Perchloro-p-xylylene

Perchloro-p-xylylene prepared by Ballester et al. 62) exhibits no tendency for polymerization and is very stable even at elevated temperature. 

Bisf trichloromethyl) chlorocarbons. The reductive condensation of perchloro-/ -xy/ene with either tin(ii) chloride or iron(ii) chloride in dioxane gives a polymeric chlorocarbon, the perchloropoly-/ -xylenediylidene (PP-xynene), a small proportion of perchloro-p-xylylene usually being formed (Ballester, 1979 Ballester et al., 1966). The configuration of this polymer is mixed cis and trans, as ascertained by its ultraviolet spectrum. The mechanism (45) has been postulated (Ballester et al., 1966). PP-xynene possesses a colossal thermal stability (up to 650°C from thermogravimetric analysis (TGA), see Fig. 6), and exceptional chemical inertness (e.g. to hot oleum, boiling red fuming nitric acid and to chlorine). 

The reaction of perchloro-p-xylene with iodide ion in acetic acid (or acetone) (Diaz-Alzamora, 1968) gives perchloro-/t-xylylene exclusively (Ballester and Castaner, 1960a). The reaction conditions (anionic reductant, acetic acid solvent) giving perchloro-p-xylylene (perchloro-p-quinodimeth-ane) are remarkably different from those affording PP-xynene (cationic... 

When this reaction is performed in acetic acid containing hydrogen chloride, the yield of perchloro-p-xylylene diminishes further (53%) and that of a//,a //-octachloro-p-xylene increases (42%). This result shows that hydrogen iodide, formed from iodide ion, is an efficient hydrogen-atom donor. 

Some aspects of the synthesis of this chlorocarbon have already been considered (p. 304). Perchloro-p-xylylene is a diamagnetic chlorocarbon, gives no esr signal, and its ground state is therefore singlet it is a true p-quinodimethane (as represented in (45)). 

Around 300°C, in a sealed container, perchloro-p-xylylene decomposes mainly to perchlorostyrene and perchlorobenzene. This suggests that some transient oligomerization takes place (see PP-xynene, p. 301) at that temperature, with evolution of chlorine, which causes chlorinolysis, yielding those products (Monso, 1969). This might be related to its conversion into the diradical form at high temperature. 

The following reaction mechanism was postulated. Due to its remarkable inertness, perchloro-p-xylylene [59] was considered to be an unlikely intermediate in this polymerization. 

Pent-2-yne-4-ene-l-ol, polymers of, 60 Perchlorocoumalin polymers with 4,4 -diphenylmethane-bis(maleimide), 117 with AT,A( -Hexamethylenebis-(maleimide), 116 Perchloro-4,4 -dimethylbiphenyl, polymers of, 26 Perchloro-p-dipropenylbenzene polymerization of, 11 polymers of, 26 Perchloro-p-xylylene polymerization of, 11,12 polymers of, 15,26 Perfluoro-1,3-pentadiene, polymers of, 58 Perfluoro-1,4-pentadiene,... 

Thermal dimerization of 2,3,5,6-tetrachloro-p-phenylenediimine 351 A remarkable benzidine rearrangement 352 Condensation of aromatic perchloroamines 353 Perchlorinated organic radicals and related intermediates 354 Perchlorobenzyl radicals 354 Perchlorodiphenylmethyl radicals 355 Perchlorotriphenylmethyi radicals 361 Perchloro-9-phenylfluorenyl radicals and related species 384 Inert perchloro-aza-radicals 389 Perchloro-p-quinodimethanes, perchloro-/ -xylylenes and related compounds 390... 

Another possibility is that, as in polycondensation, the formation of per-chloro-p-methylbenzyl radical is also brought about by iodide ion, but its subsequent reaction with iodide ion occurs so fast that its dimerization to perchloro-p,/7 -dimethylbibenzyl or subsequent vicinal chlorine elimination is prevented. Accordingly, when the reaction is carried out in the presence of toluene as hydrogen-atom donor (see preceding section) the yield of per-chloro-p-xylylene diminishes (72%), the rest being a, a //-octachloro-p-xylene, benzyl acetate, and, according to H-nmr spectroscopy, a mixture of cis- and tra 5-a/7,a //-tetradecachlorostilbene (46) (Diaz-Alzamora, 1968). 

It is noteworthy that unsymmetrical perchloro-a,a-diphenyl-/7-xylylene, formed probably with HO in DMSO/ethyl ether, reacts further. Presumably, this is due to its being in equilibrium with its dimeric diradical on account of the front strain of the latter (p. 354), allowing reversion to its singlet state, which undergoes subsequent reaction (184) (p. 294). 

---