Phenolic activity

Scheme 1. Phenol activation by base. Phenol is treated with a metal hydroxide or other strong base to form the activated salt.

As with resoles, we can use a three-phase model to discuss formation of a novolac. Whereas the resole is activated through the phenol, activation in novolacs occurs with protonation of the aldehyde as depicted in Scheme 12. The reader will note that the starting material for the methylolation has been depicted in hydrated form. The equilibrium level of dissolved formaldehyde gas in a 50% aqueous solution is on the order of one part in 10,000. Thus, the hydrated form is prevalent. Whereas protonation of the hydrate would be expected to promote dehydration, we do not mean to imply that the dehydrated cation is the primary reacting species, though it seems possible. 

In a related publication, Kobayashi and his team reported on Zr-catalyzed asymmetric Mannich reactions that utilize the more electron-rich oxygenated ketene acetals shown in Scheme 6.28 [93], A noteworthy aspect of this study was that the levels of syn/anti diaste-reocontrol proved to be dependent on the nature of the alkoxide substituent whereas the (3-TBS acetals predominantly afforded the syn isomer, the OBn derivatives afforded a larger amount of the anti isomer. As before, the presence of an additive, this time 1,2-dimeth-ylimidazole (DMI), proved to be important with regard to the level of Ti-facial selectivity. The phenol activating group can be removed by the same procedure as reported previously, with essentially identical degrees of efficiency (see Scheme 6.27). 

The presence of -OH group In phenols activates the aromatic ring towards electrophilic substitution and directs the Incoming group to ortho and para positions due to resonance effect. Reimer-Tiemann reaction of phenol 5delds sallcylaldehyde. In presence of sodium hydroxide, phenol generates phenoxlde Ion which Is even more reactive than phenol. Thus, In alkaline medium, phenol undergoes Kolbe s reaction. 

Table 4. Tertiary butylation of phenol activity on Cni xC0xFc2O4 at 200 C...

Masunaga S, Urishigawa Y, Yonezawa Y. 1986. Biodegradation pathway of o- cresol by heterogeneous culture. Phenol activated sludge. Water Res 20 477- 484. 

Although hydroxyquinolines in which the hydroxy substituent is present in the benzene ring are known and show phenolic activity, 2- and 4-hydroxyquinoline exist solely as the quinolone tautomers (Box 3.2). 

Coupling of amidrazones with phenols, active methylene compounds, or aromatic amines [116] (Eq. 57). 

Estradiol A notable application of phenol activation by [Os] is the CIO alkylation of estradiol 89 (Figure 5). The metal fragment preferentially binds to the a face of the steroid (to form 90) and thus promotes the addition of MVK to the ji face. This forms a quaternary... 

The hydroxyl group of a phenol activates the aromatic ring towards electrophilic attack, whilst the aromatic ring increases the acidity of the hydroxyl group compared to an aliphatic alcohol. Thus many phenols are soluble in sodium hydroxide solution to form the phenoxide anion. Electron-withdrawing nitro groups in the ortho and para positions provide additional resonance stabilization for the phenoxide anion. 2,4,6-Trinitrophenol (picric add) is quite a strong acid. 

HEXACHLOROEPOXYOCTAHYDRO-e rfo,exo-DIMETHANO-NAPHTHA-LENE or HEXACHLORO-6,7-EPOXY-l,4,4A,5,6,7,8,8A-OCTA-HYDRO-l,4 5,8-DIMETHANONAPHTHALENE (60-57-1) C HgClgO Noncombustible or very difficult to bum solid. Incompatible with concentrated mineral acids, acid catalysts active metals strong oxidizers strong acids phenols, active metals and their salts (e.g., copper, iron, magnesium, potassium, sodium, zinc). Corrosive to some metals. 

ALVIT (60-57-1) Incompatible with concentrated mineral acids, acid catalysts, strong oxidizers, phenols, active metals such as copper, iron, magnesium, sodium, potassium, zinc, and their salts. 

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