Lucas Test: Overview, Questions, Preparation

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This chapter has multiple topics listed below:

Functional Groups Difference between Alcohol and ...Benzyl Alcohol Ethanol Formula Types of Alcohols Uses of Propanol Lucas Test Methyl Acetate Acid Anhydrides Ammonium Acetate Dehydration of Alcohols Ester Hydrolysis Eugenol Uses of Phenol Preparation of Phenols Bismuth Subsalicylate Potassium Acetate

Yamini Saini

Updated on Apr 17, 2021 04:23 IST

"Lucas' reagent" of distilled hydrochloric acid is a solution of anhydrous zinc chloride. This solution is used to distinguish the alcohols of low molecular weight. The reaction is a substitution in which a hydroxyl group is substituted by chloride. A positive test is seen by a transition from smooth and colourless to turbid, signalling the forming of a chloroalkane. In tertiary alcohols, the best results for this test are also found, as they form the respective alkyl halides more rapidly due to higher intermediate tertiary carbocation stability.

Table of Contents

What is Lucas Test?
FAQs regarding Lucas Test

What is Lucas Test?

Based on their reactivity with the Lucas reagent, major, secondary, and tertiary alcohols are graded. A nucleophilic replacement reaction can be used as the reaction occurring in the Lucas test. The chloride in the zinc-chloride bond is substituted with a hydroxyl group derived from the alcohol in question in this reaction.

The reaction reveals the difference in the reactivity of the various forms of alcohol, as well as the difference in the ease with which the alcohol forms corresponding carbocations. For e.g., with the added Lucas reagent, primary alcohols do not react readily at room temperature, whereas tertiary alcohols react immediately.

The observation of a transition in which the solution's smooth and colourless function transitions to a turbid, cloudy, and hazy one suggests that a chloroalkane has formed. For the Lucas test, this finding is a good indicator.

Main, secondary, and tertiary alcohols react at various rates with the Lucas reagent to form the chloroalkane. Due to the fact that organic chloride has comparatively poor solubility in the aqueous mixture, tertiary alcohols react the fastest.

Lucas Test in Class 11:

In General Organic Chemistry, you will get to learn about the Lucas test and how it performs, although this class only has the basics of organic chemistry, and so of the Lucas test.

Lucas Test in Class 12:

In class 12, there is more application part of the Lucas test. In the chapter alcohol, aldehyde, and carboxylic acid, you will get to apply it and to solve many questions.

A. The Lucas alcohol test is a test intended to discriminate between major, intermediate, and tertiary alcohols. It is based on the reactivity difference of the three groups of hydrogen halide alcohols through the SN1 reaction: ROH + HCl -- RCl + H2O.

A. If the reactions proceed through SN1 or SN2, mechanisms are determined by the existence of R. If R is a primary alkyl, SN2 if R is a bulky tertiary alkyl, SN1 if R is a primary alkyl. With the Lucas reagent, secondary and tertiary alcohols react through the SN1 mechanism.

A. Primary alcohols do not react readily at room temperature with the added Lucas reagent, whereas tertiary alcohols react immediately.

A. The Lucas test is conducted to differentiate between major, secondary, and tertiary alcohols and the quickest alkyl halide provided by the alcohol. The Lucas test is based on the difference in hydrogen halide alcohol reactivity.

A. In condensed hydrochloric acid, the Lucas reagent is a solution of anhydrous zinc chloride (Lewis acid). It is used as a reagent for measuring and classifying alcohols according to their reactivity.

A. To define the type (degree) of alcohol, Lucas's Reagent (ZnCl2+conc. HCl) is used. Phenol does not give Lucas Test as it is a primary alcohol.

A. Owing to the formation of empty d-orbitals on Zinc, ZnCl2 is a Lewis acid. ZnCl2acts as a catalyst and, when reacting with hydrochloric acid, forms H2ZnCl4 (HCl).

A. A screen for such alcohol is the Lucas reagent (concentrated HCl and ZnCl2). Like tertiary alcohols, benzyl alcohols (Ph-C-OH), allylic alcohols (C=C-C-OH), and propargyl alcohols (C-C-C-OH) also provide immediate results.