Die Oxydation von Alkoholen mit Bleitetraacylaten; Einfluss der Acylreste bei der thermischen Reaktion

The competitive thermal oxidation of a 6β-hydroxy steroid (to a 6β, 19-ether) and the thermal oxidative decarboxylation of various carboxylic acids by lead⁴⁺ was investigated. The alcohol oxidation is faster than acetate and benzoate oxidation, about as fast as the oxidative decarboxylation of higher primary carboxylic acids (propionic, butyric acid), and much slower than the oxidative decarboxylation of secondary and tertiary carboxylic acids.     

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

The aerobic decarboxylation of saturated carboxylic acids (from C₂ to C₅) in water by TiO₂ photocatalysis was systematically investigated in this work. It was found that the split of C¹? C² bond of the acids to release CO₂ proceeds sequentially (that is, a C₅ acid sequentially forms C₄ products, then C₃ and so forth). As a model reaction, the decarboxylation of propionic acid to produce acetic acid was tracked by using isotopic‐labeled H₂¹⁸O. As much as ≈42 % of oxygen atoms of the produced acetic acids were from dioxygen (¹⁶O₂). Through diffuse reflectance FTIR measurements (DRIFTS), we confirmed that an intermediate pyruvic acid was generated prior to the cut‐off of the initial carboxyl group; this intermediate was evidenced by the appearance of an absorption peak at 1772 cm^?1 (attributed to C?O stretch of α‐keto group of pyruvic acid) and the shift of this peak to 1726 cm^?1 when H₂¹⁶O was replaced by H₂¹⁸O. Consequently, pyruvic acid was chosen as another model molecule to observe how its decarboxylation occurs in H₂¹⁶O under an atmosphere of ¹⁸O₂. With the α‐keto oxygen of pyruvic acid preserved in the carboxyl group of acetic acid, ≈24 % new oxygen atoms of the produced acetic acid were from molecular oxygen at near 100 % conversion of pyruvic acid. The other ≈76 % oxygen atoms were provided by H₂O through hole/OH radical oxidation. In the presence of conduction band electrons, O₂ can independently accomplish such C¹? C² bond cleavage of pyruvic acid to generate acetic acid with ≈100 % selectivity, as confirmed by an electrochemical experiment carried out in the dark. More importantly, the ratio of O₂ participation in decarboxylation increased along with the increase of pyruvic acid conversion, indicating the differences between non‐substituted acids and α‐keto acids. This also suggests that the O₂‐dependent decarboxylation competes with hole/OH‐radical‐promoted decarboxylation and depends on TiO₂ surface defects at which Ti_4c sites are available for the simultaneous coordination of substrates and O₂.     

Visible-light-promoted oxidative decarboxylation of arylacetic acids in air: Metal-free synthesis of aldehydes and ketones at room temperature

A metal-free photocatalytic oxidative decarboxylation reaction at room temperature was developed for the synthesis of aromatic aldehydes and ketones from the corresponding arylacetic acids. The reaction was realized under blue-light irradiation by adding 1 mol% of 4CzIPN as photocatalyst and air as oxidant. This reaction represents a novel decarboxylation of a sp³-hybridized carboxylic acids without traditional heating, additional oxidants, and metal reagents under mild conditions.     

Novel photopolymerizations initiated by alkyl radicals generated from photocatalyzed decarboxylation of carboxylic acids over oxide semiconductor nanoparticles: Extended photo-Kolbe reactions

Polymerizations of vinyl acetate are photocatalyzed by TiO₂ nanoparticles in presence of carboxylic acids including propionic acid, n-butyric acid and pivalic acid. Nuclear magnetic resonance (NMR) analysis using ¹³C-labeled n-butyric acid as the probing molecule demonstrates that the polymerization of vinyl acetate is initiated by alkyl radicals generated from photocatalytic decarboxylation of the carboxylic acid. A universal mechanism is established with extending the photo-Kolbe reaction from acetic acid to the carboxylic acids with longer chains. Kinetics studies find that n-butyric acid has higher initiation rate than acetic acid, indicating more efficient decarboxylation for butyric acid than acetic acid in their aqueous solutions. It is proved that carboxylates participate in the decarboxylation. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectra are obtained with aqueous solutions of the carboxylic acids in contact with a layer of the TiO₂ nanoparticles, and the observations are discussed with respect to the interaction between the TiO₂ and carboxylic acids.     

