Synthesis of Carbynoid Materials by Chemical Dehydrohalogenation of Halogen-Containing Polymers - Polyynes: Synthesis, Properties, and Applications - page 250

In a search for new starting materials for synthesizing carbynoid
structures, Evsyukov et al. studied dehydrohalogenation of poly(ethylene-
alt-chlorotrifluoroethylene) [18]. The starting polymer currently supplied
by Aldrich is claimed to be an alternating co-polymer of ethylene and
chlorotrifluoroethylene. Considering theoretically possible pathways of the
dehydrohalogenation reaction of poly(ethylene-alt-chlorotrifluoroethylene)
[PE-a-CTFE], one can conclude that the latter might be used as a precursor
for synthesizing the polyyne form of carbyne. The first stage of dehydro-
halogenation should bring about the formation of a fluorine-substituted
polyene structure of poly(3,4-difluoro-2-butene-1,4-diylidene), regardless of
the initiation site (Scheme 12.5).
SCHEME 12.5
Here it is pertinent to note that elimination of HCl from PE-a-CTFE
should create an intermediate structure identical to that of poly(1,1,2-tri-
halobutadiene) (cf. Scheme 12.2 ) in the case of 1,4-polymers (Scheme 12.6).
SCHEME 12.6
Therefore, it is evident that further elimination of HF should give rise to
the formation of analogous head-to-head polyhalovinylene, and complete
dehydrohalogenation must yield the polyyne structure (Scheme 12.5).
12.3 DEHYDROHALOGENATING AGENTS
Generally, basic reagents intended to be used for synthesizing carbynoid
structures by a dehydrohalogenation reaction should meet three require-
ments. First, they should be strong enough to effect exhaustive elimination
of hydrogen halides, particularly at the second stage of the reaction (i.e. the
dehydrohalogenation of halogen-substituted polyenes, cf. Schemes 12.1 to
12.3 , and 12.5). Secondly, their nucleophilicity must be low to avoid side