Cl3CCONH2/PPh3: A Versatile Reagent for Synthesis of Esters

Cl₃CCONH₂/PPh₃ was a versatile reagent to convert carboxylic acids into their corresponding acid chlorides. This intermediate was clearly confirmed by spectroscopic methods (IR, ¹H, ¹³C NMR). This one-pot reaction of in situ acid chloride generated with various alcohols successfully furnished the corresponding esters in moderate to excellent yields.     

CeCl3-Catalyzed Reduction of Methyl Esters of Carboxylic Acids to Corresponding Alcohols with Sodium Borohydride

A wide range of methyl esters, including esters of aromatic carboxylic acids, alkenyl carboxylic acids, aliphatic carboxylic acids, and protected amino acids, were reduced to the corresponding alcohols with NaBH₄ in ethanol in the presence of a catalytic amount of CeCl₃. The reaction was completed within 24 h at ambient temperature and showed high functional group compatibility and chemoselectivity. With esters containing nitro, methoxyl, halogen, alkenyl, and protected amino functionalities, only the ester group was reduced. The alcohols were isolated after evaporation of the solvent and routine aqueous workup in good yields (75–95%).     

Transition metal free oxidative esterification of alcohols with toluene

Using Bu₄NI as the catalyst and tert-butyl hydroperoxide as the oxidant, direct esterification of alcohols with toluene derivatives was achieved. Mechanistic investigations indicate that the alcohols are sequentially oxidized to aldehydes, carboxylic acids, and then to benzyl esters. Bu₄N⁺ functions as a phasetransfer reagent and iodide catalyzes the reaction.     

Highly Efficient System for Reduction of Carboxylic Acids and Their Derivatives to Alcohols by HfCl4/KBH4

HfCl₄/KBH₄ was found to be a facile, efficient, convenient, and chemoselective system for the reduction of carboxylic acids and their derivatives to the corresponding alcohols under mild conditions. HfCl₄/NaBH₄ was also utilized to reduce the same carboxylic acids and their derivatives, and it was found that the reducing ability of HfCl₄/NaBH₄ was similar to that of HfCl₄/KBH₄. The action of HfCl₄/KBH₄ on other types of substrates, such as benzyl chloride, peracid, epoxide, ketone, amide, imine, pyridine-N-oxide, and nitrile, was investigated, too. In addition, some competitive reductions of styrene oxide in the presence of carboxylic acid, carboxylic ester, nitrile, and amide were achieved.     

An expedient route for the reduction of carboxylic acids to alcohols employing 1-propanephosphonic acid cyclic anhydride as acid activator

A simple and efficient method for the synthesis of alcohols from the corresponding carboxylic acids is described. Activation of carboxylic acid with 1-propanephosphonic acid cyclic anhydride (T3P) and subsequent reduction using NaBH₄ yield the alcohol in excellent yields with good purity. Reduction of several alkyl/aryl carboxylic acids and N^α-protected amino acids/peptide acids as well as N^β-protected amino acids was successfully carried out to obtain corresponding alcohols in good yields. All the products were fully characterized by ¹H NMR and mass spectral analyses. The procedure is mild, simple and the isolation of the products is easy.     

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.     

Effect of different dispersing agents in the non-isothermal kinetics and thermomechanical behavior of PET/TiO2 composites

This work is based on the analysis of the influence of dispersing agents on the non-isothermal kinetics, thermomechanical behavior and dispersing action of PET/TiO₂ nanocomposites. The influence of two montanic waxes and an amide wax used as dispersing agents in the nucleating effect of the nanoparticles is studied. The dispersing agents are the following: a) a partly saponified ester of montanic acids (PSEMA), b) an ester of montanic acids with multifunctional alcohols (MAWMA) and c) an amide wax based on N,N′-Bisstearoyl ethylenediamine (AW). The non-isothermal kinetics based on the Avrami method revealed that MAWMA and PSEMA favors the nucleating effect of the nanoparticles when are included in PET. Birefringence microscopy points out the good dispersing capacity of MAWMA and AW and the termomechanical analysis confirmed that the ester of montanic acids with multifunctional alcohols MAWMA shows the best dispersing properties and best promotes the nucleating effect of the TiO₂ nanoparticles when used for PET/TiO₂ nanocomposites production.     

