Group liquid ammonia

In organic chemistry the term refers to compounds containing the NH2 ion or the > NH group. These are prepared by the action of heat on amides or by metathetica reactions in liquid ammonia. The heavy metal imides are explosive. 

The less hindered f/ans-olefins may be obtained by reduction with lithium or sodium metal in liquid ammonia or amine solvents (Birch reduction). This reagent, however, attacks most polar functional groups (except for carboxylic acids R.E.A. Dear, 1963 J. Fried, 1968), and their protection is necessary (see section 2.6). 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

A useful alternative to catalytic partial hydrogenation for converting alkynes to alkenes IS reduction by a Group I metal (lithium sodium or potassium) m liquid ammonia The unique feature of metal-ammonia reduction is that it converts alkynes to trans alkenes whereas catalytic hydrogenation yields cis alkenes Thus from the same alkyne one can prepare either a cis or a trans alkene by choosing the appropriate reaction conditions... 

Group I metals—sodium is the one usually employed—in liquid ammonia as the solvent convert alkynes to trans alkenes The reaction proceeds by a four step sequence in which electron transfer and proton transfer steps alternate... 

We saw m Section 9 10 that the combination of a Group I metal and liquid ammonia is a powerful reducing system capable of reducing alkynes to trans alkenes In the pres ence of an alcohol this same combination reduces arenes to nonconjugated dienes Thus treatment of benzene with sodium and methanol or ethanol m liquid ammonia converts It to 1 4 cyclohexadiene... 

Section 1111 An example of a reaction m which the ring itself reacts is the Birch reduction The ring of an arene is reduced to a nonconjugated diene by treatment with a Group I metal (usually sodium) m liquid ammonia m the presence of an alcohol... 

Birch reduction (Section 11 11) Reduction of an aromatic nng to a 1 4 cyclohexadiene on treatment with a group I metal (Li Na K) and an alcohol in liquid ammonia Boat conformation (Section 3 7) An unstable conformation of cyclohexane depicted as... 

Methylpyridazine can be oxidized with selenium dioxide to give 3-formylpyridazine, and methyl groups attached to any position in pyridazine N-oxides are transformed with pentyl nitrite in the presence of sodium amide in liquid ammonia into the corresponding... 

It would appear that this type of addition may not be confined to the addition of NH2 in liquid ammonia, since it has been observed that treatment of 2-chloro-3-dichloromethyl-pyrazine with an excess of methoxide results in the introduction of a methoxy group into the 6-position of the pyrazine ring (Scheme 9) (68TL5931). This reaction is best rationalized in terms of addition of the methoxide ion at the 6-position, followed by loss of chloride ion from the dichloromethyl side chain. 

Pyrazoles and imidazoles with free NH groups are readily alkylated, e.g. by Mel or Me2S04. A useful procedure is to use the alkyl salt of the azole in liquid ammonia (80AHC(27)241). However, alkylation can also occur under neutral conditions, particularly with imidazoles. 

Most of the alkylations were carried out by adding a solution of 3,3-ethylenedioxypregna-5,16-dien-20-one in tetrahydrofuran to a solution of lithium in liquid ammonia to the point of color discharge. Treatment with the alkyl halide then furnishes the corresponding 17a-alkyl derivative (10). After hydrolysis of the 3-ketal group, 17a-methyl-, ethyl-, propyl-, butyl-, hexyl-, octyl-, allyl-, and benzylprogesterones are obtained. 

Sodium chloroacetylide in liquid ammonia will also react selectively at C-17 in the presence of a 3-keto-A group. 

Initial C-perfluoroalkylation of p diketonesoccurs dunng thenUV irradiation in the presence of perfluoroalkyl iodides in liquid ammonia Pluorinated enami-noketones are obtained by subsequent ammonolysis of a difluoromethylene group and removal of the acetyl group [131] C-alkylation of dimethyl malonate takes... 

Sulfur dissolves in liquid ammonia to give intensely coloured solutions. The colour is concentration-dependent and the solutions are photosensitive.Extensive studies of this system by several groups using a variety of spectroscopic techniques, primarily Raman,... 

Sodium, liquid ammonia. The utility of this method depends on the nature of the substituents on the aromatic ring. Rings containing electron-withdrawing groups will be reduced, as in the classic Birch reduction. 

The most ionic of the organometallic derivatives of Group 1 elements are the acetylides and dicarbides formed by the deprotonation of alkynes in liquid ammonia solutions ... 

Arynes are intermediates in certain reactions of aromatic compounds, especially in some nucleophilic substitution reactions. They are generated by abstraction of atoms or atomic groups from adjacent positions in the nucleus and react as strong electrophiles and as dienophiles in fast addition reactions. An example of a reaction occurring via an aryne is the amination of o-chlorotoluene (1) with potassium amide in liquid ammonia. According to the mechanism given, the intermediate 3-methylbenzyne (2) is first formed and subsequent addition of ammonia to the triple bond yields o-amino-toluene (3) and m-aminotoluene (4). It was found that partial rearrangement of the ortho to the meta isomer actually occurs. 

As discussed before, in liquid ammonia/potassium permanganate nucleo-phugal substituents at C-2, such as ones present in the naphthyridines (84c, 84e, 84h, 84i, 841, and 84m), could not be replaced by the amino group only SnH substitution takes place. However, it has been observed that in the reaction of the 2-chloro-3-nitro-l,8-naphthyridine (92c) with liquid methylamine/potassium permanganate S H substitution as well as methylamino-dechlorination takes place, yielding 2,4-bis-(methylamino)-3-nitro-l,8-naphthyridine (93c). 

---