# Phenyl-2-propanone (P2P) from Phenylacetic Acid and Acetic Acid (Tube Furnace Method) by Mastermind This is what I came up with for a write up (P2P from PAA and acetic acid; tube furnace method). ### Description of the apparatus The apparatus utilizes a 98% silica glass (pyrex also works according to Organic Synthesis) combustion tube (refered to as catalyst tube here) about 1.1 meters long and about 2.5 cm in diameter with a ground glass 29/42 female to 24/40 male straight adapter glued onto the outlet end of the catalyst tube using epoxy glue. The thermocouple used to monitor the temperature includes a number of cylindrical ceramic beads (arranged in a line), each having two holes, with each hole adapted to receive a thermocouple wire. The cylindrical beads hold the two thermocouple wires parallel to each other while providing electrical insulation. The thermocouple wires are twisted at one end and bent upward slightly so that they contact the catalyst tube when held against it. The thermocouple is placed about 0.3 meters from the inlet end and on the outside of the catalyst tube (pointing away from the inlet end of the catalyst tube) and the catalyst tube and thermocouple are wrapped with a heating tape rated at about 800°C maximum along about 0.5 meters length at the center of the catalyst tube leaving about 0.3 meters uncovered at both ends of the catalyst tube. Glass ribbons or strings provided at each end of the heaing tape are tied around the tube to hold the heating tape and thermocouple in place. The portion of the catalyst tube covered with the heating tape is then wrapped with glass wool for insulation. A glass wool plug is placed through the outlet end of the glass tube and pushed using a wooden or glass rod to the point where the heating tape ends to support the catalyst. The part of the catalyst tube covered with the heating tape is filled with pea sized pumice supporting the catalyst (described later) and supported using standard ring stands and clamps at an angle of about 10-15 degrees from the horizontal. An angled (110 degree) adapter adapted to receive a #4 stopper at one end and narrows to about 3/8 inches in diameter at the other end is connected to the inlet of the catalyst tube using a one hole stopper. A two hole #4 stopper supporting a seperatory or dropping funnel and a short piece of glass tubing having a 90 degree bend is connected to the inlet of the angled adapter. A standard angled (110 degree) adapter having 24/40 ground glass joints at both ends is connected to the straight adapter at the outlet or lower end of the catalyst tube and a round bottom flask is connected to the outlet end of the vacuum adapter to receive the products from the catalyst tube. A length of rubber tubing is connected to the side arm of the vacuum adapter. A stiff piece of tubing, such as, metal or glass can be connected to the other end of the rubber tubing and can bee lead outside through a window, to a window fan or, preferably, to a container of water to allow observation of the rate of gases passing through the catalyst tube by observing bubbles produced in the container of water. The seperatory funnel at the inlet end is used to control the addition of a mixture of PAA and acetic acid in the catalyst tube and the 90 degree piece of glass tubing at the inlet end (supported by the two hole #4 stopper) is used to introduce air to process or regenerate the catalyst, or to introduce an inert gas, such as CO2 or N2, into the catalyst tube when making the ketone. Here's a picture of the tube furnace. ### The catalyst The magnesia catalyst was made using pea sized pumice (some patents were seen supporting similar catalytic materials using perlite for cracking petroleum hydrocarbons; other art). Enough pea sized pumice to fill FOAF's combustion (now catalyst) tube was covered with enough Milk of Magnesia so that the pumice 'had looked like it had been white washed' (good description) and at the same time the pores were not clogged (for maximum catalytic surface area). A 98% silica combustion tube was used which was wrapped with a heating tape (max temp 800°C) and was covered with glass wool as insulation. 2-3 teaspoons of calamine lotion (ZnO and Fe oxide; see US patent 5750795, for example, especially tables 1 and 2) was added to the catalyst and it was heated, alternately, on a gas stove and in a microwave oven to dry it and convert it to MgO. It was found that when the catalyst was placed in the tube and heated to about 500°C+ (with air pumped through it) that the Mg(OH)2 could more easily be dehydrated (H2O given off and condensed) and converted to MgO. Note: add calamine lotion before putting in combustion tube ### P2P tube furnace process The tube furnace is heated to 430-450°C, and simultaneously the tube is swept out thoroughly with an inert gas, such as N2 or CO2, introduced through the 90 degree glass tubing bend (at the inlet end). The inert gas can be passed first through a wash bottle to estimate the rate of flow or the flow can be observed by placing the rubber tubing from the vacuum adapter in a container of water (for observing the rate in bubbles per second). A solution of 136 g. (1 mole) of phenyl acetic acid (PAA) in 120 cc. of glacial acetic acid (120 g., 2 moles) is placed in the seperatory funnel and introduced into the tube furnace at a rate of twelve to fifteen drops per minute. Meanwhile, a very slow stream of the inert gas (one bubble per second) is passed through the tube to keep the gases in motion. After all of the solution has been added, the seperatory funnel is rinsed with 10ml of glacial acetic acid, and this is passed through the catalyst tube to facilitate removal of the product. The distillate consists of a red or brown red oily layer and an aqueous layer. Both layers are treated with about 300 cc of water and NaHCO3 is added until the effervescence stops and the mixture is alkaline to