K. K. GEORGIEFF I Research Laboratories, Shawinigan Chemicals, Ltd., Shawinigan Falls, Quebec, Canada Preparation of Acetylacetone Using Sodium Alkoxide and Dispersed Sodium as Catalysts

Reduction in costs, hazards, and time of re- action makes this process commercially attractive

1NDUSTRIAL production of acetylacetone ester, length of time required to complete The yields with methyl acetone, which by the Claisen condensation of acetone the reaction, and effect of temperature on had been dried with acetic anhydride, and aliphatic acetate esters, using sodium yield are lacking. This information is were identical to those obtained with or sodium alkoxide as catalyst, has been given in the present article. The amount chemically pure synthetic mixtures of the made economically impossible by the of by-product acetoacetic ester produced same composition. hazards of the reaction, the low yields, in the author’s experiments was small as The inert diluent materially affected and the great length of time required compared to that divulged in the patent. the yield, but the amount was not crit- for reaction of the last few per cent of the This was probably due to a difference in ical within wide ranges of concentra- sodium, because of coating of the par- the amount of diluent used, although the tion. Best results were obtained with ticles. The latter disadvantage has, to a slightly different order of adding the re- medium boiling hydrocarbons such as small extent, been alleviated by use of so- agents may have had a minor effect. toluene. Isohexane gave somewhat called “sodium sand.” Within recent lower yields, while Varsol (a commercial years, dispersed sodium of 1- to 20- petroleum fraction, boiling point 154’ micron particle size has become commer- Sodium Alkoxide as Catalyst to 175’ C.) gave much poorer results. cially available and it was conjectured The use of sodium ethoxide and meth- When prepared in isohexane, the sodium that its use might solve many difficulties. oxide was first investigated. The over- methoxide was granular and the par- Therefore, experimental work was car- all reactions on which the yields were ticles were about the same size as the ried out on both dispersed sodium and based are expressed by the following original sodium; that prepared in tolu- sodium alkoxide prepared from sodium equations : ene was somewhat gelatinous. This dif- sand, to make a valid comparison. ference in physical form, as well as the Published yields of acetylacetone are CHsOH + Na + CH30Na + l/zHz slightly higher reaction temperature pos- not directly comparable because dif- CHa.CO.OCH3 CHa.CO.CH8 * + + sible in toluene, probably accounts for ferent ratios of reagents have been used, CH30Na = CH,.C(ONa)=CH.C0.CH3 the higher yields. With Varsol as dilu- but all have been low on sodium or so- 4- 2CH30H ent, reactions of sodium with methanol dium alkoxide (7-3, 6, 7, 77). Some CH3.C(ONa)=CH.CO.CH3 + CH3- and of acetone with methyl acetate were authors (I, 77) state that 2 gram-atoms sluggish. Treatment of the Varsol first of metallic sodium are required per mole with concentrated sulfuric acid and then of product, in contrast to 1 gram-mole of To make a direct comparison with pre- with sodium, followed by distillation, sodium ethoxide. However, in this in- viously published work (Z), a mole ratio made no difference. vestigation, 1 gram-atom of sodium was of ester-acetone-sodium alkoxide of Increasing the ratio of ester to the found equivalent to 1 gram-mole of so- about 4.07 : 1 : 1 was used in most experi- other reactants increased the yields based dium alkoxide. The advantages of using ments. Ethyl and methyl acetates gave on sodium and acetone (Table I). The dispersed sodium in the preparation of about the same yield, based on alkoxide. yields given are based on the amount of ethyl acetoacetate have been described by The yield was only slightly lower when acetylacetone recovered on distillation. Frampton and Nobis (5). Since com- the acetone and ester were added to- The total loss in the conversion of the pletion of this work, a patent (4)was is- gether to the sodium methoxide than sodium salt to free acetylacetone and in sued on the preparation of acetylacetone when acetone alone was added to the the distillation may be as high as 5 to from ethyl acetate, acetone, and dis- ester and catalyst. However, part of this 6%. This is indicated by comparison be- persed sodium. However, considerable difference was due to the lower tempera- tween the amount of free diketone re- doubt exists as to how the yield figure ture used. This is economically im- covered on distillation and the amount of was derived, and experimental data on portant, as it permits the use of cheap dry sodium acetyl acetonate originally particle size of the sodium, amount of commercial “methylacetone” as raw ma- produced, as determined by the copper diluent, yields based on acetone and terial, after removal of alcohol and water. method of analysis (70).

