I S D C S T R I A L A S D E S G I S E E R I S G CHEIIIISTRY
January 15. 1930
115
Quantitative Hydrogenation of the Principal Unsaturated Components of Turpentine, Pine Oil, and Rosin' W. E. Shaefer HERCULES POWDER COMPANY, EXPERIYESTAL STATION, KEXVIL, N. J.
SA study of various methods for measuring the uiisaturation of naval stores products and their components, a considerable amount of time was devoted to quantitative hydrogenation. It was recognized that quantitative hydrogenation, if it could be applied to these compounds, might be of value in the analysis of pine oil and turpentine.
A simple and accurate method for quantitative hydrogenation at ordinary temperature and atmospheric pressure with palladium as catalyst is described. This should prove of value in the study of pure compounds of unknown constitution. After good quantitative results had been obtained in the hydrogenation of maleic acid, the method was applied to a-pinene, dipentene, diterpene, a-terpineol, abietic acid, and ethyl abietate. Pinene and dipentene were found t o react with almost identical amounts of hydrogen under the experimental conditions imposed. Some of the results are plotted to show the rate of hydrogenation.
Apparatus
After a careful study of the various forms of apparatus ( 1 , 2. 4, .5, 6,7 , 8, 10, 11, 13, 15, 1.5, 16, 17') which have been employed by previous workers in the field of quantitative hydrogenation, it seemed that the most satisfactory apparatus for the present purpose was that designed by Piccard and Oppenheim 19). This apparatus is shown in Figure 1. It consists of an inverted 500-cc. graduated cylinder, A , and a long-neck reaction flask, B , which are connerted by a glass tube as indicated and are attached to a wooden frame. The frame is fastened t o a horizontal iron axis and shaken mechanically; in this TTay a very vigorous oscillatory motion is obtained. The upper end of the glass tube inside the cylinder A is bent over and protected from injury by being wrapped with a cloth; the lower end is provided with several bulbs t o prevent the glacial acetic acid in the flask from coming in contact with the rubber stopper and extracting sulfur which would poison the catalyst. The leveling bulb is filled with water saturated with hydrogen. The cylinder A was calibrated while it contained the hydrogen inlet tube. 4 correction of 2.3 per cent for the volume of the tube was always applied.
the flask B by means of a bent wire or hoohed glass rod. The apparatus is alternately evacuated and filled with hydrogen s e v e r a l t i m e s a s before. The volume of hydrogen in the apparatus, the temperature of the cylinder and of the bulb, and the barometric pressure are noted. By shaking the apparatus the thin glass stern a t the base of tube C is broken. whereuoon the tube falls down and the sample is dissolved in the gla'cial acetic acid. I n every experiment the stem broke readily and in only one case did i t break prematurely. Readings of volume, temperature, and pressure are made occasionally until the weight of hydrogen in the apparatus becomes constant. The palladium hydroxide is prepared by the addition of sodium carbonate-avoiding an unnecessary excess-to a solution of palladium chloride. Care must be taken that the
rm3COEN
FRAME
-3
Procedure
I n the reaction flask B are placed 25 cc. of glacial acetic acid, a weighed quantity of palladium hydroxide paste (12) (usually 0.5 gram), and a few milligrams of freshly reduced palladium. The pailadium is used to start the autocatalytic reduction of the palladium hydroxide. After transferring practically all of the water from the cylinder to the leveling bulb and closing stopcock 1, the apparatus is alternately evacuated and filled with hydrogen several times. A gaswashing bottle containing concentrated sodium hydroxide solution is placed in the vacuum line in order to absorb acetic acid vapor and prevent i t reaching the vacuum pump. After the apparatus has been filled with pure hydrogen, stopcock 2 is closed and stopcock 1 is opened. The apparatus, attached rigidly t o its wooden frame, is shaken until reduction of the palladium hydroxide is complete, as shown by occasionally measuring the hydrogen in the cylinder A a t atmospheric pressure. The reaction flask B is disconnected from the rest of the apparatus. A weighed sample of the substance to be examined, contained in tube C, is lowered into 1
Received November 1, 1939.
wL
'Figure 1-A
LC A_
LET iA C 3
paratus for Quantitative Eydrogenation
palladium chloride solution is free of hydrochloric acid, because palladium hydroxide cannot be precipitated in the presence of much sodium chloride on account of the formation of a soluble complex salt. The precipitate, washed by decantation and filtered by suction, is dried to a stiff paste on a porous plate and preserved in a tightly stoppered bottle. B y the ignition of a sample of this paste it was shown t o contain 18 per cent of palladium.
