A mild and efficient reaction for conversion of carboxylic acids into acid bromides with ethyl tribromoacetate/triphenylphosphine under acid-free conditions

Acid bromides were prepared efficiently from carboxylic acids with readily available ethyl tribromoacetate and triphenylphosphine at room temperature under neutral conditions. The present process is applicable to the preparation of various acid bromides from aromatic and aliphatic carboxylic acids. Aromatic carboxylic acids were found to be more reactive than aliphatic carboxylic acids under reaction conditions.     

High-performance CE: an effective method to study lactonization of alpha2,8-linked oligosialic acid

A sensitive and efficient method using high-performance CE (HPCE) and neuraminidase hydrolysis was developed to study the lactonization and hydrolysis of alpha2,8-pentasialic acid. Eleven lactone species of pentasialic acid formed in glacial acetic acid were detected and classified into three groups based on the number of carboxylic acids: monolactones with four carboxylic acids, dilactones with three carboxylic acids, and trilactones with two carboxylic acids. These lactones eluted between the original pentamer (with five carboxylic acids) and the fully lactonized species (with one carboxylic acid) in HPCE. Eight of the isomers were identified by hydrolysis with neuraminodase. Results obtained from previous reports and from this study together reveal a general rule for predicting the subtle difference in the acidity of each carboxylic acid in oligosialic acids: the closer the carboxylic acid is to the nonreducing end, the more acidic it is. Therefore, the elution order of lactone isomers having the same number of carboxylic groups can be predicted from the position of the free carboxylic groups in pentasialic acid. We used this principle and the results of hydrolysis with neuraminidase to identify hexamer lactone isomers separated by HPCE.     

Mild and efficient boronic acid catalysis of Diels-Alder cycloadditions to 2-alkynoic acids

The concept of boronic acid catalysis (BAC) for the activation of unsaturated carboxylic acids is applied to the Diels-Alder cycloaddition between 2-alkynoic acids as dienophiles and various dienes. These [4+2] cycloadditions produce cyclohexadienyl carboxylic acids, which can be oxidized in situ to produce polysubstituted aromatic carboxylic acids. The boronic acid catalyst is suspected to provide activation by a LUMO-lowering effect of the unsaturated carboxylic acid likely via a covalent, monoacylated hemiboronic ester intermediate.     

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.     

Facile synthesis of methylthiomethyl esters through Pummerer-type rearrangement of carboxylic acids and DMSO under metal-free conditions

A green and cost-effective Pummerer-type rearrangement between readily accessible carboxylic acids and DMSO has been achieved under metal-free conditions in satisfactory to excellent yields. The transformation for the synthesis of valuable methylthiomethyl esters is shown to be a convenient strategy for various (hetero)aromatic acids, α,β-unsaturated carboxylic acids and saturated alkyl carboxylic acids with good functional group tolerance.     

Silver‐Catalyzed Arylation of (Hetero)arenes by Oxidative Decarboxylation of Aromatic Carboxylic Acids

A long‐standing challenge in Minisci reactions is achieving the arylation of heteroarenes by oxidative decarboxylation of aromatic carboxylic acids. To address this challenge, the silver‐catalyzed intermolecular Minisci reaction of aromatic carboxylic acids was developed. With an inexpensive silver salt as a catalyst, this new reaction enables a variety of aromatic carboxylic acids to undergo decarboxylative coupling with electron‐deficient arenes or heteroarenes regardless of the position of the substituents on the aromatic carboxylic acid, thus eliminating the need for ortho‐substituted aromatic carboxylic acids, which were a limitation of previously reported methods.     

Purification and dual-column HPLC determination of carboxylic acids in tissues,phloem and xylem saps of soybean plants

Summary A method for the determination of carboxylic acids in phloem sap, xylem sap and tissue extracts of soybean plants is reported. An easy and rapid procedure for the purification of the samples has been developed. Carboxylic acids were determined by isocratic HPLC. The separation of the first-eluting carboxylic acids and the unretained solutes have been improved by connecting an ion-exclusion column to the reversed-phase column. This chromatographic method also improved the separation of some carboxylic acids. The optimized method was applied to the determination of the carboxylic acids transported in xylem and phloem saps of soybean plants, or accumulated in their root tissues.     

Resolution of carboxylic acids using copper(I)-promoted removal of propargylic esters under neutral conditions

A method for the optical resolution of carboxylic acids is described. Condensation of racemic carboxylic acids with chiral terminal propargyl alcohols gave separable diastereomeric esters. Chromatographic separation followed by heating the individual diastereomers in methanol with catalytic copper(I) halide regenerated the carboxylic acids in good yields and in enantiomeric ratios of ≥94%. This method is particularly useful for the resolution of carboxylic acids that are incompatible with conventional ester hydrolysis.     

