FORMIC ACID AS A REAGENT IN ESSENTIAL OIL ANALYSIS 491 FORMIC ACID AS A REAGENT IN ESSENTIAL OIL ANALYSIS. BY WM. H. SIMMONS, B.Sc. (Read at the Meeting, December 1, 1915.) THE action of formic acid on some of the alcoholic constituents of essential oils was examined by Bertram and Walbaum as long ago as 1892 (J. f. prakt. Chem. II., 45, 598 et Seq.), but its use as a reagent for the quantitative analysis of essential oils appears to have been first suggested by Schimmel (Half-Yearly Report, April, 1901, pp.47-49) for the estimation of citronellol in Otto of rose, in which by its means they found 26 to 29 per cent. Satie (Amer. Perf., 1907, p. 12) applied the method to the analysis of geranium oils, and in 1912 (Half-Yearly Report, October, 1912, p. 43) Schimmel unsuccessfully attempted to use it for the ,estimation of citronellic aldehyde in citronella oils.The process is based on the fact that geraniol is very largely converted into terpenes by treatment with formic acid, whilst citronellol is esterified to citronellyl formate; it is carried out by heating a mixture of 1 vol. of oil with 2 vols. of I00 per cent. formic acid under a reflux condenser for one hour on a boiling-water bath, washing the esterified oil with brine until free from soluble acid, rendering it neutral to phenolphthalein, and then saponifying it with excess of alcoholic potash, and titrating back excess of potash with standard acid.Then the percentage of citronellol may be calculated from the formula, : Per cent. citronellol = Weight of esteritied oil taken-(number of C.O.2 KOH absorbed x 0.014). Number of C.C. KOH absorbed x 0.078 x 100492 8IMMONS: FORMIC ACID AS A In. a paper before the British Pharmaceutical Conference in July, 1913, on the “ Compositionof the Alcoholic Constituents of Geranium Oils” (Year-Book of Plzarrn., 1913, pp. 565-8), I showed that by this process one obtains : 1. Incomplete decomposition of geraniol.2. Incomplete esterification of citronellol. 3. An apparent citronellol ” content of about 14 per cent. for prtlmarosa oil, probably due to (1) 4. A much larger proportion of oitronellol in Bourbon than in African geranium oils, the quantities being respectively 44 to 57 per cent., and 32 to 43 per cent. And that further it is immaterial whether the mixture is heated on a boiling- water bath or boiled on a sand-bath, though in the latter case considerable bumping occurs. Beyond reducing this bumping, no effect is produced by adding 2 grms.anhydrous sodium formate to the mixture. Further experiments on the subject have since been made by Schimmel (Hslf-Yearly Report, October, 1913, p. 64), who confirm the incomplete decomposition of geraniol by formylation, but find that with freshly prepared citronellol the results obtained by the formylation process are too high, though they decrease as the preparation ages.Umney (Perf. and Ess. Oil Record, 1914,5, 51) has also examined four different samples of commercial citronellol, which showed 9794 to 99.7 per cent. by acetylstion, but 96.6 to 119.8 per cent. by formylation.Umney has, further, returned to the subject of formylation of Otto of rose (Perf. and Ess. Oil Record, 1913, 4, 328-9), and concludes that the percentage of citronellol, determined in this way, in the finest French, Bulgarian, and Anatolian Otto of rose, varies between 32 and 39 per cent. Since the publication of my previous results with geranium oils some two years ago, I have had the opportunity of examining some fifty further samples of Bourbon geranium oil, including practically all the most important brands, and several African oils, and find that the proportion of citronellol in Bourbon oils invariably lies between 45 and 57 per cent., all, with the exception of six, being under 65 per cent., while in African oils it is between 32 and 43 per cent., thus confirming the previous results.I have since extended my investigations