litmus or pH paper (NaHCO3 turns pH paper green). The P2P layer is seperated (the emulsion can be easily seperated with a centrifuge if available) and the aqueous layer is extracted with an organic solvent (ie. 3x30 ml of toluene). The solvent is dried and evaporated to get more the P2P. The P2P can be distilled under a vacuum or at atmospheric pressure (fraction collected at 210-230°C). The yield is typically about 70%. ### References: Vogel's Practical Organic Chemistry Organic Synthesis Col. Vol. II pg. 389-391 (methyl benzyl ketone) US patents: 2108156, 2612524, 2697729, 2811559, 3075016, 3660491, 4172097, 4754074, 5750795 Addendum by Mastermind Maybe the description of the apparatus is too detailed. Various ways to set it up are possible. The tube itself can be glass, ceramic or metal. One problem with metal is that it conducts electricity and might be a problem if a heating tape becomes frayed (starts to lose insulation). Also, you don't want to short out the thermocouple either. Glass has the advantage that you can see through it and both glass and ceramic have been used in combustion tubes. Ceramic also might be a good choice since its tougher than glass and doesn't conduct electricity. The apparatus was modeled as closely as possible to the apparatus from the Organic Synthesis article which shows a picture of the tube furnace tilted slightly from the horizontal. I've seen other similar things where the reaction tube is horizontal or vertical. For example, US patent 2,811,559 shows a vertical tube furnace which is used for the same type of reaction (ie. cross decarboxylation of carboxylic acids). The catalyst is MgO and the products in examples I-IV are methyl undecyl ketone and stearaldehyde. The problem with having the tube furnace vertical is that maybe the reactants would come through too fast and wouldn't have time to react, depending on the porousity of the catalyst. It was felt that if pea sized pumice was used as in the Organic Synthesis article that the catalyst tube should be set at the same angle as shown in the article. The combustion (catalyst) tube is wrapped with a heating tape which is coated with a woven fiber glass covering. The heating tape was supposed to be rated at 800°C. Over time the fiber glass covering tended to fray (come apart) and expose the wire heating element. After it was used for some ketene experiments at 800°C that was when the fiber glass covering started to come apart. The point of using the magnesia catalyst is as an alternative to the thoria catalyst in the Organic Synthesis article. Thorium is radioactive and isn't OTC anyway. It was found, surprising, that the magnesia catalyst gave high yields of P2P. Also, it was found that when the thoria catalyst was fresh the yield of P2P wasn't too bad, but the catalyst tended to lose activity after a couple of runs. ## Tube Furnace method from Vogel's Practical Organic Chemistry (5th Ed) ### Preparation of thorium carbonate-pumice catalyst Dissolve 294 g (0.5 mol) of thorium nitrate hexahydrate in the minimum of water (450 ml) and add slowly a solution of 106 g (1 mol) of anhydrous sodium carbonate in 400 ml of water with stirring. Allow the thorium carbonate to settle, decant as much as possible of the mother-liquor and wash the sediment once by decantation with 500 ml of water. Make the resulting moist solid into a thick paste with distilled water and stir in pumice (4-8 mesh) until most of the suspension appears to be absorbed. Dry the impregnated pumice in quantities of 200 g by heating in a large evaporating dish upon an electric hotplate and stirring constantly with a glass rod. Stop the heating when the pumice particles no longer cling together. Sieve the resulting pumice, 250 g of a white powder (consisting largely of thorium carbonate but containing some oxide) are recovered and can be used for impregnating more pumice. The total weight of pumice catalyst thus prepared is about 1400 g; the exact weight will depend upon the grade of pumice used. ### Benzyl methyl ketone (P2P) Pack the catalyst into the Pyrex glass combustion tube of the pyrolysis apparatus illustrated in the figure and assemble the remaining components. Displace the air in the apparatus with nitrogen, and while maintaining a continued gentle gas flow, heat the pumice for 6-12 hours at 400-450°C (while a slow stream of nitrogen is maintained through the combustion tube) in order to convert the thorium carbonate into thorium oxide. If necessary the catalyst may be allowed to cool in a stream of nitrogen if the preparation needs to be interrupted at this point. Place a solution of 170 g (1.25 mol) of pure phenylacetic acid (mp 77°C) in 225g (3.75 mol) of glacial acetic acid in the funnel, and adjust its rate of flow into the catalyst tube to 1 drop every 2 or 3 seconds. Also pass a slow stream of nitrogen (1 bubble per second) through the apparatus in order to keep the gases in motion; the rate of flow may be estimated by passing the inert gas through a concentrated sulphuric acid wash-bottle or 'bubbler' before it enters the furnace. When all the acid mixture has passed through the catalyst tube, separate the lower aqueous layer of the product and treat the organic layer with 14-20 per cent sodium hydroxide solution until the washings are alkaline to litmus and then twice with water. Extract the aqueous layer twice with 50 ml portions of ether, wash the extracts successively with sodium hydroxide solution (until alkaline) and water, and add the resulting ether solution to the main product. Dry with magnesium sulphate, remove the ether on a rotary evaporator and distil the residue under reduced pressure preferably through a fractionating column. Collect the benzyl methyl ketone at 102-102.5 °C/20 mmHg; the yield is 85 g (51%). The residue in the flask is dibenzyl ketone; it may be purified by transferring to a smaller flask and redistilling (bp 200°C/21 mmHg; mp 34-35°C).