Chloranil Subject

Dioxazine Violet. Carba2ole Dioxa2ine Violet is prepared by the reaction of two moles of 2-ainino-A/-ethylcarba2ole with chloranil. This violet may be used in most plastics for shading phthalocyanine blues, because it has comparable light fastness. At relatively high temperatures, it may be subject to slow decomposition. 

A reaction time of one hour at —7° to — 10°C was found to give maximum yields of 7a-methyl compounds. In some cases it is necessary to subject the reaction mixture to chloranil dehydrogenation this transforms (32) to the A -compound, thereby facilitating separation of the 7a-methyl isomer (31). The latter isomer is not attacked by the quinone since it lacks an axial hydrogen at C-7. 

The kinetics of these pyrolysis reactions were followed by several complementary methods under conditions as close to the product studies as possible. The most frequently-used ampule technique14 17) with gc analysis of 5 and the scavenger technique, with chloranil or Koelsch radical as scavenger 18), for very labile compounds 5 were complemented by the DSC method, in which the heat flow under conditions of linear temperature increase is analysed. It proved to be a particularly convenient and reliable technique 18- 21). Rates were followed over a temperature span of at least 40 °C with temperature control of 0.1-0.2 °C. All rate data and activation parameters were subjected to a thorough statistical analysis including statistical weights of errors. The maximum statistical errors in k were 3%, in AH 1 kcal mol-1 in AS 513 e.u. and in AG (at the temperature of measurement) g0.5 kcal mol-1. 

The synthesis of the novel tetrafuran-containing macrocycle 4.178 was reported in 1992. This macrocycle was prepared by the aldol-type condensation between diketone 4.176 and dialdehyde 4.177 in 20% yield (Scheme 4.5.2). Subjecting this macrocycle to reductive deoxygenation using lithium aluminum hydride and aluminum trichloride afforded the tetraoxaporphyrinogens-(3.0.3.0) 4.179 and 4.180 in combined 35% yield (Scheme 4.5.3). These two isomeric products, formed in 55% and 45% relative abundance, respectively, could not be readily separated. Instead, they were treated together (i.e., as a mixture) with p-chloranil to afford the conjugated tetraoxa[22]porphyrin-(3.0.3.0) species 4.181 in 15% yield (Scheme 4.5.4). 

Cycloaddition reactions of alkene radical cations have been the subject of a number of mechanistic studies and are potentially useful synthetic reactions. - - - Most of the initial work on radical cation mediated cycloadditions focused on the dimerization of arylalkenes. with one of the first examples being Ledwith s report of the chloranil-sensitized dimerization of M-vinylcarba-zole to generate a diarylcyclobutane. This work led to the development of the mechanism outlined in Scheme 2, in which addition of the radical cation to neutral alkene generates an acyclic 1,4-radical cation as the primary intermediate. This intermediate cyclizes to a cyclobutane radical cation that is then reduced by the neutral alkene and regenerates a second radical cation to carry the chain. 

For electromotive force measurements there are many suitable electrodes, and only the most novel features can be summarised here. The glass electrode is generally usable in these solvents. It has been found that in solutions of hydrochloric acid in anhydrous acetic acid, the glass electrode is subject to acid errors of as much as 70 mV relative to the chloranil electrode, owing to the incorporation of chloride ions in the surface gel layer of the glass. ° Since ethylenediamine reacts with calomel but not with mercury (II) chloride, a suitable reference electrode for this solvent can be constructed of a mercury pool in contact with ethylenediamine saturated with respect to both HgClg and LiCl. °... 

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