Formaldehyde aldol condensation

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

Trimethylolpropane (TMP), the reduced crossed aldol condensation product of //-butyraldehyde and formaldehyde, competes in many of the same markets as glycerol (qv) and pentaerythritol. The largest market for TMP is as a precursor in unsaturated polyester resins, short-oil alkyds, and urethanes for surface coatings (see Alkyd resins). 

The principal markets for neopentyl glycol (NPG), the hydrogenated, crossed aldol condensation product of isobutyraldehyde and formaldehyde, are in water-borne and alkyd-surface coatings. 

The aldol reaction is a carbonyl condensation that occurs between two aldehyde or ketone molecules. Aldol reactions are reversible, leading first to a /3-hydroxy aldehyde or ketone and then to an cr,/6-unsaturated product. Mixed aldol condensations between two different aldehydes or ketones generally give a mixture of all four possible products. A mixed reaction can be successful, however, if one of the two partners is an unusually good donor (ethyl aceto-acetate, for instance) or if it can act only as an acceptor (formaldehyde and benzaldehyde, for instance). Intramolecular aldol condensations of 1,4- and 1,5-diketones are also successful and provide a good way to make five-and six-inembered rings. 

The raw materials are usually mutually contaminated to about 5 %. Thus, DSC can be ruled out. The compounds are made by aldol condensations and cross Canizzaro reactions between acetaldehyde and formaldehyde. An elegant method of distinguishing between the two raw materials takes advantage of the 10 fold solubility difference between the two in methanol and water. 

The Cannizzaro reaction is by no means confined to aromatic aldehydes. Formaldehyde undergoes the same change, yielding formic acid and methyl alcohol. That the aliphatic aldehydes from acetaldehyde upwards do not undergo the reaction is due to the fact that the aldol condensation (mentioned above), in virtue of its much greater velocity, takes precedence over the Cannizzaro reaction. 

The reason why the acyloin synthesis is especially characteristic of aromatic aldehydes, depends on the circumstance that in the aromatic series the tertiary carbon atom in the ring does not allow of the aldol condensation, a reaction for which conditions are otherwise much more favourable. The simplest example of the acyloin condensation, moreover, was already encountered in the case of formaldehyde (p. 218) glycollic aldehyde is the simplest acyloin. Acyloin compounds are also produced, in the aliphatic series, by the action of sodium or potassium on esters, and hence are also formed as by-products in the acetoacetic ester synthesis (Bouveault, Scheibler). 

Polyacetal resins have a repeating unit of -O-CH2-. They are strong, stiff polymers for valves, hoses, and tube connectors. Pentaerythritol finds end-uses in alkyd resins and explosives (pentaerythritol tetranitrate). To appreciate this synthesis, the student should review two condensation reactions, the crossed aldol and the crossed Cannizzaro. Acetaldehyde reacts with 3 mol of formaldehyde in three successive aldol condensations. This product then undergoes a Cannizzaro reaction with formaldehyde. 

Pentaerythritol, used in the production of alkyds, is produced by a crossed Cannizzaro reaction of the aldol condensation product of formaldehyde and acetaldehyde. The by-product formate salt is a major source of formic acid. 

Aldols can be obtained as result of the so-called aldol condensation reaction. Hiis takes place between an aliphatic aldehyde and another aldehyde or ketone. The second aldehyde has at least one CHaCHO group. Formaldehyde is the most frequently used aldehyde for this reaction. A small amount of weak alkali serves as a catalyst. The reactions may be represented as follows RCHa. CHO + R CH2. CHO -> RCHa. CH(OH) CHR. CHO and RCHO + CH3. CO - CH3 - RCH(OH). CHa... 

Tracer studies with 13C showed that the carbon of methoxy species formed in CO hydrogenation appeared as the central C atom of isobutylene.531 Methoxy was shown to be reduced to surface methyl species that was transformed to surface acetyl group via insertion of CO into the methyl-metal bond. Aldol condensation of C2 oxygenates with formaldehyde affords iso-C4 products.532 Earlier results of a different approach for isosynthesis using metal-zeolite catalyst systems are summarized in a 1998 review.533... 

