Reactions of models of the growth center during anionic polymerization of methacrylate esters

Reactions of α-lithioisobutyric acid esters were studied as models of partial reaction taking place during anionic polymerization of methacrylate esters. The rates of selfcondensation reactions and condensations with nonmetalated esters were determined for these models. In both cases ketoesters were the final products. Besides esters of α,α,α′-trimethylglutaric acid expected according to Michael's reaction scheme the addition of methacrylate esters to α-lithio esters also yielded oligomeric compounds due to repeated addition of methacrylate esters. The α-lithio oligomers of methacrylate esters underwent cyclization condensation which gave rise to esters of substituted cyclohexanonedicarboxylic acids. The alkali metal alkoxides slowed down all the condensation reactions of α-lithio esters investigated here. Such effect of alkoxides also appeared in the cyclization condensation of compounds formed by repeated addition of methacrylate esters, because in the presence of alkoxides the reaction mixture contained a higher amount of higher molecular weight compounds than in a system without alkoxide. The effect of alkoxides observed here is in accordance with the view that the cyclization condensation is one of the termination reactions of the anionic polymerization of methacrylate esters.     

Vinylidene Homologation of Boronic Esters and its Application to the Synthesis of the Proposed Structure of Machillene

Alkenyl boronic esters are important reagents in organic synthesis. Herein, we report that these valuable products can be accessed by the homologation of boronic esters with lithiated epoxysilanes. Aliphatic and electron‐rich aromatic boronic esters provided vinylidene boronic esters in moderate to high yields, while electron‐deficient aromatic and vinyl boronic esters were found to give the corresponding vinyl silane products. Through DFT calculations, this divergence in mechanistic pathway has been rationalized by considering the stabilization of negative charge in the C?Si and C?B bond breaking transition states. This vinylidene homologation was used in a short six‐step stereoselective synthesis of the proposed structure of machillene, however, synthetic and reported data were found to be inconsistent.     

油脂性食品中脂肪酸氯丙醇酯检测方法的研究进展

脂肪酸氯丙醇酯污染是近年来国际上新出现的热点食品安全问题之一,尤其是3-氯-1,2-丙二醇脂肪酸酯(3-MCPD酯)污染问题更为突出。3-MCPD酯在食用油、婴幼儿奶粉等多种食品中的含量较高,以3-MCPD的最大耐受剂量(TDI)评估时所引起的健康风险较高。国外已对3-MCPD酯等氯丙醇酯的检测方法、污染调查和形成机制等开展了不少的研究,国内开展的研究较少。本文主要对油脂食品中3-MCPD酯的检测方法(包括前处理过程,如3-MCPD酯的提取、水解和衍生)、3-MCPD酯总量以及3-MCPD单酯和双酯的检测方法进行了综述。     

Effects of Organic Acids on the Release of Fruity Esters in Water: An Insight at the Molecular Level

It is well known that organic acids (OAs) could affect the flavour of fruit juices and beverages. However, the molecular mechanism of aroma release is still unclear. In this study, the effects of citric acid (CA), L-(-)-malic acid (MA) and L-lactic acid (LA) on the release of six selected esters and their sensory perception were investigated by means of HS-GC-MS analyses and odour detection threshold determination, respectively. Meanwhile, the density functional theory (DFT) calculation was employed to explore the interaction modes between esters and OAs. HS-GC-MS analyses showed that the concentration and the type of OAs regulated the release of esters. The results were basically consistent with the detection threshold change of those esters. The DFT calculation suggested that the main intermolecular interaction was hydrogen bonds, and several esters could form a ternary ring structure with OAs through hydrogen bonds. The interactions can induce the different release behaviours of esters in OAs water solution. The number of carboxyl functional groups in OAs and the spatial conformation of esters appeared to influence the magnitude of the interaction. The above results demonstrated the mechanism of OAs affecting the release of esters and indicated a possible flavour control way by using different OAs and OA concentrations.     

New three-component reaction: novel formation of a seven-membered ring by the unexpected reaction at the gamma-position of the beta-keto ester

[reaction: see text] The novel three-component reaction of aromatic aldehydes, ethylenediamine, and beta-keto esters is described. In this reaction, beta-keto esters react at the gamma-position which is generally unreactive to produce the seven-membered ring compounds. Products have secondary amines and beta-enamino esters, which can serve in further functionalizations to produce molecular diversity.     

