Step 1: Understanding the Question:
The question asks to identify the specific chemical composition of the "Lucas reagent," which is used in the Lucas test to differentiate between primary (1°), secondary (2°), and tertiary (3°) alcohols.
Step 2: Key Formula or Approach:
The Lucas test is based on the difference in reactivity of 1°, 2°, and 3° alcohols with hydrogen halides. The reaction converts the alcohol (which is soluble) into an alkyl halide (which is insoluble), causing the solution to become cloudy (turbid). The rate of this reaction depends on the stability of the carbocation intermediate formed during the reaction, which follows the order 3°>2°>1°.
Step 3: Detailed Explanation:
The reagent used for this test is called the Lucas Reagent.
The Lucas Reagent is a solution of anhydrous zinc chloride (\(ZnCl_2\)) dissolved in concentrated hydrochloric acid (HCl).
- The concentrated HCl provides the chloride ion (\(Cl^-\)) to form the alkyl chloride.
- The anhydrous \(ZnCl_2\) acts as a Lewis acid catalyst. It coordinates with the oxygen atom of the alcohol's \(-OH\) group, making it a better leaving group (\(H_2O\)) and facilitating the formation of the carbocation intermediate.
The observations of the test are:
- Tertiary alcohols react almost immediately, causing instant turbidity.
- Secondary alcohols react more slowly, with turbidity appearing after 5-10 minutes.
- Primary alcohols do not react significantly at room temperature, so the solution remains clear.
Step 4: Final Answer:
The Lucas reagent consists of concentrated HCl and anhydrous \(ZnCl_2\).