(13) Hastings, S. H., Watson, A. T.,
Williams, R. B., Anderson, J. D., Jr., ANAL.CHEM.24, 612 (1952). (14) Landa, S., Machacek, V., Collection Czechoslov. Chem. Communs. 5, 1 (1933). (15) Mair, B. J., ANAL. CHEM. 28, 52 (1956). (16) Mair, B. J., Eberly, P. E., Li, K., Rossini, F. D., Division of Petroleum chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956. (17) Mair, B. J., Glasgow, A. R., Jr., Rossini, F. D., J . Research h’atl. Bur. Standards 26, 591 (1941).
(18) Mair, B. J., Montjar, M. J., Rossini, F. D., ANAL.CHEM.28, 56 (1956). (19) . . Prelog. V.. Seiwerth. R.. Chem. Ber. 74,-1644(1941). ’ ’ (20) Roberts J. P., Gorham, W. F., J . Am. khhem. SOC.74, 2278 (1952). (21) Rossini, F. D., Mair, B. J., Streiff,
A. J., “Hydrocarbons from Petroleum,” Reinhold, Few York, 1953. (22) Rytina, A. W., Schiessier, R. W., Whitmore, F. C., J . Am. Chem. SOC.71, 751 (1949). (23) White, J. D., Rose, F. W., Jr., J . Research Natl. Bur. Standards 13, 799 (1934). (24) White, J. D., Rose, F. W., Jr., Ibid., 17, 943 (1936).
(25) Willingham, C. B., Rossini, F. D., Ibid., 37, 15 (1946). (26) . , Zelinskii. N. D., Kazanskii, B. A., Plat6,’A. F., Chem. Ber. 66, 1415 (1933).
RECEIVED for review June 6, 1957. Accepted November 2, 1957. Investigation performed as part of the Fork of the American Petroleum Institute Research Project 6. The material is taken from a dissertation submitted to the .Carnegie Institute of Technology in partial fulfillment of the requirements for the degree of doctor of philosophy by Paul E. Eberly, Jr., holder of a fellowship of the American Petroleum Institute Research Project 6.
Analysis of Phenol-Containing Volatile Oils MARTIN I. BLAKE School o f Pharmacy, North Dakota Agricultural College, Forgo, N. D.
b Phenol-containing volatile oils are analyzed b y nonaqueous titrimetry, with sodium methoxide in benzenemethanol as titrant. Dimethyl formamide, acetonitrile, and ethylenediamine are used as solvents. The titrations are performed potentiometrically with a sleeve-type calomel and platinum electrode system. A number of advantages over the conventional extraction procedure are indicated.
T
phenol content of volatile oils is usually estimated by extraction with alkali solution. Guenther (6) describes the method and its modifications and points out its sources of error and weaknesses. The extraction method is recognized by the official drug standards (11, 12) for the analysis of several phenol-containing volatile oils. Although numerous procedures involving nonaqueous titrimetry are reported for the analysis of phenolic compounds, little has been done to apply these methods to volatile oils. HE
Cundiff and Markunas (4) report the successful potentiometric titration of thymol, a phenol found in thyme oil, using pyridine as the solvent. The visual titration proved unsuccessful. KOdata were given. Karner and Haskell ( I S ) successfully titrated thymol with sodium methoxide in benzene-methanol, The solvent was butylamine. They employed a specially prepared antimony electrode and a glass electrode. A titration curve is shown but no data are given t o indicate the quantitative nature of the procedure. Butler and Czepiel (3) determined phenolic groups in lignin preparations. They used a n antimony-saturated calomel electrode system and dimethyl 400
ANALYTICAL CHEMISTRY
formamide as the solvent. The titrant was potassium methoxide in benzenemethanol. Eugenol and isoeugenol, common volatile oil constituents, were studied as model compounds. Suitable titration curves were obtained. Guenther and Langenau (9) in a review article on essential oils recognize the potential application of nonaqueous titrations t o t h e analysis of volatile oils containing phenolic constituents.
