Methylol derivatives Addition reactions

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). 

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. 

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 ... 

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 - ... 

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]. 

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