Cyclohexanones dissolving metals

Dissolving metal reductions remain the method of choice, and are frequently the only viable method, for the reduction of sterically hindered cyclohexanones to equatorial alcohols. In the early 1950s it was found that reduction of 11-keto steroids using either Na-propan-l-oP or Li-NHs-dioxane-ethanol gave good yields of the equatorial I la-alcohol. 11-Keto steroids, such as androstan-11-one (29 equation 12) have two axial methyl groups in a 1,3-relationship to the carbonyl group and afford exclusively the axial 11 P-ol (30) on reduction with metal hydrides. 

The electrochemical properties of many functional groups have been described in reviews by Steckhan, Degner (industrial uses of electrochemistry), Kariv-Miller,543 and Feoktistov. The synthetic applications of anodic electrochemistry has also been reviewed. There are interesting differences between dissolving metal reductions (secs. 4.9.B-G) and electrochemical reactions. Cyclohexanone, for example, can be reduced to cyclohexanol (sec. 4.9.B) or converted to the 1,2-diol (556) via pinacol coupling by controlling the reduction potential, the nature of the electrode and the reaction medium. 46 Presumably, the more concentrated conditions favor formation of cyclohexanol via reduction of the carbanion. More dilute solutions appear to favor the radical with reductive dimerization to 556. More important to this process, however, is the difference in reduction potential (-2.95 vs. -2.700 V) and the transfer of two Faradays per mole in the former reaction and four Faradays per mole in the latter. 

Metal oxides have often been used as catalysts for the autoxidation of hydrocarbons.1 In many cases the metal probably dissolves in the reaction medium and catalysis involves homogeneous metal complexes. However, according to a recent report56 cerium oxide catalyzes the liquid phase oxidation of cyclohexanone in acetic acid (5-15 bar and 98-118°C) without dissolving in the reaction medium. 

In liquid-liquid systems, a chemical reaction is encountered for three distinct purposes. Firstly, the reaction may be a part of the process, such as nitration and sulphonation of aromatic substances, alkylation, hydrolysis of esters, oximation of cyclohexanone, extraction of metals and pyrometallurgical operations involving melts and molten slag. Secondly, a chemical reaction is deliberately introduced for separation purposes (e.g. removal of dissolved acidic solutes from a variety of hydrocarbons). Finally, the yield and the rate of formation of many single phase reactions are affected and often can be favourably increased by the deliberately controlled addition to the reaction system of an immiscible extractive phase, whose major purpose is to extract the product from the reactive phase. Such operations are sometimes referred to as "extractive reactions" and have been discussed previously in some detail (14-17). 

A simple possibility to obtain a detailed information about the stabilizer system in PVC waste can be seen in the classic analysis methods which are common practice in inorganic chemistry of the separation and determination of cations. The only difficulty is to find an easily practical way to get the metallic cations into water phase. For this purpose, the PVC sample is dissolved in cyclohexanone and the received solution used for a liquid/liquid-extraction with nitric acid containing water. After phase separation, the different cations are found in water solution. 

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