Alcohols dissolving metals

Compound (12) can also be obtained by dissolving metal reactions through treatment with an excess of lithium—hquid ammonia in tert-huty alcohol (54). 

Lead nitrate [10099-74-8] Pb(N02)2, mol wt 331.23, sp gr 4.53, forms cubic or monoclinic colorless crystals. Above 205°C, oxygen and nitrogen dioxide are driven off, and basic lead nitrates are formed. Above 470°C, lead nitrate is decomposed to lead monoxide and Pb O. Lead nitrate is highly soluble in water (56.5 g/100 mL at 20°C 127 g/100 mL at 100°C), soluble in alkalies and ammonia, and fairly soluble in alcohol (8.77 g/100 mL of 43% aqueous ethanol at 22°C). Lead nitrate is readily obtained by dissolving metallic lead, lead monoxide, or lead carbonate in dilute nitric acid. Excess acid prevents the formation of basic nitrates, and the desired lead nitrate can be crystallized by evaporation. 

Reduction of Ketones and Enones. Although the method has been supplanted for synthetic purposes by hydride donors, the reduction of ketones to alcohols in ammonia or alcohols provides mechanistic insight into dissolving-metal reductions. The outcome of the reaction of ketones with metal reductants is determined by the fate of the initial ketyl radical formed by a single-electron transfer. The radical intermediate, depending on its structure and the reaction medium, may be protonated, disproportionate, or dimerize.209 In hydroxylic solvents such as liquid ammonia or in the presence of an alcohol, the protonation process dominates over dimerization. Net reduction can also occur by a disproportionation process. As is discussed in Section 5.6.3, dimerization can become the dominant process under conditions in which protonation does not occur rapidly. 

Dissolving-Metal Reduction of Aromatic Compounds and Alkynes. Dissolving-metal systems constitute the most general method for partial reduction of aromatic rings. The reaction is called the Birch reduction,214 and the usual reducing medium is lithium or sodium in liquid ammonia. An alcohol is usually added to serve as a proton source. The reaction occurs by two successive electron transfer/proto-nation steps. 

Solvated electrons were first produced in liquid ammonia when Weyl (1864) dissolved sodium and potassium in it the solution has an intense blue color. Cady (1897) found the solution conducts electricity, attributed by Kraus (1908) to an electron in a solvent atmosphere. Other workers discovered solvated electrons in such polar liquids as methylamine, alcohols, and ethers (Moissan, 1889 Scott et al, 1936). Finally, Freed and Sugarman (1943) showed that in a dilute metal—ammonia solution, the magnetic susceptibility corresponds to one unpaired spin per dissolved metal atom. 

A weight of compound, containing about 0-05 g. of fluorine, was dissolved in 10 ml. of dry alcohol and metallic sodium (about 0 5 g., i.e. at least 5 equivalents) was added. After the sodium had dissolved, the mixture was gently heated under reflux for 5 min.,8 and then washed out with about 100 ml. of water into a beaker, made acid to bromophenol blue with dilute nitric acid and then just alkaline with 10 per cent sodium hydroxide solution. Three ml. of 10 per cent sodium chloride solution were added and the solution was diluted to 250 ml. One ml. of concentrated hydrochloric acid was added, and the solution heated on a water-bath to about 80°. Then 5-0 g. of finely powdered A.R. lead nitrate were added with stirring (still at 80°). As soon as all the lead nitrate had dissolved, 5-0 g. of crystalline sodium acetate were added, with vigorous stirring. The product was then heated on the water-bath for 15 min. and cooled in ice, and the precipitate was filtered off on a Swedish filter paper. It was washed once with water, four times with saturated PbClF solution... 

Electrochemical reduction of camphor-and norcamphoroxime at a Hg cathode proceeds with a high degree of stereoselectivity to give products of opposite stereochemistry to those formed in the dissolving metal (Na-alcohol) reduction of the oximes. The electrolyses are proposed to proceed by a kinetically controlled attack by the electrode on each oxime from the less hindered side (Fig. 62) [348]. In contrast, the corresponding N-phenyl imines yield products of the same stereochemistry as those isolated from a dissolving metal reduction. Cyclic voltammetry and polarographic data point to RH and intermediates in this case that are proto-nated from the least hindered side [349]. 

Benzene and its homologs can be converted to the corresponding cyclo-hexadienes and cyclohexenes, and even cyclohexanes, by treatment with dissolving metals lithium, sodium, potassium or calcium in liquid ammonia or amines. Conversions are not complete, and the ratio of cyclohexadienes to cyclohexenes depends on the metal used, on the solvent, and on the presence of hydrogen donors (alcohols) added to the ammonia or amine [392, 393, 394]. 

