Shows positive test for:

All carbohydrates. Monosaccharides give a rapid positive test. Disaccharides and polysaccharides react slower.

Reactions:

The test reagent dehydrates pentoses to form furfural (top reaction) and dehydrates hexoses to form 5-hydroxymethyl furfural (bottom reaction). The furfurals further react with -naphthol present in the test reagent to produce a purple product (reaction not shown).