Methylol derivatives

Melamine reacts similarly to produce methylol derivatives, which form the familiar melamine—formaldehyde resins on heating (63) (see Aminoresins). 

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). 

Most amino resins used commercially for finishing textile fabrics are methylolated derivatives of urea or melamine. Although these products are usually monomeric, they may contain some polymer by-product. 

Negatwe P/ate Coatings. The bulk of negative plates have a diazo-based coating. This often comprises an A/-aryl- or alkyl aminobenzenedia zonium salt condensed with formaldehyde (66) or a methylol derivative (67) to form a low molecular weight polymer such as the following ... 

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. 

Cellulose dissolved in suitable solvents, however, can be acetylated in a totally homogeneous manner, and several such methods have been suggested. Treatment in dimethyl sulfoxide (DMSO) with paraformaldehyde gives a soluble methylol derivative that reacts with glacial acetic acid, acetic anhydride, or acetyl chloride to form the acetate (63). The maximum degree of substitution obtained by this method is 2.0 some oxidation also occurs. Similarly, cellulose can be acetylated in solution with dimethylacetamide—paraformaldehyde and dimethylformamide-paraformaldehyde with a potassium acetate catalyst (64) to provide an almost quantitative yield of hydroxymethylceUulose acetate. 

A number of disinfectants apparentiy owe their activity to formaldehyde, although there is argument on whether some of them function by other mechanisms. In this category, the dmg with the longest history is hexamethylenetetramine (hexamine, urotropin) [100-97-0] which is a condensation product of formaldehyde and ammonia that breaks down by acid hydrolysis to produce formaldehyde. Hexamine was first used for urinary tract antisepsis. Other antimicrobials that are adducts of formaldehyde and amines have been made others are based on methylolate derivations of nitroalkanes. The apphcations of these compounds are widespread, including inactivation of bacterial endotoxin preservation of cosmetics, metal working fluids, and latex paint and use in spin finishes, textile impregnation, and secondary oil recovery (117). 

These materials will then slowly react with further formaldehyde to form their own methylol derivatives which in turn rapidly react with further phenol to produce higher polynuclear phenols. Because of the excess of phenol there is a limit to the molecultir weight of the product produced, but on average there are 5-6 benzene rings per molecule. A typical example of the many possible structures is shown in Figure 23.11. 

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. 

In a typical process a jacketed still fitted with a stirrer and reflux condenser in charged with 240 parts 37% w/w (40% w/v) formalin and the pH adjusted to 8.0-8.5 using sodium carbonate solution with the aid of a pH meter. One hundred and twenty six parts of melamine (to give a melamine formaldehyde ratio of 1 3) are charged into the still and the temperature raised to 85°C. The melamine goes into solution and forms methylol derivatives. For treatment of fabrics, paper and leather this product may be diluted and cooled for immediate use. It may also be spray dried to give a more stable product. Cooling the solution would yield crystalline trimethylolmelamine, which may be air dried but which is less soluble in water than the spray-dried product. 

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. 

Paraformaldehyde/DMSO dissolves cellulose rapidly, with neghgible degradation, and forms the hydoxymethyl (methylol) derivative at Ce [ 140-142]. Therefore, cellulose derivatives at the secondary carbon atoms are easily obtained after (ready) hydrolysis of the methylol residue. Additionally, fresh formaldehyde may add to the methylol group, resulting in longer methylene oxide chains, that can be functionahzed at the terminal OH group, akin to non-ionic, ethylene oxide-based surfactants [143,144]. 

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. 

Fluoro-2,2-dinitroethanol, the methylol derivative of fluorodinitromethane, has been used extensively for the synthesis of fluorodinitromethyl compounds. The fluorine atom is similar in size to that of a proton and so rotation in the fluorodinitromethyl group is much less hindered compared to the trinitromethyl group. Consequently, these compounds are far less sensitive to impact than trinitromethyl compounds but only slightly less energetic. The explosive performance of fluorodinitromethyl compounds has been reviewed. ... 

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. ... 

Many of the nitronate salts of polynitroaliphatic compounds, particularly salts of gem-nitronitronates, exhibit properties similar to known primary explosives. Consequently, the storage of such salts is highly dangerous. Treatment of these nitronate salts with formaldehyde yields the corresponding methylol derivative via the Henry condensation. These methylol... 

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). ... 

Under aqueous conditions formaldehyde reacts with primary nitramines to form the corresponding methylol derivatives. The versatility of the terminal hydroxy group of these methylol derivatives is illustrated by their facile conversion to more reactive functional groups, like isocyanates, which can then be reacted with compounds containing hydroxy or carboxy functionality. Diisocyanates like (215), (216) and (217) have been reacted with various polyni-troaliphatic diols for the synthesis of energetic polymers. ... 

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. 

Figure 5. DTA curves of pine kraft lignin and its methylol derivative...

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. 

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