Methylol derivatives Addition

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). 

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]. 

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. 

Not surprisingly, N-sulfonyl imines, which are highly electrophilic species, are quite prone to hydrolysis. Thus, addition of water to imine 41 initially produces a methylol derivative 42 which in certain cases can be reasonably stable (R = CC13, C02R) [2,6]. However, this type of intermediate usually dissociates to an aldehyde and a primary sulfonamide (Scheme 10). 

Figure 22 illustrates typical DSC thermograms for UF and PF resins. The PF resin had larger exothermic heat of curing as compared to the UF resin. For illustration purposes, the reaction between phenol and formaldehyde in alkaline conditions to form PF adhesives is briefly discussed here. The first step is an exothermic addition reaction forming methylol derivatives at the ortho or para positions ... 

These thermosetting resins find applications in coatings, adhesives, laminating, and molding compositions. The materials are formed in water at a pH above 7 at the start of the reaction, because the methylol derivatives that form condense rapidly at acidic conditions. The initial step, where urea undergoes a nucleophilic addition of formaldehyde, can be shown as follows ... 

Urea/formaldehyde (UF) or melamine/formaldehyde (MF) thermoset resins are also formed via the initial addition of HCHO to form methylol derivatives (dimethylol urea and hexamethylol melamine). Curing or cross-linking with acids yields thermoset polymers. 

Addition Reactions. Type reaction RCH OH -F R R RCHo R -R OH. Under some conditions, methylol derivatives are capable of adding to ethylenic linkages. For example, methylene glycol adds to prop3dene under presSiii e and in the presence of an acidic catalysfc - ... 

XTnder acid conditions, the situation is reversed in that the conversion of methylol derivatives to methylene derivatives is usually more rapid than their formation. Granger suggests that this is because mono-methylol derivatives are converted to methylene derivatives as soon as they are formed.. s a result, the introduction of more than one methylol group in the simple phenol is prevented and the polynuclear phenols thus obtained, as would be expected, react less readily with additional formaldehyde. 

Aldehydes form addition products with sulfamic acid salts. These are stable ia neutral or slightly alkaline solutions but are hydroly2ed ia acid and strongly alkaline solutions. With formaldehyde, the calcium salt of the methylol (hydroxymethyl) derivative [82770-57-8], Ca(02SNHCH20H)2, is obtained as a crystalline soHd. 

Orthophosphoric and benzylphosphonic acids have been selectively alkylated with triethyl phosphite in a new synthesis of mono-, di-, and triethyl phosphates and of mono- and di-methyl phosphonates.62 A-Methylol carboxamides and sulphonamides react with trialkyl phosphites to give the phosphonate derivatives (78) and (80), respectively.63 However, the mechanism appears to be quite different in each case while the carboamides react by a transesterification-rearrange-ment pathway, the sulphonamides undergo elimination-addition via the imine (79). 

The basic amino group of the 1-position in semicarbazide or thiosemi-carbazide may be used to react by a substitution reaction with activated halides [52], ethers [51], hydroxy [53], phenoxy [54], and amino groups [55] to yield substituted 1-semicarbazides or thiosemicarbazides. In addition, the amino group of the 1-position may add to electron-deficient double bonds [56]. Formaldehyde and other aldehydes may add to all the available free NH groups to give methylol, alkylol, or polymeric products under basic conditions [57]. Aldehydes or ketenes usually give semicarbazone derivatives, and these in turn are used analytically to identify the purity or structure of a known aldehyde [3]. 

Selected 13C chemical shifts in azines derived from 4-acetyl-3-methyl-l-phenyl-5-pyrazolones,62 methylol groups in formaldehyde-fast bisazo dyes63 and pyridyl-substituted azobenzenes64 are available. The 13C chemical shifts in 16 substituted azobenzenes were published by Savarino et al.65 (however, most of them are mentioned in ref. 1) and some additional data can be found in ref. 66 by Fedorov et al. 

These benzaldehydes could then be directly used as a feedstock for various polymeric products or reduced to form phenolic benzylic alcohol derivatives (i.e., p-methylol groups). The p-methylol groups would thus be active sites, whereas in unmodified lignins, the C-l site is blocked and unreactive. In addition, the oxidative-cleavage step will hydrolyze a portion of the lignin interunit ether bonds, and thus increase the total fraction of free phenolic units to further enhance the reactivity. Other possible benefits are that the lignin would be extensively depolymerized and would form a more uniform feedstock material both conditions would give a product that is easier to handle. 

BINOL-derived methylols (126) catalyse the previously challenging enantioselective addition of methylmagnesium bromide and other Grignards to aldehydes. (g)... 

General Chemistry. Phenolic polymers are formed with a phenolic or phenol derivative monomer and formaldehyde crosslinking agent in two discrete steps. The first step, shown in Fig. 2, is an addition or methylolation step. Formaldehyde reacts with an active ortho or para proton to form the addition product which... 

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