INDUSTRIAL AND ENGINEERING CHEMISTRY
1526
in swelling values observed for different carbon black loadings are less than would be expected had the vulcanizates been compared a t equivalent states of cure. The effect of carbon black on the cure of neoprene appears to be a controversial issue, however. Buist and Mottram (3)reported t h a t in neoprene GN, neither the type nor amount of black affected the rate of vulcanization. If this is the case, all the vulcanizates compared in this study had the same state of cure; hence, differences in swelling values must be attributable only t o differences in carbon black.
Vol. 40, No. 8
( 2 ) Brunauer, S., Emmett, P. H., and Teller, E., J . Am. Chem. Snc., 60, 309 (1938). (3) Buist, J. M . , and Mottram, S., T r a n s . I n s t . Ru56er Ind.. 22 82 (1946). (4) Catton, N. L., and Fraser, D. F., ISD.ENG.C r r s ~ . 31, , 956
(1939). (5) Columbian Carbon Co. Research Lab., "Columbian Colloidal Carbons," Vol. 111, 1945. (6) Drogin, I.,I n d i a Rubber, W o r l d , 106,561-9 (1942). (7) Drogin, I., Grote, H. W.,and Dillingham, F. W., ISD.ENG. CHEX.,36, 124 (1944). (8) Emmett, P. H., and De TYitt, T., IXD.KSG. CHCM.,ANAL.ED., 13, 28 (1941). (9) Forman, D. B., and Radcliff, R. R., IND. ENG.CHEM.,38, 1048 (1946). (10) Ishieuro. K.. Rubber Chem. Technol.. 6. 278 11933). (11) Xaukton, M7. S. J., Jones, M., and Smith,'W. F., T ~ a n sI.n s t . Rubber I n d . , 9, 169 (1933). (12) Rostler, F. S., and Morrison, RachelE., I b i d . , 61, 59 (1947). (13) Rubber Age, "Nomenclature of Carbon Blacks," 52, 353 (1943'). (14) Scott, J. R., Ibid., 5, 95 (1929). (15) Smith, W.R., Thornhill, F. S., and Bray, R. I., IXD. ENG.CHEM.. 33 1703 (1941).
I n addition t o the observations already discussed this work has shown t h a t there is a lack of Correlation between the modulus and swelling characteristics of these vulcanizates as is apparent from a consideration of the physical data presented in Table 11. There is, however, a high degree of correlation between the hardness of the vulcanixates and the surface area of the oarbon black as shown in Figure 5. LITERATURE CITED
(1) Amon, F. H., Smith, W. R., and Thornhill, F. S., IND.ENG.
RECEIVEDJune 10, 1947. Presented before the Division of Rubber Chemistry, AMERICAN CHEWCAL SOCIETY, Cleveland, Ohio, M a y 1947.
CHE'M.,15, 256 (1943).
reparation and
ethylcyclope K. C. EDSON', J. S. POWELL, AND E. L. FISHER Southern Cali$ornia Gas Company, Los Angeles, Calif. T h e separation of pure methylcyclopentadiene from a hydrocarbon fraction obtained from the pyrolysis of a petroleum naphtha by a series of fractional distillation operations is described. Some physical constants of methylcyclopentadiene and its dimer are given. The dimerization rate of methylcyclopentadiene and the fulvene formation rate are compared to those of cyclopentadiene.
D
I
URIKG recent years, considerable attention has been given t o cyclopentadiene because of its wide use in resins and potential use in the synthetic field. X thorough review of the chemistry and utilization of cyclopentadiene was given by Wilson and Wells (9). However, little is known about the higher homologs, and in particular, methylcyclopentadiene. This lack of attention for the methyl homolog is understandable as there is no commercial source of supply, although methylcyclopentadiene as well as cyclopentadiene is formed during the pyrolysis of hydrocarbons at high temperatures. Methylcyclopentadiene was prepared by Zelinsky and Lewina (10)from 8-methyl cyclopentanol by dehydration t o the methylcyclopentene, bromination of the unsaturated product, and then the splitting off of two molecules of hydrobromic acid. This method of preparation would yield two of the three possible isomers-namely, 1-methyl- and 5-methyl-l,3-~yclopentadiene. The authors state t h a t no attempt was made t o separate the isomers and further t h a t the quantity of end product was not large enough t o permit complete purification. The physical constants listed by these authors are: boiling point, C. = 69 t o 70; nlB = 1.4460; di8 = 0.8200, These constants have been used by Doss ( 1 ) for the lack of better data. A method of separating methyl cyclopentadiene from cyclo1 Present address, Petroleum Cheniicals Dixision, E. I. du Pont de Nemours & Company, Inc , El Monte, Calif.
