Methylol derivatives Reactions

Reaction with Aldehydes and Ketones. Formaldehyde combines with primary and secondary alkanolamines in the presence of alkali to give methylol derivatives. For the reaction of monoethanolamine with formaldehyde (12), the reaction scheme shown in Figure 1 occurs. 

Quinone Methides. The reaction between aldehydes and alkylphenols can also be base-cataly2ed. Under mild conditions, 2,6-DTBP reacts with formaldehyde in the presence of a base to produce the methylol derivative (22) which reacts further with base to eliminate a molecule of water and form a reactive intermediate, the quinone methide (23). Quinone methides undergo a broad array of transformations by way of addition reactions. These molecules ate conjugated homologues of vinyl ketones, but are more reactive because of the driving force associated with rearomatization after addition. An example of this type of addition is between the quinone methide and methanol to produce the substituted ben2yl methyl ether (24). 

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. 

As an alternative to the wet process described above, moulding compositions may be made by mixing a powdered resin or a methylol derivative with other ingredients on a two-roll mill or in an internal mixer. The condensation reaction proceeds during this process and when deemed sufficiently advanced, the composition is sheeted off and disintegrated to the desired particle size. This dry process is not known to be used in any current commercial operation. 

Thiourea will react with neutralised formalin at 20-30°C to form methylol derivatives which are slowly deposited from solution. Heating of methylol thiourea aqueous solutions at about 60°C will cause the formation of resins, the reaction being accelerated by acidic conditions. As the resin average molecular weight increases with further reaction the resin becomes hydrophobic and separates from the aqueous phase on cooling. Further reaction leads to separation at reaction temperatures, in contrast to urea-formaldehyde resins, which can form homogeneous transparent gels in aqueous dispersion. 

The reaction rate increases when heated to temperatures up to 40°C. The amino derivatives can then be quaternized if desired. The N-methylol derivatives of polyacrylamide can be made cationic by heating with amines, or they can be made anionic by heating with aqueous bisulfite solution under basic conditions. 

Resole syntheses entail substitution of formaldehyde (or formaldehyde derivatives) on phenolic ortho and para positions followed by methylol condensation reactions which form dimers and oligomers. Under basic conditions, pheno-late rings are the reactive species for electrophilic aromatic substitution reactions. A simplified mechanism is generally used to depict the formaldehyde substitution on the phenol rings (Fig. 7.21). It should be noted that this mechanism does not account for pH effects, the type of catalyst, or the formation of hemiformals. Mixtures of mono-, di-, and trihydroxymethyl-substituted phenols are produced. 

There are reactive softeners, some of which are N-methylol derivatives of long-chain fatty amides (10.241) while others are triazinyl compounds (10.242). The N-methylol compounds require baking with a latent acid catalyst to effect reaction, whereas dichloro-triazines require mildly alkaline fixation conditions. The N-methylol compounds are sometimes useful for combination with crease-resist, durable-press, soil-release and water-repellent finishes. In this context, the feasibility of using silane monomers such as methyltri-ethoxysilane (10.243), vinyltriethoxysilane (10.244), vinyl triace tylsilane (10.245) and epoxypropyltrimethoxysilane (10.246) in crosslinking reactions to give crease-resist properties and softness simultaneously has been investigated [492]. 

Figure 3.1 Two essential steps of chemical reaction of formaldehyde (HCHO) with nucleic acid exemplified by adenine that are similar to formaldehyde-protein reactions, (a) Addition reaction as the first step, resulting in a methylol derivative, methylol adenylic acid (b) Second step is a condensation reaction, a stable product methylene-bis-adenylic acid is derived between the methylol derivative and another adenine. Reproduced with permission from Shi et al.,AIMM 2001 9 107-116. 

Both 1,1-dinitroethane (26) and 1,1-dinitropropane, and their methylol derivatives, 2,2-dinitropropanol (25) and 2,2-dinitro-l-butanol respectively, have been synthesized via the Ter Meer reaction. - The formal and acetal of 2,2-dinitropropanol in the form of a 1 1 eutectic is an energetic plasticizer and so the synthesis of 2,2-dinitropropanol has been the subject of much investigation. On a pilot plant scale 2,2-dinitropropanol (25) is synthesized in 60 % overall yield from nitroethane (22). Thus, treatment of 1 -chloronitroethane (23) with potassium nitrite... 

It must be emphasized that em-nitronitronate salts should never be stored on safety grounds. These salts readily react with formaldehyde to give the methylol derivatives which are more stable and less hazardous to handle. The latter are often used directly in condensation reactions where treatment with aqueous base forms the em-nitronitronate salt in situ. 

Primary and secondary nitroalkanes, dinitromethane, and terminal em-dinitroaliphatic compounds like 1,1-dinitroethane, all contain acidic protons and have been used to generate Mannich products. Formaldehyde is commonly used in these reactions although the use of other aliphatic aldehydes has been reported. The nitroalkane component is frequently generated in situ from its methylol derivative, a reaction which also generates formaldehyde. Ammonia, " aliphatic amines, " hydrazine, and even urea have been used as the amine component of Mannich reactions. 