A highly convenient,efficient, and selective process for preparation of esters and amides from carboxylic acids using Fe(3+)-K-10 montmorillonite clay

In the presence of Fe(3+)-K-10 montmorillonite clay as a catalyst, aliphatic carboxylic acids selectively produced the corresponding esters in the presence of aromatic carboxylic acids by treatment with alcohols. Both the aliphatic and aromatic carboxylic acids formed the amides by reacting with the aliphatic amines, but only the aliphatic carboxylic acids yielded the anilides by treatment with aromatic amines. The catalyst is recoverable and recyclable.     

Mass spectrometric analysis for carboxylic acids as viable markers of petroleum hydrocarbon biodegradation

The characterization of metabolites, which are considered markers of bacterial degradation of hydrocarbons, is gaining in importance. Over the years, carboxylic acids have served as useful indicators of aerobic and anaerobic hydrocarbon biodegradation. This interest has been accompanied by the extensive and robust development of analytical methods for monitoring, untargeted identification, and specific and sensitive determination of carboxylic acids in complex matrices. This review discusses critically the state-of-the-art of mass spectrometry as a reliable analytical technique to identify and quantify carboxylic acid metabolites. Attention is paid to sample pre-treatment, selective group pre-concentration, and gas and liquid chromatography preceding mass spectrometry to alleviate matrix effects and ionization discrimination. Recent specific applications of mass spectrometry in monitoring carboxylic acids for assessing hydrocarbon biodegradation are reviewed. Presently, no single technique is sufficient for holistic profiling of carboxylic acids. The direct characterization of carboxylic acids by mass spectrometry is the ultimate goal but despite recent significant developments, challenges persist.     

Lipase catalyzed synthesis of epoxy-fatty acids

Lipase catalyzed synthesis of epoxy-fatty acids from unsaturat-ed carboxylic acids was investigated. Under mild conditions unsaturated carboxylic acids were converted to peroxycarboxylic acids by lipase with hydrogen peroxide, then the unsaturated peroxycarboxylic acids epoxidised the C = C bond of themselves.     

Recent topics in the syntheses of β-keto carboxylic acids and the derivatives

β-Keto carboxylic acids are key intermediates in organic syntheses, used for the development of fine chemicals, natural products, and various biologically relevant molecules. Their utilities stem from the structural features and facile bond formations, e.g., asymmetric reduction of carbonyl groups for the synthesis of β-hydroxy carboxylic acids and conjugated addition reactions through decarboxylative enolate nucleophiles, which utilize the amphiphilic reactivity of β-keto carboxylic acids. Despite their versatility and utilities, development of efficient and straightforward synthetic methods for β-keto carboxylic acids has not attracted considerable attention owing to their instability. As efficient synthetic strategies for β-keto carboxylic acids and their derivatives, reactions of α-diazoesters, acylation of malonate anions, cross-coupling reactions, and CO₂ insertion reactions are summarized in this review.     

O‐Arylation of Carboxylic Acids using (Phenyl)[2‐(trimethylsilyl)phenyl]iodonium Triflate as a Precursor of Arynes

Using (phenyl)[2‐(trimethylsilyl)phenyl]iodonium triflate as a precursor of arynes, Larock's method for O‐arylation of carboxylic acids and arynes was developed. A variety of acids including simple aliphatic carboxylic acids, aromatic carboxylic acids, allenoic acids, and p‐toluenesulfonic acid under mild reaction conditions could generate the aryl esters.     

Significant improvement in the pore properties of SBA-15 brought about by carboxylic acids and hydrothermal treatment

A comparative study of the pore properties of SBA-15 samples prepared under nonhydrothermal and hydrothermal conditions, in the absence and presence of carboxylic acids such as succinic, tartaric and citric acids has been carried out. In the absence of carboxylic acid, flake-like and spheroid particles were generally obtained irrespective of the preparative procedures. On the other hand, stirring of the pre-mix induces a rod-like morphology in presence of carboxylic acids. The samples prepared under non-hydrothermal conditions exhibit a higher degree of silicate condensation compared to those synthesized under hydrothermal conditions. SBA-15 samples prepared under hydrothermal conditions show higher values of the d (100) spacing independent of the presence of carboxylic acids. Presence of carboxylic acids as well as hydrothermal treatment improves the pore properties of SBA-15.     

