Pinacones

Colourless liquid b.p. 69 5 C. Manufactured from propanone by conversion to pinacone and passing its vapour over heated KHSO4. Slowly changes to a rubber-like substance the change is hastened by metallic sodium or peroxides. Used in the manufacture of artificial rubber. 

On reduction, benzaldehyde yields, in addition to benz 1 alcohol, a pinacone known as Itydrobenzoin,... 

Translate names of compounds the chief function of which is alcoholic (or phenolic) so that the name ends in -ol as, glycerol, resorcinol, mannitol, pinacol (not pinacone). 

A., 194, 310.)—When aromatic ketones are reduced by zinc dust in the presence of glacial acetic acid pinacones are formed (see p. 70). 

B., 27, 456.)—When ketones are reduced to secondary alcohols, some intermolecular condensation usually also occurs, and a pinacone is formed. 

This side reaction cannot be avoided when reducing aliphatic ketones, but in the aromatic series either product can be obtained by varying the conditions of the reduction. An alkaline reduction favours alcohol production pinacones are formed when acid reducing agents are employed (see Preparation 16). 

Pinacones can also be obtained by using suitable electrolytic reductions. Aldehydes, too, have been brought within the scope of the reaction. Thus hydrobenzoin [s-diphenyl-ethan-diol] has been prepared from benzalde-hyde by an acid reduction. 

Acetone, the simplest ketone, gives the simplest pinacone. 

The pinacones formed from acetophenone, benzophenone, and many... 

Ketones are converted by electrolytic reduction into secondary alcohols or pinacones.2 A mercury cathode gives a good yield of the former class, but other cathodes give a mixture8 of the two compounds. 

The same product together with phenvl-p-t oly 1 pinacone, is produced in sulphuric-acid solution at a low current density and temperature. With a higher current density and temperature the formation of carbinol is trifling, and a good yield of phenyltolylpinacone is obtained ... 

Phthalyl-p-aminobenzophenone.—This compound, by reduction in sulphuric-acid solution, gives a poor yield of pinacone. 

Glycols are aliphatic dihydric alcohols. Primary and secondary glycols are thick liquids, and tertiary glycols (pinacones) are crystalline solids. The principal glycols to which people are or have been exposed, either occupationally or in medicinal products, are ... 

The carbon skeleton is obtained from a pre-existing one by rearrangement. Example pinacolin from pinacone. 

Formation of isobornyl chloride from camphene hydrochloride corresponds to that of pinacolin from pinacone. 

Alkaline reducing agents are usually recommended for reduction of ketones to secondary alcohols since pinacones are formed preferentially in an acid medium. Sodium in alcohol or in moist ether or benzene, sodium amalgam, and zinc dust in sodium hydroxide solution, etc., are often used for this purpose. 2-Heptanol, for example, is formed in good yield on addition of sodium to an aqueous-alcoholic solution of methyl w-pentyl ketone.306 Reduction is also often carried out by adding sodium to an aqueous-ethereal suspension but by this method the double bond of unsaturated ketones is also partially reduced. 

If, however, there is no hydrogen attached to the carbon atom carrying the acetyl group, then the ketone is converted into the acid containing only one fewer carbon atoms e.g., chromic-sulfuric acid converts pinacone into 2,2-dimethylpropionic acid 130... 

Pinacone can, however, be converted into the oc-oxo acid, 3,3-dimethyl-2-oxo-butyric acid, under other conditions — by alkaline permanganate — and this product can then yield 2,2-dimethylpropionic acid on oxidative decarboxylation by hydrogen peroxide in alkali 131... 

This two-stage degradation of methyl ketones to carboxylic acids containing one fewer carbon atoms cannot be realized in all cases, but only when the acetyl group is attached to a quaternary carbon as in pinacone and a series of aryl methyl ketones of the acetophenone type. 

Aceto - phenone, C.H..CO.CH,. — Aceto - phenone yields aceto-phenone pinacone,... 

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