Chemoselective synthesis of 1,1-diacetates from aldehydes in the presence of Al(HSO<Subscript>4</Subscript>)<Subscript>3</Subscript> under mild solvent-free conditions

A novel efficient procedure has been developed for the preparation of acylals in high yields by reaction of the corresponding aldehydes with acetic anhydride in the presence of Al(HSO₄)₃ as catalyst under mild (room temperature) solvent-free conditions. Published in Russian in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 6. pp. 855–857. The text was submitted by the authors in English.     

The use of silica sulfuric acid as an efficient catalyst for deprotection of trimethylsilyl ethers to the corresponding alcohols under mild and heterogeneous conditions

Silica sulfuric acid was used as a suitable catalyst for the conversion of trimethylsilyl ethers to the corresponding alcohols in the presence of wet SiO2 in high yields at room temperature.     

SnCl4/SiO2: An Efficient Heterogeneous Alternative for One‐Pot Synthesis of β‐Acetamidoketones

Enolizable ketones have been reacted in a one‐pot method with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of SnCl₄/SiO₂ to furnish the corresponding β‐acet‐amidoketones in improved yields. Acetylation of an aromatic hydroxyl group was observed while using 4‐hydroxybenzaldehyde or vanillin and the corresponding β‐acetamidoketones were isolated in an excellent yield.     

Oxidative Deprotection of Acetals and Trimethylsilylethers by γ‐PCC‐SiO2

Acetals, ketals and trimethylsilyl ethers mildly and selectively underwent oxidative deprotection to carbonyl compounds by silica gel supported γ‐picolinium chlorochromate under non‐aqueous conditions in good to excellent yields.     

H3PW12O40/SiO2: An Eco‐Friendly Alternative for the Stereo‐, Regio‐ and Chemoselective Claisen‐Schmidt Condensation

H₃PW₁₂O₄₀/SiO₂ or (PW/SiO₂) promotes the regio‐, stereo‐ and chemoselective Claisen‐Schmidt condensation with improved yields.     

Effects of QCD Vacuum and the Instanton Induced-Contributions to the Nucleon Structure Functions

The instanton induced cross section in deep inelastic kinematics is a subject which people are tendentious to investigate it. Instanton induced contributions are well defined for the nucleon structure function. The non-perturbative contribution to the quark distributions of structure function, F2 (x, Q2 ), is considered within an instanton model for the QCD vacuum. We find that the structure function may possess numerically large non-perterbative contributions which are related to the violation of chirality and correspond to the correction of parton distribution of the leading twist. It is shown that the instantons give a negative contribution to the structure function at the NLO approximation. A comparison between our results, considering instantaon effect, and the case when we do not take this effect is done. Taking into account the instanton size, ρ, via the modified running coupling constant we get to a good agreement between our results at the NLO and NNLO approximations and the available experimental data, specially at the low values of the Bjorken variable x0.1 which confirms the validity of our calculations.     

QCD Predictions for Spin Dependence of Parton Distributions

We introduce the polarized valon distributions to describe the spin dependence of parton distributions. The polarized valon distributions in the proton and polarized parton distributions inside the valon can help to obtain polarized parton distribution in a proton. In order to be able to obtain the spin contribution of sea quarks, we need to improve the valon model. We employ the Bernstein polynomial averages to obtain the unknown parameters which exist in our calculations. Our results for the polarized proton structure function, xg^p₁, are in good agreement with the experimental data for some values of Q².     

Nanomolar determination of hydrazine by TiO2 nanoparticles modified carbon paste electrode

In the present paper, the use of a novel carbon paste electrode modified by N,N′(2,3-dihydroxybenzylidene)-1,4-phenylene diamine (DHBPD) and TiO₂ nanoparticles prepared by a simple and rapid method for the determination of hydrazine (HZ) was described. In the first part of the work, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. A linear segment was found with a slope value of about 48 mV/pH in the pH range 2.0–12.0. The apparent charge transfer rate constant (k _s) and transfer coefficient (α) for electron transfer between DHBPD and TiO₂ nanoparticles-modified carbon paste electrode were calculated. In the second part of the work, the mediated oxidation of HZ at the modified electrode was described. It has been found that under optimum condition (pH 8.0) in cyclic voltammetry, a high decrease in overpotential occurs for oxidation of HZ at the modified electrode. The values of electron transfer coefficients (α) and diffusion coefficient (D) were calculated for HZ, using electrochemical approaches. Differential pulse voltammetry exhibited a linear dynamic range from 1.0 × 10⁻⁸ to 4.0 × 10⁻⁶ M and a detection limit (3σ) of 9.15 nM for HZ. Finally, this method was used for the determination of HZ in water samples, using standard addition method.     

Zr(HSO4)4/SiO2: An effective heterogeneous alternative for one-pot synthesis of β-acetamido ketones

In a one-pot procedure, enolizable ketones reacted with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of Zr(HSO₄)₄/SiO₂ to furnish the corresponding β-acetamido ketones in improved yields.     

Nano-TiCl2/cellulose: an eco-friendly bio-based catalyst for one-pot synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives

Research on Chemical Intermediates - Cellulose is among the most abundant natural carbon-based biopolymers containing free OH groups with nucleophilic character for bonding to Lewis acids such as...