Urea-aldehyde condensations

Other types of resin modifiers compatible with resols may also be used. Examples include UF (urea-aldehyde condensation product) and epoxide. Japanese workers have found that the most effective and economical ingredients as modifiers for phenolic foam are resorcinol, o-cresol, and fulfuryl alcohol. 

The synthesis of the hydantoins 33 was realized by Beller s group in the context of their work devoted to the synthesis of amino acid derivatives by palladiumacid-promoted hydroxy-halogen exchange on the P-hydroxy-N-acyl derivative obtained from urea/aldehyde condensation, fohowed by oxidative palladium addition and CO insertion (Scheme 13.15) [42]. 

Uses of Formaldehyde. Formaldehyde is the simplest and most reactive aldehyde. Condensation polymerization of formaldehyde with phenol, urea, or melamine produces phenol-formaldehyde, urea formaldehyde, and melamine formaldehyde resins, respectively. These are important glues used in producing particle hoard and plywood. 

P. Biginelli, Gazz. Chim. Itcd. 1893, 23, 360-413. In this 54-page article ( ), Biginelli comments that his research was inspired by earlier work on bimolecular urea-aldehyde and urea-jS-ketoester condensations, respectively. 

Through a modified Biginelli condensation using urea, aldehydes, and p-oxodithioesters 243, DHPM 244 have been synthesized employing a Si02-H2S04 as a recyclable catalyst (Scheme 93) (10JOC7785). 

Polyvinyl - methyl- ether Vinyl chloride polymers Urea- and melamineform-aldehyde condensates (uncured) Crosslinked (cured, vulcanized) polymers... 

Urea/aldehyde resins (Figures 9.7 and A3.23) (de la Rie et al., 2002) are made by condensing urea, formaldehyde and i-butyraldehyde. These resins wet pigment particles well because of their polar groups. 

This volume continues in the tradition of Volume I in presenting detailed laboratory instructions for the preparation of various types of polymers such as urea, melamine, benzoguanamine/aldehyde resins (amino resins-amino-plasts), phenol/aldehyde condensates, epoxy resins, silicone resins, alkyd resins, polyacetyls/polyvinyl acetals, polyvinyl ethers, polyvinyl pyrroli-dones, polyacrylic acids, and polyvinyl chloride. Polyvinyl acetate and related vinyl esters, allyl polymers, acetylene polymers, maleate and fumarate polymers, and several other addition-condensation polymer types will be covered at a later date in Volume III. 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Reactions. The chemical properties of cyanoacetates ate quite similar to those of the malonates. The carbonyl activity of the ester function is increased by the cyano group s tendency to withdraw electrons. Therefore, amidation with ammonia [7664-41-7] to cyanoacetamide [107-91-5] (55) or with urea to cyanoacetylurea [448-98-2] (56) proceeds very easily. An interesting reaction of cyanoacetic acid is the Knoevenagel condensation with aldehydes followed by decarboxylation which leads to substituted acrylonitriles (57) such as (29), or with ketones followed by decarboxylation with a shift of the double bond to give P,y-unsaturated nitriles (58) such as (30) when cyclohexanone [108-94-1] is used. 

Group of plastics generated by the condensation of amines (e.g., urea and melamine with aldehydes). 

Group of plastics whose resins are derived from the condensation of urea and aldehydes. 

The addition of phenylisocyanate to aldehyde-derived enamines resulted in the formation of aminobutyrolactams (438,439). As aminal derivatives these produets can be hydrolyzed to the linear aldehyde amides and thus furnish a route to derivatives of the synthetically valuable malonaldehyde-acid system. With this class of reactions, a second acylation on nitrogen becomes possible and the six-membered cyclization products have been reported (440). Closely related to the reactions of enamines with isocyanates is the condensation of cyclohexanone with urea in base (441). 

The Biginelli reaction involves an one-pot reaction between aldehyde 1, 1,3-dicarbonyl 2, and urea 3a or thiourea 3b in the presence of an acidic catalyst to afford 3,4-dihydropyrimidin-2(l//)-one (DHPM) 4. This reaction is also referred to as the Biginelli condensation and Biginelli dihydropyrimidine synthesis. It belongs to a class of transformations called multi-component reactions (MCRs). 

The ever-popular Biginelli synthesis of dihydropyrimidines, by condensation of urea with a keto ester and an aldehyde, and variations on it, has been applied in a number of areas. 

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