STUDY OF FUROIC
Ma\. 20, I937
L~~~
[ COXTRIBUTION FROM
JOHN
THENOIC -\CIDS
AND
2547
ESTERS
HARRISON LABORATORY O F CHEMISTRY, UNIVERSITY O F PENNSYLVANIA]
A Further Study of the Dissociation and Association of Furoic and Thenoic Acids and of the Rates of Saponification of Their Ethyl Esters BY SHIGERU OAE AND CHARLES C. PRICE RECEIVED DECEMBER 17, 1956 Additional data on the pX,'s for furoic and thenoic acids and on the rates of saponification of their ethyl esters indicate that the latter are not accurately predicted from the former by the Hammett equation. The difference is not due to differing degrees of association of the acids and, unlike the case of a-naphthoic acid, does not appear to be steric.
We have reported' that the saponification of ethyl 2-furoate proceeded a t a rate considerably slower than predicted from the pKa for 2-furoic acid. I n seeking additional evidence for the nature of this alleged effect, we have discovered a regrettable error of a factor of ten in the calculation of the rate constant for ethyl 2-furoate, which largely eliminates the discrepancy. We do, however, wish to report additional data on the pKa's for furoic and thenoic acids, on the rates of saponification of their ethyl esters over a wider range in temperature and on the degree of their association.
Experimental 2-Furoic, benzoic, 1- and 2-naphthoic acids were coinmercial products (Eastman Kodak Co.), while the preparation and propertie? of 2-thenoic acid were described in the previous paper.* 3-Thenoic acid was kindly supplied by Dr. E. E. Campaigne of Indiana University. All these acids were recrystallized a t least twice. The preparations of
RAn?
C O X S T A X T S FOR TIIF, L%LKALISE HYDROLYSIS OF IO3
Compound 2-Thenoate 3-Thenoate 2-Furoate Benzoate' I -Naphthoatec 2-Xaphthoatec
7.50
4 . 1 7 i 0 05
20.00 3.36 zt 0 . 0 3 2.20 i ,04 1 1 . 2 j; , 1
The saponification rate constants were determined as previously.* All the volumetric apparatus used was calibrated a t each temperature under which kinetic measurements were made, while the thermostat used was maintained within the range of 10.02'. Typical data are shown in Table I and all of the data are summarized in Table 11.
TABLE I ALKALINE SAPONIFICATION OF ETHYL %THESOATE IS $0 % DIOXANE AT 45.00 Z!Z 0.02" (Ethyl 2-thenoate) = (SaOH) = 0.02500N = a 1 , sec. X a(a - x)I kg, mole-', s e e . - ] . 1. 0.110541 0,01673 191 0.001850 ,01656 ,004325 ,261022 505 ,393446 ,01664 853 ,006550 ,008355 ,489791 ,01685 1170 .590246 ,01653 1549 ,009758 ,688209 ,01671 1881 . 011003 2255 ,730056 ,01650 ,012030 ,797596 ,01651 2698 ,013175 Mean 0.0166 f 0.0001
TABLE I1 ETHYL ESTERSO F DIOXAXE
X k?, mole-', sec. - 1 , 1.
