Trioxane ring

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

One variation of rearrangement polymerisation is ring-opening polymerisation. Important examples include the polymerisation of trioxane, ethylene oxide and e-caprolactam Figure 2.8 (a) to (c) respectively). It is to be noted that... 

Ring opening polymerization may also occur by an addition chain reaction. For example, a ring opening reaction polymerizes trioxane to a polyacetal in the presence of an acid catalyst. Formaldehyde also produces the same polymer ... 

Lewis acid-promoted chloromethyl group installation onto the aromatics rings with 1,3,5-trioxane and HCl. 

Commercial polymers of formaldehyde are also produced using cationic polymerization. The polymer is produced by ring opening of trioxane. Since the polyacetal, POM, is not thermally stable, the hydroxyl groups are esterified (capped) by acetic anhydride (structure 5.22). These polymers are also called poly(methylene oxides). The commercial polymer is a... 

Polyoxymethylene, also referred to as acetal resin or POM, is obtained either by anionic polymerization of formaldehyde or cationic ring-opening copolymerization of trioxane with a small amount of a cyclic ether or acetal (e.g., ethylene oxide or 1,3-dioxolane) [Cherdron et al., 1988 Dolce and Grates, 1985 Yamasaki et al., 2001]. The properties and uses of POM have been discussed in Sec. 5-6d. 

Besides in the liquid phase, some polyreactions are also performed in the solid state, for example, the polymerization of acrylamide or trioxane (see Example 3-24). The so-called post condensation, for example, in the case of polyesters (see Example 4-3), also proceeds in the solid phase. Finally, ring closure reactions on polymers with reactive heterocyclic rings in the main chain (e.g., poly-imides, see Example 4-20) are also performed in the solid state. 

The solubility of polyoxymethylene is very poor so that the ring-opening polymerization of 1,3,5-trioxane proceeds heterogeneously both in bulk (melt) and in solution. 1,3,5-Trioxane can also be readily polymerized in the solid state this polymerization can be initiated both by high-energy radiation and by cationic initiators (see Example 3-24). 

Cationic Copolymerization of 1,3>5-Trioxane with 1,3-Dioxolane (Ring-Opening Copolymerization)... 

The first ring expansion of a 1,2,4-trioxolane to a 1,2,4-trioxane was observed with (47) where the orientation of the peroxide group was crucial in assisting the triflate to leave (Equation (2)). A 1,2-peroxide shift then follows with loss of silicon giving the methylene substituted 1,2,4-trioxane (48) as the product <91JA8168>. The equatorial triflate does not undergo rearrangement. 

Section II covers the synthesis of the cyclic peroxides with medium ring size from 5 to 7. Section HI covers the synthesis of 1,2,4-trioxanes. Classification in sub-sections and sub-sub-sections is done according to the type of reaction by which the cyclic peroxide system is formed. Syntheses of dioxirans, 1,2-dioxetanes, trioxolanes (ozonides), tetrox-anes, and macrocyclic peroxides are not discussed in this review. 

Additional examples for the syntheses of tricyclic trioxanes 606, which are substituted at the position 7, are given in Scheme 172a , whereas compounds 607, substituted at C4 and/or C9, are shown in Scheme i72b . Asymmetric syntheses of two non-racemic trioxanes 608, bearing cyano- or ethoxycarbonyl substituents at the ring-junction (position 5 ), are outlined in Scheme 172c . 10-Alkylthio- and arylthio-... 

Treatment of compound 222, containing a 1,2,4-trioxane ring fused to a cyclopentene ring, with O2 leads to formation of a hydroperoxide (223) with ene displacement, as shown in equation 76. The structure of 223 was determined by single-crystal XRD analysis. A contact of the hydroperoxy group with the endocyclic ether O atom of a neighboring molecule (287.4 pm) points to weak H-bonding. ... 

The compounds appearing in equation 102 (Section Vin.C.b.a), containing a 1,2,4-trioxane ring, were examined by single-crystal XRD analysis. The 0—0 distances in this ring (143.3, 147.2 and 148.8 pm) are in accord with the mean value (147.0 pm) measured for the Csp —OO—Csp moiety. ... 

It should be noted that, in addition to the product shown in Scheme 3, the ring-contracted THF product 21 was also observed. Indeed, significant quantities of both 21 and deoxyartemisinin 3 (using iron(II) bromide in THF) were observed in a ratio 13 21 3 of 1 6 3, determined from the proton NMR spectrum. A second pathway (in which SET occurs from iron(II) to Ol the 01 route ) leading to formation of a similar THF product was suggested in 1992 when investigating the degradation of an 0-labelled trioxane (Scheme 1). ... 

By organic chemistry formalism, polyacetals are reaction products of aldehydes with polyhydric alcohols. Polymers generated from aldehydes, however, either via cationic or anionic polymerization are generally known as polyacetals because of repeating acetal linkages. Formaldehyde polymers, which are commercially known as acetal resins, are produced by the cationic ring opening polymerization of the cyclic trimer of formaldehyde, viz., trioxane [29-30] (Fig. 1.5). 

Figure 1.5 Cationic ring opening polymerization of a cyclic trimer of formaldehyde (viz., trioxane)...

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