Para-substituted Benzaldehydes Research Articles

The Impact of Electron Donating and Withdrawing Groups on Electrochemical Hydrogenolysis and Hydrogenation of Carbonyl Compounds.

The hydrogenolysis or hydrodeoxygenation of a carbonyl group, where the C═O group is converted to a CH2 group, is of significant interest in a variety of fields. A challenge in electrochemically achieving hydrogenolysis of a carbonyl group with high selectivity is that electrochemical hydrogenation of a carbonyl group, which converts the C═O group to an alcohol group (CH-OH), is demonstrated not to be the initial step of hydrogenolysis. Instead, hydrogenation and hydrogenolysis occur in parallel, and they are competing reactions. This means that although both hydrogenolysis and hydrogenation require adding H atoms to the carbonyl group, they involve different intermediates formed on the electrode surface. Thus, revealing the difference in intermediates, transition states, and kinetic barriers for hydrogenolysis and hydrogenation pathways is the key to understanding and controlling hydrogenolysis/hydrogenation selectivity of carbonyl compounds. In this study, we aimed to identify features of reactant molecules that can affect their hydrogenolysis/hydrogenation selectivity on a Zn electrode that was previously shown to promote hydrogenolysis over hydrogenation. In particular, we examined the electrochemical reduction of para-substituted benzaldehyde compounds with substituent groups having different electron donating/withdrawing abilities. Our results show a strikingly systematic impact of the substituent group where a stronger electron-donating group promotes hydrogenolysis and a stronger electron-withdrawing group promotes hydrogenation. These experimental results are presented with computational results explaining the substituent effects on the thermodynamics and kinetics of electrochemical hydrogenolysis and hydrogenation pathways, which also provide critically needed information and insights into the transition states involved with these pathways.

Influence of para-substituted benzaldehyde derivatives with different push/pull electron strength groups on the conformation of human serum albumin and toxicological effects in zebrafish

Excessive intake of benzaldehyde and its derivatives can cause irreversible damage to living organisms. Hence, benzaldehyde derivatives with different para-substitutions of push/pull electronic groups were chosen to investigate the effect of different substituent properties on the structure of human serum albumin (HSA). The binding constants, number of binding sites, major interaction forces, protein structural changes, and binding sites of benzaldehyde (BzH) and its derivatives (4-BzHD) with HSA in serum proteins were obtained based on multispectral and molecular docking techniques. The mechanism of BzH/4-BzHD interaction on HSA is mainly static quenching and is accompanied by the formation of a ground state complex. BzH/4-BzHD is bound to HSA in a 1:1 stoichiometric ratio. The interaction forces for the binding of BzH/4-BzHD to HSA are mainly hydrogen bonding and hydrophobic interaction, which are also accompanied by a small amount of electrostatic interactions. The effect of BzH/4-BzHD on HSA conformation follows: 4-Diethylaminobenzaldehyde (4-DBzH) > 4-Nitrobenzaldehyde (4-NBzH) > 4-Hydroxybenzaldehyde (4-HBzH) > 4-Acetaminobenzaldehyde (4-ABzH) > BzH, which means that the stronger push/pull electronic strength of the para-substituted benzaldehyde derivatives has a greater effect on HSA conformation. Furthermore, the concentration-lethality curves of different concentrations for BzH/4-BzHD on zebrafish verified above conclusion. This work provides a scientific basis for the risk assessment of benzaldehyde and its derivatives to the ecological environment and human health and for the environmental toxicological studies of benzaldehyde derivatives with different strengths of push/pull electron substitution.

Effect of the Electronic Structure of Para-Substituted Benzaldehyde Benzohydrazone on Its Antimicrobial Activity: A DFT Analysis

Bacillus subtilis is a bacterium that has demonstrated its efficacy across various domains, including industry, agriculture, and commerce, owing to its protective, inhibitory, and biological mechanisms against specific microbes. However, at high concentrations, it can lead to food poisoning and severe infections, resulting in symptoms such as diarrhea and vomiting. Bacterial spores produced by Bacillus subtilis can induce conditions like gas gangrene and tetanus. In this context, benzohydrazones are recognized for their antimicrobial activity, particularly against Bacillus subtilis. This study aims to elucidate the relationship between the electronic structure of para-substituted benzaldehyde benzohydrazone derivatives and their antimicrobial activity. This leads to the proposal of a 2D pharmacophore for predicting the antibacterial activity of these derivatives. The quantitative structure-activity relationship (QSAR) approach employed is the KPG method. The electronic structures were optimized using the density functional theory (DFT) method with the B3LYP functional and the 6-31G (d,p) basis set. Charge and local molecular orbitals were considered in the optimization process. The resulting prediction equation (R=98.95%, R²=97.91%, Adjusted R²=96.76%, F(5,9)=84.52) derived from multiple linear regression provides the basis for the proposed 2D pharmacophore. This equation shows that antimicrobial activity of benzohydrazone derivative is on charge and orbital controlled. This pharmacophore holds potential utility in designing new molecular structures with enhanced activity against Bacillus subtilis.

