<p>Air-free sublimation
</p><p><u>Apparatus</u>
</p><p><b>a</b> = Rubber cone (typically used to form a vacuum seal in a <a href="//commons.wikimedia.org/w/index.php?title=B%C3%BCchner_flask&amp;action=edit&amp;redlink=1" class="new" title="Büchner flask (page does not exist)">Büchner flask</a> filtration) which is selected so as to fit snugly around the neck of the <a href="//commons.wikimedia.org/w/index.php?title=Schlenk_tube&amp;action=edit&amp;redlink=1" class="new" title="Schlenk tube (page does not exist)">Schlenk tube</a>
</p><p><b>b</b> = <a href="//commons.wikimedia.org/w/index.php?title=Schlenk_tube&amp;action=edit&amp;redlink=1" class="new" title="Schlenk tube (page does not exist)">Schlenk tube</a>
</p><p><b>c</b> = Gas/vacuum inlet
</p><p><b>d</b> = Teflon tap (or stopcock)
</p><p><b>e</b> = Syringe
</p><p><u>Method steps</u>
</p><p><b>1</b> = Impure solid to sublime (brown) is placed in a Schlenk tube, avoiding contaminating the sides of the tube (e.g. by careful evaporation from a solution containing the brown solid).
</p><p><b>2</b> = Rubber cone (black) is pushed near top of the Schlenk tube (forming a tight seal around flask) and filled with a coolant such as dry ice/acetone (blue/white) to cool the neck of the Schlenk tube. The bottom of the Schlenk tube is heated (red shading) under vacuum (blue arrow), so that the impure solid (brown) sublimes as a pure solid (purple) at the cooled neck area (blue shading).
</p><p><b>3</b> = After sublimation, the cooling-cone (black) is removed, leaving the concentrated impurity as a residue (dark brown) in the bottom of the flask, and the purified sublimed solid (purple) at the neck of the Schlenk tube.
</p><p><b>4</b> = Solvent (blue) is inserted via syringe to dissolve the residue (green/brown), taking care to avoid washing off the sublimed solid (purple).
</p><p><b>5</b> = Residue solution is then removed by syringe (green/brown) (Steps <b>4</b> and <b>5</b> can be repeated as required).
</p><p><b>6</b> = Purified sublimed solid (purple) is washed off the neck of the flask with fresh solvent (blue) via a syringe.
</p><p>(In steps <b>3</b> to <b>6</b> the flask is held under an atmosphere of an inert gas via Schlenk tube side arm).
</p><p><b>7</b> = Solvent is removed under vacuum to give the purified sublimed solid (dark purple).
</p>
Steps <b>6</b> and <b>7</b> are not essential
<a href="//commons.wikimedia.org/w/index.php?title=User:Quantockgoblin&amp;action=edit&amp;redlink=1" class="new" title="User:Quantockgoblin (page does not exist)">Quantockgoblin</a>
<span class="int-own-work" lang="en">Own work</span>