Scandium Trifluoromethanesulfonate as an Extremely Active Lewis Acid Catalyst in Acylation of Alcohols with Acid Anhydrides and Mixed Anhydrides

Scandium trifluoromethanesulfonate (triflate), which is commercially available, is a practical and useful Lewis acid catalyst for acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The remarkably high catalytic activity of scandium triflate can be used for assisting the acylation by acid anhydrides of not only primary alcohols but also sterically-hindered secondary or tertiary alcohols. The method presented is especially effective for selective macrolactonization of omega-hydroxy carboxylic acids.     

Highly Efficient Esterification of an Equimolar Amount of Carboxylic Acids and Alcohols Catalyzed by ZrOCl_2·8H_2O

Esterification of carboxylic acids with alcohols is one of the most fundamental and useful transformations in organic synthesis. The most common catalysts are H2SO4 and TsOH. However, H2SO4 or TsOH-catalyzed esterification procedure has some problems such as corrosion, side reactions, difficulty in separation. Hence, recently, various solid acid catalysts such as ion-exchanged resins, molecular sieve, and heteropoly acids etc. have been employed for esterification reaction. However, the s…     

酸性聚乙烯基吡咯烷酮—杂多酸杂化催化剂的合成及其催化酯化反应性能

合成并表征了聚乙烯基吡咯烷酮修饰的杂多酸杂化催化剂PVP-PW,比较了它与其它催化剂上乙酸和正丁醇的酯化反应性能.结果表明,PVP-PW是催化酯化反应的高效多相催化剂,所得酯收率和选择性分别高达98.4%和100%;反应结束后,催化剂通过简单过滤即可分离回收,重复使用6次后,其催化活性没有明显下降.通过改变反应底物羧酸和醇,发现催化剂PVP-PW在众多酯化反应中均具有较高的催化活性.     

Selective Esterification Reaction Involving Hexaalkyl Guanidinium Chloride Catalyst

A new efficient and selective esterification reaction of carboxylic acids with chloroformates is described using silica-supported catalyst (PBGSiCl). The chemioselectivity of the reaction was high particularly for sterically hindered carboxylic acids supported by a single pathway reaction.     

Selective Esterification of Aliphatic Carboxylic Acids in the Presence of Aromatic Carboxylic Acids Over Monoammonium Salt of 12‐Tungstophosphoric Acid

Monoammonium salt of 12‐tungstophosphoric acid [(NH₄)H₂PW₁₂O₄₀] was found to be a practical and useful heterogeneous catalyst for an efficient and selective esterification of aliphatic carboxylic acids with alcohols in the presence of aromatic carboxylic acids. The heteropoly acid–based heterogeneous catalyst has the advantages of a simple workup procedure, water insolubility, and good activity.     

Direct Esterification of Carboxylic Acids with Alcohols Catalyzed by Iron(III) Acetylacetonate Complex

Direct condensation of carboxylic acids and alcohols with electronic, steric, and functional group variations was carried out using the environmentally benign, moisture-stable, inexpensive, and recoverable iron(III) acetylacetonate [Fe(acac)₃] as catalyst (5 mol%). This iron salt efficiently catalyzed the esterification of several primary and secondary alcohols in refluxing xylene, without the need for a dehydration reagent. The chemoselectivity of the proposed protocol was demonstrated by the selective esterification of primary alcohol functionality in racemic 1-phenylethane-1,2-diol with benzoic acid. The esterification was also applicable to unmasked α -hydroxyacid, guasiaromatic, heterocyclic, and N-protected amino acids.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

硅磷酸铝分子筛催化羧酸的酯化反应研究

用新型硅磷酸铝分子筛和改性的硅磷酸铝分子筛催化脂肪族羧酸与脂肪族醇的酯化反应，以正戊酸分别与正丙醇、正丁醇、正戊醇和正辛醇以及正辛醇分别与乙酸、丙酸、正丁酸、正戊酸和正己酸的酯化反应作为探针实验进行了系统研究，实验结果显示，改性的硅磷酸铝分子筛比不改性的硅磷酸铝分子筛具有更高的酯化催化活性，实验发现，反应物的结构对酯化反应产生了显著的影响，文章揭示了新型硅磷酸铝分子筛和改性的硅磷酸铝分子筛对于羧酸的直接酯化反应的系列规律性。     

Esterification of Octanoic Acid with Octanol in Microemulsion and Emulsion System

The esterification of octanoic acid with octanol in microemulsion and emulsion system is studied. In the presence of 5–10% dodecylbenzene-sulfonic acid (DBSA), which is a surfactant-type catalyst, high conversion of esterification can be given both in microemulsion and in emulsion system. Compared with emulsion system, single-phase microemulsion is a more effective reaction system for esterification, with the advantages of comparatively little influence by the amount of water, no need of hard stirring, and stable state when laid long. The esterification of other fatty acids and alcohols in this reaction system were also accomplished in favorable conversion.     