A novel derivatization reagent possessing a bromoquinolinium structure for biological carboxylic acids in HPLC‐ESI‐MS/MS

A novel bromoquinolinium reagent, i.e. 1‐(3‐aminopropyl)‐3‐bromoquinolinium bromide (APBQ), was synthesized for the analysis of carboxylic acids. A simple and practical precolumn derivatization procedure using the APBQ in RP chromatography and MS (HPLC‐MS) has been developed using bile acids and free fatty acids, as the representative carboxylic acids in biological samples. The APBQ efficiently reacted with carboxylic acids at 60°C for 60 min in the presence of N,N‐dicyclohexylcarbodiimide and pyridine as the activation reagents. Because the APBQ possesses a bromine atom in the structure, the identification of a series of carboxylic acids was easily achieved due to the characteristic bromine isotope pattern in the mass spectra. The APBQ also has a quaternary amine structure, thus the positively charged derivatives are predominate for the highly sensitive detection of carboxylic acids. The APBQ was successfully applied to the selective determination of biological carboxylic acids in human plasma. The bile acids (chenodeoxycholic acid and deoxycholic acid) and several saturated (stearic acid and palmitic acid) and unsaturated free fatty acids (oleic acid and linoleic acid) were reasonably determined by HPLC‐MS under the proposed procedure. Based on the results of analyses of human plasma and saliva, the proposed procedure using APBQ seems to be applicable for the qualitative and quantitative analyses of a series of carboxylic acids in biological samples.     

Polymer Supported Synthesis of 2,3,4,6-Tetra-O-Acetyl-β-D-Glucopyranosyl Esters of Aromatic Carboxylic Acids

Aromatic carboxylic acids bound to Amberlyst A-26 react with α-acetobromoglucose to form 2,3,4,6-tetra-O-acetyl-1-0-aroyl-β-D-glucopy ranose derivatives in good yield. Glucosylation occurs satisfactorily with carboxylic acids and nitrophenols (pKa 7–4), but not with phenols whose pKa values are higher (pka ～ 10). Selective glucosylation at the carboxylic group is easily achieved in the case of phenolic acids.     

Preparation of ferrocenyl imidazolines using bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate

An efficient synthesis of ferrocenyl imidazolines starting from ferrocenyl carboxylic acids has been developed. Bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate was used to convert smoothly ferrocenyl carboxylic amides bearing an amine side chain, derived from ferrocenyl carboxylic acids and 1,2-diamines, to their corresponding ferrocenyl imidazolines.     

含氧光敏引发体系的研究——Ⅲ.二苯甲酮/叔胺/氧/羧酸引发体系的研究

本文研究了含氧的二苯甲酮/叔胺引发体系中添加羧酸的作用,实验结果表明:体系中添加羧酸可以大幅度加快聚合反应。聚合速度与使用羧酸的浓度、系统中氧的含量、羧酸的碳链长度以及酸性等因素有关,并讨论了羧酸的加速机理。采用此体系引发MMA本体聚合时,量子收率达8.7×10~2。     

Direct Ruthenium‐Catalyzed Hydrogenation of Carboxylic Acids to Alcohols

The “green” reduction of carboxylic acids to alcohols is a challenging task in organic chemistry. Herein, we describe a general protocol for generation of alcohols by catalytic hydrogenation of carboxylic acids. Key to success is the use of a combination of Ru(acac)₃, triphos and Lewis acids. The novel method showed broad substrate tolerance and a variety of aliphatic carboxylic acids including biomass‐derived compounds can be smoothly reduced.     

Directly Bridging Indoles to 3,3′‐Bisindolylmethanes by Using Carboxylic Acids and Hydrosilanes under Mild Conditions

A straightforward Lewis acid‐promoted protocol for 3,3′‐bisindolylmethanes (BIMs) synthesis by reductive alkylation of indoles at the C3 position with carboxylic acids in the presence of hydrosilane was developed for the first time. Instead of aldehydes, more readily available, stable, and easy‐to‐handle carboxylic acids have been employed as alternative alkylating agents. As an efficient organocatalyst, B(C₆F₅)₃ enables the reductive alkylation of various substituted indole derivatives with carboxylic acids with up to 98 % yield at room temperature and under neat conditions. This metal‐free strategy offers an alternative approach for the direct functionalization of indoles to BIMs with carboxylic acids and such protocol allows selective reduction of carboxylic acid to aldehyde in combination with C−C bond formation.