Water-acetic Acid Medium Research Articles

Fractionation of Aspen Wood to Produce Microcrystalline, Microfibrillated and Nanofibrillated Celluloses, Xylan and Ethanollignin.

A new method for extractive-catalytic fractionation of aspen wood to produce microcrystalline (MCC), microfibrillated (MFC), nanofibrilllated (NFC) celluloses, xylan, and ethanollignin is suggested in order to utilize all of the main components of wood biomass. Xylan is obtained with a yield of 10.2 wt.% via aqueous alkali extraction at room temperature. Ethanollignin was obtained with a yield of 11.2 wt.% via extraction with 60% ethanol from the xylan-free wood at 190 °C. The lignocellulose residue formed after the extraction of xylan and ethanollignin was subjected to catalytic peroxide delignification in the acetic acid-water medium at 100 °C in order to obtain microcrystalline cellulose. MCC is hydrolyzed with 56% sulfuric acid and treated with ultrasound to produce microfibrillated cellulose and nanofibrillated cellulose. The yields of MFC and NFC were 14.4 and 19.0 wt.%, respectively. The average hydrodynamic diameter of NFC particles was 36.6 nm, the crystallinity index was 0.86, and the average zeta-potential was 41.5 mV. The composition and structure of xylan, ethanollignin, cellulose product, MCC, MFC, and NFC obtained from aspen wood were characterized using elemental and chemical analysis, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analyses, Gas chromatography (GC), Gel permeation-chromatography (GPC), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Dynamic light scattering (DLS), Thermal gravimetric analysis (TGA).

OXIDATION KINETICS OF ANILINE BY ZINC DICHROMATE

The kinetics of oxidation of aniline by Zinc Dichromate (ZDC) has been studied in 50% acetic acid-water medium. The reaction shows unit order dependence each with respect to oxidant and substrate. The rate of reaction increases with increase in the [H+]. The rate of oxidation increases with decrease in dielectric constant of solvent suggests ion-dipole interaction. Increase in ionic strength by the addition of sodium perchlorate has no effect on the rate constant. There is no polymerization with acrylonitrile and absence of free radical is proved. The rate of the reaction has been conducted at four different temperatures. Thermodynamic parameters have been calculated. Based on the kinetics results, a suitable mechanism has been proposed.

Numerical Optimization of the Process of Cellulose Isolation by Peroxide Delignification of Birch Wood in Acetic Acid-Water Medium in the Presence of TiO₂ Catalyst

The possibility of isolation of high-quality cellulose by peroxide delignification of birch wood in an acetic acid-water medium in the presence of a TiO2 catalyst at a temperature of 100 °C was shown. The influence of the process conditions (concentration of hydrogen peroxide and acetic acid, liquid/wood ratio (LWR)) on the yield and composition of cellulose products was established. Numerical optimization of the process was carried out using a full factorial experiment. The optimal conditions for isolation from birch wood a cellulose product with residual lignin content of ≤ 1 wt.% are: СН3СООН concentration 23.8 wt.%, Н2О2 concentration 4.9 wt.%, LWR14.9, temperature 100 °C, time 4 h. Under these optimal conditions, the yield of a cellulose product with a cellulose content of 92.5 wt.% was 49.9 wt.%

Catalytic peroxide fractionation processes for the green biorefinery of wood

A kinetic study and optimization of pine wood peroxide fractionation in the medium acetic acid–water over TiO2 catalyst were accomplished for the first time. Kinetic regularities and the product composition of green processes of catalytic peroxide fractionation of softwood (pine, abies, larch) and hardwood (aspen, birch) over 1 wt% TiO2 catalyst in the acetic acid–water medium were compared at the temperature range 70–100 °C. For all type of wood, the processes of peroxide delignification are described by the first order equations and their activation energies are varied at the range 76–94 kJ/mol. According to FTIR, XRD, SEM, NMR data, the cellulosic products of peroxide delignification have a structure similar to microcrystalline cellulose regardless of the nature of wood. Soluble products are presented by organic acid and monosaccharides. The scheme of green biorefinery of pine wood based on extractive-catalytic fractionation of wood biomass on microcrystalline cellulose, hemicelluloses, aromatic and aliphatic acids, monosaccharides, turpentine and rosin was developed. Green and non-toxic reagents and solid catalyst are used in the developed scheme of biorefinery.

