Ethers, cyclic oxidation

ClCHjCHjOH + NaHCOj —> HOCHjCHjOH + COj + NaCl When ethylene chlorohydrin is heated with sodium hydroxide solution, the highly reactive cyclic ether, ethylene oxide, is formed ... 

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

Cationic ROP of ethylene oxide is not useful for the synthesis of linear polymer, but is used to produce crown ethers. Propylene oxide gives less cyclic dimer than does ethylene oxide for steric reasons cyclic tetramer predominates. 

Chromium-Containing Ionic Species Chromate Ion, Hexavalent Chromium Cobalt Copper Cyclic Ethers Cyclic Ethers Dioxane-1,4 Ethylene Oxide... 

Polyethers are prepared by the ring opening polymerization of three, four, five, seven, and higher member cyclic ethers. Polyalkylene oxides from ethylene or propylene oxide and from epichlorohydrin are the most common commercial materials. They seem to be the most reactive alkylene oxides and can be polymerized by cationic, anionic, and coordinated nucleophilic mechanisms. For example, ethylene oxide is polymerized by an alkaline catalyst to generate a living polymer in Figure 1.1. Upon addition of a second alkylene oxide monomer, it is possible to produce a block copolymer (Fig. 1.2). 

Grown Ethers. Ethylene oxide forms cyclic oligomers (crown ethers) in the presence of fluorinated Lewis acids such as boron trifluoride, phosphorus pentafluoride, or antimony pentafluoride. Hydrogen fluoride is the preferred catalyst (47). The presence of BF 4, PF y, or SbF 6 salts of alkali, alkaline earth, or transition metals directs the oligomerization to the cyclic tetramer, 1,4,7,10-tetraoxacyclododecane [294-93-9] (12-crown-4), pentamer, 1,4,7,10,13-pentaoxacyclopentadecane [33100-27-6] (15-crown-6), andhexamer, 1,4,7,10,13,16-hexaoxacyclooctadecane [17455-13-9]... 

Other attempts to avoid the experimental difficulties of measuring the thermal properties of gas hydrates have been to choose the easier route of thermal property measurements of cyclic ethers-ethylene oxide (EO) for structure I, or tetrahydro-furan (THF) for structure II. Since both compounds are totally miscible with water, liquid solutions can be made at the theoretical hydrate compositions (EO 7.67H20 or THF 17H20). 

Hernandez, G. J. Vacuum-Ultraviolet Absorption Spectra of the Cyclic Ethers Trimethylene Oxide, Tetrahydrofuran, and Tetrahydropyran. J. chem. Phys. 38, 2233 (1963). 

Oxidation ofS,6-dihydropyranes. These cyclic allylic ethers are oxidized by PCCr directly to a, 3-unsaturated 8-lactones. 

Cyclic ethers are oxidized to lactones in the presence of cerium(IV) salts. Treatment of tetrahydiofu-ran with cerium(rV) ammonium nitrate in the presence of primary, secondary or tertiary alcdiols leads to the formation of the corresponding tetrahydrofuranyl ethers in quantitative yield. Fuitfaermoie, 4-meth-oxybenzyl ether derivatives of carbohytbates are selectively deprotected to the parent alcohols on reaction with cerium(IV) ammonium nitrate in aqueous acetonitrile. ... 

The rp.action described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons. Reactions of /-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons, - esters, dialkyl and aryl alkyl ethers, benzylic ethers, cyclic ethers, straight-chain and benzylic sul-fides, cyclic sulfides, amides, and certain organo-silicon compounds. ... 

Ethers, cyclic ethers. The complex UCl3(THF) was reported by Moody et al and subsequently used by a number of researchers as a precursor for entry into chemistry. The molecular nature of the complex was not well characterized, however. Subsequently, the complex Ul3(THF)4 was prepared via halide oxidation of uranium metal and structurally characterized. The metal center is found to lie within a pentagonal bipyramidal coordination environment, with... 

Thiolation of secondary alcohols is not the preferred route to synthesize secondary mercaptans, because of the facile dehydration that occurs under reaction conditions of the secondary alcohols. H2S can also react with aliphatic or cyclic oxides, viz., ethers to produce the corresponding thioethers or sulfides. This is one of the preferred ways to make tetrahydrothiophene or thiophene. 

The scope of applications of cationic oxetane polymerization is rather limited, with one exception [3,3-bis(chloromethyl)oxetane, BCMO] polyoxetanes have not found any practical application. BCMO, is not as easily available as some of the 3-or 5-membered cyclic ethers (ethylene oxide, propylene oxide, epichlorohydrin, tetrahydrofuran) which are made from simple petrochemical products. 

Grown Ethers. Ethylene oxide forms cyclic oligomers (crown ethers) in the presence of fluorinated Lewis acids such as boron trifluoride, phosphoms pentafluoride, or antimony pentafluoride. Hydrogen fluoride is the preferred catalyst (47). The presence of PF , or SbF salts of... 

Reaction of the aldehyde, Na-methylvellosimine (168), with 37% aqueous formaldehyde (25 equiv.) and 2 N KOH (10 equiv.) in methanol at room temperature for 10 h afforded optimum yields of the desired diol 211. The two prochiral hydroxymethyl functions in 211 were differentiated by the DDQ-mediated oxidative cyclization of the hydroxyl group at the 3-axial position of C-17 with the benzylic position at C-6. This gave the desired cyclic ether 212. Oxidation of the hydroxymethyl functionality was achieved with (PhSe0)20 to provide the aldehyde, which was further oxidized with KOH/R/MeOH to the methyl ester 210. Consequently, the total synthesis of (-l-)-dehydrovoachalotine (210) was achieved in 28% overall yield from D-(- -)-tryptophan. 

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