Scope and Mechanistic Studies on the Ruthenium-Catalyzed Multicomponent Deaminative C–H Coupling Reaction of Phenols with Aldehydes and Enamines for the Formation of Xanthene and Dioxacyclic Derivatives

The in situ generated catalytic system from the tetranuclear Ru–H complex [(PCy3)(CO)RuH]4(O)(OH)2 (1) with 3,4,5,6-tetrachloro-1,2-benzoquinone (L1) has been found to mediate a multicomponent deaminative coupling reaction of phenols with aldehydes and enamines to form xanthene products. The multicomponent C–H coupling reaction of phenols with 2-hydroxybenzaldehydes and cyclic enamines efficiently installed the tricyclic 1,3-dioxacin derivatives, while the analogous coupling reaction of phenols with 2-hydroxybenzaldehydes and triethylamine selectively formed bicyclic 1,5-dioxacyclic derivatives. The density functional theory (DFT) calculations established two energetically viable mechanistic pathways for the formation of xanthene products, in which both pathways identified the C–O bond cleavage step as the turnover limiting step. A Hammett plot from the coupling reaction of 3,5-dimethoxyphenol with an enamine and para-substituted benzaldehydes p-X-C6H4CHO (X = OMe, Me, H, Cl, CF3) showed a negative slope (ρ = −0.98). The calculated energy analysis showed a similar trend (ρ = −0.59) for the mechanism via the C–O cleavage rate-limiting step. The combined experimental and DFT computational results support a mechanistic path that involves the dehydrative C–H coupling of phenol with aldehyde, followed by the deaminative coupling reaction with an enamine in forming the xanthene product.

A post-synthetic modified NH2-MIL-125 (Ti) catalyst for boosting photochemical Cr (VI) reduction

MOFs-based composites with visible light response have gradually attracted wide researchers’ attention to water environmental remediation. Herein, a series of post-synthesis modified (PSM) NH2-MIL-125 (Ti) (R-BA-MIL-125 (Ti)) with phenyl-Schiff base-phenyl conjugate systems were successfully synthesized by a simple post-synthetic modification method. Under the optimization of catalyst structure designing, the photocatalytic reduction of Cr (VI) follows the order: –OH > -CH3 > -H > -Cl > -NO2-BA-MIL-125 (Ti) > NH2-MIL-125 (Ti). Among them, 4-hydroxybenzaldehyde-modified NH2-MIL-125 (Ti) (OH-BA-MIL-125 (Ti)) exhibited the highest photocatalytic removal efficiency of hexavalent chromium (Cr (VI)) at visible light conditions and the removal rate for Cr (VI) reached 98.3% under 90 min with only 5 mg photocatalyst, which displayed 2.07 times that of NH2-MIL-125 (Ti). The introduction of para-substituted benzaldehydes not only extended the conjugated chain length, but also subtly reduced the band-gap energy (Eg) of NH2-MIL-125 (Ti). Benefitting from broadening the range of photo-response and enhancing the ability of photoelectron generation, it could significantly enhance the ability of NH2-MIL-125 (Ti) to remove Cr (VI). ESR analyses indicate that e- and •O2- are the main active species. In addition, OH-BA-MIL-125 (Ti) exhibited good reusability and stability over 5 cycles. Therefore, this work will provide new insights into the fabrication of highly active catalysts by PSM for the remediation of chromium-containing wastewater.

