1,2-Dichlorobenzene → 2,4-Dimethyl-3-fluorobenzaldehyde

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62.4 g of aluminum chloride (mol. Wt. 133.34; 468.0 mmol), 450.0 g of 1,2-dichlorobenzene (mol. Wt. 147.00; 3,061 mmol), and about 48.00 g of 2-fluoro-m-xylene (mol. Wt. 124.16; 386.6 mmol) were charged to a 2 liter Parr®-brand 4522 stainless steel reaction vessel. To this mixture was added 5 drops of concentrated HCl. The vessel was sealed, heated to 50° C., and purged three times with carbon monoxide with the pressure of the vessel increased to 100 psi for each purging. After the third purge, the vessel was vented and a final introduction of CO was made at a pressure of about 200 psi, the pressure at which the reaction was maintained for the total reaction time of about 16 hours (the reaction temperature was maintained at 50° C. for the duration as well). Once the reaction was complete, the resultant mixture (exhibiting a dark orange color) was poured into about 500 mL of ice water (which turned the solution a yellow color), to which was added 500 mL of cyclohexane. The top, organic layer was removed and washed three times with water using a separatory funnel and dried over magnesium sulfate. The residual organic phase was then distilled under vacuum to remove excess cyclohexane, 2-fluoro-m-xylene, 1,2-dichlorobenzene, and left about 40.39 g of a benzaldehyde mixture consisting of 4-fluoro-3,5-dimethylbenzaldehyde (73.8%) and 3-fluoro-2,4-dimethylbenzaldehyde (26.2%) (mol. Wt. 152.17; 265.4 mmol; yield of approximately 68.6%).

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