Formaldehyde aldol condensation with acetone

Although aldol condensation is another type of ionic reaction, it deserves special consideration. It can lead to two classes of sugars. Condensation of an aldehyde in an a-position of a free carbonyl group under mildly akaline conditions still seems possible. This very simple reaction can also be quite efficient. Thus diacetal 7.59, quantitatively prepared by treatment of mannose with acetone in an acidic medium, is at equilibrium with the carbonyl tautomer. Condensation with formaldehyde, used in aqueous solution in the presence of potassium carbonate, gives the hydroxymethylated sugar 7.60 in 86% yield (Ho 1979). 

The aldol condensation of formaldehyde and acetone to methylvinylketone has been investigated by Suzuki and Ono [20] on a series of solids MgAl hydrotalcite was found to be the best catalyst, leading to 21 % conversion of acetone at 673 K, with 96 % selectivity for acetone and 64 % for formaldehyde. The carbonate form was the most suitable. Exchange by sulfates or chromates resulted in poor activity. 

The synthesis in Figure 9.11 starts with an aldol condensation between formaldehyde and acetone to give methyl vinyl ketone. This is then heated with isobutylene and an ene reaction takes place giving ketone... 

The importance of catalyst basic properties was emphasized by Malinowski et d They studied aldol condensation of formaldehyde with acetaldehyde, acetone, and acetonitrile. The rate constants for these reactions on Si02 mounted NaOH catalyst show correlation with NaOH content in the catalysts as shown in Fig. 4.37. Essentially the same linear relationship was observed for aldol condensation of acetaldehyde, and acetaldehyde with benzaldehyde. The linear relations support the view that basic properties are actually the cause of the catalytic activities. On Si02-supported NaOH catalysts, the groups - Si —ONa are assumed to be the active sites. 

Hydrotalcite, an anionic clay mineral with the formula Mg6Al2(0H)i6C034H20, shows a high activity for cross aldol condensation of formaldehyde with acetone to form... 

Aldol condensations at one or both a-methylene groups of 3-thietanone have been accomplished with formaldehyde, aromatic aldehydes (e-g-, the formation of 359), acetylenic aldehydes, and acetone. ... 

Aldol condensation of acetone with formaldehyde gives methyl vinyl ketone. This can undergo the ene reaction with isobutylene to give an isomer of methylheptenone, 2-methylhept-l-en-6-one. Isomerization to methylheptenone is easy using an acidic catalyst, and acetylene can be added to either isomer. From methylheptenone, the process leading to linalool is the same as in the examples above. If the acetylene is added to 2-methylhept-l-en-6-one, then isodehydrolinalool results. This is actually advantageous when the monoterpene unit is to be used as a precursor for ionones and vitamins, since the 1,1-disubstituted double bond is more reactive in the cyclization reaction than is the normal 1,1,2-trisubstituted bond. (The cyclization reaction is described in detail below.) The preparation of these two acetylenic ketones is shown in Scheme 4.9 and is the basis of a process commercialized by BASF. 

Butlerov found out that in alkaline medium (calcium hydroxide), formaldehyde HCHO polymerizes to form about 20 different sugars as racemic mixtures, Butlerov 1861. The reaction requires a divalent metal ion. Breslow found a detailed mechanism of reaction that explains the reaction products, (Breslow 1959). He found that glycol-aldehyde is the first product that is subsequently converted into glyceral-dehyde (a triose), di-hydroxy-acetone, and then into various other sugars, tetrose, pentose, and hexose. The formose reaction advances in an autocatalytic way in which the reaction product is itself the catalyst for that reaction with a long induction period. The intermediary steps proceed via aldol and retro-aldol condensations and, in addition, keto-enol tautomerizations. It remains unexplained how the phosphorylation of 3-glyceraldehyde leads to glycral-3-phosphate (Fig. 3.6). Future work should study whether or not ribozymes exist that can carry out this reaction in a stereo-specific way. 

Aldol condensation of acetone with formaldehyde gives methyl vinyl ketone. This can undergo the ene reaction with isobutylene to give an... 

According to these thermodynamic data, significant conversion can be obtained for the condensation of acetone with formaldehyde. Diacetone alcohol can be formed in low yield only and has a lower tendency to dehydrate than the aldols formed from benzaldehyde. The energy balance of the process is so displaced by the formation of water that the unsaturated ketone is usually obtained. The... 

A second industrial process for preparing j/-ionone (2) starts form wo-butene (10) and formaldehyde (11) to give 12 and is based on linking 3-methylbut-2-en-l-ol (13) and 3-methylbut-2-enal (14) o give citral (15) (Scheme 2) [12]. The dienol ether formed from the acetal 76 by elimination of 13 undergoes a sigmatropic rearrangement [13]. V /-Ionone (2) results from aldol condensation of 15 with acetone (3). 

Note 1,3-Cyclohexandione (dihydroresorcinol) is available from 1,3-diphenol (resorcinol) by hydrogenation of its mono-sodium salt with one mole of hydrogen at temperatures below 50 °C catalyzed by RaNi in basic medium. Methyl vinyl ketone is a broadly used C4 building block produced by gas-phase formylation, aldol condensation of acetone with formaldehyde catalyzed by metal oxides (Scheme 4.33) [28, 29]. 

Other reports deal with a pyrrolidine-catalysed homo-aldol condensation of aliphatic aldehydes (further accelerated by benzoic acid), a diastereoselective aldol-type addition of chiral boron azaenolates to ketones,the use of TMS chloride as a catalyst for TiCU-mediated aldol and Claisen condensations, a boron-mediated double aldol reaction of carboxylic esters, gas-phase condensation of acetone and formaldehyde to give methyl vinyl ketone, and ab initio calculations on the borane-catalysed reaction between formaldehyde and silyl ketene acetal [H2C=C(OH)OSiH3]. ... 

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