Ammonia-metal solutions

The above results are concordant with the recent finding" that saturated alkyl fiuorides are not reduced by alkali metals in liquid ammonia at — 33°, although unsaturated fiuorides are reduced rapidly. All types of fiuoro compounds are reported to be reduced by metal-ammonia solutions at 0-25°. 

Metal-ammonia solutions reduce conjugated enones to saturated ketones and reductively cleave a-acetoxy ketones i.e. ketol acetates) to the unsubstituted ketones. In both cases the actual reduction product is the enolate salt of a saturated ketone this salt resists further reduction. If an alcohol is present in the reaction mixture, the enolate salt protonates and the resulting ketone is reduced further to a saturated alcohol. Linearly or cross-conjugated dienones are reduced to enones in the absence of a proton donor other than ammonia. The Birch reduction of unsaturated ketones to saturated alcohols was first reported by Wilds and Nelson using lithium as the reducing agent. This metal has been used almost exclusively by subsequent workers for the reduction of both unsaturated and saturated ketones. Calcium has been preferred for the reductive cleavage of ketol acetates. 

Eq. (4e)] is not reduced by metal-ammonia solutions so that the existence of this equilibrium cannot lead to further reduction of the saturated ketonic product only protonation on carbon can result in further reduction (see page 39). 

REDUCTIONS OF STEROIDS BY METAL-AMMONIA SOLUTIONS / 45 3, Reduction of Ketol Acetates... 

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 chemical resistance of PTFE is almost universal It resists attack by aqua regia, hot fummg nitnc acid, hot caustic, chlorine, chlorosulfonic acid, and all solvents. Despite this broad chemical resistance, PTFE is attacked by molten alkali metals, ammonia solutions of such metals, chlorine trifluoride, and gaseous fluonne at elevated temperature and pressure PTFE swells or dissolves m certam highly fluonnated oils near its melting point. Specific lists of chemicals compatible with PTFE are available [/.8]... 

Metal-ammonia solutions. W. L. Jolly, Prog. Inorg. Chem., 1959,1,235-281 (174). 

The alkali metals also release their valence electrons when they dissolve in liquid ammonia, but the outcome is different. Instead of reducing the ammonia, the electrons occupy cavities formed by groups of NH3 molecules and give ink-blue metal-ammonia solutions (Fig. 14.14). These solutions of solvated electrons (and cations of the metal) are often used to reduce organic compounds. As the metal concentration is increased, the blue gives way to a metallic bronze, and the solutions begin to conduct electricity like liquid metals. 

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. 

The absorption spectrum of radiation-produced eam is identical to that in dilute metal-ammonia solutions. It has a broad, structureless absorption in the red and IR, with a peak at about 1.88 pm and a half-width of 0.2 eV on the high-energy side. The absorption is intense with max = 4.8 x 104 M 1cm 1, giving an... 

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