-Kesuirs .
As a test of the method, maleic acid was hydrogenated t o succinic acid. The specimen of maleic acid possessed a n acidity corresponding to a purity of 99.31 per cent. T h e
AA\-dLYTICdL E D I T I O S
116
results of four consecutive experiments, s1ion.n a t the top of Table I, gare assurance that the method \%-assuitable for the quantitative hydrogenation of easily hydrogenated compounds. The results of the hydrogenation of dipentene, a-pinene, diterpene, and of two specimens of a-terpineol are presented in Table I and some of them are plotted in Figures 2 and 3. Dipentene and a-pinene are the principal constituents of
20
40
80
BO
IO0
I20
140
io0
180
200
,
I
220
240
,
steam-distilled wood turpentine; a-terpineol is the chief unsaturated constituent of pine oil. The diterpene used in this work is a polymer of dipentene. The dipentene and a-pinene were freshly distilled from sodium through a Hempel column containing solid glass beads. The fraction of dipentene was collected a t 175.7-177.7' C.; that of apinene a t 156.9-157.9' C. The a-terpineol was freshly distilled and boiled a t 217-218' c. Table I-Experimental Data Pd(OH)z PASTE WEIGHTHYDROGEN ABSORBED EXPT. USED SAMPLE o s SHAKING
1 2 3 4
Gram
Gram
0.5 0.5
0,9639 1.1135 0.9968 1.4946
0 5 0.5
5
Gram MALEIC 0,01681 0,01964 0,01746
Yo]. 2, s o . 1
drogenation of dipentene to carvomenthene during the first 20 minutes of the reaction proceeded about one hundred times as fast as the hydrogenation of the carvomenthene to p-menthane after the end of the first hour. Armstrong anti Hilditch ( 3 ) ,using nickel as a catalyst. found the rate of tlic first phase of hydrogenation of dipentene to be four time5 that of the second. Since dipentene and a-pinene react with almost identical amounts of hydrogen under the experimental conditions of this work, it is clear that quantitati\e hydrogenation cannot be used to shorv the relative proportion of these substances ill a mixture containing them uiiless the Conditions of temperature, prewure, or catalyst are so changed that both of the double bonds in dipentene are caused t o react with hydrogen within a reasonable length of time. However, the method is capable of showing quite accurately the total amount of dipentene arid a-pinene present in a mixture which contains no other substances capable of being hydrogenated. It was be!ieved that the crystalline a-terpineol used in the above experiments was quite pure. S o explanation is offered for the fact that the results are variable and, on the average, almost 5 per cent too high. The hydrogenation of diterpene was continued over a lorig period in order to find if the absorption of hydrogen would finally stop. The data show conclusively that it did stop, there being no change in the volume of hydrogen in the apparatus during the last 12 days of the experiment. The data are plotted in Figure 3. ,
6-
THEORY
,'
c-
ACID
0,02609
1.74
1.75 Li5
1.74 1.74 1.74 1.74
1.76
(r-PINENE
1 0.2Q (Curve 1) 2 0.5 (Curve 2) 1 0.5 (Curve 3) 2 1.0 (Curve 4) 1 1 2
1
1.0 0.5 0.5
0,7934
0,01161
1.46
1.48
1.9290
0,02899
1.50
1.48 1.48
1.51
1 48
1.0586
DIPENTESE 0,01603 1.51
0,9903
0.01493
1.036i
DITERPESE 0,01531 1.481
For one double bond only
1 . 4 8 For two double bonds
a-TERPIXEOL-FIRST S P E C I M E N 0.00758 1.37 1.31 0,5521 1.40 1.31 0.9855 0.01337 e-TERPINEOL-SECOSD SPECIMEN 1.31 0.01333 1.29 1.0483 1.36 1.31 0,9900 0,01351 1.31 0,01454 1.42 1,0256
0.5 0.5 0.4 T h e P d ( O H ) ? paste used in this experiment had dried t o such a n ext e n t t h a t 0 2 gram of it contained the same amount of palladium as w a s present in 0 5 gram of t h e standard paste b This represents t h e hydrogen absorbed on shaking 3 hours and stdnding 41 days. 2 3
I n several evperiments this method was applied to abietic acid and ethyl abietate. The amorphous abietic acid had an acid number of 184.0, which corresponds to a purity of 99.1 per cent. The results are shomi in Table I1 and Figure 2.