Optimizing Single-Stage Processes of Microcrystalline Cellulose Production via the Peroxide Delignification of Wood in the Presence of a Titania Catalyst

The conventional way of producing microcrystalline cellulose (MCC) from wood raw materials is multistage; it is based on integrating the environmentally hazardous processes of pulping and bleaching of cellulose and the acid hydrolysis of the amorphous phase of cellulose. This work describes an improved single-stage catalytic method for the production of MCC from softwood and hardwood that is based on the peroxide delignification of wood in an acetic acid–water medium under mild conditions (100°C, atmospheric pressure) in the presence of an environmentally safe TiO2 solid catalyst. The processes of MCC production via the peroxide catalytic delignification of various wood species are optimized experimentally and mathematically. The following optimum modes for the production of MCC with a yield of 36.3–42.0 wt % of absolutely dry wood, a residual lignin content of ≤1.0 wt %, and a hemicellulose content of ≤ 6.0 wt % are determined: For aspen: 5 wt % H2O2, 25 wt % CH3COOH, and a liquid/wood ratio of 10. For birch: 5 wt % H2O2, 25 wt % CH3COOH, and a liquid/wood ratio of 15. For silver fir: 6 wt % H2O2, 30 wt % CH3COOH, and a liquid/wood ratio of 15. For larch: 6 wt % H2O2, 30 wt % CH3COOH, and a liquid/wood ratio of 15.

Green biorefinery of larch wood biomass to obtain the bioactive compounds, functional polymers and nanoporous materials

The first green biorefinery of larch wood based on the fractionation of biomass into dihydroquercetin (DHQ), arabinogalactan (AG), microcrystalline cellulose (MCC) and soluble lignin (SL) is reported. The new green method of one-step isolation of DHQ and AG from larch wood by ethanol–water solution was developed. The first results of kinetic studies and optimization of the process of extracted larch wood peroxide fractionation into MCC and SL in acetic acid–water medium in the presence of green TiO2 catalyst are described. The products obtained from larch wood were characterized by FTIR, NMR, XRD, AFM and chemical methods. The scheme of larch wood biorefinery is suggested which integrates the developed processes of woody biomass fractionation into DHQ, AG, MCC and SL. All developed methods use non-toxic and less-toxic reagents, such as water, ethanol, hydrogen peroxide and acetic acid.

Optimization of One-Stage Processes of Microcrystalline Cellulose Obtaining by Peroxide Delignification of Wood in the Presence of TiO2 Catalyst

The traditional method for obtaining microcrystalline cellulose (MCC) from wood raw material is multi-stage and it is based on the integration of environmentally hazardous processes of pulping and bleaching of cellulose and acid hydrolysis of amorphous part of cellulose. The paper describes an improved one-stage catalytic method of microcrystalline cellulose obtaining from softwood and hardwood based on peroxide delignification of wood in acetic acid-water medium under the mild conditions (100 °C, atmospheric pressure) in the presence of an environmentally safe solid catalyst TiO 2 . Experimental and mathematical optimization of the processes of MCC preparation by peroxide catalytic delignification of various types of wood was carried out. The following optimal modes of obtaining MCC with the yield 36.3–42.0 wt.% of abs. dry wood and residual lignin content ≤1.0 mas.%, hemicellulose ≤6.0 mas.% was established: for aspen – 5 wt.% H 2 O 2 , 25 wt.% CH 3 COOH, hydromodule = 10; for birch – 5 wt.% H 2 O 2 , 25 wt.% CH 3 COOH, hydromodule = 15; for abies – 6 wt.% H 2 O 2 , 30 wt.% CH 3 COOH, hydromodule = 15; for larch – 6 wt.% H 2 O 2 , 30 wt.% CH 3 COOH, hydromodule = 15.

Kinetics and thermodynamics of oxidation of 4-oxo-4-phenyl butanoic acid by benzimidazolium fluorochromate in acetic acid-water medium

Kinetics and thermodynamics of oxidation of 4-oxo-4-phenyl butanoic acid by benzimidazolium fluorochromate in acetic acid-water medium

Efficient Synthesis of Homoallylic Alcohols/Amines from Allyltributylstannane and Carbonyl Compounds/Imines Using Iodine as Catalyst Under Acetic Acid–Water Medium

This paper describes a general method for the synthesis of homoallylic alcohols and amines by nucleophilic addition reaction of allyltributylstannane to carbonyl compounds and aldimines where iodine acts as a catalyst in H2O/acetic acid (1:1) medium. Only 10 mol% of I2 is required for various organic transformations. By using this process, various homoallylic alcohols and amines are produced in good to excellent yields.

Studies on the Kinetics of Oxidation of 4-Oxo-4-phenylbutanoic Acid by Benzimidazolium Fluorochromate in the Presence of Oxalic Acid in Acetic Acid-Water Medium

Kinetics of oxidation of 4-oxo-4-phenyl butanoic acid (4-oxo acid) by benzimidazolium fluorochromate (BIFC) in acetic acid-water medium with perchloric acid in the presence of oxalic acid (OA) has been studied. The reaction is first order each in (BIFC), (4-oxo acid) and (H + ). The reaction has been found to be catalyzed by H + ions. The reaction rate increased remarkably with the increase in the proportion of acetic acid in the solvent medium. Various thermodynamic parameters have been determined at different acetic acid-water composition. A suitable mechanism has been proposed.

