Question

write equations for the reactions of two carbohydrates that gave Fehling's tests

Answer 1

This is an important test to detect the presence of reducing sugars. Fehling's solution A is copper sulphate solution (blue colour solution) and Fehling's solution B is potassium sodium tartrate. On heating, carbohydrate reduces deep blue solution of copper (lI) ions to red precipitate of insoluble copper oxide. this test used for differntiate from reducing and non reducing sugars A reducing sugars react with fehiling solution in alkaline medium OO-Na+ HO HOH но Tartrate ions 3H20+ Cu2O HoH . 2 Cu(OH)2 +2 NaOH Red ppt H20H CH2OH sodium salt of glucoric acid CH2OH OH HO Keto-enol tautomerismHC HOH 2 HO OH Cu(OH)2 COO-Na* H 2 NaOH HOH HO H20H H20H H20H glucose fructose H20H sodium salt of glucoric acid COO-Na но HOH HOH H20H Mannose H20H However, fructose reduces such reagents even though it contains no aldehyde group. Reduction occurs because the reagents are basic solutions and fructose is readily isomerized to a mixture of aldoses (glucose and mannose) under basic conditions