Quinone and Quinol

1 Or an equivalent quantltj of sodium bichromate (75 qrams), which may be dissolved m 3—4 times its weight of water and delivered from a tap funnej 

Quinol. The other half nt the iiiodiul is Ireattd with. 1 

A l iZi// ()//1. -1. To i solution of (. Uinol in water, add a few droi-is of feriic ehloiide. The solution tiiin.s brow n and ether now extiacts i[uinone. 

Add to the solution of (. uinol in watm, a drop of copper sulphate, and caustic soda, uul w.um. Cuprous u.xide is pie-cipitated, 

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Quinone and Quinol. (ininonc, which weis oiiginally obtai ied h the oxiilation of quinlt acid (the add associated... 

Experiment.—On a small hand balance, having two sheets of paper counterpoised in the pans, weigh out equal quantities (about 0-5 g.) of quinone and quinol dissolve the two substances separately in warm water and mix the solutions. Magnificent green needles of quinhydrone crystallise almost at once. After some time collect them at the pump, wash with water, and dry between filter papers over calcium chloride in a non-evacuated desiccator. Boil a few of the crystals with water and smell the vapours. 

A useful compilation of EPR data is J. A. Pedersen (ed.). Handbook of EPRSpectra from Natural and Synthetic Quinones and Quinols, CRC Press, Boca Raton, FL (1985). 

The functionally relevant redox potentials of the semiquinone couples are obviously those of quinone-enzyme complexes, not of free quinone molecules. For instance, the effective E of the QHj/Q couple bound to the enzyme is shifted from the corresponding value of free couple by an amount that is determined by the relative affinities of binding of quinone and quinol to the binding-site. The effect of binding on the E is given by the equation (see Ref. 247)... 

Fig. 6. Electron-transfer reactions occurring between the primary and secondary quinone acceptors, Qa and Qb, respectively. D stands for the electron donor to P. AB(1) and AB(2) represent the reduction of Qg by Qa and Qb by Qa , respectively. H (1) and H (2) indicate the first and second protonation steps associated with the formation of the Qb quinol. Q and QHj are quinone and quinol not closely associated with the reaction center. Figure adapted from Diner, Nixon and Farchaus (1991) Site-directed mutagenesis of photosynthetic reaction centers. Curr Opinion Struct Biol 1 548.

Calkins, V. P. 1947. The mechanism of the antioxygenic synergism of quinones and quinols with phosphoric acid and other acids in fat systems. J. Am. Chem. Soc. 69, 384. 

Fe7-ric chloride reaclion.—Dissolve a drop of the free phenol in water and add a drop of ueutral ferric chloride. A green (catechol), blue (orcinol, pyiogallol) or purple (phenol, resorcinol) colouration is produced, which is often destroyed by acid or alkali. Quinol is o.xidised to quinone, and turns biown (p. 193). The naphthols give precipitates of dinaphthol (p. 220). 

Anthraquinol + 02 —i> Anthraquinone + H202 The anthraquinone derivative is usually 2-ethyl- or 2-pentyl-anthraquinone. The solvent is usually a mixture of two solvents, one for the quinone and one for the quinol. The... 

Me3SiCN reacts with both saturated and unsaturated aldehydes and ketones to given silylated cyanohydrines. This reaction has been particularly useful for the regioselective protection of a carbonyl in p. quinones and p. quinol antibiotic metabolite has been prepared. 

Chemically, conversion into a vat consists in a 1 6-addition of hydrogen and recalls exactly the conversion of quinone into quinol. Like quinol, indigo white , also a dihydric phenol , is a weak add, the alkali salts of which are coloured intensely yellow. 

Scheme 3 Carbazole-l,4-quinone and carbazole-l,4-quinol alkaloids...

Phenylhydrazine and hydroxylamine also reduce quinone to quinol they do not react with it as with other carbonyl compounds. 

Method I.—10 gms. (1 mol.) of quinone and 10 gms. (1 mol.) of quinol are separately dissolved in the minimum quantity of water, and the solutions mixed and warmed. After cooling, the precipitate is filtered off and washed with water. 

Quinol and Derivatives. See under Hydro-quinone and Derivatives in Vol 7, H227-R to H228-R... 

