Para-substituted Benzaldehydes Research Articles

Efficient Hydrogenation of Benzaldehydes Over Mesopolymer‐Entrapped Pt Nanoparticles in Water

Pt nanoparticles entrapped in the matrices of FDU-14 periodic mesoporous organic polymer (abbreviated as mesopolymer), prepared by a simple and facile method, serve as an efficient catalyst for the liquid-phase hydrogenation of benzaldehydes under mild conditions. Water was confirmed to be a better choice of solvent for the hydrogenation of benzaldehydes on the Pt/FDU-14 catalyst. The highest activity (turnover frequency) was about 5700 mol mol(-1) h(-1) for 3-fluorobenzaldehyde hydrogenation in water and no distinct loss of activity or selectivity was observed after the catalyst was recycled nine times. For the para-substituted benzaldehydes, the catalytic performance of Pt/FDU-14 was superior to the commercial Pt/alumina catalyst owing to the more hydrophobic nature of the FDU-based catalyst.

A Boron-Substituted Analogue of the Shvo Hydrogenation Catalyst: Catalytic Hydroboration of Aldehydes, Imines, and Ketones

The boron-substituted hydroxycycylopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COBpin)Ru(CO)2H] (Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) 5 was synthesized by the addition of pinacolborane to ruthenium dimer [2,5-Ph2-3,4-Tol2(η5-C4CO)Ru(CO)2]2 4. Complex 5 reacts with aldehydes both stoichiometrically and catalytically, providing hydroboration products under mild reaction conditions. A Hammett correlation plot of para-substituted benzaldehydes provided a ρ value of +0.91. Catalytic hydroboration of aryl imines provided high yields of the corresponding amines. The hydroboration of aryl ketones, however, required strongly electron-withdrawing substituents to induce hydroboration in reasonable reaction times.

Correlation analysis of reactivity in the oxidation of substituted benzaldehydes by morpholinium chlorochromate

Oxidation of thirty six monosubstituted benzaldehydes by morpholinium chlorochromate (MCC) in dimethylsulphoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is of first order with respect to MCC. A Michaelis-Menten type kinetics is observed with respect to benzaldehydes. The reaction is promoted by hydrogen ions; the hydrogen-ion dependence has the form k obs = a + b [H + ]. The oxidation of [ 2 H]benzaldehyde (PhCDO) exhibited a substantial primary kinetic isotope effect. The reaction was studied in nineteen organic solvents and the effect of solvent was analysed using Taft's and Swain's multi-parametric equations. The rates of the oxidation of para- and meta-substituted benzaldehydes showed excellent correlation in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated well with tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalized effect than is the oxidation of ortho- and meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the ortho-substituents. A suitable mechanism has been proposed.

Reactivity of a cobalt(III)-peroxo complex in oxidative nucleophilic reactions

A mononuclear cobalt(III)-peroxo complex bearing a macrocyclic tetradentate N4 ligand, [CoIII(TMC)(O2)]+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was generated in the reaction of [CoII(TMC)]2+ and H2O2 in the presence of triethylamine in CH3CN. The reactivity of the cobalt(III)-peroxo complex was investigated in aldehyde deformylation with various aldehydes and compared with that of iron(III)- and manganese(III)-peroxo complexes, such as [FeIII(TMC)(O2)]+ and [MnIII(TMC)(O2)]+. In this reactivity comparison, the reactivities of metal-peroxo species were found to be in the order of [MnIII(TMC)(O2)]+>[CoIII(TMC)(O2)]+>[FeIII(TMC)(O2)]+. A positive Hammett ρ value of 1.8, obtained in the reactions of [CoIII(TMC)(O2)]+ and para-substituted benzaldehydes, demonstrates that the aldehyde deformylation by the cobalt(III)-peroxo species occurs via a nucleophilic reaction.

