Aromatic methyl ethers determination

Yet another metabolite of aflatoxin Bj(i) is derived through the demethylation of the aromatic methyl ether. The resultant compound was isolated, and christened aflatoxin Pj83> 84. The structure was determined to be that depicted in (18). 

Acid catalyzed cleavage of aromatic methyl or ethyl ethers Quantitative methoxy group determination Also ether cleavage with tnmethylsilyl Iodide ... 

The ionization of (E)-diazo methyl ethers is catalyzed by the general acid mechanism, as shown by Broxton and Stray (1980, 1982) using acetic acid and six other aliphatic and aromatic carboxylic acids. The observation of general acid catalysis is evidence that proton transfer occurs in the rate-determining part of the reaction (Scheme 6-5). The Bronsted a value is 0.32, which indicates that in the transition state the proton is still closer to the carboxylic acid than to the oxygen atom of the methanol to be formed. If the benzene ring of the diazo ether (Ar in Scheme 6-5) contains a carboxy group in the 2-position, intramolecular acid catalysis is observed (Broxton and McLeish, 1983). 

The methods outlined here deal with methylation and other techniques used to prepare samples of oxidation products for GLC analysis. Aliphatic acids have been determined either as free acids or methyl esters. Aromatics have been determined as methyl ethers of phenolics, methyl esters of carboxylic acids, or methyl ether esters of phenolic acids. 

Oxidations of l-(4-methoxyphenyl)-2-(4-substituted phenyl)ethanols, (6), [identical to alcohols (4a) to (4e) except for methylation of the 4-OH group] were also studied with cerium(IV) as the catalyst (Fisher, T. H., et al., J. Org. Chem., in press). To determine if oxidation occurs by electron abstraction from the benzylic hydroxyl or the aromatic ring, a competitive oxidation procedure was examined on the diaryl ethanol 6a and its methyl ether analog, 1-methoxy-l-(4-methoxyphenyl)-2-phenylethane, (7), (Fisher, T. H., et al., J. Org. Chem., in press). 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

Acid catalyzed cleavage ot aromatic methyl or ethyl ethers. Quantitative methoxy group determination. Also ether cleavage with trimethylsilyl iodide.6... 

Flavonoids are characterized by having an aromatic ring with different degrees of substitution, including functional derivatives such as esters, methyl ethers, and glycosides. These structural characteristics determine the general physicochemical properties of these compounds. 

HNMR determination of aromatic protonialiphatic ether and aromatic protonisiloxane methyl protons to confirm composition C and SiNMR using (acac)3Cr shift reagent for complete analysis of composition and microstructure... 

Rapid, simple, quaUtative methods suitable for determining the presence of benzene in the workplace or surroundings have been utilized since the 1930s. Many early tests offered methods for detection of aromatics but were not specific for benzene. A straightforward test allowing selective detection of benzene involves nitration of a sample to y -dinitrobenzene and reaction of the resultant ether extract with an ethanoHc solution of sodium hydroxide and methyl ethyl ketone (2-butanone), followed by the addition of acetic acid to eliminate interferences from toluene and xylenes. Benzene imparts a persistent red color to the solution (87). The method is claimed to be sensitive to concentrations as low as 0.27 ppm benzene from 10 mL air samples. 

---