Formaldehyde hydrogen bridge

Let us apply Eq. (3.86) to phenol - formaldehyde polymers synthesized in an acid medium with a phenol excess (novolacs). Phenol is a trifunctional reactant (A3), the functional groups being the aromatic hydrogens located in positions 2, 4, and 6 of the phenolic ring. Formaldehyde acts as a bifunctional monomer (B2), forming methylene bridges between the reactive positions of phenol. Novolacs are synthesized with a phenol excess, such that gelation does not occur at full formaldehyde conversion. From Eqs (3.83) and (3.86), we obtain... 

The product of the Mannich reaction may occasionally behave as a sub.strate undergoing aminomcthylation. Thus, when several mobile hydrogen atoms arc present in the substrate, it is possible that formaldehyde reacts to give Mannich bases 170, with a methylene bridge placed between two substrate moieties. ... 

The partial oxidation of methanol to formaldehyde over metal oxides is important industrially, and the results of experiments done in the transient regime are summarized for M0O3 (249). The results in Fig. 41 show that the conversion of methanol and the selectivity toward formaldehyde in a Mars-van Krevelen process are both favored by a relatively oxidized surface. Weber (250) has shown by theoretical calculations that the surface methoxy intermediate should lose one of its hydrogens as a hydride ion attracted to Mo and not as a hydrogen atom or proton attracted to a doublely bonded or bridging oxygen. 

A novel approach has been to allow serotonin to react with protein via the Mannich reaction. This is a simple reaction that enables one to use formaldehyde as a bridge between the amino groups of a protein and compounds containing one or more reactive hydrogens. The Mannich reaction has also been used to prepare reserpine conjugates. The antibody titers were not as satisfactory as those elicited by conjugates prepared by a p-carboxyazobenzene derivative linked to BSA by the mixed anhydride procedure. 

To top off the appeal, the polymerization of furfuryl alcohol can be made to run with almost any partner containing reactive hydrogen. Thus, furfuryl alcohol can be reacted with formaldehyde to give a series of thermosetting resins featuring more methylene bridges than are obtained by the resinification of furfuryl alcohol alone. Such resins are commonly used for the bonding of wood. 

Methylene bridging with formaldehyde Replacement of hydrogen by methyl... 

The next step to discuss in the hypothetical pathway in Scheme I is addition of H to the formyl group and f ormation of a bound formaldehyde complex. Two types of formaldehyde complex have already been prepared, i.e., the rj -bound formaldehydeand the bridging formal-dehyde complexes. The latter can be hydrogenated into complexes with a methoxy group.Lavalley et also report that, when... 

Cured urea-formaldehyde adhesive is characterized by the presence of methylene bridges between strongly hydrogen-bonded urea linkages. Consequently, cured UF adhesives are inherently stiff and brittle. Incorporation of DDDU with its 12 methylene groups into the resin structure results in cured UF adhesive with a more flexible network. The increased flexibility decreases internal stress and the associated flaws, and hence the fracture energy increases. 

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