Question

PCC is
(A) ${C_5}H\mathop {_5N}\limits^ + HCr{O_3}\mathop C\limits^ - l$
(B) ${C_6}H\mathop {_5N}\limits^ + HCr{O_3}\mathop C\limits^ - l$
(C) ${C_5}H\mathop {_{11}N}\limits^ + HCr{O_3}\mathop C\limits^ - l$
(D) ${C_6}H\mathop {_{13}N}\limits^ + HCr{O_3}\mathop C\limits^ - l$

Answer 1

PCC stands for pyridinium chlorochromate. Pyridinium chlorochromate is formed by the reaction of pyridine and chromium oxide, hydrochloric acid. You can now protonate the nitrogen atom present on the pyridine molecule and then perform the reaction. Based on this you can determine the possible structure of PCC i.e. pyridinium chlorochromate.

Complete step by step answer:
Pyridinium chlorochromate (PCC) consists of a pyridinium cation, ${\left[ {{C_5}{H_5}NH} \right]^ + }$, and a tetrahedral chlorochromate anion ${[Cr{O_3}Cl]^ - }$. It is a yellow-orange salt, used as an oxidant. It is commercially available. This reagent was discovered by accident which was originally prepared via addition of pyridine into a cold solution of chromium trioxide in concentrated hydrochloric acid. You can see the equation that represents the chemical reaction of Pyridinium chlorochromate formation below:
${C_5}{H_5}N{\text{ }} + {\text{ }}HCl{\text{ }} + {\text{ }}Cr{O_3}\; \to {\text{ }}\left[ {{C_5}{H_5}NH} \right]\left[ {Cr{O_3}Cl} \right]$
PCC is the most suitable reagent to oxidise primary alcohol to aldehydes and secondary alcohols to ketones without affecting any other functional group. Thus it offers the advantage of selective oxidation. In fact it is more selective than the related Jones reagent, so there is little chance of over-oxidation to form carboxylic acids as long as water is not present in the reaction mixture. It also converts suitable unsaturated alcohols and aldehydes to cyclohexanes. One disadvantage to the use of PCC is its toxicity. Other more convenient or less toxic reagents for oxidising alcohols is the dimethyl sulfoxide. PCC is soluble in solvents like acetone, acetonitrile.

Thus, the correct answer is option (A) ${C_5}H\mathop {_5N}\limits^ + HCr{O_3}\mathop C\limits^ - l$.

Note: Generally the confusion may arise to choose in between option a and b. Pyridinium chlorochromate is formed by combining the compounds, pyridinium cation ${\left[ {{C_5}{H_5}NH} \right]^ + }$ and a chlorochromate anion ${[Cr{O_3}Cl]^ - }$. We have to choose the option resembling these.