Separation of acetylated amino acids

Acetylated amino acids (Nac-AA) are separated as anions on a reversed stationary phase from a mobile phase containing a quaternary ammonium (R₄N⁺) salt as a mobile phase additive. If the counteranion accompanying the R₄N⁺ or ionic strength salt is detector active than the separated NAc-AA derivatives can be detected by an indirect detection strategy. Variables influencing the separations are NAc-AA side chain structure and the mobile phase parameters such as hdyrophobicity of the alkyl groups in the R₄N⁺ salt, R₄N⁺ salt concentration, counteranion eluent strength, counteranion concentration, solvent composition, and pH. Indirect detection is influenced by these same mobile phase parameters as well as the properties of the detector active counteranion. The detection limit for indirect photometric detection at 287 nm using a tetrapentylammonium salt with a disodium 1,5-naphthalenedisulfonate—sodium benzoate counteranion mixture was about 70 pmol of NAc-AA depending on the amino acid injected as a 10-μ1 sample.     

Phase-transfer agents as catalysts for a nucleophilic substitution reaction in microemulsions

The reaction between 4-tert-butylbenzyl bromide and potassium iodide was carried out in microemulsions based on different nonionic surfactants, and the reaction rates were compared with those obtained in two-phase systems with added phase-transfer agent, either a quaternary ammonium salt or a crown ether. The reactions were relatively fast in the microemulsions and extremely sluggish in the two-phase systems without additional phase-transfer agent. Addition of a phase-transfer agent did not accelerate the reaction when a hydrocarbon was used as organic solvent, neither in the two-phase system nor in the microemulsion. When a chlorinated hydrocarbon was used as solvent, phase-transfer catalysis became effective and the rate obtained in the two-phase system with an equimolar amount of phase-transfer agent added was higher than that obtained in the microemulsion. When a catalytic amount of phase-transfer agent was used, the rate in the two-phase system was about the same as the rate obtained in the microemulsion without the phase-transfer agent. The combined approach, that is, use of a microemulsion as the reaction medium and addition of a phase-transfer agent, gave the highest reaction rate. The quaternary ammonium salt (tetrabutylammonium hydrogen sulfate) was a more efficient catalyst in the microemulsion system than the crown ether ([18]crown-6).     

Colloidal metal dispersions and metal complexes in hydrocarbons

Stable dispersions of colloidal metals in hydrocarbons have been prepared by a novel phase-transfer method. The metals were gold, silver, palladium and ruthenium; the hydrocarbons were n-hexane, cyclohexane and benzene. The phase transfer of colloidal metal particles from an aqueous phase to a hydrocarbon phase was achieved by adding salt to the emulsion of hydrocarbon in the aqueous suspension of metal with sodium oleate. The salts were sodium chloride, magnesium chloride, sodium sulfate, etc. The size distributions of the metal particles in the resulting hydrocarbon suspensions were almost the same as that of the original aqueous suspension. The dispersions of colloidal metals in hydrocarbons were stable for a long period of time without the addition of hydrocarbon-soluble stabilizer. The critical phase-transfer concentrations of various salts were determined. The phase-transfer powers of cations were larger than those of anions. Those of divalent and trivalent cations were exceedingly larger than that of the monovalent cation. The concentration of colloidal metal dispersed in hydrocarbon was achieved by using the phase-transfer method.     

Hydrogen‐Bonding Catalysis of Tetraalkylammonium Salts in an Aza‐Diels–Alder Reaction

A piperidine‐derived tetraalkylammonium salt with a non‐coordinating counteranion worked as an effective hydrogen‐bonding catalyst in an aza‐Diels–Alder reaction of imines and a Danishefsky diene. The hydrogen‐bonding interaction between the ammonium salt and an imine was observed as part of a ¹H NMR titration study.     

采用相转移催化法制备苯二甲酰亚胺基甲基聚苯乙烯

以邻苯二甲酰亚胺钾盐为亲核取代试剂, 采用相转移催化体系通过Gabriel反应, 将氯甲基聚苯乙烯转变为苯二甲酰亚胺基甲基聚苯乙烯, 考察了各种因素对相转移催化反应的影响规律, 探讨了相转移催化机理. 结果表明, 采用相转移催化体系, 相转移催化剂将邻苯二甲酰亚胺负离子从水相中转移至油相, 与氯甲基聚苯乙烯发生亲核取代, 顺利地将氯甲基聚苯乙烯大分子链上的氯甲基转变成了甲基化的苯二甲酰亚胺基, 成功地实现了高分子的功能化转变. 影响相转移催化反应的主要因素有催化剂种类与用量、溶剂的极性、油相与水相比例及温度等. 当以十六烷基三甲基溴化铵为催化剂且以甲苯为有机相时, 反应效果最佳, 反应温度为50 ℃时, 反应8 h氯甲基的转化率可达到87%.     