Optimized methods for obtaining cellulose and cellulose sulfates from birch wood

The methods of obtaining cellulose and cellulose sulfates from birch wood based on the use of one-step catalytic delignification of wood by hydrogen peroxide in acetic acid–water medium were studied. The conditions of birch wood oxidative delignification by acetic acid/hydrogen peroxide mixtures in the presence of sulfuric acid catalyst were optimized in order to obtain an acceptable yield of cellulose product with low content of residual lignin. Cellulose extracted from birch wood by green method was used for preparation of cellulose sulfates in dioxane solution. The homogeneous sulfation of obtained cellulose by chlorosulfonic acid in dioxane allows to reduce the fragmentation of polymer and to synthesize cellulose sulfates with a finer and more homogeneous structure as compared to cellulose sulfates prepared by heterogeneous sulfation in harmful pyridine. Obtained samples of cellulose and cellulose sulfates were characterized by XRD, SEM, AFM, NMR, FTIR, Raman, XPS and chemical methods.

A reusable Mn(ii)-dampy-MCM-41 system for single step amination of benzene to aniline using hydroxylamine

Reaction methodology for C–H bond amination of benzene catalyzed by Mn(II)-dien (ampy) immobilized organo modified MCM-41 in the presence of hydroxylamine in acetic acid–water medium is described. The organic–inorganic hybrid heterogeneous catalyst achieves high catalytic activity and selectivity for one step amination of benzene. Characterization of the immobilized catalyst by powder X-ray diffraction (XRD), N2 adsorption–desorption, CP MAS NMR spectroscopy (13C and 29Si), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–Vis spectroscopy demonstrates the successful grafting of the complex into functionalized mesoporous silica and that the mesostructure has not been destroyed in the multistep synthetic procedure. The variation of reaction conditions such as solvent, temperature, time, catalyst concentration etc. is well demonstrated to achieve high catalytic activity. Moreover, the anchored catalyst can be recovered and reused for multiple cycles without appreciable loss in catalytic activity, which is an alternative to the conventional industrial process.

Synthesis, characterization and catalytic activity of copper incorporated and immobilized mesoporous MCM-41 in the single step amination of benzene

The paper reports the synthesis, surface and textural characterization of copper and amine modified MCM-41 and its application for the single step amination of benzene to aniline at 70 °C. Varying the amount of Cu different Cu/amine modified MCM-41 samples was synthesized by co-condensation and impregnation method. The samples were characterized by nitrogen adsorption–desorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FT-IR), 29Si magic-angle spinning (MAS) and 13C Nuclear Magnetic Resonance (NMR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. FT-IR and DRS results indicated that Cu and amino groups are incorporated into the Si–O framework and frame wall respectively. NMR showed higher degree of condensation of materials in framework position. Cu-amine-MCM-41 samples showed significant catalytic activity for single step amination of benzene in acetic acid–water medium under mild reaction conditions using hydroxylamine as aminating agent. The Cu-amine-MCM-41 (Si/Cu = 20) showed highest benzene conversion (72.2%) and 100% selectivity for aniline.

Structural properties and catalytic activity of Mn-MCM-41 mesoporous molecular sieves for single-step amination of benzene to aniline

Abstract Mesoporous MCM-41 and Mn-MCM-41 with varying Si/Mn ratios such as 100, 60, 40, 20 and 10 were synthesized at room temperature under basic conditions by direct insertion of metal ions during synthesis. The bulk and surface properties of the synthesized catalysts were examined by XRD, nitrogen adsorption/desorption, FT-IR, TG-DTA, Raman spectra, ESR technique and UV–vis diffuse reflectance spectra (DRS). Results indicated that Mn ions are partially incorporated into the Si O framework and lead to the vibration of Si O Mn bonds. ESR spectra showed a well-resolved sextet centred at g = 2.0 indicating distorted octahedral symmetry of Mn(II) species in Mn-MCM-41. UV–vis DRS showed co-existence of Mn2+ and Mn3+ in Mn-MCM-41; these coordinated to Si(IV) by disordered octahedral and tetrahedral environments, respectively. Mn-MCM-41 materials showed significant catalytic activity for single-step amination of benzene in acetic acid–water medium under mild reaction conditions using hydroxylamine as aminating agent. Mn-MCM-41 (Si/Mn = 20) showed the highest benzene conversion (68.5%) and 100% selectivity for aniline.