Charge development in the transition state for decarboxylations in water: spontaneous and acetone-catalyzed decarboxylation of aminomalonate

A covalent imminium adduct, formed by condensation of aminomalonate with acetone, undergoes decarboxylation (k = 0.03 s-1 at 25 degrees C) in water 30 000 times more rapidly than does aminomalonate in the absence of acetone. A Br?nsted plot of the observed rates of decarboxylation of these and other ionized carboxylic acids, as a function of the pKC-H values of the carbon acids generated by their decarboxylation, exhibits a betalg value of 0.7, indicating that the structures of the transition states for decarboxylation of the carboxylate forms of these acids approaches the structures of the carbanions generated by their decarboxylation. On the basis of an estimated pKC-H value for benzene in water ( approximately 43), extrapolation of that Br?nsted plot leads to the prediction that benzoate decarboxylation should proceed at detectable rates in water at temperatures below the critical point. That prediction was confirmed experimentally. Using this same relationship, and extrapolating to the observed rate constant for enzymatic decarboxylation of orotidine 5'-monophosphate, we estimate that the "effective" pKa value of the 6-CH group of uridine 5'-monophosphate, the product of decarboxylation, is 9.5 at the active site of yeast OMP decarboxylase.     

Catalytic Effect of Cesium Cation Adduct Formation on the Decarboxylation of Carboxylate Ions in the Gas Phase

The effect of Cs⁺ ligation on the decarboxylation of malonic acids (unsubstituted and methyl‐, dimethyl‐, ethyl‐, and phenyl‐substituted) in their carboxylate form was studied in the gas phase using tandem mass spectrometry. The study is based on the comparison of the decarboxylation of the bare monoanion (hydrogen malonates) and of the cesium adduct of the cesium salt (Cs⁺[cesium hydrogen malonates]) under collisional activation. Energy‐resolved dissociation curves of the negative and positive ions exhibit major differences. Decarboxylation of the cationic adducts of substituted malonic acid salts occurs at significantly lower collisional activation than for the corresponding bare hydrogen malonate anions. The conclusions from these experiments are supported by DFT calculations. The calculated activation parameters (enthalpy and Gibbs energy) confirm that the cesium cation coordination assists the decarboxylation of the carboxylate form.     

Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates

Unstable N-heterocyclic carbenes can be masked and stabilized as pseudo-cross-conjugated hetarenium-carboxylates which decarboxylate on warming. This study deals with the decarboxylation of carboxylates of mesoionic compounds to generate anionic N-heterocyclic carbenes. Lithium sydnone-4-carboxylates were therefore prepared via 4-bromosydnones by halogen-lithium exchange with nBuLi and subsequent treatment with carbon dioxide. Protonation gave the corresponding sydnone-4-carboxylic acids. Thermogravimetric measurements in addition to temperature dependent IR spectroscopy proved the decarboxylation of lithium sydnone-4-carboxylates and formation of the corresponding sydnone anions which can be represented as anionic N-heterocyclic carbenes. In DMSO-d6 solution, water favors the decarboxylation. Calculations have been performed to elucidate the mechanism of the decarboxylation in the absence and presence of water.     

Efficient and selective oxidative decarboxylation of arylcarboxylic acids into the corresponding aldehydes and ketones using K5CoIIIW12O40 as a green oxidant under microwave and conventional heating

The oxidative decarboxylation of various ??-aryl- and ??,??-arylcarboxylic acids having electron-donating and electron-withdrawing groups by using a stoichiometric amount of potassium 12-tungstocobaltate(III), K₅Co^IIIW₁₂O₄₀, in 50% aqueous acetonitrile solution resulted in the corresponding aldehydes and ketones in high yields within short reaction times under microwave irradiation. This transformation was also carried out under the conventional heating conditions which produced the corresponding aldehydes and ketones in relatively longer reaction times. The arylacetic acids with electron-withdrawing substituents required longer reaction times and produced lower yields. In contrast to arylacetic esters which were inert toward decarboxylation, the sodium arylacetates were decarboxylated in shorter times with yields better than those of the parent acids.     

Enantioselective catalysis,C. Decarboxylation of malonic acids in the presence of copper(I) compounds — Not a copper(I) catalysis but a base effect

Summary The catalytic decarboxylation of malonic acids, claimed to be catalyzed by copper(I) compounds, has been investigated. Decarboxylation of different malonic acid derivatives (1–5) in acetonitrile was far more effective with Cu₂O than with CuCl. Thus, the decarboxylation is obviously influenced by the basicity of the anion. In the decarboxylation of phenylmalonic acid (3),bis(tricyclohexylphosphane)copper(I) hydrogenphenylmalonate (6) and potassium hydrogenphenylmalonate (7) show nearly identical rate constants. It is concluded that the monoanions of the malonic acid derivatives are the reactive species undergoing decarboxylation. Further experiments are presented which demonstrate that everything that increases the concentration of the monoanions also increases the rate of decarboxylation. In the enantioselective decarboxylation of the monoethyl ester of methylphenylmalonic acid (2), the enantiomeric excess of (S)-(+)-ethyl 2-phenylpropionate could be raised to 34.5%ee using the alkaloid cinchonine.Dedicated to Prof. Dr.J. Müller on the occasion of his 60^th birthday.     

