Benzene derivatives 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. 

However, benzene and its derivatives can be reduced to cyclohexa-dienes by solutions of metals such as Li, Na, K, Zn, and Hg in a weakly acidic solvent, such as liquid ammonia, amines, or ether-alcohol mixtures. This general type of reaction is known as the Birch reduction after the Australian chemist, A. J. Birch. With benzene, reduction with metals leads to 1,4-cyclo-hexadiene ... 

PAHs and soils contaminated with PAHs are readily remediated by solvated electrons in NH3. Oligomeric reduced products are obtained. These reactions are slower than dehalogenation, as was demonstrated by the rapid formation of benzene, toluene, and naphthalene in Na/NH3 from their corresponding monochloro derivatives [24,28], Table 12 summarizes data on the destruction of pure PAHs. Soils contaminated with PAHs have been remediated to below detection levels. Mononuclear aromatics (benzene, toluene, anisole, and nitrobenzene) undergo ring reduction according to the well-known Birch reduction [11-18]. 

Several examples of the Birch reduction of substituted benzene derivatives are shown in the following equations. Note that substituents such as alkyl and alkoxy groups prefer to be attached to one of the carbons of the double bonds of the product, while a carboxyl group prefers to be attached to one of the singly bonded carbons. Benzene derivatives with other types of substituents are usually not employed as reactants in the Birch reduction because the substituents are not stable to the reaction conditions. 

Table 11 shows some representative results from the cathodic reduction of some aromatic hydrocarbons. These include cases with Ei j2 near the cathodic limit or in the discharge region of the SSE (benzene, toluene) and cases with Ex j2 at considerably more positive potential (naphthalene, anthracene again we must anticipate the discussion of reactivity and refer to Table 21). Reactions nos. 1, 2, 6, and 7 immediately demonstrate one difficulty with such studies in that the catholyte of a divided cell becomes strongly basic as electrolysis progresses. In sufficiently basic medium, the initial product, a 1,4-dihydro derivative (cf. the Birch reduction Birch and Subba Rao, 1972), will rearrange to a conjugated system which, in contrast to the 1,4-dihydro derivative, is further reducible to the tetrahydro product (nos. 1 and 6). In a non-divided cell the acid production at the anode balances the base production and thus only a little rearrangement occurs. It is therefore not a trivial problem to find out if the tetrahydro product is formed from the conjugated dihydro product, formed directly or by rearrangement [eqn (78)].

Aromatic Substitutions Using Organometallic Reagents 790 17-14 Addition Reactions of Benzene Derivatives 796 Mechanism 17-9 The Birch Reduction 797 17-15 Side-Chain Reactions of Benzene Derivatives 798... 

In 1944, the Australian chemist A. J. Birch found that benzene derivatives are reduced to nonconjugated cyclohexa- 1,4-dienes by treatment with sodium or lithium in a mixture of liquid ammonia and an alcohol. The Birch reduction provides a convenient method for making a wide variety of interesting and useful cyclic dienes. 

TTHE REACTION OF benzene or one of its derivatives with an alkali metal in liquid ammonia containing an alcohol cosolvent is known as the Birch reduction (1-6). As expected with anionic intermediates, 1-substituted-1,4-dihydro products result from electron-withdrawing groups, and 2,5-dihydro products result from electron-donating groups, as shown in Scheme I. Application of these conditions to polynuclear aromatic compounds produces complications because the products formed initially are subject to reduction under the reaction conditions (3). Although methods such as the use of iron salts minimize side reactions, more recently developed procedures avoid... 

Claisen-Schmidt condensation, 720, 728 with methylamine, 673, 873 nitration, 467, 873 reductive amination, 881 with vinyllithium, 556 Benzenamine, 859. See also Aniline Benzene, 54, 399-406, 433 34 acidity of, 552, 577 Birch reduction of, 413-414 derivatives, nomenclature of, 406-408 electrophilic aromatic substitution in,... 

This reaction was first reported by Wooster in 1937d and subsequently by Hiickel et al in 1939, for the reduction of aromatic compounds by sodium in liquid ammonia with water however, no structural information was provided. It was Birch who extended Wooster s protocol in 1944 and since then had extensively explored the reduction of benzene and aromatic derivatives with alkali metal (i. e Li, Na, K) in liquid ammonia in the presence of an alcohol (as the proton donor) to produce corresponding cyclohexa-1,4-diene derivatives." Therefore, the reduction of aromatic compounds by alkali metal in liquid ammonia in the presence of alcohol is generally known as the Birch reduction or metal-ammonia reduction. In addition, this reaction is also referred to as the Birch reaction, and in one instance is cited as the Birch-Hiickel reduction. ... 

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