Kinetics and Correlation Analysis of Reactivity in the Oxidation of Aromatic Aldehydes by Butyltriphenylphosphonium Dichromate

The oxidation of a number of para-, meta- and ortho-substituted benzaldehydes by butyltriphenylphosphonium dichromate (BTPPD), in dimethyl sulphoxide, leads to the formation of the corresponding benzoic acid. The reaction is first-order with respect to BTPPD. Michaelis-Menten type kinetics were observed with respect to the aldehyde. The formation constants of the aldehyde-BTPPD complexes and the rates of their decomposition were determined at different temperatures. The reactions are catalysed by hydrogen ions and the dependence is of the second order. The oxidation of [2H] benzaldehyde (PhCDO) exhibited the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzaldehydes were correlated in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated with tetraparametric LDRS equation. The oxidation of para- and ortho-substituted benzaldehydes are more susceptible to the delocalization effect than is the oxidation of meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric hindrance by the ortho-substituents. The rates of oxidation of benzaldehyde were determined in nineteen organic solvents. An analysis of the solvent effect by multiparametric equations indicated the greater importance of the cation-solvating power of the solvents. Suitable mechanisms have been discussed.

Catalytic Mechanism and Substrate Specificity of the β-Subunit of the Voltage-Gated Potassium Channel

The beta-subunits of voltage-gated potassium (Kv) channels are members of the aldo-keto reductase (AKR) superfamily. These proteins regulate inactivation and membrane localization of Kv1 and Kv4 channels. The Kvbeta proteins bind to pyridine nucleotides with high affinity; however, their catalytic properties remain unclear. Here we report that recombinant rat Kvbeta2 catalyzes the reduction of a wide range of aldehydes and ketones. The rate of catalysis was slower (0.06-0.2 min(-1)) than those of most other AKRs but displayed the expected hyperbolic dependence on substrate concentration, with no evidence of allosteric cooperativity. Catalysis was prevented by site-directed substitution of Tyr-90 with phenylalanine, indicating that the acid-base catalytic residue, identified in other AKRs, has a conserved function in Kvbeta2. The protein catalyzed the reduction of a broad range of carbonyls, including aromatic carbonyls, electrophilic aldehydes and prostaglandins, phospholipids, and sugar aldehydes. Little or no activity was detected with carbonyl steroids. Initial velocity profiles were consistent with an ordered bi-bi rapid equilibrium mechanism in which NADPH binding precedes carbonyl binding. Significant primary kinetic isotope effects (2.0-3.1) were observed under single- and multiple-turnover conditions, indicating that the bond-breaking chemical step is rate-limiting. Structure-activity relationships with a series of para-substituted benzaldehydes indicated that the electronic interactions predominate during substrate binding and that no significant charge develops during the transition state. These data strengthen the view that Kvbeta proteins are catalytically active AKRs that impart redox sensitivity to Kv channels.

Combined Experimental and Theoretical Mechanistic Investigation of the Barbier Allylation in Aqueous Media

The Barbier allylation of a series of para-substituted benzaldehydes with allylbromide in the presence of Zn, In, Sn, Sb, Bi, and Mg was investigated using competition experiments. In all cases, the slope of the Hammett plots indicated a build-up of negative charge in the selectivity-determining step. For Zn, In, Sn, Sb, and Bi, an inverse secondary kinetic isotope effect was found (kH/kD = 0.75-0.95), which was compatible with the formation of a discrete organometallic species prior to allylation via a closed six-membered transition state. With Mg, a significantly larger build-up of negative charge along with a small positive secondary kinetic isotope effect (kH/kD = 1.06) indicated that the selectivity-determining step was the generation of the radical anion of benzaldehyde. The reaction through a six-membered transition state was modeled using density functional theory with the effect of solvent described by a polarized continuum model. The calculated secondary deuterium isotope effects based on this mechanism were found to be in good agreement with experimental values, thus adding further support to this mechanistic scenario.

Structure-reactivity correlation in the oxidation of substituted benzaldehydes by 2,2' -bipyridinium chlorochromate

Oxidation of thirty six monosubstituted benzaldehydes by 2,2'-bipyridinium chlorochromate (BPCC) in dimethylsulphoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is of first order with respect to both BPCC and aldehydes. The reaction is promoted by hydrogen ions; the hydrogen ion dependence has the form k obs = a + b[H + ]. The oxidation of [ 2 H]benzaldehyde (PhCDO) exhibited a substantial primary kinetic isotope effect. The reaction was studied in nineteen different organic solvents and the effect of solvent was analysed using Taft's and Swain's multi-parametric equations. The rates of the oxidation of para- and meta-substituted benzaldehydes showed excellent correlation in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated well with tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalized effect than is the oxidation of ortho- and meta-substituted compounds, which display a greater dependence on the field effect. The positive value of n suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the ortho-substituents. A suitable mechanism has been proposed.

