Acetone aldol condensation

Aldol condensation of acetone is a well-known base-catalyzed reaction, and barium hydroxide is one of the catalysts for this reaction mentioned in textbooks. A family of barium hydroxide samples hydrated to various degress determined by the calcination temperature (473, 573, 873, and 973 K) of the starting commercial Ba(OH)2 8H2O were reported to be active as basic catalysts for acetone aldol condensation (282,286). The reaction was carried out in a batch reactor equipped with a Soxhlet extractor, where the catalyst was placed. The results show that Ba(OH)2 8H2O is less active than any of the other activated Ba(HO)2 samples, and the Ba(OH)2 calcined at 473 K was the most active and selective catalyst for formation of diacetone alcohol, achieving nearly 58% acetone conversion after 8h at 367 K in a batch reactor. When the reaction temperature was increased to 385 K, 78% acetone conversion with 92% selectivity to diacetone alcohol was obtained after 8h. The yield of diacetone alcohol was similar to that described in the literature in applications with commercial barium hydroxide, but this catalyst required longer reaction times (72-120 h) (287). No deactivation of the catalyst was observed in the process, and it could be used at least 9 times without loss of activity. 

One cannot help but notice that the above reactions lead to related products characterized by the presence of two oxygens in a 1,3-relationship as either a jS-hydroxycarbonyl (if both components are aldehyde or ketones) or a )S-dicarbonyl system (in the case of esters). Both of these functionalities are useful in subsequent conversions and we see that the synthetic utility of the reactions used to prepare these adducts is broadened further. Typical transformations are shown in Scheme 2.26 for the product 70 of an acetone aldol condensation. Oxidation of 70 leads to the formation of the corresponding dicarbonyl compounds 71, while the 1,3-diol 72 is formed as a result of reduction of 70 and the a,j8-unsaturated carbonyl compound 73, formed via dehydration of 70. 

Experimentally, the acetone aldol condensation was found to proceed slowly on HZSM-5 at room temperature if physisorbed acetone was present together with neutral" species on OH groups in zeolite cavities We believe that quantum chemical calculations of energetics will help to solve the problem of transition state intermediates. 

Acetone aldol condensation proceeds on either acidic or basic catalysts. On basic catalysts, the reaction products are mainly a,P-unsaturated ketones [5] whereas on acidic materials formation of aromatics and olefins is favored [6]. In our catalytic tests, the main reaction products were mesityl oxides (MO s) and isophorone (IP). MO is formed from the initial selfcondensation of acetone whereas IP is a secondary product arising from the consecutive aldol condensation between MO and acetone. Over all the samples the reaction rate diminished as a function of time-on-stream as shown in Fig. 1 for the MgjAlOx sample which lost about 60 % of its initial activity after 10 h-run. Initial reaction rates (r ) and product selectivities (S j) were calculated by extrapolating the reaction rates vs. time curves to zero. 

Fig. 4 Coke burning experiments after acetone aldol condensation at 473 K on MgyAlOx catalysts. r = A1/(A1 + Mg)...

Diacetone alcohol decomposition to acetone (reverse reaction of acetone aldol condensation) proceeds over alkidine earth catalysts. The active sites are poisoned by COz- The slope of the activity decrease with increasing amount of adsorbed CO2 represents the activity per unit base site. The activities per unit site are in order BaO>SrO>CaO>MgO. The order coincides with the base strength order the stronger the base strength the more effective the active sites. 

Concerning the reaction mechanisms, analogy between the homogeneous and heterogeneous reactions is usually assumed. For acetone aldol condensation, the following mechanisms are accounted for in homogeneous systems. 

Reaction mechanisms of acetone aldol condensation over MgO and La20s were studied using deuterium as a tracer. Analysis of the isotopic distributions of the product and reactant revealed that the slow step is involved in Step II in accordance with homogeneous systems. 

The situation for butyraldehyde tddol condensation is different from that for acetone aldol condensation. The active sites for butyraldehyde aldol condensation are not OH groups but ions, and easily poisoned by trace amounts of water and carbon dioxide. ... 

Faba, L., Diaz, E., Ordonez, S., 2012. Aqueous-phase furfural-acetone aldol condensation over basic mixed oxides. Applied Catalysis B Environmental 2012 (113), 201—211. 

With concentrated alkali, a resin is formed from repeated aldol condensations between aldol, crotonaldehyde and acetaldehyde. A similar condensation occurs with acetone (b.p. 56°), but the equilibrium mixture contains only a few per cent, of diacetone alcohol (III), b.p. 166° ... 

Difunctional target molecules are generally easily disconnected in a re/ro-Michael type transform. As an example we have chosen a simple symmetrical molecule, namely 4-(4-methoxyphenyl)-2,6-heptanedione. Only p-anisaldehyde and two acetone equivalents are needed as starting materials. The antithesis scheme given helow is self-explanatory. The aldol condensation product must be synthesized first and then be reacted under controlled conditions with a second enolate (e.g. a silyl enolate plus TiCl4 or a lithium enolate), enamine (M. Pfau, 1979), or best with acetoacetic ester anion as acetone equivalents. 

Diacetone Alcohol. Diacetone alcohol (DAA) (4-hydroxy-4-methyl-2-pentanone) is a colorless, mild smelling Hquid which is completely miscible with water and most organic solvents. It is the simplest aldol condensation product of acetone, and because of its keto-alcohol functionahes it has special utility in the coatings industry where it is used to dissolve cellulose acetate to give solutions with high tolerance for water (115). 

Early patents indicated that because water inhibits the aldol condensation mechanism, it was necessary to dry recycle acetone to less than 1% water (139—142). More recent reports demonstrate DAA production from waste acetone containing 10—50% water (143), and enhanced DAA production over anion-exchange resins using acetone feeds that contain 3—10% water (144,145). 