Solvent-modulated chemoselective deprotections of trialkylsilyl esters and chemoselective esterifications

A series of trialkylsilyl esters were deprotected or transesterificated into their corresponding carboxylic acids or methyl esters under a catalytic amount of CBr₄ in alcohol reaction system. This method enables to desilylate secondary sp³-carbon, sp²-carbon, sp-carbon and aryl tethered trialkylsilyl esters to carboxylic acids, whereas primary sp³-carbon tethered trialkylsilyl esters were further converted into their methyl esters under CBr₄/MeOH reaction conditions. The highly chemoselective deprotections can be modulated and achieved by the introduced protecting trialkylsilyl groups and the used alcohols such as MeOH and EtOH under this photochemically-induced reaction conditions.     

Friedel-Crafts acylation of aromatic compounds with carboxylic acids in the presence of P2O5/SiO2 under heterogeneous conditions

A convenient and efficient procedure for the Friedel-Crafts acylation of aromatic compounds with carboxylic acids in the presence of P₂O₅/SiO₂ is described. Both aromatic and aliphatic carboxylic acids reacted easily to afford the corresponding aromatic ketones. The use of non-toxic and inexpensive materials, simple and clean work-up, short reaction times and good yields of the products are the advantages of this method.     

Ru-Catalyzed Oxidations with Iodosylbenzene Derivatives. Substituent Effects on Selectivity in Oxidation of Sulfides and Alcohols

Oxidation of sulfides with PhIO/RuCl₂ (PPh₃)₃ leads to sulfones. Electronwithdrawing substituents in the aromatic ring of PhIO reduce the reactivity and improves selectivity of the system. Thus, with m-iodosylbenzoic acid sulfides are converted to sulfoxide. Under the same conditions aliphatic primary alcohols are transformed to aldehydes with m-iodosylbenzoic acid, while PhIO affords carboxylic acids.     

Studies on transition metal nitrido and oxo complexes. Part 161. The nature of the oxoruthenates involved in some rutheniumcatalysed organic oxidations

Summary Electronic spectroscopy has been used to ascertain the nature of the oxoruthenates present in a number of organic oxidations catalysed by ruthenium complexes reported in the literature. The utility of oxoruthenates as catalysts with [Fe(CN)₆]^3– as co-oxidant for the conversion of primary alcohols to carboxylic acids and secondary alcohols to ketones has been assessed.     

A practical and efficient procedure for reduction of carboxylic acids and their derivatives: use of KBH4-MgCl2

The use of KBH₄-MgCl₂ to reduce carboxylic acids and their derivatives to the corresponding alcohols or the respective reduced products is described. Methyl (S)-3,4-O-isopropylidene-3,4-dihydroxy butanoate 2 used as a reference substrate was reduced with KBH₄ and MgCl₂ in 1:1 mol ratio to (S)-1,2-O-isopropylidene-1,2,4-butanetriol 1.     

Carbon-13 spin–lattice relaxation in strongly associated molecules: Carboxylic acids

¹³C spin–lattice relaxation times determined for the protonated carbons of carboxylic acids and methyl esters give indications of solution dimerization with the free acids. Since isopthalic and fumaric acids have two carboxyl functions they are able to polymerize in solution. Unlike the case for molecular aggregation due to weak hydrogen bonding in solution (e.g. alcohols, phenols), the ¹³C T₁ values of mono carboxylic acids are not significantly affected by dilution to c. 10^?2 M. Variable temperature T₁ measurements of both the mono and dibasic acids gave activation energies for molecular reorientation of the order of 2 kcal mol^?1, considerably lower than E_a for hydrogen bonded alcohols and comparable with E_a for the unassociated methyl esters of propionic and benzoic acids.     

5H-3-oxa-Octafluoropentanesulfonyl fluoride: a novel and efficient condensing agent for esterification, amidation and anhydridization

The use of 5H-3-oxa-octafluoropentanesulfonyl fluoride (HCF₂CF₂OCF₂CF₂SO₂F) as a novel and efficient condensing reagent for esterification of carboxylic acids with alcohols and amidation of carboxylic acids with amines in the presence of 1,3-diazabicyclo[5.4.0]-undec-7-ene (DBU) is reported. HCF₂CF₂OCF₂CF₂SO₂F cannot serve as a condensing agent for anhydridization of carboxylic acids, however, HCF₂CF₂OCF₂CF₂SO₂F/(CH₃)₃SiCN system can mediate anhydridization of some aromatic carboxylic acids.     

