Acetone self-condensation

The physicochemical properties of HTs and the solid solutions produced after their calcination can be easily tuned by changing the nature and amount of metal cations and anions (10). Therefore, to elucidate the role of the chemical composition on the gas phase acetone self-condensation reaction, a series of bimetallic and trimetallic HTs were prepared, characterized and tested. 

Figure 2 shows illustrated mechanism for acetone self-condensation over calcined hydrotalcites, where the enolate ion is formed in a first step followed by two possible kinetic pathways 1) In the first case the subtracted proton is attracted by the basic sites and transferred to the oxygen of the enolate ion to form an enol in equilibrium. 2) In the second case the enolate ion reacts with an acetone molecule in the carbonyl group, to produce the aldol (diacetone alcohol). Finally, the p carbon is deprotonated to form a ternary carbon and then loses an OH group to obtain the final products. 

Figure 2. Pathway proposed for acetone self-condensation.

Pd-containing aluminophosphate molecular sieves have been used to carry out crossed aldol condensations between an aldehyde and a ketone by using a 0.5 % Pd/ MnAPSO-31 catalyst in a vapour-phase fixed bed reactor.[14] Thanks to the excess of the ketone with respect to the aldehyde (4 1), it is possible to get high selectivity to the desired product, i.e. 70 % of heptan-2-one from n-butyraldehyde and acetone and 89 % of pentan-2-one from acetaldehyde and acetone, the major by-product being, in both cases, MIBK from acetone self-condensation. 

The selective intermolecular addition of two different ketones or aldehydes can sometimes be achieved without protection of the enol, because different carbonyl compounds behave differently. For example, attempts to condense acetaldehyde with benzophenone fail. Only self-condensation of acetaldehyde is observed, because the carbonyl group of benzophenone is not sufficiently electrophilic. With acetone instead of benzophenone only fi-hydroxyketones are formed in good yield, if the aldehyde is slowly added to the basic ketone solution. Aldols are not produced. This result can be generalized in the following way aldehydes have more reactive carbonyl groups than ketones, but enolates from ketones have a more nucleophilic carbon atom than enolates from aldehydes (G. Wittig, 1968). 

MIBK is a flammable, water-white Hquid that boils at 116°C. It is sparingly soluble in water, but is miscible with common organic solvents. It forms an a2eotrope with water as shown in Table 2. Condensation of MIBK with another methyl ketone can produce ketones containing 9—15 carbons. For example, condensation with acetone produces diisobutyl ketone, and self-condensation of two MIBK molecules produces 2,6,8-trimethyl-4-nonanone [123-17-1]. Condensation with 2-ethylhexanal gives 1-tetradecanol (7-ethyl-2-methyl-4-undecanol), avaluable surfactant intermediate (58). 

The reaction mechanism is shown in Figure 4 and is adapted from work by Fiego et al. [9] on the acid catalysed condensation of acetone by basic molecular sieves. The scheme has been modified to include the hydrogenation of mesityl oxide to MIBK. The scheme begins with the self-condensation of acetone to form diacetone alcohol as the primary product. The dehydration of DAA forms mesityl oxide, which undergoes addition of an addition acetone to form phorone that then can cyclise, via a 1,6-Michael addition to produce isophorone. Alternatively, the mesityl oxide can hydrogenate to form MIBK. 

Figure 1. Kinetic parameters for the selection of antibody-catalyzed aldol and retro-aldol reactions, reflecting the biocatalyst s ability to accept substrates that differ clearly with respect to their molecular geometry. No background reaction was observed for the self-condensation of cyclopentanone. The indicated value for cyclopentanone addition to pentanal was estimated using the published kuncat value of 2.28 X 10 M s for the aldol addition of acetone to an aldehyde. Reproduced with permission of the authors and the American Association for the Advancement of Science.

Recently, Di Cosimo et al. 14) investigated the self-condensation of acetone in the gas-phase at 573 K, with the catalysts being MgO or MgO promoted with alkali metal ions. On pure MgO, the acetone conversion was initially 17%, and this... 

