Workup for Removing Tin Byproducts

Methods for removal of various forms of tin waste from reaction mixtures are listed below:

[Bu3SnX]
  1. Wash with a saturated aqueous solution of KF and/or Filter through a mixture of KF/Celite. Sample procedure:
    1. Dilute reaction with suitable organic solvent
    2. Add appropriate aqueous phase (water, saturated NH4Cl, etc.)
    3. Remove aqueous layer and wash organic phase 2-3 times with 1M KF aqueous solution. Shake in separatory funnel for up to 1 minute for each wash. Solid Bu3SnF precipitate may form at organic/aqueous interface. If this is a problem, filter through Celite.
    4. Wash organic phase 1X with brine, dry organic phase and remove solvent.

    (contributed by Thomas Pettus)

  2. In many Stille reactions, the Bu3SnX byproducts can be almost entirely removed by filtering through silica made up with ~2-5% triethylamine in the eluent (or immediately purifying by standard column chromatography). Run the flash column using the same solvent. This method is quicker than stirring with aq, KF, and more fun than grinding a big bowl of toxic KF with silica or Celite for a good dispersion.

    (contributed by Graham Cumming)

  3. Byproducts can be removed by treatment with AlMe3 (to create the nonpolar Bu3SnMe) or NaOH (to create the polar Bu3SnOH). See: P. Renaud, E. Lacote, L. Quaranta Tetrahedron Lett. 1998, 39, 2123. (taken from The Organic Chemist’s Companion; maintained by the Merlic Group at UCLA.) [link]
[Bu3SnH]

Add I2 to convert Bu3SnSnBu3 and unreacted Bu3SnH to Bu3SnI, then subject to KF treatment (see #1 above). This converts Bu3SnI to Bu3SnF, which is more easily removed. (contributed by Thomas Pettus)

[SnCl2]

Method for workup of large scale reduction of nitro group in EtOH (contributed by Mike Reader) “On completion of the reaction, addition of a solution of tetraethylammonium chloride (4 equiv) in EtOH produced a very insoluble tin salt. An easy filtration later, my work-up problem was solved to give a tin-free product and a solid tin salt for easy disposal.” adapted from MORRISON, JAMES SIDNEY, "SOME REACTIONS OF TIN(II)CHLORIDE IN NON-AQUEOUS SOLUTION" (1965). Doctoral Dissertations. 808. See pages 23 and 39 [link]