The Steric Course of the Cationic Polymerization of Vinyl and Related Monomers. The Counterion Effect

Polymerization with many triphenylmethyl salts was conducted for α-methylstyrene, isobutyl vinyl ether, t-butyl vinyl ether, and spiro[2,4]hepta-4,6-diene (SHD). The variation of polymer structure (the isotactic unit content for the first three monomer systems and the amount of the 1,4-addition structure for SHD) showed fairly simple correlations with the counteranion size. The results can be interpreted in terms of the tightness of the propagating ion pair within the framework of a theory of the cationic propagation which had been proposed. When the counteranion radius was greater than 3.5 Å, the counteranion exerts a parallel influence on the tightness of the growing ion pair without regard to the monomer structure. However, in the case of smaller counterions, the tightness appears to be determined by the relative sizes of counteranion and monomer. The penta-coordinated counteranions gave rise to the polymer structure which would arise from tighter ion pairs than expected from their sizes alone. The polymer structure was also affected by the initiator concentration in these cases. These results are attributed to peculiar characteristics of penta-coordinated anions.     

Didecyldimethylammonium bromide (DDAB): a universal, robust, and highly potent phase-transfer catalyst for diverse organic transformations

Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in variety of liquid-liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst (PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyanation, bromination, and oxidation under very mild conditions of temperature and mixing. It was confirmed that DDAB is an exceedingly accessible and concurrently a highly liphophilic phase-transfer catalyst. This unprecedented characteristic renders DDAB to be a multipurpose catalyst that functions effectively both in mass transfer controlled and chemically controlled phase-transfer reactions.     

Synthesis of thioether using dimethyloctyl(3-sulfopropyl)ammonium betaine and di-active site quaternary ammonium salt as new phase-transfer catalysts

The novel phase-transfer catalysts S-8 (dimethyloctyl(3-sulfopropyl) ammonium betaine) and DB-2 (di-active site quaternary ammonium salts) were synthesized and employed as the phase-transfer catalysts for synthesizing thioethers from various alkyl bromides of high conversion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.     

Cover Picture: Recent Asymmetric Phase-Transfer Catalysis with Chiral Binaphthyl-Modified and Related Phase-Transfer Catalysts over the Last 10 Years (Chem. Rec. 7/2023)

In this personal account, we describe our recent advances in the three types of phase-transfer catalysis for various transformations including asymmetric induction: Firstly, asymmetric phase-transfer catalysis with Maruoka-type C₂-symmetric chiral biaryl-modified tetraalkylammonium salts and phosphonium salts; Secondly, asymmetric phase-transfer catalysis under base-free and neutral conditions; Thirdly, hydrogen-bonding catalysis using tetraalkylammonium and trialkylsulfonium salts. These three different strategies are illustrated by using various phase-transfer catalyzed transformations.     

Polyaminoalkohole als bifunktionelle Extraktionsmittel für Kupfer(II)

Polyamino Alcohols as Bifunctional Extractants for Copper(II) Polyamino alcohols obtained by the addition of mono- or bifunctional epoxides to disecondary diamines are studied with regard to their applicability to copper(II) extraction. The simple diamino diols IV, V , and VI proved to be inefficient. But, depending on the anion, distribution ratios D up to 1000 were measured with the polyamino alcohol III (chloroform as a diluent) in weakly acidic solution. This is a result of the special structure of the copper(II) complex of III which is both a metal chelate and a substituted ammonium salt. The ammonium part, because of its high affinity to the chloroform phase, has the function of a phase-transfer reagent of the chelate part.     

Concise synthesis of a pentasaccharide related to the anti-leishmanial triterpenoid saponin isolated from Maesa balansae

Concise synthesis of the glycone part (a pentasaccharide) of the anti-leishmanial triterpenoid saponin isolated from Maesa balansae is reported. A late-stage TEMPO-mediated oxidation of a primary hydroxyl group to carboxylic acid has been achieved under phase-transfer conditions. Glycosylations were performed either by thioglycoside or glycosyl trichloroacetimidate activation using sulfuric acid immobilized on silica (H2SO4-silica) in conjunction with N-iodosuccinimide and alone, respectively. H2SO4-silica was proved to be a better choice as promoter than conventional Lewis acid promoters such as TfOH or TMSOTf.     

