April 1955 Table V.
INDUSTRIAL AND ENGINEERING CHEMISTRY Soil Removal at 75’ C., 0.5-AVinute Cleaning Time, 0.5% Detergent Concentration
Detergent Sodium metasilicate Trisodium phosphate Sodium carbonate Sodium sesquicarbonate Diphase cleaner 1 : 1 Sodium metasilicate and sodium tripolyphosphate 1 : 1 Sodium carbonate and sodium tripolyphosphate
(Duplicate runs) Soil Removal. % A B C D E F 45.8 5 5 . 0 7 1 . 3 6 6 . 3 7 9 . 0 6 6 . 4 56.6 7 7 . 8 6 4 . 6 8 2 . 3 7 3 . 1 7 3 . 0 4 4 . 4 6 6 . 5 69.8 6 8 . 3 7 9 . 7 5 6 . 5 52.5 68.5 8 0 . 4 7 5 . 2 8 2 . 0 66.4 77.5 80.1 86.0 86.6 77.3 87.9
G 75.8 72.2 74.2 77.2 82.9
55.4
60.1
71.4
68.3
81.4
70.9
71.1
56.6
550
73.3
72.0
81.0
72.8
77.3
841
the alkaline cleaners rose rapidly with an increase in temperature, while the diphase cleaner maintained a high level of cleaning efficiency regardless of temperature. The pH values for the alkaline cleaners a t 2% concentration ranged from 9.1 for sodium sesquicarbonate to 11.7 for sodium metasilicate pentahydrate. This difference in pH had no effect on cleaning effectiveness. Tor alkaline salts soils containing oleic acid were more readily removed than those containing saturated fatty acids. The latter soils were more readily removed than those that did not contain fatty acids. The viscosity of the soil was not a factor, for a t a given temperature all soils had the same viscosity. Results using the Stormer viscometer are plotted in Figure 1. Undoubtedly the polarity of the double bond in oleic acid is a factor promoting the ease of removal of soils containing it. ACKKOWLEDGMENT
still appeared substantially more effective than the alkaline salts, which did not differ greatly from each other in performance. The soil without free fatty acids continued to be most difficult to remove, while the two containing oleic acid were removed most readily. DISCUSSION
Soils containing high levels of fatty acids would be expected to be most readily removed by alkaline salts because of soap formation. Nonetheless, the diphase cleaner was most effective in the removal of soil under all test conditions. The effectiveness of
The investigation described herein was supported by Solventol Chemical Products, Inc., Detroit, Mich. LITERATURE CITED (1) Campbell, C. A , , U. S. Patent 2,399,205 (1946); 2,583,165 (1952). (2) Osipow, Lloyd, Begura, Gonaalo, Jr., Snell, C. T., and Snell, F. D., IND. ESG.CHEM.,45, 2779-82 (1953). (3) Reich, Irving, a n d Snell, F. D., Ibid., 40, 1233-7, 2233-7 (1948).
ACCEPTEDOctober 30, 1954. Presented before the Divlaion of Colloid Chemistry a t the 126th Meeting of the A a f E R I C A N C H E Y I C d L S O C I E T Y , x e w York, 9.Y . , 1954. RECEIVED for review August 24, 1954.
Process Development Data
Heat of Combustion of Some
Organosilicon Compounds K. B. GOLDBLUM AND L. S. MOODY Chemical Development Department, Chemical and Metallurgical Division, General Electric Co., Pittsjield, MQSS.
