Which one of the following tests used for the identification of functional groups in organic compounds does not use copper reagent ?
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Many common tests for sugars (like Benedict's, Fehling's, and Barfoed's) rely on the ability of reducing sugars to reduce Cu\(^{2+}\) (blue) to Cu\(^+\) in the form of Cu\(_2\)O (red precipitate). Seliwanoff's test is different; it's based on the different rates of acid-catalyzed dehydration of ketoses versus aldoses.
Step 1: Understanding the Question:
We need to identify which of the listed chemical tests for organic functional groups does not use a reagent containing copper. Step 2: Detailed Explanation:
Let's examine the reagents used in each test:
- (A) Biuret test: This test is used to detect the presence of peptide bonds. The Biuret reagent consists of an alkaline solution of copper(II) sulfate (CuSO\(_4\)). A positive test gives a violet color due to the formation of a copper coordination complex. It uses copper.
- (B) Barfoed's test: This test is used to distinguish reducing monosaccharides from reducing disaccharides. Barfoed's reagent is a solution of copper(II) acetate (Cu(CH\(_3\)COO)\(_2\)) in a slightly acidic medium. A positive test is the formation of a red precipitate of copper(I) oxide (Cu\(_2\)O). It uses copper.
- (C) Seliwanoff's test: This test is used to distinguish between aldose and ketose sugars. Seliwanoff's reagent consists of resorcinol and concentrated hydrochloric acid (HCl). When heated, ketoses react faster to give a deep cherry-red color. This reagent does not use copper.
- (D) Benedict's test: This is a general test for reducing sugars. Benedict's reagent is a complex mixture of copper(II) sulfate (CuSO\(_4\)), sodium carbonate (Na\(_2\)CO\(_3\)), and sodium citrate. A positive test gives a precipitate ranging in color from green to yellow to brick-red, depending on the concentration of the sugar. It uses copper. Step 3: Final Answer:
Seliwanoff's test is the only one among the options that does not use a copper reagent.