Absolute methanol, reagent grade, Merck. Benzene, anhydrous, reagent grade, Merck. Benzoic acid, primary standard grade, Merck. Ethylenediamine, 95 to loo%, Eastman. 600-
This paper reports the successful titration of certain phenols as pure compounds and as constituents in volatile oils. A platinum and calomel electrode system was employed. The solvents were dimethyl formamide, acetonitrile, and ethylenediamine. The procedure has merit as a general method for analyzing phenol-containing volatile oils. EXPERIMENTAL
T h e phenols a n d volatile oils studied were titrated potentiometrically with a Fisher Titrimeter equipped with a sleeve-type calomel electrode a n d a platinum electrode. A 150-ml. beaker served as t h e titration cell a n d was covered with a piece of heavy cardboard t o protect the contents from carbon dioxide and moisture in t h e air during t h e titration. Three holes in t h e cardboard cover admitted the electrodes and buret tip into the titration beaker. A magnetic stirrer and a glass-covered stirring bar were used to stir the solution during titration. The titrant was stored in the reservoir of an automatic buret and in titration was delivered from a 50-ml. buret. Titrations were performed in a specially constructed hood to protect the operator from the caustic fumes of the chemicals. Reagents and Chemicals. Sodium, reagent grade, Merck. Sodium methoxide, 0.1N, prepared as described below. Apparatus.
2
4
6
8
1 0 1 2
ML. O.IN SODIUM METHOXIDE
Figure 1. thyme oil
Titration of thymol and
A.
In dimethyl formamide In acetonitrile C. In ethylenediamine
8.
2 4 6 8 1012 V L . 0.1N SODIUM METHOXIDE
Figure 2. Titration of eugenol, clove oil, and bay oil A. B. C.
In dimethyl formamide In acetonitrile In ethylenediamine
Table 1.
Analysis of Phenols and Phenol-Containing Volatile Oils
Phenol or Volatile Oil Thymol Thyme oil (red)
Variety N.F. X N.F. VI1
n.1.t." 20% phenols
Eugenol
U.S.P.
Clove oil
xv U.S.P. xv
n.1.t. 85% phenols
Wintergreen oil
U.S.P.
Carvacrol
Commercial
Origanum oil
Commercial
63-74% phenols
Bay oil
N.F. X
50-65% phenols
Isoeugenol
Commercial
e
xv
Requirement
n.1.t. 98% methyl salicylate
Solvent Dimethyl formamide Dimethyl formamide Acetonitrile Ethylenediamine Dimethyl formamide Acetonitrile Dimethyl formamide Acetonitrile Ethylenediamine Dimethyl formamide Ethylenediamine Dimethyl formamide Acetonitrile Ethylenediamine Dimethyl formamide Acetonitrile Ethylenediamine Dimethyl formamide Acetonitrile Ethylenediamine Dimethyl formamide Acetonitrile Ethylenediamine
% ' Phenols 98.37 f 0.16 (5)* 28.89 f 0 . 4 3 (5) 28.67 i.0.38 (4) 28.80 i 0.08 (4) 97.70 & 0.19 (3) 100.15 f 0.15 (3) 88.82 + 0.13 (4) 89.01 f 0 . 4 1 (3) 89.71 i:0.15 (3) 99.38 i 0 . 2 4 (5) 99.18 i 0 . 1 8 (4) 100.05 f 0.35 (4) 100.57 i 0.23 (4) 99.57 i 0.43 (4) 74.57 i 0.07 (3) 74.44 i 0.40 (3) 75.14 i 0.06 (3) 63.86 i 0.35 (5) 0 . 4 6 (4) 64.24 63.11 i 0.22 (4) 100.01 f 0.28 (4) 99.67 i 0.42 (4) 99.38 f 0 . 2 4 (4)
+
Not less than.
Chief Constituent Thymol Thymol Thymol Thymol Eugenol Eugenol Eugenol Eugenol Eugenol Methyl salicylate Methyl salicylate Carvacrol Carvacrol Carvacrol Carvacrol Carvacrol Carv a cro1 Eugenol Eugenol Eugenol Isoeugenol Isoeugenol Isoeugenol
* Number of determinations. 600-
600
A C B v)
I-
0
A500
0
2
400
4
-
H
400 ML. O.IN SODIUM METHOXIDE
Figure 3.
Titration of methyl salicylate A. C.
In dimethyl formamide In ethylenediamine
2 4 6 8 1 0 1 2 M L . O.IN SODIUM METHOXIDE
Figure 4. Titration of carvacrol and origanum oil A.
