Oct.,
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
I920
from this point in order t o be sure t h a t the reaction had become thoroughly established and t h a t everything about the apparatus was in a state of equilibrium which could be maintained until the end of the experiment; and t o obviate the large error inherent in the apparatus, due t o the fact t h a t i t took some time for the benzene vapors t o displace all the air in the apparatus, and for the sulfuric acid t o wet all the surfaces of the baffles and the walls of the tower, during which time the apparatus did not operate a t its maximum capacity. TABLEI
Catalyst
...
Con c en tration Per cent
...
c u . . . . . . . . . . 0.1 Hg.. . . . . . . . . 0.1 v . . . . . . . . . . . 0.1 Na(1) . . . . . . . 0 . 1 Cr.. . . . . . . . . . 0.1 K . . . . . . . . . . . 0.17 L i . . . . . . . . . . . 0.094 Na(I1) . . . . . . 0 . 5 Nn(II1) ...... 0 . 1 N a . ,. , , , , , . , 0.1 V . .’.. , , . , , , 0.05 V . , . . . . . . . . . 0.223 Na. . . . . . . . . 0.025}
1
.
Mean Temp. C. 243 25 1 243 249 252 249 257 246 255 259 242
’
Wt. W t Benzene Duration Sulfonic Sulfonated per Min. of Expt. Acids Min. Grams Grams 580 734 0.63 185 301 0.80 232 386 0.82 249 356 0.71 291 649 1.10 202 278 0.67 292 479 0.82 283 405 0.61 300 492 0.83 355 601 0.84 274 626 1.13 232
249
592
1.26
Tables I and I1 give the critical data so far as the catalysts are concerned. The “weight of sulfonic acids” in Table I was found as follows: Total acidity, expressed in terms of sulfuric acid, was determined by titration with standard alkali, using phenolphthalein or thymolsulfophthalein for indicator. Actual sulfuric acid was determined with barium chloride as usual. The difference of these two determinations represented sulfuric acid equivalent t o the sulfonic acid present. The latter was temporarily assumed t o be benzene monosulfonic acid, and its amount : zHSO3.CeH6. calculated according t o the ratio From this value i t was a simple matter t o calculate the amount of benzene sulfonated per minute. TABLE I1
..
........... ........... v ............ Cr ............ Li ............ Na(I1) ....... Na(II1) ....... Na. . . . . . . . . . . v............ cu Hg
v............ Na.
..........
...
0.1 0.1 0.1 0.1 0.094 0.5 0.1
0 223 0:025
243 251 243 249 249 246 255 259 242
580 185 232 249 202 283 300 356 274
705 294 377 355 274 380 463 574 595
147 28 36 6 13 95 111 101 121
0.56 0.76 0.78 0.66 0.66 0.61 0.70 0.75 1.00
0.25 0.15 0.16 0.03 0.06 0.34 0.37 0.29 0.44
249
232
569
88
1.15
0.39
These figures, however, were subject t o error, inasmuch as some benzene disulfonic acid was always formed. Table I1 contains corrected values, based on the following calculation: The amount of disulfonic acid was determined by analysis of the barium salt of the sulfonic acids, making necessary corrections for the catalyst itself when i t was found in the barium salt. The weight of sulfonic acids was then corrected and, by using the t’wo ratios C&s : CsHsS03H and CsH,; : C&(S03H)2, the amount of benzene actually sulfonated per minute was calculated.
