Replacement of oxygen by nitrogen

Whenever other methods of esterification fail for any reason, e.g., because of the sensitivity of the acid, or when small amounts of valuable carboxylic acids are to be esterified, the reaction can be carried out by use of a diazoalkane. Esterification with these reagents occurs in an inert medium, in ether, 

Diazomethane is extremely poisonous and experiments with it must be carried out under a hood. Undiluted gaseous nitromethane is highly explosive, and large amounts of carboxylic acids should not be subjected to this reaction. 

For esterifications it is best to prepare an ethereal solution of diazomethane. Such solutions are not stable, decolorizing gradually with evolution of nitrogen. Diazomethane solutions can be dried with potassium hydroxide, but losses must then be allowed for. Alcoholic solutions of diazomethane are less stable than ethereal ones. 

Alcoholysis of carbimidic ester hydrochlorides leads to orthocarboxylic esters.15, 895 It is essential to use well-dried alcohols and acid-free imidic ester hydrochlorides and completely to exclude moisture. 

Carboxamides and sometimes carboxylic esters and carbonitriles are formed as by-products of the alcoholysis. 

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Isothermal in oxygen atmosphere. Heating under nitrogen from room temperature up to a chosen temperature followed by replacement of nitrogen by oxygen and start of the isothermal experiment. Polypropylenes (PP) and acrylonitrile-butadiene-styrene (ABS) copolymers have been evaluated under these conditions. Isothermal experiments have been carried out also with nylon samples. 

Ether formation by replacement of nitrogen by oxygen alkylation by diazomethane... 

M ercuryj nitrogen d i oxi d e I oxygen Preferential replacement of halogen by oxygen Carboxylic acid fluorides from polyhalides... 

In most zinc enzymes, the metal is tetrahedrally coordinated by either nitrogen atoms alone or by a combination of nitrogen and oxygen atoms. To model zinc enzymes having the much rarer S-donor environments, a number of approaches have been pursued. The most direct routes to such ligands involve the replacement of one or more... 

Important reactions of this type include the replacement of a ring oxygen by a ring sulfur or nitrogen. Table 8 gives some examples and references to the section where they are discussed. 

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