pentadiene and from the other components present in a cracked hydrocarbon fraction boiling up t o 120" C. was given by Stern and Hoess ( 6 ) . This was accomplished by reacting 1,4-naphthoquinone in small aliquots a t room temperature w-ith the cracked fraction, and separating success-ve addition compounds. Methyl cyclopentadiene will react preferentially until it is nearly exhausted; then a mixture of the addition products of methylcyclopentadiene and cyclopentadiene will separate; and finally the cyclopentadiene addition product will be formed. One use of methylcyclopentadiene has been presented by Soday ( 4 ) who copolymerized methylcyclopentadiene with butadiene, isoprene, or piperylene t o form a copolymer suitable for use in coating inner surfaces of food and beverage containers. SEPARATION O F PURE METHYLCYCLOPENTADIENE
Methylcyclopentadiene like cyclopentadiene dimerizes rapidly and is difficult to maintain in the monomeric state. In the hydrocarbon condensate coming from high temperature cracking these two compounds originally occur as the monomer but because of their high dimerization rate soon are converted to the corresponding dimers and the codimer. The monomers can be prepared conveniently by depolymerizing these dimers. This polymerization can be effected by heating the dimers to above 170" C. The starting material for the separation of pure methylcyclopentadiene was a high boiling aromatic fraction (140' to 260" C.) containing the dimers of cyclopentadiene and methylcyclopentadiene in concentrations of approximately 4.5 and 21 weight 7c, respectively. This fraction was derived by the cracking of a straight-run petroleum fraction (94" to 207" C.) a t a temperature of 760" C., a contact time of 0.9 second, and steam to feedstock weight ratio of 1 to 1 in a regenerative type of generator packed with firebrick. The yields of cyclopentadiene and methylcyclopentadiene from the naphtha were 1.9 and 1.2 weight 7c, respectively. A drum sample of this material was charged to a 36-theoretical-plate semiworks column and distilled at atmos-
August 1948
1521
INDUSTRIAL AND ENGINEERING CHEMISTRY
pheric pressure a t a reflux ratio of 10 to 1. At the boiling point of the charge the polymers of cyclopentadiene and methylcyclopentadiene depolymerized. A light fraction boiling between 38"and 60' C. was taken overhead; this fraction contained a large percentage of the cyclopentadiene in the charge. A second fraction boiling between 60' and 82" C. was collected; this contained a large percentage of contaminated methylcyclopentadiene and cyclopentadiene. This crude fraction of methylcyclopentadiene was then charged to a 200-theoretical-plate laboratory column immediately after it was obtained. A fractionation, in which cyclopentadiene was taken overhead from the column, was made at 30 mm. pressure a t a reflux ratio of 10 to 1. At this pressure the kettle temperature was low enough initially to prevent rapid dimerization of the cyclopentadiene and methylcyclopentadiene in the kettle. However, as the distillation progressed the kettle temperature increased because of the slow dimerization of the cyclopentadiene and methylcyclopentadiene present; this in turn increased the rate of dimerization, and consequently, not all of the cyclopentadiene could be removed in one operation. It was necessary to depolymerize the kettle bottoms at the point where the overhead temperature of the product from the column increased above the cyclopentadiene boiling point. This depolymerization was accomplished by passing the kettle bottoms through a cracking coil in which the vapors leaving were heated to a temperature of approximately 370" C. The cracked bottoms were again charged to the column and the fractionation was continued to remove cyclopentadiene. The procedure of depol merization and fractionation was repeated several times untirall of the cyclopentadiene was removed. Methylc clopentadiene was t i e n taken overhead from the column in a simiyar manner. l'he purified fraction of methylcyclopentadiene monomer thus obtained was dimerized a t 70" C. for 64 hours and the dimer f a m e d was