Of benzaldehyde with acetone

Another approach involved encapsulation of a bulky guanidine, N,N,N-tricyclohexyl-guanidine, in the super-cages of hydrophobic zeolite Y (Sercheli et ai, 1997). The resulting ship-in-a-bottle guanidine catalysed the aldol reaction of benzaldehyde with acetone to give 4-phenyl-4-hydroxybutan-2-one. 

For the mixed aldol reaction to be of value in synthetic work, it is necessary to restrict the number of combinations. This can be accomplished as follows. First, if one of the materials has no a-hydrogens, then it cannot produce an enoiate anion, and so cannot function as the nucleophile. Second, in aldehyde plus ketone combinations, the aldehyde is going to be a better electrophile, so reacts preferentially in this role. A simple example of this approach is the reaction of benzaldehyde with acetone under basic conditions. Such reactions are synthetically important as a means of increasing chemical complexity by forming new carbon-carbon bonds. 

Price and Hammett s rule has found confirmation in the reaction of benzaldehyde with acetone and ethyl methyl ketone (Gettler and Hammett, 1943), in the acid-catalyzed hydration of olefins (Taft, 1956a), in the hydrolysis of esters catalyzed by ion-exchange resins (Samelson and Hammett, 1956), in acid-catalyzed deoxymercuration (Kreevoy et al., 1962), and in the esterification of carboxylic acids in methanol (Smith, 1939). Taft (1956b) has noted that the rule seems to require the following modifications. The entropy-bearing substituent... 

The specific properties of hydrated hydrotalcites appear not only in the aldoli-zation of acetone, but in many other aldolization reactions. For example, in the aldol condensation of benzaldehyde with acetone the hydrated form catalyzes the reaction at 273 K, yielding aldol as the main product instead of benzalacetone, obtained on the calcined sample. Competitive adsorption kinetics are still observed, with a much greater adsorption coefficient for benzaldehyde. As suggested earlier from Hammett relationships, this reaction can be generalized with success to many substituted benzaldehydes [32], although the reaction could be performed selectively at 273 K with benzaldehyde only, and substituted benzaldehydes required a reaction temperature of 333 K. Because of this high temperature the reaction usually gives a, unsaturated ketones isolated yields are > 95 %. 

Table 3. Effect of the solvent on the initial rate of the aldol condensation of benzaldehyde with acetone in the liquid phase at 273 K.

The location of the OH leaving group in a position that is beta to a carbonyl, along with the formation of a stable, conjugated pi bond, makes this reaction much easier than a dehydration of an ordinary alcohol. The dehydration of an aldol product requires much milder reaction conditions than a typical alcohol, and can even occur spontaneously at room temperature. For example, in the reaction of benzaldehyde with acetone, the double aldol product shown is the only one isolated the presence of the two benzene rings makes the newly formed pi bonds highly conjugated and very stable. 

Nolen et al. also reported the self-condensation reaction of butyraldehyde and the cross-aldol condensation of benzaldehyde with acetone (Figs. 9.58 and 9.59) at 250°C. The butyraldehyde self-condensation produced a number of products, including 2-ethyl-2-hexenal, 2-butyl-2-butenal, and 2-ethyUiexanal. The results from the condensation of butyraldehyde indicate that a 40% yield of 2 -ethyl-2 -hexenal is achieved before the formation of by-products becomes dominant. In addition, investigations of the back reaction show that a substantial quantity of butyraldehyde is formed when 2-ethyl-2-hexenal is subjected to water at 250°C. The condensation reaction of benzaldehyde with acetone produced a 15% yield of trans-4-phenyl-3-buten-2-one in 5 h and very small quantities of trans,trans-dibenzylidene acetone during this same period of time. The authors suggest that the low yield could be a result of equilibrium limitations. 

Figure 9.59 Cross-aldol condensation of benzaldehyde with acetone.

By this process phenylglycine derivatives have been resolved by crystallization of the tartaric acid ammonium salts. The equilibration is induced at the amino ester stage by forming the configurationally labile imines with a catalytic amount of benzaldehyde or acetone (Table 11). 

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. 

Dioxocin 206 (X = CH=CH) was also obtained from the hydroperoxide-substituted phenanthrene-fused oxepine 281 upon reaction with stoichiometric amount of benzaldehyde or acetone and TFA. The formation of the dioxocin goes through the elimination of MeOH and consequent intramolecular cyclization of the oxygen on the stabilized carbocation (Scheme 55) <1998J(P1)3053>. 

The yields of nitro alcohols from simple nitroparaffins and aliphatic aldehydes or benzaldehyde are usually above 60%. The condensations are generally carried out with aqueous ethanolic sodium hydroxide, although weaker bases are sometimes desirable to prevent polymerization of the aldehyde. Sodium bisulfite addition compounds of the aldehydes are sometimes used. Better results are obtained with sodium methoxide than with alkali hydroxides in the condensation of nitroethane with formaldehyde. Sodium alkoxides are also used to effect the condensation of nitroethane with acetone and cyclohexanone. Condensation proceeds to the nitroalkanediol stage in certain cases with both nitromethane and with formaldehyde. ... 

