1.3- dioxepan, oxidation

The noncatalytic oxidation of 4,7-dihydro-l,3-dioxepin 46a with nitrous oxide in liquid phase at 220 °C produces 1,3-dioxepan-5-one however, the conversion is very slow <2004ASC268>. 

Oxidation of benzo-fused 1,3-dioxepane 79 with cerium ammonium nitrate afforded the />-diquinone 80 <2006T635>, and oxidation of 2-hydroxydioxepin 81 with manganese dioxide gave l,3-dioxa-4-cyclohepten-6-one 82 <2004RJ01830> (Scheme 14). 

B-90 and B-91, respectively.390 Another route coupled with cationic ring-opening polymerizations is accomplished for polymer B-92 with the use of a hydroxyl-functionalized initiator with a C—Br terminal, where the OH group initiates the cationic polymerizations of 1,3-dioxepane in the presence of triflic acid.329 Polyethylene oxide)-based block copolymers B-93 are obtained by living anionic polymerization of ethylene oxide and the subsequent transformation of the hydroxyl terminal into a reactive C—Br terminal with 2-bromopropionyl bromide, followed by the copper-catalyzed radical polymerization of styrene.391... 

Pentyl-hydroperoxide was prepared from the corresponding alcohol by oxidation with 50% H2O2 in the presence of 85% H3PO4 at 60°C for 6 h to give the hydroperoxide in 48% yield, which was then treated with Pb(OAc)4 in pentane under reflux for 18-45 h to generate 1,2-dioxepane (5) in 10-14% yield (Equation (1)) <81S633>. 

Dioxepanes have been manufactured by treatment of alkenes in the liquid phase with oxygen and carbon monoxide with PdCyCuCl as a catalyst, for example synthesis of (12 X = CN) from acrylonitrile <94JAP0608778i>, or by oxidation of alkenes with Th(III)-acetate in 1,4-diols <76BCJ3285>. Treatment of perfluoro(2-methyl-2-pentene) with 1,4-butanediol and triethylamine leads to (27)... 

The parent member of this class of compounds, l,3-dioxepan-2-one (169) has been synthesized either by treating 4-chloro-l-butanol with ammonium bicarbonate in acetonitrile under a CO2 atmosphere <80MIP479522> or by reaction of butylene oxide and solid CO2 in the presence of MnBr2 <72JAP47026786> (Equation (25)), and (169) has b n used as a solvent for the halogenation of ketene <73GEP(0)2247764>. 

The parent member of this class of compounds, l,4-dioxepan-5-one, and its methyl derivatives (119) have been prepared by Baeyer-Villiger oxidation, and the methyl derivative has been transformed to the dioxepinone (121) <89MM3838,94CC687>. l,4-Dioxepan-5-one could also be obtained by cyclization of (122) and hydrolysis of the intermediate iminoether hydrochloride (123) (Scheme 11) <89MM3838>. 

Examples given in this volume are the papers by Yang (on the cationic copolymerization of trioxane and 1,3-dioxepane) (58) and by Luther (on labelled polyphosphazenes) (71). Poly(ethylene oxide) is also included in the HPLC-NMR studies by Hiller and Pasch (66). 

The stereocopolymers of lactic acid, prepared by the polymerization of various stereoisomers, are discussed in a subsequent section in this book and will not be discussed here. Typical comonomers that have been used for lactic acid or lactide copolymerization are glycolic acid or glycolide (GA) [11-17], poly (ethylene glycol) (PEG) or poly(ethylene oxide) (PEG) [15 3], poly(propylene oxide) (PPO) [16-18], (7 )- 3-butyrolactone (BL), 6-valerolactone (VL) [44-46], E-caprolactone (CL) [47-54], 1,5-dioxepan-2-one (DXO) [55-60], trimethylene carbonate (TMC) [61],... 

This unzipping depolymerization occurs during polymerization, but it may also occur under thermal stress with the neutralized polymer, unzipping then starts from neutral but unstable end groups such as -OH or -CHO or from statistical chain sdssion. Unzipping will stop at comonomer units such as those from ethylene oxide, dioxepane, and similar monomers, which are not able to depolymerize, and a then stable copolymer will result. Homopolymers, which are usually polymerized anionically from formaldehyde (see Section 7.2.3) will not be stable unless unstable end groups are transformed to stable ones. 

Figure 12 Insertion of isolated oxybutane-1,4-diyl (tetramethylene oxide) units (B) in the crystalline phase of trioxane-dioxepane copolymers ...

III-E-13.2. Summary of the Atmospheric Fate of 1,3-Dioxepane, and the End Productsof Its Oxidation... 

The atmospheric lifetime of 1,3-dioxepane is about 8 h, assuming a daytime [OH] = 2.5 X 10 molecule cm . No data are available regarding the products of its oxidation. 

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