Which of the following alcohols would not be oxidized by chromic acid reagent wi
ID: 852394 • Letter: W
Question
Which of the following alcohols would not be oxidized by chromic acid reagent within 5 seconds: 1-pentanol, cyclohexanol, 2-methyl-1-propanol, 2-methyl-2-butanol?
Do primary or tertiary alcohols react more rapidly with the Lucas reagent? Why?
Between these test: Solubility in Water, Lucas Test, Oxidation using Chromic Acid, Ester formation.Using the test described in this experiment, how could you distinguish between the following pairs of compounds? Tell what regent or test your would use and what you would observe.
a.1-butanol and 2-butanol
b.isobutyl alcohol and tert-butyl alcohol
c.1-propanol and 1-heptanol
d.cyclohexanol and cyclohexane
Explanation / Answer
Chromic acid reagent is a strong oxidising agent. This reagent oxidises primary alcohol, secondary alcohol and aldehydes but cannot oxidise tertiary alcohol. Thus, the 2-methyl-2-butanol, being tertiary alcohol, will not oxidise with chromic acid in 5 seconds.
The tertiary alocohols react more rapidly with Lucas reagent as compared to the primary alcohols. This is because the tertiary alcohol forms stable carbocation due to the presence of three methyl groups in it. These three methyl groups increase the electron density over the central carbon atom and thus, increases the stability of carbocation. While in primary alcohol, there is only one methyl group which will not be able to stabilize the carbocation to such an extent as that of tertiary alcohols.
(a) 1-butanol and 2-butanol: To distinguish between these two chemicals, I would first dissolve them in water. The 2-butanol will dissolve more rapidly in water than 1-butanol.
To confirm the test, I would perofrm Lucas test. In this test, the secondary alcohol (2-butanol) will become turbid in short time as comapred to the primary alcohol (1-butanol).
(b) Isobutyl alcohol and tertiary butyl alcohol: These chemicals can be differentiated using Lucas reagent. The tertiary butyl alcohol will become turbid in a short time as compared to isobutyl alcohol.
The oxidation test with chromic acid can be a confirmative test because the tertiary butyl alcohol will not be affected by chromic acid reagent while secondary alcohol will react and show change in color of the solution.
(c) 1-Propanol and 1-heptanol: Both being primary alcohol, cannot be differentiated by either Lucas test, chromic acid test or ester formation.
These both chemicals have different number of methyl groups in their chains. The less the number of methyl groups in an alcohol, the more it is soluble in water because the long chains hinder the chemicals during dissolution. Thus, the solubility in water can be used to differentiate between 1-propanol and 1-heptanol because 1-propanol will dissolve easily in water as comaperd to 1-heptanol.
(d) Cyclohexane and cyclohexanol: These chemicals can be differentiated by Lucas test. The cyclohexanol will show turbidity while cyclohexane will not show any turbidity even after heating.
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