25.04 3.5Ia(3.00') 3.33' (3.17') 15.9' (22.7') 3.42 1.28 3.46
32.50 6.51 f 0.05 6 . 2 1 3= .06 31.1 i. .-I
IN 70"~
A\ROr*IATIC AND I I E T E R O C Y C L l C .\CIDs
40.00
8.3Sb I! 2' 10.7 3.77 11.3
45.0° 16.6 i 0 . 1 16.3 i .I
AS,$
lop
Ed
14.69 14.42 13.74 14.0 13.4 14.7
PZ 8.31 8.09 8.29 7.82 6.9 8.38
e,u. -22.45 -23.46 -22.54
A€J:d,e
14.11 13.84 13.16
These kinetic values were calculated by interpolating from the values of E and log PZ. Taken from the data in ref. 2. Taken from the data by C. C. Price and R. H. Michel, THISJOURNAL, 74,3652 (1952). Kcal./mole. e Calculated from kT the equation, k = - e - A H * / R T e A S + / R and AH* = E - R T , see Glasstone, Laidler and Eyring "The Theory of Rate Proch esses," McGraw-Hill Book Co., Inc., New York, S . Y., 1941. HAMMETT U-CONSTASTS FOR Acid
THE
TABLE I11 ACID DISSOCIATION CONSTANTS IN 78.1y0 ETHANOL A N D THE RATES OF ALKALINESAPONIFICATION OF THE ESTERS,IN 70% DIOXANE
PKB
kzsapn. X 103 a t 2 5 O
saa
usb
Benzoic 6 . 7 0 (6.37") (3.42') (0.00) ( 0.00) 2-Thenoic 5 . 9 5 (5.72") 3.51 (3.00') 0 . 3 6 ( .31") 0.005 (-0.02)" 3-Thenoic (6 23") 8 . 3 3 (3.17") ( ,077 - ,005 ( - .01") 2-Furoic 5 4 3 (5.37)d 15.9 (22.7d) 0 . 6 1 ( .47d) .29 ( .36") 1-Naphthoic 6 . 2 5 (6.13") ( 1,287 2 2 ( ,127 (-- . I % ) 2-Naphthoic 6.30 (3 .46") .03 ( 0 . ooq us = (pK. for benzoic -pK,)/2.07. us = log (k,,,./3.42)/2.31. Taken from the data in ref. 2. data in ref. 1. C. C. Price and R. H . Michel, THISJOURNAL, 74, 3652 (1952). (I
'
ethyl thenoates were also described elsewhere,Z while the ethyl 2-furoate was obtained from Norwich Pharmacal Co. The esters were redistilled just before use. Dioxane was purified as before.2 Benzene was purified by repeated crystallization after fractional distillation through an efficient column. (1) C. C. Price and E. A . Dudley, THISJOURNAL, 78, 68 (1956).
( 2 ) C C. Price, E. C. Mertz and J. Wilson, ihid., 76, 5131 (1956).
As
(0.00)
.35 08 .32 . 40 .03
Taken from the
New measurements of the acid strengths of benzoic, 2thenoic, 2-furoic, 1- and 2-naphthoic acids at 25' in 78.1:& ethanol by volume were made as before,2 using a Beckman glass electrode pH meter model H2. The values obtained are listed in Table 111. Freezing point determinations were made for each acid using 43.60 g. (50.0 ml. a t 25') of pure benzene. Benzoic acid is quite soluble in benzene, but 2-thenoic acid is not very soluble (less than 2.3 g. in 100 ml. of benzene a t s o ) ,
2548
while 2-furoic acid is still much less soluble (less than 0.6 g. in 100 ml. of benzene a t 5"). Therefore, the freezing point determination of 2-furoic acid was made only in a rather lower concentration. The determined values are listed in Table IV.
TABLE IV THE VALUES OF OBSERVEDMOLECULAR WEIGHTS AZO DEGREE O F ASSOCIATION O F 2-FUROIC, 2-THENOIC AND BENZOIC ACIDSIN BENZENE SOLUTION Acid
Mol. wt.
2-Furoic
112
Discussion The data on rates of saponification, outlined in Tables I1 and 111, shorn clearly that the rates of saponification of ethyl benzoate, 2-naphthoate and 3-thenoate are in reasonable agreement with values predictable from pKa (indicated by reasonable agreement between ua and us in Table 111). The earlier discrepancy1z2 between ua and us for 1naphthoate, 2-furoate and 2-thenoate persists. However, as judged from energy and entropy of activation, the reasons for these discrepancies are dissimilar. For example, the 1-naphthoate has very niuch the lowest temperature independent factor (log PZ = 6.9), whereas the 2-furoate and 2-thenoate have the largest (log PZ = 8.29 and 8.31, respectively). A redetermination of pKa values for benzoic, 2furoic, 2-thenoic, 1- and 2-naphthoic acids (Table I N F R A R E D SPECTRA O F Benzoic
2-Thenoic Y
Rel. % ' ah.
3400 3 100-2800 ' 2670 * 2550*
35 57 55 55
3400 3 100-2800 * 2620 * 2530 *
42 79 78 78
1690* 1605 1585
83 46 47
1680*
1500
35
1525
1450 1425*
65 66
1330 1285*
75 79
1180
55
1130 1100 1075 1028 1000
50 37 47 50 37
933*
707 683 665 Bands so marked
63
Weight of sample, g.
hlol. wt. AT, "C. (ohsd.)
