Amberlyst-15 is an acidic ion exchange resin, which is simply filtered off after the reaction and is regenerated by washing it with aqueous bicarbonate, water and finally a dilute acid. 500g costs at most $50 and it can be reused over and over again. This reaction should be really nifty for iodinating (pseudo)ephedrine to iodoephedrine for use together with other methods of reduction than HI/P.Selective Iodination of Alcohols with NaI/Amberlyst-15 in AcetonitrileMahmood Tajbakhsh, Rahman Hosseinzadeh, Zahra LasemiSynlett 2004; 01/29/2004 (eFirst)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/iodination.nai-amberlyst15.pdf)
DOI:
10.1055/s-2004-815445
AbstractA simple and effective procedure for conversion of primary, secondary, allylic and benzylic alcohols into the corresponding iodides is described using NaI/Amberlyst-15 in acetonitrile at room temperature. Selective conversion of benzylic alcohols in the presence of saturated alcohols into the corresponding benzylic iodides is achieved under these conditions.A number of synthetic methods for transformation of alcohols into iodides has been developed during the past two decades. Some methods involve mild conditions and the use of iodotrimethylsilane, bromotrimethylsilane, chlorotrimethylsilane-sodium iodide, hexamethyldisilazane-iodine, P
2I
4 in CS
2, N,N-diethylaniline-borane-I
2, CeCl
3·7H
2O/NaI system, sodium iodide over KSF-clay under microwave irradiation, and KI/H
2SO
4 supported on natural kaolinitic clay under microwave irradiation as reagents. However, some of these suffer from drawbacks, which include the use of toxic and/or hazardous materials, reagents that are not commercially available, long reaction times, low yields and tedious work-up procedures. As such mild and efficient methods that can be used to promote the transformation of hydroxyl groups into iodides are of increasing importance to overcome such difficulties.
We report herein an exceedingly mild preparation of iodides from alcohols by the use of a NaI/Amberlyst-15 system in acetonitrile at room temperature.The results of the iodination reactions are summarized in
Table 1. The data indicate that iodination of a variety of allylic or benzylic and saturated primary or secondary alcohols occurs using a NaI/Amberlyst-15 system in acetonitrile at room temperature. The iodination of benzyl alcohol was selected for optimization of the reaction conditions. It was observed that when benzyl alcohol was treated with NaI without Amberlyst-15, no change took place, implying that Amberlyst-15 plays an important role in this reaction.
We have also examined the effect of solvent in this reaction. When benzyl alcohol reacted with NaI/Amberlyst-15 in various solvents such as acetonitrile, ethyl acetate, chloroform, dioxane, dichloromethane and THF, we found that the reaction proceed most rapidly and give optimal yields in acetonitrile.
Benzyl alcohol with NaI/Amberlyst 15 provided benzyl iodide in excellent yield. In the case of primary alcohols the conversion into the corresponding iodides requires longer reaction times. Likewise, secondary alcohols such as cyclohexanol and 5-nonanol were also converted into the corresponding alkyl iodides.
General Procedure for the Conversion of Alcohols to Iodides
To a stirred suspension of alcohol (1 mmol) and NaI (0.150 g, 1 mmol) in MeCN (10 mL) was added Amberlyst-15 (H+-form, 1 g), and the resulting mixture was stirred at r.t. After completion of the reaction (TLC or GC), Et2O (10 mL) was added and washed with aq sat. NaHCO3 solution, followed by NaHSO4. The resultant organic layer was extracted with Et2O (3×10 mL) and the combined extract dried over anhyd Na2SO4. The solvent was removed under reduced pressure to afford iodides in almost pure form. If necessary, products were purified by column chromatography (eluent: hexane-EtOAc).About Amberlyst-15
(
http://www.medibix.com/detail.jsp?view=detail&sku_id=1377501&product_id=462525)
About Ion Exchange Resins
(
https://www.sigmaaldrich.com/aldrich/brochure/al_pp_ionx.pdf)