Jan. 5 , 1954
DECARBOXYLATION OF MALONIC ACIDIN QUINOLINE [CONTRIBUTION FROM THE NOYE3 CHEMICAL
LABORATORY, UNIVERSITY
15
OR ILLINOIS]
Decarboxylation of Malonic Acid in Quinoline and Related Media BY GIDEON FRAENKEL, R.LINNBELFORDAND PETERE. YANRWICH RECEIVED JULY 10, 1953 A kinetic study of the quinoline-catalyzed decarboxylation of malonic acid in organic media has been made. Two species decompose, monoanion and free acid ; only the decarboxylation of the latter exhibits strong quinoline catalysis. Kinetic and other evidence lead to the postulate that the reaction proceeds by quinoline solvation of the carboxyl carbon.
Introduction I n the course of studies’J on the intermolecular carbon isotope effect in the decarboxylation of malonic acid, we observed that the decomposition was about a hundred times as fast in quinoline as in aqueous sulfuric acid. Though quinoline catalysis of decarboxylation has been employed widely, little work seems to have been done to elucidate the details of the effect. The kinetics of the decarboxylation have been investigated for molten malonic acid3 and for the acid in aqueous s ~ l u t i o n ~ -in~ each ; case first-order kinetics were obtained. Hall5 found that monoanion and the diacid have different rates of decomposition in aqueous solution. Ogata and Odas measured the decarboxylation rates of solutions of malonic acid in xylene, aniline and dimethylaniline. I n the study to be reported here, there were four principal phases: (1) determination of the rates of decarboxylation of malonic acid and its monoanion in quinoline solution; (2) determination of the effect of varying quinoline concentration in a noncatalytic medium (here dioxane) ; (3) observation of the relative catalytic power of other amines; and (4) determination of enthalpies and entropies of activation where possible.
latter (Fig. 1) consisted essentially of a 50-cc. reaction flask (B) fitted by means of a ball joint (N) with a rod used for crushing in the hot solvent the thin-walled glass capsule (A) containing malonic acid. This vessel was connected to a 300-cc. gas reservoir (F) which was the high pressure arm of a mercury manometer (M). The entire apparatus except the manometer tube was immersed in a n oil-bath maintained within 0.02’ of the desired temperature.
G
M
-L
Experimental Materials.-Malonic acid was Eastman Kodak Co. white label grade, m.p. 135’, 99.9% pure byacidimetric titration. Quinoline was purified by fractional distillation under reduced pressure (68.5”, 0.5 mm.). Pyridine was J. T. Baker purified grade. Aniline was Mallinckrodt purified grade. Dimethylaniline was purified by distillation at reduced pressure (80°, ca. 10 mm.) after being dried over barium oxide. Dimethyl-a-naphthylamine was Eastman Kodak Co. “for sulfanilamide test.” Dioxane was purified by distillation from sodium wire a t 100-101 ’. N-Ethylpiperidine (NEP) was Eastman Kodak Co. “suitable for penicillin G determination.” Quinolinium nitrate was made by mixing equimolar quantities of purified quinoline and reagent grade concentrated nitric acid. The resulting solid was filtered, washed several times with ether and recrystallized from 95% ethanol. Apparatus and Procedure.-Malonic acid was decarboxylated in various solvents and at different temperatures. The carbon dioxide evolved was measured by observing its volume in a constant pressure apparatus or its pressure in a constant volume apparatus as a function of time. The former equipment has been described elsewhere.’ The
Fig. 1 . S c h e m a t i c diagram of the constant volume rate measuring apparatus (letters refer to text).
Before the start of each decarboxylation, the solvent was saturated with carbon dioxide. For each run, 0.3-0.4-g. samples of malonic acid and about 12 ml. of solvent were used. Infrared spectra were determined with a Perkin-Elmer double beam instrument. Matched cells were used, one containing the solvent and the other containing malonic acid dissolved in that solvent. Results.-For each run the quantity of carbon dioxide (1) P. E. Yankwich, R. L. Belford and Gideon Fraenkel, THIS evolved was plotted against time. From the smoothed J O U R N A L , 75, 832 (1953). experimental plots, representative points were used for the (2) P. E. Yankwich and R. L. Belford, ibid., 75, 4178 (1953). preparation of graphs of log. (N, - N t ) vs. t , where N, (3) C. N. Hinshelwood, J . Chem. Soc., 156 (1920). represents the maximum yield of carbon dioxide (98% or (4) A. L. Bernoulli and W. Wege, Hclu. Chim. Acta, 8, 511 (1919). more of theoretical in every run tested), and Nt is the amount ( 5 ) G.A. Hall, THIS J O U R N A L , 71, 2691 (1949). of gas evolved at any time t . Every decarboxylation proved (6) Y. Ogata and R. Oda, Bull. Inst. Phys. Chcm. Research (Tokyo), to be first order excepting run V-3, where two separate Chem. E d . , 23, 217 (1944); C. A . , 43,79044 (1949). first-order processes operated simultaneously. The appar(7) E. J. Corey and Gideon Fraenkel, THISJOURNAL, 75, 1168 ent first-order rate constant was in each case taken as the (1853). absolute slope of the logarithmic plot.
GIDEONFKAESKEL, K. L. BELFOKDAND P. E;. Y ~ i w w x c i i
16
The results are collected in Table I* along with those obtained by Ha116 for aqueous decarboxylations. Id Fig. 2 are shown typical plots of the original data and their logarithm-plot equivalent. Figure 3 shows k' as a function of quinoline concentration9 as obtained in runs V-6, 7 , 8, 9 and
L-01. T ( i
TABLE I FIRST-ORDER RATECONSTANTS FOR L)ECARBOXYl,A O F h f A L O N I C ACID I N \'ARIOUS hfEDIA AT VARIOUS TEMPERATURES
PSEUDO TION
10.
Apparent rate constant, k' X 104, OC. sec. - 1 u7.5 4 06 f 0 01 100.0 4 9 i .1 118.7 1 6 2 2
I emg.,
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Fig. 2.-Data for a typical run, as functions of t h e : A, the volume of carbon dioxide evolved; B, log ( V w - ITc). I
I
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v-7 V-s I--$) v-10 v-11 V-12
V-I3 v-1.4 V-1.i V-1G
Medium Quinoline Quinoline Quinoline IZ moles quinoline 4 . 5 i r moles quinolinium nitrate (0.5 mole h-;EP/mole Quinoline diacid) ( 1 . 0 mule KEP/mole Quinoline diacid) Quinoline (.5.0 moles NEP/mule diacid) Quinoline 12.3 moles NEP/mole diacid) ( 2 . 3 moles S E P / m d e Quinoline diacid) Quinoline t- ( 2 . 3 mr,lrs NEP/mole diacid) Dioxane 0 . 27 .1.I qiiinuliiie in dioxane 0 53 .',I quinoline in dioxane 1 ,ZQ J I quinoline i n dioxane 4 . 2 6 .W quinoline in dioxane ( 2 0 nmles N EPjniulr Diuxane diacid) Dioxane + ( 5 . 0 moles NBP/mulc diacid ) Pyridine 1)imcthylaniline .\niline I)imethyl- a-naphthylarniiie \L'ater: free acid dcconiyusiiii>ii (Hal 1 ) \Vater: anion decomposition
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