A N A L Y T I C A L E D I T 1O N PUBLISHED
BY
THE
AMERICAN
CHEMICAL
SOCIETY
0
HARRISON
E.
HOWE,
EDITOR
Determination of Unsaturation in the Terpene Series LLOTD $1. JOSHEL, S T A S L E I -1.H I L L , AhD S. PILKIN, Naval Stores Research Division, Bureau of Agricultural Chemistry and Engineering, U. S. Department of Agriculture, Washington, D. C. the iodine liberated by the excess perbenzoic acid rather than during the original reaction of the perbenzoic acid with the terpene.
The usual halogen absorption methods as well as those using standard potassium permanganate or standard perbenzoic acid were found unsatisfactor\- for the determination of unsaturation in terpenes. Quantitative hydrogenation using either a platinum or a palladium catalyst furnished satisfactory results wTith a variety of terpenes, but not with the resin acids. Highpressure reduction was also shown to be a suitable quantitative method for terpenes.
T
Quantitative hydrogenation has been used to determine unsaturation in several terpenes by Shaefer (18) using a palladium hydroxide catalyst, and a micromethod has been reported b y Skarblom and Linder (19). The present authors found this general method, modified as described below, to be the most useful one investigated. Shaefer (18) reported difficulty in effecting the addition of more than one mole of hydrogen to dipentene and Conant and Carlson (4) found the hydrogenation of this compound to stop after the absorption of about 1.6 moles. We found that dipentene recently fractionated through a good column readily absorbed the calculated amount of hydrogen, whereas low results were obtained with material purified merely b y distillation over sodium. Under the conditions used the method was not satisfactory for the quantitative determination of unsaturation in the
HE quantitative determination of unsaturation in the
t'erpene series presents a rather different problem from that met with in determining unsaturation in most other classes of compounds. Because of the ease with JThich these compounds undergo substitution and ibonierization, the usual halogen absorption methods are of very little use. Particularly with the Hanus method (9) it was noticed t h a t the value obtained for a-pinene varied regularly with the size of the sample used. When the amount of reagent was kept constant, the smaller samples yielded higher values (Figure 1). Ot,lier halogen absorption methods, some specifically claiming to eliminate substitution, such as a modified Hanus method using mercuric acetate (8), the pyridine-bromine-sulfuric acid reagent of Rosenmund and Kuhnhenn (fj),and the Kaufmann method (IO), were likewise found to be unsatisfactory. Similar observations have been recorded previously: Kubelka and Zuravlev found the iodine number of pinene and turpentine as determined by the Hanus and t'wo other halogen absorption methods to be dependent upon the weight of sample (1-5') and the time of reacreported that the tion ( I C ) ; Kranz, Hrach, and Franta (1) iodine number of turpentine increased with increasing concentration of the iodine solution; Gal'pern and Vinogradova (6) obtained high values for pinene using the Kaufmann method; nnd Winkler (20) using a bromine-acetic acid solution found almost identical values for a-pinene and I-limonene which agreed with the theoretical value of neither. Two methods not involving halogen absorption-namely, the use of a standard permanganate solution (11) and of a standard perbenzoic acid solution-were equally ineffective in solving the problem. The dependence of the double bond value of a- and ,+pinene upon the ratio of the amount of reagent to the size of the sample taken, noted n-ith the Hanus method, was again observed when perbenzoic acid x-as used (Figure l), suggesting that the abnormal reaction occurred during the back-titration of
FIGURE 1. DOUBLE BOSD\-.ILGES 0 Hanus method A Perbenzoic acid
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FOR a - P I N E S E
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 13, No. 7
TABLEI. HYDROGENATION RESULTS
Compounda a-Pinene (1) @-Pinene(1) Terpineol (1) Pinocarveol (1) Dioentene (2’)
C a m hor ( 0 ) Fencgone ( 0 ) Borneol (0) Fenchyl alcohol ( 0 ) Dehydroabietic acid (one aromatic ring)
PalladiumZirconium Oxide Double Time, ’ bonds hours 0.99 3 1.00 3 1.01 3 0.94 1 1.90 1.5 1.96 1 2.98 1 2.91 1 1.67b 23 0 : 00
i:5
0 02 0.02 0 00
23 6
0 02
21
2
-4dams’ Catalyst Double Time, bonds hours 1.03 0.5 0.99 0.25 0.5 1.00 0.25 0.99 0.5 1.99 1.95 0.3 2.93 0.2 0.2 2.90 1.68C 23 1.84d 47 0.02 3 0.01 2 1 0.00 2 0.01 0.06
1.5
Number in parentheses following name of compound indicates number of double bonds present. b 100 mg. of catalyst used initially and 50 mg. more added after 3 hours A t this time 1.57 moles of hydrogen had already been absorbed. C 50 mg. of catalyst used initially and 25 mg. more added after 2 hours. Hydrogen equivalent t o 1.63 moles absorbed during first hour. d Total of 200 mg. of catalyst added in 60-mg. portions used. 1 58 moles of hydrogen absorbed in first hour a
CATALYST resin acids as exemplified by abietic and 2-pimaric acids, since in these cases, despite the addition of fresh catalyst, the reduction became extremely slow after the initial rapid absorption of hydrogen corresponding to about 1.6 double bonds. It has been shown that it is possible to introduce two moles of hydrogen into these acids using elevated temperatures and with repeated reactivation of the catalyst (16, 17). Experiments with terpene alcohols and ketones possessing no double bonds showed that they were not attacked. I n a like manner dehydroabietic acid, which contains a n aromatic ring, remained unaffected under the conditions used. Exploratory experiments showed that high-pressure hydrogenation using Raney nickel catalyst was also suitable for the determination of unsaturation in terpenes.
