Generation and trapping of ketenes in flow

Ketenes were generated by the thermolysis of alkoxyalkynes under flow conditions, and then trapped with amines and alcohols to cleanly give amides and esters. For a 10 min reaction time, temperatures of 180, 160, and 140 °C were required for >95?% conversion of EtO, iPrO, and tBuO alkoxyalkynes, respectively. Variation of the temperature and flow rate with inline monitoring of the output by IR spectroscopy allowed the kinetic parameters for the conversion of 1-ethoxy-1-octyne to be easily estimated (Ea = 105.4 kJ/mol). Trapping of the in-situ-generated ketenes by alcohols to give esters required the addition of a tertiary amine catalyst to prevent competitive [2+2] addition of the ketene to the alkoxyalkyne precurso

Reagent-free flow chemistry

A range of flow chemistries unified by the overlapping concepts of Reagentless Synthesis and Reactive Intermediate Trapping were developed. Thermochemically-promoted transformations for the generation and trapping of reactive intermediates, such as ketenes and N-acyliminium species, are reported. A particular emphasis was given to acquire kinetic data by means of in-situ spectroscopy techniques. Photochemistry is another ‘reagentless’ technique that is much less used in organic synthesis than might be expected from its capabilities. Flow chemistry provides a timely opportunity to develop ‘user friendly’ photochemical flow reactors and validate the equipment on selected photochemical reactions. Organometallic compounds impose particular challenges when handled in flow. Homogeneous or immobilised cobalt reagents were tested in combination with commercial flow equipment. Flow syntheses of selected piano stool iron complexes are also presented. Finally mixing properties of simple-shaped commercial flow mixers were assessed due to their critical role in commercial flow platforms. A mixing test was developed and compared against established procedures

Thermolysis of 1,3-dioxin-4-ones: fast generation of kinetic data using in-line analysis under flow

International audienceRapid acquisition of kinetic data is demonstrated with a commercial meso-scale flow reactor, using a step-change in flow rate or ‘push-out’ from the flow line. For thermolysis of 1,3-dioxin-4-ones (1), we obtain excellent reproducibility in the activation energies measured from spectroscopic data collected by in-line UV or transmission FT-IR monitoring of the output during the transitional period between two flow rates (±3 kJ mol−1, 0.7 kcal mol−1). Analysis of multi-component UV and IR data is conducted using an orthogonal projection approach (multivariate curve resolution by alternating least squares) for complex spectra, or by calibration-less integration of non-overlapping peak absorbance. All analysis methods were validated using off-line 1H NMR analysis, and kinetic parameters obtained using the method of a flow rate step-change were validated against conventional steady-state measurements in which time-series data were acquired across multiple experiments. Thermal transfer and dispersion effects are addressed. The experimental methods described herein are valuable for accelerated reaction study and in process development

Análisis teórico del algoritmo de compresión LLRUN para la compresión de cadenas de bits sparse

The purpose of this research was to make a theoretical analysis about the performance of LLRUN compression algorithm on sparse bit strings. Fraenkel and Klein (1985) proposed a method to compress sparse bit strings, using run length encoding (RLE), Elias - gamma coding and Huffman coding, with promising performance. The results of this research showed that LLRUN offers a theoretical compression ratio between 87,5% and 50%, being an effective tool to compress sparse bit strings. Keywords: compression, sparse bit strings, LLRUN, performance.La presente investigación tuvo como finalidad realizar un análisis teórico sobre el funcionamiento del algoritmo de compresión LLRUN, para determinar su posible uso en la compresión de cadenas de bits sparse. Fraenkel y Klein (1985) plantearon un método para comprimir cadenas de bits sparse mezclando las técnicas run length encoding (RLE), Gamma coding y Huffman coding, mostrando un rendimiento prometedor. El resultado del presente estudio permitió determinar que LLRUN ofrece una relación de compresión teórica entre 87,5% y 50%, siendo una herramienta efectiva para la compresión de cadenas de bits sparse. Palabras clave: compresión, cadenas de bits sparse, LLRUN, rendimiento

Microwave irradiation and flow chemistry for a straightforward synthesis of piano-stool iron complexes

Two series of piano-stool iron(II) complexes bearing bidentate phosphine or mixed phosphoruse-nitrogen ligands have been prepared upon reaction with CpFe(CO)(2)I or [CpFe(naphthalene)][PF6] under microwave irradiation or using flow chemistry

Intra- and Intermolecular Alkylation of <i>N</i>,<i>O</i>‑Acetals and π‑Activated Alcohols Catalyzed by in Situ Generated Acid

Intramolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, principally <i>N</i>,<i>O</i>-acetals, without the use of an exogenous reagent have been developed. The reactions are carried out in 1,1,2,2-tetrachloroethane (TCE) and take advantage of the ability of this solvent to continuously release small amounts of HCl by thermolytic elimination. A study of the reaction led to several improved protocols such as (1) preheated TCE, (2) microwave-assisted reactions, and (3) flow or sealed-tube conditions, which allow significant reaction rate enhancements and made possible some challenging reactions such as the α-amidoalkylation of ketones. Studies using flow chemistry confirmed not only that very low concentrations of HCl generated from the solvent were responsible for the reactivity but also that TCE had additional beneficial properties in comparison to other chlorinated solvents such as dichloroethane. The method can easily be extended to the alkylation using proelectrophiles such as π-activated alcohols, which are normally unreactive toward HCl catalysis. This work represents the first successful use of HCl, the simplest strong Brønsted acid, as an efficient alkylation catalyst

Intra- and Intermolecular Alkylation of N,O-Acetals and π-Activated Alcohols Catalyzed by in Situ Generated Acid

Intramolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, principally N,O-acetals, without the use of an exogenous reagent have been developed. The reactions are carried out in 1,1,2,2-tetrachloroethane (TCE) and take advantage of the ability of this solvent to continuously release small amounts of HCl by thermolytic elimination. A study of the reaction led to several improved protocols such as (1) preheated TCE, (2) microwave-assisted reactions, and (3) flow or sealed-tube conditions, which allow significant reaction rate enhancements and made possible some challenging reactions such as the alpha-amidoalkylation of ketones. Studies using flow chemistry confirmed not only that very low concentrations of HCl generated from the solvent were responsible for the reactivity but also that TCE had additional beneficial properties in comparison to other chlorinated solvents such as dichloroethane. The method can easily be extended to the alkylation using proelectrophiles such as pi-activated alcohols, which are normally unreactive toward HCl catalysis. This work represents the first successful use of HCl, the simplest strong Bronsted acid, as an efficient alkylation catalyst