418 THE CHEMISTEY OF ESSENTIAL OILS
Analysis agreed with the formula C 8 H]6 or C 8 H 18. It is probably octy-
lene. Pinene appears to be present in traces, as well as camphene,
phellandrene, and y-terpinene. The bulk of the oil, however, consists of
d-limonene which is present to the extent of about 90 per cent. Methyl-
heptenone, octyl aldehyde, nonyl aldehyde, citronellal, terpineol, linalyl
acetate, geranyl acetate, bisabolene, cadinene and methyl anthranilate
have all been found present in traces.
Citraptene, or " lemon camphor," a solid substance, which appears to
be dimethoxy-coumarin, is present to the extent of about 2 per cent, in
the oil. This is a non-volatile substance dissolved out from the peel by
the expressed essential oil.
Citraptene, which appears to be identical with limettin, has been care-
fully examined byE. Schmidt.^1
The early work of Brissenot, Blanchet, and Sell and Mulder is referred
to, as is also the analysis by Berthelot. This brings us up to the first of
the recent workers, Crismer, who gave 143° to 144° as the melting-point,
and C 10 H 10 O 4 as the formula of the stearoptene of lemon oil. Schmidt
isolated a crystalline body melting at 146° to 147° and having a blue
fluorescence in alcohol solution, and he states that this body is the
citraptene of Crismer, and the limettin of Tilden and Beck. Theulier
had already stated that a crystalline body melting at 145° and an
amorphous one melting at 76° were the chief constituents of the solid
mass obtained on the distillation of lemon oil; of these citraptene is the
principal.
Schmidt gives 146° to 147° as the melting-point of this body, for
which the name citraptene is retained. Three analyses gave the fol-
lowing results:—
Carbon. Hydrogen. Calculated for CnH 10 O4.
63-92 C5'04 C 63-98
63-83 5-01 H 4-85
63-82 4-75 O 31*17
This formula is in agreement with that assigned to limettin by Tilden
and Beck.
Citraptene contains two methoxyl groups ; when treated by Zeisel's
anethod to remove the methyl groups, the demethylated citraptene,
<C 9 H 6 O 4 , yields phloroglucin and acetic acid on fusion with alkali.
Citraptene has the general character of an acid anhydride, according
to Schmidt, its corresponding acid being unstable and rapidly converted
into a lactone.
Citraptene appears to be a di-methoxy-coumarin of the formula—
C. OCH,
HCX\C.CH:CH
CH 3 OC\/CO. CO
Lemon oil has the following characters :—
Specific gravity.. 0'854 to 0'862 (usually 0'857 to 0'860).
Optical rotation
Refractive index
Fixed residue (at 100°)
Citral+ 54° „ + 66° ( „ + 57° „ + 62°).
1-4745 „1*4760 (rarely below 1-4750).
2 to 6 per cent. ( ,, over 4 per cent.).
4 ,, 6 ,, (usually 4'2 to 5*5 per cent.).
1
Archiv. der Pharm. (1904), 288.