Formaldehyde condensation

Holzer [10] (1884) and Ludy [11] (1889) isolated a white precipitate by the reaction of urea with formaldehyde under acid conditions. 

Goldschmidt in 1896 [121 studied the reaction of urea with formaldehyde in various strength acid solutions and obtained a granular white deposit of the empirical formula C5H10N4O3. In 1908, Einhorn and Hamburger [13] studied the same reaction in the presence of hydroxyl ions and, depending on the mole ratio of formaldehyde to urea, isolated mono- or dimethylolurea. 

In 1927, Schiebler et ai, [14] found that in acid solution the methylolureas are converted to insoluble substances similar to Goldschmidt s compound. Today the polymerization mechanisms involved are similar to those discussed for other methylol compounds such as phenolic resins (Chapter 2) or melamine resins (see Section 3 of this chapter). It is interesting to note that because urea has four active hydrogens and three sites for polymerization, linear, branched, and cyclic structures are possible. In fact, Kadowaki [15] has isolated several low-molecular-weight condensation products of urea-formaldehyde and has described their properties. The cyclic structures commonly called urones, such as dimethylolurone (iV,N -dimethyloltetra-hydro-4//-l,3,5-oxidiazin-4-one), have also been prepared by Kadowski. 

Experimenal NMR data have been obtained on the urea-formalde-hyde polymer reactions. The techniques of solid state NMR with cross polarization and magic-angle spinning (CP/MAS) provided a powerful technique to overcome the limitation in solubility in the use of liquid-state NMR for urea-formaldehyde (U-F) cured resins [19]. 

Some reactions involved in these U-F polymers as determined by NMR are described in equations 7 and 8. 

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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 ) ... 

Fig. 13. Polymerization chemistry of phenol—formaldehyde condensation synthesis of novolac resia. The phenol monomer(s) are used ia stoichiometric excess to avoid geUation, although branching iavariably occurs due to the multiple reactive sites on the aromatic ring.

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

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) ... 

An early source of glycols was from hydrogenation of sugars obtained from formaldehyde condensation (18,19). Selectivities to ethylene glycol were low with a number of other glycols and polyols produced. Biomass continues to be evaluated as a feedstock for glycol production (20). 

Figure 4d represents in situ encapsulation processes (17,18), an example of which is presented in more detail in Figure 6 (18). The first step is to disperse a water-immiscible Hquid or soHd core material in an aqueous phase that contains urea, melamine, water-soluble urea—formaldehyde condensate, or water-soluble urea—melamine condensate. In many cases, the aqueous phase also contains a system modifier that enhances deposition of the aminoplast capsule sheU (18). This is an anionic polymer or copolymer (Fig. 6). SheU formation occurs once formaldehyde is added and the aqueous phase acidified, eg, pH 2—4.5. The system is heated for several hours at 40—60°C.

Naphthalenesulfonic Acid—Formaldehyde Condensates. The sodium salts of the condensation products of naphthalenesulfonic acid with formaldehyde constitute an important class of compounds which are mainly used in the area of concrete additives (32,33), agricultural formulations, mbber formulations, and synthetic tanning agents. They are also used in photographic materials (34). Hampshire Chemical Co. and Henkel of America, Inc., are the largest suppHers of naphthalene sulfonate in concrete additives (superplasticizer) and reportedly hold 75—80% of this market. It was estimated that naphthalene sulfonate demand from U.S. producers would reach approximately... 

In 1994 estimated naphthalene consumption in western Europe and Japan for the production of alkylnaphthalene sulfonates, naphthalene sulfonate formaldehyde condensates, and synthetic tanning agents was... 

Naphthalenolsulfonic acid formaldehyde condensates are used in tanning agents. Other uses of 2-naphthalenol are in the manufacture of perfuming agents, eg, 2-naphthyl methyl e e [93-04-9] (Yara Yara), R = CH (30), and 2-naphthyl ethyl ether/Pi-/ -37 (nerolin, BromeUa) R = ... 

Aniline—formaldehyde resins were once quite important because of their excellent electrical properties, but their markets have been taken over by newer thermoplastic materials. Nevertheless, some aniline resins are stiU. used as modifiers for other resins. Acrylamide (qv) occupies a unique position in the amino resins field since it not only contains a formaldehyde reactive site, but also a polymerizable double bond. Thus it forms a bridge between the formaldehyde condensation polymers and the versatile vinyl polymers and copolymers. 

Includes naphthalene sulfonates and naphthalene sulfonate formaldehyde condensates. 

There are three main uses for naphthalene sulfonic acid derivatives (75—79) as naphthalenic tanning material alkyl naphthalene sulfonates for industrial appHcations as nondetergent wetting agents and as dye intermediates. Consumption of naphthalene sulfonates as surfactants accounts for a large portion of usage. Naphthalene sulfonate—formaldehyde condensates are also used as concrete additives to enhance flow properties. Demand for naphthalene sulfonates in surfactants and dispersent appHcations, particularly in concrete, was expected to increase into the twenty-first century. Consumption as of 1995 was 16 x 10 kg/yr. 