Dimethyl formamide, technical, D u Pont. Acetonitrile, reagent grade, Fisher. Azo violet (p-nitrobenzeneazoresorcinol) indicator solution, saturated solution in benzene. Phenols and volatile oils, varieties indicated in Table I. Sodium Methoxide Solution, 0.1N. Approximately 5 grams of clean sodium was added s l o ~ l yto 100 ml. of absolute methanol in a flask immersed in a n ice bath. After all the sodium dissolved, 150 ml. more of methanol was added, followed by 1500 ml. of dry benzene. The solution was stored in t h e reservoir of a n automatic buret protected from moisture and carbon dioxide in the atmosphere. Prior to the titration of a sample, 50 ml. of titrant was transferred from the automatic buret to the buret of the titration assembly. The sodium methoxide solution was standardized against benzoic acid (1). Procedure. Approximately 30 ml. of solvent was placed in a 150-mi. beaker. A stirring bar was added
B. C.
In dimethyl formamide In acetonitrile In ethylenediamine
and the solution was magnetically stirred. Three drops of azo violet indicator solution were added and t h e solvent was titrated visually with 0.1N sodium methoxide solution t o t h e first permanent clear blue color. Less than 0.05 ml. of t i t r a n t was usually required to neutralize the acidic impurities of the solvent. One to 2 meq. of the phenol was accurately weighed and added to the titration beaker. For the volatile oils a n amount was weighed which contained approximately 1 to 2 meq. of the phenolic constituent. This was most conveniently done by placing the oil in a 2-dram dropper bottle. The system was weighed, oil was transferred by dropper to the titration beaker, and the system was again weighed. The solution, magnetically stirred, was titrated with 0.1N sodium methoxide solution, using the Fisher Titrimeter equipped with a sleeve-type calomel and platinum electrode system. Increments of
2 4 6 8 1 0 ' 2 ML O I N SODIUM METIiOXIDE
Figure 5. A.
E. C.
Titration of isoeugenol In dimethyl formamide In acetonitrile In ethylenediamine
0.1 ml. of titrant were added in the vicinity of the end point. The end point !vas indicated by the idection in the curve obtained by plotting millivolts against titrant added. The exact end p$nt was determined plotting AE/AT' 0s. V (ml.), DISCUSSION
The standard method for analyzing volatile oils which contain phenolic constituents is by extracting the oil with aqueous alkali solution and measuring the amount of extracted material in a cassia flask. According to Guenther (6), the method was first used by Gildemeister for the estimation of phenols in thyme oil. Guenther discusses the procedure, its modifications, difficulties, and shortcomings. The disadvantages have been indicated in a paper (2) dealing with colorimetric determination of thymol in thyme oil. VOL. 30. NO. 3, MARCH 1958
401
Table I s h o w data on the phenols and volatile oils investigated. Typical titration curves in the different solvents are shown in Figures 1 to 5. The most basic solvent, ethylenediamine, produced the greatest inflections. The end point may be obtained from the curves by inspection. Phenols are too weak to titrate in water, but they behave as weak acids in ethylenediamine. Although the inflections are not so marked with dimethyl formamide or acetonitrile as the solvent, the end point is readily obtained from a differential plot or even by inspection-for example, isoeugenol. Titration curves for thymol and thyme oil, the chief phenolic constituent of which is thymol, are shown in Figure 1. Thyme oil (red variety), K , F , VI1 (10) (containing not less than 20% phenols), was used in this investigation. According to N.F. X ( 2 1 ) thyme oil must contain not less than 40% phenols to meet official requirements. The results using the three solvents are in excellent agreement. The determination of thyme oil in dimethyl formamide by the procedure described was reported in an earKer paper ( 2 ) . A colorimetric method, the conventional procedure, and the titrimetric analysis yielded comparable results with the red and Iyhite varieties of thyme oil. Clove oil, bay oil, and eugenol (the main constituent in clove and bay oils) show similar titration curves (Figure 2) in the three solvents. The curves for eugenol and isoeugenol (Figure 5 ) compare favorably with those shown by Butler and Czepiel(3). The results in Table I for clove and bay oils and the nature of the curves demonstrate the applicability of nonaqueous titrations to the analysis of volatile oils of this type.
