Wallach

The formation of a sulfur-containing ring was justified by the attack of the halogenated carbon of the cMoroacetyl derivative by the sulfur atom of thiourea, a fact in accordance with the results just discussed by Wallach (49,50) and Claus (51). The new formula (37) of thiohydantoine explained why, contrary to thiourea, its desulfuration was difficult. 

The German chemist Otto Wallach (Nobel Prize m chemistry 1910) determined the structures of many terpenes and is credited with setting forth the isoprene rule ter penes are repeating assemblies of isoprene units normally joined head to tail... 

Wagner equation Wagner number Wakamatsu reaction Waldhof fermentor Walkman Wallace plasticity Wallach procedure Wall baffles Wallboard Wall geometries Wallpaper paste Wallpaper pastes Wallpapers Wall plaster Walnut oil... 

FAWORSKI WALLACH Rearrangement Reanangement of a-haloketones or a,a -dihalokeiones to acids or acrylic adds (via cyclopropanones). 

LEUCKART - WALLACH ReductiveAmination Reductive amination of cartx)nyi groups with amines arxl formic add or Hj-NI (Miquonac) or NaBH4 (see Botch). 

Ruzicka s modiftcation of Wallach s original directions for the rearrangement of the oxime. 

The present procedure was developed from those of Wallach and Freylon, based upon the general method discovered by Leuckart. a-Phenylethylamine also can be prepared satisfactorily by the reduction of acetophenone oxime with sodium and absolute alcohol or sodium amalgam, but the reagents are more expensive and the processes less convenient. The amine has been obtained by reducing acetophenone oxime electro-lytically, by reducing acetophenone phenylhydrazone with sodium amalgam and acetic acid, from a-phenylethyl bromide and hexamethylenetetramine, and by the action of methyl-magnesium iodide upon hydrobenzamide, as well as by other methods of no preparative value. 

The discovery of the Balz-Schiemann reaction in 1927 replaced the earlier Wallach procedure (1886) based on fluorodediazoniation of arenediazonium piper-idides (aryltriazenes) in aqueous hydrogen fluoride [40 41]... 

Applications in agrochemicals [42, 43], pharmaceuticals [44,45], and positron emission tomography (PET) [46, 47, 48 49] have resulted in the resuscitation of the Wallach reaction The Wallach technique provides high-specific-activity F-radiolabeled aromatic fluoride for PET studies, in contrast to the low-specific-ac-tivity product by the Balz-Schiemann route... 

An illustration of a modified Wallach fluorination is the synthesis of 2 4 di chloro-5-fluorotoluene, an intermediate in the preparation of the fluoroquinolone antibacterial ciprofloxacin This was prepared in 69% overall yield by heating W(2,4-dichloro-5-methylphenyl) N, N dimethyltriazene in anhydrous hydrogen fluoride [44] (equation 11)... 

A variety of media have been used for the Wallach fluorination reaction anhydrous hydrogen fluoride alone or with cosolvents such as methylene chloride, benzene, or tetrahydrofuran and hydrogen fluoride-pyridine alone or with co solvents such as benzene, glyme, or acetic acid [42,43, 46 50] Solutions of cesium fluoride, tetraethylammonium fluoride, or tetrabutylammonium fluoride in strong acids such as methanesulfonic acid or trifiuoroacetic acid with numerous cosolvents have also been studied [48, 49]... 

A recently discovered variant of the Wallach technique is the silver ion cata lyzed fluorination of aryl diazo sulfides in hydrogen fluonde-pyridine-toluene solvent [57] (equation 12) Electron withdrawing substituents such as acetyl give higher yields of aryl fluoride (71%) than electron donating groups (butyl 39%, methoxy, 2-14%), reductive dediazoniation competes with fluorination... 

H. Reaction with Formic and Trichloroacetic Acids Enamines derived from aldehydes have been treated with formic acid under the conditions of the Leuckart-Wallach reaction 141) to give saturated tertiary amines 142). The enamine (98) reacts vigorously with formic acid at room temperature to give N-isobutyl morpholine (204). 

The previous sections have dealt with stable C=N-I- functionality in aromatic rings as simple salts. Another class of iminium salt reactions can be found where the iminium salt is only an intermediate. The purpose of this section is to point out these reactions even though they do not show any striking differences in their reactivity from stable iminium salts. Such intermediates arise from a-chloroamines (133-135), isomerization of oxazolidines (136), reduction of a-aminoketones by the Clemmensen method (137-139), reductive alkylation by the Leuckart-Wallach (140-141) or Clarke-Eschweiler reaction (142), mercuric acetate oxidation of amines (46,93), and in reactions such as ketene with enamines (143). 

It has been shown (140) that enamines react as well, if not better, under the conditions of the Leuckart-Wallach reaction to give amines than do ketones in the presence of ammonia, primary amines, or secondary amines. This implies that in the Leuckart-Wallach reaction the pathway may be through the enamine and, of course, the iminium salt. The Leuckart-Wallach reaction has been reviewed (141). Examples of enamines reduced under the conditions of the Leuckart-Wallach reaction are listed in Table 12. 

O. Wallach (Gottingen) pioneer work in the field of alicyclic compounds. 

By application of the Leuckart-Wallach reaction,amines 2 can be alkylated with a carbonyl compound 1 formic acid is used as reductive agent, and is in turn oxidized to give carbon dioxide. 

The usual procedure is to simply heat a mixture of the starting materials. A common side-reaction is the polyalkylation it can be suppressed by employing an excess of amine. In addition carbonyl substrates with a-hydrogens may undergo competitive aldol reactions the corresponding reaction products may then undergo a subsequent Leuckart-Wallach reaction. 

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