Domino Rhodium/Palladium‐Catalyzed Dehydrogenation Reactions of Alcohols to Acids by Hydrogen Transfer to Inactivated Alkenes

The combination of the d⁸ Rh^I diolefin amide [Rh(trop₂N)(PPh₃)] (trop₂N=bis(5‐H‐dibenzo[a,d]cyclohepten‐5‐yl)amide) and a palladium heterogeneous catalyst results in the formation of a superior catalyst system for the dehydrogenative coupling of alcohols. The overall process represents a mild and direct method for the synthesis of aromatic and heteroaromatic carboxylic acids for which inactivated olefins can be used as hydrogen acceptors. Allyl alcohols are also applicable to this coupling reaction and provide the corresponding saturated aliphatic carboxylic acids. This transformation has been found to be very efficient in the presence of silica‐supported palladium nanoparticles. The dehydrogenation of benzyl alcohol by the rhodium amide, [Rh]N, follows the well established mechanism of metal–ligand bifunctional catalysis. The resulting amino hydride complex, [RhH]NH, transfers a H₂ molecule to the Pd nanoparticles, which, in turn, deliver hydrogen to the inactivated alkene. Thus a domino catalytic reaction is developed which promotes the reaction R‐CH₂‐OH+NaOH+2 alkene→R‐COONa+2 alkane.     

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.     

Catalyzed oxidation of alcohols and aldehydes with iodosylbenzene

RuCl₂(PPh₃)₃ catalyzes oxidation of alcohols to carbonyi compounds by iodosylbenzene and that of aldehydes to carboxylic acids. Catalyzed oxidation of primary alcohols with phenyliodosodiacetate affords aldehydes.     

Novel and efficient method for esterification, amidation between carboxylic acids and equimolar amounts of alcohols, and amines utilizing Me2NSO2Cl and N,N-dimethylamines; its application to the synthesis of coumaperine, a natural chemopreventive dieneamide

Various carboxylic esters or amides were prepared in good to excellent yield between carboxylic acids and equimolar amounts of alcohols or amines under very mild conditions (0-45°C; within 3 h) using dimethylsulfamoyl chloride (Me₂NSO₂Cl; 1) combined with N,N-dimethylamines (Me₂NR: 2a; R=Me, 2b; R=Bu). The choice of the sulfamoyl chloride and the amine is crucial for the reaction; that is, sterically uncrowded amines accelerated the present esterification and amidation. This agent had some advantages over methanesulfonyl chloride (3)/amines as for the atom-economy, avoidance of side reactions, and had very high chemoselectivity toward the carboxyl group vs the hydroxyl group; the experiment was performed by the addition of 1 to the mixture of carboxylic acids and alcohols. Application of this method to the synthesis of coumaperine, a chemopreventive natural product, was performed using the present amidation as a key step.     

Cyclic mechanism in the trapping of carbonyl oxides with alcohols and carboxylic acids

The reaction of diphenylcarbonyl oxide with alcohols and carboxylic acids, which has been classified as a nucleophilic trapping, is shown to be in the reactivity order: AcOH ? MeOH > CF₃CH₂OH > EtOH ? t-BuOH. A laser-flash spectroscopy indicated that the reaction of carboxylic acids is very fast, that is, one-tenth of the diffusion rate. These results suggest that the hydroxyl compounds react as an acid and a nucleophile at the same time and the major reaction is via the seven- and five-membered cyclic mechanism for RCO₂H and ROH, respectively.     

Imidazolinium sulfonate and sulfamate zwitterions as chiral solvating agents for enantiomeric excess calculations

The synthesis of enantiopure unsymmetrical N-heterocyclic based zwitterions incorporating imidazolinium and alkylsulfonate or sulfamate groups is described. The desired compounds were prepared in good yields from 1,3-propanesultone or cyclic sulfamidates and imidazolines. The imidazolinium based zwitterions proved to be versatile chiral solvating agents for Mosher’s acid, alcohols, cyanohydrins, amino alcohols, nitro alcohols, thiols, and carboxylic acids with very high shifts in the ¹H and ¹⁹F NMR.