The use of DSC curves to determine the acetylation degree of chitin/chitosan samples

The use of DSC curves is proposed as an alternative method to determine the degree of N-acetylation (DA) in chitin/chitosan samples, based in both peak area and height of the decomposition signal. Samples with DA from 74 to 16% were prepared from a chitin commercial sample and the DA was determined by ¹H NMR, ¹³C CP/MAS NMR and IR spectra. The effect of water content, heating rate, sample mass and gas flow on the DSC peaks were evaluated and optimized. Using optimized conditions a linear relationship between peak area and height with the DA could be achieved with linear correlation coefficients of −0.998 and −0.999 (n = 7), respectively. The calibration graphs were used to determine the DA of a commercial chitosan sample with relative errors ranging from 2 to 3% for both peak area and peak height, when compared with the DA determined by ¹H NMR method.     

Selective acetylation of toluene to 4-methylacetophenone over zeolite catalysts

The vapour phase acetylation of toluene has been catalysed by acidic H-ZSM-5, H-mordenite and REY zeolite catalysts at 453 K in a tubular reactor at atmospheric pressure. H-ZSM-5 exhibited the best results during the reaction with respect to rate of acetylchloride conversion (TOF=7.5 mol s⁻¹ mol⁻¹ Al×10⁻⁴), conversion of acetyl chloride (60.2 wt.%) and selectivity for 4-methylacetophenone (88.3%) compared to both H-mordenite and REY zeolites. It is revealed that the activity and selectivity of the catalyst strongly depend on the acidic properties and pore openings of the zeolites, respectively. It is observed that isomer ratio (4-methylacetophenone/2-methylacetophenone) is influenced by the reaction conditions and type of zeolite used in the reaction. With increasing reaction temperature and toluene to CH₃COCl molar ratio, the conversion of CH₃COCl (ACT) increases, while it decreases with the increase in reaction time, weight hourly space velocity (WHSV), Na-content and silica to alumina molar ratio of H-ZSM-5 in the acetylation of toluene. H-ZSM-5 is deactivated under the reaction conditions.     

Fluoride removal from water by chitosan derivatives and composites: A review

Fluoride is an essential element, indispensable for maintenance of dental health. Nevertheless, fluoride concentrations in drinking water above 1.5 mg L⁻¹ may be detrimental to human health. Many methods have been developed for removing excessive fluoride from drinking water, adsorption seems to be an effective, environmentally friendly and economical one. Since the sorption capacity of fluoride below 2 mg L⁻¹ on most conventional adsorbents is not satisfactory, much effort has been devoted to develop new and cost-effective fluoride adsorbents. This review reports the recent developments in the F⁻ removal in water treatment, using chitosan derivatives and composites in order to provide useful information about the different technologies. When possibly the adsorption capacity of chitosan derivatives and composites under different experimental conditions is reported to help to compare the efficacy of the fluoride removal process. A comparison with the adsorption capacity of other low cost adsorbents is also tabled.     

An unusual involvement of NaIO4 in the acetylation of bisphenol during attempted oxidative acetylation

An unexpected behaviour of compilation of reagent sodium metaperiodate in acetic anhydride for acetylation of bisphenols was observed during attempted oxidative acetylation of bisphenols for the synthesis of a bis-acetoxy cyclohexadienone. The products were characterized by their spectral and analytical data and a probable mechanism for acetylation involving role of NaIO₄ is proposed.     

壳聚糖的表面活性和聚集

壳聚糖是甲壳素的脱乙基产物 ,作为唯一的阳离子型聚电解质天然多糖 ,具有许多独特的性质 ,在生物、医学、食品、水处理等许多领域有广泛的应用或呈现出诱人的应用前景 [1～ 4].然而 ,从表面化学的角度 ,壳聚糖是否具有表面活性、在水溶液中是否聚集尚是一个有争议的问题 [5、 6].本研究结果表明壳聚糖具有表面活性 ,在水溶液中单个分子就能聚集 ,临界聚集浓度 cac≈ 0,对非极性有机物芘具有明显的增溶作用 .属于结构特殊的阳离子型高分子表面活性 剂 .1实验部分 1.1试剂 　　壳聚糖：以虾壳为原料 ,用稀碱处理除去蛋白质 ,再用稀酸处理除去…     

