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Z a | NOTES ON SCIENTIFIC RESEARCH. 87 
Azgulene. The blue substance, to which some essential oils, such as Roman 
chamomile oil, wormwood oil, &c., owe their intense colour, has been closely in- 
vestigated by A. E. Sherndal*). He calls it azulene, a name which was proposed 
already in 1864 by S. Piesse*). Azulene dissolves in concentrated mineral acids and 
separates unchanged when water is added. He shook 50 g. of an intensely blue 
fraction®) with 10 g. of 63 p.c. sulphuric acid and allowed the mixture to stand during 
the night. The acid layer was then decanted, diluted with water and treated with light 
petroleum, until this did not colour blue any more. The petroleum solution was then 
shaken with 85 p.c. phosphoric acid, until the blue colour had disappeared. The acid, 
which then showed a dark red colour, was decanted, diluted with water and extracted 
with ether, when 0,141 g. (0,28 p.c.) of a blue oil was obtained. In the same way, 
Sherndal prepared larger quantities of azulene, which he purified by distillation in vacuo. 
Pure azulene in a thin layer shows a dark blue colour; in thicker layers it looks black. 
It has a faint odour like phenol, recalling a little that of thymol. By combustion, as 
well as by ascertaining its molecular weight in benzene, the composition Ci;His was 
found. It resinifies quickly when exposed to the air. B.p. 295 to 300° (ordinary 
pressure) under partial decomposition, 185 to 195° (25 mm.); dos. 0,9738. It dissolves 
in most of the organic solvents. The solution in 60 to 65 p.c. sulphuric acid is yellow 
and fluoresces strongly; that in phosphoric acid fluoresces in reddish yellow and apple- 
green tints. From acid solutions, light petroleum does not take up any azulene, so 
that sesquiterpenes can easily be removed. Azulene remains unchanged when heated 
on the water-bath with 94 p.c. sulphuric acid. The action of nitric acid in acetic acid 
solution led to a yellow, amorphous mass. The oxidation with potassium permanganate 
did not afford any characteristic resolution products. Through the action of acetic 
anhydride and sulphuric acid a substance was obtained which dissolved in water and 
was most likely a sulphonic acid. 
_ It seems that azulene is closely allied to the terpenes and contains several double 
linkings. 
Sherndal points out that blue bodies have often beet noticed in reactions of acids 
on essential oils, for example in the reaction of phosphorus pentoxyde on guayol, 
or also when heating gurjunene under pressure. He further mentions the well-known 
colour reactions with sulphuric and glacial acetic acids. It remains to be investigated 
whether azulene or allied bodies are formed in these reactions. 
“Benzoterpenes’ is the name given by F. W. Kay and A. Morton*) to terpene- 
like hydrocarbons, which are derived from tetrahydronaphthalene. Similar compounds 
have not been met with in nature so far, but they are of theoretical interest, as they 
are closely allied to the sesquiterpenes. The authors think that benzo-p-menthane is 
the basis of the benzoterpenes (I). In order to arrive at the benzo-nor-p-menthene, the 
authors proceed as follows: «-naphthonitrile is saponified to «-naphthoic acid, which is 
reduced by means of sodium and alcohol to tetrahydro-e-naphthoic acid (II). By bromi- 
nating ethyl tetrahydro-«-naphthoate, ethyl «-bromotetrahydro-«-naphthoate (III) is ob- 
tained, from which hydrogen bromide is separated by treatment with diethylaniline, 
when ethyl 4*-dihydro-«-naphthoate (IV) is formed. Ethyl tetrahydro-«-naphthoate can 
be converted into benzo-nor-p-menthan-10-ol (V) with the aid of magnesium methy! 
iodide. It is a liquid of camphorlike smell and boils at 166° (30 mm.). By splitting 
1) Journ. Americ. chem. Soc. 87 (1915), 107. —- 2) Compt. rend. 57 (1864), 1016. — *%) Unfortunately the 
' author does not indicate from what oil the fraction was taken. — +4) Journ. chem. Soc. 105 (1914), 1565. 
