-point may be used. The amount of acid titrated ranges from 10 to 60 muequiv, and the precision and accuracy of the method are excellent.     

MNDO calculations of the effects of substitution on antioxidant activity of phenols and Vitamin E

MNDO calculations are reported for the O-H bond dissociation energy in phenol and -OH, -CH₃, and -NH₂ substituted phenols. The phenol dissociation energy agrees well with the experimental result, as does the change due to a para -OH group; the agreement is less good for methyl substitution. The effect of rotating the O-H substituent out of the benzene plane is explored and analyzed, and the calculations are related to corresponding effects in Vitamin E chemistry.     

Advances in the studies of bisphosphorylated dihydric phenols

The data on the synthesis, structure, and chemical properties of bisphosphorylated dihydric phenols are summarized. All the currently known methods for the synthesis of the systems in question are shown. Specific features of their structure, chemical and complexation properties, as well as areas of application of these compounds were analyzed.     

Reactions of bicyclic phosphonates with halides of α-halocarboxylic acids

Novel types of substituted framework phosphonates have been synthesized via functionalization of bicyclic compounds obtained in the reaction of 2-ethoxyvinyl dichlorophosphonate with different phenols. The reactions of functionalized bicyclic phosphonates with triphenyl phosphine have been studied; antimicrobial activity of the prepared compounds has been investigated.     

Correlation of the acidity of substituted phenols,anilines, and benzoic acids calculated by MNDO,AM1, and PM3 with Hammett-type substituent constants

Heats of formation and net atomic charges of some 120 structures involving substituted phenols, anilines, and benzoic acids and the corresponding anions were calculated by MNDO, AM1, and PM3 semiempirical methods. The gas phase acidities of substituted phenols and anilines and the net atomic charges on the anionic heteroatoms of the corresponding anions have been successfully correlated with σ^? constants. Moreover, good correlations with σ were found for the charges on the acidic hydrogens of substituted phenols and anilines. In contrast, the gas phase acidities of substituted benzoic acids and the charges on the anionic oxygens of the corresponding anions are better correlated with Taft σ° constants. Comparisons of these results with experimental data and ab initio theoretical calculations indicate that AM1 and PM3 methods are much better than MNDO in predicting the acidity of aromatic compounds.     

Thin-layer chromatography of dihydric phenols

Summary Phenol, resorcinol, catechol, and hydroquinone were separated on thin layers of silica gel impregnated with silver nitrate. The incorporation of silver nitrate in the adsorbent layer results in the oxidation of ortho and para dihydric phenols to the corresponding benzoquinones, meta dihydric phenols are not changed, hence the separation of the dihydric isomers is possible.

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Zusammenfassung Phenol, o-, m- und p-Dihydroxybenzole werden auf mit Silbernitrat imprägnierten Kieselgel-Dünnschichtplatten aufgetrennt. Diese Trennung wird dadurch möglich, daß in Anwesenheit von Silbernitrat o- und p-Dihydroxybenzole zu den entsprechenden Benzochinonen oxydiert werden, bei m-Dihydroxybenzol diese Oxydation jedoch nicht eintritt.

     

Organic chemistry of superoxide. I. Oxidations of aromatic compounds.

Potassium superoxide is a selective oxidant for aromatic compounds with the order of susceptibility of substituent groups being -SH>-NH₂-OH. Only o- and p- disubstituted amines and phenols are oxidized but monosubstituted thiols react.     

Potentiometric titrations in non-aqueous solution : Anomalous behaviour of weak oxygen acids in inert and weakly basic solvents

A number of carboxylic acids, phenols and certain related compounds have been found to yield anomalous titration curves in inert and weakly basic solvents. Amongst the effects observed are reproducible potential rises in the region of half-neutralization and irrcproducible potential drops often at stages of the titration corresponding to simple fractions of total neutralization.An investigation has been made into the influence of the basic and amphiprotic character of the solvents, of steric hindrance in the acid molecules, of substitution of —OH (in phenols) by —SH, and of —COOH (in carboxylic acids) by —SOOH, and of the type of electrodes on the occurrence and type of anomalies.These, and the other observed anomalies are interpreted.     

Laser Desorption Ionization of Arylene Phenylphosphonites Formed by Condensation of Dihydric Phenols with Phenylphosphonous Bis(diethylamide)

Step high-temperature condensation of dihydric phenols [1,4-dihydroxybenzene, 4,4′-dihydroxybiphenyl, and 2,2′-bis(4-hydroxyphenyl)propane] with phenylphosphonous bis(diethylamide) is carried out. The molecular weight, composition, and structure of the resulting oligomeric arylene phenylphosphonites were assessed by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The widest mass range was observed in the mass spectrum of 4,4′-dihydroxybiphenyl, which corresponds to an oligomer having about 30 elementary units. The obtained data agree with the the molecular weight measured by high-speed sedimentation. The reactions of phenylphosphonous bis(diethylamide) with dihydric phenols give both acyclic and cyclic arylene phenylphosphonites.     