Task-oriented use of ionic liquids: efficient acetylation of alcohols and phenols

The ionic liquid 1-butyl-3-methylimidazolium acetate proves to be an excellent reaction medium for the acetylation of alcohols and phenols, providing better conditions than the acidic 1-butyl-3-methylimidazolium bisulfate. Reactions were carried at room temperature, with only a 10% excess of acylating agent and with no other solvent or catalyst added.     

Lipase-mediated selective acetylation of primary alcohols in ethyl acetate

An environmental friendly process to selectively acetylate primary alcohols was demonstrated. The esterification process consists of treatment of a primary alcohol in the presence of immobilized C. antarctica lipase (Novozyme-435) in ethyl acetate at room temperature. Primary alcohols were acetylated in the presence of secondary alcohols and phenols.     

Metal chloride-catalyzed acetylation of starch: Synthesis and characterization

Acylation of polysaccharides is a commercially important reaction and is usually performed in a process involving the polysaccharide, an acid anhydride, and an inorganic acid. As an alternative to inorganic acid, many catalysts, including some metal chlorides, have been previously reported as catalysts. In this work, we took a more comprehensive look at several metal chlorides to observe trends and reactivities among them, particularly relating to reaction temperature, time, and amount of acetic anhydride used. Iodine was also included for comparison. Almost all the metal chlorides studied were found to be active as catalysts for the acetylation of starch under suitable reaction conditions. However, each metal chloride had a somewhat different reactivity with a different optimal temperature needed for satisfactory reactions to take place. The molecular weight of the starch acetate products decreased in all cases observed. The reactivity trends among the metal halides seemed to correlate both with the ease of complexation between the halide and the substrate and with the acidity of the metal chloride. Characterization was achieved through ^13?C NMR, FT-IR, thermogravimetric analysis and size exclusion chromatography.     

Fluorous distannoxane-catalyzed acetylation of alcohols in heterogeneous single fluorous solvent system

Acetylation of alcohols with an equivalent amount of acetic anhydride is feasible in the presence of fluorous distannoxane catalyst in heterogeneous single fluorous system. The fluorous layer containing catalyst can be recycled and reused at least 10 times.     

DABCO: an efficient promoter for the acetylation of carbohydrates and other substances under solvent-free conditions

A simple, mild and efficient solvent-free method for the acetylation of carbohydrates, and their partially protected derivatives, as well as non-carbohydrate substances in excellent yields in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) is described with the advantage of tolerance to various functional groups, short reaction time and ease of product isolation.     

Characterization and in vitro release kinetics of chitosan based biocomposites from Scotch Bonnets

The main aim of this study is to formulate the combination of the bioactive composite containing chitosan/β -tricalcium phosphate (CH/β-TCP) as potential drug delivery platforms for the sustained release of antibiotics. Herein the mode of amoxicillin (AMX) maintained in the β-TCP/chitosan composite was characterized using XRD, FT-IR to confirm the phase purity and functional groups. SEM was used to examine the size and shape of particles. The SEM images of the biocomposites after drug release confirmed that they are biodegradable. In vitro drug release experiments in PBS (pH 7.4) revealed a sustained release profile in a neutral medium. Drug release profiles were evaluated according to five different kinetic models including Zero Order, First Order, Higuchi, Hixon Crowel, and Korsmeyer-Peppas. The release profile was best expressed by the Korsmeyer Peppas model because the results showed high linearity. Overall, the positive effect of chitosan coating on the drug elution profile of β-TCP as carriers for the controlled delivery of antibiotics was regarded as biocompatible for the controlled drug delivery system.     

Unprecedented acetylation of phenols using a catalytic amount of magnesium powder

The acetylation of phenols with acetic anhydride was achieved using a catalytic amount of magnesium metal powder under air and solvent-free conditions to afford corresponding phenyl acetates in excellent yield (up to 98%).     