In 1987, Kita and co-workers first developed a general and high yielding (59% quant.) route to p-benzoquinone monoacetals (2a) and spirolactones from para-substituted phenols (la) with PIFA in MeCN in the presence of alcohols (R"OH) [27]. Similar methods for preparing quinone monoacetals and quinol ethers have been developed independently by Lewis et al. (PIDA/CH2C12-R"OH (11-65% yields)) [28] and Pelter et al. (PIDA/R"OH (65-99% yields)) [29] [Eq.(l)]. 

Mild and high yielding oxidation reactions of phenol derivatives to the corresponding quinone monoacetals, quinols, and quinones using PIDA or PIFA [Eqs. (1) - (3)] have been developed independently by Kita et al. [27], Lewis et al. [28], and Pelter et al. [29], and have been utilized extensively for the syntheses of... 

Addition to quinone monoketals and quinol ethers.2 Complexation of quinone monoketals or quinol ethers with MAD permits 1,4-addition of organo-lithium and Grignard reagents. Highest yields obtain with aryl, vinyl, and acetylenic organometallics. 

Baylis-Hillman adducts such as 55 and 56 derived from 2-nitrobenzaldehydes were shown to function as useful precursors to functionalized (1H)-quinol-2-ones and quinolines. Treatment of 55 and 56 with iron and acetic acid at 110 °C afforded 57 and 58, respectively <02T3693>. A variety of other cyclization reactions utilized in the preparation of the quinoline scaffold were also reported. An iridium-catalyzed oxidative cyclization of 3-(2-aminophenyl)propanols afforded 1,2,3,4-tetrahydroquinolines <02OL2691>. The intramolecular cyclization of aryl radicals to prepare pyrrolo[3,2-c]quinolines was studied <02T1453>. Additionally, photocyclization reactions of /rans-o-aminocinnamoyl derivatives were reported to provide 2-quinolones and quinolines <02JHC61>. Enolizable quinone and mono- and diimide intermediates were shown to provide quinolines via a thermal 6jt-electrocyclization <02OL4265>. Quinoline derivatives were also prepared from nitrogen-tethered 2-methoxyphenols. The corresponding 2-methoxyphenols were subjected to a iodine(III)-mediated acetoxylation which was followed by an intramolecular Michael addition to afford the quinoline OAc O... 

Glycal-substituted quinols and quinol ketals, derived from the 1,2-addition of lithiated glycals to quinones or quinone monoketals, are versatile intermediates for the synthesis of aryl C-glycosides, providing access to all four substitution patterns found in the natural products. For example, reduction of a quinol provides a p-hydroxyaryl glycal (8 9,11 -> 12). On... 

Fig. 13. Relationships between lipophilic antioxidants and lipid hydroperoxides in irradiated skin. (A) There was no relationship between decrease in a-tocopherol and appearance of lipid hydroperoxides. (B) There was a significant (p < 0.05) relationship between decrease in total Q (quinols + quinones) and appearance of lipid hydroperoxides.

In flashing light, there are limitations on the minimum and maximum times between flashes. The rate-limiting step in turnover of PSII is exchange of quinone for quinol, which occurs at the QB site. Consequently, the electron acceptors will produce a bottleneck if the time between... 

Complex III is also analogous to the Cyt bef complex of chloroplasts, both with respect to contents (two Cyt b s, one Cyt c, an Fe-S pro tern, and a quinone) and function within the membranes (e.g., interaction with a quinol) the isolated Cyt b f complex can also pass electrons to Cyt c as well as to its natural electron acceptor, plastocyanin. Complex III is also structurally and functionally analogous to a supramolecular protein complex in bacteria. 

Disposition in the Body. Rapidly absorbed from the gastrointestinal tract and readily penetrates the skin. It is metabolised by conjugation to yield phenyl glucuronide and phenyl sulphate small amounts are oxidised to catechol and quinol which are also conjugated. Oxidation of these metabolites to quinones may tint the urine green. Acid-labile phenol conjugates are present endogenously in serum at concentrations of about 0.1 pg/ml. Phenol is a metabolite of benzene. 

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