Quantitation of a Ketone Enolization and a Vinyl Sulfonate Stereoisomer Formation Using Inline IR Spectroscopy and Modeling

Reaction mechanism of the green synthesis of glutaric acid

In this study, the reaction mechanism underlying the green synthesis of glutaric acid was studied via joint test technology. Density functional theory calculations were used to verify the mechanism. Quantitative analysis of glutaric acid via infrared spectroscopy and HPLC was established. The linear correlation between the two methods was good, from 0.01 to 0.25 g mL^-1. The analysis results of the two methods were consistent as the reaction progressed.

Ketone Enolization with Sodium Hexamethyldisilazide: Solvent- and Substrate-Dependent E-Z Selectivity and Affiliated Mechanisms

Ketone enolization by sodium hexamethyldisilazide (NaHMDS) shows a marked solvent and substrate dependence. Enolization of 2-methyl-3-pentanone reveals E-Z selectivities in Et₃N/toluene (20:1), methyl-t-butyl ether (MTBE, 10:1), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA)/toluene (8:1), TMEDA/toluene (4:1), diglyme (1:1), DME (1:22), and tetrahydrofuran (THF) (1:90). Control experiments show slow or nonexistent stereochemical equilibration in all solvents except THF. Enolate trapping with Me₃SiCl/Et₃N requires warming to -40 °C whereas Me₃SiOTf reacts within seconds. In situ enolate trapping at -78 °C using preformed NaHMDS/Me₃SiCl mixtures is effective in Et₃N/toluene yet fails in THF by forming (Me₃Si)₃N. Rate studies show enolization via mono- and disolvated dimers in Et₃N/toluene, disolvated dimers in TMEDA, trisolvated monomers in THF/toluene, and free ions with PMDTA. Density functional theory computations explore the selectivities via the E- and Z-based transition structures. Failures of theory-experiment correlations of ionic fragments were considerable even when isodesmic comparisons could have canceled electron correlation errors. Swapping 2-methyl-3-pentanone with a close isostere, 2-methylcyclohexanone, causes a fundamental change in the mechanism to a trisolvated-monomer-based enolization in THF.

Aggregation and Solvation of Sodium Hexamethyldisilazide: Across the Solvent Spectrum

We report solution structures of sodium hexamethyldisilazide (NaHMDS) solvated by >30 standard solvents (ligands). These include: toluene, benzene, and styrene; triethylamine and related trialkylamines; pyrrolidine as a representative dialkylamine; dialkylethers including THF, tert-butylmethyl ether, and diethyl ether; dipolar ligands such as DMF, HMPA, DMSO, and DMPU; a bifunctional dipolar ligand nonamethylimidodiphosphoramide (NIPA); polyamines N,N,N',N'-tetramethylenediamine (TMEDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and 2,2'-bipyridine; polyethers 12-crown-4, 15-crown-5, 18-crown-6, and diglyme; 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane ([2.2.2] cryptand); and tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1). Combinations of 1H, 13C, 15N, and 29Si NMR spectroscopies, the method of continuous variations, X-ray crystallography, and density functional theory (DFT) computations reveal ligand-modulated aggregation to give mixtures of dimers, monomers, triple ions, and ion pairs. 15N-29Si coupling constants distinguish dimers and monomers. Solvation numbers are determined by a combination of solvent titrations, observed free and bound solvent in the slow exchange limit, and DFT computations. The relative abilities of solvents to compete in binary mixtures often match that predicted by conventional wisdom but with some exceptions and evidence of both competitive and cooperative (mixed) solvation. Crystal structures of a NaHMDS cryptate ion pair and a 15-crown-5-solvated monomer are included. Results are compared with those for lithium hexamethyldisilazide, lithium diisopropylamide, and sodium diisopropylamide.

Use of Standard Addition to Quantify In Situ FTIR Reaction Data

FTIR spectroscopy is a common in situ reaction monitoring technique used in modern academic and industrial environments. The FTIR signals collected during the course of a reaction are proportional to the concentration of the reaction components but not intrinsically quantitative. To make FTIR data quantitative, precalibration or offline analyses of reaction samples are required, which diminishes the unique benefits of in situ reaction monitoring techniques. Herein, we report the use of standard addition as a convenient method to obtain quantitative FTIR data.

The rise of continuous flow biocatalysis – fundamentals, very recent developments and future perspectives

Very recent developments in the field of biocatalysis in continuously operated systems. Special attention on the future perspectives in this key emerging technological area ranging from process analytical technologies to digitalization.