Triphenylphosphine Dibromide: A Simple One-pot Esterification Reagent

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

In this paper we present the first electrochemical generation of NHC carried out in a divided flow cell. The flow cell operated in the recycle mode. The need for a divided cell derived from the anodic electroactivity of the electrogenerated carbene. In order to have NHC accumulation in the catholyte, the Nafion membrane (cell separator) was pretreated with an alkaline solution. The formation of NHC was quantified as its reaction product with elemental sulfur. The NHC was successfully used as organocatalyst in two classical umpolung reactions of cinnamaldehyde: its cyclodimerization and its oxidative esterification.

Polymer-Bound Triphenylphosphine and 4,4'-Dinitroazobenzene as a Coupling Reagents for Chromatography-Free Esterification Reaction

AIM AND OBJECTIVE

Sustainable production of fine chemicals both in industries and pharmaceuticals heavily depends on the application of solid-phase synthesis route coupled with microwave technologies due to their environmentally benign nature. In this report, a microwave-assisted esterification reaction using polymer-bound triphenylphosphine and 4,4'-dinitroazobenzene reagent system was investigated.

MATERIALS AND METHODS

The solvents were obtained from Merck India. Polymer-bound triphenylphosphine (~3 mmol triphenylphosphine moiety/g) was acquired from Sigma-Aldrich. The progress of the reaction was observed by thin-layer chromatography. All the reactions were performed in Milestones StartSYNTH microwave. The NMR spectra were recorded on Bruker Avance III 300, 400, and 500 MHz FT NMR Spectrometers. Using azo compound and polymer-bound triphenyl phosphine as a coupling reagent, esterification of different carboxylic acids with alcohols was performed under microwave irradiation.

RESULTS

Esterification of benzoic acid with 1-propanol under microwave irradiation gave a high yield of 92% propyl benzoate in 60 minutes only. Isolation of the ester products was relatively simple as both the byproducts polymer-bound triphenylphosphine oxide and hydrazine could be removed by simple filtration. The rates of reactions were found to be directly proportional to the pKa of the benzoic acids.

CONCLUSION

4,4'-Dinitroazobenzene was introduced as a novel coupling reagent, in conjugation with polymer-bound triphenylphosphine, for esterification reactions under microwave irradiation. The low moisture sensitivity of the reaction system, easy separation of the byproducts, and column chromatographyfree isolation of esters help our methods with application significance, particularly from the 'Sustainable Chemistry' perspective.

Characterization of the Key Aroma Compounds in Two Commercial Dark Chocolates with High Cocoa Contents by Means of the Sensomics Approach

The overall aroma of two orthonasally distinguishable dark chocolates with high cocoa content (90% CC and 99% CC) was decoded using the systematic sensomics approach, including solvent extraction, separation of the volatiles, identification using aroma extract dilution analysis (AEDA) based on gas chromatography-olfactometry (GC-O) combined with gas chromatography-mass spectrometry (GC-MS), quantitation by stable isotope dilution analysis (SIDA), calculation of odor activity values (OAVs), and recombination experiments. Sixty-nine aroma-active compounds were identified and quantitation of 49 compounds revealed 28 odorants in 90% CC and 30 aroma-active compounds in 99% CC with OAVs ≥ 1. Among them, dimethyl trisulfide, acetic acid, 2-methoxyphenol, 3-methylbutanoic acid, phenylacetic acid, vanillin, and linalool showed the highest OAVs. Subsequently, very high similarities of the reconstitution models, containing all odorants with OAVs ≥ 1 in their naturally occurring concentrations in odorless sunflower oil as matrix, proved the correct identification and quantitation of all key odorants in both dark chocolates.

Imido-substituted triazines as dehydrative condensing reagents for the chemoselective formation of amides in the presence of free hydroxy groups

In this paper, we discuss the synthesis of imido-substituted chlorotriazines and demonstrate their use in dehydrative condensation reactions. Chemoselective amide-forming reactions of amino alcohols using succinimido-substituted chlorotriazine (2A) proceeded smoothly. Occasionally, nonselectivity was problematic during the synthesis of hydroxy-substituted amides. Moreover, it was noteworthy that this method was applicable to hydroxy-substituted carboxylic acids that could have formed a lactone or an ester during the carboxylic acid activation step. The imido-substituted chlorotriazine (2A) was superior to the amido-substituted chlorotriazine and 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) in terms of reaction rates and yields.

In this paper, we discuss the synthesis of imido-substituted chlorotriazines and demonstrate their use in dehydrative condensation reactions.

A microwave-assisted highly practical chemoselective esterification and amidation of carboxylic acids

The ubiquitousness of esters and amide functionalities makes their coupling reaction one of the most sought-after organic transformations.

A novel aromatic carbocation-based coupling reagent for esterification and amidation reactions

Driven by aromatization: a novel tropylium-based coupling reagent has been developed to facilitate nucleophilic coupling reactions of carboxylic acids.