Both the Henry reaction and the reverse demethylolation are synthetically useful in the chemistry of polynitroaliphatic compounds. The Henry reaction is commonly used to mask the natural chemistry of an aliphatic nitro or terminal em-dinitro group by removing the acidic a -proton(s). In Section 1.7 we discussed the conversion of Q ,ty-dinitroalkanes to their bis-methylol derivatives before subjecting them to oxidative nitration and subsequent demethylolation with base, a procedure which results in the formation of Q ,Q , y, y-tetranitroalkanes. ... 

The use of primary nitramines in Mannich reactions is an important route to numerous secondary nitramines. However, a far more common route to such nitramines involves the Mannich condensation of a terminal gem-dinitroalkane, formaldehyde, and an amine, followed by IV-nitration of the resulting polynitroalkylamine. The preformed methylol derivative of the gem-dinitroalkane is often used in these reactions and so formaldehyde can be omitted. This route has been used to synthesize explosives like (92) and (209). ... 

Melamine (MF) resins (Cymel, Melmac, Resimene) are produced by the formylation of melamine (2,4,6-triamino-1,3,5-triazine). Melamine has six active hydrogen atoms and hence forms mono-, di , tri-, tetra-, penta, and hexamethylo melamines. The methylol derivatives may be etherified with alcohols such as 1-butanol. A hexamethyl ether (hexamethoxymethylmela-mine) is commercially available and may be used as an intermediate. Some of the reactions leading to resinification of melamine are shown in Figure 15.6. 

Imino Diels-Alder reactions. The neurotoxic fungal toxin slaframine (2) has been synthesized by an intramolecular imino Diels-Alder reaction. The substrate is obtained from the amide 1 via a methylol derivative. These derivatives are best prepared by reaction of the amide with Cs2C03 and paraformaldehyde in dry THF (equation I). When heated they lose acetic acid and undergo cyclization. 

In alkaline media, phenolic units may react with formaldehyde, forming methylol derivatives that condense with themselves or with another phenol (J, Fig. 1.4). This formaldehyde condensation reaction forms the basis for using technical lignins in the production of adhesives. 

Miyamoto et al. [165] observed a more uniform acetylation among different hydroxyl groups in LiCl dimethylacetamide (DMAC) as compared to heterogeneous reactions (Table 3). Cellulose dissolved in DMSO-PF is known to form methylol derivatives, especially for the 6-OH group. Acetylation of cellulose in this system [174-176] was shown to occur preferentially at the methylol hydroxyl group generated in situ. 

The common procedure for adding reactants consists either in simultaneously mixing all the chemical species involved in the reaction, or in allowing the amine and the aldehyde to react first and then adding the substrate. In some cases, however, the condensation of substrate and formaldehyde is carried out first in order to isolate the corresponding methylol derivative, which is subsequently submitted to react with the amine (X-methylation of amino derivatives see Fig. 12) this is advantageous with several substrates, such as nitroalkanes, ferrocenes,- sulfonic acids, and phosphines. ... 

The reaction conditions (pH, medium) may also affect the predominance of one type of cleavage, as reported for some oxadiazolc derivatives (226, Fig. 82), which by deamination give a methylol derivative (227) instead of the unsaturated product. ... 

These reactions have a general relevance in organic synthesis, as they allow the performance of X-methylation reactions such as cyano-, thio-, amidomethylations, etc. starting from hydrogen cyanide, amides, etc. When, in particular, the abovemen-tioned methylol derivatives are allowed to react with amine (R —YH = primary or secondary amine), a Mannich base is produced. 

The use of water for the production of hydroxymethyl derivatives 268 is of little synthetical interest, except for a few cascs, as these compounds arc better prepared by reaction of the Mannich substrate R —H with formaldehyde. It is in fact well known that methylol derivatives may be intermediate species of Mannich synthesis (Chap. I,... 

Urea (NH2CONH2) reacts with formaldehyde similarly to phenol to produce methylol derivatives that then condense further to yield a cross-linked network (Scheme 1). Actually, at a mole ratio of 1.5-2 mol of formaldehyde to urea and a pH of 7.5, a mixture of the monomethylol, dimethylol, trimethylol, and tetramethylol ureas are formed. For further extensive condensation to take place, the pH of the system must be made acidic. Thus, it is possible to concentrate the initial resin solution or spray-dry it to a soluble powder that can be dissolved and mixed with an acid catalyst at the time of application to induce the curing reaction. The ratio of formaldehyde to urea used in commercial resins varies with the manufacturer, but is always less than 2 1. 

Thermosetting phenolic resins include a number of polymers, the most common being obtained from the condensation of phenol with formaldehyde. The OH group on the benzene ring increases the reactivity in the o- and p- positions leading to three reactive centers for the phenolic component, while formaldehyde acts as having two active centers that can lead to a fully crosslinked polymer. The process may take place in neutral or alkaline conditions when in the first stage of the reaction, compounds known as methylol derivatives are formed. The condensation of phenol with formaldehyde occurs randomly at ortho- or para- position of the phenol, as shown below ... 

Amino-5-imino-3-pyrazolidinones react with formaldehyde at the 4-amino group giving methylol derivatives.644 The 4-arylimino derivatives are reduced catalytically to give 4-arylamino analogs.1538 An interesting reaction of the 4-arylazo-5-imino-3-pyrazolidinones is the replacement of the 4-arylazo group by arylimino (eq. 272).1255 1296... 

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