Additives Elbs reaction

More recently, Newman reported the attempt to synthesize a variety of methylcholanthrene derivatives. The work reported confirmed the above work and determined additional sites in which elimination of certain groups occurred. The authors were able to synthesize the corresponding 8-fluoro-and lO-fluoro-3-methylcholanthrenes 42 and 44 via the Elbs reaction in 21% and 47% yields from the corresponding ketones 41 and 43, respectively. However, the Elbs reaction starting with appropriately substituted substrates failed to provide the corresponding 10-methoxy, 11-methoxy, 11- fluoro- and 12-fluoro-3-methylcholanthrene derivatives. The 8-methoxy- and 9-methoxycholanthrene derivatives have previously been reported. 

Reduction of substituted nitrobenzenes under alkaline conditions, usually with aqueous sodium acetate as electrolyte and a nickel cathode, is the classical method due to Elbs [45] for the formation of azo- and azoxy-compounds. Protons are used in the electrochemical reaction so that the catholyte becomes alkaline and under these conditions, phenylhydroxylamine reacts rapidly with nitrosobenzene to form azoxybenzene. Finely divided copper has long been known to catalyse the reduction of nitrobenzene to aniline in alkaline solution at the expense of azoxybenzene production [46]. Modem work confirms that whereas reduction of nitrobenzene at polycrystalline copper in alkaline solution gives mainly azoxybenzene, if the electrode is pre-oxidised in alkaline solution and then reduced just prior to the addition of nitrobenzene, high yields of aniline are obtained with good current efficiency... 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

In addition to the small dependence of the second limit on vessel surface, Table 6 also shows a small dependence of the limit on the vessel size. Thus, Lewis and von Elbe [4] quote a variation in the second limit for 2H2 + O2 from 88 torr with a 10 cm diameter spherical KCl coated vessel at 530 °C to 68 torr for a 1.8 cm diameter vessel. They invoke a special mechanism for this, involving the postulated reaction H + O2 +... 

The reaction is autocatalytic, resembling in this respect the situation already encountered with uncoated quartz or glass vessels. However, in contrast with the results of Lewis and von Elbe [23] for a quartz vessel, Baldwin and Mayor [45] found little or no effect of addition of up to 22 torr added water on either the induction period or the maximum rate, irrespective of whether the water was added a short time before, or together with, the reactants themselves. They concluded that the autocatalytic effect cannot be due to poisoning (by absorption of water vapour produced in the reaction) of the ability of the surface to destroy chain centres, as had previously been suggested. 

Chloroform and Bromoform are formed if the chloride or bromide of the alkalies is used (comp. Elbs and Herz, who deny this ). Analogous to these substitution reactions is the formation of aristol, a di-thymol-di-iodide, as made by Messinger and Vortmann, by the electrolysis of thymol with the addition of potassium iodide. Similar to this also is the preparation of nosophene, a tetra-iodo-phenol-phthalein (Classen and L6b ). 

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