Formation of a carboxyl group satellite line in the n.m.r. spectra of solid carboxylic acids

The structural factors resulting in the formation of the carboxyl group satellite line on the low field side of the ¹H n.m.r. spectra of carboxylic acids in the solid state have been determined from the temperature dependences of the carboxyl proton chemical shifts of acetic, dimethylacetic, ethylacetic, phenylacetic, benzoic, o-methylbenzoic, p-methylbenzoic and adamantyl carboxylic acids. The carboxyl group low field satellite forms at temperatures near the melting point only in the case of carboxylic acids with bulky hydrocarbon radicals (o-methylbenzoic and adamantyl carboxylic acids).     

Determination of hydroxyl radical by capillary electrophoresis and studies on hydroxyl radical scavenging activities of Chinese herbs

High-performance capillary electrophoresis (CE) with electrochemical detection (ED) was employed to determine hydroxyl radicals in the Fenton reaction. Hydroxyl radicals can react with salicylic acid to produce 2,3-dihydroxy benzoic acid and 2,5-dihydroxy benzoic acid, which can be analyzed by CE-ED. Based on this principle, hydroxyl radicals were determined indirectly. In a 20 mmol/L phosphate running buffer (pH 7.4), 2,3-dihydroxy benzoic acid and 2,5-dihydroxy benzoic acid would elute simultaneously from the capillary within 6 min. As the working electrode, a 300 m diameter carbon-disk electrode exhibits good responses at +0.60 V (vs. SCE) for the two analytes. Peak currents of the two analytes are additive. Excellent linearity was obtained in the concentration range from 1.0×10^-3 mol/L to 5.0×10^-6 mol/L for 2,3-dihydroxy benzoic acid. The detection limit (S/N=3) was 2.0×10^-6 mol/L. This method was successfully applied for studying hydroxyl radical scavenging activities of Chinese herbs. It is testified that Apocynum Venetum L., Jinkgo bibola L., Morus alba L. and Rhododendron dauricum L. have strong hydroxyl radical scavenging activities.     

On the Structure and Chiral Aggregation of Liquid Crystalline Star-Shaped Triazines H-Bonded to Benzoic Acids

The ability of a star-shaped tris(triazolyl)triazine derivative to hierarchically build supramolecular chiral columnar organizations through the formation of H-bonded complexes with benzoic acids was studied from a theoretical and experimental point of view. The combined study has been done at three different levels including the study of the structure of the triazine core, the association with benzoic acids in stoichiometry 1:3, and the assembly of 1:3 complexes in helical aggregates. Although the star-shaped triazine core crystallizes in a non-C₃ conformation, the C₃-symmetric conformation is theoretically predicted to be more stable and gives rise to a favorable C₃ supramolecular 1:3 complex upon the interaction with three benzoic acids in their voids. In addition, calculations at different levels (DFT, PM7, and MM3) for the 1:3 host-guest complex predict the formation of large stable columnar helical aggregates stabilized by the compact packing of the interstitial acids by π–π and CH⋅⋅⋅π interactions. The acids restrict the movement of the the star-shaped triazine cores along the stacking axis causing a template effect in the self-assembly of the complex. Theoretical predictions correlate with experimental results, since the interaction with achiral or chiral 3,4,5-(4-alkoxybenzyloxy)benzoic acids gives rise to supramolecular complexes that organize in bulk hexagonal columnar mesophases stable at room temperature with intracolumnar order. The existence of supramolecular chirality in the mesophase was determined for complexes formed by acids derived from (S)-2-octanol. Chiral aggregation was also evidenced for complexes formed in dodecane.     

Palladium‐Catalyzed ortho‐Selective C?H Deuteration of Arenes: Evidence for Superior Reactivity of Weakly Coordinated Palladacycles

We disclose a protocol for the palladium‐catalyzed ortho‐selective C H deuteration of arenes. Phenylacetic acids and benzoic acids are suitable substrates for this reaction. This reaction offers a catalytic route to ortho‐deuterated phenylacetic acids and benzoic acids and demonstrates the sharp difference in reactivity of palladacycle intermediates held together by weak and strong coordination.     

Palladium‐Catalyzed ortho‐Selective CH Deuteration of Arenes: Evidence for Superior Reactivity of Weakly Coordinated Palladacycles

We disclose a protocol for the palladium‐catalyzed ortho‐selective C? H deuteration of arenes. Phenylacetic acids and benzoic acids are suitable substrates for this reaction. This reaction offers a catalytic route to ortho‐deuterated phenylacetic acids and benzoic acids and demonstrates the sharp difference in reactivity of palladacycle intermediates held together by weak and strong coordination.     

