( i 2 l(i
HILDAHOWELL AKD
c.s. FISHER
[CONTRInUTIOhT FROM THE XAVAL STORES STATIOS,
Vol. xo
u.s.DEPARTMENT OF ~ C . R I C U I , l . l l R E 1 l
The Dissociation Constants of Some of the Terpene Acids Rs HILDAHOWELLAND G. S. FISHER RECEIVED hfARCH
17, 1958
Using Speakman's equation, the dissociation constants in aqueous solutions have been determined for the terpene acids: d-pinononic, dl-pinonic, dl-pinolic, nopinic, cis-norpinic, trans-norpinic, dl-pink (m.p. 101'), l-pink (m.p. 135"), s y m homopinic, cis-d-camphoric and camphenic. The interprotonic distances have been calculated for sym-homopinic, p i n k and the norpinic acids by Bjerrum's formula, by the X'estheimer equations and on the basis of the geometry of the assigned parameters. I n contrast t o many other acids previously reported, the cis-pinic and cis-norpinic acids showed K I / K sratios which were very close t o the ratios for the corresponding trans forms. Also, the interprotonic distances calculated by the various methods d o not provide an adequate basis for assignment of configuration or conformation for these 1,3-cyclobutanedicarboxylic acids.
Recent investigations2-4 of the production and utilization of acids obtained from a-pinene have revealed the lack of reliable values for the ionization constants of these acids. Values have been reported in the literature for cis- and trans-norpinic (I),>camphoric (IV)6 and pinonic (VII)' acids. However, the constants for both camphoric and pinonic acids were determined in solutions with a concentration significantly higher than that recommended by Speakmans for the elimination of error in the calculation of the ionic strength. Abichandani and Jatkar, who reported the values for cisand trans-norpinic acids, also in the same article reported values for cis- and trans-caronic acids which were widely different from the values reported e l s e ~ h e r e . ~I n addition, the material designated as trans-norpinic acid was probably the cis-trans mixture which until quite recently'O was erroneously identified as the trans-norpinic acid. Consequently, the dissociation constants of these acids have been redetermined using the method of Speakman* and are presented with the constants determined in the same way for pinic, .sy:ym-homopinic (1111, camphenic (V), pinononic \ V I ) , pinolic (VIII) and nopinic (IX) acids. By utilizing dilute solutions of acids and rigorous exclusion of foreign salts, the method of Speakman permits the activities of the various ions to be calculated from the usual potentiometric titration data. X first-order equation .I' = K1 +- K I K ~ Y where S and k' are functions of pH, initial acid concentration and titrant added, can be derived from the equations defining the thermodynamic (1) One of t h e laboratories of t h e Southern Utilization Research &. Development Division, Agricultural Research Service, U. S. Department of Apriculture. Article not copyrighted. ( 2 ) J. S. Stinson a n d R a y V. Lawrence, J . O i g . Chem., 19, 1047 1~1954)
LIoore, C. Golumbic and G. 5 Fisher, THISJ O C R N A L , 78,
(-1) 11. HoIlona>-, €I. J. Andersou and TV. Rodin, I n d . Eng. Chem., 47, 2111 (1056). C. T . Abichandhni and S . K . F;.J a t k a r , .I. I n d i u n I n I f . Sci., 21A, 3 i B (1!138). (0) n'. Ostwald, 2.p h r s i k . C h i n . , 3, 3(i9 (18b9); P. Walden, H e r . , 2 9 , llj'J'2 (1SLfii); E. E . Chandler, THISJ U U R N A L , 30, 694 (1908); \V, nieckmann and Albin Hardt, Be?., S2B, 1134 (1919). ( 7 ) \V.A . R u t h and G . J . Ostling, ibid., 46, 309 (1913). ( 8 ) J . C . Speakman, J . Chein. S o c . , S55 (1940). ( 9 ) Values of ? A 2 X I O - ' and 4,76 X 10-6 for cis-caronic acid and 9.32 X 10-4, 3.60 X 10-6 for tvans-caronic acid are reported. I . Jones and F. G. Soper, J . Chem. Soc., 133 (1936), report 4.59 X 10-8 a n d 4.94 X 1 0 - 0 for cis-caronic acid and 1.52 X 10-3 and 4.78 X 10-7 for trans-caronic acid. (10) Unpublished work.