T
HE paucity of data on the heat of combustion of organosilicon compounds has proved frustrating to workers in need of these data for thermodynamic calculations. This work was undertaken principally to determine the heat of combustion of octamethylcyclotetrasiloxane, as part of the evaluation of a proposed industrial method for the preparation of this valuable silicone intermediate. A search of the literature failed to reveal any information on the heat of formation or combustion of this compound or of analogous compounds from which these values might have been calculated. The thermal stability and oxidation resistance of the silicones, in general, are well established. I n initial experiments, it was found exceedingly difficult to oxidize the selected compounds completely in an oxygen bomb calorimeter. The error arising from incomplete combustion in this equipment has been emphasized ( l a , IS). Special precautions and techniques had to be used by these workers to give reliable results. Because of the necessity for special precautions and techniques, i t was decided to investigate sodium peroxide fusion as a means of obtaining complete oxidation of the selected organosilicon compounds. The use of the Parr sodium peroxide bomb calorimeter (manufactured by The Parr Instrument Co., Moline, Ill., hereafter called the calorimeter), was suggested by the successful use of sodium compounds t o determine silicon quantitatively in the
General Electric Research Laboratory, in this laboratory, and in other laboratories (1, 2, 4, 5, 10, 14, 16). The use of the calorimeter was complicated by the fact that this instrument is semiempiric?l and has a narrow range of accuracy for certain types of carbon- and hydrogen-containing compounds, mainly coal samples (6, 8, 9 ) . It is assumed in the instructions for the use of this instrument (6) that 73% of the heat liberated is due to heat of combustion and the remaining 27% is due to the reaction of the oxidation products, carbon dioxide and water, with the sodium peroxide melt. Further, the manufacturers state ( 7 ) that there are “difficulties involved in attempting precise calorimetric tests in a peroxide bomb calorimeter because of the numerous side reactions involved, some of which may not go to completion and for which heats of reaction may not be well established.” Despite these limitations and complications, it was decided t o use this equipment in view of the excellent record of the sodium peroxide fusion method for the quantitative estimation of silica in organosilicon compounds. Nine pure compounds containing only carbon, hydrogen, and oxygen, whose heats of conibustion are given in the literature, were oxidized. From a statistical analysis method of least squares, values attributable to the heats of reaction of carbon dioxide and of water with the sodium peroxide melt and the energy equivalent of the calorimeter system were determined for
INDUSTRIAL AND ENGINEERING CHEMISTRY
848
Vol. 47. No. 4
Table I. Data for Standard Compounds Compound Benzoic acid Sucrose
Source and Description of Sample NBS combustion standard NBS carbon and hydrogen standard
Temp. Rise, F./ 0.5 Gram Sample Av. Range 3.89' 2.8212154 2.53
N ~ of, Combuptions
..
Analysis Found C
C
...
6.52 &:io 6.68 3.09 2.08-2.10 3 5.25 Merck & Co. purified crystals 40.68 Succinic acid 5,44-5.46 4 10.3 78.90 Resublimed for molecular weight determinations a . 45 Camphor 9.13 3.29-3.34 4 J. T. Baker Chemical Co., C.P. grade 3.31 5.04 60.87 Salicylic acid 4.52 Dow Chemical Co., purified 1 . 5 3 1.47-1.5q 7 3 . 9 9 3 4.62 Malonic acid 4.17 3.84 Merck & Co., reagent grade 5.29 5.25-5.33 5 9.35 79.95 Thymol 9.39 3.70 3.65-3.73 6 Merck & Co., U.S.P. grade 5,50 63.15 Vanillin 5.72 5.43 3.35-3.39 3.37 4 3.05 64.87 Phthalic anhydride Distillation Products, Inc., white label 64.5 2.88 65.0 2.94 ' Calculated statistically from 17 samples which contained benzoic acid alone or mixed with other compounds (see Table 111)
the particular instrument used. By burning benzoic acid (n'ational Bureau of Standards combustion standard) with a pure silica sample (which had been dried by firing a t 650" C. for 96 hours in a muffle furnace and then cooled in a desiccator), a value attributable to the heat of reaction of silica with the sodium peroxide melt was obtained, also statistically. From the above constants for the instrument, it was possible to determine (admittedly somewhat roughly) the heat of combustion of an organosilicon compound by the following equatioh:
AH,
=
WAT
- AHc0,a
- AHE,ob
- AHs,o,c
(1)