Synthesis of 4H-3,1-benzoxazin-4-ones and 4-(3H)quinazolinones from anthranilic acids and their derivatives by the use of triphenyl phosphite and pyridine

A series of 2-substituted 4H-3,1-benzoxazinones and 2,3-disubstituted 4-(3H)quinazolinones have been synthesized in mild conditions by the use of triphenyl phosphite and pyridine as cyclising medium. Benzox-azinones are produced either by ring closure of 2-(acylamino)benzoic acids or in the reaction of benzoic acid with anthranilic acids. In the presence of aniline, the reaction leads to quinazolinones.     

Direct Synthesis of γ-Substituted Phthalides by Cyclization of Benzyl Radicals Generated from o-(Arylmethyl)benzoic Acids*

Direct oxidation of o-(arylmethyl)benzoic acids with sodium peroxysulfate-copper(II) chloride in water yields -substituted phthalides. The reaction is highly regioselective, and the corresponding -butyrolactones are the only products formed through intermediate stable arylmethyl radicals.     

Linear free energy ortho-correlations in the thiophene series. Part IX . Kinetics of esterification with diazodiphenylmethane of some 3-, 4-, and 5-substituted thiophene-2-carboxylic acids in methanol

The rate constants for the esterification of some 3-, 4-, and 5-substituted thiophene-2-carboxylic acids with diazodiphenylmethane in methanol at 25° have been measured. The reactivity of some para- and ortho-substituted benzoic acids has also been determined. Logarithmic kinetic constants for ortho-, meta-, and para-like substituted thiophene-2-carboxylic acids furnish an excellent linear free energy relationship when plotted versus Δpk_a (β 0.89, r 0.989, C.L. > 99.9%, n 18, i 0.04), thus confirming the peculiar behaviour of five-membered ring derivatives. The correlation with σ^H values offers an additional proof of the hyper-ortho character of the 2,3-relation in thiophene derivatives. para- and ortho-Substituted benzoic acids show the usual behaviour of six-membered ring derivatives.     

The ortho‐Substituent Effect on the Ag‐Catalysed Decarboxylation of Benzoic Acids

A combined experimental and computational investigation on the Ag‐catalysed decarboxylation of benzoic acids is reported herein. The present study demonstrates that a substituent at the ortho position exerts dual effects in the decarboxylation event. On one hand, ortho‐substituted benzoic acids are inherently destabilised starting materials compared to their meta‐ and para‐substituted counterparts. On the other hand, the presence of an ortho‐electron‐withdrawing group results in an additional stabilisation of the transition state. The combination of both effects results in an overall reduction of the activation energy barrier associated with the decarboxylation event. Furthermore, the Fujita–Nishioka linear free energy relationship model indicates that steric bulk of the substituent can also exert a negative effect by destabilising the transition state of decarboxylation.     

Preparation of 5-substituted benzylbarburituric acids and investigation of the effect of the benzyl and substituted benzyl groups on the acidity of barbituric acid

The acidity of 5-benzylbarbituric acid and a series of 5-substituted benzylbarbituric acids has been determined in 50% ethanol/water and they were found to be more acidic than barbituric acid. The pK_as of these derivatives obey Hammett's equation indicating that their acidity is affected by substituents in the same manner as the benzoic acid ionization constants. A synthesis of these acids is described.     

The mechanism of the sonochemical degradation of benzoic acid in aqueous solutions

The sonolytic degradation of benzoic acid in aqueous solution was investigated at an ultrasonic frequency of 355 kHz. The degradation rate was found to be dependent upon the solution pH and the surface activity of the solute. The degradation rate was favoured at a solution pH lower than the pK _a of benzoic acid. At pH < pK _a, HPLC, GC and ESMS analysis showed that benzoic acid could be degraded both inside the bubble by pyrolysis and at the bubble/solution interface by the reaction with OH radicals. At higher pH (> pK _a) benzoic acid could only react with OH radicals in the bulk solution. During the sonolytic degradation of benzoic acid, mono-hydroxy substituted intermediates were observed as initial products. Further OH radical attack on the mono-hydroxy intermediates led to the formation of di-hydroxy derivatives. Continuous hydroxylation of the intermediates led to ring opening followed by complete mineralization. Mineralization of benzoic acid occurred at a rate of < 40μM/h.     

