ArCOR can be prepared by the combination of $\mathrm{ArH}+\mathrm{RCOCl}$ and not by $\mathrm{ArCOCl}+\mathrm{RMgX}$ because here the ArCOR formed will further react with $\mathrm{RMg} \mathrm{X}$ to form $3^{\circ}$ alcohol, $\mathrm{ArC}(\mathrm{OH}) \mathrm{R}_{2}$ as the final products.
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