Hydrogen atom transfer fluoride

These studies differ in that, whereas Wells and co-workers have spectrally characterised an intermediate and suggested from the data that the substitution rate for Mn" is 5 x 10 1 mol s" (c/. the recent study by Diebler on the formation of fluoride species), since it should lie between that for the chromium(ii) species and the oxidation rate for the Mn" -hydroquinone complex, Davies and Kustin postulate in the acid range 0-6—3-60 mol 1 an inner-sphere mechanism with hydrogen atom transfer as the predominant mode of reaction for MnOH +, with rates not too different from those derived from studies on other systems (Table 1). The reaction is first-order in each reactant and the observed second-order rate constant is invariant with [Mn" ]o, [H2Q], and [Mn"]. A mechanism consistent with intermediate formation may be written... 

The growing vinyl fluoride free radical is not resonance stabilized. Therefore it is quite reactive and capable of abstracting a hydrogen atom from active hydrogen compounds such as isopropanol or acetonitrile with consequent chain termination by a ehain-transfer mechanism. In the case of a solvent such as dimethyl sulfoxide, such processes do not take place. As a result, the precipitating polymer has difficulties finding appropriate radieals for termination reactions. As in other examples of the gel or TrommsdorfF effect, an acceleration in rate is observed because the free radical propagation is not terminated while the viscosity of the product increases and the rate of the transfer of the released heat to the outside is severely limited. 

The triphenylphosphine oxide complexes (13.24a,b) have relatively simple structures. In the case of the fluoride, however, the hydrogen atom is located closer to F than to O and it may be argued that proton transfer has not taken place. In crystalline PhjPO HNO3 (13.24c) the proton remains closer to the nitrate group while in PhjAsO HNO3 it appears to lie closer to the 0=As unit (13.24d). 

Sulfides are selectively fluorinated a to the sulfur atom via a reaction similar to the Pummerer rearrangement (Table 2). The fluorination wa.s originally achieved by the direct fluorination of sulfides with xenon difluoride.This reaction is proposed to occur by initial oxidative fluorination of the sulfide to give an unstable sulfur(IV) difluoride of type 1, followed by loss of hydrogen fluoride to give intermediate 2, followed by fluorine transfer to give the a-fluoro sulfide. This fluorination has also been achieved with diethylaminosulfur trifluoride (DAST) in the absence or presence of catalytic amounts of antimony(III) chloride (see Vol. ElOa, pp 421-423). ... 

---