INDUSTRIAL AND ENGINEERING CHEMISTRY
850
G. R. Lucas, N. C. Frisch, R. G. Linville, and R. C. Osthoff for the preparation and purification of some of the compounds used in this study; and Lillian Wilcox for the determination of the carbon and hydrogen values of the standard combustion compounds. LITERATURE CITED (1) Gilliam, W. F , Liebhafsky, H. A., and Winslow, A. F., J . Am. Chem. Soc., 63, 801 (1941). (2) Gilman, H., Clark, R. N., Wiley, R. E., and Diehl, H., Ibad., 68, 2728 (1946). (3) “Handbook of Chemistry,” N. A. Lange, ed., 6th ed., pp. 152030, Handbook Publishers, Sandusky, Ohio, 1946. (4) McHard, J. A . , Servais, P. C., and Clark, H. A., Anal Chem., 20, 325 (1948). ( 5 ) Marvin, G. G., and Schumb, W C., J . Am. Chem. Soc., 52, 574 (1930).
Vol. 41, No. 4
(6) Parr Instrument Co., Noline, Ill., “Parr Manual No. 122,” 1951. (7) Parr Instrument Co., private communication. (8) Parr, S. W., J . Am. Chem. SOC.,22, 646 (1900). (9) Ibid.,29, 1606 (1907). (10) Schumb, W. C., Ackerman, J., Jr., and Saffer, C. M., Jr., Ibid., 60, 2486 (1938). (11) Tanaka, T., Takahaski, V., Okawara, R., and Watase, T., J . Chem. P h y s . , 19, 1330 (1951). (12) Tannenbaum, S..Kaye, S., and Lewenz, G. F., J . Am. Chem. SOC.,75, 3753 (1953). (13) Thompson, R., J . Chem. SOC.,1953, p. 1908. (14) Tseng, C., and Chao, T., Sei. Repts. Natl. Univ. Peking, 1 (4), 21 (1936). (15) Whitmore, F. C., and coworkers, J . Am. Chem. S o c , 68, 480 (1946). RECEIVED for review July 2 , 1954.
ACCEPTED October 20, 1984.
Solubility of Acetylene in Donor Solvents A. C. RIcKINIhS Union Oil Co., P.O. Box 218, Brea, Calif.
HERE I S A FORMULA for testing compounds as acetylene solvents
. . .which eliminates
unsatisfactory compounds immediately
. ..which allows choice of superior compounds for actual synthesis and testing , . . predicts solubility with 9.6% average deviation
based on the assumption t h a t several active centers in a molecule, even though they were adjacent, would be additive in contributing to the solvent power of the solvent for acetylene. -4n active center is considered to be an electronegative atom which has electrons that are available for hydrogen bond formation with the protons of acetylene. T h e extent of this availability is awumed t o determine the solvent power of any solvent which dissolves more acetylene than that predicted from Raoult’s law. An attempt to apply the formula t o polyfunctional compounds such as biacetyl or the dimethyl ether of tetraethylene glycol shows that Huemer’s assumption is erroneous. For example, on the basis of Huemer’s rule, methylene diacetate should dissolve twice as much acetylene per mole of solvent as does methyl acetate. Actually, methylene diacetate dissolves only two thirds as much acetylene per mole as does methyl acetate. This fact is further substantiated by the heats of mixing studies of Zellhoefer and Copley (IO), which indicated that only alternate oxygen atoms are available for hydrogen bonding in the molecule of the dimethyl ether of tetraethylene glycol.
