Daniela Vuluga

Influence of the structure of polyfluorinated alcohols on Brønsted acidity/hydrogen-bond donor ability and consequences on the promoter effect.

The influence of substituents on the properties of tri- and hexafluorinated alcohols derived from 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was examined. Measurements of specific solvent-solute interactions revealed that H-bond donation (HBD) of fluorinated alcohols is sensitive to the steric hindrance of the OH group, whereas their Brønsted acidity is dependent only on the number of fluorine atoms. For hexafluorinated alcohols (HFAs), their association with amines characterized by X-ray diffraction showed that the balance between HBD and acidity is influenced by their structure. Moreover, the ability of HFAs to donate H-bonds is exerted in synclinal (sc), synperiplanar (sp), and also antiperiplanar (ap) conformations along the C-O bond. Comparison of the effects of fluorinated alcohols as promoting solvents in three reactions is reported. The positive correlation between rate constants and H-bonding donation ability for sulfide oxidation and imino Diels-Alder reaction brings to light the role of this property, while acidity might have a minor influence. In the third reaction, epoxide opening by piperidine, none of these properties can clearly be put forward at this stage.

Synthesis of pyrazoles through catalyst-free cycloaddition of diazo compounds to alkynes

The synthesis of pyrazoles via1,3-dipolar cycloaddition of diazo compounds to alkynes proceeds easily by heating. With α-diazocarbonyl substrates the reactions are conducted under solvent-free conditions affording the pyrazole products in high yields without any work up or purification.

Fluorous 4‐N,N‐Dimethylaminopyridine (DMAP) Salts as Simple Recyclable Acylation Catalysts

The recyclability of organicand metal-based catalysts is of prime interest for the development of sustainable synthesis processes. Since the pioneering work of the groups of Litvinenko and Steglich, who independently reported organocatalyzed acylation reactions with 4-N,N-dimethylaminopyridine (DMAP), dialkylaminopyridines still remain in the limelight. Thus, remarkable developments are regularly reported, as exemplified by the emergence of more potent analogues, even chiral, as catalysts for a diverse range of reactions. Unfortunately, these powerful organocatalysts exhibit acute dermal toxicity, whereas the corresponding salts only produce local irritation by skin contact. To avoid dissemination of these harmful chemicals in the environment, recyclable 4-aminopyridines have been prepared through immobilization on organic or inorganic supports. Although some remarkable systems emerged, those exhibiting significant activity coupled with complete recyclability are scarce. In 2007, Gun ko, Connon, and coworkers reported a very elegant magnetic-nanoparticle-supported DMAP that can be used several times without loss in activity and that is simply recovered by using an external magnet. 12] However, a limit in the molecular weight of the support is highly desirable to avoid the use of a quantity of immobilized catalyst larger than that of the substrate. Alternatively, fluorous techniques also offer a very attractive way to selectively recover a compound tagged with perfluorinated chains from a complex reaction mixture. Although this strategy originally involved fluorous solvents or silica, the current trend tends toward simple solubility modulation of fluorous catalysts in conventional media, for recovery through precipitation. In the field of catalysis, the fluorous approach has been widely applied to metal catalysts by means of fluorinated ligands. In contrast, reports on fluorous organocatalysis are still scarce, 19] and the field is only at an early stage of development. In this context, we recently reported the preparation of an efficient fluorous aminopyridine for esterification of hindered alcohols, which suffered from poor recyclability. We now report the use of an easily accessible fluorous salt of DMAP, 1-Rf, as an active and recyclable acylation catalyst, under simple conditions.

Solvatomagnetic Comparison Method: A Proper Quantification of Solvent Hydrogen-Bond Basicity.

The hydrogen-bond-acceptor basicity of an important class of solvents, the amphiprotic solvents (water, alcohols, primary and secondary amides, and carboxylic acids), has not yet been properly parametrized. In this work, the first scale of solvent hydrogen-bond basicity applicable to amphiprotic solvents is established by means of a new method that compares the 19F NMR chemical shifts of 4-fluorophenol and 4-fluoroanisole in hydrogen-bond-acceptor solvents. This so-called solvatomagnetic comparison method is free of the shortcomings of the solvatochromic comparison method used so far and is easier to carry out than the pure base calorimetric method. The validity of the new scale is assessed by good linear correlations with spectroscopic, thermodynamic, and kinetic solute properties depending on the solvent hydrogen-bond basicity. In such correlation analysis of solvent effects on physicochemical properties, solvent and solute hydrogen-bond basicity scales must not be mixed, since it is shown here that solute and solvent scales are not equivalent. A comprehensive collection of parameters quantifying the hydrogen-bond basicity is presented for 168 solvents.

Solubility switch of gold nanoparticles through hydrogen bond association

Gold nanoparticles (AuNPs) coated with hexafluoroisopropanol moieties were prepared, and their surface was changed through simple hydrogen bond association with various amines, which allow orientation of the solubility of these AuNPs in determined organic solvents.

Photoinitiated thiol–epoxy addition for the preparation of photoinduced self-healing fatty coatings

Herein, we report the use of the photoinitiated thiol–epoxy chemistry for the preparation of a new biosourced self-healing coating. Epoxidized cottonseed oil is used as the main reagent (>80 wt%) and photocrosslinked in the presence of 0.25 equivalents of 7-mercapto-4-methyl coumarin, used as a photodimerizable and healable reactant. The reaction is initiated with 2 wt% of a photobase generator (PBG). The stability of the thiol–epoxy mixture under storage and the oxygen-promoted photoinitiating system are some of the advantages illustrated in this study. The physicochemical properties of the resulting coatings as well as the photoreversibility of the coumarin derivative once grafted on the vegetable oil are studied. The photoinitiation step is demonstrated to be efficient for the grafting of the healing reagent as well as for epoxy homopolymerization.

Thiol–ene chemistry of vegetable oils and their derivatives under UV and air: a model study by using infrared spectroscopy and mass spectrometry

Herein, a model study of the photoinitiated thiol–ene reaction was carried out on unsaturated fatty methyl esters at room temperature and without photoinitiator. Reaction kinetics were monitored by FTIR spectroscopy and reaction products were identified by high resolution mass spectrometry coupled to ion mobility spectrometry. This set of analytical tools enabled us to highlight the concomitance of fatty double bond oxidation and thiol–ene addition when such a formulation was exposed to UV radiation. Indeed, thiol–ene adducts were identified on fatty moieties oxidized or not, without prevalence of one reaction over the other: photoinitiated thiol–ene addition could occur on preoxidized products, and photooxidation could occur on thiol–ene adducts. However, the presence of oxidized fatty products such as peroxides and zwitterionic species was proved to be favourable to the photocrosslinking of fatty coatings by thiol–ene addition.