1l1dian Joumal of Chemistry VoL )8B, January 1999, pp 24 - 28 Catalytic Cyclocondensation of acetone to isophorone K V Ramanamurty & G S Salvapati * Indi an Institute of Chemical Techn ology, Coal and Gas Tec hno logy Di vision Hyderabad 500007, Indi a Received 12 March 1997; accepted (revised ) 13 Feb ntary 1998 Cyclocondensation of acetone in vo lves aldol co ndensati on leadin g initiall y to the primary condensation prod ucts (PCP), di acetone alcohol and mesityl ox ide, whi ch again react with acetone to form phorone, isop horone, mesitylene. etc. Relative selectiv ities of chromi a, y-alumin a, mag nesia and calci um ox id e catalys ts have been stud ied in a flow reac tor at 360-520 'c. Alu mi na and magnesia are fo und to favo ur isop horone fo rmation at 360 'c with 45 % selectivi ty but the selectivity steeply fa ll s with the in crease in temperatu re to 520 'c due to rise in decomposition prod ucts.' Primary condensation products are formed more wi th magnesia; selec ti vity to mes it ylene is mo re wi th CaO (-66% at 40U-480 'C) and Cr20 ] (50-55% at 480-520 ' C). Cyclocondensation of acetone proceeds initiall y by aldol (24 g) was packed in the iso th er-mal region of th e reactor. condensation of acetone to form diacetone alcohol, whi ch Nitrugen' gas was passed at th e rate of 180 mLlhr through on rapid dehydrati on gives mesityl ox ide. The sequence of the s:istem during the heating peri od to purge the system reactions that follow thereafter give ri se to a compl ex free of air and also during the experimental ru n to maintain mixture of products due to competiti ve self-condensati on uniform now of reaction products. Acetone (SOH reagent and cross condensati on between different ketones that are grade) was fed at the rate of 0. 5mLlmin from th e top of the fo rmed in the reacti on as well as by condensati on of acetone reactor by means of a mi cro feed pump. The system was with ketones. Main products fo rmed in these reactions are fo und to attain a steady state aft er 30 min . of process isophorone, mesitylene, phorone, 3,5-xyl enol, m-cresol and period. xylenes. Schemes for formati on of th ese products are l Catalysts (a) Y -alumina: Alumi nium scrap (AI 99.9%, Fe described in detail in our earli er publicati ons .] However, a 0. 1% max) was di ssolved in 5N HCI and ammonia soluti on general scheme is give n in Figure 1. ( 17 %) added to it dropwise under constant sti rring to bring The two primary intermedi ate condensati on products pH to 8. The aluminium hydroxide ge l was filtered, dried at (di acetone alcohol and mesityl oxide) and other pro-ducts 110 'c and calcined at 550 'c for 24 hr. The final materi al find many industri al applicati ons: Isophorone is a well was found to contain a chl oride content of 166 ppm (as kn own industri al solve nt for epoxy and phenoli c res inso. It determined by Mohrs method). Pellets of 4mm x 4mm size is also used for the preparati on of 3,5-xylenol whi ch find s we re prepared. applicati on in the manufact.ure of formaldehyde res ins6 and 7 formul ati ons with ant ibac- teria l and fun gicidal properti es . (b) Magnesia: Magnesi um carbonate (Sarabhai Chemi -cals, Other intermediates also find industri al applicati ons, for Baroda, India) was calcined at 600 'c fo r 6 hr to get 8 example di acetone alcohol in hydrauli c nuids , its aqueous magnestum ox ide. Pell ets of 4mm x 4mm size were solution (25 %) as bacteri cide to staphylococciY and mesit yl prepared. oxide as solve nt for phenol formaldehyde resinslo and PVC (c) CalciUlm oxide: Calcium oxide was prepared by composition II . calcining calcium carbonate (BOH reagent grade) at 600 'c In th e present study, th e catalys ts CaO, MgO, AI20 J and fo r 6 hr. Pell ets of 4mm x 4mm size we re prepared. Cr20] have been evaluated at 360-560 ·C and LHSV 1.0 for th eir selecti vit y in direct conve rsion of acetone to (d) Chmmium oxide: Chromium oxide ge l was isoph orone. prec ipitated from chromiu m sul phate (Apex Chemicals, Materials and Methods: Bombay, Indi a, reagent grade) by ad ding ammoni a solut ion ( 17 %) dropwise under constant stirring. The result ing ge l Apparatus: The experimental unit is essent ia ll y th e same as was fi It ered, dried at I 10 "c, and calcined at 500 "c fo r 4 hr. desc ri bed in our earli er paper I. The reactor consists of a Pel lets of 4mm x 4mm size we re prepared. ve rti cal tuhul ar r:.., ac tor (2 2 mm i.d. and 25mm o.d.) heatrd hy an elec trical furn ace. The catalys t (4 mm x 4mm pell ets) Phys ical propert ies of the catalysts arc given in Table L RAMANAMURTY et al. : CYCLOCONDENSAnON OF ACETONE TO ISOPHORONE 25 (~ I +(H3-(&0 (H'3 .