Phenolic groups, chemical modifications

Chemical Modifications to Pitch. The earlier attempts to improve the commercial value of pitch residues must have been essentially exploratory research. Sanada et al, (71) in 1973 methylated the hydroxyl groups of 3,5-dimethyl phenol formaldehyde resin and noted, on carbonization, the formation of spheres of mesophase, the original resin giving an optical texture of mosaics in resultant carbons. Mochida et al. (72) carbonized naphthalene, anthracene and pyrene with aluminium chloride, sodium and potassium and examined the structure of the resultant carbons by optical microscopy and high resolution, fringe-imaging transmission electron microscopy (TEM),... 

Chiral groups may be attached to both the narrow and the wide rims of the calixarene skeleton I (or even to the bridges14) and this may be done by chemical modification of the calixarene or by the use of appropriate chiral phenols for the calixarene synthesis. With resorcarenes II chiral groups may be introduced at the hydroxy groups or at the 2-position between the OH-functions. Their attachment at the bridges (CHR ) was also realized. 

Since in terms of leaving group ability in SN2 reactions I > Br > Cl, a-iodoalkyl alkyl carbonates are the reagents of choice for the chemical modification of either carboxylic acid or phenolic functions. However, these a-iodo carbonates exhibit severe instability (Ref. 78) and are generally prepared in-situ or just before use (Ref. 79,80, 81). 

Calix[n]arenes are cyclic condensation products of para-substituted phenol derivatives and formaldehyde [29], They are highly interesting for the development of sensitive coatings due to their conformational flexibility and the ease by which they may be modified chemically. Chemical modification can be done either in the meta position, or by reactions at the hydroxy group. In this way, bulky substituents [30], chelating substituents [31], aromatic residues [32], crown ethers [33,34], peptides [35,36], etc. can be introduced. A first approach to combinatorial synthesis of calix[4]arene receptors has been published by Reinhoudt and co-workers [37,38], who prepared calixarenes with different substituents. In solution, these calixarenes lead to formation of hetero-oligomers with barbiturates, and these hetero-oligomers were detected by MALDI-TOF mass spectrometry and H-NMR spectroscopy. 

Hydrolysis of trimethylsilyl (TMS) ether [129,130] and alcoholysis of a tetrahy-dropyranyl (THP) [131,132] group have been also employed in acid-catalyzed conversion to PHOST (Fig. 24) (or novolac). Another acetal-protected PHOST, poly[4-(l-phenoxyethoxy)styrene], was prepared by radical polymerization of the corresponding monomer and also by chemical modification of PHOST [133]. This acetal polymer produces a phenolic polymer and phenol upon aci-dolysis (Fig. 24). 

The study of the outer root bark of T. hypoglaucum collected in China afforded three new structures of phenolic triterpenes. Duan et al. isolated triptohypol A (80), B (81) and C (82), a series of new phenolic compounds related to celastrol [29]. Triptohypol A (80) was isolated as an amorphous powder and spectroscopic means and chemical modification determined its structure. By HREIMS the formula C30H40O6 was determined, and H-NMR spectrum showed five methyl signals, a methoxy moiety, a methylene attached to an oxygen atom and two vinyl protons. Data from 13C-NMR experiments indicated the presence of a pair of carbonyl groups and was quite similar to that of wilforol A (78). The analysis of HMQC and HMBC experiments allowed to establish the structure for rings A and B, based on the correlations observed between the proton H-l (8 6.95 ppm) and the carbons C-3, C-5 and C-10. Finally, the position of the carbonyl group was established at C-6 based on a NOESY experiment of the dimethyl derivative. 

The study of these reactions allowed to acquire a series of data on the chemical modification of oleuropein that is particularly rich in functional groups, and of phenol present in O. europaea. 

Chemical modification with dopamine was also used as strength and water-resistance aids for SPI adhesives (Liu et al., 2002). Dopamine is an amino acid with two adjacent phenolic hydroxyl groups, and is the primary component responsible for marine adhesive properties. The Liu modification scheme creates an SPI that is similar to mussel proteins used for surface adhesion. Increased water-resistance compared to other stand-alone SPI adhesives was achieved. Bond strength depends on the phenolic functionality in the synthesized compounds (Liu, 2002). Much interest in this adhesive has developed because it is a strong and resilient adhesive, which is formaldehyde-free, making it suitable for interior wood products. 

The methodology of active ester synthesis, as shown in Fig. 2, is generally applicable and covers a wide range of nucleophiles, including primary, secondary and aromatic amines, primary alcohols and phenols. Thus, chemical modification d polymeric active esters (i.e. active ester synthesis) provides a single-step route for the preparation of functional polymers in general. The syntl sis of various polymer types by the active ester method is advanced in Sects. 5-7. Here, an example of a relativdy simpk fiinctional group (OH) is discussed to illustrate the versatility of the active ester method, as compared with conventional methods of polymer functionalization. 

Chemical modification of polymer-bound active ester groups is also subject to strong solvent effects. In copolyfAOTcp-styrere), both aminolysis and transesterification with primary alcohols are positively influenced by solvents in the order of dimethylformamide (DMF) > dioxan > diloroform > chlorobenzene > dimethylsulfoxide (DMSO). However, trans-esterification with phenols proceeds in dioxan, but not in DMF. The last-nan d solvent effect is probably related to inactivation of the phenolate ion in DMF, as observed ako for the acylation of polymer-bound phenolic groups by soluble trichlorophenyl esters [64]. 

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