Experimental All the compounds used were freshly distilled or freshly crystallized and had physical constants closely agreeing with the accepted values. The apparatus described by Fieser and HYDROGENATION. Hershberg ( 5 ) was preferred t o the many others described in the literature because of its simplicity of construction and ease of adaptation to the Burgess-Parr hydrogenation apparatus which is available in many laboratories and also because it eliminates rubber tubing in the absorption system. A 100-ml.buret was used instead of the 50-ml. buret mentioned by Fieser and Hershberg and a long-necked 50-ml. round-bottomed flask served as the reaction vessel. A series of experiments indicated that acetic acid (distilled over potassium permanganate) was a better solvent than ethyl alcohol or ethyl acetate. Both Adams’ catalyst (1) and a paIladium on zirconium oxide catalyst (10 per cent palladium) were found satisfactory. Adams’ catalyst has the advantage of effecting the reduction in a much shorter time, whereas the palladium-zirconium oxide has the advantages of a smaller blank and availability by purchase. Blanks were run using 10 ml. of acetic acid and given amounts of the catalysts and the corresponding blanks were subtracted from the gross volumes of hydrogen absorbed in the subsequent determinations. The size of sample chosen was such that 3 or 4 millimoles of hydrogen would be absorbed and 10 ml. of acetic acid and 25 mg. of Adams’ catalyst or 50 mg. of the palladiumzirconium oxide catalyst were used in all cases, except as noted in Table I. (Later batches of the palladium catalyst purchased after the completion of this work were less active and the use of 100 mg. of catalyst was then advisable.) The times given for complete absorption can only be considered as approximate figures, and the shaking was of course always continued for some time longer to make certain that the absorption of hydrogen had definitely stopped. Some of the values obt,ained are given in
FIGURE3. HYDROGESATIOXS L-SING A~anis’CATALYST
FIGURE4. HYDROGEXATIOS O F ABIETIC ACID
July 15, 1941
ANALYTICAL EDITION
Table I1 for comparison with the results obtained by the other methods and a more complete list of results is compiled in Table I. Some typical rates of hydrogenat’ion curves are shown in Figures 2 , 3 , and 4. PERBENZOIC ACIDTITRATIONS. Perbenzoic acid was readily and reproducibly prepared in good yield by the method of Braun (3) using benzoyl peroxide. One to 1.5 milliequivalents of the terpene were dissolved in 10.00 ml. of a dried, approximately 0.5 N solution of perbenaoic acid in chloroform and allowed to stand a t 5’ for 24 hours and then the excess perbenzoic acid was titrated in the usual manner ( 3 ) . Blanks were simultaneously run on 10.00-ml. portions of the reagent. Other samples were allowed to stand a t 5’ from 48 to 96 hours, but the results showed clearly that in all cases the reaction was over at the end of 24 hours. The other determinations, results of which are indicated in Table 11, were carried out as described in the literature. HIGH-PRESSUREHYDROGEKATION. A bomb with a total void of 183 ml. was used, but the use of a glass liner (7) reduced the void to 142 ml. Calibration of this bomb and liner using acetone made up to a volume of 40 ml. with alcohol showed the pressure drop to be 3800 pounds per mole of hydrogen absorbed. Reduction of 17.09 grams of or-pinene made up to 40 ml. with alcohol was complete in about 12 hours at 75” (initial pressure 1670 pounds at room temperature). The pressure-drop was 480 pounds, which corresponds to 1.01 moles of hydrogen per mole of a-pinene. A similar experiment with P-pinene gave a value of 1.06 double bonds. Raney nickel catalyst ( 2 ) was used in all these experiments.
Literature Cited (1) Adams, Voorhees, and Shriner, Org. Syntheses, Call. Val. I, 452 (1932). (2) Adkins, “Reactions of Hydrogen”, p. 20, Madison, Wis., University of Wisconsin Press, 1937. (3) Braun, Org. Syntheses, 13, 86 (1933). (4) Conant and Carlson, J . Am. Chem. Soc., 51, 3464 (1929). (5) Fieser and Hershberg, Ibid., 60, 940 (1938). (6) Gal’pern and Vinogradova, Khim. Tverdogo Topliva, 8 , 384 (1937).