Baeyer and Drewsen, ortho-Nitro Benzaldehyde.—A later synthesis of Baeyer and Drewsen was by the condensation of ortho-nitro benzaldehyde with acetone in the presence of sodium hydroxide. 

Mix 0.05 mole of benzaldehyde with the theoretical quantity of acetone, add one-half the mixture to a solution of 5 g of sodium hydroxide dissolved in 50 mLofwaterand40 mL ofethanol at room temperature (<25°C). After 15 min add the remainder of the aldehyde-ketone mixture and rinse the container with a little ethanol to complete the transfer. After one-half hour, during which time the mixture is swirled frequently, collect the product by suction filtration on a Buchner funnel. Break the suction and carefully pour 100 mL of water on the product. Reapply the vacuum. Repeat this process three times in order to remove all traces of sodium hydroxide. Finally, press the product as dry as possible on the filter using a cork, then press it between sheets of filter paper to remove as much water as possible. Save a small sample for melting point determination and then recrystallize the product from ethanol using about 10 mL of ethanol for each 4 g of dibenzalacetone. Pure dibenzalacetone melts at IIO-IITC, and the yield after recrystallization should be about 4 g. 

The catalytic activity of the NHs-grafted mesoporous silica, FSMN, was examined in some base-catalysed condensations (eqn. 1). The results were listed in Table 1. The FSMN catalyst used here was FSMN-5 that was prepared by the pre-activation at 1073 K followed by NH3-treatment at 973 K. The Aldol condensation of benzaldehyde and acetone did not proceed in this condition (entry 1). The Knoevenagel condensation of benzaldehyde and diethyl malonate (entry 2) did not occurred. On the other hand, the reactions with malononitrile (entry 3) and with ethyl cyanoacetate (entry 4) were catalysed by the FSMN-5. This shows that the NHa-grafted mesoporous silica would function as base catalyst. 

Biphilic Reactions. Reactions between carbonyl compoimds and halogenophosphines continue to be prominent in the literature. Thus hexafluoro-acetone has been converted into halogenophosphoranes by reaction with (45), chlorodi-n-propylphosphine (49), or l-chloro-2,2,3,4,4-pentamethyl-phosphetan (50). By contrast, the analogous reactions of benzaldehyde with... 

An exhaustive kinetic investigation of the aldol condensation of benzaldehyde and acetone on calcined MgAl HDT has been performed in the liquid phase with a batch reactor at 383 K [25]. The aldol, benzalacetone, and dibenzalacetone in small amounts were observed as products. Benzalacetone resulted from dehydration of the aldol, and dibenzalacetone from the addition of a second mole of acetone to benzalacetone. 

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. 

Some examples of the addition of one carbonyl compound to another are the aldol condensation the formation of acetoacetic ester the condensation of benzaldehyde with one of the components of a mixture of an acid anhydride and a carboxylate salt the formation of mesityl oxide, phoroiie, and mesitylene from acetone and the condensations of aromatic aldehydes and ketones. Acids and bases are generally catalysts for these reactions. They have sufficient in common to warrant their being classed together as the aldol type of... 

Another variation of this classic reaction is called the aldol-transfer reaction, reported by Nevalainen. In the presence of a suitable catalyst, usually an aluminum compound, an aldol product reacts with an aldehyde, gen-erating a ketone and a new aldol. An example is the reaction of benzaldehyde with aldol 143 in the pres-ence of 5% of aluminum catalyst (144). In dichloromethane at ambient temperatures, a 62% yield of aldol 145 was obtained after a reaction time of 43 h. The other product of this reaction was acetone, which was readily removed. This transformation involves a retro-aldol reaction of 143 (see sec. 9.5.A.vi.) and the resul-tant enolate anion reacts with benzaldehyde. This reaction has been done with several aldehydes and 143 is particularly attractive (the aldol condensation product of acetone), because acetone is the second product. 

In contrast to the acetalization of 370 with acetone, which favors the 5-membered acetonide 437 over the 6-membered acetonide 338 (9 1), acetalization of 370 with benzaldehyde in the presence of trifluoroacetic acid [164] or transacetalization with benzaldehyde dimethylacetal [102,165,166] produces only the 6-membered acetal 754. This phenomenon makes it possible for the chemist to conduct operations at the C-1 hydroxyl of 370. 

The n.m.r. spectroscopic investigation of the reactions of pentonolactones with acetone and benzaldehyde in acidic media is covered in Chapter 21, as are conformational studies on 2,3-G-isopropylidene-a-L-sorbopyranose derivatives. l,2-0-Isopropylidene-a-D-t /o-pentodialdo-l,4-furanose dimers are referred to in Ch er 22, and some 7-carbon sugar lactones which were characterized as their isopropylidene-and cyclohexylidene-acetals are noted in Chtytters 2 and 16. 

---