Benzoquinone dichloro

The para-diamines cannot be estimated by means of the diazo reaction. The following estimation is based on the formation of benzoquinone dichloro-imide when p-phenylenediamine in hydrochloric acid solution is added to a solution containing excess of sodium hypochlorite and sodium carbonate. 

Chloranilic acid (2,5-dichloro-3,6-dihydroxy-l,4-benzoquinone)/57-5S-77 M 209.0, m 283-284° pK l.22, pK 3.01. A soln of 8g in IL of boiling water was filtered while hot, then extracted twice at about 50° with 200mL portions of benzene. The aq phase was cooled in ice-water. The crystals were filtered off, washed with three lOmL portions of water, and dried at 115°. It can be sublimed in vacuum. [J Phys Chem 61 765 1957.] The diacetate has m 182-185° [7 Am Chem Soc A6 1866 1924 Thamer and Voight J Phys Chem 56 225 7952]. 

The best yields of 5-hydroxyindoles are obtained when equimolar amounts of the quinone and enamine are used. An excess of enamine gives rise to non-indolic products derived from reaction of two enamine units and one quinone unit or the product which results from the initial Michael addition of the enamine to the quinone. Use of excess quinone has been reported less frequently, but limited studies indicate no advantage. When 2,5-dichloro-l,4-benzoquinone (32) was treated with a 50% excess of ethyl 3-... 

Pyrido[l,2-6]pyridazinium inner salt 61 was prepared from 1,2-dihydropyrido[l,2-6]pyridazinium inner salt 54 by treatment with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone in CH2CI2 at room temperature in 95% yield (99JOC9001). 

The next major obstacle is the successful deprotection of the fully protected palytoxin carboxylic acid. With 42 protected functional groups and eight different protecting devices, this task is by no means trivial. After much experimentation, the following sequence and conditions proved successful in liberating palytoxin carboxylic acid 32 from its progenitor 31 (see Scheme 10) (a) treatment with excess 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in ie/t-butanol/methylene chloride/phosphate buffer pH 7.0 (1 8 1) under sonication conditions, followed by peracetylation (for convenience of isolation) (b) exposure to perchloric acid in aqueous tetrahydrofuran for eight days (c) reaction with dilute lithium hydroxide in H20-MeOH-THF (1 2 8) (d) treatment with tetra-n-butylammonium fluoride (TBAF) in tetrahydrofuran first, and then in THF-DMF and (e) exposure to dilute acetic acid in water (1 350) at 22 °C. The overall yield for the deprotection sequence (31 —>32) is ca. 35 %. 

A. Mercury(II) chloranilate method Discussion. The mercury(II) salt of chloranilic acid (2,5-dichloro-3,6-dihydroxy-p-benzoquinone) may be used for the determination of small amounts of chloride ion. The reaction is ... 

Dehydrogenation is a rarely used method for the production of fully unsaturated azepines, and there are no examples of its use for the formation of simple monocyclic systems, although 3-hydroxy- and 3-methoxy-2//-azepin-2-ones can be obtained by dehydrogenation of the corresponding l,5-dihydro-2//-azepin-2-ones with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in benzene in a sealed tube at 100 48-51-52-67... 

The dihydrodiazepine 3 obtained from diaminomaleonitrile and A. A -dimethylacrylamide is dehydrogenated to the diazepine 4 by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ).186... 

D. 2,5-Dichloro-3 fi-di-tert-but.yl-1,4-benzoquinone. A 2-1. Erlenmeyer flask is charged with a solution of 116.6 g. (0.357 mole) of 2,3,5-trichloro-3,6-di-ferf-butylcyclohex-5-enc-l,4 dione dissolved in 800 ml. of ether. To the vigorously swirled solution is added, in one portion, 26.2 g. (0.36 mole) of diethylamine dissolved in approximately 50 ml. of ether. The reaction, which is instantaneous, results in a voluminous... 

The solution may have a brown tint, partially masking the yellow color of the quinone. The dark color is probably due to reaction of the diethylamine with the 2,5-dichloro-3,6-di-fcr -butyl-l,4-benzoquinone. 

Theoretically there remains about 22% of product to be isolated. Some of this material can be recovered indirectly by converting it to the diazide. With 500 ml. of methanol the submitters diluted the mother liquor, which contains at most 23 g. (0.08 mole) of 2,5-dichloro-3,6-di-ter -butyl-l,4-benzoquinone, and then added, with swirling, a solution of 10.4 g. (0.16 mole) of sodium azide in 30 ml. of water over a 2-minute period. The yellow solution turns orange in color. It is cooled to —5° to —10°, and the resulting orange precipitate is collected to yield 12 g. of the diazide. The minimum yield is thus 88%. 

Cl2, ammonium nitrate on Clayfen, Oxone on wet alumina, silver nitrate and iodine,2,3-dichloro-5,6-dicyano -1,4-benzoquinone (DDQ) in acetonitrile... 

Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) and DDQ (2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone). The latter is more reactive and can be used in cases where the substrate is difficult to dehydrogenate. It is likely that the mechanism involves a transfer of hydride to the quinone oxygen, followed by the transfer of a proton to the phenolate ion °... 

Benzyloxybenzylamine (BOBA) 48 is a new class of an amine support and was prepared from Merrifield resin in two steps [56]. BOBA resin was treated with an aldehyde in the presence of an acid to give an imine that subsequently reacted with Yb(OTf)3-catalyzed silyl enolates (Scheme 18). Cleavage with trimethylsilyl triflate (TMSOTf) or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) gave either phenols or amines, respectively. 

EPR techniques were used to show (Polyakov et al. 2001a) that one-electron transfer reactions occur between carotenoids and the quinones, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), and tetrachlorobenzoquinone (CA). A charge-transfer complex (CTC) is formed with a -values of 2.0066 and exists in equilibrium with an ion-radical pair (Car Q ). Increasing the temperature from 77 K gave rise to a new five-line signal with g=2.0052 and hyperfine couplings of 0.6 G due to the DDQ radical anions. At room temperature a stable radical with y=2.0049 was detected, its... 

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