URING the course of investigations to find solvents with exceptional solvent power for acetylene, an empirical formula was developed for predicting the solubility of acetylene in liquids. For 35 solvents of widely varying structure whose solvent power for acetylene varied about tenfold on a mole basis, t h e average deviation between calculated and experimental values was 9.6%. When solubility data existed for only one compound containing a specific substituent group, the k value for this substituent was calculated from the one compound. These solubilities, calculated and predicted, were not included in t h e average deviation calculation, since of course the deviation in this instance is always zero. T h e high solvent power of hexamethylphosphoramide for acetylene was predicted from this formula, and on testing it proved t o be t h e most powerful nonreacting acetylene solvent known. T h e use of hexamethylphosphoramide for an acetylene solvent was disclosed by Levine and Isham (6). AN EARLIER CORRELATION
Huemer ( 4 ) developed an empiiical formula which was applicable in a restricted number of cases. This formula was
DEFIXITION OF FORMULA FOR PREDICTING SOLUBILITY
T h e form of the function used for correlating acetylene solubilities is
s
=
k A v “ 2 (~ ~X s ) d 3
(1)
where S is grams of acetylene dissolved by one mole of the solvent a t 25” C. and one atmosphere of acetylene; X A is the electronegativity as given b y Pauling (8) of the atom, A , forming the hydrogen bond with acetylene; ZB is the electronegativity of the atom, B , to which A is bonded; iV is the bond order-Le., I, 2, or 3 for -C-Cl, -C=O, and --C=N, respectively; d is the bond distance, as determined by the summation of atomic radii of the electronegative atom and the one to which it is bonded as given by Pauling (9); and k is a factor assigned to substituent groups comprising the rest of the molecule. I n a polyfunctional Eolvent molecule, the two atoms, A and B, which give the largest value for N ~ ‘ ~ ( x-A z ~ ) d 3are chosen, while the rest of the molecule is considered to be merely substituents influencing the value of k . If the atom pair, A B , is separated
I N D U S T R I A L A N D E N G IN E E R I N G C HE M I S T R Y
April 1955
Table I. Relative Hydrogen Bonding Power (for Acetylene) of Various Donor Centers Donor Center
N1'2(xA
\
-p.=o
/ \ / \
/ \
P-0--P
- sB)d3
Donor Center
7.66
/
h'1/2(eA
\
2.09
-C-Br
/ \
-C--N
7.64
- xB)@
/
1,59
/
\
s=o
4.97
-C-F
1.32
-X=O
1.16
\
F--
4.21
/ -C.--O\
\ -C3 N
corresponding k values calculated by fitting the data for one or several solvents. The common groups ( 8 ) in this table show an increasing electron attraction (+I) as follows:
F
> C1 > SCHI > CO(H) > CO(C&&) > C.5H6 > OC2HS > H > CO(CH3) > CH3 > C ~ H > S N(CHa)a
When the donor center atoms have more than one free valence and the free valences are bonded to different substituent groups, k is calculated as a first approximation to be the arithmetic average of the k for each group.
0
\
2 93
851
0
/ \ -C-H
2 73
0
/ 2.70
by more than two methylene groups from another active center, the two centers may be considered individually. The donor strengths (electron availability for H bond formation) of various atom pairs or active center groups of the solvent molecule as measured by the value of N1'2(2a - ze)d3 are given in Table I. I n this table the substituents on the free bonds are assumed in each case t o have identical effects in order to give a constant k in Equation 1.
N
V
-E
12
T=20°C.
Figure 2. Solubility of acetylene in dimethylformamide as affected by acetylene pressure
- 53
I 0.5
1.0
LOG V/V'
1
Substituent groups having more than two carbon atoms in the alkyl chain do not give reasonable k values. For example, propyl, butyl, and diethylamino groups give much lower k values than would be anticipated from the acceptable electron release tendencies of these groups. Unfavorable steric factors may be the cause of these unexpected low solubilities.
2.0
Figure 1. Solubility of acetylene in various solvents as influenced by temperature
The solubility of acetylene in solvents possessing no centers for hydrogen bond formation, such as hydrocarbons, alkyl iodides, and alkyl sulfides, is determined largely by internal pressure differences ( 3 ) and is equal t o or less than that predicted for an ideal solution. When the solvent is capable of intermolecular association-i.e., water, amides, alcohols, and other molecules containing both active hydrogens and donor centers-the donor centers are utilized by the solvent, and the solvent power for acetylene is low (6). Solvents such as carbon disulfide and carbon tetrachloride, which are characterized by'resonating positive and negative charges on the electronegative atoms of their molecules (7), show a solvent power for acetylene much less than that predicted by Raoult's law. The hydrogen bonding power of solvents such as these is negligible. ELECTRONEGATIVITY VALUES (k)
The value of k in Equation 1 is dependent on the substituent groups and is assumed to be a measure of the electron releasing power of the group. Table I1 lists substituent groups and the
Table 11.