Preparation of peptides and active esters by a hydrolysis-dehydration reaction with phosphonites,and the application of the reaction to polymer synthesis

Dehydration reactions accompanied by hydrolysis of the condensation reagent itself, generalized as “hydrolysis-dehydration,” are seen in the formation of amides and esters using phosphites. The proposed concept was shown to be applicable also to the reactions with other phosphorus compounds, such as phosphinites, phosphonites and phosphonates. Aryl esters of these phosphorus compounds were effective for producing amides and esters, whereas alkyl esters were ineffective. Several peptides and active esters of amino acids were prepared using diphenyl phosphonites in the presence of tertiary amines and extended to the preparation of polypeptides and polyamides. Linear polypeptides and high molecular weight polyamides were obtained by means of diphenyl ethylphosphonite in N-methylpyrrolidone containing pyridine.     

A study of the tautomerism of the N-butyl-4(2)-methoxycarbonyl-pyrrolid-3-ones and their hydrochlorides

The tautomerism of N-butyl-2-methoxycarbonyl-4-methylpyrrolid-3-one (I), N-butyl-4-methoxycarbonylpyrrolid-3-one (II), N-butyl-4-methoxycarbonyl-2-methylpyrrolid-3-one (III), N-butyl-4-methoxycarbonylpyrrolid-3-one hydrochloride (IV), and N-butyl-4-methoxy-carbonyl-2-methylpyrrolid-3-one hydrochloride (V) has been studied by UV and IR spectroscopy. It has been found that the esters I–V are highly ionized in aqueous and ethanolic solutions at concentrations of 10^?2–10^?3 M. On passing from methyl cyclopentran-1-one-2-carboxylate to the esters II and III the position of the equilibrium in heptane and CCl₄ shifts in the direction of the keto form. On passing from the esters II and III to the esters IV and V, the position of the equilibrium shifts in the direction of the enol. Meyer's relationship is not satisfied for the esters II and III, while it is satisfied for the esters IV and V. Hypotheses have been put forward on the causes of the phenomena mentioned.     

Novel Methods for the Synthesis of Phosphonate Esters on the Solid Surface

Phosphonate esters are versatile intermediate in organic synthesis. These compounds have found a wide range of application in the areas of industrial, agricultural, and medicinal chemistry owing to their physical properties as well as their utility as synthesis intermediates. The synthesis of some phosphonate esters under solvent free condition was described. These methods are easy, rapid, and high-yielding reactions for the synthesis of phosphonate esters.     

A study of the tautomerism of the N-butyl-4(2)-methoxycarbonyl-pyrrolid-3-ones and their hydrochlorides

The tautomerism of N-butyl-2-methoxycarbonyl-4-methylpyrrolid-3-one (I), N-butyl-4-methoxycarbonylpyrrolid-3-one (II), N-butyl-4-methoxycarbonyl-2-methylpyrrolid-3-one (III), N-butyl-4-methoxycarbonylpyrrolid-3-one hydrochloride (IV), and N-butyl-4-methoxy-carbonyl-2-methylpyrrolid-3-one hydrochloride (V) has been studied by UV and IR spectroscopy. It has been found that the esters I–V are highly ionized in aqueous and ethanolic solutions at concentrations of 10^–2–10^–3 M. On passing from methyl cyclopentran-1-one-2-carboxylate to the esters II and III the position of the equilibrium in heptane and CCl₄ shifts in the direction of the keto form. On passing from the esters II and III to the esters IV and V, the position of the equilibrium shifts in the direction of the enol. Meyer's relationship is not satisfied for the esters II and III, while it is satisfied for the esters IV and V. Hypotheses have been put forward on the causes of the phenomena mentioned.     

Selective reductions. 59. Effective intramolecular asymmetric reductions of alpha-, beta-, and gamma-keto acids with diisopinocampheylborane and intermolecular asymmetric reductions of the corresponding esters with B-chlorodiisopinocampheylborane

A comparison of the stereochemistry of the products obtained from the intramolecular asymmetric reduction of a series of keto acids with (-)-diisopinocampheylborane and intermolecular asymmetric reduction of the corresponding series of keto esters with (-)-B-chlorodiisopinocampheylborane ((-)-DIP-Chloride) has been made. The stereochemistry of the hydroxy acids from the reduction of keto acids is dependent only on the enantiomer of the reagent used. The stereochemistry of the products from the reduction of keto esters is also consistent, except those of aliphatic alpha-keto esters. alpha-, beta-, and gamma-keto acids provide the corresponding hydroxy acids in 77-98% ee, and the alpha- and gamma- keto esters afford the hydroxy esters in 82->or=99% ee. beta-Keto esters do not undergo reduction. Although the reduction of delta-keto acids does not proceed under the same reaction conditions, the reduction of delta-keto esters is facile. All of the products from the reduction of gamma-keto acids and esters and delta-keto esters were converted to the corresponding lactones. This study revealed that DIP-Chloride is an efficient reagent for the reduction of alpha-keto esters at low temperatures.     

