The situation has been cleared up by the work of C. Engler6). He showed that the action of atmospheric oxygen or pure oxygen on turpentine oil results in the formation of a peroxide-like oxidation product, C10H16O4. This can give off one half of its oxygen, whereas the other half remains with the oil. He confirmed the observation previously made by Berthelot7), that 1 mol.
1) Bardsky (Chem. Zentralbl. 1882, 803) found hydrogen peroxide and, as he believes, nitric acid in water which had been shaken with oxidized turpentine oil.
2) According to Papasogli (Chem. Zentralbl. 1888, 1548) water, that has stood in contact with turpentine oil for a longer period, contains hydrogen peroxide, camphoric acid (m. p. 176°), formic acid, acetic acid and an acid C10H18O2 isomeric with campholic acid. In the oxidized turpentine oil itself hydroxysylvinic acid is supposed to be contained.
3) Although the correctness of these observations has nowhere been doubted, and the presence of hydrogen peroxide in turpentine oil may be regarded as settled, nevertheless numerous text books still contain the statement that ozone is contained in turpentine oil and in volatile oils in general. Inasmuch, however, as hydrogen peroxide and ozone destroy each other in accordance with the equation of turpentine oil absorbs 4 atoms of oxygen, of which two are readily removed. Thus far, however, the isolation of either the compound C10H16O, or C10H16O2 has not been successful.
03 + H202 = H20+202
(Schone, Liebig's Annalen 196 , 239), the presence of ozone is excluded. 3Comp. also C. Harries, Chem. Ztg. 31 (1907), 804.
4) Zeitschr. f. Chem. II. 6 (1870), 609; Chem. Zentralbl. 1870, 821.
5) Loc. cit.
6) C. Engler and J. Weisberg, Ober Aktivierung des Sauerstoffs. Der aktive Sauerstoff des Terpentinols. Berl. Berichte 31 (1898), 3046. C. Engler, Die Autoxydation des Terpentinols. Ibidem 33 (1900), 1090.
7) Annal. de Chim. et Phys. III. 58 (1860), 435; Jahresber. d. Chem. 12 (1859), 58.
When absolutely dry turpentine oil is activated, neither hydrogen peroxide nor ozone results. Turpentine oil activates oxygen most rapidly at 100°. Above this temperature no active oxygen is formed, but it is used up in the oxidation of the turpentine oil. 1 cc. of turpentine oil can activate 100 cc. of oxygen at 100°.
The turpentine oil charged with oxygen, whether moisture be present or not, is capable of transmitting oxygen to such substances which are not directly oxidizable by atmospheric oxygen. Thus, as has already been pointed out, iodine is liberated from potassium iodide. Indigo solution is bleached and arsenous acid is oxidized to arsenic acid. In the dark, activated turpentine oil retains its property for years.
These oxydation phemomena and the same changes in the turpentine oil take place more rapidly when warmed air saturated with moisture is passed through the oil1).
As to the nature of the oxidation products, but little is known.
Definitely established is the presence of formic acid2), acetic acid and camphoric acid C10H16O43), whereas the presence of hydroxysylvinic acid is doubtful. Traces of an aldehyde4) have also been found, the composition of which agrees with that of the aldehyde of camphoric acid, viz. C10H16O3. It possesses a benumbing odor and is probably the cause of the peculiar odor of the old "rancid" turpentine oil.
1) A turpentine oil, sp. gr. 0,864, when thus treated for 44 hrs. revealed a sp. gr. of 0,949. Kingzett observed in connection therewith an appreciable rise in the boiling temperature.
2) The exact proof of the presence of formic acid was first brought by Kingzett in 1910. Journ. Soc. .chem. Industry 29 (1910), 791. - Comp. also ibidem 31 (1912), 265.
3) Papasogli, Chem. Zentralbl. 1888, 1548.
4) Schiff, Chem. Ztg. 20 (1896), 361. This aldehyde appears to be most readily formed when turpentine oil is kept in partly filled and imperfectly stoppered flasks exposed to light. The amount of the unstable aldehyde formed does not exceed 1 p.c. As already mentioned, it can be removed by shaking the oil with sodium acid sulphite solution.
When exposed to the air on a watchglass for several days, the aldehyde resinifies, looses its toxic odor, and no longer reacts with rosaniline sulphate.
In a turpentine oil that had been completely resinified by exposure in shallow dishes, Tschirch and Bruning1) demonstrated the presence of a resin-like substance and of a small amount of a resinolic acid. They could not, however, find a peculiar resin acid, such as abietic acid, pimaric acid, etc. According to Tschirch2), the resenes are related to the terpenes and are probably to be regarded as hydroxypolyterpenes.
The action of direct sunlight on moist turpentine oil in the presence of air, or better still, of oxygen results in the formation of pinol hydrate (sobrerol), C10H18O2. According to the solvent employed it crystallizes in laminae or needles. The inactive modification melts at 131°, the active modifications at 150°8).
Detection of Adulterations of Turpentine Oil. If the determination of the specific gravity, solubility, boiling temperature and residue upon evaporation have revealed any abnormal qualities in an oil of turpentine, further examination is necessary to ascertain whether the oil is adulterated, also the nature of the adulterant. Inasmuch as the adulterants, as a rule, reveal a different additive capacity for halogens than does the oil of turpentine, the determination of iodine and bromine absorption should here be considered. Whereas both methods have been universally adopted in the analysis of fats, the opinions as to their applicability to turpentine oil are greatly divergent. For the sake of completeness, however, they should be mentioned, all the more since the German Customs Authorities demand the examination of turpentine oil as to its additive capacity for bromine.
Iodine Absorption. The iodine value expresses the number of parts of iodine absorbed by 100 parts of turpentine oil. Hence an iodine value of 373 for turpentine oil implies that 100 g. of turpentine oil absorb 373 g. of iodine. For the method as well as for the preparation of the necessary solutions, reference should be had to treatises dealing with the analysis of fats, e.g. Lunge-Berl's Chemisch-technische Untersuchungsmethoden, 6th ed., vol. 3. p. 671.
1) Arch. der Pharm. 238 (1900), 645.
2) Grundlinien einer physiologischen Chemie der pflanzlichen Sekrete. Arch. der Pharm. 245 (1907), 386.
3) Sobrero, Liebig's Annalen 80 (1851), 106. - Wallach, ibidem 259 (1890), 313. - Armstrong and Pope, Journ. chem. Soc. 59 (1891), 315; Chem. Zentralbl. 1891, II. 168.