Sustainable solutions for removing aged wax-based coatings from cultural heritage. Exploiting hydrophobic deep eutectic solvents (DESs)

This study describes the investigation on the use of hydrophobic Deep Eutectic Solvents (DESs) for the removal of nonpolar coatings from works of art to replace toxic solvents. Beeswax and two microcrystalline waxes (R21 and Renaissances) have been selected as reference nonpolar coatings since they are commonly present in their aged state on metal and stone artifacts. The interaction between the DESs and three waxes has been evaluated through contact angle measurements, solubility tests, and cleaning tests carried out by implementing a method that is ordinarily used by restorers. Tests have been conducted on mockups consisting of microscope glass slides covered by wax. The effective removal of the wax-based coating from the mockups has been assessed through spectrocolorimetry and multispectral imaging under visible (VIS) and ultraviolet light (UV) at 365 nm by loading the waxes with a fluorescent marker (Rhodamine 6G). Fourier Transform Infrared (FT-IR) spectroscopy in the Attenuated Total Reflectance (ATR) mode was performed to assess the presence of both the wax and the solvent on the swabs used for the cleaning tests, confirming the actual interaction among the solvent and the solute. The experimental process proved DESs’ potential of being used as green solvents for cleaning treatments on Cultural Heritage

Palladium catalysis with sulfurated substrates under aerobic conditions: A direct oxidative carbonylation approach to thiophene-3-carboxylic esters

The first example of a palladium-catalyzed oxidative carbonylative S-cyclization process carried out under aerobic conditions is reported. The method is based on the use of the PdI2/KI catalytic system and an acetylenic substrate bearing a sulfurated group in suitable position for attacking the coordinated triple bond. To avoid the possible oxidation of a free thiol group, a methylthio group was used as sulfur nucleophile, since the methyl group on sulfur could be removed under the reaction conditions by reaction with the iodide anion to give methyl iodide. In particular, we have employed as substrates 1-(methylthio)-3-yn-2-ols, which, upon S-cyclization, demethylation, and alkoxycarbonylation, led to thiophene-3-carboxylic esters in one step, in alcohols as external nucleophile and solvents, and under 40 atm of a 4:1 mixture of CO-air (air being the source of oxygen, used as external oxidant). The Pd(0) species deriving from the alkoxycarbonylation process was reoxidized back to catalytically active PdI2 by the action of oxygen in combination with the hydrogen iodide ensuing from the alkoxycarbonylation step and from water attack to methyl iodide. This new synthetic transformation could be successfully applied to a variety of differently substituted 1-(methylthio)-3-yn-2-ols, including substrates bearing geminal dialkyl substituents

Iodocyclization of 2-Methylthiophenylacetylenes to 3-Iodobenzothiophenes and their coupling Reactions under More Sustainable Conditions

We report the first example of iodocyclization of readily available 2-methylthiophenylacetylenes in a deep eutectic solvent (ChCl/urea 1/2, mol/mol) as recyclable and more sustainable solvent with respect to the classical VOCs employed so far. The process successfully afforded a variety of 3-iodobenzothiophenes in good to high yields starting from differently substituted substrates, with the possibility to recycle the DES several times without appreciable lowering of the product yield. The 3-iodothiophenes thus synthesized are known to be important precursors of biologically active molecules and functionalized heterocycles, and were successfully employed for performing representative Sonogashira and Suzuki cross-coupling reactions. The solvent-catalyst system could be conveniently recycled several times without any loss of activity in both coupling processes, thus further demonstrating the practical usefulness of our approach