The water‐promoted Diels–Alder reaction in quaternary ammonium salts

Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO₄ act as salting‐in (S/I) and LiCl, NaCl act as salting‐out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO₄ and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R₄NX, R = alkyl group, X = Br group) behave like salting‐in salts. The physicochemical origin of the salting in effect of R₄NX type of salts has been discussed elaborately in the present work. The role of cations in terms of substitution of various alkyl groups on R₄NX has been systematically presented here on the basis of experimental kinetic and thermodynamic studies. The abnormal behaviour of R₄NX salts in aqueous solution has also been explained by the Setschenov equation (k_s) and Δμ_solvation values, which highlights their individual nature out of common properties of R₄NX. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of the spontaneous formation of organic layers on carbon and metal surfaces from diazonium salts

This study investigates the spontaneous grafting of different para-substituted phenyl groups on carbon and metallic surfaces from diazonium salts solutions. Glassy carbon, nickel, zinc and iron plates were allowed to react with an acetonitrile solution of aryldiazonium tetrafluoroborate salt by simple dipping. The surfaces were characterized before and after their immersion by XPS and AFM to evidence the formation of a coating on the different materials. The results are indicative of the presence of substituted phenyl groups on all the investigated surfaces. This study also aims at correlating grafting efficiency with metal reactivities and diazonium salt electronic properties by means of AFM and FT-IRRAS. For this purpose, zinc and nickel were chosen due to their opposite reducing properties and two diazonium salts were selected with electron-donor or -withdrawing para-substituents. The results tend to indicate that redox properties of both partners (diazonium + metal) are of prime importance for grafting to occur.     

碱金属无机酸盐催化的硫醇的β-羟乙基化反应

在常压、无溶剂、120℃条件下,考察了14种碱金属无机酸盐(MA,M=Li^+,Na^+,K^+)催化正辛硫醇与碳酸乙烯酯的S-羟乙基化反应性能。普遍的规律是:在阴离子A相同的情况下,钾盐的催化活性高于相应的钠盐,而锂盐无催化活性。在各种无机酸钾盐中,如果共轭酸酸性越强,则相应的钾盐的催化活性越低。为探究钾盐催化剂活化-SH的机理的普适性,以K_3PO_4为催化剂,考察了在不同反应温度下,6种不同结构的硫醇与碳酸乙烯酯的β-羟乙基化反应催化活性,得出规律是硫醇的酸性越强,其反应活性越高,S-H键越容易解离。该反应无溶剂参与,硫醇与碳酸乙烯酯的物质的量之比接近理论量,产物β-羟乙基硫醚的选择性>99%,产物中无卤素盐副产物生成,易于分离。     

苯基重氮盐-冠醚分子嵌合物的FAB-MS及其准分子离子生成机理的研究

Fast atom bombardment mass spectra of a series of arenediazonium salts with various substituents complexed with 18-crown-6 and dibenzo-24-crown-8 ethers were examined. The correlation between quasi-molecular ion abundance of various complexes and the properties, coordination ability of donor-acceptor linkages in the complexes were studied. By using molecular orbital calculation we have successfully demonstrated that the correlation cited is related to the electron cloud densities on the heteroatoms α-N and β-N of arenediazonium salts.     

Kinetics of Alkaline Hydrolysis of Quaternary Phosphonium Salts. The Influence of Protic and Aprotic Solvents on the Hydrolysis of Alkyl Phenylphosphonium Salts

Abstract

Third order rate constants have been determined for the alkaline hydrolysis of four series of alkylphenylphosphonium salts and alkylphenylbenzylphosphonium salts at various temperatures in 50%–70% ^v/_v aqueous tetrahydrofuran and 70% ^v/_v aqueous methanol. Thermodynamic activation parameters have been calculated for the reactions of each substrate and the effects of varying the ratio of alkyl to phenyl groups have been compared, as well as the effects of changes in the nature of the alkyl group. Solvation, as revealed by trends in entropy of activation, plays a largely counter-balancing role with respect to enthalpy and energy of activation. The role of the isokinetic effect is discussed. In aqueous tetrahydrofuran, solvation effects on the hydrolyses of phosphonium salts change as the mole fraction of water changes, and for aqueous methanol the trends in the thermodynamic activation parameters actually reverse.     

STEREOSELECTIVE VINYLATION OF METHYL-2-HYDROXY-3-NAPHTHOATE MEDIATED BY VINYL TRIPHENYLPHOSPHONIUM SALTS

Protonation of the highly reactive intermediate produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylate 1a–c by methyl-2-hydroxy-3-naphthoate lead to vinyl triphenylphosphonium salts which undergo aromatic electrophilic substitution reaction with phenolate-conjugated base to produce 2a–c.     

Stimulated by cyclodextrins high yield synthesis of azocrown analogues comprising pyrrole or imidazole residues

The influence of cyclodextrins (CDs) on the formation of azocrown ethers comprising pyrrole, imidazole and substituted imidazole has been studied. Pyrrole, imidazole, 2-methyl-, 4-methyl- and 4-phenylimidazole were coupled with bis-diazonium salts derived from bis-1,5-(2-aminophenoxy)-3-oxapentane or bis-1,8-(2-aminophenoxy)-3,6-dioxaoctane to form macrocyclic compounds with two azo units. The syntheses were performed under standard conditions in the presence of α-, β- or γ-CDs and the yield of the reaction products was compared with the results of plain experiments, i.e. without CDs. The results are discussed in terms of co-conformation of azole molecules embedded in CD cavity.

Pyrrole or imidazole or imidazole derivatives were coupled with bis-diazonium salts to form macrocycles with two azo units. The syntheses were performed under standard conditions in the presence of α-, β-, or γ-cyclodextrin and the yield of the reaction products was compared with the results of plain experiments, i.e. without CDs. The results are discussed in terms of co-conformation of azole molecules embedded in cyclodextrin cavity.     

Efficient Synthesis of Bicyclo[3.3.1]nonane Systems via Tandem 1,3-Dinucleophilic Addition of 4-Hydroxy-2-quinolinones to Quinolinium Salts

The synthesis of bicyclo[3.3.1]nonane systems is reported. The synthesis is based on the tandem 1,3-dinucleophilic addition of 4-hydroxy-2-quinolinone to quinolinium salts.     

Reaction of 4-(2′-Hydroxyaryl)-1,3-dithiolium Salts with Sodium Sulfide. A Selective Synthesis of 2′-Hydroxyacetophenones

Abstract

The treatment of 4-(2′-hydroxyaryl)-2-(N,N-dialkylamino)-1,3-dithiolium perchlorates (1a–g) with sodium sulfide nonahydrate in ethanol at room temperature affords the corresponding 1,3-dithiole-2-thiones (2a–g). When these reactions are conducted in boiling ethanol, 2′-hydroxyacetophenones (3a–g) have been obtained in good to excellent yield. A tentative mechanism for the formation of 3a–g shows that this reaction is regioselective, this being established by the presence of hydroxyl group in 2′-position. That has been confirmed in a control experiment, 4-phenyl-2-(piperidin-1-yl)-1,3-dithiolium perchlorate affording a mixture of condensation products of acetophenone and phenylacetaldehyde, under similar reaction conditions.