Reaction XVIII.—Ring Formation by Elimination of Water from certain Molecules

Reaction XVIII. Ring Formation by Elimination of Water from certain Molecules. (B., 41, 3632, A., 311, 178.)—Many important syntheses of ring compounds come under this heading. Only a few can be mentioned. 

A further reaction then takes place in this particular instance (see Preparation 26), but in the general case the reaction goes no further. The compounds so obtained are all derivatives of cyclohexenone. These latter compounds may be transformed by various reactions into cyclo-paraffins on the one hand, and aromatic compounds on the other. This affords a method of passing from simple aliphatic to aromatic compounds (see Preparation 446). (A., 281, 25.) 

These compounds have an odour of violets, and are used in the manufacture of violet essence. Irone itself has the formula— 

10 gms. (1 mol.) of o-benzoylbenzoic acid are mixed with 60 gms. of cone, sulphuric acid, heated to 150° for 1 hour, cooled and poured on to ice. The precipitated anthraquinone is collected and thoroughly washed, first with hot water, then with warm dilute (5 N) caustic soda and finally with warm water. It is dried in a steam oven, and completely purified by sublimation, at 250° (see p. 31). 

—Theoretical (9 gms.). Yellow needles insoluble in water somewhat soluble in benzene and the usual organic solvents soluble in glacial acetic acid M.P. 277° sublimes at 250° B.P. 382°. (Z. a., 19, 669.) 

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