Liquid ammonia Subject

The Birch reduction of a benzenoid compound involves the addition of two electrons and two protons to the ring. The order in which these additions occur has been the subject of both speculation and study. Several reviews of the subject are available and should be consulted for details. The present discussion is concerned with summarizing data that is relevant to understanding the reaction from the preparative point of view. For convenience, reaction intermediates are shown without indicating their solvation by liquid ammonia. This omission should not obscure the fact that such solvation is largely responsible for the occurrence of the Birch reduction. 

Reduction of aromatic compounds to dihydro derivatives by dissolved metals in liquid ammonia (Birch reduction) is one of the fundamental reactions in organic chemistry308. When benzene derivatives are subjected to this reduction, cyclohexa-1,4-dienes are formed. The 1,4-dienes obtained from the reduction isomerize to more useful 1,3-dienes under protic conditions. A number of syntheses of natural products have been devised where the Birch reduction of a benzenoid compound to a cyclohex-1,3-diene and converting this intermediate in Diels-Alder fasion to polycyclic products is involved (equation 186)308f h. 

Similar experiments were carried out with 6-bromo-5-deuterio-4-phenylpyrimidine. When subjected to treatment of potassium amide/liquid ammonia, it was observed that the 6-aminopyrimidine did not contain deu-... 

Physical properties of the solvent are used to describe polarity scales. These include both bulk properties, such as dielectric constant (relative permittivity), refractive index, latent heat of fusion, and vaporization, and molecular properties, such as dipole moment. A second set of polarity assessments has used measures of the chemical interactions between solvents and convenient reference solutes (see table 3.2). Polarity is a subjective phenomenon. (To a synthetic organic chemist, dichloromethane may be a polar solvent, whereas to an inorganic chemist, who is used to water, liquid ammonia, and concentrated sulfuric acid, dichloromethane has low polarity.)... 

Certain octahedral complexes, particularly the acido—amine complexes of cobalt(III), undergo substitution in protonic solvents at rates that are proportional to the concentration of the conjugate base of the solvent (e.g. OH- in water) or inversely proportional to the concentration of the conjugate acid of the solvent (e.g. retardation by H30+ in water or NH4+ in liquid ammonia). Such reactions have received considerable attention since systematic studies of ligand substitution commenced, and figured amongst the earliest kinetic studies in the field.298 The subject has been... 

It is not surprising that the behavior of naphthyridines toward nucleophiles has been a subject of numerous studies1 8 and that nucleophilic substitution in naphthyridines has become a very valuable and efficient method to synthesize substituted naphthyridines. In the last decade many important and new features of nucleophilic substitution in naphthyridines using nitrogen nucleophiles (especially liquid ammonia and potassium amide/liquid ammonia) have been found. In view of these recent results it seems worthwhile to review this area of research. The present chapter is concerned with the reactions of naphthyridine with nitrogen nucleophiles for a full review of naphthyridine chemistry, see the chapter by Paudler and Sheets, p. 147 of this volume. 

For the same reasons as discussed for the 3-nitro-1,8-naphthyridines, addition at C-4 is strongly promoted. If position 4 is occupied, no addition takes place 4-amino-3-nitro-l,6- and -1,5-naphthyridine do not undergo addition at C-2 when subjected to treatment with liquid ammonia. It is interesting that 46a does not undergo covalent hydration in neutral nor in acidic medium.9... 

In 1799, M. van Marum5 tried the effect of press, on ammonia, and found that drops of liquid ammonia were produced at 3 atm. press. A. F. de Fourcroy and L. N. Vauquelin subjected ammonia to a low temp., and claimed to have liquefied the gas at —40°. L. B. Guyton de Morveau also cooled the gas to —43-25° and... 

E. P. Perman, D. P. Konowaloff, and H. Riesenfeld. The rate of escape of ammonia from aq. soln. when air is aspirated at a uniform rate through the liquid was represented by E. P. Perman by log q=a+bt, where q represents the amount of ammonia in the soln. at the time t and a and b are constants—vide infra. D. P. Konowaloff also made observations on this subject. A. Stock and E. Pohland, and H. Reiblen and K. T. Nestle used liquid ammonia in the tensimetric determination of mol. wts. For the vap. press, of aq. soln. of ammonia, vide infra. 

The mechanism of the chemical reduction of enones with metal (Li, Na, etc.) in liquid ammonia can be described by the following equation in which the substrate 212 receives two electrons from the metal to give the dianion intermediate 213. This intermediate is then successively transformed into the enolate salt 214 and the ketone 2T5 with an appropriate proton donor source. It can readily be seen that the stereochemical outcome of this reaction depends on the stereochemistry of the protonation step 213 - 214. An excellent review on this topic has been recently written by Caine (60). This subject will be only briefly discussed here. 

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