Platinum Dioxide (Adam's Catalyst)
Platinum dioxide for use in hydrogenations is available commercially. It may alternatively be prepared by either of the following methods.
Method 1 (from ammonium chloroplatinate).
Place 3.0 g of ammonium chloroplatinate and 30 g of sodium nitrate (AnalaR)
(1) in a Pyrex beaker or porcelain dish and heat gently at first until the evolution of gas slackens and then more strongly until a temperature of 300 °C is reached. This occupies about 15 minutes, and there is no spattering. Maintain the fluid mass at 500 - 530 °C for 30 minutes, and allow the mixture to cool. Treat the solid mass with 50 ml of water. The brown precipitate of platinum oxide (PtO
2.H
2O) settles to the bottom. Wash it once or twice by decantation, filter through a hardened filter paper and wash on the filter until practically free from nitrates. Stop the washing process immediately when the precipitate tends to become colloidal
(2): traces of sodium nitrate do not affect the efficiency of the catalist. Dry the oxide in a dessicator, weigh out portions of the dried material a required.
Method 2 (from chloroplatinic acid).
Dissolve 3.5 g of the purest commercial chloroplatinic acid in 10 ml of water contained in a 250-ml Pyrex beaker or porcelain basin, and add 35 g of sodium nitrate (AnalaR)
(1). Evaporate the mixture to dryness by heating gently over a Bunsen flame while stirring with a glas rod. Then raise the temperature to 350-370 °C within about 10 minutes: fusion will occur accompanied by the evolution of brown oxides of nitrogen and the gradual separation of a precipitate of brown platinum oxide. If foaming occurs, stir the mixture more vigorously and direct an additional flame at the top of the reaction mixture, if necessary. If the burned beneath the beaker is removed when frothing commences, the top of the fused mass solidifies and material may be carried over the sides of the vessel. After 15 minutes, when the temperature has reached 400 °C, the evolution of gas decreases considerably. Continue the heating until at the end of 20 minutes the temperature is 500 - 550 °C; at this stage the evolution of oxides of nitrogen has practically ceased and there is gentle evolution of gas. Maintain the temperature at this point (best with the full force of a Bunsen burner) for about 30 minutes, by which time fusion is complete. Allow the mass to cool (the Pyrex beaker may crack), add 50 ml of water and proceed as in
Method 1.
Notes:
(1) The use of an equivalent quantity of potassium nitrate (AnalaR) is said to produce a more active catalyst.
(2) It is advisable to test a small portion of the filtrate from platinum by acidifying with hydrochloric acid and adding a few drops of SnCl
2 solution: a yellow or brown colour develops according to the quantity of platinum present. The yellow colour is soluble in ether, thus rendering the test more sensitive. If platinum is found, treat the filtrate with excess of formaldehyde and NaOH solution and heat; platinum black separates on standing and may be filtered and worked up with other platinum residues.
Platinum residues from hydrogenation reactions should be carefully preserved and subsequently recovered by conversion into ammonium chloroplatinate by the following method. Dissolve the platinum or platinum residues in aqua regia, evaporate just to dryness several times with concentrated hydrochloric acid, dissolve the final residue in a little water and filter. Precipitate ammonium chloroplatinate from the filtrate by addition of excess of a saturated solution of ammonium chloride. Filter and dry the precipitate at 100 °C
ref.: Vogel's Textbook of practical organic chemistry (5
th ed) p 459 - 460
Further info about the preparation of this catalyst can be found in JACS, sept. 1923 p 2171 - 2179 (damn, I forgot to write down the vol. and n° ... well, sorry about that ...). However, this is a very interesting article: read it!)
So, you might wonder: why the hell do I need this catalyst. You can oxidize alcohols with it an all kinds of usefull stuff, however you might also check out this:
Freifelder, Catalytic Hydrogenation in Organic Synthesis: Procedures and Commentary (John Wiley & Sons, Inc., 1978) 101-2; Freifelder, Practical Catalytic Hydrogenation: Techniques and Applications (John Wiley & Sons, Inc., 1971) 366.
This appears to be the highest yielding published procedure for synthesizing methamphetamine from phenyl-2-propanone and methylamine. This is not surprising, considering Mr. Freifelder's vast knowledge of and experience with heterogenous catalytic hydrogenation and his many years as head of catalytic hydrogenation at Abbott Laboratories, maker of Desoxyn(r) brand d-methamphetamine.
1-Phenyl-2-propanone, 68.5 g. (~0.5 mole) in 150 ml ethanol was reacted with 51.8 g. (0.5 mole) 30% w/w aqueous methylamine solution, (fn.1),(fn.2) and hydrogenated at 3 atm. pressure (fn.3) with 1.4 g. of platinum oxide. (fn.4) There was a lag period of 1-2 hours, during which time there was little or no uptake of hydrogen (prereduction of catalyst did not change the lag period). Thereafter uptake was usually complete in an additional 2-4 hours. (fn.5) After removal of catalyst and concentration of filtrate and washings, high yields of the racemic N- methylphenylisopropylamine (methamphetamine) were obtained (90% or greater yield).
This procedure is taken from
https://www.thevespiary.org/rhodium/Rhodium/chemistry/reductive.alkylation.html