Una propuesta para el tratamiento del enlace químico en el segundo ciclo de educación secundaria obligatoria

El enlace químico es considerado como elemento organizador dentro de la Química y por tanto su aprendizaje en educación secundaria es fundamental para la comprensión del cuerpo epistemológico de dicha ciencia. En este trabajo se propone una unidad didáctica para 4º ESO en la que, a partir de la observación de las propiedades físicas de las sustancias, se busca que los alumnos construyan un modelo de enlace químico que permita explicar tales observaciones, utilizando el concepto de electronegatividad como elemento unificador y a la vez diferenciador de casos particulares de enlace químico

Desarrollo de Reacciones de Oxidación de Enlaces C-H. Aplicación a la Síntesis de Guayanolidas

Los productos naturales, y en especial lactonas sesquiterpénicas como las guayanolidas, han servido de inspiración para el diseño de fármacos contra el cáncer. Un ejemplo de ello es el profármaco de tapsigargina G202, que ha superado con éxito las fases iniciales de ensayos clínicos. En este contexto, el desarrollo de metodología sintética que permita alcanzar en pocos pasos de reacción la complejidad estructural presente en la naturaleza ha adquirido una especial relevancia. Concretamente, las oxidaciones de enlaces C-H permiten la instalación eficiente de grupos funcionales en un esqueleto carbonado determinado, y su uso estratégico se ha empleado en la síntesis tanto de productos naturales como de análogos bioactivos. En esta memoria se presenta el estudio y optimización de oxidaciones alílicas, gamma‑hidroxilaciones y alfa'‑aciloxilaciones como herramientas de funcionalización de enlaces C-H. Para ello, se han empleado técnicas estadísticas que garantizan la eficiencia de dichas transformaciones y se ha extendido su aplicación a la obtención de guayanolidas de cierta complejidad.Ministerio de Educación (Programa de Formación del Profesorado Universitario

Multivariate optimization of the KharascheSosnovsky allylic oxidation of olefins

The multivariate optimization method known as simplex is applied to the KharascheSosnovsky allylic oxidation of double bonds. By applying this method, the amounts of three variables (copper source, oxidant, and additive) are optimized at the same time. Under the conditions thus obtained the reaction takes place in a considerable shorter time, being the alkene the limiting reagent. These conditions are applied to some monoterpenes and sesquiterpenes leading regioselectively to the corresponding benzoate esters, opening a route to the employment of this reaction in the synthesis of more complex molecules

Nonafluorobutanesulfonyl Azide: A Shelf-Stable Diazo Transfer Reagent for the Synthesis of Azides from Primary Amines

6 páginas, 2 esquemas, 2 tablasNonafluorobutanesulfonyl azide is an efficient, shelf-stable and cost-effective diazo transfer reagent for the synthesis of azides from primary amines. The reagent can also be successfully applied to the one-pot regioselective synthesis of 1,2,3-triazoles from primary amines by a sequential diazo transfer and azide–alkyne 1,3-dipolar cycloaddition process catalyzed by copper. The cycloaddition step can be conducted in an inter- or intramolecular way to afford 1,4- or 1,5-disubstituted triazoles, respectively. The atypical 1,5-regioselectivity under copper catalysis is a consequence of geometrical constraints of the amino-alkyne substrates used in the intramolecular version. Nonafluorobutanesulfonyl azide offers an advantageous alternative to the better known and most commonly used trifluoromethanesulfonyl azide.We thank the Spanish Ministerio de Ciencia e Innovación (projects CTQ-2006-15515-C02-02/BQU and CTQ2009- 14551-C02-02) and Comunidad de Madrid (project S2009/ PPQ-1634 “AVANCAT”) for financial support. We also thank Ministerio de Ciencia e Innovación for a FPU predoctoral fellowship to B. T. and C.S.I.C. for a JAE-Doc contract to J. R. S., a JAE-Predoc fellowship to M. E. P.-O., and a JAE-Intro fellowship to R. M.-B.Peer reviewe

Optimization by Response Surface Methodology (RSM) of the Kharasch−Sosnovsky Oxidation of Valencene

Response surface methodology (RSM) has been employed to model and optimize the Kharasch−Sosnovsky allylic oxidation of valencene. The detailed effects of the amounts of oxidant, substrate, copper catalyst, 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU), and temperature have been studied. The concentration of substrate and quantity of oxidant have been determined as the most significant variables. The interaction effects on the yield have been investigated using a three-level full-factorial design. The yield of benzoyloxyvalencene has been improved to 99%. Analysis of variance (ANOVA) has been used to evaluate the goodness of fit of the model