DIBK can be produced by the hydrogenation of phorone which, in turn, is produced by the acid-catalyzed aldol condensation of acetone. It is also a by-product in the manufacture of methyl isobutyl ketone. Diisobutyl ketone ( 1.37/kg, October 1994) is produced in the United States by Union Carbide (Institute, West Virginia) and Eastman (Kingsport, Teimessee) (47), and is mainly used as a coating solvent. Catalytic hydrogenation of diisobutyl ketone produces the alcohol 2,6-dimethyl-4-heptanol [108-82-7]. 

Ma.nufa.cture. Isophorone is produced by aldol condensation of acetone under alkaline conditions. Severe reaction conditions are requited to effect the condensation and partial dehydration of three molecules of acetone, and consequendy raw material iaefftciency to by-products is limited by employing low conversions. Both Hquid- and vapor-phase continuous technologies are practiced (186,193,194). 

Citral reacts in an aldol condensation using excess acetone and a basic catalyst, usually sodium hydroxide. The excess acetone can be recovered for recycle. The resulting intermediate pseudoionone [141-10-6] (83) after cyclization with phosphoric acid gives predominantly a-ionone [127-41 -3] (84), which is the isomer commercially important in flavors and fragrances. A hydrocarbon solvent is generally necessary in order to get high yields. P-Ionone [14901-07-6] (85) is the predominant isomer if sulfuric acid is used as the catalyst but lower temperature than that for cyclization to a-ionone is required. y-Ionone [79-6-5] (86) is also produced. 

Methyl amyl ketone, derived from the crossed aldol condensation of -butyraldehyde and acetone, is used predominandy as a high soHds coatings solvent. It is also employed as a replacement for the very toxic 2-ethoxyethyl acetate [111 -15-9J. 

Methyl isoamyl ketone (MIAK), a product derived from the aldol condensation of isobutyraldehyde and acetone, is used principally as a solvent for lacquers, ceUulosics, and epoxies. 

Kelkar and McCarthy (1995) proposed another method to use the feedforward experiments to develop a kinetic model in a CSTR. An initial experimental design is augmented in a stepwise manner with additional experiments until a satisfactory model is developed. For augmenting data, experiments are selected in a way to increase the determinant of the correlation matrix. The method is demonstrated on kinetic model development for the aldol condensation of acetone over a mixed oxide catalyst. 

Tiic synthesis of enone (34) requires an aldol condensation between acetone and KCHO this may not give a good yield as RCHO may prefer to condense with Itself if it has enolisable protons. The alternative disconnection (33b) avoids this problem as we can use acetoacetatc for the synthon (34) and a specific enol equivalent for (35),... 

Aldol condensation is another undesirable reaction that can occur during saponification. Carotenals undergo aldol condensation, with the extension of the polyene chain in the presence of alkali and acetone remaining from the extraction... 

As in the case of homogeneous acids as catalyst, we would also benefit from using solid ba.ses instead of dissolved bases as catalyst. A number of industrially important reactions are carried out with bases as catalyst. A well know example is the aldol condensation of acetone to diacetone alcohol, where dissolved NaOH in ethyl alcohol is u.sed as a catalyst at about 200 to 300 ppm level. However, heterogeneous pelleted sodamide can be used as a catalyst for this reaction and it obviates the problem of alkali removal from the product, which would otherwise lead to reversion of diacetone alcohol to acetone during distillation of the product mixture. 

A CD process for the production of DAA from acetone was developed previously in our laboratory and the kinetics of the aldol condensation of acetone were characterized (13,14). CD is a green reactor technology that provides enhanced yield and selectivity in addition to significant energy savings (15). The one-step synthesis of MIBK by CD appears to be a simple extension of this process. However, the introduction of hydrogen to this system opens... 

The Aldol Condensation of Acetone Over a CsOH/Si02 Solid Base Catalyst... 

The solid base catalysed aldol condensation of acetone was performed over a CsOH/Si02 catalyst using a H2 carrier gas. The products observed were diacetone alcohol, mesityl oxide, phorone, iso-phorone and the hydrogenated product, methyl isobutyl ketone. Deuterium tracer experiments were performed to gain an insight into the reaction mechanism. A mechanism is proposed. 

The aldol condensation of acetone to diacetone alcohol is the first step in a three-step process in the traditional method for the production of methyl isobutyl ketone (MIBK). This reaction is catalysed by aqueous NaOH in the liquid phase. (3) The second step involves the acid catalysed dehydration of diacetone alcohol (DAA) to mesityl oxide (MO) by H2S04 at 373 K. Finally the MO is hydrogenated to MIBK using Cu or Ni catalysts at 288 - 473 K and 3- 10 bar (3). 

The aldol condensation reaction of acetone was performed over CsOH/Si02 at a range of reaction temperatures between 373 and 673 K (a typical product distribution is shown in Figure 2). Table 1 displays the conversion of acetone along with the selectivities for the products produced once steady state conditions were achieved. Figure 3 presents the effect of temperature on the yield of the products. The activation energy for acetone conversion was calculated to be 24 kJ. mol 1. 

The condensation of acetone can also occur over acidic sites as shown by a number of authors [1,9], Generally, when this occurs other products are formed such as isobutene and acetic acid, by the cracking of DAA. Additionally mesitylene can be formed by the internal 2,7-aldol condensation of 4,6-dimethylhepta-3,5-dien-2-one which is in turn obtained by the aldol condensation of MO with a deprotonated acetone molecule [7, 8], As these species are not observed we can concluded that any acidic sites on the silica support are playing no significant role in the condensation of acetone. 

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