Release of rifampicin from chitosan, PLGA and chitosan-coated PLGA microparticles

Recently three groups of rifampicin (RIF)-loaded microparticles (MPs), consisting of chitosan (CHT), PLGA and PLGA/CHT mixtures, were assessed in terms of RIF-loading and retention during nebulisation. The CHT-coated PLGA MPs were found to exhibit high RIF-loading ability together with nebulisation ability, stability, and mucoadhesive properties. All MP types had comparable toxicity towards alveolar cells which was significantly lower than that of the free drug. Herein, we study the release of RIF from all MP-types, during incubation in buffer with pH values: 4.40 and 7.40. Results show that CHT particles exhibit a higher burst release compared to PLGA MPs; at pH 4.40, which is explained by the higher solubility of CHT in acidic media. At pH 7.40 burst release from CHT MP's is significantly lower when CHT is crosslinked with glutaraldehyde, which is consistent with their - previously observed - increased stability during nebulization. From PLGA MPs, RIF release was pH independent under the conditions applied, while the amount of PVA (stabilizer) considerably affected drug release. When PLGA MP's were coated with CHT, at pH 7.40 the retention of RIF increased further (compared to non-coated MPs), while at pH 4.40 the release was faster from the CHT-coated particles. Concluding, it is proven that when PLGA MPs are coated with CHT, in addition to increased particle mucoadhesive properties, the release kinetics of RIF are modified.     

Ethyl acetate as an acetyl surrogate for the iodine catalyzed acetylation of alcohols

The use of readily available ethyl acetate in the presence of iodine as an alternative acetylating agent is reported. Amines and phenols were unreactive under the examined reaction conditions, indicating that the method is highly chemoselective.     

New approach to the quaternization of chitosan and its amphiphilic derivatives

Regioselective quaternization of chitosan and its amphiphilic derivatives has been carried out by means of reaction with betaine in the presence of the coupling reagent 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ) in aqueous media at pH 5.5 ± 0.5. This reaction results in preparation of N-/(trimethylammonio)acetyl/chitosan chloride and its amphiphilic derivatives. The degree of quaternization increases with increasing EEDQ/chitosan ratio and is partly accompanied by N-ethoxycarbonylation. That side-product formation can be minimized by increasing betaine/EEDQ ratio.     

Ni/Silica catalyzed acetylation of phenols and naphthols: An eco-friendly approach

A method for 10% Ni/SiO₂ catalyst is developed for acetylation of phenol, substituted phenols, naphthols, substituted alcohols under mild liquid phase conditions affording aromatic esters with maximum conversions of 50–80% and 100% selectivity. The catalyst showed remarkable reusability for up to 4 cycles. This methodology is eco-friendly, economic with Ni/SiO₂ catalysts exhibiting no loss of activity the first report for acetylation of substituted phenols to esters with 10% Ni/SiO₂ catalyst.     

Adsorption of acid yellow dye on flakes of chitosan prepared from fishery wastes

Chitosan flakes, extracted from prawns and labeo rohita scales, with high adsorption capacity were prepared after chemical treatment and were used to remove acid yellow dye from water. The results showed that adsorption capacity is dependent on pH, initial concentration of dye, BET, Langmuir surface area and pore volume of the adsorbent. In acidic conditions, the polymer amino groups were protonated (positively charged polymer chain), which showed attraction with negative ions of anionic dye. Chitosan from prawns scales showed higher dye adsorption under the same experimental conditions. Adsorption isotherms were developed and equilibrium data fitted well to Langmuir and Freundlich isotherm models.     

p-Toluenesulfonyl chloride as a new and effective catalyst for acetylation and formylation of hydroxyl compounds under mild conditions

<正>The catalytic application of p-toluenesulfonyl chloride for efficient acetylation of various types of alcohols and phenols with acetic anhydride in solvent-free conditions is reported.Also structurally diverse alcohols were formylated using formic acid based on the use of catalytic amount of p-toluenesulfonyl chloride under solvent-free condition.The reactions were carried out in short reaction time and in good to excellent yields at room temperature.