dissociation constants of a dibasic acid. X comparable derivation gives the value for monobasic acids. Thus, absolute values of K 1 and K z can then be calculated from a single titration without need for extrapolation to zero ionic strength. Furthermore, the relationship is much less cumbersome than other derivations in common use such as the one by Gane and 1ngold.l' COOH
6:roH6:H COOH
I
I1
&OOH I11
COOH
eH COOH
G O O H VI1
J-,
;.IC 3.7: 7.127 7.li7 !I.%
!L35 !I.X
h.G.3 ! I 08 !1.3J
7.12 095 8.08 9 . 2 5 8.98 0 . 3 ;
7.88 C,.M . ... 8.0'3 . ... 8.47 - 002 5 7 0 .. .. . $1 48 - , b l U 8.38 - , 577 8 . 30 - .:;:IC 7 . 3 7 _ . . . 9.21 . . , , , !L38
Tr lti 5.76 7 .67 7 67 5 . (is 7 ii7 8 .US 9 . 36 7.05 9.35 7 .(I2 P . 3 5 6 . 5 5 9.35 8.08 9 35 S.98 '3.:15
- ,C50
.,,. ..,.. ,
:in"
iillipse Sphere 15lli1,se
!I.OiiS"
osb
(i.51
-
e
5:4S 5.25 7:i-1 7.32 7 8,'< 8 . 7 0 H 2 2 8.1!1 !J.72 8 . 9 8 !!.80 8.98 8 . 3 8 6.80
...
,
- .ti00
7.17 (LlO 8 . 19 8.19
Carboxyls are assumed t o be extended and coplanar with Ct, CB and the hydrogens of the ring. Carboxyls arc turned 45" from the pnsitions in ( a ) and located on the snnie Carboxyls are turned 45' from the side of t h e plane. position in ( a ) and 1oc:ited on opposite sides of the plane. COOH axial. e CH2COOI-I axial. a
In the case of the norpinic acids, where the cis and trans configurations are known, there are significant differences in the interprotonic distances calculated for the tn-o isomers, but if less pucker were assumed even this difference would disappear. I n the case of homopinic acid conformations, (b) can probably be rejected on the basis of the poor (17) P. C. Guha, IC. Ganapathi and V. 1505 (1937).
K. Suhramanian, Ber., 7 0 ,
DISSOCIATION CONSTANTS OF TERPENE ACIDS
Dec. 5 , 1958
agreement of RT with either Rw or Rg. Conformation (c) gives better agreement than conformation (a) but planar and puckered conformations and cis and truns configurations are indistinguishable. On the basis of infrared spectra the two samples of pinic acid used had different cis-trans configurations, but both gave the same dissociation constants. The better agreement of RT with Rw would favor the puckered conformation of the cis form over the planar one; but no choice can be made for the trans form. As might be anticipated the values for RB agree well with RT values for homopinic acid, but less well for pinic and norpinic acids. Experimental T h e terpene acids were obtained by reactions . appropriate .. . with -a- and @-pinene. Nopinic Acid.--8-Pinene was oxidized with Permanganate in an- ammonium sulfate-buffered solution a i d the ciystalline product recrystallized from benzene; m.p. 125-126". dl-Phonic Acid.--a-Pinene was oxidized in t h e same wayla and the solid product was recrystallized from water and then from acetone; m.p. 104'. dl-Pinalic Acid.-dl-Pinonic acid with 1yo by weight of platinum oxide catalyst was placed in a rocking-type hydrogenator and an excess of aqueous alkali was added. T h e system was flushed with hydrogen in the usual manner and the addition of hydrogen at forty pounds pressure was begun without delay. Complete reduction a t room temperature usually took from 2 t o 5 days. T h e product was recovered from the acidified solution with chloroform which was evaporated under vacuum with little or no heat. T h e residue was recrystallized from acetonitrile to m.p. 100". dl-Pinic Acid.-dl-Pinonic acid was oxidized with hypohromite by the conventional procedure.lg The product was recrystallized from water; m.p. 99-101". I-Pinic Acid.-The dimethyl ester of crude pinic acid, obtained from a-pinene having a z 5 D +23", was refluxed with sodium methylatez0 followed by saponification. The product when recrystallized from water melted 135', [ a ] in ~ ether -3'. syni-Homopinic Acid.-The homopinic acid was obtained b y the Willgerodt reaction with pinonic acid according to Stinson and Lawrence* and was supplied by these authors; m.p. 113-117'. cis-dl-Camphenic Acid.-Camphene was oxidized with permanganate by the procedure of AschanZ1to give czs-dlcamphenic acid, m.p. 136-137". d-Pinononic Acid.--a-Pinene was oxidized with air3 and distilled to give a cut rich in verbenone and verbenol. This fraction was then oxidized with permanganate in an ammonium sulfate-buffered solution t o save Dinononic acid. The crude acid was recrystallizecj t o i i v e a' product, m.p. 131°, [ a ] D +42.5' in ether.
