Anisole (Fisher Scientific)

Sodium bromide

Potassium monopersulfate, triple salt with potassium bisulfate and potassium sulfate ("Oxone," Alfa Aesar)

Water, deionized

Anisole (1.08g, 10 mmol), sodium bromide (3.6g, 35 mmol), oxone (10.72g, 17.5 mmol) were added together with approximately 20 copper-plated steel beads to a 50mL centrifuge tube on a vortex mixer and the mixture was vortexed for approximately 60 minutes. (See Notes) The contents of the tube were poured out onto a Buchner funnel and rinsed well with deionized water and the beads removed with a magnet. Air was pulled through the collected product for ca. 10 minutes to remove water and traces of bromine vapor, yielding 0.65 g dense white flakes of product. During this time, a second crop of crystalline product separates from the filtered reaction mixture and can be collected by a second vacuum filtration yielding 0.86 g solid for a total of 1.51 g (5.5 mmol, 55%) 2,4-dibromoanisole, >90% pure by GC/MS.

• This reaction is part of a continuing effort to develop practical mechanochemical procedures for the synthetic lab. In contrast to its sister procedure, Synthetic Page 789, the vortex mixer-based procedure is particularly suitable for more electron-rich (rapidly reaction) substrates and for liquid starting materials.

• For this reaction, we used a Maxi-Mix II vortex mixer (Thermo Scientific).

• It was not necessary to pre-grind any starting materials for this reaction.

• The "beads" used were copper-plated steel "BB" 4.5 mm shot, readily available in the US. Beads show some surface discoloration but can be reused indefinitely if rinsed and dried after each reaction. Ball bearings of similar size should be usable as well.

• Particularly reactive substrates can be vortexed by hand but vortexing for more than ca. 10 minutes is tiring to the operator due to noise and vibration. For longer reaction times, the centrifuge tube can simply be taped onto the vortex mixer platform. Alternatively, commercial tube holders are available for many vortex mixers.

• Impurities consist of minimal traces of 4-bromoanisole and 2,4,6-tribromoanisole, which can be removed by recrystallization of the product from boiling absolute ethyl alcohol.

GC-MS m/z (% relative intensity, ion): 263.9 (50, M+), 265.9 (100, M+2), 267.9 (49, M+4). tr of the 2,4-dibromoanisole product was 8.66 min on a Restek 30m RXI-17 fused silica column (see Temperature Program below).

1H NMR  (CDCl3, δ vs. TMS, 300 MHz) 7.65 (s, 1H) 7.351 (d, 1H) 6.78 (d, 1H) 3.87 (s, 3H).

Wang, Guan-Wu and Jie Gao, Green Chem., 2012, 14, 1125. DOI: 10.1039/C2GC16606B

N. Marshall, Chemspider Synthetic Pages, 2014, http://cssp.chemspider.com/789