SUBSTITUTED AMINOCHALCONES AS STARTING COMPOUNDS FOR RECEIVING NEW 1,4-BENZODIAZEPINES DERIVATIVES

The aim of this work is the synthesis of a number of substituted E‑1-(2-amino‑5-R1-phenyl)-3-(4-R2-phenyl)prop‑2-en‑1-ones (2-aminochalcones) as precursors for obtaining new derivatives of 7-R1–5-[2-R2-phenylvinyl]-1,4-benzodiazepin‑2-ones. Starting 5-substituted 2-aminoacetophenones with bromo and nitro group were synthesized from 2-aminoacetophenone by bromination of the latter with N‑bromosuccinimide in acetonitrile and nitration of 2-acetaminoacetophenone with a nitrating mixture followed by removal of acetyl protection. 2-Aminochalcones were synthesized according to standard methods during the interaction of a number of 5-substituted 2-aminoacetophenones with para-substituted benzaldehydes under basic catalysis conditions. The target products turned out to be brightly colored compounds with low melting points, their isolation and purification did not cause any difficulties. According to the data of 1H NMR spectroscopy, all synthesized 2-aminochalcones were individual trans isomers, which was also confirmed by X‑ray structural analysis of one of the obtained 2-aminochalcones. A number of new substituted E‑1-(2-amino‑5R1-phenyl)-3-(4-R2-phenylprop‑2-en‑1-ones) were synthesized – compounds with amino and ketofunctions and are precursors for obtaining of a new series of 5-substituted 1,4-benzodiazepines with various arylvinyl groups. 2-aminoacetophenone, 2-amino‑5-bromoacetophenone, and 2-amino‑5-nitroacetophenone were selected as substrates for this series. The methyl groups of these acetophenones were condensed according to Claisen-Schmidt with parasubstituted benzaldehydes. Condensation was carried out under alkaline conditions in an aqueous solution. Yields of aminochalcones reached 60–85%. The methyl group of 2-aminoacetophenones smoothly reacted with aromatic aldehydes to form the corresponding 2-aminophenylchalcones. The structure of the obtained compounds was confirmed by mass spectrometry and 1H NMR spectroscopy. The structure of one of the chalcones was proved by X‑ray structural analysis. The obtained compounds can be used for the synthesis of 1,4-benzodiazepines with 5-arylvinyl substituents.

Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach.

In a recent report on the synthetic approach to the novel substance class of 1-alkylidene/arylidene-1,2,4-triazolinium salts, a reaction mechanism suggesting a regioselective outcome was proposed. This hypothesis was tested via a combined NMR and density functional theory (DFT) approach. To this end, three experiments with 13C-labeled carbonyl reactants were monitored in situ by solution-state NMR. In one experiment, an intermediate as described in the former mechanistic proposal was observed. However, incorporation of 13C isotope labels into multiple sites of the heterocycle could not be reconciled with the “regioselective mechanism”. It was found that an unproductive reaction pathway can lead to 13C scrambling, along with metathetical carbonyl exchange. According to DFT calculations, the concurring reaction pathways are connected via a thermodynamically controlled cyclic 1,3-oxazetidine intermediate. The obtained insights were applied in a synthetic study including aliphatic ketones and para-substituted benzaldehydes. The mechanistic peculiarities set the potential synthetic scope of the novel reaction type.

Study of ALDH from Thermus thermophilus-Expression, Purification and Characterisation of the Non-Substrate Specific, Thermophilic Enzyme Displaying Both Dehydrogenase and Esterase Activity.

Aldehyde dehydrogenases (ALDH), found in all kingdoms of life, form a superfamily of enzymes that primarily catalyse the oxidation of aldehydes to form carboxylic acid products, while utilising the cofactor NAD(P)+. Some superfamily members can also act as esterases using p-nitrophenyl esters as substrates. The ALDHTt from Thermus thermophilus was recombinantly expressed in E. coli and purified to obtain high yields (approximately 15–20 mg/L) and purity utilising an efficient heat treatment step coupled with IMAC and gel filtration chromatography. The use of the heat treatment step proved critical, in its absence decreased yield of 40% was observed. Characterisation of the thermophilic ALDHTt led to optimum enzymatic working conditions of 50 °C, and a pH of 8. ALDHTt possesses dual enzymatic activity, with the ability to act as a dehydrogenase and an esterase. ALDHTt possesses broad substrate specificity, displaying activity for a range of aldehydes, most notably hexanal and the synthetic dialdehyde, terephthalaldehyde. Interestingly, para-substituted benzaldehydes could be processed efficiently, but ortho-substitution resulted in no catalytic activity. Similarly, ALDHTt displayed activity for two different esterase substrates, p-nitrophenyl acetate and p-nitrophenyl butyrate, but with activities of 22.9% and 8.9%, respectively, compared to the activity towards hexanal.

