2. The reaction between sec-butanol and Lucas reagent: the solution turns into a cloud within 5 ~ 10 minutes;
3. Tert-butanol reacts with Lucas reagent: the solution immediately becomes a cloud and phase separation occurs.
Reaction principle:
Lucas reagent consists of zinc chloride and hydrochloric acid. Under the action of hydrochloric acid, the hydroxyl group in alcohol is protonated, and a molecule of water is removed to form carbocation, which combines with chloride ion to form chloroalkane. The reaction rate is related to the stability of carbocation corresponding to alcohol. Due to the electron-pushing properties of hydrocarbon groups, tertiary carbocation is the most stable and easy to generate, while primary carbocation is the most unstable and difficult to generate, so the structure of lower alcohols can be judged by the reaction speed.
Extended data:
The reason why this experimental phenomenon is unclear is:
1, Lucas reagent is not sensitive enough.
The reaction between alcohol and Lucas reagent is a monomolecular nucleophilic substitution mechanism, and both HCl and zinc chloride participate in the reaction process. The concentration of zinc chloride and HCl in the reagent is an important factor to determine the reaction rate.
Zinc chloride and concentrated hydrochloric acid should not only have a suitable ratio, but also have a high enough concentration, so that the reagent will have a high enough sensitivity.
2. The generated lower chlorinated hydrocarbons are volatile.
The lower chlorinated hydrocarbons produced by Lucas test have lower boiling point and relative density than Lucas reagent, so the lower chlorinated hydrocarbons produced by Lucas test are easy to volatilize and dissipate.
Because the reaction of secondary alcohol is slow, the reaction of primary alcohol is slow, and chloroalkanes volatilize while forming, so it is not easy to form obvious turbidity or stratification; It is found in the experiment that even the tertiary alcohol with the fastest reaction will disappear after a long time, so the volatilization loss of chlorinated hydrocarbons is also one of the reasons for the failure of Lucas experiment.
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