PHOTOCHEMICAL REDUCTION OF CARBON-HALOGEN BONDS. 3. REGIOSELECTIVITY OF THE REACTION IN FLUORINATED HALOGENOPROPANOATES.

Article abstract of DOI:10.1016/S0022-1139(00)81610-3

The ester group exhibits a strong directive effect in the photochemical reduction of a carbon-halogen bond and directs the reduction in perhalogenated chlorofluoropropanoates of the type CFXY-CClZ-COOR (X,Y,Z = Cl, F) to the α-position in the acyl part of an ester.The reduction takes place with the same regioselectivity even in esters CFCl2-CHCl-COOR (10).In esters containing an α -CCl2- group the reductions to the first and the second stages can be separated and the individual reduction products can be obtained preparatively.The α C-F bond is more difficult to reduce and therefore in the ester CFCl2-CHF-COOR (11) the β C-Cl bond was reduced specifically and in the ester CF2Cl-CHF-COOR (12) both the α C-F bond and the β C-Cl bond were reduced parallely.The relative reactivity of fluorinated halogenopropanoates with an α C-Cl bond showed only small differences in the reduction with 2-propanol in the presence of acetone as a sensitiser; the quantum yield Φ reached values of about 28-35 under kinetic measurements and thus proved the existence of a chain radical mechanism.