Substituent Groups and Their k Values for Acetylene Solvents
Substituent ---N(CHs)z ---P(0CHa)z --NCaHs -CHzOCHa -CzHs ---C(CHa) (0CHs)z -CHa ---CO(CHs) -H -0CzHa --.B(0CHa)z
k Value 1.24 1.15 1.08 0.94 0.68 0.64 0.63 0.60 0.53 0.48 0.46
Substituent -C6Hfi -Si(OCzHr)s -CO(CsHfi) -CHO --CzHaOCO(CHa) -CPHP -SCHa -C HzOCO (C Ha) -CO(CaFT) -c1 -F
k Value 0.43 0.41 0.39
0.37
0.36 0.29 0.28
0.22 0.14 -0.07 -1.43
ACETYLENE SOLUBILITIES, LITERATURE VALUES
The solubility of acetylene in different solvents is given in the literature a t a number of different temperatures. I n order t o compare the solubilities a t the same temperature, a correction factor was used to adjust all the solubilities t o 25" C.: log V' = log V
+ 0.0113(T - 298)
(2)
where V' is the solubility (ml. CZHza t standard temperature and pressure per ml. of solvent at 25' C.) of acetylene in the solvent
852
INDUSTRIAL AND ENGINEERING CHEMISTRY Table 111.
Vol. 47, No. 4
Solubility of Acetylene in Organic Solvents a t 25" C. Solubilitya
...Experimental Grams IVU.
Donor Solvents (without intermolecular association) HexamethvlDhosDhoramide Dimethylfbrmamide N ,N,N',N'-Tetramethylmethylphosphondiamide Dimethylsulfoxide Tetramethylenesulfoxide Tetramethylurea Dimethylacetamide Acetylpyrrolidine Acetaldehyde Tritetramethylenephosphoramide Methylal
Formula
CzHz/ m1: solvent
'
CzHd mole solvent
Calculated, grams CzHd mole solvent
k k Value 1.24 0.94
Substituents used (CHs)?N(CHo)?N-, H-
43 33.5
8.806 2.5
9.50 2.41
33 32 30.7 25.6 24.4 24.2 24.1 22.3 22.3
5.3 3.10 3.00 3.57 2.6: 2.9 1.57 6.4) 2.3
7.95 3.13 3.13 3.35 2.54 2.33 1.56 8.25 2.14
1.24 0.94 0.86 0.58 1.0s 0.79
22
2.1)
1.70
0.29
HCOOCHa CHsCOOCHs (CHa0)sP (CzHs0)aPO
20.0 19.5 19 19
1.45 2.6 3.7
1.q
1.47 1.82 2.60d 3.68d
0.62 0.89 0.48
[(CHs)zN]zPOF
19
2.7b
2.68d
0.35
(CHs)zN--. F-
(CHaOCzH4OCzHa)zO (CHdzCO CHsCOOCzHs
4.8 1.62 2.06 2.35 1.64 2.14 1.83C 1.41 1.32
4.95 1.70 1.88 2.41 1.55 2.32 2.18 1.42 1.32
0.56
(CHa)?NCOOCHs C4HA CHO CzHsBr rOCHzCHzCHzCO,,
19 18.9 18.2 18.1 17 5 16.8 16.8 16.2 15
CzHsO--, CHfCH3 CHaCO--, GHs(CHs)ZN--, HCHO--, CzHs(CH3)2N--, CZH~OCdHsS-, HCzHs-CZH4--, CHsCO
N ,N , N ' &"-tetramethylaminoaminoacetamide Ethylene oxide Glyoxol tetramethyl acetal Acetonitrile Diethyl oxalate dimethyl acetal
CHsCON [N (CHs)?lz CaHaO CH(OCHa)zCH(OCHa)z CHsCN C(OCHa)z(OC?Hs)COOC?Ha
14.8 14.2 14.2 14.0 14
2.59 0.8 2.5b
2.54 0.85 3.75 0.83 3.25
0.93 0.29 0.64 0.63 0.59
Methyl orthoacetate Trimethylmercaptophosphate 2-Methyl-2-methoxy-l,3-dioxolane
CHsC(0CHs)s (CHsS) sPO rCHzOC(OCHs) (CHa)OCHm
13.6 13 13
1.9b 2.1;
2.33 2.15d 1.88
0.64 0.28 0.64
-C(CHa) (0CHl)z C H a , -C(CHa) (OCHa)? CHsS-cZH4-
Methyl borate Acetal N-Nitrosopyrrolydine Methyl benzoate Propionaldehyde Methylene diacetate Ethyl perfluorobutyrate n-Propyl carbonate Dioxane satd. with trioxane
(CHs0)aB CHaCH(0CzHs)a C4HsNh 0 CnHsCOOCHa CzHsCHO
12 11.9 11 10.2 9.8
CSF~OOCZHI (n-CsH7O)zCO rOCzHaCCzH4,
8.5 8.3 8.1
l.tib 2.0 1.16) 1.5 0.8% 1.2 1.26
1.60d 2.14 1.08 1,524 1.656 1.20d 1.23d 1.93'
-B(OCHs)z, CHsCHsOCHz-, CzHt.C4HaNC6HsCO--, CHaCzHs-, HCHsCO--, CHzOCOCHs CsH7CO--, CZH6CZHS,-COzR7 -cZH4CHsOCHs--, CzHs(CZHKO)~S~--, CzHsC6HsCnHs--, CHsCzHs-, CHa-
Methylnaphthodioxane
bHz
\o/
Methvl formate Methj.1 acetate Methyl phosphite Ethyl phosphate Tetramethyldiamidophosphonyl fluoride Dimethvl ether of tetraethvlene giyooi A r..e..h n e . .... Ethyl acetate Diethylformamide Ethyl formate Trimethyl carbamate Form ylpyrrolidine Ethyl bromide Butyrolactone
Hb
\o/
(CHa)zN-, CHI C H a CHs(CHdzN(CHa)?N--, CHsCaHaN--, C H a CHs--, HC4HsNCHaOCH-, CHs-
bHa
g;&y&y) ?