Degree of association, 7'
0 2343
0 160 183 82 ,127 181; 83 1-14 174 78 2-Thenoic 128 130 192 73 205 190 74 ,370 223 87 e-.iOJl .420 211 82 1.0186 .j20 230 90 1.2553 ,670 220 86 Benzoic 226 0.3268 ,205 190 78 ,7551 .420 211 87 ,7393 ,390 226 93 1.2553 ,670 220 90 Infrared spectra of benzoic, 2-thenoic, 2-furoic, 1- and 2naphthoic acids were obtained in potassium bromide disks, using a Perkin-Elmer, model 21, autorecording spectrophotometer, as shown in Table V. 2011 ,2128 0 2131 ,3268 .'io18
TABLE V BENZOIC, 2-THENOIC, 2-FUROIC, 1- AND 2-NAPHTHOIC ACIDS(IX POTASSIUM BROMIDE)
Rel. % abs.
Y
*
Vol. 79
SHIGERU OAE AND CHARLES C. PRICE
95
2-Furoic Y
3400 3150-2800* 2650 * 2560*
52 77 78 78
1685*
93
1585
89
1476
91
92
1433* 1405 1355 1283*
95 82 89 97
1428* 1387
86 73
1300*
91
1230
82
1240 1180
83 87
1107 1078 1045
930* 910 866 858
I-Xaphthoic Rel. % Y abs.
Rel. % abs.
1125
88
84 66 85
1078 1020
68 88
71 84 72 88
933* 926-913 887 851
86 80 86 60
3450 3100-2800* 2620 * 2520 * 1950 1820 1680* 1625 1595 1575 1515 1465 1450 1420* 1395 1350 1300*
59 73 68 65 48 42 90 72 77 66 75 57 63 69 54 54 83
1250 1205 1145
74
1082 1028 998 945 928* 890-880
58 50 54 48 47 64
855 808 794 772 755-745
57 61 49 89 66
720
56
76 76 1 90 770-755 87 748 84 92 735 56 95 722 64 are characteristic for the associated form of the acid.
72 68
2-Naphthoic Rel. % abs. Y
3450 3080-2750 2640 * 2560 * 1960 1810 1680 ' 1635 1595 1575 1510 I475 134.3 142.5*
*
53 64 63 64 45 43 83 69 56 57 52 61 52
69 66
1360 1305* 1265 12-10 1200 1155 1130 1100 1080 1015 985
82 62 74 68 57 66 50 49 43 47
945-925* 905 864 832
64 65 69 60
778 755 732 728
84 80
56 56
THERMAL SYNTHESIS OF TELOMERS OF PERFLUOROPROPENE
May 20, 1957
111) leads to values of aa in reasonable agreement with those from earlier Recently there have appeared two papers which are related to our study, the one dealing with the alkaline hydrolysis of ethyl 2-thenoate and 2furoate3and the other of ethyl 1-and 2-naphthoateP4 both in 85% ethanol. Using these data3s4together with the rates of saponification and p in the same ~ o l v e n twe , ~ can calculate the Hammett a-constants for the saponification rates of ethyl benzoate, 2furoate, 2-thenoate, 1- and 2-naphthoate, as shown in Table VI. Although the temperature-independent factors in these two separate experiments314are quite far apart, the over-all picture thus calculated is in fairly reasonable agreement with our data. To test the hypothesis that the heterocyclic acids might have intra- rather than intermolecular hydrogen bonding, the degree of association of benzoic, 2-thenoic and 2-furoic acids were determined cryoscopically in benzene. These data, summarized in Table IV, indicate that all three acids have almost the same degree of association, and our data do not support the earlier claim that 2-furoic acid is largely monomeric in benzene.6 (3) E.Imoto, Y.Otsuji, T. Hirai and H. Inoue, J . C h e w SOC. Japan (Pure Chem. Section), 7 7 , 804, 809 (1956). (4) P.Fitzgerald, J. Parker, J. Vaughan and A. F. Wilson, J. Chem. Soc., 170 (1956). (5) (a) D.P. Evans, J. J. Gordon and H.
B. Watson, ibid., 1430 (1937): (b) C. K. Ingold and W. S.Nathan, ibid., 222 (1936); (c) H.H. Jaffe, Chem. Reus., 63, 191 (1963). (6) L. M. Nazarova and Y.K. Syrkin, Isvesl. Akad. Nauk. S. S. R., Odiel. Khim. Nauk., 56 (1949) (C. A., 43, 4913 (1949)).