Reactions between cellulose diacetate and alkenylsuccinic anhydrides and characterization of the reaction products

Cellulose diacetate (CDA) with degree of substitution (DS) of 2.4 was dissolved in dimethylsulfoxide and reacted with octadecenyl succinic anhydrides (OSAs) using 1-methylimidazole as a promoter. FT-IR and ¹H-NMR analysis of the reaction products revealed that half-esterification occurred on residual hydroxyl groups of CDA by OSA, providing CDA/octadecenyl succinic acid (OSAcid) half esters at yields of more than 90%. The effects of reaction time and temperature on DS of CDA/OSAcid esters were studied in detail. The higher the reaction temperature, the higher the esterification rate to form CDA/OSAcid half esters. The maximum DS values were 0.41 and 0.33 for CDA/n-OSAcid and CDA/i-OSAcid esters, respectively. The original X-ray diffraction pattern of CDA changed with the introduction of OSAcid substituents into CDA, and CDA/OSAcid esters seemed to have thermoplasticity, depending on DS and the chemical structure of the OSAcids. A soil-embedding test of films of CDA and CDA/OSAcid esters indicated that the CDA/OSAcid esters that were prepared maintained the biodegradability of the original CDA.     

Simple thin-layer chromatographic purification procedure for the determination of cholesterol ester fatty acid compositions

A mild procedure for the purification of methyl esters of the fatty acid components of cholesterol esters, from interfering free cholesterol and other contaminating residues, is described. Methyl esters and free cholesterol are formed during the methylation of cholesterol esters. When co-extracted, cholesterol and other contaminating residues interfere with the methyl esters because minute proportions of these residues tend to elute at the same retention times as palmitoleic and stearic acids, to yield unreliable but significantly higher values for palmitoleic (p less than 0.001) and stearic acids (p less than 0.0001), and correspondingly lower values for oleic acid (p less than 0.0001). Purification of methyl esters by thin-layer chromatography eliminates this problem and yields reliable analysis of cholesterol ester fatty acids, without measurable oxidation of unsaturated fatty acids.     

Smart cleavage reactions: the synthesis of benzimidazoles and benzothiazoles from polymer-bound esters

The preparation of an array of benzimidazoles and benzothiazoles from polymer-bound esters is described. Polymer-bound esters were treated with 2-aminothiophenols or 1,2-phenylenediamines in the presence of a Lewis acid to afford the corresponding benzothiazole or benzimidazole cleavage products. The reaction of 2-aminophenols with the polymer-bound esters failed to give the desired benzoxazole products using this procedure.     

Intramolecular catalysis in the mass spectrometer: Mechanisms for loss of methanol from methyl esters upon electron-impact

A review of the literature indicates compelling evidence that: (1) loss of ROH from esters requires protonation of the alkoxy oxygen; (2) the (symmetry forbidden) [1,3] hydrogen migration from protonated carbonyl to alkoxy oxygen does not occur in the mass spectra of esters; (3) hydrogen abstraction in esters occurs almost exclusively to the carbonyl oxygen. Mechanisms are proposed which account for all examples of ROH loss from esters. Alkanol loss from molecular ions in esters requires the presence of a second functional group to act as an intramolecular catalyst, either as a general acid in transferring a proton to the alkoxy oxygen, or as a general base in assisting the [1,3] carbonyl oxygen to alkoxy oxygen proton transfer. Loss of ROH from fragment ions requires proton transfer from an atom α to the positive charge to the alkoxy oxygen. These mechanisms are generalized to include a wide class of bifunctional esters and a selection of natural products.     

A Novel Approach to the Synthesis of Some 2-Aryl Alkanoic Acid Esters

A novel route to the synthesis of some 2-aryl alkanoic acid esters has been achieved. Aromatic nucleophilic substitution of various arene cyclopenta-dienyliron complexes with ethyl ethylacetoacetate and ethyl methylacetoacetate produced the complexed alkanoic acid esters. Photolysis of these complexes resulted in the liberation of the free esters in good yields.     

