A mixture of p-methoxybenzyl alcohol (41.40 g, 0.30 mol) and hydrochloric acid (37%; 75 mL, 0.90 mL) was stirred for 30 min at room temperature. The product was extracted with petroleum ether (40 mL), the extract washed with water (3 × 50 mL), dried over anhydrous sodium sulfate and the solvent removed under reduced pressure to give p-methoxybenzyl chloride as a colorless oil (45.35 g, 97% yield).

The product is pure by ¹H NMR. Unstabilized p-methoxybenzyl chloride tends to decompose to a solid resin. Trace amounts of HCl are likely increase the rate of decomposition. It should therefore be either prepared before use or stabilized and kept in a refrigerator. It has some commercial sources, but given its price, stability issues and the simplicity it might be best prepared before use from the inexpensive p-methoxybenzyl alcohol (anisyl alcohol). The present procedure is an adaptation from Organic syntheses which might be of use to those who use this reagent for the introduction of the p-methoxybenzyl protecting group.

¹H NMR (CDCl₃)   3.81 (s, 3H, CH₃), 4.57 (s, 2H, CH₂), 6.88 (AA'XX', J = 8.7 Hz, 2H), 7.31 (AA'XX', J = 8.7 Hz, 2H).

K. Rorig, J. D. Johnston, R. W. Hamilton, and T. J. Telinski, Org. Synth., 1956, 36, 50. Link