Appendix Five
Although hydrogenation can be carried out as described in the main section without elaborate equipment the consumption of hydrogen will be high. This is not too great a disadvantage as cheap electrolytic hydrogen is available in cylinders (from welding suppliers) and can be used without special purification. The consumption can also be lowered considerably if good agitation, preferably by vigorous shaking, is performed during the reduction. Suitable equipment is described in the Organic Syntheses reference given in the main section.
Recently a particularly active catalyst has been prepared by reducing a palladium salt in the presence of charcoal with sodium borohydride. The increase in activity is such that it is possible to hydrogenate 100-200 gram quantities of olefin in a simple flask in about 2 hours. It is strongly suggested that this catalyst be prepared and used in (e)
For this purpose the apparatus is set up as in (e), using an Erlenmeyer flask or tall graduated cylinder (500 ml. capacity) for the hydrogenation vessel. From the gas-cylinder hydrogen is conducted to the bottom of the hydrogenation vessel and the olefin to be reduced is added together with 10 ml. of glacial acetic acid (the acid serves to decompose excess sodium borohydride in the catalyst mixture). Just before the catalyst mixture (prepared below in (2)) is added the flow of hydrogen should be started through the olefin so that after the addition the vessel can be closed and the hydrogenation will proceed.
The addition of the catalyst mixture is made slowly enough so that there is no danger of loss through foaming. The catalyst is prepared as follows.
(1) Stabilized sodium borohydride solution (1 Molar).
To 8 grams of sodium hydroxide add sufficient water to make l00 ml. solution. Place 5 ml. of this solution in another graduated flask (discard the remainder) and add anhydrous ethyl alcohol (commercial denatured anhydrous alcohol can be used) to make 100 ml. solution. To this add 3.8 grams sodium borohydride (l00% analysis; if the commercial sodium borohydride is less pure use a proportionately increased amount).
(2) Palladium catalyst.
In a 500 ml. flask there is placed 100 ml. dry ethyl alcohol, 5 grams decolorizing charcoal powder, and one gram of palladium chloride. The solution in the flask is strongly swirled by hand and 20 ml. of the sodium borohydride solution prepared in (1) is added. After about one minute this solution is poured into the hydrogenation flask and the hydrogenation allowed to proceed.
It is also possible to conduct the hydrogenation with hydrogen generated in the vessel itself by means of sodium borohydride instead of using an external source. For details on the method the original papers (References 391, 392 and 393) should be consulted. The simple apparatus required can be constructed easily, or it is commercially available from Delmar Scientific Laboratories, 317 Madison Street, Maywood, Illinois.
Appendix Four
Appendix Six