969
It should be noted here t h a t two experiments given in Table I do not appear in the second, viz., Na(1) and K. Through a n unfortunate oversight the amount of benzene disulfonic acid was not correctly determined, because no determination of the amount of catalyst contained in the barium salt was made. The experiment with no catalyst is typical of many in which the amount of benzene sulfonated per minute was always approximately 0.5 g. This figure represents the normal capacity of the apparatus. DISCUSSION O F R E S U L T S
A study of Table I shows t h a t all the substances used increased the amount of benzene sulfonated per minute, a n d t h a t these catalysts are divided into two general groups, viz., those which have a slight catalytic action, copper, mercury, vanadium, chromium, potassium, lithium, and two of the experiments with sodium; and those which have a marked catalytic action, the first experiment with sodium, and the two experiments using both sodium and vanadium. The more marked effect in the first experiment with sodium was caused by a small amount of vanadium, which had been used in the experiment just preceding i t , and which had not been completely removed from the tower. The most active catalyzer is obviously a mixture of sodium and vanadium in any reasonable proportion. The results also clearly show t h a t the sodium and potassium sulfates in sulfonation mixtures have a distinct catalytic effect, and t h a t the advantages gained by their use are not entirely due t o the increased boiling point of the sulfuric acid. Another interesting fact brought out is the effect of the catalyst on the amount of disulfonic acid formed per minute. This subject is t o be investigated further. Apparently the members of the first group of t h e periodic system, represented here by sodium and lithium, accelerate the formation of disulfonic acid in this type of sulfonation, while the mixture of vanadium pentoxide d i t h sodium sulfate is still more effective. The other catalysts apparently inhibit t h e formation of disulfonic acid. PHTHALIC ANHYDRIDE. IV-THE VAPOR PRESSURE O F PHTHALIC ANHYDRIDE By K. P. Monroe COLORLABORATORY, U. S. BUREAUon CHEMISTRY, WASHINGTON, D. C. Rec:ived June 1, 1920
The investigation of the vapor-pressure curve of phthalic anhydride was initiated t o assist in the solution of certain problems arising in the air-oxidation process recently developed by Gibbsl and his coworkers. Although the results were obtained in a preliminary series of measurements, and are not of the order of accuracy which i t was hoped t o obtain by repetition with a more refined mercury gage, they are presented, since i t appears unlikely t h a t the author will resume the investigation. Phthalic anhydride, purified by a method previously described,2 was placed in a static isoteniscope of the 1 See the previous articles of this series: “Phthalic Anhydride,” I, by H. D Gibbs, THIS JOURNAL, 11 (1919), 1031, “Phthalic Anhydride,” I1 and 111, by K P Monroe, I b i d . , 11 (1919). 1116 and 1119 1 Part 11, LOC.cit.
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1701.
970
12,
NO. r 0
type designed by Smith and Menzies,' which was clamped vertically in a paraffin bath and connected, after the fashion described by these authors, t o a vacuum pump, mercury gage, and a large iron cylinder which served as low pressure reservoir. The bath was a large unsilvered Dewar flask supported by feltcovered rings and filled nearly to the brim with paraffin which was stirred violently by a turbine. Constant temperature was maintained by an electrical heating device consisting of a nichrome coil wound on a glass tube snugly fitted into an outer glass tube sealed at one end. By means of a lamp-board connected t o the I Io-volt lighting circuit the current passing through the coil was accurately adjusted t o maintafn t h e temperature, which was measured by a calibrated Reichsanstalt thermometer completely immersed in the bath. After constant temperature (within * 0.05") had been maintained for ~j min., the anhydride contained in t h e isoteniscope was boiled by maintaining a pressure somewhat less than the vapor tension. Air was then admitted cautiously in the reservoir until t h e levels of liquid anhydride became equal, and the gage was read. The boiling-out process was then repeated and another reading taken. This procedure was continued until t h e gage readings became constant and all dissolved gases had been expelled. T h e gage readings were corrected t o 0 " C. The molar latent heat of vaporization of phthalic anhydride may also be calculated by Equation I , for this equation is of t h e simple type obtained by integrating the Clausius-Clapeyron equation:l
TABLEI-VAPOR PRESSUREOP PHTHALIC ANHYDRIDW t ( 0 C.)
0 (Mm of Hg) 130.5 172.1 241.2 287.1 369.4 i59.3 :
212.0 222.0 234.6 241.5 252.4 284.6'
Compare 276O, Lossen, Ann., 144 ( 1 8 6 7 ) , 7 6 ; 284.S0, Graeke, B c v . ,
1'7 (I884), 1176.
