Res. Chem. Intermed.
, Vol. 28, No. 2,3, pp. 143–158 (2002)
Also available online - www.vsppub.com
Phosphoryl and thiophosphoryldithioformates as spin
traps: from EPR studies to practical applications
, MASSIMO BENAGLIA and DANTE MACCIANTELLI
ICoCEA — Area della Ricerca del CNR, Via P. Gobetti 101, I-40129 Bologna, Italy
Abstract—This paper is aimed at providing an overview of our studies on the title compounds as
spin trapping agents, and at emphasising the links between purely cognitive, academic research and
industrial applications. Phosphoryl- and thiophosphoryl-dithioformates exhibit a comparable and
interesting spin trapping ability, their ef ciency being analogous to that of some aromatic thioketones.
The spectral hyper ne structure may provide valuable information on the nature of the trapped radical
but the phosphorus hfs constant cannot be used as an useful indicator. Thionformates are less ef cient
spin traps than the corresponding dithioformates, being inert towards stabilised radicals such as benzyl
or relatively hindered radicals as
-butoxyl. In no case could spin adducts to thiolformates be
detected, this being an indication that their carbonyl group is signi cantly deactivated with respect to
that of organic and organometallic ketones. Because of their ability in trapping either alkyl or alkoxy
radicals both kind of dithioformates were exploited as stabilisers in the processing of such polymers
as polypropylene, but their outstanding performance could not compensate for some organoleptic
drawbacks that were intrinsic of the thiocarbonyl function. A much more promising application
of dithioesters is instead their use as RAFT chain transfer agents in the controlled polymerisation
of styrene. Preliminary experiments with benzyl diethoxyphosphoryldithioformate have afforded
polystyrene with a polydispersity as low as 1.17, but further studies are needed to fully elucidate
the RAFT-polymerisation mechanism and to optimise its outcome.
: EPR; spin trap; controlled radical polymerisation; RAFT.
Phosphoryl- (1) and thiophosphoryl-dithioformates (2), as well as the corresponding
thionformates (3, 4) and thiolformates (5, 6) are long since known compounds, and
indeed some of them have been the object of industrial patents , mainly in the
eld of agriculture as pesticides.
From its origin, our group has been interested in the chemistry of free radicals
and is endeavoured in a continuing search for new and ef cient spin trapping
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