[Read before the Wellington Philosophical Society, 9th August, 1911.]

Introduction.

In a former paper^* it was shown that under the action of metallic iron abietic acid is rapidly deprived of its carboxyl group with production of a hydrocarbon. It is well known that the higher fatty acids under conditions which should lead to deprivation of a carboxyl group yield ketones more easily than hydrocarbons, according to the equation

2×.CO₂H=X₂CO+CO₂+H₂O.

It therefore seemed probable that heating the higher fatty acids with iron filings would be a simple method for obtaining ketones in good yield.

Upon heating stearic acid with cast-iron turnings to a temperature of 360–365° C. it was found that over 80 per cent, of the acid was converted to stearone. As the usual method of preparing the ketone of stearic acid only gives about 50 per cent. of the theoretical yield, the advantage of the new process is obvious. Another and equally important point is that the quantity of acid which can be treated in one operation is almost unlimited. In the ordinary process of distilling calcium or barium stearate with slaked lime under diminished pressure from a combustion-tube the quantity of ketone prepared in each operation is necessarily small.

The method was also found to give good yields of ketone with lauric, palmitic, cerotic, montanic, and melissic acids, so that it may be regarded as a general method for the preparation of the ketones of the saturated fatty acids with from 12 to 30 atoms of carbon in the molecule. With acetic, butyric, phenyl-acetic, suberic, and sebacic acids no satisfactory results were obtained.

The ketones of the higher unsaturated fatty acids have not hitherto been prepared, but the “iron” method allows these compounds to be obtained without difficulty in the oleic series. In the linoleic series no experiments have been made, owing to the difficulty of obtaining the acids in a state of purity. During the progress of these experiments it was pointed out by Mailhe^† that the vapours of the fatty acids from acetic to stearic acid yield ketones if passed over gently heated “reduced” metals, including iron, copper, nickel, cadmium, and lead. There is, however, an extraordinary difference between the catalytic action of the “reduced” metals (which are in general pyrophoric) and the same metals in the state of powder. (Compare, for example, the inertness of ordinary platinum with the intense catalytic action of platinum-black). Sabatier has, indeed, recently drawn attention^‡ to the fact that “reduced” nickel exhibits quite different catalytic effects upon mixtures of hydrogen and acetylene, according to the conditions under which the reduction has been carried out.