on the effect of formylation on various other essential oils arid their alcoholic constituents, and give in Table I. the results obtained by formylation in the usual way for one hour with 2 vols. of 100 per cent. formic acid and 1 vol. of oil. To make $he figures complete, I have also included my already-published results for geraniol, citronellol, and palmarosa oil. The results with menthol and peppermint oils being so promising, I tried reducing the quantity of formic acid to I volume of acid to 1 volume of oil, in case treatment with the larger quantity was too drastic, and the results are given in Table II,, compared with those obtained by acetylation.Inability to obtain 100 per cent.formic acid owing to the war has prevented experiments on these lines being carried further for the present, but as 85 per cent. formic acid is still available, I have made one or two experiments to determine whether this was of any use for the purpose, and the results obtained are given in Table III., compared with thoee already found with 100 per cent. acid.REAGENT IN ESSENTIAL OIL ANALYSIS 493 Acctylated Alcohols.~ ~~ Geraniol ... ... ... ... Ci tronellol ... ... ... Mixture of geraniol and citron- ellol .in equal proportions .... Geranium oils : Bourbon (56) ... ... Asian ... ... ... Corsican ... ... Trappe de Staouelii . . . . Palmarosa oil ... ... ... Ginger-grass oils (2) ... ... Linalol ... ... ... ... Ter pineol ... ... ... Rosemary oil ...Sandal-wood oil (East India& * ' Menthol ... ... ... ... Peppermint oils : American ... ... ... Japanese ... ... ... African (16) ... ... Formylatcd Alcohols. TABLE I. I I Per Cent. Calculated as- Acetylttted Alcohols. Per Cent. Calculated as- ! Per Cent. - 99.6 100.4 ::: - 66-7-79 -5 68-4 69.8 71.5 91.4 48-8-49.2 68.5 67 -6-75 *8 - - 92.0 - 55.3 51.2 Calculated as- Geraniol 9 9 - Geraniol 9 9 9 9 P ? 9 9 PI Lidkol - - San talol - Menthol 1 s Forrnylated Alcohols.Per Cent. 13.7 83.4 47.3 32 -0-42 -3 63.9 30.3 27.9 13.9 15.4-15.9 22.0 3.0 14.9 63.6 99.5 51.6 44.7 44 *0-57 02 Calculated as- Ci tronellol. ....... - 9 9 9 9 > > 9 9 9 ) 2 9 9 ) 3 9 9 9 Linalol. Terpineol. Borneol. Sant alol. Menthol. 9 9 8 9 TABLE 11. I I American peppermint oil (1) ...9 9 9 3 9 9 (2) *.' Japanese dementholised oil ... 55.3 55.0 49.1 Menthol 9 3 9 ) 52.8 I Menthol. 52.3 46.4 j ,',' TABLE 111. With 100 Per Cent Formic ! With 85 Per Cent. Formic Acid. i Acid. -. .- ..... . I I__. I I Per Cent. I Calculated as- 1 Per Cent. I Calculated as- American peppermint oil ... Bourbon geranium oil ... 52.3 51.7 Menthol Ci t r onellol 52.0 I Menthol.49.0 Citronellol. * Or calculated as citronellol 101.6 per ccnb.494 BOLTON AND REVIS: RECENT ADVANCE8 RELATING TO THE The results show that terpineol is almost completely decomposed by formyla- tion; geraniol and linalol are both converted into an appreciable quantity of ester, while santalol is only very partially decomposed, and citronellol, menthol, and the borneol in rosemary oil may be approximately estimated by the PrOCeSB.The use of formic acid as a reagent is undoubtedly of value in the examination of geranium oils and-if the right conditions as to strength and proportion of acid and duration of heating can be determined-enables an accurate measurement of the proportion of menthol in peppermint oils to be made; it appears also to offer advantages over the ordinary acetylation process for this purpose. The heating of the mixture on a boiling-water bath ensures a more Vniform temperature than is possible when boiling on a sand-bath, and no addition of sodium acetate or formate is necessary. As soon as 100 per cent. formic acid is again obtainable, it is hoped to define the conditions under which menthol can be satisfactorily determined by formy lation. I desire to acknowledge the help of my former assistant, Mr. L. V. Shatwell, who has carried out many of the estimations recorded in this paper.