Experimental and Computational Studies on the Ruthenium-Catalyzed Dehydrative C-H Coupling of Phenols with Aldehydes for the Synthesis of 2-Alkylphenol, Benzofuran, and Xanthene Derivatives.

The cationic Ru-H complex [(C6H6)(PCy3)(CO)RuH]+BF4- (1) was found to be an effective catalyst for the dehydrative C-H coupling reaction of phenols and aldehydes to form 2-alkylphenol products. The coupling reaction of phenols with branched aldehydes selectively formed 1,1-disubstituted benzofurans, while the coupling reaction with salicylaldehydes yielded xanthene derivatives. A normal deuterium isotope effect was observed from the coupling reaction of 3-methoxyphenol with benzaldehyde and 2-propanol/2-propanol-d8 (kH/kD = 2.3 ± 0.3). The carbon isotope effect was observed on the benzylic carbon of the alkylation product from the coupling reaction of 3-methoxyphenol with 4-methoxybenzaldehyde (C(3) 1.021(3)) and on both benzylic and ortho-arene carbons from the coupling reaction with 4-trifluorobenzaldehdye (C(2) 1.017(3), C(3) 1.011(2)). The Hammett plot from the coupling reaction of 3-methoxyphenol with para-substituted benzaldehydes p-X-C6H4CHO (X = OMe, Me, H, F, Cl, CF3) displayed a V-shaped linear slope. Catalytically relevant Ru-H complexes were observed by NMR from a stoichiometric reaction mixture of 1, 3-methoxyphenol, benzaldehyde, and 2-propanol in CD2Cl2. The DFT calculations provided a detailed catalysis mechanism featuring an electrophilic aromatic substitution of the aldehyde followed by the hydrogenolysis of the hydroxy group. The calculations also revealed a mechanistic rationale for the strong electronic effect of the benzaldehdye substrates p-X-C6H4CHO (X = OMe, CF3) in controlling the turnover-limiting step. The catalytic C-H coupling method provides an efficient synthetic protocol for 2-alkylphenols, 1,1-disubstituted benzofurans, and xanthene derivatives without employing any reactive reagents or forming wasteful byproducts.

Benchmark calculations of proton affinity and gas-phase basicity using multilevel (G4 and G3B3), B3LYP and MP2 computational methods of para-substituted benzaldehyde compounds.

This study presents the benchmark calculations of proton affinities (PAs) and gas-phase basicities (GBs) of 8-para substituted benzaldehyde compounds using the multilevel model chemistries (G3B3 and G4), density-functional quantum model (B3LYP) and ab initio model (MP2). The results show that the computed properties are strongly correlated with the available experimental data. The PAs and the GBs of other eight para-substituted benzaldehyde compounds, for which the experimental data does not currently exist, have been calculated using G3B3 and B3LYP methods. The correlations between the experimental PAs and GBs with the computed properties such as PA, GB, chemical properties (bond lengths, electron density and δ1 H NMR chemical shift) of the investigated benzaldehydes have been studied and statistically analyzed. The influence of the substituted groups has been discussed in terms of inductive effect and electron donating and electron withdrawing effect. The results obtained show that the chemical properties of the benzaldehyde compounds are controlled by the strong coupling between the CHO group and the nature of the para-substituent groups through the benzene ring as a conducting linkage.

A side-on Mn(III)-peroxo supported by a non-heme pentadentate N3Py2 ligand: synthesis, characterization and reactivity studies.

A mononuclear manganese(iii)-peroxo complex [MnIII(N3Py2)(O2)]+ (1a) bearing a non-heme N,N'-dimethyl-N-(2-(methyl(pyridin-2-ylmethyl)amino)ethyl)-N'-(pyridin-2-ylmethyl)ethane-1,2-diamine (N3Py2) ligand was synthesized by the reaction of [Mn(N3Py2)(H2O)](ClO4)2 (1) with hydrogen peroxide and triethylamine in CH3CN at 25 °C. The reactivity of 1a in aldehyde deformylation using 2-phenyl propionaldehyde (2-PPA) was studied and the reaction kinetics was monitored by UV-visible spectroscopy. A kinetic isotope effect (KIE) = 1.7 was obtained in the reaction of 1a with 2-PPA and α-[D1]-PPA, suggesting nucleophilic character of 1a. The activation parameters ΔH‡ and ΔS‡ were determined using the Eyring plot while Ea was obtained from the Arrhenius equation by performing the reaction between 288 and 303 K. Hammett constants (σp) of para-substituted benzaldehydes p-X-Ph-CHO (X = Cl, F, H, and Me) were linear with a slope (ρ) = 3.0. Computational study suggested that the side-on structure of 1a is more favored over the end-on structure and facilitates the reactivity of 1a.

