Synthesis
The general procedure for the synthesis of 1,10-dibromodecane from 1,10-decanediol is as follows: 1,10-decanediol (1 eq.), 48% aqueous hydrobromic acid (ca. 3 eq./hydroxyl), and octane (ca. 7:1 volume-to-weight ratio to the diol) were added to a single-necked, round-bottomed flask and assembled with a fractionating column/Dean-Stark trap. The reaction mixture was placed in a heated oil bath (145-150°C) with rapid magnetic stirring. The aqueous (lower) layer at the initial boiling point (89-92°C) was condensed and gently separated, and subsequently collected at about half the theoretical volume of water; at this point the temperature of the azeotrope (still at head temperature) began to rise. The condenser was set to full reflux for a few hours, then turned back on and the aqueous-phase material continued to be collected for 1 hour (top temperature 96-100°C). The final volume of the aqueous phase distillate reaches 90-100% of the theoretical value (up to 24% hydrobromic acid in the high boiling distillate). When the octane phase (which is light tan in color) contains dibromides and brominated streptanols (e.g., 6 band 6c), it is washed with cold 85% v/v sulfuric acid (10 mL first, then 5 mL) to remove all color and brominated streptanols. For all three dibromides (3b, 4b, 6b), the neutralized octane solution was passed through a Vigreux column under reduced pressure to remove the solvent, and the residue (which was confirmed to be essentially pure by 1H NMR) was purified by Kugelrohr distillation. Trace amounts of 4-methyltetrahydropyran were detected prior to distillation of 4b.
References
[1] Tetrahedron Letters, 2015, vol. 56, # 4, p. 630 - 632
[2] Green Chemistry, 2014, vol. 16, # 2, p. 836 - 843
[3] Journal of Organic Chemistry, 2015, vol. 80, # 11, p. 5386 - 5394
[4] Journal of the American Chemical Society, 1936, vol. 58, p. 488
[5] Journal of the Chemical Society, 1958, p. 2068
