Amine formaldehyde catalysis

Compounds containing carbon-nitrogen double bonds can be hydrolyzed to the corresponding aldehydes or ketones. For imines (W = R or H) the hydrolysis is easy and can be carried out with water. When W = H, the imine is seldom stable enough for isolation, and hydrolysis usually occurs in situ, without isolation. The hydrolysis of Schiff bases (W = Ar) is more difficult and requires acid or basic catalysis. Oximes (W = OH), arylhydrazones (W = NHAr), and, most easily, semicarbazones (W = NHCONH2) can also be hydrolyzed. Often a reactive aldehyde (e.g., formaldehyde) is added to combine with the liberated amine. 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

A novel Mannich reaction between A -alkoxycarbonylpyrroles 739, formaldehyde, and primary amine hydrochlorides catalyzed by Y(OTf)3 gave a monoaminoalkylation product 741 some times in good yield (14-81%) in aqueous media (Scheme 146) <2001TL461>. When formaldehyde was replaced by acetaldehyde or benzaldehyde, no reaction occurred. There was no formation of the 2,7-diazabicyclo[2.2.1]hept-5-ene 740 (through the aza-Diels-Alder reaction of an N-protected pyrrole with an aldehyde and amine salts by catalysis with triflate). 

In a related reaction, aqueous allylation of imines has been reported by Bel-luci and co-workers using allyltributylstannane under lanthanide triflate catalysis [130]. Alternatively, the reaction can be performed without catalysis directly with the formaldehyde-generated immonium salts in aqueous media to give, in excellent yields, bis-homoallylamines and tertiary homoallylamines with primary and secondary amines, respectively [131]. These homoallylic amines were also prepared by Sc(OTf)3-catalyzed three-component reactions of aldehydes, amines and allyltributylstannane in micellar systems [132]. 

Considerable rate enhancements have been observed when water is used as solvent compared with alcoholic or hydrocarbon media for Mannich reactions, i.e. condensations of ketones with secondary amines in the presence of formaldehyde [65]. Allylsilanes [66] and allylstannanes [67] in aqueous media were used in organic synthesis under Mannich-like conditions. More recently, Kobayashi reported the catalysis of the reaction of vinyl ethers with iminium salts by ytterbium triflate in tetrahydrofuran-water mixtures [68]. 

The protected propargylamines 224 (R = H, CH2C02Me or CH2CH2C02Me) react with aqueous formaldehyde under copper(I) bromide catalysis to yield the allene derivatives 225. Deprotection with ethereal hydrogen chloride affords the free amines. ... 

Polymerization Chemistry. The amine groups of urea react very readily with formaldehyde, forming methylol nreas (Fig. 3.9). The A-stage reaction is controlled by the urea/formaldehyde ratio (1/1.3 to 1/2.2), an alkalme buffer at pH 7.5-8.0, and refluxing up to 8 hr, to produce a mixture of mono-, di-, and trimethylol ureas. These condense to form oligomers and Anally, with acid catalysis and heat, highly cross-linked thermoset polymers. 

Some resoles contain latent acid catalysts, which on heating generate moderately strong acids. Examples inclnde aryl phosphites such as diphenyl hydrogen phosphite and ammonium sulfate (48,49). The use of latent acid catalysis broadens the range of applications of phenolic resins to include areas such as liquid composite molding and pultrusion. Also resoles, which can contain so-called free formaldehyde, can be formulated with formaldehyde scavengers in form of amines such as melamine. 

A plausible mechanism for the reaction is shown in Scheme 11.2. The carbonyl group undergoes two a-amino-methylation reactions on the same a-carbon of the ketone 12, which is catalyzed by L-proline through enamine catalysis. The cyclocondensation of the resulting substituted amines 19 with formaldehyde affords the desired spiro[indoline-3, 5 -pyrimidin]-2-one and spiro[indene-2,5 -pyrimidin]-l (3H)-one (Scheme 11.2). 

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