Esterification of Carboxylic Acids and Diacids by Trialkyl Borate under Solvent- and Catalyst-Free Conditions

Esterification or transesterification reactions are usually carried out in the presence of homogeneous or heterogeneous catalysts. However, recently a new method was reported for the esterification of carboxylic acids by tributyl borate under solvent- and catalyst-free conditions. In order to show the synthetic ability of trialkyl borate esters in the esterification reactions, here, the esterification of other carboxylic acids and diacids by tributyl-, triisoamyl-, and tribenzyl borate under the same conditions were reported. Some of the prepared ester and diester products have found wide applications as plasticizers and synthetic ester base lubricants. The esterification reactions have been cleanly carried out in the absence of any solvent under catalyst-free conditions. The maximum rate belongs to isoamyl trichloroacetate （VIb） which reached about 76% within about 6.5 h. On the basis of obtained findings, it seems that electron withdrawing groups on carboxylic acid facilitate the esterification reaction.     

Esterification and Chemoselective Synthesis of R-Tetrahydrothiazo-2- thione-4-carboxylic Esters Catalyzed by TiCl4

A series of esters of R-tetrahydrothiazo-2-thione-4-carboxylic acid[R-TTCA] was synthesized by direct esterification of R-TTCA with alcohols(CH3OH,C2H5OH,n-C3H7OH,i-C3H7OH,n-C4H9OH,sec-C4H9OH)in the presence of TiCl4 as the catalyst at room temperature without using any other solvent or dehydrant in high yields,91.6%-99.1% for primary alcohols and 55%- 80% for secondary alcohols.The catalyst has a strong chemoselective activity for the esterification of primary alcohols with R-TTCA in the presence of secondary alcohols.Owing to high yield,high chemoselectivity,and mild conditions used,this is an efficient method for the esterification of primary alcohols with R-TTCA.     

N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate as a highly active and selective esterification catalyst

N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate (1) was found to be a very active esterification catalyst that promotes condensation of equal mole amount of carboxylic acids and alcohols under mild conditions. This catalyst is also highly selective towards carboxylic acid and alcohol substrates at ambient temperature.     

Amberlyst 15: A Practical,Mild and Selective Catalyst for Methyl Esterification of Carboxylic Acids.1

Mild and selective methyl esterification of carboxylic acids are realized using Amberlyst 15 as acid catalyst in methanol. No race mization, epimerization or ketalization products have been observed with this method. Excellent results are obtained in the esterifications of bile acids.     

Esterification of free fatty acids (Biodiesel) using nano sulfated-titania as catalyst in solvent-free conditions

Nano sulfated titania was tested as catalyst for esterification of free fatty acids, specially methanolic and ethanolic esterification of stearic acid (biodiesels). Factorial design evidenced a positive effect of reaction temperature, amount of catalyst, and solvents on ester conversion. This nano-sized sulfated titania has been prepared by a sol-gel hydrothermal process. This prepared sulfated titania showed high catalytic activity in direct esterification of fatty acids as well as benzoic acids with various alcohols and phenols under solvent-free conditions. This method is of great value because of its environmentally benign character, easy handling, high yields, convenient operation, and green. FT-IR studies are shown that the catalyst can be reused for acylation without loss of catalytic activity.     

PEG型酸性温控离子液体中芳香酸和醇的酯化反应

报道了该催化体系在芳香酸和醇酯化反应中的应用. 研究发现, 该离子液体具有优良的催化性能, 产品易分离, 催化剂可循环使用且活性不降低, 催化剂不易流失, 实现了均相催化剂的高效回收和再利用.     

3-氧杂多氟戊磺酸催化羧酸的酯化反应及其铜（Ⅱ)盐催化芳烃的Friedel-Crafts酰基化反应

研究使用催化量的3-氧杂多氟戊磺酸催化等摩尔的羧酸和醇的酯化反应和催化 量3-氧杂多氟戊磺酸铜催化芳烃的Friedel-Crafts酰基化反应，并取得较好结果．     

3-氧杂多氟戊磺酸催化羧酸的酯化反应及其铜(II)盐催化芳烃的Friedel-Crafts酰基化反应

研究使用催化量的 3 氧杂多氟戊磺酸催化等摩尔的羧酸和醇的酯化反应和催化量 3 氧杂多氟戊磺酸铜催化芳烃的Friedel Crafts酰基化反应 ,并取得较好结果 .     