GC analysis of trichloroacetic acid in water samples by large-volume injection and thermal decarboxylation in a programmed-temperature vaporizer

Summary AGC method has been developed for the analysis of tricholoroacetic acid (TCA) in water samples. It entails large-volume injection (LVI) and programmed-temperature vaporization (PTV) of water samples, thermal decarboxylation of TCA to chloroform in the injector, and GC-ECD analysis of the decarboxylation product. Conditions such as final injector temperature, splitless time, and injection volume were optimized. The limit of detection is approximately 0.1 μg L⁻¹ Several real samples were analyzed. The method presented is an easy means of determination of TCA and eliminates sample-preparation steps such as extraction and derivatization.     

Spectroscopy of hydrothermal reactions,part 26: Kinetics of decarboxylation of aliphatic amino acids and comparison with the rates of racemization

The kinetics of decarboxylation of six α‐amino acids (glycine, alanine, aminobutyric acid, valine, leucine, and isoleucine) and β‐aminobutyric acid were studied in aqueous solution at 310–330ˆC and 275 bar over the pH₂₅ range 1.5–8.5 by using an in situ FT‐IR spectroscopy flow reactor. Based on the rate of formation of CO₂, the first‐order or pseudo‐first‐order rate constants were obtained along with the Arrhenius parameters. The decarboxylation rates of amino acids follow the order Gly > Leu ≈ Ile ≈ Val > Ala > α‐Aib > β‐Aib. Differences in the concentration between 0.05 and 0.5 m had only a minor effect on the decarboxylation rate. The effect of the position of the amino group on the decarboxylation rate was investigated for α‐, β‐, and γ‐aminobutyric acid and the order was found to be α > β ≫ γ. Although the pH dependence is complex, the decarboxylation rates of α‐amino acids qualitatively have the inverse trend of the racemization rates. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 602–610, 2003     

Hydrolysis kinetics of 2‐cyanopyridine, 3‐cyanopyridine,and 4‐cyanopyridine in high‐temperature water

We report herein the kinetic studies on hydrolysis of three cyanopyridines in high‐temperature water. 3‐Cyanopyridine, 4‐cyanopyridine and 2‐cyanopyridine underwent consecutive hydrolysis to the corresponding pyridinecarboxamides and picolinic acids. Further decarboxylation to pyridine was observed for 2‐cyanopyridine hydrolysis. Experiments at different initial reactant concentrations revealed that these compounds exhibited the first‐order kinetics. Experiments at different temperatures showed that the first‐order rate constants displayed an Arrhenius behavior with activation energies of 74.3, 40.3, and 83.7 kJ mol^?1 for 3‐cyanopyridine, 4‐cyanopyridine, 2‐cyanopyridine, respectively. The activation energies obtained for 3‐pyridinecarboxamide, 4‐pyridinecarboxamide and 2‐pyridinecarboxamide hydrolysis are 80.1, 32.7, and 70.5 kJ mol^?1, respectively. The effect of substituent position on activation energies for cyanopyridine and pyridinecarboxamide hydrolysis is ortho ≈ meta > para. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 641–648, 2012     

The ortho‐Substituent Effect on the Ag‐Catalysed Decarboxylation of Benzoic Acids

A combined experimental and computational investigation on the Ag‐catalysed decarboxylation of benzoic acids is reported herein. The present study demonstrates that a substituent at the ortho position exerts dual effects in the decarboxylation event. On one hand, ortho‐substituted benzoic acids are inherently destabilised starting materials compared to their meta‐ and para‐substituted counterparts. On the other hand, the presence of an ortho‐electron‐withdrawing group results in an additional stabilisation of the transition state. The combination of both effects results in an overall reduction of the activation energy barrier associated with the decarboxylation event. Furthermore, the Fujita–Nishioka linear free energy relationship model indicates that steric bulk of the substituent can also exert a negative effect by destabilising the transition state of decarboxylation.     