VOL. 49, NO. 7 JULY 1957 1067 I I I I I tate I I I Ac I I I I I I I I I I I I I I I I

The yields on ester Iz'ere 50 to Sl%, toluene or xylene \vas added to a mis- The total reaction time was about 2 but much of the loss was mechanical. ture of acetone, methyl acetate, and hours. one for preparation of the dis- In one run with ethyl acetate, the high diluent for safety as 1141 as economy in persed sodium and another for the boilers formed (including ethyl acetoace- using methyl acetone. After a small por- Claisen condensation. This compares tate and tar) accounted for not more than tion of the sodium had been added, an with 24 hours if small pieces of sodium 14.7y0 of the ester consumed. even if it induction period of several minutes oc- are used (6) and 40 to 50 hours by the ivere assumed that they were derived curred. The reaction then proceeded sodium alkoxide route starting with entirely from it. with a rapid liberation of heat and had to sodium sand. be cooled rapidly, otherivise it might have The yields increased with rise in the Dispersed Sodium as Catalyst gotten out of control. However, by add- maximum reaction temperature up to ing several per cent of crude reaction mix- about 70". But in contrast to the results The over-all reaction may be repre- ture from a previous run, this induction of Frampton and Sobis (5) on the prep- sented by the equation : period was reduced and the hazard de- aration of ethyl acetoacetate, higher creased. In the experiments reported in temperatures (up to 92") obtained by Table 11, less sodium acetoacetonate operating under pressure gave no in- CHI*CO.OCHa T CH3.CO.CHa + than that needed for maximum safety crease in yield. The temperature at Na -+ CHa.C(ONa)=CH.CO.CH3+ was added, to minimize its effect on the which the sodium was added did not ap- CH30H $. '/zHz final equilibrium. On completion of ad- pear to affect the yield appreciablv, dition of sodium (20 to 25 minutes), the within the range of 5' to 35". In all runs: the sodium dispersed in mixture was heated for 30 minutes. Medium boiling aromatic hydrocar-

Table I. Preparation of Acetylacetone Using Sodium Alkoxide as Catalyst Ester- A41cohol Acetone- Max. Re- Na AIkoxide Di lu en t Temp. of Yield, Yo coveled, Charge, Acetate Amount, Reaction, 011 0 11 % of Coni- Moles Ester Compound O c. alkoxide acetone Theoryh ments 12.18 :3:3 Ethyl Isohexane 150 62-63 56.0 74.8 85.4 c 12.23 :3 :3 Methyl Isohexane 155 57 56.7 83.6 85.6 560 47 54.6 .,. ... 1 Toluene 565 59 60.1 ...... d 12.3 :3:3 Methyl Toluene 1000 59 61.6 79.2 75.7 d* Varsol 910 60 52.4 58.7 78.0 de 6:3:3 Methyl Toluene 975 63 48.0 55.0 71.5 d

a During acetone-ester condensation. Includes alcohol origmally charged to form alkoxide. Acetone added to estei-alkoxide mixture. Acetone-ester mixture added to methoxide. e Commercial methyl acetone used.

7 068 INDUSTRIAL AND ENGINEERING CHEMISTRY ACETYLACETONE PREPARATION

Table II. Preparation of Acetylacetone Using Dispersed Sodium

I) Preformed Na Acetyl Maximum Temaerature. ___Ardnnnte - - - .. - c. Yield, % HZRe- MeOH Added to During After On On covered, Recovered, Charge", Diluent Na addn. Na addn. Na acetone % Theory % Theory Mole yo Xylene 26-34 26 50.5 69.6 75.5 ...... 22-27 72 71.4 77.8 86.6 ...... 16-20 74 69.5 75.6 79.4 ... 1.7 Toluene 25-30 69 67.5 74.2 69.3 ... 0.7 5-6 81.2 68.0 74.1 76.9 73.0 0.7 14-20 92.0 68.4 74.0 80.0 88.6 0.7 Cumene 23-28 70 60.4 62.8 68.4 96.4 0.95 Based on Na used.

bons were the most satisfactory diluents. Toluene and xylene gave approximately the same results, but cumene appeared to give lower yields. The results are summirized in Table 11. In all runs, the molar ratio of methyl acetate-acetone-sodium was 8.2 : 2 : 2 and the total weight of diluent was about 950 grams except in the case of cumene, which was 535 grams. The yields on methyl acetate were 45 LO 55%, but again mechanical losses were relatively high.

