Ammonia solution, aromatic

C. A typical aromatic amine. Best prepared by the prolonged action of concentrated ammonia solution at a high temperature upon anthraquinone-l-sulphonic acid in the presence of BaClj and by reduction of the corresponding nitro compound or by amination of the chloroanthraquinone. 

Method (1) is most frequently used for aliphatic acid amides, while Methods (2a), (2b) and (zc) are used most frequently for aromatic acid amides. Of the last three methods, the Acid Chloride Method (zb) is the most rapid and certain. The Ester Method (za) is practicable only when the amide is insoluble in water, and even then is often very slow unless the ester itself is appreciabb soluble in the aqueous ammonia solution. 

Picrates, Many aromatic hydrocarbons (and other classes of organic compounds) form molecular compounds with picric acid, for example, naphthalene picrate CioHg.CgH2(N02)30H. Some picrates, e.g., anthracene picrate, are so unstable as to be decomposed by many, particularly hydroxylic, solvents they therefore cannot be easily recrystaUised. Their preparation may be accomplished in such non-hydroxylic solvents as chloroform, benzene or ether. The picrates of hydrocarbons can be readily separated into their constituents by warming with dilute ammonia solution and filtering (if the hydrocarbon is a solid) through a moist filter paper. The filtrate contains the picric acid as the ammonium salt, and the hydrocarbon is left on the filter paper. 

Birch s procedure for tropone synthesis appears to be widely applicable to 2,3- or 2,5-dihydroanisole derivatives which are readily obtained by reduction of appropriate aromatic methyl ethers by alcoholic metal-ammonia solutions. " Additional functional groups reactive to dibromocarbene or sensitive to base such as double bonds, ketones and esters would need to be protected or introduced subsequent to the expansion steps. 

The appropriate aromatic or heteryl- aldehyde (2 mmol freshly distilled if liquid) and 25% methanolic ammonia solution (5 mL) were added to a solution of 1-naphthol (1 mmol) in absolute MeOH (5 mL).The mixture was left to stand at ambient temperature for 2 days, during which oily products separated. The solvent was evaporated and the crade oily products were purified by column chromatography. The physical data for the compounds la-f are listed Table 39.1. 

Physical chemical studies of dilute alkali metal-ammonia solutions indicate the principal solution species as the ammoniated metal cation M+, the ammoniated electron e , the "monomer M, the "dimer" M2 and the "metal anion" M. Most data suggest that M, M2, and M are simple electrostatic assemblies of ammoniated cations and ammoniated electrons The reaction, e + NH3 - lf 2 H2 + NH2 is reversible, and the directly measured equilibrium constant agrees fairly well with that estimated from other thermodynamic data. Kinetic data for the reaction of ethanol with sodium and for various metal-ammonia-alcohol reductions of aromatic compounds suggest that steady-state concentrations of ammonium ion are established. Ethanol-sodium reaction data allow estimation of an upper limit for the rate constant of e + NH4+ 7, H2 + NH3. 

In view of the mechanism suggested above for the ethanol-sodium reaction, it seems likely that reduction of aromatic compounds by solutions of alcohols and alkali metals in liquid ammonia proceeds by a general mechanism involving a steady-state concentration of ammonium ion. Krapcho and Bothner-By (29) observed that the reduction of benzene and several substituted benzenes in lithium-alcohol-ammonia solutions,... 

Alcoholysis of amides was first reported for the preparation of alkaline alkoxides. The reaction was carried out in liquid ammonia solutions and was aimed at the obtaining of the derivatives of aromatic alcohols ... 

A. J. Birch and G. Subba Rao (1972). Reduction by metal-ammonia solutions and related reagents , in Advances in Organic Chemistry. Ed. E. C. Taylor, New York Wiley-Interscience, Vol. 8, p. 1. See also A. A. Akhrem, I. G. Reshetova and Y. A. Titov (1972). Birch Reduction of Aromatic Compounds. New York IFI/Plenum. 

Aromatic hydrocarbons react with chlorosulphonic acid to yield the corresponding sulphonyl chlorides (the process is known as chlorosulphonatiori). These do not usually crystallise well and are therefore converted into the sulphona-mides by treatment with concentated ammonia solution or with solid ammonium carbonate. (See also Section 6.4.2, p. 877.)... 

In order to prepare these macrocycles it was necessary to synthesize the previously unknown o -bis(phosphino)benzene (IV). Lithium aluminum hydride reduction of the o-bis(phosphonate) III gave IV in 50% yield (31P NMR, 6 -123.8 ppm, Jpy = 207 Hz). The phosphonate III could be obtained in modest yields by the photo-activated nucleophilic aromatic substitution by sodium diethyl-phosphite on o-chloroiodobenzene in liquid ammonia solution (4). 

Since amines are organic bases, water solutions show weakly basic properties. If the basicity of aliphatic amines and aromatic amines are compared to ammonia, aliphatic amines are stronger than ammonia, while aromatic amines are weaker. Amines characteristically react with acids to form ammonium salts the nonbonded electron pair on nitrogen bonds the hydrogen ion. 

