Diazomethane reaction with hydroxyl

The acid 350 was demethylated with pyridine hydrochloride, then realkylated with benzyl bromide in aqueous potassium hydroxide to give 351. The latter was converted to the diazoketone 352 by the sequential treatment of 351 with oxalyl chloride and etheral diazomethane. Reaction of 352 with concentrated hydrobromic acid gave the bromoketone 353. The latter was reduced with sodium borohydride at pH 8 -9 to yield a mixture of diastere-omeric bromohydrins 354. Protection of the free hydroxyl as a tetrahydro-pyranyl ether and hydrogenolysis of the benzyl residue afforded 355. The phenol 355 was heated under reflux with potassium m/V-butoxide in tert-butyl alcohol for 5 hr to give a 3 1 epimeric mixture of dienone ethers 356 and 357 in about 50% yield. Treatment of this mixture with dilute acid gave the epimeric alcohols 358 and 359. This mixture was oxidized with Jones reagent to afford the diketone 349. 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

The first involves a known functional group derivatization to quantify specific types of carbons found in humic substances, the derivatization being carried out by chemical reactions with l C-labeled reactants.( d-27) For example, methylation with C-labeled diazomethane or methyl iodide has been used to distinguish between and quantify hydroxyl functionalities in humic acids. The second labeling methodology involves the use of C-labeled reactants to follow the course of a complex reaction or association such as the interaction of pollutants with humic acids.(6-9,22,2J) The first structural evidence for the type of interaction of pollutants with humic substances was provided using and site specific labeling in combination with and NMR, respectively. 

In addition, phenolic hydroxyl adjacent to a carboxyl group on an aromatic ring constitutes the major entity responsible for the chelation of metals in coal, particularly in the lower-rank coals. Phenolic hydroxyl is also determined by reaction with diazomethane (CH2N2) to form the methoxyl group (-OCH3) with the release of elemental nitrogen. 

Poly(itaconic acid) has also been prepared in a 0.2M/liter aqueous solution using potassium persulfate at 50 C over a 5-hr period under reduced pressure. After the polymer is reprecipitated twice into methanol-ethyl acetate, a polymer is isolated with a molecular weight of 1.64 x 10, determined by vapor pressure osmometry of a methanolic solution of the methyl ester prepared from the polymer [49]. Unfortunately Tsuchida and coworkers did not report on the quantitative extent to which poly(methyl itaconate) had been formed from this polymer (presumably by reaction with diazomethane). Consequently, there is little in the literature to confirm or dispute the paper by Braun and Azis el Sayed [97], which offered evidence that during the free-radical polymerization of itaconic acid, carbon dioxide evolves to a considerable extent. During the process, it seems that hydroxyl and formyl radicals are generated and incorporated in the macromolecule. It is proposed by these authors that the homopolymer of itaconic acid contains virtually no itaconic acid repeat units but rather intramolecular lactone rings and acetal- or hemiacetal-like moieties. Since the polymer remains soluble in the reaction solvent (dioxane). 

Alkoxycarbonyl or acyl substituents usually render the hydroxypyrroles alkali-soluble, capable of coupling with diazonium salts, of being nitrosated, O-acylated and, in a few cases, O-methylated by diazomethane. Hydroxypyrroles carrying alkoxycarbonyl or acyl groups adjacent to the hydroxyl group give colour reactions with ferric ions. Some hydroxypyrroles give... 

Thus, the acidity oi a lactam is evidently not a reliable quantity for predicting the course of the methylation. The acidity gives information only as to the reaction velocity. In this connection the reaction course of isomethylreductone (6) is illuminating, " With diazomethane in ether containing 1 mole of water, the enolraethyl ether (7) is formed. However, if water is present only in traces, then the alcoholic hydroxyl group is selectively attacked to give 8. 

A special influence on the course of a reaction by a neighboring group is shown in the reactions of 5-acetyl-leuco(iso)alloxazines - with diazomethane. The methylation occurs neither in the pyrimidine nor in the pyrazine ring, but on the hydroxyl group of a newly formed oxazoline ring. For example,... 

Treatment of D-glucoascorbic acid (XV) with diazomethane gives a 2,3-dimethyl derivative (LXXIX) and this upon repeated treatment with silver oxide and methyl iodide yields 2,3,5,6,7-pentamethyl-D-glucoascorbic acid (LXXX). Ozonization of the latter followed by hydrolysis gives oxalic acid and 3,4,5-trimethyI-D-arabonic acid (LXXXI). This acid was shown to possess a free hydroxyl group at C2 by reason of the fact that the amide of LXXXI gives a positive Weerman reaction for a-hydroxy amides, i.e., when the amide is treated with sodium hypochlorite, sodium isocyanate is produced, the latter being identified by... 

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