1.3.5.7- Tetroxane, formation

Recently, the enthalpies of combustion and sublimation were measured for formaldehyde diperoxide, i.e. 1,2,4,5-tetroxane , from which the enthalpies of formation could be derived. These results were shown to be in good agreement with quantum chemical... 

A related study of 3,6-diphenyl-l,2,4,5-tetroxane resulted in enthalpies of formation of the sohd and gaseous species of 134.0 1.3 and 99.7 1.3 kJmor. Again, while computational theory and experiment are in good agreement, the sublimation enthalpy of 34.3 kJmoU seems too low. We would have suggested a lower bound of ca 71 kJmoU based on our enthalpy of vaporization estimation approach given above. 

An additional problem with the enthalpies of formation of the two tetroxane species is irreconcilable. The —288 kJmoU difference between the enthalpies of formation of the parent and diphenylated species is much too large. After all, the difference between the enthalpies of formation of 1,3-dioxolane and its 2-phenyl derivative is —93 kJmoU and doubling this value for two substituents is but —186 kJmor. No explanation for this discrepancy is apparent. 

The polymerization of trioxane in solution has been studied by Okamura (26) and his co-workers and by Kern and Jaacks (56, 58, 63). The initiators were borontrifluo-ride or its complexes and anhydrous perchloric acid. During the polymerization the eight-membered ring, tetroxane, is formed rapidly but this compound takes part in the polyoxymethylene formation. This results in an equilibrium concentration of tetroxane when the rate of formation becomes equal to the rate of consumption (27). Minor amounts of the ten-membered ring, pentoxane, are also formed (28). The authors conclude that tetroxane and pentoxane are formed by a back-biting mechanism. It is assumed that the active species in the reaction is a carbenium ion. Although this ion... 

The occurrence of a back-biting reaction is further indicated by the observation that in copolymerizations of trioxane or tetroxane with vinyl monomers various 1,3-dioxane derivatives are formed (29,56). With styrene for example, the derivative was 4-phenyl-l,3-dioxane, the formation of which was explained as follows ... 

The theoretical value of the enthalpy of formation of the tetroxane 14, 276.27 kcal mol , was in good agreement with the experimental value, 262.47 kcal mol <2005BMC5826>. 

Treatment of 127 with cysteinate-iron in the presence of excess of methyl cysteinate led to formation of a sulfur-alkylated methyl cysteinate derivative 153 in 33% yield (Scheme 20), suggesting a possible mechanism for antimalarial action by tetroxanes <2003CHJ875>. 

A recent improvement to this type of reaction often selects for the formation of tetroxanes over the trimeric hexaoxonane analogs. The use of fluorinated alcohols such as trifluoroethanol (TEE) or, often better, HFIP, as solvent and methyltrioxorhenium (MTO) as catalyst, as well as a substrate concentration of 1 M, are considered important for success (Equation (26) Table 3) <2003TL6309, 2006T1479, 2006BMC7790>. 

Chain growth in this reaction is accompanied by formations of tetroxane and 1,3-dioxolane through backbiting. ... 

---