Cuprous oxide reduction method

Ofner Method. This method is for the determination of invert sugar in products with up to 10% invert in the presence of sucrose and is a copper-reduction method that uses Ofner s solution instead of Fehling s. The reduced cuprous oxide is treated with excess standardized iodine, which is black-titrated with thiosulfate using starch indicator. 

Colorimetric Methods. Numerous colorimetric methods exist for the quantitative determination of carbohydrates as a group (8). Among the most popular of these is the phenol—sulfuric acid method of Dubois (9), which rehes on the color formed when a carbohydrate reacts with phenol in the presence of hot sulfuric acid. The test is sensitive for virtually all classes of carbohydrates. Colorimetric methods are usually employed when a very small concentration of carbohydrate is present, and are often used in clinical situations. The Somogyi method, of which there are many variations, rehes on the reduction of cupric sulfate to cuprous oxide and is appHcable to reducing sugars. 

The methods of measuring the amount of cuprous oxide formed are numerous but the one most frequently used involves the reduction of either phosphomolybdic acid or arsenomolybdic acid by the cuprous oxide to lower oxides of molybdenum. The intensity of the coloured complex produced is related to the concentration of the reducing substances in the original sample. The colour produced with arsenomolybdic acid is more stable and the method is more sensitive than with phosphomolybdic acid. 

When a suspension of cuprous oxide in alcohol is used for reduction of the diazonium salts, the deaminated products are formed immediately and without appreciable side reactions. This method seems to be generally applicable, but, in particular, compounds such as nitroanilines and aminoanthraquinones... 

Diphenic acid has been prepared by the reduction of diazotized anthranilic acid with cuprous ion,6 Ullman coupling of potassium o-bromobenzoate,6 and oxidation of phenanthrene or phen-anthrenequinone with various oxidizing agents.7 The latter methods have been reviewed recently.7 The ozonolysis method has also been carried out in solvents 8 that do not react with the zwitterion intermediate. ... 

A gasometric method for the estimation of cupric salts is based on the reduction of cupric-ammonia solutions by a hydrazine salt, a cuprous-ammonia solution being formed, and the hydrazine oxidized to nitrogen and water ... 

Under alkaline conditions, oxides and hydroxides of metals including silver, gold, copper (cuprous and cupiic oxides), mercury, bismuth and niekeF are. reduced to metals by foimaldehyde. The quantitative reduction of freshly precipitated bismuth hydroxide by excess formaldehyde in the presence of sodium hydroxide affords a method for the determination of bismuth . 

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