where L = molar heat of vaporization, V = volume of mole of gaseous phase, II = volume of mole of liquid phase, T = absolute temperature, with t h e assumptions: ( I ) t h a t the volume of a mole of liquid phase 2823.5 loglo P = 7.94234 - T is negligible compared with t h a t of a mole of gaseous phase; ( 2 ) t h a t the gaseous phase obeys the perfect gas when p = vapor pressure in millimeters of mercury, law; and (3) t h a t the heat of vaporization does not and T = absolute temperature. vary with temperature.2 Integrating and introducing - T A B L E 11-COMPARISON OF OBSERVED AND CALCULATED TEMPERATURSS Napierian logarithms: The following interpolation formula was found to fit these data:
P
130.5 172.1 241.2 287.1 269.4 ,59.3
T (Observed) 485.0 495.0 507.6 514.5 525.4 557.6
T (Calculated) 484.6 494.8 507.8 514.8 525.3 557.8
log10
Since Ramsay and Young2 have'carried out a series of measurements of t h e vapor pressure of phthalic anhydride over a different temperature range than the one explored in this investigation, and with a different type of apparatus, i t is of interest t o compare the vapor tensions found by these investigators with the values calculated by Equation I . TABLE111-CONPAHISON
O F CALCULATED VAPOR PRESSURES WITH OF RAMSAY AND YOUNG
DATA
0 (Calculated by t ("C.)
159.5 168.6 177.1 196.9 210.1
p (Observed) 22.8 32.2 46.9 87.3 142.0
J . A m . Chem. S O L . ,92 (1910), 1412, 1434, 1448 Trans. Roy. SOC.London, 1886, I, 102.
Equation 1 ) 26.0 35.3 46.7 85.8 I125.3
P
=
L c - 0.4343 7
(3
when R = the gas constant, and C is a constant of integration. Since
the molar heat of vaporization of phthalic anhydride is calculated t o be 12,910 calories. According t o the criterion suggested recently by Hildebrand,3 phthalic anhydride is shown by t h e data of this investigation t o behave as a normal liquid, for the value 13.6 is obtained for the entropy of vaporiza1 Washburn, "Principles of Physical Chemistry," McGraw-Hill Book Co., New York, 1915, p . 123. 2 None of these assumptions is, of course, strictly valid. The accompanying fiqure, however, reveals their justification by the experimental data over the somewhat limited temperature range, which is probably far below the unknown critical temperature of phthalic anhydride. 3 J . A m . Chem. Soc., 8'7 (1915), 970.
Oct.,
a920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
tion divided by R a t the temperature (near 218’) a t which the concentration of vapor is 0.00507 mole per liter. This value coincides with the average obtained from Hildebrand’s table, based upon the vapor pressure curves of fifteen normal liquids. THE EFFECT OF CERTAIN ACCELERATORS UPON THE ‘ PROPERTIES OF VULCANIZED RUBBER-11’ By G. D. Kratz and A. H. Flower THEFALLSRUBBERCo., CUYAHOGA FAI,LS, OHIO
I n a recent paper,Z H. P. Stevens has given new figures, and from them made a number of deductions in regard t o certain discrepancies between results obtained by the present authors3 and earlier results obtained b y him.4 We do not entirely agree t h a t these latest deductions will suffice for the complete coordination of his former results with ours. This view is confirmed by the repetition and amplification of our former experiments, including work with extra light instead of heavy calcined magnesia. This work was carried out with a sample of the rubber previously employed and also with another rubber of similar physical appearance. Entirely different results were obtained with the two rubbers. I n neither instance, however, was extra light magnesia found t o develop greater activity t h a n Accelerator 9,and, in one case, i t was markedly inferior t o the latter. I n both cases where Accelerator A was employed, the load required t o effect a given extension led t o erroneous conclusions, if used as a criterion of the rate of cure. As these results were obtained with accelerators of definite composition and purity, the differences may be attributed t o variations existing in the rubbers themselves, and most probably in the nature, amount, or condition of the extraneous materials present. As a considerable portion of this extraneous matter was extractable with acetone, a n investigation was made of the relative effect of the two accelerators upon the two rubbers after extraction. Since the nature of the substances removed by the extractions was not studied, no attempt can be made to correlate the effect of the extra light magnesia with any definite one of the extraneous substances originally present in the rubber. Certain facts, however, have been well enough established t o deserve brief consideration. It was noted by Spence6 t h a t the nitrogen in rubber was not entirely of protein origin, and t h a t nitrogenous bodies of well-defined alkaloidal character could be detected in the acetone extract of Para rubber. This was subsequently confirmed by Spence and Kratz? for plantation crepe (Hevea), although a difference in the character of the protein material in the two rubbers was found. Further, certain of their results 1 Presented a t the 59th Meeting of the American Chemical Societv, St. Louis, Mo., April 12 to 16, 1920. 