Aromatic compounds ortho-hydroxylation

Besides a variety of other methods, phenols can be prepared by metal-catalyzed oxidation of aromatic compounds with hydrogen peroxide. Often, however, the selectivity of this reaction is rather poor since phenol is more reactive toward oxidation than benzene itself, and substantial overoxidation occurs. In 1990/91 Kumar and coworkers reported on the hydroxylation of some aromatic compounds using titanium silicate TS-2 as catalyst and hydrogen peroxide as oxygen donor (equation 72) . Conversions ranged from 54% to 81% with substituted aromatic compounds being mainly transformed into the ortho-and para-products. With benzene as substrate, phenol as the monohydroxylated product... 

Reaction LXXL Replacement of Halogen by Hydroxyl. (B., 14, 2394 16, 2954 25, 3290 J. pr 11, 229 A. Ch., [3], 55, 400.)—When alkyl halides are refluxed with dilute caustic alkali or alkali carbonate, hydro-xylation occurs smoothly. If the halide be tertiary the replacement takes place with great ease, warming with water being sufficient a secondary halide reacts less readily, but more so than a primary. Halogen in aromatic compounds is replaced with great difficulty unless there be present negative substituents in the ortho- or para-position. The replacement, however, can be effected under pressure (U.S.P., 1996745). 

Aromatic compounds which contain two amino groups, two hydroxyl groups, or one amino group and one hydroxyl group, located para or ortho to each other, are not suitable as coupling components. These compounds reduce diazo compounds, being oxidized to quinones in the process. (Smooth coupling may be achieved in many cases by the addition of thiosulfates or thiocyanates. )... 

The phenolic compounds characteristically display high field chemical shifts for the aromatic hydrogens ortho and para to the hydroxyl substituent. The single hydroxyl proton resonates at much lower field than the corresponding OH group of the alcohols but at higher field than that of the carboxylic acids. 

Cyclodextrins exhibit remarkable ortho-para selectivity in the chlorination of aromatic compounds by hypochlorous acid (HOCl) [22] (Scheme 5). Chlorination takes place via formation of a covalent intermediate, a hypochlorite ester of cyclodextrin. In the chlorination of anisole by hypochlorous acid, pura-chlorination occurs almost exclusively in the presence of sufficient cyclodextrin, although in control experiments maltose had no effect on the product ratio. For example, selectivity for para-chlorination in the presence of 9.4 X 10 M a-cyclodextrin is 96%, which is much larger than that in the absence of a-cyclodextrin (60%). In the proposed mechanism, one of the secondary hydroxyl groups reacts with HOCl to form a hypochlorite ester, which attacks the sterically favorable para position of the anisole molecule included in the cyclodextrin cavity in an intracomplex reaction. The participation of one of the secondary hydroxyl groups at the C-3 position in the catalysis was shown by the fact that dodecamethyl-a-cyclodextrin, in which all the primary hydroxyl groups and all the secondary hydroxyl groups at the C-2 positions are methylated, exhibited equal or larger ortho-para specificity than native a-cyclo-... 

Hydroxylation of Aromatics The aromatic compounds photoadsorbed on the catalyst surface undergo two competing reaction pathways (a) hydroxylation of the aromatic ring or (b) multi-step oxidation reactions to complete mineralization. In the first case, the OH radical attack follows the selectivity rules known for homogeneous electrophilic aromatic substitution when the oxidized compound contains an electron donor group. Hence the only ortho- and para-isomers are obtained. In the presence of an... 

DFT study of the oxidative abilities of Fe(III)-OOH, Fe(IV)=0 and Fe(V)=0 in the ortho-hydroxylation of aromatic compounds through two different pathways and the H-abstraction and electrophilic attack indicates that Fe(III)-OOH is a sluggish oxidant. The transient Fe(IV)=0 oxidant, which triggers the catalytic reaction, results from the heterolytic cleavage of the 0---0 bond in Fe(III)-(X)H. The potential energy surface calculations favour the formation of Fe(V)=0 over Fe(IV)=0 species because of a lower... 

Aromatic esters The most common plasticisers based on aromatic esters are benzoates of one type or another. The infrared spectra of benzoates all have a strong band near 715cm ( 13.99 im). Another reasonably common type of aromatic ester is that based on salicylic acid. The spectra of salicylates, in common with other aromatic compounds which have a hydroxyl group adjacent to a carbonyl group (i.e. at the ortho position), do not have the band near 3340cm ( 2.99 im). 

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