(0.(H _ 3 Acetone I so x ylitone s Figure 1-Scheme of formation of reaction products in the cyc1ocondensation of acetone. 0.98 respectively. Gaseous products collected during these Analysis. Liquid products collected during the experi-ments experiments at 480-520 °c accounted for -4% based on the were analysed using 115" X 8' column of Ov-17 as feed, and the coke formation was -3%, the rest was liquid chromosorb W with flame ionization detector (FlD) by products. Analysis of the gas samples showed the presence programming the oven temperature at 5 °C/min between 60 of ethylene, propylene, isobutene, CO and CO which are and 180 °C, acetone content in the product was analysed by 2 formed by the decomposition of mesitylene, diacetone internal standard method using n-propanol as standard over alcohol and acetone respectively. 15% Carbo wax -20M on Chromo sorb W at 60 °C. Analysis Results and Discussion: of the product mixtures was done by internal normalisation method by taking diacetone alcohol as standard. The Conversion of acetone to isophorone is visualized along relative weight response factors of mesityl oxide, phorone, the reaction path: acetone ~ diacetone alcohol ~ mesityl iso-phorone and mesitylene were to be 1.08, 0.82, 0.79 and oxide ~ isophorone l.2·12. Thus, the reactions involved are aldol condensation to diacetone alcohol, its dehydration to mesityl oxide and cyclization reaction leading to isophorone Table I - Physical properties of catalysts the formation of (as shown in Figure 1). Maj or side Property Catalyst reactions are decomposition reactions of mesityl oxide or Cr203 y-AI 2O, MgO Cao diacetone alcohol giving isobutene, which is cyc1ized to 3 Surface Area (m2/g) 80 160 120 60 mesitylene . Bulk density (glmL) 0.61 0.75 0.83 0.89 Alumina catalyst was tried at low temperatures (60- 100 Mean pore radius (A) 40.0 45 .5 38.0 42.5 0c) to give mainly diacetone alcohol 13. At 300-500 °c and Cumulative pore volume 0.35 0.48 0.31 0.52 under a pressure of 200 atmospheres, the main product was (mUg at STP) I4 15 mesitylene . , the formation of which was considerably 26 INDIAN J CHEM, SEC. B, JANUARY 1999 hig her than in the case of H2S04 as catalyst I S In the present work , formation of isophorone was fav oured at 300-360 ·C 100 (- II %) but thereafter it decreased due to the mu lt iplicity of products (Figure 2). Mesitylene formation was also more 80 (2 1%) at 480-520 .c. Magnesia is well known to promote aldol condensa-tion of acetone but its efficacy in the 60 cycl izati on reac-ti on leading to isophorone is not well 0~ establi shed 17.18.19 ItO Mag nesia was found to be more active at 440-520 ·C 20 (Figure 3) to give primary the condensation products MgO (mainl y mesit yl oxide) ( 19%) rather than isophorone. CI However, formati on of 7% mesity lene with 27 % selecti -v it y 360 1.00 1.1.0 1.60 at 520 ·C and a max imum of 6% isophorone at 440 ·C (Figure 4) TEMPERATU RE " C Figure 4--Erfect of temperature on selecti vit y to mesit ylene. 1.0 30 ~ 50 •-J 20 o • ~ 10 40 ~ 30 300 TE MPERATURP C 20 f>..c.---o.---.:~~.. A 1203 10 t. ( 00 H gl) Figure 2--Effect of temperatu re on produci composi ti on with - Cr203 AI o 20 , catalyst. 360 400 1. 40 480 520 TEMP ERA TUR E • C Figure 5-EITcc t of temperature on selecti vi ty tl) isophorone . .-. PCP ~ Mesitylene renders it less selec ti ve to isoflhorone. Both alumina and lr--A Isop hor one Magnes ia have hett er se lec tivi ty compared to isophorone at low tem peratures (- 360 "C) than oth er catalys ts , but there was a steep fall in se lectivit y with the increase in reaction 20 temperature to 520 'c (Figure 5) due to the rise in the amount of decompositi on products. 16 Chro mi a is a we ll kn own catal ys t in the Jromatiza ti on of hydrocarhons.