Addition of copper salts permits substantial improvement of yield. The reaction appears to proceed in two stages. Initially an aldol condensation occurs between three molecules of formaldehyde and one molecule of acetaldehyde ... 

Some methylotrophic bacteria dehydrogenate methanol to formaldehyde. The latter undergoes an aldol condensation to form a hexulose-6-phos-phate ... 

In the present paper we have studied four acid catalyzed reaotions involving carbonyl compounds alkylation of benzene with formaldehyde, esterification of phenylacetic acid, Friedel-Crafts acylation by phenylpropanoyl chloride, and the cross aldolic condensation of acetophenone with benzaldehyde in the presence of three Hp zeolites with different framework Si-to-Al... 

An Oppenauer reaction produces the selective oxidation of a secondary alcohol, leading to a (3-hydroxyketone that suffers a retro-aldol condensation under the basic reaction conditions, resulting in the evolution of formaldehyde. 

Kraft cooking of dihydrodehydrodiconiferyl alcohol (I) as a model for the phenylcoumaran system shown to be present in native lignin (/, 2), resulted (3, 13) in the opening of the hydrofuran ring and splitting ofF of formaldehyde, probably through a reverse aldol condensation of an intermediate quinonemethide (77, 18). The resulting p,0 -dihydroxystilbene... 

Thus, IQ may arise from creatinine, 2-methylpyridine and formaldehyde or a related Schiff base, formed from glycine through Strecker degradation. The initial step may be a Mannich reaction or an aldol condensation. By analogy MelQ may arise from creatinine, alanine and 2-methylpyridine, and MelQx from creatinine, glycine and 2,5-dimethylpyrazine according to the scheme in Figure 1. 

The most useful examples of the Cannizzaro reaction as applied to aliphatic aldehydes are those involving /3-hydroxyaldehydes formed by aldol condensation of aldehydes which have a-hydrogen atoms or of these aldehydes with formaldehyde. Since, in these reactions, the 0-hydroxyaldehyde is not isolated, examples will be classified under the headings of the reactants which serve as the actual starting materials. 

Formaldehyde also does not contain an a-H atom. However, formaldehyde is such a reactive electrophile that it tends to undergo multiple aldol additions instead of a simple aldol condensation. This type of reaction is exploited in the pentaerythritol synthesis. 

Glyoxal can be formed by oxidation of glycolaldehyde (e.g., in Scheme 2.5), but it can also be formed by autoxidation of unsaturated fats and by enzymic degradation of serine.60 2-Oxopropanal can be obtained by retroaldolisation of 1- and 3-deoxyglucosone or by hydrolysis of diacetylformoin (see Scheme 2.5). Butanedione can also be derived from diacetylformoin, but by reduction, dehydration, and hydrolysis (see Scheme 2.5). 2,3-Pentanedione can be formed from butanedione by aldol reaction with formaldehyde, dehydration, and reduction or by aldol condensation of hydroxyacetone and acetaldehyde, followed by dehydration. 

An important intermediate for synthetic p-ionone (36) is the C8 building block methyl heptenone (37). In addition to the synthesis shown above, two further processes are known for its industrial production. In the process of Rhodia INC 36), the starting material is isoprene, and methyl heptenone (37) is obtained via prenyl chloride. At BASF, methyl heptenone (37) is produced, for economic reasons, in the form of its double bond isomer (37 a) by thermal condensation of isobutylene, formaldehyde and acetone 37) (see page 13). By suitable choice of the reaction conditions, various side-reactions, such as the Cannizzarro reaction of formaldehyde, the oligomerization of isobutene and aldol condensation between formaldehyde and acetone, can largely be suppressed. 

Sugars play a dual role in all living organisms they are the principal source of energy for cellular processes and are indispensable components of DNA and RNA information carriers. The possibility of prebiotic synthesis of various sugars was demonstrated by Butlerow in 1861 [28], who showed that a simple prebiotic molecule - formaldehyde - can be used for the synthesis of a mixture of various sugars in a Ca(OH)2-catalyzed series of aldol condensations. The reaction starts... 

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