where AH, is the heat of combustion in B.t.u. per pound W is the energy equivalent of the system and equals 453 6 B.t.u./" F./lb./gram/O.S = (B.t.u./' F.) 0.5 A T is the temperature rise, ' F., calculated for a 0.5-gram sample
A H c o ~ ,A H H ~ oand , AHaio, are related to the heat of reaction of carbon dioxide, water, and silica with the sodium peroxide melt expressed in B.t.u. per pound of reacted carbon dioxide, water, and silica, respectively. a, b, and c are the pounds of carbon dioxide, water, and silica theoretically calculated t o be formed from 1 pound of the particular sample. STANDARDIZATION OF CALORIMETER
General Procedure. A sample of the compound to be oxidized was weighed to the nearest 0.1 mg. on a Gramatic balance into a Parr nickel crucible and mixed with 1.0 gram of potassium perchlorate accelerator (weighed within 5 2 % ) . To this was added a level scoop (provided with the instrument) of about 15 grams of sodium peroxide, calorimetric grade. The mixing cover of the crucible was put on and the contents of the crucible were well mixed by shaking vigorously. The particles of mixture adhering to the mixing cover were brushed into the crucible with a camel's-hair brush. The crucible was assembled into the holder and cover. The cover was equipped with 7 cm. of iron fuse wire for ignition of the charge. After being well tightened, the crucible assembly was equipped with clip-on stirring fins and put into the calorimeter bath. The bath held 2000 f 1 gram of water, weighed in. The cover of the calorimeter was then put on, the stirring wheel slipped on the crucible assembly shaft, the electrical connections to the crucible made ready, and the stirring motor turned on. The temperature of the bath was read using a thermometer furnished by the manufacturers. The thermometer is divided in degrees Fahrenheit to a 0.1' and is accompanied by the manufacturer's calibration over the temperature range of 67" to 94.5" F. a t 2.5" intervals. With a masnifying glass, the temperature was estimated to the nearest 0.01 . The water in the calorimeter was cooled so that heat of reaction in the crucible would raise the temperature of the water 1 minute after firing to approximately the same amount above room temperature as the starting temperature was below room temperature. After the temperature in the calorimeter had come to equilibrium and was rising at a constant rate, the fuse was fired
4
44.1 42.1 40.8 78.9 78.4 60.9 61.1 34.0 34.3 34.6 79.4 79.7 63.2 63.5 63.2 65.3
6.48
Heat of Combustion, B.t.u./Lb. ( 9 ) 11,368 7,097
5.12 10.59
5,443 1 6 ,685
Calcd. H
H
...
4.38
9,424
3.87
3,584
9.39
16,175
5.30
10.816
2.72
9,521
electrically. Readings of the temperature were taken every 30 seconds from the starting temperature (instant of firing) until enough readings had been taken to estimate the point of temperature peak and the radiation correction. The total temperaturerise was noted and corrected for thermometer calibration, radiation corrections, and accelerator corrections. The last value is given (6) as 0.20" F. for 1.0 gram of potassium perchlorate. The crucible assembly was opened and examined for completeness of combustion. A smooth grayish appearing melt indicated a successful combustion. Flecks of carbon or a lumpy appearance made the combustion suspect. The crucible was then immersed in hot water under a good hood. In the organosilicon compound oxidations, the crucible was inspected again when the frothing had subsided. A complete wetting by the aqueous solution of the inner surface of the crucible was an indication of complete combustion. Any areas, especially the bottom, of the crucible which appeared not wetted indicated that some silicone still was unoxidized and that the combustion was incomplete. Experimental Data and Calculations. The corrected temperature rise was calculated on the basis of a 0.5-gram sample for convenience in calculations. The results of the combustion of the nine pure standard compounds are given in Table I. For the standardization of the caIorimeter, the data for the nine standard compounds were substituted in Equation 1 (for these compounds c = 0). A least square method of calculation , W as 2194 B.t.u. per pound, gave the values of AHco2, A H H ~ oand 1521 B.t.u. per pound, and 4500 B.t.u./' F./lb./gram/0.5, respectively. The values of AHco, and A H H ~ oare calculated constants. These values are related to the actual heat of reaction of carbon dioxide and of water with the peroxide melt, but are not t o be taken as the true heat of reaction. A comparison of the heat of combustion calculated from Equation 1 using the above constants against the literature heat of combustion affords a measure of the standard deviation. The data are given in Table 11.