2 Indka Rubber J . , 68 (1919), 527. 3 Chem. and Met. Eng., 20 (1919), 417. 1 J . SOC.Chem I n d , 87 (1918), 156t. 6 A qualitative determination showed the presence of nitrogen in the extracts of both rubbers. 8 Herbert Wright, “Hevea B r a s , or Para Rubber,” 1912, p 439 London. 7 I C d l o i d - 2 , 14 (1914), 268
973
indicated t h a t in plantation Hevea the non-protein nitrogenous substance was not easily extractable with acetone. Dekkar’ also noted the presence of nitrogen in the acetone extract, and gave figures for nitrogen distribution in the extracted rubber and its acetone extract which closely confirmed those originally obtained by Spence. Prior t o Dekkar’s observations, Beadle and Stevens2 noted t h a t the rate of vulcanization of certain rubbers decreased if the rubbers were previously extracted with acetone. After vulcanization the physical properties of the acetone-extracted1 samples were so greatly impaired, due either t o the loss of the resin or the physical effect of the solvent upon the rubber, t h a t the decrease in the rate of cure. I was considered of secondary importance. It would therefore appear t h a t the removal of the acetone-soluble nitrogenous constituent is responsible for the decrease in the rate of cure of the rubbers, rather than either of the causes originally assigned’ by Beadle and st even^.^ This is also in accordance with the later results of Eat,on, Grantham and Day,“ and of st even^,^ wherein the accelerating substance of plantation Hevea rubber was found t o be an organic base or mixture of bases, probably formed by the degradation of the protein portion of the nitrogenous. material originally present in the rubber.6 The possibility that magnesia may hasten t h i s degradation, with the formation of a n accelerator similar t o t h a t produced by the biological decomposition of the proteins, has already been pointed out by Eaton7 in commenting upon the patent of Esch.8 I n view of the well-known action of many synthetic organic accelerators in the presence of certain mineral oxides, such as t h a t obtained by Cranorg with zinc oxide, we are led t o t h e conclusion t h a t the effect of small amounts of magnesia in accelerating the vulcani-zation of rubber is of a secondary or contributory,. rather than a primary nature, and consists largely in effecting a response from the. natural accelerator in’ the rubber. This finds further confirmation in the. observation of Stevens in his previous paper, wherein: he pointed out t h a t the accelerating effect of extra: light magnesia decreases when a sulfur coefficient of1 Comm. of the Neth. Govt. Inst. for Advising the Rubber Trade and. Rubber Industry, Part 11, p. 55. 2 Intern Congr. A p p l . C h e m , 26 (1912), 581. I n a previous paper [THIS J O U R N A12 ~ , (1920), 3171, we have mentioned that results obtained with certain synthetic organic substances indicate, in some cases, that the accelerator may be closely bonnd t o tharubber. Should this also be found true in the case of the natural accelerator, the removal of this substance by extraction would markedly impair the physical properties of the sample after vulcanization, as well as slow down the rate of cure. (Compare with footnote, p. 974.) 4 “Variability in Plantation Rubber,” J . SOC. Chem. I n d . , 35 (1916), J
715.
J . SOC.Chem I n d . , 36 (1917), 365. The protein portion of this nitrogenous material which is insoluble in acetone and benzene has been shown to act as an accelerator (Beadle and Stevens, Kolloid-Z., 11 (1912), 61; 12 (1913). 46; 14 (1914), 91). IC. has the further advantage of being present in reiatively large amount as. compared with the acetone-solublo constituent. As it does not, however, respond to magnesia t o the same extent as the latter substance, and, as certain results (not included in this paper) indicate that the extraction with acetone does not cause a marked degradation of this protein material intc, the soluble variety, w2 have not made reference t o it. 7 Agr. Bull. Federated M a l a y Slates, 5 (1915). 38. 8 Ger. Patent 273,482 (Nov. 22, 1912) 9 I n d i o Rubber World, 61 (1919). 131 5
6