-~
CHaCOOH CzHsOH n-CnHiiOH
Nondonor solvents Benzene Chloroform Dimethyldisulfide E t h 1 iodide Carcon disulfide Carbon tetrachloride a Solubilities from literature except as noted. Solubilities determined by the author. c Solubilities determined by Don Anderson. d Sihgle compounds used to calculate IC values and therefore are not included in e Long alkyl groups may provide steric hindrance to H bonding and therefore experimental values.
and V is the solubility of acetylene in the solvent a t T o C. Figure 1 shows that this correction is valid over a temperature range of a t least 40" C. in the regiop of 25' C. for several donor solvents. When applying a pressure correction, the solubility was assumed to be directly proportional to the partial pressure of the acetylene in the vicinity of one atmosphere. A linear curve is obtained when the solubility of acetylene in dimethylformamide is plotted versus the pressure (I).
.0.82
2.8 1.6
0.50
0.68
0.64 0.89 0.53 0.86
0.81 0.68 0.45
A:ib
0.85
0.55 0.79 1.25 0.52 0.61 0.41 0.42 0.66 0.29
6.0
1.5h 1.6 1.15 0.62 0.75
1.93 1.60d 1.15d 0.89 1.78e
0.66 0.55 0.43 0.56 0.66
5.8 5.8 3.4
0.39 0.39 0.43
5.6 3.9 3.8 3.6 1.0 0.23
0.58 0.36 0.44" 0.34 0.07 0.03
8.8
7.7 6.2 6.0 6.1
Ethyl orthoformate Ethyl orthosilicate Benzophenone Dimethylaniline Methyl n-propyl ketone Donor solvents (intermolecularly associated) Acetic acid Ethanol 1-Pentanol
1.04 0.63 0.63
... ... ... 0
0.36d 0 0 0 0
.. .. ..
HCO--, CHsCHsCO-, C H a (CHsO)?P--, CHsCZHKO-
(CHdiN-, CHa-CzHd-C(CHa)(OCHs)Z, CHB CsHs-, -CHzOCO(CHs) CHs-
...
... ...
0.13
... ... ...
...
C1--, H-
... ...
-0.07
determining average deviation between calculated and experimental values. are not included in determining average deviation between calculated and
ACETYLENE SOLUBILITIES, EXPERIMENTAL VALUES
T h e experimental values were determined in most cases by bubbling acetylene through a weighed amount of solvent until either the weight of solvent and dissolved acetylene was constant or until the weight loss per volume of acetylene passed through was constant. The acetylene was purified by washing with water, drying over calcium chloride, and passing through a bed of activated charcoal. When the solvent had an appreciable vapor pressure a t room
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1955
temperature, the solubility was determined by contacting a known volume of gas with a known volume of liquid. The essential parts of the apparatus are a gas buret for determining the volume of acetylene before and after absorption and an absorption flask for contacting the acetylene with the solvent.
,
I n operation, the entire system from the gas buret to the absorption flask is first swept free of air with acetylene. After the system has been purged, the pressure of the acetylene remaining is brought to atmospheric pressure b y adjusting the mercury level in the gas buret. A reading of the gas buret is taken, and a known amount of solvent is introduced through a specially designed funnel on the absorption flask. The solvent is then cooled in an ice bath and stirred with a magnetic stirrer until no more acetylene dissolves. The ice bath is removed and allowed to warm to room temperature, under constant stirring, until equilibrium is established. A new reading on the gas buret is taken with the acetylene a t atmospheric pressure. Table I11 shows the “normalized” experimental solubility of acetylene in a number of solvents compared to the calculated solubility.
