Layered Group(IV) Metal Phosphates as Catalysts for MTBE Synthesis

Layered group(IV) metal phosphates and their phenylsulfonic acid derivatives were used as catalysts for the synthesis of methyl tert-butyl ether (MTBE) from methanol and isobutene. Because zirconium and titanium phosphates have only moderate acidic strength, relatively high temperatures are required to activate their Brønsted acidic sites. The optimal activity was obtained at ca. 443 K. Their phenylsulfonic acid derivatives, however, demonstrated higher acidic strength by giving much higher activity toward MTBE formation at relatively low temperaures. The catalysts were characterized in terms of their structure, thermal stability, surface area and acidic strength.     

Novel triazolyl derivatives for acidic release of amines

Triazolyl derivatives of amines were prepared using click chemistry and evaluated as releasing systems in mildly acidic environments. Triazolylcarbamates and alkylamines were obtained, depending on the reactivity of the propargylic intermediates used for the Huisgen cycloaddition. A fast hydrolysis of some derivatives in mildly acidic conditions was achieved. The relative rates were correlated to a proposed mechanism highlighting the complementary role of the triazole ring and carbocation reactivity/stability.     

Highly efficient synthesis of dicoumarols and xanthene derivatives in presence of Brønsted–Lewis acidic ionic liquids catalyst

A series of metal chloride-based acidic ionic liquids have been prepared and used as an efficient catalyst in one-pot multicomponent synthesis of biscoumarins and substituted xanthenes derivatives under solvent-free conditions. Among the acidic ionic liquids, N-methylpyrrolidonium zinc chloride (Hnmp/ZnCl₃)-based Brønsted–Lewis acidic ionic liquids were found to be an effective and recyclable catalyst for a one-pot synthesis of biscoumarins through the domino Knoevenagel–Michael reaction of a variety of aldehydes with 4-hydroxycoumarin in short reaction times. The reactions which occur under relatively mild conditions afforded the biscoumarin derivatives employing a very low loading of catalyst in satisfactory isolated yields and high purity after simple work-up. The Brønsted–Lewis acidic ionic liquid catalyst was reused four times without any variation in yield.     

Neutral and acidic products derived from hydroxyl radical‐induced oxidation of arabinotriose assessed by electrospray ionisation mass spectrometry

The oxidation of α‐(1 → 5)‐l ‐arabinotriose (Ara₃), an oligosaccharide structurally related to side chains of coffee arabinogalactans, was studied in reaction with hydroxyl radicals generated under conditions of Fenton reaction (Fe²⁺/H₂O₂). The acidic and neutral oxidation products were separated by ligand exchange/size‐exclusion chromatography, subsequently identified by electrospray ionisation mass spectrometry (ESI–MS) and structurally characterised by tandem MS (ESI–MS/MS). In acidic fraction were identified several oxidation products containing an acidic residue at the corresponding reducing end of Ara₃, namely arabinonic acid, and erythronic, glyceric and glycolic acids formed by oxidative scission of the furanose ring. In neutral fractions were identified derivatives containing keto, hydroxy and hydroperoxy moieties, as well as derivatives resulting from the ring scission at the reducing end of Ara₃. In both acidic and neutral fractions, beyond the trisaccharide derivatives, the corresponding di‐ and monosaccharide derivatives were identified indicating the occurrence of oxidative depolymerisation. The structural characterisation of these oxidation products by ESI–MS/MS allowed the differentiation of isobaric and isomeric species of acidic and neutral character. The species identified in this study may help in detection of roasting products associated with the free radical‐mediated oxidation of coffee arabinogalactans. Copyright © 2014 John Wiley & Sons, Ltd.     

Chemical modification of oleanene type triterpenes and their inhibitory activity against HIV-1 protease dimerization

Oleanolic acid derivatives with different lengths of 3-O-acidic acyl chains were synthesized and evaluated for their inhibitory activity against HIV-1 protease. The lengths of the acidic chains were optimized to 6 and 8 carbons. Changing a 3-ester bond to an amide bond or dimerization of the triterpenes retained their inhibitory activity against HIV-1 protease. Introduction of an additional acidic chain to C-28 of oleanolic acid increased the inhibitory activity appreciably, though a derivative with only one acidic chain linked at C-28 also showed potent activity against HIV-1 protease. The inhibitory mechanism was proved directly by size exclusion chromatography to be inhibition of dimerization of the enzyme polypeptides. The ester bonds of the triterpene derivatives were found to be stable to lipase under mild alkaline conditions.     

Urea cyclisation reaction studies

Synthetic approaches of N-α-hydroxyalkyl amides or urea derivatives are described. In particularly, a new 1,4,6-oxadiazocine-2,5,8-trione was obtained by condensation of glyoxylic acid on urea derivatives in acidic catalysis condition.     

Brønsted acidic magnetic nano-Fe3O4-adorned calix[n]arene sulfonic acids: synthesis and application in the nucleophilic substitution of alcohols

Three magnetically recoverable Brønsted acidic calix[n]arene derivatives were successfully constructed by immobilizing calix[n]arene sulfonic acids onto silica-coated magnetic nanoparticles, a process, which allows calix[n]arene derivatives to acquire magnetic properties. All of the magnetically recoverable Brønsted acidic calix[n]arenes efficiently catalyze the coupling of electron-rich arenes with some alcohols in water. After separation and recovery from the reaction mixture by a simple magnet, these Brønsted acidic calix[n]arenes can be recycled many times without losing their catalytic activity.     

Transformation of solvent-derived ozonolysis products to bicyclic peroxides: Isolation and characterisation of novel pentoxonane derivatives

-Hydroperoxyisochroman derivatives 5 react with formaldehyde under acidic conditions to produce mixtures of bicyclic 1,2,4,6-tetroxepane 9 and 1,2,4,6,8-pentoxonane 10 derivatives. The structure of the compound 10a was unambiguously established by the X-ray analysis. With acetaldehyde, only the corresponding 1,2,4,6-tetroxepanes 9 were obtained.     