Redox-Inactive Metal Ions That Enhance the Nucleophilic Reactivity of an Alkylperoxocopper(II) Complex.

The importance of redox-inactive metal ions in modulating the reactivity of redox-active biological systems is a subject of great current interest. In this work, the effect of redox-inactive metal ions (M3+ = Sc3+, Y3+, Yb3+, La3+) on the nucleophilic reactivity of a mononuclear ligand-based alkylperoxocopper(II) complex, [Cu(iPr2-tren-C(CH3)2O2)]+ (1), was examined. 1 was prepared by the addition of hydrogen peroxide and triethylamine to the solution of [Cu(iPr3-tren)(CH3CN)]+ (iPr3-tren = tris[2-(isopropylamino)ethyl]amine) via the formation of [Cu(iPr3-tren)(O2H)]+ (2) in methanol (CH3OH) at 30 °C. 1 was characterized using density functional theory (DFT) calculations and spectroscopic methods such as UV-vis, resonance Raman (rR), and electron paramagnetic resonance (EPR). DFT calculations support the electronic structure of 1 with an intermediate geometry between the trigonal-bipyramidal and square-pyramidal geometries, which is consistent with the observed EPR signal exhibiting a signal with g⊥ = 2.03 (A⊥ = 16 G) and g|| = 2.19 (A|| = 158 G). The Cu-O bond stretching frequency of 1 was observed at 507 cm-1 for 16O2 species (486 cm-1 for 18O2 species), and its O-O vibrational energy was determined to be 799 cm-1 for 16O2 species (759 cm-1 for 18O2 species) by rR spectroscopy. The reactivity of 1 was investigated in oxidative nucleophilic reactions. The positive slope of the Hammett plot (ρ = 2.3(1)) with para-substituted benzaldehydes and the reactivity order with 1°-, 2°-, and 3°-CHO demonstrate well the nucleophilic character of this copper(II) ligand-based alkylperoxo complex. The Lewis acidity of M3+ improves the oxidizing ability of 1. The modulated reactivity of 1 with M3+ was revealed to be an opposite trend of the Lewis acidity of M3+ in aldehyde deformylation.

Rotational Barrier and Quantification of Electron-Donating Substituent Effects: a Computational Study of para-Substituted Benzaldehydes

Rotational Barrier and Quantification of Electron-Donating Substituent Effects: a Computational Study of para-Substituted Benzaldehydes

Synthesis, optical, and thermal properties of 2,4,6-tris(4-substituted phenyl)pyrylium tosylates and triflimides

A group of five 2,4,6-tris(4-substituted phenyl)pyrylium tosylates were synthesized in one-pot reaction from para-substituted benzaldehyde and para-substituted acetophenones using tosic acid as a condensing agent. The tosylate salts were converted to the corresponding triflimide salts by metathesis reactions. Chemical structures, as well as optical spectroscopic and thermal properties of these salts were studied using pertinent experimental techniques. Trimethyl- and trihalo-substituted pyrylium salts emitted strong blue light with peaks in the 456 nm–479 nm range and trimethoxy-pyrylium salts emitted intense green light with maxima around 526 nm in acetonitrile solution. Quantum yields of the solutions were rather low, but the salts were also fluorescent in the solid state. Acetonitrile solution of trichloro-substituted pyrylium triflimide showed significant spectral line narrowing and fluorescence lifetime shortening under intense excitation, and laser action with minimal feedback. The salts have low melting transitions compared to the corresponding –BF4 salts, and their thermal stability is excellent with decomposition temperature in the 268–402 °C range in nitrogen.

Stoichiometric Aldehyde Deformylation Mediated by Nucleophilic Peroxo-diiron(III) Complex as a Functional Model of Aldehyde Deformylating Oxygenase.

