S. Chloranil

The radical cation of 1 (T ) is produced by a photo-induced electron transfer reaction with an excited electron acceptor, chloranil. The major product observed in the CIDNP spectrum is the regenerated electron donor, 1. The parameters for Kaptein s net effect rule in this case are that the RP is from a triplet precursor (p. is +), the recombination product is that which is under consideration (e is +) and Ag is negative. This leaves the sign of the hyperfine coupling constant as the only unknown in the expression for the polarization phase. Roth et aJ [10] used the phase and intensity of each signal to detemiine the relative signs and magnitudes of the... 

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.)... 

Dipping solution Dissolve O.S g p-chloranil in 90 ml ethyl acetate, cautiously make up to 100 ml with 10 ml sulfuric acid (ca. 96<9b) and homogenize for S min in the ultrasonic bath or by vigorous shaking. 

Note It is reported that the use of chlorobenzene as solvent is essential when the agent is to be used to detect aromatic amines [1]. In the case of steroids, penicilt diuretics and alkaloids the reaction should be accelerated and intensifled by spr afterwards with dimethylsulfoxide (DMSO) or dimethylformamide (DMF), indeed i step makes it possible to detect some substances when this would not otherwise be p sible [5,9-11] this latter treatment can, like heating, cause color changes [S, 9]. Peni lins and diuretics only exhibit weak reactions if not treated afterwards with DMF 11]. Steroids alone also yield colored derivatives with DMSO [9]. Treatment afterws with diluted sulfuric acid (c = 2 mol/L) also leads to an improvement in detection s sitivity in the case of a range of alkaloids. In the case of pyrrolizidine alkaloids i possible to use o-chloranil as an alternative detection reagent however, in this cas is recommended that the plate be treated afterwards with a solution of 2 g 4-(dimet] amino)-benzaldehyde and 2 ml boron trifluoride etherate in 100 ml anhydrous etha because otherwise the colors initiaUy produced with o-chloranil rapidly fade [12]. 

Khashaba et al. [34] suggested the use of sample spectrophotometric and spectrofluorimetric methods for the determination of miconazole and other antifungal drugs in different pharmaceutical formulations. The spectrophotometric method depend on the interaction between imidazole antifungal drugs as -electron donor with the pi-acceptor 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, in methanol or with p-chloranilic acid in acetonitrile. The produced chromogens obey Beer s law at Amax 460 and 520 nm in the concentration range 22.5-200 and 7.9-280 pg/mL for 2,3-dichloro-5,6-dicyano-l,4-benzoquinone and p-chloranilic acid, respectively. Spectrofluorimetric method is based on the measurement of the native fluorescence of ketoconazole at 375 nm with excitation at 288 nm and/or fluorescence intensity versus concentration is linear for ketoconazole at 49.7-800 ng/mL. The methods... 

Mahrous et al. [43] determined primaquine and other antimalarials by use of chloranilic acid for the colorimetry. Primaquine was treated with 0.2 chloranilic acid solution in acetonitrile to give a purple solution with absorption maximum at 522 nm. Beer s law was obeyed from 0.04 to 0.2 mg/mL. Analysis of pharmaceutical formulation by this method is as accurate as the official method. 

An alternative new synthetic approach to chrysene 1,2-dihydro-diol based on Method IV has recently been developed (60). This method (Figure 12) entails synthesis of 2-chrysenol via alkylation of 1-1ithio-2,5-dimethoxy-1,4-cyclohexadiene with 2-(1-naphthyl) e-thyl bromide followed by mild acid treatment to ge nerate the diketone 12. Acid-catalyzed cyclization of 12 gave the unsaturated tetracyclic ketone 13 which was transformed to 2-chrysenol via dehydrogenation of its enol acetate with o-chloranil followed by hydrolysis. Oxidation of 2-chrysenol with Fremy s salt gave chrysene... 

In dichloromethane, the acidic ESE cation radical undergoes a rapid proton transfer (k = 1.9 x 109 s ) to the CA anion radical within the contact ion pair (CIP) to generate the uncharged radical pair (siloxycyclohexenyl radical and hydrochloranil radical) in Scheme 6. Based on the quantum yields of hydro-chloranil radical (HCA ), we conclude that the oxidative elimination occurs by geminate combination of the radical pair within the cage as well as by diffusive separation and combination of the freely diffusing radicals to yield enone and hydrochloranil trimethylsilyl ether, as summarized in Scheme 6. 

Fig. 3 Transient spectra obtained upon the application of a 200-fs laser pulse to a solution of stilbene (S) and chloranil (Q) in dioxane. (a) The fast decay ( 20 ps) of the contact ion-radical pair S+ , Q generated by direct charge-transfer excitation (CT path), (b) The slow growth ( 1.6 ns) of the ion pair S+ Q due to the diffusional quenching of triplet chloranil (A path) as described in Scheme 13. Reproduced with permission from Ref. 55.