Synthesis and Supramolecularity of C-Phenylcalix[4] Pyrogallolarenes: Temperature Effect on the Formation of Different Isomers

A family of C-(4-substituted phenyl)calix[4]pyrogallolarene hosts was synthesized through the acid-catalyzed condensation of pyrogallol with a series of para-substituted benzaldehydes at different reaction temperatures. The effect of reaction temperature and substitution pattern on the benzaldehyde was investigated. Different isomers of C-(4-substituted phenyl)calix[4]pyrogallolarene were observed at room temperature or under reflux conditions as indicated in the solid-state structures of compounds 1 and 2. The conformational rigidity of the resulting C-(4-substituted phenyl)calix[4]pyrogallolarene was also affected by the halogen substitution. X-ray analyses of single crystals of C-(4-substituted phenyl)calix[4]pyrogallolarene revealed the formation of inclusion complexes with different stoichiometries.

Kinetics and mechanism of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate

Kinetics of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate (DMAPCC) in protic solvent system has been studied at 303 K. The product of oxidation has been identified as benzoic acid. A unit order dependence of the reaction with respect [DMAPCC] and [benzaldehyde] has been observed. The reaction has been found to be catalysed by H+ ions. Decrease in the dielectric constant of the medium decreases the rate. To study the effect of structure reactivity relationships some para-substituted benzaldehydes were subjected to oxidation kinetics by DMAPCC at four different temperatures and thermodynamic parameters were calculated. The isokinetic plot and Exner plot shows that all the para-substituted benzaldehydes are oxidised by the same mechanism. The Hammett plot is linear with positive ρ value. From the observed kinetic results a suitable mechanism was proposed.

Kinetics and mechanism of the oxidation of substituted benzaldehydes by tetrabutylammonium tribromide

The oxidation of thirty-six monosubstituted benzaldehydes by tetrabutylammonium tribromide (TBATB), in aqueous acetic acid solution, leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to both TBATB and aldehydes. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride ions on the reaction rate. The oxidation of [ 2 H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the medium. The rates of oxidation of meta- and para-substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation whereas the oxidation of ortho-substituted benzaldehydes correlated well with tetraparametric LDS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho- and meta-substituted compounds displayed a greater dependence on the field effect. The positive value of η) suggests the presence of an electron-deficient reaction center in the rate-determining step. The reaction is subjected to steric acceleration when ortho-substituents are present.

The Hammett Equation: Probing the Mechanism of Aromatic Semicarbazone Formation

An organic class project is described where upper-level undergraduates measure kinetic rate constants for semicarbazone formation, by reacting semicarbazide with a meta- or para-substituted benzaldehyde. UV-vis spectroscopy is used to follow product formation. Individual results are compiled to yield a class data set, which is used to construct a linear Hammett plot applying empirical σX values. Students determine the reaction ρ value and use it to elucidate the rate-determining step of the multistep mechanism. An opportunity exists to interpret the form and meaning of a concave-downwards Hammett plot from the literature.

Heterocyclizations of 5-methylpyrazol-3-amine with unsaturated arylaliphatic carboxylic acid derivatives

Cyclocondensation of 5-methylpyrazol-3-amine with methyl cinnamate and arylmethylidenemalonic acids in DMF and methanol leads to the formation of 7-aryl-2-methyl-6,7-dihydropyrazolo[1,5-a]-pyrimidin-5(4H)-ones. Arylmethylidenemalonic acids react with the title amine at a ratio of 1:2 in nitrobenzene to give 4-aryl-3,5-dimethyl-1,7-dihydrodipyrazolo[3,4-b:4′,3′-e]pyridines. Heterocyclizations of 5-methylpyrazol-3-amine with 5-arylmethylidene-2,2-dimethyl-1,3-dioxane-4,6-diones or their precursors, para-substituted benzaldehydes and 2,2-dimethyl-1,3-dioxane-4,6-dione (Meldrum’s acid) in all solvents (methanol, DMF, and nitrobenzene) give the corresponding 4-aryl-3-methyl-2,4,5,7-tetrahydropyrazolo[3,4-b]pyridin-6-ones. The structure of 3-methyl-4-(4-nitrophenyl)-2,4,5,7-tetrahydropyrazolo[3,4-b]pyridin-6-one was proved by X-ray analysis.

