Acetone, base-catalyzed condensation

In all processes an acyclic precursor, called a pseudoionone, pseudoirone, etc., is prepared by base-catalyzed condensation of citral or 6-methylcitral with acetone, methyl ethyl ketone, or allylacetone, as appropriate. 

Oxopyran-2,6-dicarboxylic acid (chelidonic acid) is obtained from the base-catalyzed condensation of acetone with ethyl oxalate. The initial product is cyclized in acid... 

A new synthetic method for preparing 2-methylpyndine has been commercialized. This process involves the acid/base-catalyzed condensation of acetone with acrylonitrile to make 5-oxo-hexanonitnle. Then the nitrile is converted to a 2-methylpyndine by catalytic cyclizahon/dehydroge-nation ... 

A common side reaction during Oppenauer oxidations consists of the base-catalyzed condensation of the carbonyl compound, resulting from the oxidation, with the carbonyl compound used as oxidant. Sometimes, advantage is taken from this side reaction for synthetic purposes. For example, oxidation of primary alcohols with an aluminium alkoxide and acetone results in the formation of an intermediate aldehyde that condenses with acetone, resulting in a synthetically useful formation of an enone.59... 

Roelofs, J. C. A. A., van Dillen, A. J. and de Jong, K. P. Base-catalyzed condensation of citral and acetone at low temperature using modified hydrotalcite catalysts, Catal. Today, 2000, 60, 297-303. 

In 1976, Dolby reported the preparation of the hydrindan 15 (Scheme IX) (23). Dimethyl pyruvic acid 45 was prepared according to the procedure of Ramage and Simonsen (28). The condensation of hippuric acid (43) and acetone yields tFfe oxazolone 44, which affords 45 upon treatment with concentrated hydrochloric acid. The Friedel-Crafts acylation of ethylene with glutaric anhydride afforded 5-oxo-6-heptenoic acid 46 in low yield (14-45 ). Base-catalyzed condensation of 45 with 46 gave the crude dibasic acid 47 in 79 yield. Treatment of 47 with excess diazomethane provided the diester 48 in quantitative yield. The esterification also can be accomplished in 90 yield with DBU and iodomethane (L. 0. Dolby, University of Oregon, personal communication, 1979). Base-catalyzed cyclization of 48 afforded 15 in 98 yield. 

These results, which are highly analogous with those from the homogeneous base-catalyzed condensation reaction, imply that the condensation of benzaldehyde and acetone is base-catalyzed on hydrotalcites. 

Other furan monomers which polymerize cationically include 2-furfuryl vinyl ether, 2-vinyl furoate (albeit through a polyalkylation mechanism giving a polyester incorporating the ring into the pol5mer backbone), F and MF as co-monomers in conjunction with substituted styrenes and vinyl ethers, as well as 2-furfurylidene methyl ketone (obtained by the base-catalyzed condensation of F with acetone) and its homologues [4d]. 

The one-carbon bridged ligands for the Montell high-performance catalysts 11 and 12 are elegantly constructed in high yield by the base-catalyzed condensation of formaldehyde or acetone with the corresponding 3-substituted indenes. - ... 

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. 

In this study we have investigated utilizing a bi-functional catalyst with a solid base function for the aldol condensation reaction and a metal function for the hydrogenation. This work is a continuation of the study that examined the supported base catalyzed aldol condensation of acetone (5, 6). In those studies... 

Under base-catalyzed conditions, two molecules of acetone can condense to form diacetone alcohol. At room temperature (25 °C), about 5% of the acetone is converted to diacetone alcohol. Determine the value of AG° for this reaction. 

Propose a mechanism for the base-catalyzed aldol condensation of acetone (Figure 22-2). 

A material such as Na°/NaY catalyzes the aldol condensation of acetone, to form mesityl oxide and eventually isophorone. Another strong base catalyzed reaction is the side chain alkylation of toluene with ethylene. In contrast with acid catalysis, side chain reaction is strongly preferred over ring alkylation. With a Na°/NaX in the gas phase at 473 K, toluene reacts to give n-propylbenzene (66%) and the dialkylated product, 3-phenylpentane (32%) (41). 

A further evidence for the extreme reactivity of acetaldehyde with its enolate ion is provided by the fact that, when the aldol condensation is run in D2O, there is no substitution of D atoms on the a carbon positions. This is interpreted as indicating a much more rapid reaction of the enolate ion with acetaldehyde than with D2O, as might have been already anticipated from the relative slowness of the reaction with BH+. In contrast, the base-catalyzed exchange of acetone with D20 is much faster than the rate of dimerization of acetone. 