Amino Resins. Amino resins (qv) include both urea- and melamine—formaldehyde condensation products. They are thermosets prepared similarly by the reaction of the amino groups in urea [57-13-6] or melamine [108-78-1] with formaldehyde to form the corresponding methylol derivatives, which are soluble in water or ethanol. To form plywood, particle board, and other wood products for adhesive or bonding purposes, a Hquid resin is mixed with some acid catalyst and sprayed on the boards or granules, then cured and cross-linked under heat and pressure. 

The epoxy cresol—novolak resins (2) are prepared by glycidylation of o-cresol—formaldehyde condensates in the same manner as the phenol—novolak resins. The o-cresol—formaldehyde condensates are prepared under acidic conditions with formaldehyde—o-cresol ratios of less than unity. 

The parent compound, cyclic diazomethane , was first obtained from formaldehyde, ammonia and chloramine by dichromate oxidation of the initially formed higher molecular diaziridine-formaldehyde condensation product (61TL612). Further syntheses of (44) started from Schiff bases of formaldehyde, which were treated with either difluoramine or dichloramine to give (44) in a one-pot procedure. Dealkylation of nitrogen in the transient diaziridine was involved (65JOC2108). 

Reaction rates are at a minimum at pH 3, and, unlike with the phenol-formaldehyde condensates, which have a minimum at pH 7, setting can occur under neutral conditions. 

Melamine-formaldehyde condensates are also useful in textile finishing. For example, they are useful agents for permanent glazing, rot proofing, wool shrinkage control and, in conjunction with phosphorus compounds, flameproofing. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The same chemical mechanisms and driving forces presented for phenol-formaldehyde resins apply to resorcinol resins. Resorcinol reacts readily with formaldehyde to produce resins (Fig. 2) which harden at ambient temperatures if formaldehyde is added. The initial condensation reaction, in which A-stage liquid resins are formed, leads to the formation of linear condensates only when the resorcinol/formaldehyde molar ratio is approximately 1 1 [119]. This reflects the reactivity of the two main reactive sites (positions 4 and 6) of resorcinol [120]. However, reaction with the remaining reactive but sterically hindered site (2-positiori) between the hydroxyl functions also occurs [119]. In relation to the weights of resorcinol-formaldehyde condensates which are isolated and on a molar basis, the proportion of 4- plus 6-linkages relative to 2-linkages is 10.5 1. However, it must be noted that the first-mentioned pair represents two condensa-... 

The absence of methylol (-CH2OH) groups in all six lower molecular weight resorcinol-formaldehyde condensates which have been isolated [119] reflects the high reactivity of resorcinol under acid or alkaline conditions. It also shows the instability of its para-hydroxybenzyl alcohol groups and their rapid conversion to jpara-hydroxybenzyl carbonium ions or quinone methides. This explains how identical condensation products are obtained under acid or alkaline reaction conditions [119]. In acid reaction conditions methylene ether-linked condensates are also formed, but they are highly unstable and decompose to form stable methylene links in 0.25 to 1 h at ambient temperature [121,122]. 

German patent DE 3442454 (1984), European patent EP0185205, B1 (1986). Process for the preparation of melamine-urea-formaldehyde condensates. Assigned to BASF AG. 

Surely these views are not very plausible, depending as they do on the formation of such an improbable system as (23). How much more simple is it to view acid catalysis as involving enhancement of the electrophilic character of the reagent. Thus, in the formaldehyde condensation, it is protonated formaldehyde,... 

A series of phosphorus- and bromine-containing FRs were synthesized and studied to understand their role, especially their combined effects. Thus, monocar-danyl phosphoric acid, its bromo derivatives and their formaldehyde condensates and crosslinked products [28,188] were prepared and their properties compared with analogous products made from phenol [28,189]. Table 14 gives the LOI values, char yields (Cy at 600°C), and thermal stability at 50% (T6o) decomposition. 

Examples Over-reaction and reduction are the problems with formaldehyde condensations in base (page T158). In acid solution over-reaction and acetal formation, e.g, to give (41), occur.The Mannlch Reaction avoids all these problems. 

A more reliable way to control formaldehyde condensations is to use the Mannich reaction ... 

Various formaldehyde condensates have been developed to reduce the irritancy associated with formaldehyde while maintaining activity and these are described as formaldehyde-releasing agents or masked-formaldehyde compounds. 

A fluid loss additive useful in cementing oil and gas wells is a blend [423,424,1015] of a copolymer of acrylamide/vinyl imidazole. The second component in the blend is a copolymer of vinylpyrrolidone and the sodium salt of vinyl sulfonate. Details are given in Table 2-2. The copolymers are mixed together in the range of 20 80 to 80 20. Sodium or potassium salts or a sulfonated naphthalene formaldehyde condensate can be used as a dispersant. 

N-vinylpyrrolidone, and the sodium salt of vinyl sulfonate dispersants are sodium or potassium salts or a sulfonated naphthalene formaldehyde condensate ... 

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