We emphasize that the critical ion pair stilbene+, CA in the two photoactivation methodologies (i.e., charge-transfer activation as well as chloranil activation) is the same, and the different multiplicities of the ion pairs control only the timescale of reaction sequences.14 Moreover, based on the detailed kinetic analysis of the time-resolved absorption spectra and the effect of solvent polarity (and added salt) on photochemical efficiencies for the oxetane formation, it is readily concluded that the initially formed ion pair undergoes a slow coupling (kc - 108 s-1). Thus competition to form solvent-separated ion pairs as well as back electron transfer limits the quantum yields of oxetane production. Such ion-pair dynamics are readily modulated by choosing a solvent of low polarity for the efficient production of oxetane. Also note that a similar electron-transfer mechanism was demonstrated for the cycloaddition of a variety of diarylacetylenes with a quinone via the [D, A] complex56 (Scheme 12). 

Two acylation reactions as depicted in Schemes 12.7 and 12.8 had the same issue when monitored by single bead FTIR (Fig.s 12.11 and 12.12). The starting resins (13) and (15) did not have convenient signal to monitor by FTIR. A chloranil test [15] specific for the secondary amines was used to confirm the complete consumption of (13), therefore the reaction completion. An iron-chloride-pyridine test [16] was used to confirm the complete consumption of (15). In both color tests, a blue color would suggest the presence of the starting material. In both cases we observed the disappearance of the blue color that indicated the reaction completion. 

Figure 4, PMR spectra (90 MHz) observed during the irradiation of chloranil (0.02 M) in acetonitrile-d3 solutions containing 0.02 M trans- (top) or c/s-diphenylcyclo-propane (bottom), respectively. ...

Figures, h CIDNP spectra (cyclopropane resonances) observed during the electron transfer photoreaction of chloranil with c/s-1,2-diphenylcyclopropane (fop) and ben-zonorcaradiene (.bottom). The opposite signal directions observed for analogous protons in the two compounds constitute evidence that the two radical cations belong to two different structure types.

Following the structure proof of the alkaloids by degradation, Hughes et al. (.18) synthesized (—)-0-methylcryptaustoline iodide (14) by methods elaborated by Schopf and Robinson. ( )-Laudanosine was resolved by quinic acid (79), and (S)-(-)-laudanosine was 0-demethylated by Schopf s procedure, oxidized by chloranil, and remethylated to afford chiral 14 as the iodide in 40% yield. Their product had the same specific rotation and melting point as O-methylcryp-taustoline iodide obtained from the natural alkaloid 1. Methine derivatives obtained from synthetic and natural compounds had identical optical properties. 

Stadeler s discovery of the formation of chloranil from tyrosine led to the supposition that tyrosine was a derivative of salicylic acid, and on this assumption Schmidt and Nasse attempted to synthesise tyrosine from ethylamine and iodosalicylic acid, and from amidosalicylic and ethyl iodide, but did not succeed. On heating tyrosine they obtained a base CgHuNO, which they thought analogous to the one Schmidt had obtained by heating amidosalicylic acid on this account they held to the accuracy of the theory that tyrosine was ethylamidosalicylic acid. 

Koshihara S, Tokura Y, Mitani T, Saito G, Koda T (1990) Photoinduced valence instability in the organic molecular compound tetrathiafulvalene-p-chloranil (TTF-CA). Phys Rev B42 6853-6856... 

Another very instructive case concerns the alleged initiation of a cationic polymerisation by a charge-transfer complex formed by the compound chloranil (2,3,5,6-tetrachloroquinone) with the monomer N-vinyl-carb-azole. It was shown (Natsuume et al., 1969 1970) that this compound is not an initiator, but that the polymerisations were caused by a hydrolysis product, 2-hydroxy-3,5,6-trichloroquinone, which is a strong acid. One has learnt from this finding to be extremely suspicious of any claims for charge-transfer catalysis and to test one s suspicions by appropriate experiments involving progressive purification of the putative catalyst. 

Chloranilic acid (2,5-dichIoro-3,6-dihydroxy-l,4-benzoquinone) [87-88-7] M 209.0, m 283-284°. A soln of 8g in 1L 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 10ml portions of water, and dried at 115°. It can be sublimed in vacuum. pKa25 1.22 and 3.01 in H20 [JPC 61 765 1957]. The diacetate has m 182-185° [7/tC.S 46 1866 7924 Thamer and Voight JPC 56 225 7952],... 

Dehydrogenation of 1,2-dehydropyrroltzidines. Oxidation of retronecine (1) with Fremy s salt gives dehydroretronecine (2) in satisfactory yield.2 This oxidation has been conducted with chloranil, manganese dioxide, and potassium permanganate, but yields are lower.3... 

Aromatizations play a particularly prominent role in the synthesis of carbazoles since both the Fischer cyclization (Borsche s method) of cyclohexanones (Section 3.06.3.4.2) and the cycloaddition of 2-vinylindole (Section 3.06.6.1) yield tetrahydrocarbazoles. Both catalytic dehydrogenation over palladium/carbon catalyst and dehydrogenation with chloranil have been employed to effect aromatization (80JA4772,79JOC4402). 

---