'
(1st M. Delepine, Bull. SOC. ckim., [ 5 ] 3, 1369 (1936). (19) Conrad Weygand, "Organic Preparations," Interscience Publishers, Inc., New York, N. Y., 19-16, p. 459. ( 2 0 ) E. R. Buchman, A. 0. Reims and & J.ISchlatter, . THISJ O U R NAL, 64, 2703 (1942). (21) Ossian Aschan, Ann., 383, 5 2 (1911).
6319
cis-Norpinic Acid.-Pinononic acid was oxidized with hypochlorite and the product purified b y recrystallization from dilute hydrochloric acid; m.p. 176'. trans-Norpinic Acid.'O-cis-Xorpinic acid was heated a t 180" in a sealed tube with 6 ,V HC1 for two hours which gave a mixture of cis- and trans-ncrpinic acid. The fmns-norpinic acid was separated from the c i s compound by recr>-stal!ization from ether. T h e purified product melted 179'; admixed with cis-norpinic acid, m.p. 137-144'. cis-d-Camphoric Acid.-The sample of this material was obtained commercially and melted 186-188'. Adipic Acid.-This sample also was obtained commercially and recrystallized t o give m .p. 152-153 O . Procedure.-The dissociation constants were determined, with a few minor alterations, according to the method of Speakman.8 T h e titrations were made at room temperature (held between 25 and 30') using a pH meter. hleasurements were made with a glass electrode which was inserted directly into the sample solution, and a saturated calomel electrode which dipped into a saturated potassium chloride solution and was connected to the sample solution by means of a capillary tube filled with saturated potassium chloride. As indicated by Speakman, i t was necessary t h a t the capillary be drawn to a very small diameter and then bent into several loops or waves in order to avoid contarnination of the sample solution with potassium chloride. The sample solution was checked and found negative for chloride ion after each titration. The system was standardized before and after each titration with buffers recommended by Taylor and Hitchcock.22 Potassium acid phthalate, 0.05 AI, was used for pH 4.01 and 0.025 M K ~ H P O I 0.025 -11I;H2P04 for PH 6.86. Usually an additional check was made with the needle marker for the neutral position of the instrument settings when the titration had progressed to the point of about pH 7 . All solutions were made up with distilled water which had been swept free of carbon dioxide with a stream of nitrogen. T h e sample solution was prepared by pipetting 50 ml. of water into the titrating cup which contained a known amount of acid to give a molar concentration ranging from 0.727 X 10-3 to 1.348 X for monobasic acids and from 0.386 X to 0.691 X for dibasic acids. Titrations mere made with 0.106 -V carbonate-frec sodium hydroxide using a mercury-operated micro-buret of 1-ml. capacity reading to 0.0001 ml. The solution was stirred during the titration with a stream of w a t e r s t u r a t e d ni trogen, both to keep the snlution free of carbon dioxide and to avoid the pH meter fluctuation encountered when using magnetic stirrers for agitation.23 Several readings of pII value were taken between 25 and 7570 of neutralization and again toward complete neutralization t o check the concentration of the acid.
+
Acknowledgment.-The authors are indebted to Dr. C. Golumbic for his helpful suggestions during the early part of this work. We also wish to express our appreciation to Mr. J. S. Stinson and Mr. Ray V. Lawrence for the sample of sgmhomopinic acid, to Dr. Bernard H. Braun for the sample of camphenic acid and to Mr. A. A Sekul for the samples of pinononic and cis-norpinic acid which were used in these experiments. OLUSTEE, FLA.
-
( 2 2 ) D. I. Hitchcock and A. C. Taylor, THIS JOURNAL, 59, 1812 (1937). ( 2 3 ) G E. Lirinqston. Chemist-Anaiysl, 43, 106 (1954).
