Question

The most suitable reagent for the conversion of \[RC{H_2}OH{\text{ }} \to RCHO\] is?
\[
  A){K_2}C{r_2}{O_7} \\
  B)Cr{O_3} \\
  C)KMn{O_4} \\
  D)PCC\; \\
\]

Answer 1

Hint: \[RCHO\] is the aldehyde. The formation of aldehyde is done by the oxidizing primary alcohol in the presence of some suitable regents like PCC (pyridinium chlorochromate), PDC ( pyridinium dichromate) , swern and DMP ( dess- Martin )

Complete step by step answer:
Aldehydes can be easily obtained by oxidation of primary alcohol with oxidizing agents such as acidified potassium dichromate \[\left( {{K_2}C{r_2}{O_7}} \right)\], acidified potassium permanganate \[\left( {{\text{ }}KMn{O_4}} \right)\] and chromic anhydride \[\left( {Cr{O_3}} \right)\].
\[RC{H_2}OH{\text{ }} + {\text{ }}\left( O \right)\; \to RCHO{\text{ }} + {\text{ }}{H_2}O\]
During this reaction, when primary alcohol is convert into aldehyde in the presence of oxidizing agents like potassium dichromate and sulphuric acid \[\left( {{H_2}S{O_4}} \right)\]
Under this condition, aldehydes are prone to oxidation, so it is very difficult to stop the oxidation at the aldehyde stage. However, oxidation of lower aldehydes can be prevented by distilling off the aldehydes as soon as they are formed as they have lower boiling point than alcohol. For example: \[C{H_3}C{H_2}C{H_2}OH \to C{H_3}C{H_2}CHO{\text{ }} + {\text{ }}{H_2}O\;\]
In this reaction propanol is converted into propanal in the presence of basalt oxygen (O). During the process, the boiling point of propane is 370k or the boiling point of product is 322k I. e propanal. So the better reagent for oxidation of primary alcohol to aldehydes in good yield is pyridinium chlorochromate (PCC) , a complex of chromium trioxide with pyridine and hydrochloric acid.
And\[\left( {{\text{ }}KMn{O_4}} \right)\], \[\left( {{K_2}C{r_2}{O_7}} \right)\] and \[\left( {Cr{O_3}} \right)\] are strong reagent for oxidation of saturated and unsaturated secondary alcohol, converting alcohol to aldehyde and to carboxylic acid. But PCC is mild oxidation reagents which convert alcohol into aldehyde only.
Thus the correct option is D.
\[Secondary{\text{ }}alcohol{\text{ }} + l{\text{ }}\left( O \right){\text{ }} \to {\text{ }}ketone\;\]



Note:
Pyridinium chlorochromate (PCC) is yellow- orange salt. Its hazardous effect on human beings and the environment are unpleasant. It is commonly known as a suspected carcinogen that means it is an agent that causes cancer in the population and pollutant.