Methuds of Recovery The first method tried was to evapo- rate the volatiles from the sodium salt, treat the salt with aqueous acetic acid, extract the acetylacetone with ethyl ace- tate, and distill the extract. Although this method gave high recoveries, 18 to 24 hours were required to distill off the volatiles absorbed by the solid sodium salt even under vacuum, and the salt set to a very hard mass which reacted rela- tively slowly with acetic acid. The second method was a modifica- This apparatus was used for preparation of acetylacetone from dispersed sodium tion of that used by Claisen (3). The crude product was poured into a separa- tory funnel, sufficient water was added at 20' to dissolve the salt, and the mix- than 1 to 2% of the product was dis- maining acetylacetone (Table IV). This ture was shaken vigorously fori several solved in the hydrocarbon-ester layer. acid-contaminated diketone can be used minutes until solution was effected. Losses due to hydrolysis of the sodium salt to neutralize the next batch. After the two layers had separated (about may become appreciable if acidification The total amount of acetic acid re- 10 minutes), the aqueous layer was drawn is unduly delayed, as can be seen from quired was equivalent to slightly more off and immediately acidified. Not more Table 111. than the acetJ.lacetone recovered. Acidification was carried out in two steps, because unreacted acetic acid can- no; be completely removed from acetyl- Table IV. Reaction of Sodium Salt of Table 111. Rate of Hydrolysis of acetone by simple distillation. Aqueous Acetylacetone with Acetic Acid Sodium Salt of Acetylacetone acetic acid was added until the pH value fell to just below 7. Some of the dike- Acetylacetone % Na Salt Liberated", Time of Acetyl- % Loss tone floated to the top and was sepa- Hr. acetonea per Hour rated. The remainder was extracted with pH % 8.4 81-82 0.25 8.04 ethyl or isopropyl acetate. On distilla- ... 6.7 96-98 3.25 7.94 0.42 tion under vacuum, a water-white, acid- ' 5.8 100 70.25 5.60 0.43 free acetylacetone of 97 to 99% purity

(1 Determined by copper method. was obtained. However, it was neces- Determined by copper method. sary to add more acid to liberate the re-