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TABLE11. COMPARISOS O F METHODS IWESTIGATED~ Method e-Pinene (1) 6-Pinene (1) Hanus 0.95-1 61b 1. 12 Hanus mercuric acetate 1.25 1.42 Rosenmund and Kuhnhenn 1 70 1.65 KaufmannC 2.15 2.02 Potassium permanganate 1.23 0.90 Perbenzoic acidd 1 83-1.60b 1 37-1.63b Hydrogenation (Pd) 0 99 1 00 Hydrogenation (Pt) 1 03 1 0.5 a Results are expressed a s number of double bonds iound per moleoule, and t h e number in parentheses following name of terpene indicates number of bonds theoretically present. b Depending upon size of sample. Other figures represent averages of check analyses. C Kauimann method gave a value of 2.15 double bonds for alloocimene (3) and 1.99 for dipentene ( 2 ) . d Perbeneoic acid also gave following results: myrtenol (11, 0.89; pinocarve01 ( l ) , 1.23: myrcene (31, 2.17; alloocimene (3), 2 . 3 5 ; dihydromyrcene (2), 2.10; dipentene (21, 2.03; terpineol (1). 0.87.
+
(7) Hershberg and Feiner, ISD. ENG.CHEM.,Anal. Ed., 11, 73 (1939). (8) Hoffman and Green, Oil and Soap, 16,236 (1939). (9) Jamieson, “Vegetable Fats and Oils”, p. 344, New York, Chemical Catalog Co., 1932. Kaufmann, Z . Untersuch. Lebensm, 51, 3 (1926). Knowles, Lawson, and McQuillen, J. Oil Colour Chem. Assoc., 23,4 (1940). Kranz, Hrach, and Franta, Chem. Obror, 3, 365 (1928). Kubelka and Zuravlev, Chem. Listy, 25, 124 (1931). Kubelka and Zuravlev, Chem. U m c h a u Fette, O d e , Wachse H a r m , 38, 105 (1931). Rosenmund and Kuhnhenn, 2. Untersuch. Nahr. u. Gencssm., 46, 154 (1923). Ruzicka, Balas, and Vilim, Helv. Chim. Acta, 7 , 458 (1924). Rueicka and Meyer, Ibid., 5, 315 (1922). Shaefer, IND.EXG.CHEM.,Anal. Ed., 2, 115 (1930). Skarblom and Linder, T e k . T i d . U p p l . A-C. Kemi, 67, 25 (1937). Winkler, Pharm. Zentrslhalle, 68, 433 (1927) I
Colorimetric Determination of Formaldehyde in the Presence of Other Aldehydes W. J. BLAEDEL AND F. E. BLACET University of California at Los Angeles, Los Angeles, Calif.
T
HE method of detecting formaldehyde in the presence of
higher aldehydes suggested by Denigks (3) can be made semiquantitative in charact,er with the aid of a colorimeter. The errors involved vary from 2 to 10 per cent, becoming greater as the proportions of higher aldehydes are increased. The limit of sensitivity under the experimental conditions described herewith is of the order of 0.02 mg. of formaldehyde in 5 ml. of solution. The test depends upon the fact that, the magenta color given by Schiff’s reagent with formaldehyde in the presence of sulfuric acid does not fade appreciably during 6 hours, whereas the color given by the higher straightchain aldehydes, glyoxals, and their polymers fades completely within 2 hours. Trioxymethylene reacts the same as formaldehyde. The reagent is prepared by first dissolving 0.5 gram of fuchsin in 500 ml. of water, then adding 5.15 grams of sodium bisulfite. Approximately 15 minutes later, 17 ml. of 6 N hydrochloric acid are added and the whole solution is allowed to stand for 3 hours. During this time the solution fades to a permanent, pale yellow color.
In a determination, 5 ml. of an aqueous solution of the substance to be analyzed are added to a mixture of 5 ml. of the Schiff’s reagent and 1.2 ml. of 75 per cent sulfuric acid. A known comparison solution is made up at the same time using a standard formaldehyde solution and the two solutions are compared after they have stood for 2 hours in stoppered test tubes.
Too long a time should not be allowed to elapse before the comparison is made, for even the color due to formaldehyde fades slightly on standing. Before results are considered final, the formaldehyde concentrations of the unknown and standard solutions should be within 5 per cent of each other. Accordingly, an ap-
TABLE I. TYPICAL ANALYTICAL DATA AXD RESULTS Compositions of Standard Comparison Solutions Ratio of second Per cent aldehyde HzCO t o HlCO
Ratio of Second Aldehyde HzCO in Unknown to HzCO in Present Determined Unknown
5% 0.0050 0.0050 0.0040 0.0015
0.0040 0.0040
0.0040 0 0040 0.0040 0.0040
70
%
Formaldehyde Solutions 0 0067 0.0068 0.0050 0.0050 0.0040 0.0039 0.0019 0.0020
.. .. ..
Formaldehyde-Acetaldehyde Solutions 50 0 0025 0.0024 0.0048 50 0,0045 5 0.0070 0,0068 0,020 10 0.021
40 20
.. .. ..
Error
..
3 10
Formaldehyde-Propionaldehyde Solutions 0.0040 16 25 0.0043 20 25 0.0033 0.0031
+1.5 0.0
-2.5 -5.0
-4.0 +6.7 -2.9 -5.0
-7.0 -6.0