Broensted酸性离子液体催化醛（酮）与二元醇的缩合反应

研究了以Broensted酸性离子液体1-正丁基-3-甲基咪唑磷酸二氢盐（BMImH2PO4）为催化剂，在不使用其它有机溶剂且无需脱水的条件下，于室温下进行醛（酮）与二元醇的缩合反应，得到了由中至高的转化率和高选择性，产物1，3-二口恶戊烷可以和反应物自动分层，后处理操作简单过量的醇与离子液体可以多次重复使用，且醛（酮）的转化率无明显降低。     

In-Block Derivatization of Herbicidal Carboxylic Acids by Pentafluorobenzyl Bromide

Abstract

Herbicidal carboxylic acids were analyzed via ECD gas chromatography of their pentafluorobenzyl esters. The derivatives were formed by direct injection of a mixture of the acids and pentafluorobenzyl bromide in acetone; yields showed marked dependence on pKa of the acids. Carboxylic acids which have pKa values greater than 4.5 yielded the corresponding derivatives in poor yield unless triethylamine is included in the mixture. The procedure is fast and particularly convenient for low-level screening, identification and analysis of highly acidic chlorobenzoic, chlorophenoxyalkanoic, and arylacetic acids in the presence of less acidic carboxylic acids and phenols.     

Extraction preconcentration with anionic surfactants in acidic solutions

Extraction preconcentration with anionic surfactants in acidic solutions on the basis of the cloud point was studied. Advantages and disadvantages of this method were considered. Conditions of the phase separation of some anionic surfactants (sodium decyl sulfate, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate) in acidic solutions were studied. With the example of pyrene and its derivatives, it was demonstrated that these surfactants can be used for extraction preconcentration. Analytical characteristics of the determination of pyrene and its derivatives in model aqueous solutions by the fluorimetric method in combination with extraction preconcentration with sodium dodecyl sulfate were obtained     

Reactivity of Thienyl Phosphonyl Carbinols in Acidic Medium: Synthesis of Aryl- and Alkoxy-Thienyl Methan Derivatives

2-Thienyl-phosphonylcarbinols in acidic medium gave with alcohols and aromatic derivatives two classes of new compounds depending on the reaction temperature.     

N-Alkoxyl Templates for Diastereoselective Pyrrolidine Synthesis

Intramolecular cyclization of N-alkoxyl amines are studied for the stereoselective preparation of 2, 4-disubstituted pyrrolidine derivatives. Reduction of oximes under acidic conditions by NaBH3CN afforded the corresponding nucleophilic hydroxylamine derivatives,which subsequently cyclized via SN2‘ mechanism to give the desired N-alkoxyl pyrrolidines.     

Allylacetylenes and their derivatives as inhibitors of steel corrosion in sulfuric acid

New functionalized derivatives of allylacetylenes were prepared, and their ability to inhibit corrosion of St.3 low-carbon steel in 5 N sulfuric acid was studied. The effectiveness of inhibition of steel corrosion was studied in relation to the structure of acetylene derivatives, their concentration, and temperature of acidic medium.     

The Conjugate Addition-Cyclization of 3-Oxoacid Thioanilides to β-Nitrostyrenes. An Efficient Synthesis of Functionalized Thiophenes and their Transformation to Pyrroles

Summary. A new and simple method for synthesis of 2-, 3-, and 4-pyridylcarbonyl-2-aryliminothiophene derivatives based on the conjugate addition-cyclization of 3-oxoacid thioamides to β-nitrostyrenes was developed. Thiophene derivatives in acidic medium undergo ring transformation yielding corresponding pyrroles.     

Unlocking the pH‐Responsive Degradability of Fumaramic Acid Derivatives Using Photoisomerization

Fumaramic acid derivatives can be converted into their cis isomer maleamic acid derivatives under UV illumination, and these maleamic acid derivatives show pH‐responsive degradability at acidic pH only after the preceding photoisomerization. The rate of the tandem photoisomerization–degradation of fumaramic acid derivatives can be finely controlled by changing the substituents on the double bond. Photoisomerization‐based unlocking of the pH‐responsive degradability of fumaramic acid derivatives has strong potential for the development of multisignal‐responsive smart materials in biomedical applications.     

Zur synthese funktionel substituierter polysilane mittels trifluormethansulfonsäure

The cleavage of silicon phenyl bonds in phenylmethylpolysilane by CF₃SO₃H leads to triflate derivatives of polysilanes. The polymers react with lithium derivatives or acidic element hydrogen compounds under formation of numerous substituted polysilanes.     

Synthesis and structure of styryl-substituted azines

New photochromic derivatives of 2-styrylquinoline and 2-styrylquinoxaline were obtained by the condensation of the methyl derivatives of the mentioned heterocycles with substituted benzaldehydes in the presence of basic and acidic catalysts, and also under the conditions of Wittig reaction. The structure of compounds obtained was proved by physicochemical analysis methods including XRD.     

The Formation of Chlorinated and Brominated Artifacts during Extraction of Drinking Water with Dichloromethane

Abstract

Chlorinated and brominated cyclohexene derivatives were found in the neutral (N) and acidic (A) fractions of chlorinated water extracted with cyclohexene-preserved dichloromethane. The brominated cyclohexene derivatives were formed only when the water sample contained bromide ions and chlorine.     

Hydrogenation of ferrocene

Ferrocene and derivatives can be hydrogenated in acidic medium at ambien temperature and atmospheric hydrogen pressure using supported palladium as the catalyst.