One pot synthesis of α,β-epoxy ketones by oxidative coupling of methyl arenes with cinnamic acids involving C(sp3)―H activation and decarboxylative strategy

A new one pot oxidative coupling of methyl arenes with cinnamic acids has been developed for the synthesis of α,β-epoxy ketones using MnO₂/TBHP combination. The process involves a co-existing C(sp³)―H activation and decarboxylation under aqueous medium, which makes it practical and attractive.     

Direct conversion of primary and secondary carboxylic acids to trifluoromethyl ketones

Primary and secondary carboxylic acids were converted in one step to the corresponding trifluoromethyl ketones by treatment with trifluoroacetic anhydride (TFAA) and pyridine in toluene at 60-100 °C followed by hydrolysis/decarboxylation with water at 45 °C.     

Studies on decarboxylation reactions. Part 5 . Micellar catalysis and mixed solvents effects on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids

The effect of micelles and mixed solvents on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids has been studied. The data support the unimolecular decarboxylation mechanism proposed by us. Moreover, they show that mixed solvents and micelles have different effects on reactivity of the amino acids under study.     

Esterification at Room Temperature:A Mixing Affair Only

Carboxylic acids in absolute alcohols, on treatment with thionyl chloride at room temperature give good yields of corresponding esters.

Photochemistry¹ of maleianilic acid and its derivatives has been of interest to us. It was thought that the yield of the photocyclised product is less because of probable decarboxylation which may be resulting during photolysis, and hence the need for esterification. Numerous new methods of esterification have been developed and reviewed by Haslam², but we like to claim our method as the simplest and the easiest method to date. Another report by Huber and Brenner^4,5 has used absolute methanol, thionyl chloride and HCl for preparing methyl esters of two amino acids (Methionine and Leucine) using a methodology which includes an unnecessary use of HCl.     

The decarboxylation of phenylmalonamates and phenylmalonilates

Whilst decarboxylation of dibasic acids and their derivatives under alkaline conditions and on heating at elevated temperatures is well established, the decarboxylation of the brucine salt of phenylmalonamic acid (brucine-2-carbamoyl-2-phenyl-ethanoate) unusually takes place rapidly in water at room temperature. The details of the kinetics are given.

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Die Decarboxylierung von Brucinsalzen von Phenyl-malonamidsäure und N-Phenyl-phenyl-malonamidsäure

Zusammenfassung Brucinsalze von Phenyl-malonamidsäure (Brucin-2-carbamoyl-2-phenylethanoat) undN-Phenyl-phenyl-malonamidsäure (Brucin-N-phenyl-2-carbamoyl-2-phenyl-ethanoat) decarboxylieren in wäßriger Lösung bei Raumtemperatur sehr rasch. Details der Kinetik dieses Prozesses werden beschrieben.

     

Regioselective Synthesis of Fused Furans by Decarboxylative Annulation of α,β‐Alkenyl Carboxylic Acid with Cyclic Ketone: Synthesis of Di‐Heteroaryl Derivatives

α,β‐Alkenyl carboxylic acids undergo Cu^II‐mediated decarboxylative annulation reactions with aliphatic cyclic ketones to provide synthetically valuable di‐heterocycles. The annulation process tolerates a variety of aliphatic ketones and heterocyclic alkenyl carboxylic acids, producing substituted fused furan derivatives with complete regioselectivity. The current protocol offers a synthetically applicable pathway to construct a variety of oligo‐heterocycles through Cu‐mediated single‐electron transfer and decarboxylation. Notably, synthesis of relatively inaccessible di‐heterocycles has been achieved successfully using this protocol.     

Light-Driven Enzymatic Decarboxylation of Dicarboxylic Acids

Photodecarboxylase from Chlorella variabillis (CvFAP) is one of the three known light-activated enzymes that catalyzes the decarboxylation of fatty acids into the corresponding C1-shortened alkanes. Although the substrate scope of CvFAP has been altered by protein engineering and decoy molecules, it is still limited to mono-fatty acids. Our studies demonstrate for the first time that long chain dicarboxylic acids can be converted by CvFAP. Notably, the conversion of dicarboxylic acids to alkanes still represents a chemically very challenging reaction. Herein, the light-driven enzymatic decarboxylation of dicarboxylic acids to the corresponding (C2-shortened) alkanes using CvFAP is described. A series of dicarboxylic acids is decarboxylated into alkanes in good yields by means of this approach, even for the preparative scales. Reaction pathway studies show that mono-fatty acids are formed as the intermediate products before the final release of C2-shortened alkanes. In addition, the thermostability, storage stability, and recyclability of CvFAP for decarboxylation of dicarboxylic acids are well evaluated. These results represent an advancement over the current state-of-the-art.