This method involves formation of reverse micelles in the presence of surfactants at a water-oil interface. A clear homogeneous solution obtained by the addition of another amine or alcohol-based cosurfactant is termed a Microemulsion. To a reverse micelle solution containing a dissolved metal salt, a second reverse micelle solution containing a suitable reducing agent is added reducing the metal cations to metals. The synthesis of oxides from reverse micelles depends on the coprecipitation of one or more metal ions from... 

White, cubic crystal or powder density 2.226 g/cm sparingly soluble in water 1.71g/100mL (at 15°C) slightly soluble in alcohol dissolves in alkah, metal cyanides, and hydroxides. 

Silvery metal body-centered cubic structure imparts crimson-red color to flame density 0.862g/cm3 at 20°C melts at 63.25°C density of hquid potassium at 100°C is 0.819 g/cm and 0.771g/cm3 at 300°C vaporizes at 760°C vapor pressure 123 torr at 587°C electrical resistivity 6.1 microhm-cm at 0°C and 15.31 microhm-cm at 100°C viscosity 0.25 centipoise at 250°C surface tension 86 dynes/cm at 100°C thermal neutron absorption cross section 2.07 barns reacts violently with water and acids reacts with alcohol dissolves in liquid ammonia and mercury... 

Sodium and potassium salts were first prepd and examined by Nef (Ref 2). For their prepn NEt was dissolved in ether and treated with Na or K alcoholates (obtd by dissolving metallic Na or K in alcohol). Both C2H.4(N03)Na and C2H,t(N02)K are sol in w and very sol in ale. The Na salt deflgr on heating explodes at high temp. The Thalium salt, T1C2H.4N02, crysts (from aq ale), dec at... 

Fairly selective reduction of certain alkenes can be achieved using the sodium-hexamethylphosphoramide (HMPA)-tm-butyI alcohol system,193 despite the general trend, that nonconjugated alkenes are usually quite resistant to the dissolving metal reduction method (see Section 11.3.2). In the case of 9(10)-octalin, the transformation leads to a nearly equilibrium product distribution ... 

Besides heterogeneous and homogeneous catalytic hydrogenations, chemical reductions can also transform alkynes to cis alkenes. Interestingly, activated zinc in the presence of a proton donor (alcohol), although a dissolving-metal reagent, reduces disubstituted alkynes to cis alkenes 199... 

Dihalocydopropanes readily undergo reductive dehalogenation under a variety of conditions. Suitable choice of reagents and reaction conditions will allow the synthesis of monohalocyclopropanes or the parent cyclopropanes.19 " The ease of reduction follows the expected order I > Br > Cl > F. In general, complete reduction of dibromo and dichloro compounds is accomplished by alkali metal in alcohol,99-102 liquid ammonia103 or tetrahydrofuran (equations 28 and 29).104 The dihalocydopropanes can be reduced conveniently with LAH (equation 30).105 LAH reduction is particularly suited for difluoro compounds which are resistant to dissolving metal reductions.19 106 It is noteworthy that the sequence of dihalocar-bene addition to an alkene followed by the reduction of the dihalocyclopropyl compounds (equation 31) provides a convenient and powerful alternative to Simmons-Smith cyclopropanation, which is not always reliable. 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

In dissolving-metal ester reduction, the ester carbonyl is believed to accept an electron to form a radical oxyanion 37 (Scheme 12.12). Chelation with a lithium counterion then ensues to produce a tertiary radical 38 which then captures a second electron to become a carbanion. Protonation of 39 next yields 40, whose fate is to collapse to aldehyde 41. Another multiple electron transfer/protonation sequence subsequently yields the product alcohol 46. 

Primary, secondary, and tertiary alkyl halides also can be reduced with dissolving metals. The primary reduction product is an organometallic compound. Whether the latter is formed quantitatively or whether it is converted into the corresponding hydrocarbon by protonation depends on the solvent. The organometallic compound is stable in aprotic solvents (hexane, ether, THF), while it is protonated in protic solvents (HOAc, alcohols). 

Na, or Li in liquid ammonia, for example) to reduce aromatic rings and alkynes. The dissolving metal reduction of enones by lithium metal in liquid ammonia is similar to these reactions—the C=C bond of the enone is reduced, with the C=0 bond remaining untouched. An alcohol is required as a proton source and, in total, two electrons and two protons are added in a stepwise manner giving net addition of a molecule of hydrogen to the double bond. 

The boiling-point of the saturated solution in contact with excess of the salt is 113-71° C. at 760 mm. pressure,8 and the heat of solution is -4-5 Cal.9 At 25° C. 100 grams of ethyl alcohol dissolve 0-078 gram.10 The salt unites with free halogens, yielding various polyhalides,11 and also forms double chlorides with other metallic chlorides.12 It exhibits radioactivity.13... 

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