Anils, reduction

Temperature control at -15° to -25°C was also required for maximum yield. The best results were obtained by maintaining a temperature of -20 to -25°C during the addition of citral anil to the acid and at -15°C for the duration of the reaction. At this temperature range, the formation of a-cyclocitral (III) is favored. Higher temperatures caused excessive polymer formation and favored formation of e-cyclocitral whereas lower temperatures caused a reduction 1n the yield of the citral mixture. At least part of the problem with the lower temperature reaction was the fact that the sulfuric acid tended to freeze around the inside of the reaction vessel causing the effective molar ratio of acid to anil to be reduced. These lower temperature reaction mixtures were also lighter in color which indicated less polymer formation but this was accompanied by a lower yield of cyclocitrals. 

Fry and Newberg 1,2> examined the electrochemical reduction of nor-camphor oxime (109) and camphor oxime (110) to the corresponding amines. The results of this study are shown in Table 3. It is clear from a comparison of these data with those in Table 2 that the electrochemical reduction of oximes 109 and 110 takes a very different stereochemical course from reduction of the corresponding anils 103 and 104. Reduction of oximes apparently proceeds under kinetic control, affords products corresponding to protonation at carbon from the less hindered side of the carbon-nitrogen double bond, and affords the less stable epimeric amine in each case. It is not evident why the stereochemistry of reduction of anils and oximes should differ, however. 

Aniline-based amino-squaraines 40 can be obtained via reduction of oxo-squar-aines with NaBFLj in methanol followed by substitution and oxidation with chlor-anil or lead dioxide [106] (Fig. 11). 

The carbon-nitrogen double bond in imines is reduced at less negative potentials than the corresponding carbonyl function. Also imine radical-anions are more basic than carbonyl radical-anions. Imines with at least one phenyl substituent on the carbon-nitrogen double bond are sufficiently stable for examination in aprotic solvents and reversible one-electron reduction of benzaldehyde anil [179] or benzophenone anil [ISO] can be demonstrated with rigorous exclusion of moisture. 

Figure 7. First derivative ESR spectra of radical anions observed in dimethyl sulfoxide solutions of potassium tert-butoxide. Top, autoxidation product of diphenylamine. No signal was observed in the absence of oxygen. Middle, autoxidation of 4-hydroxy-diphenylamine. Bottom, spontaneous reduction product of mono-anil of p-benzoquinone.

I mm your understanding of the inert-pair clfeci anil the redox properties ol TI and I >. consider the apparent oxidation stale of 11 ui the compound I II and indicate what the realistic value is. flic standard reduction potential for the Tlm Tl1 couple is >. 25 V. 

The reduction potentials lor Ln Ln couples were estimated anil the factors identified which make them very negative. 

SONN-MIJLLER METHOED. Preparation of aromatic aldehydes from anilides by conversion of an acid anilide with phosphorus pentachloride to an imido chloride, reduction of die lmido chloride with stannous chloride, and hydrolysis of the obtained anil. 

The iV-methylamine (160) (R = Me) gives a complex mixture of products when treated under the same conditions.186 It was shown subsequently that prior reduction of the anils used as starting materials is, in fact, unnecessary since in the presence of potassamide in liquid ammonia (o-chlorobenzylidene)aniline forms phenanthridine in excellent yield, and the analogous anils from p-toluidine and a-naphthylamine undergo ring closure under similar conditions. In view of the known trans geometry of the anils and the unlikelihood of trans-cis equilibration under these conditions this reaction deserves further study.187 Potassamide in liquid ammonia also converts 2-bromo-iV-ethyl-3 -hydroxybenzanilide (162) into a mixture of iV-ethyl-3-(164) and N-ethyl-1 -hydroxyphenanthridone (165), probably via the aryne (163).188... 

In the case of phenanthridine itself, this has been achieved by reduction with lithium aluminum hydride211 presumably stoichiometric quantities were employed since the hydride can reduce phenanthridine to its 5,6-dihydro derivative.212 In a procedure which has been adopted more widely, an excess of lithium aluminum hydride is employed and the resultant 5,6-dihydrophenanthridine is dehydrogenated catalytically or,213 better, with an excess of chlor-anil.102, 200 Oxidation with aqueous potassium permanganate has been employed for the second stage,139 but the method does not appear to be general.22... 

By Reduction of Anils or Oximes of Pyrazine Aldehydes or Ketones... 

Gurtius and co-workers studied the acid-catalysed decomposition of alkyl azides such as benzyl azide. This was decomposed in either warm 1 1 (v/v) sulphuric acid-water or with concentrated hydrochloric acid to give a mixture of products corresponding to hydrogen migration [benzaldiinine (1)], phenyl migration [formaldehyde anil (2)], the azide reduction product [benzylamine (3)], and the solvolysis product [benzyl alcohol (4)]. The first two were obtained as the... 

The electrochemical reduction of nitrosobenzene in THE in the presence of fluorene or indene gives a mixture of an anil, a nitrone, and azoxybenzene and requires only a catalytic amount of electricity. The hydrocarbons act as proton donors and the anion thus formed add to nitrosobenzene [167]. The pK of the radical anion in water has been measured by pulse radiolysis to 11.7 [168]. 

In nonaqueous solution azomethine compounds are usually stable, and several types have been reductively coupled with alkyl halides or carbon dioxide. Benzophenone anil (III) gives thus on reduction in DMF-TBAI in the presence of methyl chloride a mixture of N- and C-methylated and N,C-dimethylated products [28] ... 

Reduction of an azomethine group to an amine and ring closure occurs in the reduction of phenolphthalein oxime (XVIII) and similar very stable anils [64] ... 

In the laboratory of S. Gupta, the synthesis of novel heterocyclic ring systems was accomplished utilizing the Combes reaction The condensation of 1-naphthylamine with 2-acylindan-1,3-diones produced the corresponding anils in good yield. The anils were cyclodehydrated to benz[/ ]indeno[2,1-c]quinoline-7-ones in the presence of polyphosphoric acid. Subsequent Wolff-Kishner reduction gave rise to the novel 7H-benzo[/ ]indeno[2,1-c]quinolines. 

N,N-Dimethyl-p-phenylenediamine, p-(CH3)sNCeH4NHz. Mol. wt. 136.20, m.p. 38°. Supplier Eastman. Prepared by reduction of N,N-dimethyl-)3-nitrosoaniline with zinc dust in ethanol in the presence of ammonium chloride. The reagent combines with aromatic aldehydes to give crystalline, colored anils suitable for identification. It does not react with ketones for example acetone can be used as... 

Triethyl phosphite also effects reductive cyclization of the anil (1) to the imidazole (2). 3... 

Formation of a cyanoformamidine by treatment of a symmetrical diphenylthiourea with potassium cyanide in alcohol containing lead carbonate, reduction with ammonium sulfide, and ring closure with concentrated sulfuric acid to isatin-2-anil also formed smoothly by ring closure of the cyanoformamidine with aluminum chloride in benzene or carbon disulfide. 

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