Q
The results for a-pinene are reasonably close to the theoretical value. It is noteworthy that the reaction proceeded much faster in the second experiment, in Tvhich 0 5 gram of moist palladium hydroxide paste was used, than in the first experiment in which the paste was too dry. Dipentene should react with 2.96 per cent of its weight of hydrogen. I n the above experiments with dipentene the rate of hydrogenation became very slow when about half of the theoretical amount of hydrogen had been absorbed. I n fact, under the conditions of these experiments, the hy-
T a b l e 11-Hydrogenation
COMPOLXD Abietic acid (curve 5 ) Abietic acid (curve 6) Ethyl abietate (curve 7J
of A b i e t i c Acid a n d E t h y l A b i e t a t e THEORETICAL AMI OF HYDROGEN WEIGHT HYDROGEN Pd(OH)z ABSORBED IN' REQUIRED TO SATUPASTE \vEIGHT 2 3 4 R A T E ONE DOUBLE USED SAMPLE hours hours hours BOAD Grams Grams yc ch yo C' 2 0
1.9233
0.60
0.64
0.66
0.67
2 0
1.0017
0.66
0.67
0.69
0 67
0.5
2.9674
0.625
..
,
.
0.61
Each of the above compounds has two pairs of doubly linked carbon atoms. Apparently one of the double bonds can be saturated readily, while under these experimental conditions the other one adds hydrogen very slowly. Conclusions
The method for quantitative hydrogenation which is described is a simple and accurate one which should prove of value in the examination of pure compounds of unknown
I S D U S T R I A L A S D E S G I S E E R I S G CHEXIISTRY
January 15, 1930
constitution and in the determination of the purity of compounds whose constitution is known. Maleic acid, a-pinene, and diterpene are quantitatively hydrogenated by this method. However, only one of the two double bonds in dipentene and abietic acid becomes saturated under these conditions. Acknowledgment The writer is indebted to Jean Piccard for numerous helpful suggestions which were made during the progress of the work. Literature Cited [ l ) Adams, “Organic Syntheses, ’ Vol V I I I , p 10, R‘iley, 1928 ( 2 ) Albright, J. A m Chern S O C 36, , 2189 (19141.
117
(3) Armstrong and Hilditch, Proc. Roy. SOC.(London), 108, 128 (1928). ( 4 ) Boeseken, van der Weide, and M o m , Rrv. trav. chim , 35, 260 (1916). (5) Gough and King, Chemistry Industry, 47, 410 (1928). (6) Griin and Halden, Z . d e u t . Ol-Fett-Ind., 44, 2 (1924:; C. A , , 18, 1912 (1924). (7) Lochte, Bailey, and Noyes, J . i l m . Chem. SOC.,43, 2601 (1921). (8) Maxted, “Catalytic Hydrogenation and Reduction,” p. 22, Churchill, 1919. (9) Oppenheim, University of Lausanne Thesis, p. 13 ilE124). (10) Paal and Gerum, Ber.. 41, 813 (1908). (11) Parry, “Chemistry of Essential Oils,” Vol. 11, p . 331, Scott, Greenwood, 1919. (12) Piccard and Thomas, Ilelu. Chim.A c t o , 6 , 1045 (1923). (13) Reid, J . A m . Chem. SOL.,37, 2113 (1915). (14) Skita and Meyer, Ber., 45, 3595 (1912). ( 1 5 ) Stark, Ibid., 46, 2336 (1913). (16) Vorhees with Adams, J . A m . Chem. Soc., 44, 1403 (1C22) (17) Willstatter and H a t t , Ber., 45, 1472 (1912).
