Potassium in ammonia

Reduction of the sodium salt of equilenin 17-ethylene ketal with lithium, sodium or potassium in ammonia at —70° occurs predominantly in the B-ring, affording, after acid hydrolysis, equilin (29) in up to 76% yield (55% isolated). The preferential reduction of the B-ring reflects the relative, but not absolute, resistance to reduction conferred on the A-ring by the naphthoxide ion. Some A-ring reduction does compete kinetically with B-ring reduction, since the epimeric 3-hydroxyestra-5,7,9-trien-17-ones are the major reaction by-products. Simple phenoxide ions usually reduce slowly... 

It detonates in the presence of fuming nitric acid. It detonates in contact with potassium in ammonia. 

The volume expansions of alkali metals in liquid ammonia are discussed in the light of the current available data. Special emphasis is made of the anomalous volume minimum found with sodium-ammonia and potassium-ammonia solutions. Recent studies of potassium in ammonia at —34° C. were found to exhibit a large minimum in the volume expansion, AV, vs. concentration curve. The results of these findings were compared with the previous results of potassium in ammonia at —45° C. The volume minimum was found to be temperature dependent in that the depth of the minimum increased and shifted to higher concentrations with increasing temperature. No temperature effect was observed on either side of the minimum. These findings are discussed in light of the Arnold and Patterson and Symons models for metal-ammonia solutions. 

Let us again review the previous findings for the volume expansion of sodium and potassium in liquid ammonia. Filbert (8) reported a volume minimum for sodium in ammonia at —46° C. at approximately 0.03N. Orgell (21) confirmed the existence of this minimum for sodium in ammonia at —45° C. and extended his study to potassium in ammonia at the same temperature. Potassium-ammonia solutions were found to exhibit a minimum at O.OliV which was quite sharp and not nearly as broad as the minimum for sodium at —45° C. More recently, Brendley has investigated the volume expansion of potassium in ammonia at —34° C. Once again a pronounced minimum was found. The potassium data at —45° C. and —34° C. showed differences in the position and... 

Liquid-Ammonia Solutions—Spectrum and Photolysis of Potassium Amide. Figure 6 shows the spectrum of a bleached solution of potassium in ammonia, at —48°C. Only a single peak due to the amide is seen at 335 m/z before the ammonia cutoff. The molar decadic extinction coefficient, as determined by titration, is e = (1.0 =fc 0.2) X 104 at —48 ° C. and 335 m/z. (A careful Beer s Law check on the 335 m/z band has not yet been made.) The temperature coefficient of the peak is —20 cm. 1 deg. 1 (3), which is close to the value given above for the longwave band in decomposed ethylamine solution. 

Eastham JE, Larkin DR. Effect of variables on reductions by alcohol and potassium in ammonia. J Am Chem Soc 1959 81 3652-3655. 

A systematic study of the reductive alkylation of acetophenones revealed that the desired transformation (Scheme 30) required a careful selection of reagents and conditions. The best results were obtained from reduction by potassium in ammonia at -78 °C, with t-butyl alcohol as the proton source. Exchange of the potassium counterion of the enolate (152 M = K) for lithium then ensured regioselective alkylation at C-1 to give (153) in 80-90% yields (Scheme 30). Metals other than potassium as the reductant led to undesirable side reactions with the carbonyl group, which included simple reduction to the methylcar-binol and ethylbenzene (lithium or sodium), while the absence of a proton source or presence of a strong... 

Dlhydrophenanthren-4( lA/)-one (189) is readily reduced by lithium, sodium or potassium in ammonia at -33 C, presumably to the dlenolate (190), since reaction with methyl iodide affords (191). Quenching with ammonium chloride, however, leads to the conjugated enone (192 Scheme 35). 

Stereoselective Birch reduction is possible and a number of examples have been reported, particularly for selective alkylation of the intermediate enolate anion. For example, reduction of the chiral benzamide 69 with potassium in ammonia, followed by alkylation with ethyl iodide gave essentially a single diastereomer of the cyclohexadiene 70, which was used in a synthesis of (-l-)-apovincamine (7.50). 

Many conjectures on the chemical state and role of potassium in ammonia synthesis can be made from the surface-science results. The potassium TPD results show clearly that elemental potassium will not be stable at the temperatures necessary to perform the synthesis of ammonia. The industrial reaction is usually run between 673 K and 748 K and the TPD results show that elemental potassium would rapidly desorb at these temperatures. However, with the coadsorption of oxygen, potassium can be thermally stabilized, and it desorbs at temperatures greater than 1000 K. Bulk potassium compounds such as K2O or KOH would not be stable under ammonia synthesis conditions. This suggests that the formation of potassium ferrites in the industrial catalyst results in a chemisorbed potassium and oxygen adlayer, stable under industrial ammonia synthesis conditions. 

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