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.
Laboratoire BioCIS-CNRS, Faculté de Pharmacie, Univ. Paris Sud, 5 rue Jean-Baptiste Clément, F-92296 Châtenay-Malabry, France.
Daniela
D
Vuluga
Julien
J
Legros
Benoit
B
Crousse
Alexandra M Z
AM
Slawin
Christian
C
Laurence
Pierre
P
Nicolet
Danièle
D
Bonnet-Delpon
D000143:Acids / Q000737:chemistry*; D000438:Alcohols / Q000737:chemistry*; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D020005:Propanols / Q000737:chemistry*; D011522:Protons; D012997:Solvents; D014270:Trifluoroethanol / Q000737:chemistry*; D014961:X-Ray Diffraction; D006845:Hydrocarbons, Fluorinated
D000143:Acids; D000438:Alcohols; D020005:Propanols; D011522:Protons; D012997:Solvents; D014270:Trifluoroethanol; C001337:hexafluoroisopropanol; D006845:Hydrocarbons, Fluorinated