The reaction of an aldehyde with a ketone employing sodium hydroxide as the base is an example of a mixed aldol condensation reaction, the Claisen-Schmidt reaction. Dibenzalacetone is readily prepared by condensation of acetone with two equivalents of benzaldehyde. The aldehyde carbonyl is more reactive than that of the ketone and therefore reacts rapidly with the anion of the ketone to give a /3-hydroxyketone, which easily undergoes base-catalyzed dehydration. Depending on the relative quantities of the reactants, the reaction can give either mono- or dibenzalacetone. 

Problem 21.13 (a) When acetaldehyde at fairly high concentration was allowed to undergo base-catalyzed aldol condensation in heavy water (D2O), the product was found to contain almost no deuterium bound to carbon. This finding has been taken as one piece of evidence that the slow step in this aldol condensation is formation of the carbanion. How would you justify this conclusion (b) The kinetics also supports this conclusion. What kinetics would you expect if this were the case (Remember Two molecules of acetaldehyde are involved in aldol condensation.) (c) When the experiment in part (a) was carried out at low acetaldehyde concentration, the product was found to contain considerable deuterium bound to carbon. How do you account for this (Hint See Sec. 14.20.) (d) In contrast to acetaldehyde, acetone was found to undergo base-catalyzed hydrogen-deuterium exchange much faster than aldol condensation. What is one important factor contributing to this difference in behavior ... 

An example is the base-catalyzed aldol condensation of citral and acetone (Figure 2.42a), producing pseudoionones (6,10-dimethyl-3,5,9-undeca-trien-2-one), which is utilized to obtain higher value products from essentials oils (citral), since... 

The reaction is further complicated by thermodynamic equilibrium limitations, as indicated in Table I. The condensation/dehydration of acetone to MO is limited to about 20% conversion at 120 C (16). However, there is no equilibrium limitation to the overall acetone-to-MIBK reaction. This, coupled with the possibility of numerous thermodynamically favorable side reactions that are also acid/base-catalyzed (Fig. 1), suggests the need to balance the acid/base and hydrogenation properties of the selected catalyst. 

Ketones are chemically reactive and undergo acid- and base-catalyzed selfcondensation reactions. For acetone the base-catalyzed self-condensation reaction yields a product of diacetone alcohol [854] ... 

Since the anion-exchange resins are frequently used in the hydroxy form, certain precautions should be observed when employing them with non-aqueous solvents. If acetone is used, excessive diacetone alcohol may be formed via base-catalyzed aldol condensation. A small amount of water should be present in all organic solvents containing alcohol to repress transesterification of esters (15) and esterification of acids (16) with alcohol as solvent. Without water, up to 5% of transesterification in 15 to 20 min has been observed with DEAE-Sephadex. After an overnight contact the transesterification approached 35 %. With 1 % water in the solvent, however, less than 0.3% transesterification and 0.3% saponification occurred when 70 mg of butyl stearate was passed through a DEAE-Sephadex column (15). 

Tichit et al. (538) and Kantum et al. (539) examined the substitute effect on the aldol condensation of various benezaldehydes with acetone using modified LDHs. As expected for base catalysis, electron-withdrawing substituents on the benzene ring increase the reaction rate. This has been demonstrated by the quantitative reaction of p-chlorobenzaldehyde with excess acetone at 60°C within 1.5 h. Chou-dary et al. (216) intercalated tetra-butanoate anion into MgAl-LDH in THF, which catalyzes condensation reactions selectively to aldols only at 0°C in quantitative yields in acetone. 

In the acid-catalyzed condensation of acetone, the enol is the intermediate, and it adds to the very strong Lewis acid, the protonated carbonyl group, to give initially the same product as the base-catalyzed reaction, diacetone alcohol (Fig. 19.73). Dehydration generally follows to give the a,P-unsaturated ketone, 4-methyl-3-penten-2-one (mesityl oxide). 

Base-catalyzed reactions were reviewed in general by Hattori [208,222], and from the reactions described butene isomerization, alcohol conversion, toluene alkylation, acetone condensation/diacetone alcohol decomposition, Knoevenagel condensations, diketone cyclization, ring transformation reactions, and dimerization of aldehydes to the corresponding esters were used to evaluate the acid-base properties in molecular sieves. 

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