Rhodium (Chief Bee)
08-10-02 03:27
No 343998
      Preparation of Anhydrous HI in GAA  Bookmark   

Some smart thoughts here - they add concentrated hydriodic acid to acetic anhydride, forming an anhydrous solution of HI in GAA. They also first treat the aqueous acid with Amberlite LA-2 resin to remove free iodine in the solution. They also let their anhydrous HI react with an alkene.

Organic Process Research & Development Vol. 1, No. 1, p 88 (1997)

9- and 10-Iodostearic Acids (ISA, 2 and 3).

Into an argon-purged separation vessel fitted with a mechanical stirrer is placed hydriodic acid (2.165 L, specific gravity 1.91, 65.0% w/w). A solution of Amberlite LA-2 (0.395 kg) in toluene (5.0 L) is then added to the vessel, and the agitator is used to mix the layers for 2 min. After the layers are allowed to separate, the colourless hydriodic acid layer is run into an argon-purged holding vessel prior to returning to the separator for a single wash with a quantity of degassed toluene. For solutions heavily contaminated with molecular iodine, a second wash with the LA-2 resin solution is required. Into an argon-purged reaction vessel is then placed acetic anhydride (6.94 L, 99.7%, 73.33 mol) which is vacuum degassed. Washed hydriodic acid (1.973 L, 19.15 mol of HI, 73.33 mol of H2O) is added to the mechanically stirred solution at such a rate that the temperature is maintained below 55 C by the use of external water cooling. If the temperature is allowed to rise above this limit, there is some loss of water vapour by entrainment, and this results in incomplete hydrolysis of the acetic anhydride. The mixture is stirred for a further 60 min after completion of the addition of the aqueous acid and is then cooled to 20 C prior to the addition of a vacuum-degassed solution of oleic acid (1.362 kg, 4.822 mol) in glacial acetic acid (2.0 L) over a period of 10 min. After completion of the addition, the mixture is stirred for a further 16 h prior to removal of the majority of the acetic acid by vacuum codistillation with 10 volumes of toluene (50 mmHg, <50 C). The dark residue is dissolved in toluene (14.0 L) and then transferred to a separating vessel followed by washing with a 5% solution of sodium thiosulphate (2.0 L) and then deionised water. The thiosulphate wash is first back-washed with a small quantity of toluene, which is combined with the main solution of product. The organic solution is dried over magnesium sulphate and filtered through a short bed of 100-200 mesh Florisil prior to removal of the toluene under reduced pressure, to leave the product as a colourless to very pale yellow oil (1.8728 kg, 4.564 mol, 94.6%). Yield range: 90-97%.