Selective oxidation of p-chlorotoluene with Co(OAc)2/MnSO4/KBr in acetic acid–water medium

Abstract Selective oxidation of p -chlorotoluene catalyzed by Co(OAc) 2 /MnSO 4 /KBr with molecular oxygen has been studied. Acetic acid–water is used as the reaction medium in place of pure acetic acid to avoid the nuisance of acetic acid separation. It is found that when MnSO 4 is used in place of the commonly used Mn(OAc) 2 , MnO 2 barely forms and the activity of the composite catalyst greatly enhances. Under the optimized conditions (Co/(Co + Mn) mole ratio 0.2, Br/(Co + Mn) mole ratio 0.3, and reaction temperature 106 °C), 22.4% yield of p -chlorobenzaldehyde was obtained at 33.7% conversion of p -chlorotoluene with 66.6% selectivity.

Effect of solvent on the rate of oxidation of substituted anilines with nicotinium dichromate in aqueous-acetic acid media

Mechanistic studies on the oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate in water-acetic acid medium of varying mole fractions have been performed. The reaction can be characterized by the experimental rate equation, -d[oxidizing agent] Kk [substrate] [HCrO - 4 ] dt (1 + K [substrate]) The addition of p-toluenesulfonic acid enhances the reaction. The oxidation substituted anilines at 299-322 K complies with the isokinetic relationship but not to any of the linear free energy relationships, the isokinetic temperature lies within the experimental range. Correlation of rate data with Kamlet-Taft solvatochromic parameters (a, β, π*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity.

Kinetics of Oxidation of Benzaldehydes by Quinolinium Dichromate

Quinolinium dichromate (QDC) in sulfuric acid oxidizes benzaldehydes to the corresponding acids in a 50% (v/v) acetic acid-water medium. The reaction is first order each in [QDC], [substrate] and [H+]. The reaction rates have been determined at different temperatures and the activation parameters calculated. The rate decreases with an increase in the water content of the medium. The effects of substituents have been studied. A suitable mechanism is proposed.

Kinetics of oxidation of α,β-unsaturated aldehydes by quinolinium dichromate

A series of α,β-unsaturated aldehydes (crotonaldehyde, cinnamaldehyde, acrylaldehyde, and methacrylaldehyde) were oxidized by quinolinium dichromate in sulfuric acid to the corresponding acids in 50% (v/v) acetic acid – water medium. The kinetic data have been discussed with reference to the aldehyde hydration equilibria. The kinetic results support a mechanistic pathway proceeding via a rate-determining oxidative decomposition of the chromate ester of the aldehyde hydrate.Key words: kinetics, oxidation, unsaturated aldehydes, quinolinium dichromate.

Kinetics of the Oxidation of Heterocyclic Aldehydes by Quinolinium Dichromate

Abstract Quinolinium dichromate in sulfuric acid oxidizes heterocyclic aldehydes (2-furaldehyde, 2-pyrrolecarbaldehyde, 2-thiophenecarbaldehyde) to the corresponding acids in a 50% (v/v) acetic acid–water medium. The kinetic data on the rates of oxidation of the substrates have been discussed with reference to the aldehyde hydration equilibria. The kinetic results support a mechanistic pathway proceeding via a rate-determining oxidative decomposition of the chromate ester of the aldehyde hydrate.

Spectral, thermal and electrical properties of some new azo complexes

Cobalt(II), nickel(II) and copper(II) acetates react with thymine compound (H 2L) to form complexes having the general formula [MH 2L(OAC) 2(H 2O) 2] nH 2O. However, the interaction of iron(III) chloride with thymine in acetic acid–water medium yields a new complex of the type [FeH 2L(OAC) 2H 2O]OAC.H 2O. All the thymine complexes have been characterized by elemental analyses, spectral and magnetic studies where thymine acts as a neutral ligand and the acetate ion behaves as a strong nucleophile during complexation. 6-aryl and thiazolylazo thymine compounds and their metal complexes were synthesized and characterized where the ligands act as a bidentate dibasic. The azo group is not involved in the structure. Thermal decomposition studies of the azo complexes were explained to give more information on the structure of the investigated materials. The effect of some transition metal cations such as Co II, Ni II and Cu II on the electrical behaviour of 6-(2-thiazolylazo)thymine compound is studied. The data obtained obeyed the relation σ= σ° exp (− E/2 kT) over the temperature range 30–150°C. The observed conductivities of the different complexes follow the order Co<Ni<Cu. It is clear that this trend is depending on the decreasing of the ionic radii and the increasing stability of metal complexes. The calculated mobility of charge carriers is ranged from 10 −5 to 10 −9cm 2/V s suggesting that the conduction of the studied complexes takes place by hopping mechanism.