1,3,5-Tri-tert-butylbenzene,
Bromine,
Iron Powder,
Carbon Tetrachloride.

To 1,3,5-Tri-tert-butylbenzene (10.25 g, 0.042 mol) in carbon tetrachloride (20 ml) at 0⁰C was added iron powder (2.5 g, 0.045 mol) and bromine (13.4 g, 4.3 ml, 0.084 mol). The solution was stirred at 0⁰C for 4 h. The reaction mixture was poured into cold water (ca. 40 ml), and the organic layer separated. Excess bromine was removed by shaking with a 10% NaOH (or KOH) solution. The organic phase was then washed with water until neutral, dried over magnesium sulfate, and concentrated in vacuo. The product was distilled with a Kugelrohr, and the fraction boiling at 152-156⁰C at 26 mmHg was collected. Recrystalisation from petrol (or hexane) gave white crystals in 75% yield.

Use of the correct amount of bromine (2 equivalents) is essential, as a reduction will lead to the product being contaminated with unreacted tri-tert-butylbenzene. Separation of these two compounds is extremely difficult. It is also vital to perform the reaction at 0⁰C, as this is safer, and reduces the amount of by-products. However, it is inevitable that a small quantity (ca. 3% or more) of the di-bromo substituted product will be formed. A reaction time of ca. 4 h is suggested as the minimum; the reaction can be left overnight with similar results. The product can be purified directly by recrystalisation from hexane or petroleum ether, without the distillation step, but this tends to lead to reduced yields.

¹H NMR (293 K, CDCl₃) 7.33 (s, 3H, coincident aromatic protons), 1.30 (s, 18H, ^tBu).

P. D. Bartlett, M. Roha and R. M. Stiles, J. Am. Chem. Soc., 1954, 76, 2349.