VOL. 49, NO. 7 JULY 1957 1069 Therefore, about 20 to 2S% of the so- the water and methanol to satisfactory Analytical dium was present as by-product com- levels. However, by first extracting the pounds which would not react with acetic methylacetone with a saturated solution Acetylacetone was determined by the acid. of potassium acetate in water, the amount copper method of Seaman, Woods, and An aqueous solution of the sodium salt of anhydride required was greatly re- Massad (70). Large concentrations of of acetylacetone was also treated with duced. Extraction reduced the meth- acetic acid in acetylacetone were ob- carbon dioxide, An acid-free, pure dike- anol to about 1.3%. About 87Y' of the tained from the difference between the tone was obtained, but the reaction was methyl acetate and 71% of the acetone total alkali consumed on complete sapon- slow and only 80 to SS% of the acetyl- were recovered in the organic phase. ification and the alkali equivalent of the acetone could be liberated even with a From Dispersed Sodium. Sodium acetylacetone as determined by the cop- large excess of gas. dispersed in toluene or xylene was ob- per method. Concentrations between tained from the h-ational Distillers 0.7 and 2.0% were obtained by the in- Chemical Co. Particle sizes were 1 to frared spectrometer. Sodium in disper- Preparation of Acetylacetone 20 microns, with an average of 10 sions was determined by reaction with microns. methanol, followed by titration with From Ethyl or Methyl Acetate and So- Additives to the toluene were 0.57' hydrochloric acid in aqueousmedium (9). dium Alkoxide. Sodium sand was first dimerized fatry acid and 0.25% pyri- prepared by vigorously shaking a small dine, and to the xylene O.2Sy0 alu- flask containing 69 grams of molten so- minum octoate. The dispersions were Conclusions dium under xylene at 120' to 130' C. On prepared by heating the hydrocarbon, In comparison with previous processes cooling, the xylene was replaced with 690 sodium, and additive to 110' to 120' in a using sodium alkoxide, dispersed sodium grams of isohexane. The sodium-iso- flask fitted with a high speed stirrer and permits great reductions in production hexane mixture was transferred to a 3- gradually raising the speed of the stirrer costs due to higher yields and a very liter flask previously flushed with ni- to 15.000 r.p.m. for 5 to 10 minutes much shorter reaction time, which lowers trogen and fitted with a mercury-sealed, (8, 9). labor charges. Further cost reductions bicycle-chain stirrer, a calibrated separa- The apparatus for the condensation can be realized by using cheap by- tory funnel for the ethyl alcohol, a ther- was the same as for the sodium alkoxide product methyl acetone as raw material, mometer, and a brine-cooled condenser experiments. The flask was dried, after certain treatment. which was protected from atmospheric flushed with nitrogen, and charged with The product had a purity of 98 to moisture by a calcium chloride tube. 601 grams of methyl acetate, 115 grams and was equivalent to material purified The stirrer was started and 139 grams of of acetone, 5 grams of sodium salt of by converting it to its copper salt and anhydrous ethyl alcohol was added drop- acetylacetone, and 775 cc. of xylene. then regenerating it with a nonvolatile wise, while the temperature was kept at Then 45.6 grams of sodium dispersed in acid. It was much purer than the com- 25" to 30' with cooling. When no fur- 305 cc. of xylene was added dropwise mercial product prepared from ketene. ther heat was evolved, the charge was from a separatory funnel to the charge heated to its boiling point and refluxed at 18.5'. No reaction took place for 6 to for 48 hours. (With toluene 36 to 48 8 minutes, at which time about 2070 of Acknowledgment hours were required, with Varsol48 to 72 the sodium had been added. Then the hours.) The stirrer was stopped, and all temperature rose rapidly and hydrogen The author wishes to express his except 150 grams of the isohexane re- evolution began. The addition of so- thanks to Shawinigan Chemicals, Ltd., moved by suction through a sintered dium was temporarily stopped and a cool- for permission to publish this paper and glass filter stick. Then 1073 grams (12.2 ing bath (-18') immediately applied. to Roland Prevost for his assistance in the moles) of ethyl acetate was charged and When the temperature dropped to 20°, analytical work. the mixture was heated to its boiling addition of sodium was resumed and the point as quickly as possible. Three temperature was maintained at 17' to moles (174 grams) of acetone were 20" with cooling. Addition of the Literature Cited added dropwise over a period of 20 to 25 remainder of the sodium took 16 min- (1) Adkins, H., Kutz, W., Coffman, minutes. The charge was refluxed for 2 utes. D. D., J. Am. Chem. Sac. 52, 3212 hours. As soon as the evolution of hydro- (1930). Then the volatiles were distilled, first gen stopped, the cooling bath was re- (2) Adkins, H., Rainey, J. L., Org. at atmospheric pressure and later under moved and the charge heated to its boil- Syntheses 20, 7 (1940). (3) Claisen, L., Ehrhardt, E. F., Chem. a pressure of 150 mm. of mercury ing point (74") for 30 minutes. It was Ber. 22,1009 (1889). absolute. To the dry sodium salt was then cooled to 20' and shaken vigorously (4) Decker, R., Holtz, H. (to Wacku- added a mixture of 180 grams of acetic with 900 cc. of water until solution was Chemie G.m.b.H.), Brit. Patent acid and 720 grams of water. Most of effected. The aqueous layer was quickly 741,563 (1955). the acetylacetone floated to the top and separated from the xylene-methyl ace- (5) Frampton, 0. D., Nobis, J. F., was separated. The remainder was ex- IND.ENG. CHEM. 45,404 (1 953). tate and treated with just sufficient acetic (6) I. G. Farbenindustrie A. G., U. S. tracted with six 100-cc. portions of ethyl acid (84.9 grams) to lower the pH to 6.6 Dept. Commerce, P.B. 70,254, acetate, combined with that previously to 6.8. Some of the acetylacetone floated Frames 6944-6 (1948). separated, and distilled. The low boilers to the top and was separated. The re- (7) Krister, C. J. (to E. I. du Pont de were distilled at atmospheric pressure and mainder was extracted with three 150-cc. Nemours & Co.), U. S. Patent 2,240,934 (1941). the acetylacetone at 150 to 200 mm. of portions of ethyl acetate, added to that (8) Morton, .4. A., Redman, L. M., mercury absolute. previously separated, and distilled using IND.EKG. CHEM. 40, 1190 (1948). In some experiments, Shawinigan a 3-fOOt column 3 inch in inside diameter (9) National Distillers Chemical Co., Chemicals, Ltd., commercial methyl packed with '/4 inch Berl saddles. About bulletin on "Sodium Dispersion?," acetone was used. A typical sample of 131.6 grams of acetylacetone was thus 1953. (IO) Seaman, W., Woods, J. T., Massad, this material consisted of 60.8% methyl obtained, after correcting for the sodium E. A., Anal. Chem. 19, 250 (1947). acetate, 27.5% acetone, 9.95y0 meth- salt added to the charge. Another 6.4 (11) Sprague, J. M., Beckham, L. J., anol, 1.0% water, and 0.3 to O.S% acet- grams was recovered by adding another Adkins, H., J. Am. Chem. SOC. aldehyde. The aldehyde was removed 15 grams of acetic acid to the aqueous 56, 2665 (1934). by distillation, and treatment with a layer to lower the pH to 5.6 to 5.8, and RECEIVEDfor review June 8, 1956 slight excess of acetic anhydride reduced extracting. ACCEPTEDDecember 7, 1956

1070 INDUSTRIAL AND ENGINEERING CHEMISTRY