[CONTRIBUTION FROM
THE
2549
For the solid acids, infrared spectra in potassium bromide disks, as shown in Table V, reveal no significant changes in position or relative intensity of the bands associated with the carboxyl group, in TABLE VI HAMMETT U-CONSTANTS FOR THE ACIDDISSOCIATION CONSTANTS A N D THE RATESOF ALKALINESAPONIFICATIOX OF THE ESTERSIN 85% ETHANOL Acid
pKae
Benzoic 2-Thenoic 2-Furoic 1-Naphthoic 2-Naphthoic
6.70 5.95 5.43 6.25 6.30
krsapn. X lo* a t 25'
6.07" 5.63* 24.5e 4.7Qd
10.Od
uae
0.00 .36 .61 .22 .03
usf
0.00 .01 .24
-
-
.04
.08
Aa
0.00 .37 .37 .26 .05
Taken from ref. 5. Extrapolated from the value of AE (18.9 kcal./mole) and log PZ (10.6) in ref. 3. Directly taken from ref. 3. d Extrapolated from the values of AE (14.5 kcal./mole for I-naphthoate and 16.1 kcal./mole for 2-naphthoate) and log PZ (7.3 for 1-naphthoate and 8.8 for 2-naphthoate, respectively) in ref. 4. E Taken from our ua = log (k.,,/6.07 X lo4)/ measurement-see Table 111. 2.54. a
support of the conclusion that all the acids are associated in the crystalline state, as was already pointed out previously by X-ray study,? in the case of 2-furoic acid. (7) T. Goodwin and C. M. Thomson, Acta Cryst., 7, 166 (1954) (C. A., 48, 7385 (1956)).
PHILADELPHIA 4,PENNA.
ORGANIC RESEARCH DEPARTMENT, PENNSYLVANIA SALTMANUFACTURING Co.]
Thermal Syntheses of Telomers of Fluorinated Olefins. I. Perfluoropropene BY MURRAY HAUPTSCHEIN, MILTONBRAIDAND FRANCIS E. LAWLOR RECEIVED NOVEMBER 21, 1956
A novel method of producing addition-type polymers by a process which does not proceed by chain propagation is described. The formation of telomers of perfluoropropene of formula R[CF2CF(CFs)lnIwhere R = CFJ, C3F7, C ~ F ~ C F ( C F I ) , CaFgCF(CFs)CF&F(CF3) and CFzClCFCl and n = 1 to 15 has been accomplished by purely thermal means. The unique advantages of this simple process as a method of producing telomers of certain types of relatively non-polymerizable olefins are expounded.
This is the first paper in a series dealing with the syntheses of telomers of fluorinated olefins by purely thermal means. Considerable work from both academic and industrial laboratories has been described on photochemical and peroxide-induced telomerizations of fluoroolefins which are readily polymerized by free radical initiators. Little information has been reported, however, on (1) thermally induced telomerizations and (2) telomerizations of olefins which do not readily homopolymerize in the presence of free radical initiatom2 (1) The work herein reported was carried out under contract between the Office of Naval Research and the Pennsylvania Salt Manufacturing Co. Reproduction in whole or in part is permitted for any purpose of the United States Government. (2) See R.N.Haszeldine, J. Chem. Soc., 4291 (1955),for a n excellent review of many of the factors affecting telomerization.
Although perfluoropropene has been copolymerized with fluorinatedao4and unfluorinated3J olefins as well as with ethylene oxide,6 there is no literature reference to the homopolymerization of perfluoropropene to [-CF2CF(CF3)-],, in spite of considerable study.6 We have now found that polyperfluoropropenes of molecular weights to 2500 may be synthesized by reaction of perfluoropropene with perfluoroalkyl iodides a t about 200'. Moreover, the reaction may be controlled to give products of any desired narrow molecular weight range fromn = 1to 15. Replacement of the iodine atom by fluorine or (3) J. C. Sauer, U. S. Patent 2,549,935 (1951). (4) W.T.Miller, U. S. Patent 2,598,283 (1952). (5) R. M.Adams and F. A. Bovey, J. Polymer Sci., 9,481 (1952). (8) M. Hauptschein and J. M. Lesser, THISJOURNAL, 78, 676 (1956).
