Question

Which of the following is referred to as Baeyer’s reagent?
(A) Alkaline $KMn{{O}_{4}}$
(B) Acidic ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$
(C) Alkaline $N{{a}_{2}}C{{r}_{2}}{{O}_{7}}$
(D) $Mn{{O}_{2}}$

Answer 1

Hint: Baeyer’s reagent is a strong oxidizing reagent which helps identify the presence of double or triple bonds in a hydrocarbon that is used to identify the unsaturation in organic compounds.

Complete answer:
Let us dive straight into the physical and chemical properties of Baeyer’s reagent and analyse its possible uses.
- An alkaline solution of cold potassium permanganate is known as Bayer’s reagent, which is a powerful oxidant.
- It dissolves in water to give purple colour.
- On evaporation it leaves prismatic purplish-black glistening crystals.
- $KMn{{O}_{4}}$ is used in organic qualitative analysis to test for the presence of unsaturation. Reaction with double or triple bonds (-C=C- or $-C\equiv C-$ ) causes the colour to fade from purplish-pink to brown.
- Here is the example of reaction of alkene which is an unsaturated compound and it will react with alkaline $KMn{{O}_{4}}$ to give corresponding vicinal-diols. Hence, we can conclude that here the double bond between carbon atoms will break and both of the valencies of carbon atoms will be occupied by hydroxyl groups.

- Baeyer's reagent is also used as a reagent in many organic conversions. However, it uses manganate ions which are somewhat toxic to the environment, so it is not a part of the green chemistry approach.

Thus, we can safely conclude that the required answer to the given question is quite clearly (A).

Note: Remember that Bayer’s reagent cannot oxidise the double bonds of aromatic rings because those double bonds are conjugated with each other and hence they are very stable. Also note that the neutral or acidic solution of $KMn{{O}_{4}}$ is not considered as Bayer’s reagent as they have different reactivity.