fractionated on the 200-theoretical-plate column at 33 mm. pressure and 10 to 1 reflux ratio for the final purification. A dimer cut boiling between 97" and 99" C. a t 30 mm. was obtained. Although it was not within the scope of this work to investigate the isomeys of this compound, the methylcyclopentadiene thus obtained from the thermal cracking process is essentially a mixture of only two isomers-1-methylor 2-methyl-1,3-cyclopentadiene-and does not contain a significant amount of the third isomer, 5-methyl-1,3-cyclopentadiene,because the product isolated underwent fulvene reactions. The purpose of this work was t o obtain methylcyclopentadiene for the determination of its physical properties and for use in developing an analytical procedure; consequently, no effort was made to carry out the procedure to obtain the maximum recovery of methylcyclopentadiene from the starting material. The actual recovery was approximately 3%. PHYSICAL DATA OF METEIYLCYCLOPENTADIENE
The rapid dimerization rate of the monomer and the presence of the dimer as a possible contaminant required considerable effort t o prevent dimerization. The monomer was prepared by depolymerizing the dimer in the kettle of a 30-plate column and fractionating the decomposition product to ensure that no dimer was carried over with the monomer. The physical constants were determined immediately on the overhead product. The values obtained are given in Table I together with those obtained on the pure dimer. The boiling point of the methylcyclopentadiene given is t h a t observed in the overhead product during the depolymerization of
4
10
PO
30 40 TIME, MINUTES
50
60
Figure 1. Fulvene Extinction Coefficients of Cyclopentadiene and Methylcyclopentadiene
the dimer in the 30-plate column at a reflux ratio of 10 to 1, corrected t o 760 mm. of mercury pressure. The boiling point of the dimer given is that observed in the overhead product during the fractionation of the impure dimer in the 200-plate column at 30 mm. of mercury pressure at a reflux ratio of 10 to 1. DIMER1 ZATION RATE OF METHYLCYCLOPENTADI ENE
The dimerization rate of methylcyclopentadiene was investigated a t 20 O , 30 O, and 70 O C. The change in the refractive index was used as a measure of the dimerization rate. This method of measurement was reported by Terent'ev and Soloklin ( 7 ) t p be in error by about 1.5 t o 2.07', owing to the formation of higher polymers, when it was used t o determine the dimerization rate of cyclopentadiene. Table I1 gives dimerization rate constants as determined by the authors and for comparison of rate constants given by Harkness, Kistiakowsky, and Mears (9)and by Kaufmann and Wasserman ( 3 ) for cyclopentadiene. As indicated by the data in Table 11, temperature is a vital factor in the dimerization rate of both cyclopentadiene and methylcyclopentadiene; the rate is from 50 t o 70 times as rapid at 70 as a t 20" C. This temperature effect was noted also by Stobbe and Ruess ( 6 ) in their work on cyclopentadiene. Because of stearic hindrance of the methyl radical i t would be postulated that methylcyclopentadiene would dimerize more slowly than cyclopentadiene. The values obtained by the authors on these two compounds show that little difference exists in the two rates. FULVENE REACTION OF METHYLCYCLOPENTADIENE AND CYCLQPENTADIENE
Cyclopentadiene can be determined quantitatively by the formation of the highly colored fulvenes with subsequent measurement of the color. Such a method, using benzaldehyde, has been reported by Uhrig, Lynch, and Becker (8). Because cyclopentadiene concentrate produced by the pyrolysis of petroleum fractions will contain methylcyclopentadiene as a contaminate,
TABLE 11. DIMERIZATION RATECONSTANTS OF CYCLOPENTATABLEI. PHYSICAL CONSTANTS OF METHYLCYCLOPENTADIENE AND NIETHYLCYCLOPENTADIENE DIMER Physical Constants Boiling point, C. At 760 mm. At 30 mm. Specific gravity, dzo Refractive index, ny Dispersion X 1 0 4 , F-C
F-C Specific dispersion X 104, d
Monomer 73
DIENE AND
Cyclopentadiene
98
0.8ii2
0,9396
1.4509 116 143
1.4998
110 117
Temperature,
=
Dimer
...
METHYLCYCLOPENTADIENE
Methylcyclopentadiene
c.