Acyloxylation of 1,4-Dioxanes and 1,4-Dithianes Catalyzed by a Copper−Iron Mixed Oxide

The use of a copper−iron mixed oxide as a heterogeneous catalyst for the efficient synthesis of α-acyloxy-1,4-dioxanes and 1,4-dithianes employing t-butyl peroxyesters is reported. The preparation and characterization of the catalyst are described. The effect of the heteroatoms and a plausible mechanism are discussed. The method is operationally simple and involves low-cost starting materials affording products in good to excellent yields

DoE (Design of Experiments) Assisted Allylic Hydroxylation of Enones Catalysed by a Copper–Aluminium Mixed Oxide

The allylic hydroxylation of enones using dioxygen as the oxidant has been studied. The reaction was first examined in the absence of any catalyst, using β-ionone as a model substrate. Then a new copper–aluminium mixed oxide, Cu–Al Ox, was prepared and characterized in order to be used as a catalyst. This oxide showed good activity, and provided the corresponding γ- or ε-hydroxylated enones, starting from different α,β- or α,β,γ,δ-unsaturated ketones. In all cases, the yields were significantly improved compared to experiments run in the absence of the catalyst. The reaction was selective, and the formation of epoxides or other overoxidation products was detected only to a minor extent. The described procedure is a technically straightforward synthetic alternative to those methods described to date involving many reaction steps or toxic reagents. The reactions were optimized using design of experiments techniques (DoE)

Carbon integral honeycomb monoliths as support of copper catalysts in the Kharasch–Sosnovsky oxidation of cyclohexene

Carbon integral honeycomb monoliths prepared from a natural coal were employed as support of copper catalysts for organic synthetic purposes. In particular good to excellent yields (60–100% as function of the carboxylic acid employed) were obtained in the preparation of allylic esters by the Kharasch–Sosnovsky oxidation of cyclohexene. Different characterization techniques such as chemical analysis by Inductively Coupled Plasma Spectroscopy, nitrogen physisorption, X-ray Diffraction with Rietveld analysis, X-ray Photoelectron and Raman Spectroscopies, Temperature-Programmed Reduction and Scanning Electron Microscopy allowed finding that key parameters such as textural properties, degree of copper precursor decomposition and active phase homogeneity and dispersion can be modulated as function of a simple synthetic variable: the method used to dry the monoliths after impregnation with the metal precursor, either conventional or using microwaves. The results obtained allow understanding the key role of the nature and chemical surrounding (O2 anions or OH groups) of Cu2+ ions in the catalytic activity in the reaction investigated as well as the operating deactivation mechanisms. The use of the structured catalysts here proposed also opens up an interesting alternative to homogeneous catalysis in the field of organic synthesis

Does the mass of the Earth vary? Modeling through thought experiment

El artículo analiza el efecto de la resolución de problemas cualitativos mediante experimentos mentales, en el uso de la idea de conservación de la masa. Se trata de identificar los modelos expresados por los estudiantes y cómo estos se ajustan y autorregulan a partir del trabajo en el aula. Para ello se realiza un estudio de casos múltiples con estudiantes de secundaria obligatoria, empleando métodos cualitativos de análisis de datos. A lo largo del experimento mental, los estudiantes empezaron movilizando modelos ingenuos y simples, basados en la no conservación de la materia, y más de la mitad terminó formulando otros que integraban el principio de conservación de la masa y la idea de Tierra como sistema abierto. Ello sugiere el papel de los experimentos mentales como escenarios propicios para favorecer procesos de modelización en ciencias.This paper analyzes the effect of the resolution of qualitative problems through mental experiments, in the use of the idea of conservation of mass. Its purpose is to identify the models expressed by the students, and how they adjust and self-regulate as a result of the work in the classroom. For this, a multiple case study is carried out with secondary school students, using qualitative methods of data analysis. Throughout the mental experiment, students began mobilizing simple and naive models, based on a non-conservation of matter, while more than half ended up formulating others that spontaneously integrated the principle of conservation of mass and the idea of Earth as an open system. These results show the role of mental experiments as favorable scenarios for modeling in science

Allylic Oxidation of Alkenes Catalyzed by a Copper−Aluminum Mixed Oxide

A strategy for the allylic oxidation of cyclic alkenes with a copper−aluminum mixed oxide as catalyst is presented. The reaction involves the treatment of an alkene with a carboxylic acid employing tert-butyl hydroperoxide as the oxidant. In all cases, the corresponding allylic esters are obtained. When L-proline is employed, the allylic alcohol or ketone is obtained. The oxidation of cyclohexene and valencene has been optimized by design of experiments (DoE) statistical methodology