853
LITERATURE CITED
(1) E. I. du Pont de Nemours & Co., Wilmington 98, Del., Grasselli Chemicals Dept., product information bull. (Feb. 2, 1951). (2) Gilman, H., “Organic Chemistry,” pp. 1844, 1847, Wiley, New York. 1943. (3) Hildebrand, J. E., “Solubility of Non-Electrolytes,” 2nd ed., p. 104, Reinhold, New York, 1936. (4) Huemer, H., Library of Congress, Washington 25, D. C., Microfilm Reel PB 73508, p. 7274, 1942. (5) Levine, M., and Isham, R. AI., U. S. Patent 2,623,611, 1953. (6) Xieuwland, J. A., and Vogt, R. R., “Chemistry of Acetylene,” p. 30, Reinhold, New York, 1945. (7) Ibid., pp. 154, 182. (8) Pauling, L., “Nature of the Chemical Bond,” p. 64, Cornel1 University Press, Ithaca, N. Y., 1939. (9) Ibid., pp. 154, 182. (10) Zellhoefer, G. F., and Copley, RI. J., J . Am. Chem. Soc., 60, 1343 (1938). RECEIVED for review June 7, 1964. ACCEPTED November 12, 1954. Division of Petroleum Chemistry, 125th Meeting, ACS, Kansas City, M o , 1954.
Plasticization of Polyvinyl Chloride with Alkyl Esters of Pinic Acid R. F. CONYNE AND E. A. YEHLE Rohm & Haas Co., Philadelphia 37, Pa. EVALUATION METHODS
PlNlC ACID ESTERS
.. .have interesting plasticizing prop-
These esters were evaluated as plasticizers for polyvinyl chloride in the following formulation:
erties
. . . may
be useful secondary plasticizers if they become commercially available at moderate cost
T
HE large and growing usage of the esters of phthalic,
adipic, azelaic, and sebacic acids as plasticizers for polyvinyl chloride leads to an understandable interest in the adaptability of other dibasic acids as raw materials for the preparation of similar esters. Such a raw material is pinic acid, prepared by the oxidation of a-pinene ( 3 ):
Polyvinyl chloride (Geon 101a) Plasticizer Tribasic lead sulfate (Tribaseb) Stearic acid B. F. Goodrich Chemical Co. Xational Lead Co.
.
a
b
60.0 40.0 1.0
0.5
The dry ingredients were blended; the plasticizer was added to the dry blend; and the whole was thoroughly blended a t room temperature and charged immediately to a 6 X 12 inch rubber mill operating at a rpll surface temperature of 325” F. The batch was mixed for 5 minutes after reaching the state of qualitative homogeneity which indicates that plasticizer and resin are “fluxed.” A t this point, the batch was removed from the rolls in three portions:
1. Sheet, 0.100-inch thick, subsequently molded (20 minutes at 323’ F.) to yield 6 X 6 X 0.072 inch test panels 2. Sheet, 0.070 inch thick, for heat stability tests 3. Film, 0.010 inch thick, for permanence testing
Modulus in tension (loo%), Shore A hardness, and low-temperature flexibility measurements were made on the 0,072-inch cy3 molded panels. The lorn temperature flexibility tests used included determination of torsional modulus as a function of temperature (ASTM D-1043-49T) (1) and determination of brittle point by a modification of ASTM D746-44T ( 2 ) . The modification consisted of using test specimens that had been conditioned w CH3 CH3 for 24 hours a t - 15” C. immediately prior to testing. 2 Steps Heat stability was measured as the number of ,, hours of exposure a t 350” F. necessary to cause ~ 0 - c - c/~ \CH-CH~-C-OH the first abrupt discoloration of test samples cut I1 H& ck, I/ \ / 0 0 CH, from the 70-mil test sheet. Samples of IO-mil films were exposed in a Fade-0-Meter. The minimum number of hours exposure required to cause the sample to crack The alkyl esters of pinic acid listed in Table I were prepared and when folded sharply on itself was taken as an index of light stacharacterized b y the Kava1 Stores Research Division of the U. S. bility of the film. Department of Agriculture, Olustee, Fla.
I
\g/ 1