水杨酸功能化聚苯乙烯的制备及其与铕(Ⅲ)离子配合物荧光特性研究

以氯甲基聚苯乙烯(CMPS)为出发物质,通过两步改性反应,相转移催化的酯化反应(乙醛酸钠为反应试剂)与均相的Schiff碱反应,制备了侧链键合水杨酸(ASA)配基的聚苯乙烯ASAPS,并使之与Eu(Ⅲ)离子配位螯合,制备了高分子-稀土配合物ASAPS-Eu(Ⅲ).重点研究了相转移催化的酯化反应,也初步考察了配合物ASAPS-Eu(Ⅲ)的发光性能.研究结果表明,在季铵盐相转移催化剂作用下,溶解于有机溶剂中的CMPS可有效地与水相中的乙醛酸钠发生酯化反应,形成醛基(AL)化改性的聚苯乙烯ALPS.相转移催化剂的结构与溶剂的极性对相转移催化反应有显著的影响;配合物ASAPS-Eu(Ⅲ)具有Eu(Ⅲ)的特征荧光发射,并产生显著的Antenna效应.     

Phase-transfer catalysis in the chemistry of heterocyclic compounds

Methods for the preparation of heterocyclic systems, the chemical transformations of heterocyclic compounds under conditions of phase-transfer catalysis, and the use of quaternized heterocycles as phase-transfer catalysts are considered.     

Evidence of the electronic factor for the highly enantioselective catalytic efficiency of Cinchona-derived phase-transfer catalysts

[structure: see text] The Cinchona alkaloid-derived quaternary ammonium salts containing 2'-N-oxypyridine and 2'-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H(2)O via hydrogen bonding leading to high enantioselectivity (97 approximately >99% ee), which provides evidence of an electronic factor for the high enantioselective catalytic efficiency in phase-transfer alkylation.     

开链冠醚类似物(Ⅱ)——4-氧安替比林为端基的含氮开链冠醚等效物的合成与研究

本文合成了11种以4-氧安替比林为端基的含氮开链冠醚类似物,通过元素分析和波谱鉴定了它们的结构.报道了4-羟基安替比林O-烷基化的新方法.相转移催化性能研究表明,它们可以作为液-液相或固-液相转移的良好催化剂。     

水相铜/十二烷基取代酰肼-吡啶-N-氧化物催化咪唑的N-芳基化

设计合成了5种新型烷基取代酰肼-吡啶-N-氧化物,并将其作为水相铜催化含氮杂环与芳香碘代物偶联反应的配体.实验结果表明,十二烷基取代酰肼-吡啶-N-氧化物的催化效果最佳.对影响反应的其它条件,如铜源、碱、反应时间和温度等条件进行了优化,建立了最佳反应条件:CuO(10%,摩尔分数),NaOH(1 mmol),TBAB(5%,摩尔分数),L5(20%,摩尔分数),于120℃反应12 h,无需惰性气体保护.在此条件下,芳香碘代物与咪唑偶联反应的产率为60%~92%.该方法的特点是以水作为反应溶剂,长链烷基取代酰肼-吡啶-N-氧化物同时起到了铜催化剂配体和相转移催化剂的作用.     

Radical cation of dibenzothiophene fully annelated with bicyclo[2.2.2]octene units: X-ray crystal structure and electronic properties

New dibenzothiophene 2 fully annelated with bicyclo[2.2.2]octene units was synthesized and oxidized to stable radical cation salt 2(*+)SbCl(6)(-), whose structure was determined by X-ray crystallography. Although the intrinsic electronic structure of 2(*+) is predicted to be close to structure A, an interaction with the counteranion makes structure B contribute significantly. A part of the salt 2(*+)SbCl(6)(-) underwent rearrangement to arenium ion 6(+), whose structure was also clarified by X-ray crystallography.     

Asymmetric phase-transfer reactions under base-free neutral conditions

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.     

相转移催化法实现聚苯乙烯的功能化转变

以对羟基苯甲醛的钠盐为亲核取代试剂,采用相转移催化进行了大分子氯甲基聚苯乙烯的亲核取代反应,将其转变为侧链带有功能性基团醛基的聚苯乙烯;考察了反应条件(如有机溶剂的极性、催化剂种类及用量、有机相与水相之比等)对大分子相转移催化反应的影响,并根据相转移催化反应机理与相关的动力学规律进行了分析.结果表明,通过相转移催化亲核取代反应,可将氯甲基聚苯乙烯大分子链上的氯原子转化,制得侧链带有醛基的聚苯乙烯;溶剂的极性越强,负离子的反应活性也越高;催化剂季铵正离子的亲脂性越强,相转移催化反应的速率越快.当催化剂浓度较低时,四丁基溴化铵比十六烷基溴化铵的催化效果好;当催化剂浓度较高时,十六烷基溴化铵比四丁基溴化铵的催化效果好.另外,有机相与水相之比对相转移催化反应有较大的影响.