Synthesis of partially hydrogenated pyrazolo[3,4-b]quinolinones by condensation of 3-amino-5-methylpyrazole with aromatic aldehydes and dimedone

Cyclocondensation of 3-amino-5-methylpyrazole with 2-arylmethylidene-5,5-dimethylcyclohexane-1,3-diones or 9-aryl-3,3,6,6-tetramethyl-2,3,4,5,6,7,8,9-octahydro-1H-xanthene-1,8-diones, as well as with synthetic precursors of the latter (para-substituted benzaldehydes and dimedone), in dimethylformamide or methanol gives the corresponding 4-aryl-3,7,7-trimethyl-2,4,6,7,8,9-hexahydropyrazolo[3,4-b]quinolin-5-ones. The structure of 4-(4-methoxyphenyl)-3,7,7-trimethyl-2,4,6,7,8,9-hexahydropyrazolo[3,4-b]quinolin-5-one was proved by the X-ray diffraction data.

Rhodium assisted C [sbnd]H activation of N-(2′-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2′-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH 3, CH 3, H, Cl and NO 2), with [Rh(PPh 3) 3Cl] in refluxing toluene in the presence of a base (NEt 3) afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh 3 ligands are trans. The complexes are diamagnetic (low-spin d 6, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III) Rh(IV) oxidation within 0.63–0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within −0.96 to −1.04 V vs SCE. Potential of the Rh(III) Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent.

Study of substituent effects in substituted dibenzal acetones

The present work involves a detailed study of the ultra-violet absorption spectra of various substituted dibenzylidene ketones derived from acetone, ethyl methyl ketone, diethyl ketone, cyclopentanone and cyclohexanone by condensing with several meta- and para-substituted benzaldehydes in n-hexane and in ethanol to ascertain the transition dominant in these solvents. These ketones exist as equilibrium mixtures of s-cis, cis and s-cis, trans conformations. The ultraviolet absorption spectra of the ketones exhibit two bands due to π* ← n transition around 250 and 320 nm. The 320 nm band is prominent in all the cases. There is no indication of π* ← n transition in any of the spectra. The 320 nm band is structureless in all the cases except those shown by the dibenzylidene ketones derived from cyclopentanone in hexane. Therefore it can be inferred that the dibenzylide ketones derived from all the ketones except those derived from cyclopentanone are non-planar.

Chemoselective Multicomponent Condensation of 1,3‐Cyclohexanedione, Urea or Thiourea with Aldehydes: One‐Pot Synthesis of Two Families of Fused Heterobicyclic and Spiro‐Fused Heterobicyclic Aliphatic Rings.

One-pot chemoselective condensation of 1,3-cyclohexanedione, urea or thiourea with aldehydes has been performed by using TMSCl as a Lewis acid in DMF/MeCN. This extended Biginelli-type reaction afforded two families of fused heterobicyclic and spiro-fused heterobicyclic compounds in excellent yields. para-Substituted benzaldehydes exhibited different chemical behaviors to ortho-or meta-substituted benzaldehydes and aliphatic aldehydes. The possible mechanism was discussed to account for experimental results.

Kinetic equivalence of the subunits of liver alcohol dehydrogenase.