蔗糖酯的合成研究进展

综述了蔗糖酯的合成方法及工艺的研究进展,并对其反应机理进行了阐述.蔗糖酯的合成方法主要有四种:溶剂法、微乳化法、无溶剂法以及酶催化法.溶剂法采用DMF或DMSO为溶剂,但是这两种溶剂均有毒,限制了蔗糖酯在食品等行业的应用.微乳化法采用丙二醇或水代替溶剂法所使用的有毒溶剂,并加入乳化剂,使反应体系近似为均相体系.无溶剂法则是通过在反应体系中加入乳化剂或表面活性剂等使熔融相成均一相,反应平稳.但是一般无溶剂法反应温度较高,反应不易进行,产率低,且产品质量得不到保证.酶催化合成法是一种新的生物合成方法,采用生物酶代替传统的催化剂合成蔗糖酯,该法催化活性高、反应条件温和、选择性强、产物易分离等优点.文中还对蔗糖酯粗品的纯化工艺进行了介绍.     

Separation of the insecticidal pyrethrin esters by capillary electrochromatography

A simple, rapid technique for the direct separation and quantification of the six insecticidally active pyrethrin esters in typical extracts and commercial formulations by capillary electrochromatography (CEC) has been described. The separation of the pyrethrin esters was achieved by optimizing several parameters including the length of stationary phase, the mobile phase composition and column temperature. The mobile phase composition had the most pronounced effect toward resolving these structurally similar compounds. A ternary mobile phase composed of acetonitrile-aqueous buffer-tetrahydrofuran (55:35:10) provided the elutropic solvent strength needed to resolve the six esters from an extract mixture in under 16 min. A 25 cm packed bed of Hypersil 3 microm C18 stationary phase was used with the ternary mobile phase at 25 degrees C and 30 kV voltage. These conditions also yielded excellent separation of the pyrethrin esters in two different commercially available insecticidal formulations. In addition, the developed CEC method was shown to be a fast and easy way of quantifying the amount of these esters in typical pyrethrin formulations.     

Detailed profiles of 7-O-acyl esters in plankton and shellfish from the Portuguese coast

In bivalve mollusks from the Portuguese coast contaminated by diarrhetic shellfish poisoning (DSP), most of the parent toxins, okadaic acid (OA) or dinophysistoxin-2 (DTX2), are found esterified, and toxicity assessment is only performed after an alkaline hydrolysis step to recover the parent molecules in their free form. The presence of 7-O-acyl esters with fatty acids (FAs) has already been confirmed previously in Mytilus galloprovincialis and Donax trunculus samples. This paper reports the presence of acyl esters in a wider range of estuarine and offshore bivalve species found by direct analysis in LC-MS. The total of acyl esters found in each species represented the percentages commonly found by hydrolysis in those species in previous years, justifying the majority of the esters commonly found in shellfish. This implies that any diol esters remaining after digestion of toxic microalgae would represent only a minor contribution to the ester's contents. Esters with C14:0, C16:0, C16:1, C20:5 and C22:6 FAs were the most abundant, followed by esters with C18:0, C18:1, C18:2, C18:3 and C18:4. This is the first report of OA and DTX2 esters with odd FAs: C15:0, C17:0, C17:1, and probably a branched FA: iso-C16:0. Esters with iso-C16:0 where found in high percentages particularly in two species of estuarine clams, where they represented 13-34% of total esters found. Esters were also found in plankton, predominantly with C16:0. Total esters in plankton were not higher than 10%, not enough to justify per se the high levels found in bivalves.     

Conjugate reduction of aryl acrylates with tributyltin hydride in the presence of magnesium bromide diethyl etherate

The conjugate reduction of aryl acrylates performed with tributyltin hydride in the presence of magnesium bromide diethyl etherate in dichloromethane gave the corresponding saturated esters in moderate to high yields. The reduction of α-methylene-γ-benzyloxycarboxylic acid esters proceeded syn-selectively, but α-methylene-β-oxycarboxylic acid esters afforded reductive elimination products under the reaction conditions.     

1-(2,4,6-triisopropylphenyl)ethylamine: a new chiral auxiliary for the asymmetric synthesis of gamma-amino acid derivatives

The title compound has proven to be an excellent chiral auxiliary for nitrones in SmI2-mediated reductive coupling with alpha,beta-unsaturated esters. A variety of such nitrones, prepared from aldehydes and enantiopure N-hydroxy-1-(2,4,6-triisopropylphenyl)ethylamine, afforded gamma-N-hydroxyamino esters in high yields and diastereomeric purity. These adducts, readily available as either enantiomer, could be transformed into gamma-N-acetoxyamino esters, N-Boc-gamma-amino esters, and gamma-lactams.