P- ethers

Few monofluoro vinyl ethers have been reported in the literature. The NMR data for one example is given. It can be seen that the P-ether substituent shields the fluorine much more than does a P-chlorine substituent. 

Bis (Hydroxylamino) Azide (called Dihydroxyl-Ammonium Trinitride by Dennis Isham), (NHaOH)a-HNs, mw 109.10, N64.20% col, trans, leaf-like crysts, nip 66° v sol in w, sol in ale and insol in eth. This compd was prepd in 1906 by Dennis Isham (Ref 1) upon evapg a mixt of hydroxyl amine and hydra-zoic acid, both in methyl ale solns. The recovered crysts were purified by dissolving in a mixt of 1 g methyl ale and 20 p ether, filtering and rapidly evapg the solvent in a vacuum desiccator (See also Ref 2). No expl props were determined (Also see Hydrazoic Acid)... 

In total, we prepared six new dihydroartemisinin analogues as shown in Figure 5 from the corresponding lactones and three new analogues from artemisinin itself. 9-Desmethylartemisinin 42 was transformed into the lactol 147, which was then converted to the P-ether 148. Treatment of DHQHS under anhydrous conditions with acid and terf-butylhydroperoxide gave perether 150 in 62% yield, which contains two peroxide moieties. 

Time-resolved CIDEP and optical emission studies provide further definitive characterization of the triplet and excited singlet states followed by their primary photochemical reactions producing transient radicals in individual mechanistic steps in the photolysis of a-guaiacoxylacetoveratrone. Both fluorescence and phosphorescence are observed and CIDEP measurements confirm the mainly n,n character of the lowest triplet state. The results indicate a photo triplet mechanism involving the formation of the ketyl radical prior to the P-ether cleavage to form phenacyl radicals and phenols. Indirect evidence of excited singlet photo decomposition mechanism is observed in the photolysis at 77 K. 

Selective cleavage of ether bonds is useful to determine the contribution of carbon-carbon bonds for polymer lignin. Pivaloyl iodide [90] is known to cleave a-ether bonds selectively and trimethylsilyl iodide [91,92] can cleave a- and P-ether bonds quite effectively under the proper reaction conditions. Because of the very small amount of sample required, pyrolysis GC-MS may be applied for the analysis of a specific morphologi region of a cell wall. 

Reaction A forms QC3 enol ether (52), which undergoes p-ether hydrolysis to yield ketol (55), and then Hibbert s ketones (34). Reaction B involves a carbon-carbon bond cleavage between the p and y positions to give formaldehyde and C6C2 enol ether (55), which may be degraded slowly to yield homovanillin (56). Reaction C involves intermolecular condensations to give mainly the a-6 diphenylmethane unit (58) plus some a-5 condensed structure. 

Table 9 shows the relative hydrolysis rate of lignin models reported by Johansson and Miksche [302]. Both a- and P-aryl ether hydrolysis were enhanced by the presence of a phenolic hydroxyl groups. It is evident that a-aryl ether is much more reactive than the P-ether by a factor of 25 and 65... 

Table 9 Relative Hydrolysis Rates of Lignin a- and P-Ether Models in 0.2 M HCl of Aqueous Dioxane at 50°C...

Diethyl ether (bp 35°) is the most commonly used solvent in spite of its low boiling point, low flash point, and ease of forming peroxides, a property shared by all ethers. For extracting aqueous solutions, U.S.P. ether, which contains a few per cent of alcohol and water, is usually quire satisfactory. However, for most reactions, anhydrous ether is required. The U.S.P. ether may be fairly well dried by heating to reflux with sodium wire overnight. Ether purified in this fashion is also useful in extracting compounds which have a boiling point close to that of ethanol or which may react with ethanol, since this is present in the U.S.P. ether. It may be noted that anhydrous ether is also commercially available. 

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