As has already been pointed out under citronellol (p. 365), this alcohol is converted into the formate when boiled with formic acid, whereas other terpene alcohols, such as geraniol and linalool, are either dehydrated to terpenes or are completely decomposed. The course of the reaction is so quantitative that it can be utilized for the assay of citronellol-containing oils.3) In the presence of larger amounts of other alcohols the results are apt to be too high, due to the disturbance in the ratio of constituents produced by the formation of water. For practical purposes, however, the results may suffice.
The formylation is effected by heating for an hour 10 cc. of oil with twice its volume of strong formic acid (d15o1,226) in an acetylation flask either on a water bath or better still on a sand bath so as to maintain gentle boiling. If a water bath is used the mixture should be shaken repeatedly. When cooled the contents of the flask are diluted with water and washed until neutral. The remaining part of the process is conducted as described under acetylation.
The citronellol content can be computed with the aid of the following formula:
in which a represents the number of cc. of half-normal alcoholic potassium hydroxide solution consumed in the saponification, and s the amount in grams of formylated oil saponified.
1) Berl. Berichte 34 (1901), 3354.
2) Report of Schimmel & Co. October 1904, 129.
3) Report of Schimmel & Co. April 1901, 47.
The above formula takes no account of the precence of citronellol ester in the original oil (comp. under acetylation, p. 576). Applied to mixtures of known citronellol content, Schimmel & Co. obtained the following results:
Formylation on the water bath
for one hour on the sand bath
25°/o Citronellol . . . 50°/o Geraniol .... 25°/o Limonene ....
27,1 °/o Citronellol
40°/o Citronellol . . . 35°/o Geraniol .... 25°/o Pinene......
In like manner, citronellal, which is converted into Isopulegyl-formate during the process of formylation, can be determined separately, whereas in the process of acetylation, the alcohols are determined as well. In this case, however, the value of 7,7 should be substituted for that of 7,8 in the above formula.