Condensations with formaldehyde

Formaldehyde condenses with sahcyhc acid in the presence of nitrite-containing sulphuric acid to give aurin tiicarboxyhc acid this is converted by ammonia solution into the ammonium salt, which is employed as a reagent for aluminium ( aluminon ) ... 

Formaldehyde condenses with itself in an aldol-type reaction to yield lower hydroxy aldehydes, hydroxy ketones, and other hydroxy compounds the reaction is autocatalytic and is favored by alkaline conditions. Condensation with various compounds gives methylol (—CH2OH) and methylene (=CH2) derivatives. The former are usually produced under alkaline or neutral conditions, the latter under acidic conditions or in the vapor phase. In the presence of alkahes, aldehydes and ketones containing a-hydrogen atoms undergo aldol reactions with formaldehyde to form mono- and polymethylol derivatives. Acetaldehyde and 4 moles of formaldehyde give pentaerythritol (PE) ... 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

Azomethines (Schiff bases) have been prepared in order to block the amino group, using different carbonyl compounds as reagents. Aqueous formaldehyde condenses with amino acids in the presence of palladised charcoal in a hydrogen atmosphere with the production of a dimethylamino group (the reduction time is 3—12 h at 20°C). The free carboxyl group is esterified with diazomethane [260]. The general application of this procedure is limited, however, and the N,N-dimethylaminomethyl esters produced are very volatile so that mere evaporation of the ethereal solution of diazomethane at room temperature results in losses and low yields of the derivatives of Ala, Gly, Val and Leu. 

A third homogeneously catalyzed process, on the basis of formaldehyde condensation with propanal to give methacrolein and subsequent oxidation to methacrylic acid, was commercialized in 1990 by BASF. Application of this process is limited by the availability of cheap propanal, produced by large-scale ethylene hydroformylation (cf. Section 2.1.1). 

Formaldehyde condenses with acetaldehyde in the presence of a basic catalyst to form pentaerythritol, C(CH2OH)4 ... 

The Pictet-Spengler reaction has been combined with Ugi multi-component chemistry to construct a number of polycyclic indoles. Isonitrile derivatives prepared from tryptamine (or methyl tryptophanate), a carboxylic acid and formaldehyde condense with aminoacetaldehyde diethyl acetal. A few examples employed substituted aldehydes [352]. 

Condensation of two moles of formaldehyde produces the a-hydroxymethylserinebis-(l,2-diaminoethane)cobalt(m) ion (4), and a further six moles of formaldehyde condense with the two co-ordinated 1,2-diaminoethane ligands of (4) to produce the co-ordinated dioxacyclam (3) in the [Co(dioxacyclam) (a-HOCHa-serine)] ion. The considerable enhancement of the rate of attack of bases at co-ordinated nitriles is well documented, and recently this has been used to preparative advantage in reactions of co-ordinated acrylonitrile with carbanions (Michael addition) ... 

Another important class of polymeric surfactants that are used for demulsifica-tion is those based on alkoxylated alkyl phenol formaldehyde condensates, with... 

Phenolic resins were among the first synthetic resins explored by the coating industry, initially used to modify properties of oil-based varnishes as a replacement for some natural hard resins. They are essentially solvent-soluble phenol-formaldehyde condensates with reactive methyllol groups. They are widely used as cross-linkers for thermosetting baking finishes, yielding films with excellent solvent and corrosion resistance properties coupled with favorable mechanical properties. 

Mapson did not find any pH rai at which formaldehyde condenses with ascorbic acid and does not condense with reductones. However, at pH 2.0 ascorbic acid condenses fairly rapidly with formaldehyde and the reaction of reductones with formaldehyde is slower and proceeds at a linear rate. Mapson (14), therefore, proposed that the indophenol titration be carried out at pH 2.0 after formaldehyde treatment to estimate ascorbic acid in the presence of reductones. In this procedure advantage is taken of the fact that reductones react with formaldehyde at a linear rate. To measure the reductones accurately a series of titrations is carried out at 10 minute intervals after the addition of formaldehyde a graph is constructed and the reductone titration value is obtained by extrapolation of the curve... 

Formaldehyde Condensation.—When an amino acid in neutral solution is mixed with excess of neutral formaldehyde solution, the mixture becomes acid, and can be titrated (Sorensen s reaction), thus affording an important method for the estimation of amino acids and ammonium salts. The mechanism of the change has been studied by Levy (1937). According to the older view, formaldehyde condenses with the amino group to form an unstable methylene-imino derivative, thereby destroying the basicity of the group. 

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