Q.(a) An organic compound (A) $C_3H_8O$ on treatment with Lucas reagent gives compound (B). Oxidation of (A) by $CrO_3$ gives compound (E) which is resistant to oxidation by mild oxidising agents. When (B) is heated with alcoholic KOH it gives compound (C) which can decolourise bromine water. Compound (C) undergoes hydroboration-oxidation to produce an alcohol (D) $C_3H_8O$. Predict the structure of compounds (A), (B), (C), (D) and (E). OR

The Lucas test converts an alcohol to its (water-insoluble, turbid) alkyl chloride at a rate that tracks carbocation stability, so the time taken to turn turbid tells 1°, 2° and 3° alcohols apart.

Mechanism: $R\text{-}OH + HCl \xrightarrow{ZnCl_2} R\text{-}Cl + H_2O$. $ZnCl_2$ coordinates to the $-OH$ oxygen, making it a good leaving group as water; the alcohol then ionises to a carbocation (best for 3°, poor for 1°), which is captured by chloride to give the insoluble alkyl chloride, seen as turbidity/cloudiness in the otherwise clear reagent.

• Tertiary alcohol: forms a stable 3° carbocation instantly — turbidity appears immediately at room temperature.
• Secondary alcohol: forms a less stable 2° carbocation — turbidity appears only after a few minutes (often needs gentle warming). …

Lucas reagent is the mixture of concentrated HCl and anhydrous ZnCl2, used to distinguish primary, secondary, and tertiary alcohols by the speed of turbidity formation.

Lucas reagent = conc. HCl + anhydrous ZnCl2 (a Lewis acid catalyst that helps generate the carbocation). When an alcohol is shaken with Lucas reagent, it is converted to the corresponding alkyl chloride: 3° alcohols react instantly (turbidity/oily layer appears immediately, via SN1 since a stable 3° carbocation forms easily …

The Lucas test uses the differing SN1 reactivity of 1°, 2° and 3° alcohols with Lucas reagent (conc. HCl/ZnCl2) - shown by how quickly a cloudy alkyl chloride layer forms.

Lucas reagent (a mixture of conc. HCl and anhydrous ZnCl2) reacts with alcohols to form alkyl chlorides:

$\text{R-OH} + \text{HCl} \xrightarrow{\text{ZnCl}_2} \text{R-Cl} + \text{H}_2\text{O}$

• Tertiary alcohols react immediately (turbidity appears at once) - fastest, via a stable carbocation (SN1). …

Lucas reagent = anhydrous ZnCl2 + concentrated HCl.

Lucas reagent is a mixture of anhydrous zinc chloride and concentrated hydrochloric acid. It is used to distinguish primary, secondary and tertiary alcohols by the rate at which a cloudy alkyl chloride (turbidity) appears:

• Tertiary alcohol: turbidity immediately …

Lucas reagent (conc. HCl + anhydrous ZnCl2) distinguishes 1°, 2° and 3° alcohols by how fast each reacts to give a turbid alkyl chloride.

Lucas reagent works via an SN1-type mechanism: ZnCl2 acts as a Lewis acid that activates the -OH group as a leaving group, and the alcohol is converted to the corresponding alkyl chloride, which is insoluble in the aqueous mixture and appears as turbidity/cloudiness.

• Tertiary (3°) alcohols react immediately at room temperature (turbidity appears at once) - the 3° carbocation formed is most stable.
• Secondary (2°) alcohols react within about 5 minutes (turbidity appears on standing/warming slightly). …

Immediate turbidity with HCl (the basis of the Lucas test) identifies a tertiary alcohol.

This describes the Lucas test, which distinguishes 1°, 2°, and 3° alcohols by their differing rates of SN1 reaction with HCl (conc. HCl + anhydrous ZnCl2, the 'Lucas reagent'):

• 3° alcohols: react immediately at room temperature — turbidity (insoluble alkyl chloride) appears at once, because the bulky, highly-substituted 3° carbocation forms readily.
• 2° alcohols: turbidity appears within about 5 minutes (needs mild warming/waiting). …

Lucas reagent ($ZnCl_2/\text{conc. }HCl$) reacts with alcohols via an $S_N1$-type mechanism, so tertiary alcohols react instantly, secondary alcohols within a few minutes, and primary alcohols not at all at room temperature — giving a simple, fast way to distinguish the three classes.

The reagent used is Lucas reagent: a mixture of anhydrous zinc chloride, $ZnCl_2$ (a Lewis acid catalyst), dissolved in concentrated hydrochloric acid, $HCl$.

When an alcohol reacts with Lucas reagent, it is converted to the corresponding water-insoluble alkyl chloride, which appears as turbidity/cloudiness (or a separate oily layer) in the otherwise clear/miscible mixture:

$R{-}OH + HCl \xrightarrow{ZnCl_2} R{-}Cl + H_2O$

The rate of this reaction depends on how stable the intermediate carbocation is (an $S_N1$-like pathway favoured by the Lewis-acid activation from $ZnCl_2$):

…

The Lucas test distinguishes alcohols by how fast they form an insoluble alkyl chloride (seen as turbidity), which depends on how stable the intermediate carbocation is — 3° fastest, 1° slowest.

Lucas reagent is a mixture of concentrated HCl and anhydrous $\text{ZnCl}_2$ (which acts as a Lewis-acid catalyst). When an alcohol is shaken with Lucas reagent, it is converted to the corresponding (water-insoluble) alkyl chloride, which appears as turbidity/cloudiness in the otherwise clear, miscible reaction mixture:

$\text{ROH} + \text{HCl} \xrightarrow{\text{ZnCl}_2} \text{RCl} + \text{H}_2\text{O}$

The rate at which turbidity appears depends on how readily the alcohol undergoes an SN1-type substitution — which in turn depends on the stability of the carbocation intermediate formed:

• Tertiary (3°) alcohols: React the fastest — turbidity appears immediately at room temperature, since a stable 3° carbocation forms readily (SN1 mechanism). …