Reaction of 2-aminobenzophenone with acetyl acetone in the presence of Bi(OTf)3 (5 mol%) results in the formation of 3-acetyl-2-methyl-4-phenylquinoline [117]. Various 1,3-diketones, acyclic ketones and cyclic ketone undergo the condensation with 2-aminoaryl ketones. The scope and generality of this process is illustrated with respect to various 2-aminoaryl ketones and a wide array of a-methylene ketones, and the results are summarized in Table 6. This method is free from side reactions such as the self-condensation of ketones, which is normally observed under basic conditions. Unlike reported methods, the present protocol does not require high temperature or drastic conditions to produce quinoline derivatives. 

Table 2. Results of self-condensation of acetone over various calcined hydrotalcite-like compounds.

The activity of calcined HTs was determined in self-condensation reaction of acetone (J.T. Baker) by using a fixed bed catalytic reactor with an on-line GC. Prior to the catalytic test, catalysts were pretreated in-situ under nitrogen atmosphere at 450°C for 5h. Acetone was supplied to the reactor by bubbling nitrogen gas through the acetone container at 0 °C. The reaction temperature was established at 200 C. The products were analyzed by means of GC (Varian CP-3800) using a WCOT Fused silica column, equipped with a FID detector. 

Examples are the formation of diacetone alcohol from acetone [reaction type (A)] catalysed by barium or strontium hydroxide at 20—30°C [368] or by anion exchange resin at 12.5—37.5°C [387], condensation of benzaldehyde with acetophenone [type (C)] catalysed by anion exchangers at 25—-45°C [370] and condensation of furfural with nitromethane [type (D)] over the same type of catalyst [384]. The vapour phase self-condensation of acetaldehyde over sodium carbonate or acetate at 50°C [388], however, was found to be first order with respect to the reactant. 

A series of novel styrene- and siloxane-based silanol polymers and copolymers were synthesized by a selective oxidation of the Si—H bond with a dimethyldioxirane solution in acetone from corresponding precursor polymers. The conversion of the Si—H to Si—OH in the polymer modification proceeded rapidly and selectively. The silanol polymers obtained in situ showed no tendency for self-condensation to form siloxane crosslinks in solution. Moreover, stable silanol polymers in the solid states were obtained by placing bulky substitute groups bonded directly to the silicon atom. It was found that the properties of these novel silanol polymers and copolymers depended largely on substituents bonded directly to the silicon atom and silanol composition in the copolymers as well. 

Hydroxymethylation of guaiacyl acetone (VII) yielded an amorphous solid, probably a self-condensation product after being methylolated in several positions. Veratyl acetone (VIII) gave a crystalline product in good yield which had no CO group. It can be assumed that the CO group was reduced by a crossed Cannizzaro reaction, and a dimeric product was formed, whose structure is not known yet. 

We need first of all to convert the ketone 39 completely into some enolate derivative so that there is no ketone left for self-condensation. In this chapter we shall restrict ourselves to lithium enolates 40 and anions 42 of 1,3-dicarbonyl compounds 41. Each of these reagents acts as the enolate anion of acetone 38 R2 = Me. 

When we come to 1,3-dicarbonyl compounds 4 the principle is the same but we now have a choice the keto-ester 35 could be disconnected 35b to the enolate 36 of acetone and diethyl carbonate 37 and this synthesis would work but we prefer 35a as that gives us the enolate of ethyl acetate 34 and ethyl acetate itself 33—another self condensation. 

Condensation of butanal has been carried out on alkaline earth metal oxides at 273 K[52 53] yielding 2-ethyl-3-hydroxy-hexanal as a main product the order of activity per unit surface area was equal to that in the case of self-condensation of acetone and in agreement with the order of basicity of the solids, namely, SrO > CaO > MgO. The authors found that for aldol condensation of w-butyraldehyde, the active sites are the surface O2 ions and the rate-determining step is the z-hydrogcn abstraction. The differences in rate-determining step and active sites in the condensation of butyraldehyde and self-condensation of the acetone were attributed to differences in acidity of the z-hydrogcn in the two molecules. CaO was slightly... 

A major breakthrough in the regioselectivity of enamine reactions followed from the observation by Pfau and Ughetto-Monfrin391 that the cyclohexylamine imine of acetone 191 underwent a,a-bis-alkylation to give 196, in addition to products 195 and 197 derived from self-condensation (Scheme 199). There was no evidence for the formation of the a,a -bis-alkylated product 194. Clearly, as we pointed out in 1982, this can be attributed... 

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