Table 11. Comparison of Calculated and Literature Heat of Combustion Compound Benzoic acid Sucrose Succinic acid Camphor Salicylic acid Malonic acid Thymol Vanillin Phthalic anhydride
A H s , B.t.u./Lb. Literature Calcd. 11,368 11,299 7,121 7,097 5,439 5,443 16,744 16,685 9,424 9,408 ,3,584 3,575 16,175 16,102 10,816 10,854 9,582 9,521
Difference B.t.u./lb. %
++- 59169
+ O , 61 -0.34 f0.07 -0.35 + O . 17 +o. 25
-61
-0.35 -0.64
?:; + 4
5;:
+O. 45
April 1955
The standard deviation is f 5 7 B.t.u. per pound. I n terms of temperature the standard deviation is divided by W or &57/4500 = f 0.0127' F. The standard deviation of the system is, therefore, of the order of magnitude of the accuracy of the temperature reading. Determination of Temperature Rise for Silica. A series of combustions was made with benzoic acid alone, benzoic acid plus octamethylcyclotetrasiloxane, and octamethylcyclotetrasiloxane alone, melting point 17.39' C. A statistical solution of these data (see Table 111)gave the temperature rise data for the three materials. The least square method of calculation gave the temperature rise in degrees Fahrenheit for a 0.5-gram sample of benzoic acid, silica, and octamethylcyclotetrasiloxane as 3.89, 0.335, and 3.70, respectively. AHsio, is equal to 0.335W = 0.335 X 4500 = 1507 B.t.u. per pound. The value of AHsio, is a calculated constant related to the heat of reaction of silica with the peroxide melt, and is not to be taken as the actual heat of reaction. Equation 1 may now be written as
AH,
=
4500AT
-
2194 a
-
1521 b
-
1507 c
\'.
Table \ ' d a t i o n in Temperature Rise for 0.3-Gram Sample of Octamethylcyclotetrasiloxane w i t h Sample Size
(2)
PRECAUTIONS
I n the combustion of two samples, octamethylcyclotetrasiloxane and diphenylsilanediol, the size of the sample was found to have an effect on the combustion. The data for octamethylcyclotetrasiloxane are given in Table 17.
Table 111. Data for Temperature Rise Calculations for Benzoic Acid, Octamethylcyclotetrasiloxane, and Silica
0.8675 0.5436 0.5404 0 5017 0 5974 0 7532 0 5895 0 6976 0 5024 0 5622 0 5711 0 4251 0 3759 0 2879 0 2124 0 1126 0 5327
... ...
... .... .... .... .... .... ....
.... .... ....
6.42 5.16 5.89 3.99 4.73 4.53 7.16 6.69 5.23 5.45 6.56 7.26 8.00 7.68 9.51
0:5155 0.5019 0.4092 0.5189 0.7749 0.4068 1.08i0 1.0423 1.2856
.... ....
....