Silicalite as a stationary phase for HPLC

A molecular sieve known as Silicalite was used as the column packing for HPLC. Silicalite contains channels (or cavities) approximately 6 Å in diameter but, unlike most other molecular sieves, Silicalite is hydrophobic. The retention times of methyl ketones and substituted phenols containing n-alkyl groups increase with increasing chain length of the substituent. However, phenols with very bulky substituents appear to be excluded from the Silicalite channels and elute very quickly. Excellent separations were obtained for a number of compounds with only slight differences in chemical structure. These include phenol isomers with a primary- or secondary alkyl group, position isomers of substituted phenols, and aliphatic cis-trans isomers.     

Mannich反应合成3,6(8)-二取代-2,4-二氢-1,3-苯并噁嗪及其杀菌活性

以取代苯酚、多聚甲醛和取代苯胺为原料,在无催化剂的条件下,通过Mannich缩合反应合成了一系列新型3,6(8)-二取代-2,4-二氢-1,3-苯并噁嗪类化合物。 结果表明,取代苯酚和取代苯胺的取代基为供电子基时,合成产物的产率高于吸电子取代基的。 产物的结构用1H NMR、13C NMR、IR和MS等进行了表征。 初步测试了目标化合物的杀菌活性,部分化合物具有较好的杀菌活性。 当浓度为25 mg/L时,化合物4j和4d对菌核病菌的抑制率分别为86.1％和81.5％,化合物4i对灰霉病菌的抑制率为81.6％。     

Conductimetric and potentiometric titrations of phenolic acids with triethylamine and tetrabutylammonium hydroxide in acetonitrile

Nineteen phenolic acids, namely phenol, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,5-dinitrophenol, 2,6-dinitrophenol, 2,4,6-trinitrophenol, 4-chlorophenol, 2,4,6-trichlorophenol, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,4-dihydroxybenzene, 1,2,3-trihydroxybenzene, 2-aminophenol, 3-aminophenol, 4-aminophenol, 3-cresol and 4-cresol, were titrated conductimetrically and potentiometrically with triethylamine and tetrabutylammonium hydroxide in acetonitrile under a nitrogen atmosphere at 25°C. Most exhibited normal behaviour on titration with triethylamine, but only 2,4-dinitrophenol, 2,6-dinitrophenol and 2,4,6-trinitrophenol gave useful characteristic and stoichiometric conductimetric titration curves. None of the compounds gave a meaningful conductimetric titration curve on titration with tetrabutylammonium hydroxide, which is a much stronger base than triethylamine. With three exceptions, all compounds exhibited stoichiometric well shaped potentiometric titration curves. Potentiometric titration curves of the phenolic acids with tetrabutylammonium hydroxide in acetonitrile are very similar to those of strong acids obtained in aqueous media with strong bases. Acetonitrile is a suitable solvent for titrating some of the weak phenolic acids conductimetrically with triethylamine, and is an excellent medium for titrating them potentiometrically with tetrabutylammonium hydroxide under a nitrogen atmosphere at 25°C.     

Preparation of phenolic compounds through catalyst-free ipso-hydroxylation of arylboronic acids

A novel method for the preparation of phenolic compounds through ipso-hydroxylation of the corresponding widely available arylboronic acid precursors is described. Through application of a novel PEG400-H₂O₂ reactant system, a variety of substituted phenols and other aromatic analogues have been prepared in excellent yields at room temperature in the absence of any catalyst.     

Synthesis of naphthalene and indene precursors to naphthoic and indenoic acids

As part of ongoing research to investigate structural requirements for lactate dehydrogenase inhibition by highly substituted naphthoic and indenoic acids, certain naphthalene and indene precursors to those types of compounds are required. Described here are efficient preparations of 1-naphthoic acid precursors 6-benzyl-2,3-dimethoxy-1-propylnaphthalenes, including compounds with substituted benzyl groups and 7-benzyl-2,3-dimethoxy-1-propylnaphthalene. Also described are the syntheses of indenoic acid precursors 2-benzyl-5,6-dimethoxy-7-propyl-1H-indenes, including compounds with substituted benzyl groups. These compounds were made from the key intermediates 6,7-dimethoxy-5-propyl-1-tetralone, 6,7-dimethoxy-8-propyl-1-tetralone, and 5,6-dimethoxy-4-propyl-1-indanone.