Uso de una mezcla dioxane/MeOH/NaBH4 en caliente como un medio conveniente para la reducción química selectiva del doble enlace C=C en sistemas α,β-insaturados

Productos de Knoevenagel diversamente sustituidos fueron sometidos a reducción con una solución de NaBH4 en MeOH/p-dioxano a 70 oC. A través de este proceso, se alcanzó la reducción selectiva de sus dobles enlaces C=C en todos los casos. Las condiciones de reducción establecidas toleró una variedad de grupos funcionales, aunque productos simples de condensación aldólica o de Claisen- Schmidt mostraron menos selectividad hacia la reducción del doble enlace C=C, y por el contrario, condujo específicamente a la reducción de los grupos C=O. Adicionalmente, la selectividad de nuestras condiciones de reducción mediadas por NaBH4 fue comparada con la clásica hidrogenación catalítica mediada por Raney-Nickel para encontrar algunas similitudes y diferencias. Así mismo, se propuso una secuencia de pasos mecanísticos, con el fin de intentar explicar el proceso de reducción selectiva mediada por NaBH4.

Conversion of Residual Palm Oil into Green Diesel and Biokerosene Fuels under Sub- and Supercritical Conditions Employing Raney Nickel as Catalyst

A comprehensive study of the thermal deoxygenation of palm residue under sub- and supercritical water conditions using Raney nickel as a heterogeneous catalyst is presented in this paper. Hydrothermal technology was chosen to replace the need for hydrogen as a reactant, as happens, for example, in catalytic hydrotreatment. Several experiments were carried out at different reaction temperatures (350, 370, and 390 °C) and were analyzed with different times of reaction (1, 3.5, and 6 h) and catalyst loads (5, 7.5, 10 wt.%). No hydrogen was introduced in the reactions, but it was produced in situ. The results showed the selectivity of biokerosene ranged from 2% to 67%, and the selectivity of diesel ranged from 5% to 98%. The best result was achieved for 390 °C, 10 wt.% catalyst load, and 3.5 h of reaction, when the selectivities equal to 67% for biokerosene and 98% for diesel were obtained. The Raney nickel catalyst demonstrated a tendency to promote the decarboxylation reaction and/or decarbonylation reaction over the hydrodeoxygenation reaction. Moreover, the fatty acid and glycerol reforming reaction and the water−gas shift reaction were the main reactions for the in situ H2 generation. This study demonstrated that a hydrothermal catalytic process is a promising approach for producing liquid paraffin (C11−C17) from palm residue under the conditions of no H2 supply.

One-step synthesis of imidazoles from Asmic (anisylsulfanylmethyl isocyanide)

Substituted imidazoles are readily prepared by condensing the versatile isocyanide Asmic, anisylsulfanylmethylisocyanide, with nitrogenous π-electrophiles. Deprotonating Asmic with lithium hexamethyldisilazide effectively generates a potent nucleophile that efficiently intercepts nitrile and imine electrophiles to afford imidazoles. In situ cyclization to the imidazole is promoted by the conjugate acid, hexamethyldisilazane, which facilitates the requisite series of proton transfers. The rapid formation of imidazoles and the interchange of the anisylsulfanyl for hydrogen with Raney nickel make the method a valuable route to mono- and disubstituted imidazoles.