高效钴氧化物催化羧酸可控加氢制醇（英文）

羧酸选择加氢是合成醇的重要方法,廉价高效的催化体系仍然在探索中.我们利用地球上储量丰富的钴氧化物作为催化剂,通过控制催化反应过程,进而实现高选择性地催化羧酸加氢制备醇.一系列含有不同官能团的羧酸可以被选择加氢至相应的醇类化合物,反应选择性可以满足工业生产要求.通过一系列的谱学表征以及理论计算,我们证实了钴氧化物在羧酸选择加氢反应中的优选活性位点位为氧化亚钴,从而建立了催化剂与反应活性之间的构效关系,为催化剂的理性设计提供指导.首先,我们选取硬脂酸加氢反应作为模型反应,通过对地球上储量丰富的氧化镍、四氧化三铁和四氧化三钴的催化活性对比发现,四氧化三钴催化剂活性最高,在473 K,2 MPa氢气条件下,反应速率可以达到1.2 mmol/(h·g).对四氧化三钴催化剂进行不同温度的预还原处理,我们发现催化剂的活性得到显著提高,其中573 K还原的样品活性最高,反应速率可以达到7.3 mmol/(h·g),要远远高于贵金属催化剂Pd/C(0.6 mmol/(h·g))和Pt/C(1.8 mmol/(h·g)).XRD结果表明,随着还原处理温度的不断升高,催化剂由四氧化三钴变为氧化亚钴,最终变为金属态的钴.当还原温度为573 K时,催化剂的组成为单一相氧化亚钴.XPS测试结果表明,当还原温度为573 K时,样品中只含有Co~(2+)的信号峰,并且Co/O的比例为1/1,进一步证明样品是纯态的氧化亚钴.从TEM照片中可以发现,在原始的四氧化三钴样品中观察到晶面间距为0.467和0.244 nm,分别对应四氧化三钴的(111)和(311)晶面.而对于573 K还原的样品只观察到一种晶面间距(0.246 nm),对应氧化亚钴的(111)晶面.结合表征手段和硬脂酸催化加氢活性结果,我们得出氧化亚钴是573 K还原样品催化羧酸加氢反应的活性位点.理论计算结果进一步证实了这个实验结论.理论计算结果表明,在氧化亚钴(111)晶面,硬脂酸加氢转换为十八醇是非常快速和高效的,然而,对于氢解C-C键和C-O键,需要耗费更高的能量,能垒约为1.2 e V.因为硬脂酸的吸附远远强于十八醇的吸附,硬脂酸的存在会抑制十八醇氢解形成烯烃的反应,只有当硬脂酸酸完全转化为十八醇,才会发生随后的氢解反应.通过控制催化反应过程,可以实现在氧化亚钴(111)晶面高选择性催化酸加氢至醇,也就是反应控制催化过程.基于氧化亚钴在硬脂酸加氢制备十八醇上的优异催化性能,我们进一步研究了一系列含有不同官能团的羧酸化合物的催化加氢,发现氧化亚钴表现出良好的官能团容忍度,可以实现高效、广谱的酸选择加氢至醇反应.     

ZrOCl2 x 8H2O: an efficient, cheap and reusable catalyst for the esterification of acrylic acid and other carboxylic acids with equimolar amounts of alcohols

Esterifications of carboxylic acids with equimolar amount of alcohols could be efficiently catalyzed by ZrOCl(2) x 8H(2)O. Acrylate esters were obtained in good yields under solvent-free conditions at ambient temperature. The esterification of other carboxylic acids with alcohols also proceeded at ambient temperature or at 50 oC to afford esters in high yields. If the esterification was performed in toluene under azeotropic reflux conditions to remove water, both the catalytic activity of ZrOCl(2) x 8H(2)O and the rate of esterification could be increased greatly. Furthermore, in the present catalytic system, the esters could be easily separated from the reaction mixtures and the catalyst could be easily recovered and reused.     

Effective esterification of carboxylic acids using (6-oxo-6H-pyridazin-1-yl)phosphoric acid diethyl ester as novel coupling agents

(6-Oxo-6H-pyridazin-1-yl)phosphoric acid diethyl esters (3) are efficient and selective coupling agents for equimolar esterification of carboxylic acids and alcohols. Esterification of aliphatic and aromatic carboxylic acids with aliphatic and aromatic alcohols using 3 afforded the corresponding esters chemoselectively in good to excellent yield.     

Boric acid catalyzed chemoselective esterification of alpha-hydroxycarboxylic acids

Boric acid catalyzes the selective esterification of alpha-hydroxycarboxylic acids without causing significant esterification to occur with other carboxylic acids. The procedure is simple, high-yielding, and applicable to the esterification of alpha-hydroxy carboxylates in the presence of other carboxylic acids including beta-hydroxyacids within the same molecule. [reaction: see text]