Ortho- Dihydroxybenzene

Guaiacol is the monomethyl ether of the diphenol, catechol, or ortho-dihydroxybenzene. Its constitution is—... 

The last-named reagent also cleaves ortho-dihydroxybenzenes (catechols) to give,... 

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

Oxidation of ortho-dihydroxybenzene Fe-assisted PC reaction and its comparison with the unpromoted PC reaction... 

Table 1 Estimated parameters for the unpromoted PC and Fe-assisted PC oxidation of ortho-dihydroxybenzene (20 ppm C in o-DHB)...

Beilstein Handbook Reference) AI3-03995 Benzene, o-dihydroxy- 1,2-Benzenediol BRN 0471401 Catechol, CCRIS 741 Cl 76500 Cl Oxidation Base 26 1,2-Dihydroxybenzene ortho-Dihydroxybenzene Durafur developer C EINECS 204427-5 Fouramine PCH Fourrine 68 HSDB 1436 ... 

Phenol is photooxidized via its hydroxylated compounds into CO2 and H2O. Para-dihydroxybenzene (p-DHB), ortho-dihydroxybenzene (o-DHB) and 1,2,3-trihydroxybenzene (1,2,3-THB) are identified as primary and secondary hydroxylation products (Al-Ekabi Seipone, 1988). 1,2,4-trihydroxybenzene (1,2,4-THB) and 1,4-benzoquinone (1,4-SQ) are also documented as intermediate species. These species appear to be present prior to the total phenol mineralization (Trillaseta/., 1996 Winterbottom et al., 1997). Tseng and Huang (1990) reported two intermediate species,p-DHB and 1,4-BQ, during the photodegradation of 5.10 mole/L of phenol. Several other species are also suspected as possible inteimediates with their formation following the aromatic ring break up muconic acid, maleic acid, oxalic acid, formic acid, and acetic acid. Researchers have however, experienced difficulty until now to directly detect these species. 

Targeted experiments can be developed to investigate the phenol photocatalytic conversion mechanism (Salaices et al., 2004). In this context, four main intermediates of phenol photo-degradation are identified para-dihydroxybenzene (p — DHB), ortho-dihydroxybenzene (o — DHB), 1,2,4-trihydroxybenzene (1,2,4 — 77/6), and 1,4-Benzoquinone (I, 4 — BQ). 

Norepinephrine and epinephrine are members of a class of pharmacologically active substances known as catecholamines, because they contain within their structures both an amine and ortho-dihydroxybenzene, which is known by the common chemical name of catechol. Many adrenergic drugs also are catecholamines, and their structure-activity-relationships (SARs) will be discussed. 

Quaternary structure (Section 27 22) Description of the way in which two or more protein chains not connected by chemical bonds are organized in a larger protein Quinone (Section 24 14) The product of oxidation of an ortho or para dihydroxybenzene denvative Examples of quinones include... 

Quinone (Section 24.14) The product of oxidation of an ortho or para dihydroxybenzene derivative. Examples of quinones include... 

The Dakin reaction proceeds by a mechanism analogous to that of the Baeyer-Villiger reaction. An aromatic aldehyde or ketone that is activated by a hydroxy group in the ortho or para position, e.g. salicylic aldehyde 12 (2-hydroxybenzaldehyde), reacts with hydroperoxides or alkaline hydrogen peroxide. Upon hydrolysis of the rearrangement product 13 a dihydroxybenzene, e.g. catechol 14, is obtained ... 

The hydroxylation of a phenol 1 upon treatment with a peroxodisulfate in alkaline solution, to yield a 1,2- or 1,4-dihydroxybenzene 3, is called the Elbs reaction The phenol is deprotonated by base to give a phenolate anion 4, that is stabilized by resonance, and which is activated at the ortho or the para position towards reaction with an electrophilic agent ... 

The main product of the Elbs reaction is the 1,4-dihydroxybenzene (hydro-quinone). If the para position is already occupied by a substituent, the reaction occurs at an ortho position, leading to a catechol derivative although the yields are not as good as for a hydroquinone. Better yields of catechols 7 can be obtained by a copper-catalyzed oxidation of phenols with molecular oxygen ... 