The Birch reduction involves twice adding a solvated electron, followed by a proton, to the aromatic ring. Preceding step Formation of solvated electrons in the ammonia solution. 

Equation 5 is known as the Birch reduction. This reaction is mediated by Group 1 metals (usually sodium) in a liquid ammonia solution in the presence of a certain amount of alcohol. The net result is also the addition of hydrogen, but in this case only two hydrogen atoms are added. The reason for this peculiarity becomes apparent upon examination of the mechanism of this process. When a metal like sodium is dissolved in liquid ammonia, it dissociates into a sodium cation and a solvated electron (Scheme 2.6). The first step in the Birch reduction is the attack of the solvated electron on the aromatic system of toluene to... 

Aromatic acids are reduced by metal-ammonia solutions very much more readily than simple hydrocarbons and ethers. In contrast to the normal requirements for the latter derivatives, it is often possible to achieve reduction with close to stoichiometric quantities of metal. The addition of aromatic carboxylic acids to liquid ammonia (or vice versa) results in the immediate precipitation of the ammonium salt. As the metal is added, however, the precipitate usually dissolves as reduction proceeds, especially if lithium is used. If reduction is carried out in carefully dried, redistilled ammonia, as little as 2.2 mol of lithium are consumed in some cAses, thereby demonstrating that the substrate is reduced much more readily than the ammonium ions, which instead react with the intermediates from reduction of the substrate. However, protonation by NH4 is not essential since reduction proceeds equally well on preformed metal car-boxylates (although low solubility is then often a problem). The addition of an alcohol is not necessary, but it may serve as a useful buffer and can often improve solubility. The presence of alcohol can nevertheless be deleterious, since it facilitates isomerization of the initially formed 1,4-dihydro isomer to the 3,4-isomer and in this way affords the possibility of further reduction. ... 

A new, mild and general method for the synthesis of aryl-substituted-1,3,5-triazines from aromatic aldehydes and ammonia has been found. Treatment of a 1 1 pyridine, concentrated ammonia solution of aromatic aldehyde with excess of Fremy s salt at room temperature gave a readily separable mixture of a primary amide and 1,3,5-triazine (189). A,A-Dibenzylidenephenyl-methanediamine (190) on similar treatment produced almost identical results (Scheme 56) <85S95>. Extension of the reaction to aliphatic aldehydes does not appear to be possible as attempts to oxidize 2,4,6-trimethyl-hexahydro-1,3,5-triazine with Fremy s salt gave rise to complex mixtures, in low yield. 

Trimerization of nitriles, isocyanates, isothiocyanates, imidates, and carbodiimides all lead to symmetrical 2,4,6-trisubstituted 1,3,5-triazines (see Section 6.12.9.5). The use of lanthanide trifluoromethanesulfonate and ammonia as cocatalysts is claimed as a big improvement. The trisaminal of 2,4,6-triformyl-l,3,5-triazine is also useful for further derivatization to unusual structures (see Section 6.12.7.1). Treatment of a 1 1 pyridine/conc. ammonia solution of an aromatic aldehyde with excess Fremy s salt is another development. Separation of the amide coproduct was claimed to be easy. The synthesis fails with aliphatic aldehydes (see Section 6.12.9.5.4). Aminolysis of 2,4,6-triaryl-1,3,5-oxadiazinium salts gives symmetrical 1,3,5-triazines but the reactions are limited in that electron-withdrawing groups in the aromatic rings lead to instability and difficulty in separation of products (see Section 6.12.10.4). 

The ammonia and amine solutions of alkali metals are widely used pre-paratively in both organic and inorganic chemistry. Thus lithium in methyl-amine shows great selectivity in its reducing properties, but both this reagent and lithium in ethylenediamine are quite powerful and can reduce aromatic rings to cyclic monoolefins. Sodium in liquid ammonia is probably the most widely used system for preparative purposes. The ammonia solution is moderately stable, but the decomposition reaction Na+NH3(1) = NaNH2 + iH2... 

Thioureas are obtained analogously by boiling an amine hydrochloride and an alkali thiocyanate in aqueous solution66 or an amine and a thioiso-cyanate in alcohol 67 aromatic thioisocyanates generally react even in the cold. Further, aqueous ammonia solutions are converted smoothly into mono-alkylthioureas by isothiocyanates.68 Isothiocyanates can be converted directly into symmetrical thioureas by boiling them in aqueous dimethylformamide or dimethyl sulfoxide the thiocarbamic acids formed as intermediates by partial hydrolysis add to unchanged isothiocyanate with loss of COS.69... 

Thus, optimum experimental conditions will be determined by how a particular polynuclear aromatic compound fits into Scheme IV. Burkholder and I (8) suggested the following categories on the basis of the principal intermediate that persists in ammonia solution ... 

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