Synergetic activation of CO2 by the DBU-organocatalyst and amine substrates towards stable carbamate salts for synthesis of oxazolidinones

The development of an efficient methodology to transform CO2 into valuable chemicals has attracted increasing attention concerning the challenging issues of CO2-utitlization.

Experimental and Theoretical Investigation of Excited-State Intramolecular Proton Transfer Processes of Benzothiazole Derivatives in Amino-polydimethylsiloxanes before and after Cross-Linking by CO2

The changes in the ability of three fluorescent derivatives of 2-(2'-hydroxyphenyl)benzothiazole to undergo excited-state intramolecular proton transfer (ESIPT) processes have been correlated with the rheological properties of four amino-polydimethylsiloxanes with different molar masses and containing different amounts of monomer units with amino pendant groups, in the presence and absence of a cross-linking molecule, CO₂. The changes lead to a variety of species (keto, enol, and enolate forms) in both the ground and excited states. Calculations using the density-functional theory/time-dependent density-functional theory method at the CAM-B3LYP/6-311++G(d,p) level helped to identify how ESIPT is involved in the formation of the intermediates. The results demonstrate that proton transfer in 2-(2'-hydroxyphenyl)benzothiazoles is a powerful tool to identify local changes in the viscosity and micropolarity of the environment that are attributed to the structural differences of the amino-polydimethylsiloxanes and their cross-linking.

Reversible Switching of Tb(III) Emission by Sensitization from 2,3-Dihydroxynaphthalene in an Isothermally Reversible Ionic Liquid

A reversible room-temperature ionic liquid (ILO) was prepared by the addition of CO2 to an equimolar mixture of hexylamidine (AD) and butylamine (AN). The ILO and AD/AN mixture were cycled repeatedly by alternating the passage of CO2 and N2 gases through the liquid. The ILO was utilized to sensitize very efficiently energy transfer to and emission by Tb(III) ions when 2,3-dihydroxynaphthalene (DHN) was irradiated. The emission was nearly completely quenched in the AD/AN mixture. The process described here is unique in its use of CO2 and N2 to "switch on and off" the emission by a lanthanide ion, Tb(III) in this case. In the corresponding amidinium dithiocarbamate ionic liquid (ILS), no appreciable Tb(III) emission was found due to quenching of the excited singlet state of DHN by thio groups. The ILS was not reconverted to the AD/AN mixture upon adding N2; N2 bubbling did not result in the displacement of CS2.

CO2 capture systems based on saccharides and organic superbases

In this report, novel systems, based on highly abundant saccharides, d-mannose, d-glucose, β-cyclodextrin, alginic acid and mannitol, in combination with an organic superbase, tetramethylguanidine (TMG) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), are studied for carbon dioxide capture. With d-mannose and d-glucose, several ratios of equivalents of alcohol groups of saccharide : superbase were tested: 1, 0.625, 0.5 and 0.25. High wt% values of CO₂ uptake were obtained with TMG-based systems. However, TMG itself can react directly with CO₂, and, in the presence of d-mannose, competition between carbonate and carbamate based products was established. In order to circumvent this competition and obtain exclusively the carbonate-based product, DBU was used instead as an organic superbase. In the d-mannose series the highest result was obtained with a d-mannose : DBU ratio eq. = 0.625 (13.9% CO₂ uptake, 3.3/5 alcohol groups converted into carbonates). A more effective stirring system, designed to overcome the high viscosity of the products, allowed the use of a d-glucose : DBU = 1 : 1 ratio with 11.5 wt% of CO₂ uptake and 2.47/5 alcohol groups converted into carbonates. Additionally a DSC thermal study was performed in order to study the stability/reversibility of the CO₂ loaded systems.