Hi everyone, I have one question is "When protecting the OH group of quercetin with benzyl bromide, why must it be cooled down to 0oC for 2 hours ?"

Here is its process :

3,7-Bis(benzyloxy)-2-(4-(benzyloxy)-3-hydroxyphenyl)-5- hydroxy-4H-chromen-4-one. A solution of quercetin 1 (5.00 g, 14.79 mmol), potassium carbonate (7.9 g, 51.77 mmol), and benzyl bromide (9.9 g, 51.77 mmol) were taken in DMF (10 mL) and stirred vigorously under nitrogen at 0 °C for 2 h. The reaction mixture was allowed to warm to room temperature over 2 h, and the stirring was maintained for further 12 h. The resulting mixture was diluted with water (100 mL) and extracted with EtOAc (2 × 500 mL). The organic layer was dried (Na2SO4) and evaporated, and the residue obtained was purified by flash column chromatography using 7% EtOAc as an eluent to afford product 2 as a yellow solid (60%, mp: 154 °C).