A Reductor Apparatus for Detecting Tin’ J. H. Reedy CHEMISTRY DEPARTHEST, UXIVERSITY OF ILLIXOIS,U R B A N AILL. ,
T
I S is generally detected in qualitative analysis by converting it into stannous chloride and testing for the latter by means of niercuric chloride. The second reaction Is known to be very sensitive, as little as 0.0001 gram in a volume of 10 cc. being easily detected. On the other hand, tlie rediiction of stannic tin to the stannous state is difficult and becomes quantitative only under cxrefnlly regulated conditions. The agents in most co111nion use for the qualitative reduction of stannic tin are the metals zinc, iron, and aluminum, acting in dilute hydrochloric acid. Lead has been suggested (?), but its action in the massive form is too slow to be satisfactory. Since the reduction takes place only a t the surface of the reducing metal, it is important that the solution should be brought into as intimate contact with the metal as possible. Evolution of hydrogen may interfere by forming a gaseous envelope around the metal, insulating it from the cations to be reduced. Treadwell ( 1 ) has shown that stannic tin can be quantitatively reduced to stannous chloride b y passing the solution, strongly acidified with hydrochloric acid, through a layer of specially prepared lead. This suggests that, by using lead in a modified Jones reductor, a new qualitative test for tin might he developed. -Plug of Cotton
Apparatus a n d Procedure
The apparatus (see figure) consists of a filtering column about 20 em. long, which may be easily made from glass tubing 1 to 2 em. in diameter. though a calcium chloride tube may be found quite serviceable. A plug of cotton or glass wool is placed in the bottom, and the tube is filled to a depth of about 10 cm. with pulverized (“test”) lead. The solution to be tested is acidified with about one-tenth its volume of dilute hydrochloric acid, giving a H-ion concentration of 0.5 to 0.6 S. The solution is heated to boiling and filtered through the reductor into a test tube containing 3 or 4 cc. of mercuric chloride solution. The liquid adsorbed in the Reductor Appar a t u s f o r Tin
1
Received December 9, 1929.
column is n-aslied out by means of 15 or 20 cc. of water colitailling 3 or 4 cc. of dilute hydrochloric acid. d precipitate of lead chloride may form in the filtrate, t u t it is easily recognized by its appearance and may be redissolved by Iieating. In case of doubt the precipitate is filterid out, washed with hot water containing a little hydrochloric acid, and treated with ammonium hydroxide, d blackening indicates mercurous chloride, and indirectly t,lie pr1:sence of tin. After use, the reductor limy be restored to wmking order by passing through it hot water, acidified by liytlrochloric acid, until the filtrate gives no turbidity with mercuric chloride. Usually about, 25 cc. is sufficient. There is no need of recharging a reductor until the upper half of the lead column becomes discolored or shows ot,her signs of deterioration. An occasional mashing with hot ammonium acetate solution is useful in removing lead compounds and renewing tlie active surface of the metal. Comparison with Other Methods
In order to compare the test in sensitiveness with other procedures, parallel t,ests were run with the usual zinc and aluminum methods. Results are shown in the following table: W T . OF IN
S n VOL-
SOLN. U M E Grain Cc.
0,001 0,0008 0.0006 0.0004 0.0002 0.0001
10 10 10 10 10 10
REACTIOXWITH HgCI? AFTER REDUCTION WITH: Zinc Aluminum Pb-Reductor Slight turbidity Doubtful Sone None h-one Sone
Slight ppt. Turbidity Doubtful None None Kone
Ppt. Ppt. Ppt. Turbidity Slight turbidity Doubtful
The weights of zinc and aluminum used in these tests were about 0.5 and 0.05 gram, respectively, the first, in the form of crystals and the second in the form of wire. I n both cases sufficient hydrochloric acid was added to cause a mild effervescence. Lead seems to be the only metal suitable for use in the reductor. Zinc and aluminum reduce tin salts to metallic tin, wliich is wholly retained in t,he column. Using iron, the reduction stops a t the stannous stage, but owing t o the removal of the free acid by the excess of iron the st,annous salts are hydrolyzed into insoluble forms, and the tin is again retained in the reductor. Lead, on the other hand, not only reduces bhe tin to the required valence, but has the additional advantage of being practically unatt:acked by dilute
.