Bay oil (myrcia oil) contains 50 to 65% phenols. According to Palkin and Wells, as reported by Guenther (8), 89.3% of the phenol content is eugenol, while the remaining 10.7% is chavicol (p-allylphenol). The calculation of phenol content in bay oil shown in Table I is based on eugenol. hlethyl salicylate is the principal constituent of several volatile oils (wintergreen oil, sweet birch oil) or it may be prepared synthetically. Phenolic esters of this type were successfully titrated as weak acids in ethylenediamine by Glenn and Peake ( 5 ) . Typical titration curves in dimethyl formaniide and ethylenediamine are shown in Figure 3. Titration curves for origanum oil and carvacrol are shown in Figure 4, Origanum oil contains 63 to 74% phenols ( 7 ) consisting mainly of carvacrol. Isoeugenol occurs in varying concentrations in a number of volatile oils. Typical titration curves in the three soh-ents are shown in Figure 5 . The titrimetric procedure offers a number of advantages over the classical method for analyzing volatile oils ryhich contain phenolic constituents. Once the titrant has been prepared and standardized. routine analyses can be effected in a short time. Sample weights of less than 1 gram are needed, whereas the conventional method requires 10 ml. As volatile oils are generally rather expensive, this may he an important economic consideration. Percentage content is expressed in terms of weight in weight rather than volume in volume. The former is the usual manner for expressing the concentration of constituents. The accuracy and precision are superior to those obtainable by the extraction procedure. S o prob-
lems arise from difficulties in reading the meniscus or solubility of nonphenolic alkali-soluble substances. Although a Fisher Titrimeter was used, any suitable potentiometer may be employed. ACKNOWLEDGMENT
The author thanks Fritzsche Brothers, Inc., Kew York 11, K.Y., for kindly supplying the bay oil, isoeugenol, and origanum oil used in this investigation. He wishes to thank Jack Arndt for preparing the curves. LITERATURE CITED
Blake, ill. I., J . Am. Pharm. Assoc., Sci. E d . 46,287 (195i). Blake, M. I., Fibranz, L., Miller, C. E., Zbid., in press. Butler, J. P., Czepiel, T. P., -4s.~~. CHEM.28, 1468 (1956). Cundiff, R. H., hIarkunas, P. C., Ibid., 28, 792 (1956). Glenn, R. A., Peake, J. T., Ibid., 27, 205 (1955).
Guenther, E., “The Essential Oils,” Vol. 1, p. 291, Van Nostrand, New York, 1948. Ibid., Vol. 111, p. 535, 1949. Zbid., Vol. IV, p. 395, 1950. Guenther, E., Langenau, E. E., ANAL.CHEM.27, 6 i 2 (1955). “Xational Formulary,” i t h ed.,, p. 306, American Pharmaceutical Association, Washington, D. C.,
1942. Zbid., 10th ed., pp. 385, 611, 612, 19.55.
(12) “U.-S: Pharmacopeia,” 15th rev., p. 163, Mack Printing Co., Easton, Pa., 1955. (13) Warner, B. R . , Haskell, W. W., ANAL.CHEX.26, 770 (1954).
RECEIVEDfor review June 3, 1957. -4ccepted Xovember 22, 1957.
Automatic Unit for Determination of Volatile Matter in Coal, Coke, and Char R. P. HENSEL and S. A. JONES Research and Development Division, Piffsburgh Consolidafion Coal Co., library, Pa.
b In determining the volatile content of coal, coke, and char, the American Society for Testing Materials designates a 7-minute heating period a t 950” C. with modification of the heating rate for certain nonagglomerating materials. Conventional manual control prevents close duplication of heating rates and results are often erratic. The apparatus described permits close control of the heating, is sufficiently flexible to b e adapted to a variety of
402
ANALYTICAL CHEMISTRY
materials, and automatically controls the entire operation. It is designed to operate with one or two vertical tube furnaces.
I
N DETERMIKING the Volatile matter
of coals and cokes, the American Society for Testing Materials designates a 1-gram portion of sample weighed into a 10- or 20-ml. platinum crucible and lowered into a n electrical vertical tube
furnace or heated in a muffle to 9.50’ C. After a 7-minute residence time, the crucible and contents are removed, cooled, and weighed ( I ) . The volatile content is calculated from the weight loss. The shock heating effected by the above treatment is too extreme for certain types of samples and mechanical losses occur. These losses are manifested by “sparking” of the ejected particles in the hot portion of the furnace