Hydrogen migrations in mass spectrometry. VI—the chemical ionization mass spectra of substituted benzoic acids and benzyl alcohols

The H₂ and CH₄ chemical ionization mass spectra of a series of series of substituted benzoic acids and substituted benzyl alcohols have been determined. For the benzoic acids the major fragmentation reactions of the protonated molecule involve elimination of H₂O or elimination of CO₂, the latter reaction involving migration of the carboxylic hydrogen to the aromatic ring. For the benzyl alcohols the major fragmentation reactions of [MH]⁺ involve loss of H₂O or CH₂O, analogous to the CO₂ elimination reaction for the benzoic acids. It is shown that the CO₂ and CH₂O elimination reactions occur only when a conjugated aromatic ring system is present, and that for the carboxylic acid systems, methyl groups and, to a lesser extent, phenyl groups are capable of migrating. The only discernible effect of substituents on the fragmentation of [MH]⁺ is an enhancement of the H₂O loss reaction in the benzoic acid system when an amino, hydroxyl, or halogen substituent is ortho to the carboxyl function. This ‘ortho’ effect, which differs in scope from that observed in electron impact mass spectra, is attributed to an intramolecular catalysis by the ortho substituent of the 1,3 hydrogen migration in the carbonyl protonated acid followed by H₂O elimination. Apparently, this route is favoured over the direct elimination of H₂O from the carbonyl protonated acid, since the latter has a high activation energy barrier because of unfavourable orbital symmetry restrictions.     

The Preparation of 2-(2-Oxo-2-Phenylethyl) Benzoic Acids from Dilithiated Ortho-Toluic Acid.

ortho-Toluic acid was dimetalated with excess lithium diisopropylamide, and the resulting intermediate was condensed with a variety of aromatic esters to afford new substituted 2-(2-oxo-2-phenylethyl)benzoic acids (ortho-phenacylbenzoic acids).     

Vapour pressures,enthalpies and entropies of sublimation of <Emphasis Type="Italic">para</Emphasis> substituted benzoic acids

The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure of para substituted benzoic acids at the temperature of 298.15 K are proposed.     

Direct CH Amidation of Benzoic Acids to Introduce meta‐ and para‐Amino Groups by Tandem Decarboxylation

The Ir‐catalyzed mild C?H amidation of benzoic acids with sulfonyl azides was developed to give reactions with high efficiency and functional‐group compatibility. Subsequent protodecarboxylation of ortho‐amidated benzoic acid products afforded meta‐ or para‐substituted (N‐sulfonyl)aniline derivatives, the latter being inaccessible by other C?H functionalization approaches. The decarboxylation step was compatible with the amidation conditions, enabling a convenient one‐pot, two‐step process.     

Regioselective C−H Hydroarylation of Internal Alkynes with Arenecarboxylates: Carboxylates as Deciduous Directing Groups

In the presence of catalytic [Ru(p‐cym)I₂]₂ and the base guanidine carbonate, benzoic acids react with internal alkynes to give the corresponding 2‐vinylbenzoic acids. This alkyne hydroarylation is generally applicable to diversely substituted electron‐rich and electron‐poor benzoic and acrylic acids. Aryl(alkyl)acetylenes react regioselectively with formation of the alkyl‐branched hydroarylation products, and propargylic alcohols are converted into γ‐alkylidene‐δ‐lactones. The hydroarylation can also be conducted decarboxylatively with a different choice of catalyst and reaction conditions. This reaction variant, which does not proceed via intermediate formation of 2‐vinylbenzoic acids, opens up a regioselective, waste‐minimized synthetic entry to vinylarenes.     

H-Bonded complexes of N,N-disubstituted aminophenylazo-(4)-pyridine and benzoic acid derivatives: preparation,mesogenic study and molecular modelling

N, N-Disubstituted aminophenylazo-(4)-pyridine forms complexes with a series of m-alkoxy benzoic acids by intermolecular hydrogen bonding; liquid crystalline phases of the resulting complexes are thus induced.     

The Quantitative Determination of some Phenolic Acids In Delphinium Formosum by HPLC

ABSTRACT

Some phenolic acids from the flowers of Delphinium formosum have been determined quantitatively by reversed-phase high-performance liquid chromatography with diode-array detection. A comparative study was performed by extracting the following phenolic acids: p-hydroxy benzoic, p-coumaric, caffeic, protocatechuic and vanillic acids with four different methods. The results were supported with recovery studies.     

Does deprotonated benzoic acid lose carbon monoxide in collision-induced dissociation?

Decarboxylation is known to be the major fragmentation pathway for the deprotonated carboxylic acids in collision-induced dissociation (CID). However, in the CID mass spectrum of deprotonated benzoic acid (m/z 121) recorded on a Q-orbitrap mass spectrometer, the dominant peak was found to be m/z 93 instead of the anticipated m/z 77. Based on theoretical calculations, ¹⁸O-isotope labeling and MS³ experiments, we demonstrated that the fragmentation of benzoate anion begins with decarboxylation, but the initial phenide anion (m/z 77) can react with trace O₂ in the mass analyzer to produce phenolate anion (m/z 93) and other oxygen-containing ions. Thus oxygen adducts should be considered when annotating the MS/MS spectra of benzoic acids.     

Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003