The reactivity of the previously reported peroxo adduct [FeIII 2 (μ-O2 )(MeBzim-Py)4 (CH3 CN)2 ]4+ (1) (MeBzim-Py=2-(2'-pyridyl)-N-methylbenzimidazole) towards aldehyde substrates including phenylacetaldehyde (PAA), hydrocinnamaldehyde (HCA), propionaldehyde (PA), 2-phenylpropionaldehyde (PPA), cyclohexanecarboxaldehyde (CCA), and para-substituted benzaldehydes (benzoyl chlorides) has been investigated. Complex 1 proved to be a nucleophilic oxidant in aldehyde deformylation reaction. These models, including detailed kinetic and mechanistic studies, may serve as the first biomimics of aldehyde deformylating oxygenase (ADO) enzymes.

Structure-reactivity correlation in the oxidation of meta and para-substituted benzaldehydes by Tetrakis (Pyridine) Silver Dichromate

Structure-reactivity correlation in the oxidation of meta and para-substituted benzaldehydes by Tetrakis (Pyridine) Silver Dichromate

Direct aldol and nitroaldol condensation in an aminosilane-grafted Si/Zr/Ti composite hollow fiber as a heterogeneous catalyst and continuous-flow reactor

A proof-of-concept study for a new type of continuous-flow reactor based on porous aminosilane-grafted Si-Zr-Ti/Torlon composite hollow fibers was considered for aldol and nitroaldol condensations of aromatic aldehydes with acetone and nitromethane. These novel hollow fiber reactors consist of bifunctional groups in fiber wall that make them bifunctional catalysts for cooperative interactions (i.e., acid–base catalysis). In this study, the effects of reactant flow rate, reaction time and temperature, and electron-donating and electron-withdrawing groups of para-substituted benzaldehyde derivatives on the catalytic activity of aldol and nitroaldol condensation reactions were systematically investigated. The yield of products was found to be dependent on the cooperative interactions of acid–base pairs, para-substituted benzaldehyde, and reaction conditions such as temperature and contact time. Moreover, relatively high yields of ca. 100% were obtained at higher flow rates for primary aldol and nitroalcohol products, while benzylideneacetone and nitrostyrene yields were higher at longer contact times. The obtained results indicate that the aminosilane-grafted Si-Zr-Ti/Torlon composite hollow fibers provide a new platform as flow reactors for heterogeneously catalyzed reactions that may facilitate the ultimate scale-up of practical fiber catalysts for the synthesis of complex organic compounds.

Synthesis and Antifungal and Antiviral Activity of N-Benzyl Derivatives of the Tetraene Macrolide Antibiotic Lucensomycin

Reductive amination of the tetraene macrolide antibiotic lucensomycin by para-substituted benzaldehydes and cyanoborohydride formed its N-benzyl derivatives. The physicochemical, medical, and biological properties of the obtained pimaricin derivatives were studied. Biological tests showed that the N-benzyl lucensomycin derivatives possessed high antifungal and antiviral activity. Pharmacological tests showed that the acute toxicity (LD50) of the synthesized lucensomycin derivatives was six times less than that of the starting antibiotic.

Kinetic and Mechanistic Examination of Acid–Base Bifunctional Aminosilica Catalysts in Aldol and Nitroaldol Condensations

The kinetic and mechanistic understanding of cooperatively catalyzed aldol and nitroaldol condensations is probed using a series of mesoporous silicas functionalized with aminosilanes to provide bifunctional acid–base character. Mechanistically, a Hammett analysis is performed to determine the effects of electron-donating and electron-withdrawing groups of para-substituted benzaldehyde derivatives on the catalytic activity of each condensation reaction. This information is also used to discuss the validity of previously proposed catalytic mechanisms and to propose a revised mechanism with plausible reaction intermediates. For both reactions, electron-withdrawing groups increase the observed rates of reaction, though resonance effects play an important, yet subtle, role in the nitroaldol condensation, in which a p-methoxy electron-donating group is also able to stabilize the proposed carbocation intermediate. Additionally, activation energies and pre-exponential factors are calculated via the Arrhenius ana...

CORRELATION ANALYSIS OF REACTIVITY IN THE OXIDATION OF SUBSTITUTED BENZALDEHYDES BY BIS[DIPYRIDINESILVER(I)]DICHROMATE

Oxidation of thirty six monosubstituted benzaldehydes by bis[dipyridinesilver (I)] dichromate (BDSD) in dimethylsulphoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is of first order with respect to BDSD. A Michaelis-Menten type kinetics was observed with respect to the reactants. 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 tetraperametric 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 h 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.