1 The kinetics of two-substrate enzyme reactions proceeding by an ordered ternary-complex mechanism have been analyzed theoretically with respect to the precise magnitude of amplitudes of the two slowest transients governing such reactions under single-turnover conditions. Relationships derived have been applied to the liver alcohol dehydrogenase system for detailed interpretation of amplitudes of the biphasic absorbance changes associated with the enzymic reduction of aromatic aldehydes in catalytic-suicide experiments. 2 Amplitudes of the slow phase 328–330-nm absorbance changes occurring during the enzymic reduction of various para-substituted benzaldehydes by NADH or NAD2H correspond to 6–26% of the total absorbance change under conditions of substrate and coenzyme saturation. Saturation values of amplitudes determined in the present and previous investigations agree within 2 % of the total absorbance change with those calculated theoretically for an ordered mechanism of enzyme action at equivalent sites. In particular, amplitudes observed exhibit the expected sensitivity to electronic substituent and deuterium isotope effects. 3 Enzyme recycling, aldehyde binding, and alcohol desorption provide negligible contributions to the 328–330-nm absorbance changes observed during aldehyde reduction in the presence of 20 mM pyrazole. The maximum slow phase amplitude contribution provided by pyrazole binding corresponds to 5–6% of the total absorbance change. Additional slow phase absorbance changes persisting at saturating concentrations of coenzyme and substrate reflect incomplete accumulation of the enzymic intermediate formed through hydride transfer in the rapid reaction phase. This intermediate contains no detectable amounts (less than 2 %,) of NADH, but exhibits spectral properties indistinguishable from those of enzyme. NAD+. alcohol complexes examined. 4 It has been concluded in recent publications that an ordered ternary-complex mechanism involving equivalent sites is insufficient to account for the transient-state kinetics of liver alcohol dehydrogenase catalysis. These conclusions are shown to be based on an inadequate interpretation of the observations made. Results reported up to date provide no evidence whatsoever for the kinetic significance of subunit interactions leading to a non-equivalence of the enzymic sites. Subunit interactions resulting in a “half-site7rdquo; reactivity of the enzyme are definitely not at hand.

Spectral and redox studies on mixed ligand complexes of cobalt(III) phenanthroline/bipyridyl and benzoylhydrazones, their DNA binding and antimicrobial activity

Cobalt(III) complexes of the type [Co( N- N) 2L](ClO 4) 2 · H 2O [where L = anionic form of para-substituted benzaldehyde–benzoylhydrazone (BHBX −); X = H, Me, OMe, OH, Cl or NO 2; N- N = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)] have been synthesized and characterized through UV–Vis, IR, NMR and electrochemical studies. The IR spectral frequencies support the mode of coordination of BHBX to the metal through the imino nitrogen and enolic oxygen atoms. The electronic absorption spectra exhibit metal to ligand charge transfer (MLCT) transition around 450 nm together with intraligand (IL) bands that are comparable to that of [Co(phen/bpy) 3] 3+. In acetonitrile solution these complexes show two well defined redox couples corresponding to Co III/II and Co II/I processes. Binding of these complexes with herring sperm DNA have been investigated by spectroscopic and voltammetric methods. The lower binding constant values of these complexes with respect to the [Co(phen/bpy) 3] 3+ are ascribed to the polar interaction of the substituted benzoylhydrazone moiety with the sugar-phosphate backbone of the DNA. The UV spectrum shows reasonable hypochromism with slight (2–4 nm) red shift, while the cyclic voltammogram shows decrease in current intensity along with a very small shift in the formal potential of the Co III/II redox couple. These experimental results indicate that phen mixed ligand complexes bind to DNA through an intercalative mode more effectively than their bpy counterparts. These complexes are also found to have good antimicrobial activity.

Chemoselective Multicomponent Condensation of 1,3-Cyclohexanedione, Urea or Thiourea with Aldehydes: One-Pot Synthesis of Two Families of Fused Heterobicyclic and Spiro-fused Heterobicyclic Aliphatic Rings

One-pot chemoselective condensation of 1,3-cyclohexanedione, urea or thiourea with aldehydes has been performed by using TMSCl as a Lewis acid in DMF/MeCN. This extended Biginelli-type reaction afforded two families of fused heterobicyclic and spiro-fused heterobicyclic compounds in excellent yields. para-Substituted benzaldehydes exhibited different chemical behaviors to ortho-or meta-substituted benzaldehydes and aliphatic aldehydes. The possible mechanism was discussed to account for experimental results.