Gram Molecular Weight 504 739 166 199 162 170 310 (67 222 296 370 444
78 04 88 28 32 34 58 09)s 38 51 63 76
3.38 4.54 4.99 5.08 7.68 8.00 9.51
3.50 3.53 3.57 3.58 3.68 3.69 3.70
Comparison of Heat of Combustion Values Net A H * , Kcal./Gram-Mole This study Other study
Reference
4802.4 1434.5 1401
4770 1397 1344
DISCUSSION
S.ii
0.7219 0.7531 0.9767 0.5749 0.2016 0.5846 0.1199
Table IV. Compound Formula
4.43 4.17 4.15 3.87
0,4826 0.6437 0,6985 0.7096 1,0423 1,0850 1.2856
Although, because of the method used in obtaining the data in this paper, the heats of combustion calculated in Table V are not the most precise, they should have value for approximate calculations. It is, therefore, of interest to compare the values from this study with values from other workers (Table VI). The agreement between the values in this study and those of other workers is reasonable, and within the range of &4oJ,. On the other hand, the present authors feel that in general the heats of combustion of organosilicon compounds as determined by the method described in this paper are probably correct to 1%.
Total Corr. Temp. Rise, F.
.... .... .... ....
Temp. Rise Gram, for 0.5F.
It appears that, in the case of octamethylcyclotetrasiloxane, the heat of combustion is not constant unless the weight of sample is over 1.0 gram. This may be explained by the fact that the silicones are not easily oxidized. The smaller samples do not generate enough heat in the course of their combustion to sustain a high enough temperature in the crucible to ensure complete reaction with sodium peroxide. If a large enough sample is used, the threshold temperature for complete oxidation is exceeded and good combustion results. In the case of diphenylsilanediol, the same phenomenon was observed but with a further complication. The temperature rise per 0.5-gram sample began leveling off a t about 0.8 gram. However, a t sample weights much over 0 . 9 gram, the combustions were again incomplete, as indicated by soot found in the crucible on opening. The optimum range of sample size for this compound seems very narrow'. It is recommended that the sample size for each compound to be oxidized be varied, so that if the compound is subject to the phenomena described above, steps can be taken to correct the situation.
Twelve organosilicon compounds were studied. Their physical properties are given in Table IV, with the heat of combustion values.
Sample Weights, Grams Siloxane Silica
Total Corr. Temp. Rise, F.
Compound [(CeHdz8iO1 3 [(CHa)zSiO]a [ (C Ha)rSi 1 1 0
DATA AND CALCULATIONS FOR ORqANOSILICON COMPOUNDS
Benzoic Acid
Weight of Sample, Grams
Table VI.
where the coefficients have the same meaning as in Equation 1.
b
849
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACKNOWLEDGMENT
The authors wish to thank F. E. Satterthwaite for assistance with the statistical methods of calculation used in this paper;
Net Heat of Combustion for Twelve Organosilicon Compounds Melting or Boili;g Point, C. 190-1 m. p. 200-1 m. p. 67-8 m . p. 149-50 m. p. 9 9 . 2 h. p. 133-5 b. p. 191.0-1.6 b. p.
Gela
64 m . p. 17,39 m. p. 209.6-10.0 b. p. 153,5 b. p.sa
Made by hydrolysis of purified CHsSi(OCOCH3)s. nzg 1.4016.
AV. 4.76 4.77 3.26 4.49 4.69 5.49 4.35 2.07 3.61 3.70 3.68 3.68
Temp. Rise, F./0.5 Gram Range 4,69-4.85 4.74-4.80 3 23-3.32 4.41-4 51 4.61-4.79 5 41-5.59 4.33-4.37 1.99-2.12 3.57-3,65
Calcd. above 3.65-3.70 3.67-3.69
No. of Combustions 8 6 6 6 A
3 7 5 7 9 6 4
Net A H s Calcd. from Eauation 2 B.t.u./lh. Kral./gram-moK
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). RECEIVEDfor review July 2 , 1954.
ACCEPTEDOctober 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 that 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. The 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, the 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 the average deviation calculation, since of course the deviation in this instance is always zero. The high solvent power of hexamethylphosphoramide for acetylene was predicted from this formula, and on testing it proved t o be the most powerful nonreacting acetylene solvent known. The 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
The 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 by 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