A variety of electronic effects control the relative energies of the disubstituted benzenes. For the difluorobenzenes, the meta and para isomers are of comparable energy the ortho isomer is clearly less stable. This is most likely due to the electrostatic repulsions of the two C-F bond dipoles which are aligned in the same direction. This is just like the difluoroethylenes where the 1,2-cis isomer is much less stable than the 1,1-isomer.poj. he dihydroxybenzenes. 

The piperonal synthesis (p T 9) is an example where the two ortho oxygen substituents would be very difficult to set up. We therefore (guideline 7) start with available catechol ( o-dihydroxybenzene),... 

Mercapto-l,2,4-triazole 67 reacted in a standard coulometric cell with the ortho-quinone generated electroche-mically from 1,2-dihydroxybenzene to give 4-(l//-l,2,4-triazole-3-ylsulfanyl)-l,2-benzenediol 68 via a Michael addition (Equation 23) <2005MI68>. 

In this regard, the PC oxidation of phenol produces similar hydroxylated aromatics as reaction intermediates since the oxidation occurs via hydroxyl radical attack. These intermediates might be equally harmful than the parent species. Several authors report that during the oxidation of phenol, they identified various hydroxylated intermediates such as 1,2,3-trihydrox-ybenzene (1,2,3-THB), ortho- and parfl-dihydroxybenzene (o,p-DHB) (Al-Ekabi and Serpone, 1988), 1,2,4-THB and 1,4-benzoquinone (1,4-BQ)... 

Solubility. According to our classification system, all intra-molecular bonded materials should be Class AB. Consequently, they should be soluble in solvents from Classes AB, B, and A, provided the solvent can successfully compete with the internal H bonding. Because of the internal satisfaction of the H bonding tendency. Class N solvents should be better solvents for internally H bonded materials than for nonchelated compounds. This is the behavior observed, as shown in Table 5-V for dihydroxybenzenes in CCh. In the stronger acid and base solvents, the loss of chelation is suggested. Further, for this case, the table shows a similarity in the solubilities of ortho and meta isomers. 

As sample values of viscosity, compare the data in Table 5-XI. Notice the substituted anilines. Here, even though an tn/ramolecular H bond may form in the ortho isomer, the second amino hydrogen gives intermolecular association, and ortho- and/>ara-chloroaniline have similar viscosities. Both values are larger than that shown for the nonassociated o-chlorotoluene. Dihydroxybenzenes and derivatives provide similar data (721) as do nitroanilines, zdthough these compounds are further complicated by intermolecular H bonding. They show mixed association. ... 

Phenols may have more than one hydroxy group attached to the same benzene ring - for example, the three isomeric dihydroxybenzenes catechol (ortho-dihydroxy-benzene or 1,2-benzenediol), resorcinol (meta-dihydroxy-benzene or 1,3-benzenediol) and hydroquinone (para-dihydroxybenzene or 1,4-benzenediol) see Figure 25.3. 

The ionized dihydroxybenzenes 39" behave similarly (Scheme 17). Note that, in this series, one of the phenolic hydroxyl groups acts as a hydrogen acceptor and the other as an H donor. The El mass spectrum of catechol (o-39) exhibits a significant ortho effect. While the intensity of the [M — H20]" peak in the El spectrum of o-39 is no greater than ca 15%B, the spectra of resorcinol (m-39) and hydroquinone (p-39) both show negligibly smah [M — H20] + peaks ( 2%B). It is likely that water loss from the intermediate 47 generates again bicyclic [M — H20]" ions, i.e. ionized benzoxirene 48. And, notably, the CO losses does not parallel the ortho effect of the water elimination in this series, as it is the most pronounced ion the case of m-2>9. 

This occurs preferentially for the ortho derivative [8]. Further details will be given later [9]. These secondary reactions, not only destroy some of the products, but also consume a large part of the hydrogen peroxide. Thus, they are responsible for the limitation of the conversion of hydrogen peroxide into dihydroxybenzenes. A good catalyst should therefore accelerate only the first hydroxylation step and not the secondeiry reactions. 

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