How can you say that the molisch test give positive result to a certain substance like glucose?
The Molisch’s Test is a chemical test for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric acid to produce an aldehyde. The test solution is combined with a small amount of Molisch’s reagent (α-naphthol dissolved in ethanol) in a test tube. After mixing, a small amount of concentrated sulfuric acid is slowly added down the sides of the sloping test-tube, without mixing. A positive reaction is indicated by a purple ring forming at the interface between the acid and test layers. All carbohydrates — monosaccharides, disaccharides, and polysaccharides — should give a positive reaction. Glycoproteins also give a positive reaction. Pentoses are dehydrated to furfural; hexoses are dehydrated to hydroxymethylfurfural. Either of these aldehydes, if present, will condense with two molecules of naphthol to form a purple-colored product. >O2 (furfural) + Reactions: 1. C5H10O5 (pentose) + (conc.) H2SO4 → C5H4O2 + 3 H2O 2.