20 20 30 30 70
70 20 30 70
Constant, k ( M - 1 Sec.-1) Literature Observed value value 3 . 5 5 x 10 -7 ($1 . ...... 5 . 2 5 x 10-7 ( 8 ) ....... 9 . 3 4 X 10-7 (9) 1 . 5 2 X 10-8 1 . 3 1 x 10-6 (8) ....... 2 . 5 6 x 10-5 (8) ....... 3 . 0 2 X 10-6 (5) ....... ......... 4 . 7 2 x 10-7 ......... 1 . 4 5 x 10-0 ......... 4 . 0 6 x 10 -6
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Vol. 40, No. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
it was desirable t o know t o what extent methylcyclopentadiene would interfere in the fulvene analytical procedures with acetone a n d benzaldehyde. The extinction coefficients were determined for methylcyclopentadiene and cyclopentadiene fulvene color, formed with both acetone and benzaldehvde. Figure 1 shows the extinction coefficients obtained as a function of reaction time at a constant temperature of 32” C. T h e reaction rate with benzaldehyde is more rapid than with acetone for both methylcyclopentadiene and cyclopentadiene fulvene formation. Cyclopentadiene reacts with both benzaldehyde and acetone at a greater rate than does methylcyclopentadiene. The fulvene color formed with cyclopentadiene is more intense than with methylcyclopentadiene. This apparent greater color intensity may be because of the presence of nonreactive 5-methyl-l,3-~yclopentadieneisomer in the methylcyclopentadiene used. These observations indicate t h a t methylcyclopentadiene will interfere in the determination of cvcloDentadiene bv fulvene formation; the error is greater for the benzaldehyde fulvene
method than for the acetone method. However, the difference in the reaction rates of methylcyclopentadiene and cyclopentadiene in forming the fulvene color with benzaldehyde and acetone suggests a n analytical method of analyzing for methylcyclopentadiene and cyclopentadiene in the presence of each other.
I
I
.
LITERATURE CITED
Doss, M. P., “Physical Constants of the Principal Hydrocarbons,” Nemr York, The Texas Co., 1943. Harkness, J. B., Kistiakowsky, G. B., and Mears, W. H., J. Chem. Phys., 5, 682-94 (1937). Kaufmann, H., and Wasserman, A., J . Chem. SOC.(London), 1939, 870-1.
Soday, F. J., U. S. Patent 2,352,9’79 (July 4, 1944). Stern, G., and Hoess, W.. U. S. Patent 2,067,511 (Jan. 12, 1937). Stobbe, H., and Ruess, F., Ann., 391, 151-68 (1912). Terent’ev, A. P., and Soloklin, L. A., Sintet. Kauchuk, 5, 9-12 (1933).
Uhrig, X., Lynch, E., and Becker, H. C., IND.ENG.CHEM., APTAL. ED.,18, 550-3 (1946). Wilson, P. J., and Wells, J. H., Chem.Reu., 34, 1 (1944). Zelinsky, N. D., and Lewina, R. J., Ber., 66,477-8 (1933). RECEIVED JUIY i o , 1947.
es from
ellaxlose YIELD AND COMPOSITION R. L. MITCHELL, S. C. ROGERS, AND CEO. J. RITTER Forest Products Laboratory, U . S . D e p a r t m e n t of Agriculture, Madisan, Wis. Hemicelluloses equivalent to 26.1% of the wood were extracted stepwise from maple holocellulose (a-cellulose plus hemicelluloses in wood). These were subjected to chemical analyses that characterize hemicelluloses which are composed principally of pentosans, associated with uronic acids, and the chemical side groups-acetyl and methoxyl. Concurrently, the residues resulting from the extraction of the holocellulose during isolation of the hemicelluloses were analyzed to characterize them as hemicelluloses and or-cellulose. By integrating the data from the isolated hemicelluloses with those of the corresponding holocellulose residues, it was possible to follow the degradative effect of the extractions on the hemicelluloses and the or-cellulose.
ESEARCH has been conducted by several workers on hemicelluloses from wood holocellulose (6-9). On the other hand, data are meager on the composition of the residues resulting from the extraction of hemicelluloses from the holocellulose ( 6 ) . This paper presents data on the composition of isolated maple hemicelluloses and also of the corresponding residues resulting from the extraction of holocellulose with hemicellulose solvents of increasing intensity. PREPARATION O F HEMICELLULOSES
Hemicelluloses were prepared from maple holocellulose isolated in 1-pound batches by the method of Van Beckum and Ritter (9). The holocellulose was light cream in color‘and was equivalent t o 74.0% of the extractive-free ovendry wood. The hemicelluloses were removed from the air-dried maple holocellulose of known moisture content by consecutive treatments
with the following solvents used at a 15 to 1 solvent-holocellulose ratio: (A) water at 95’ C. for 1 hour; (U) sodium carbonate solution of 2.0% concentration a t 20” C. for 24 hours; (C) sodium hydroxide solution of 4.0y0 concentration a t 20” C. for 24 hours; and (D) boiling 10.0% sodium hydroxide solution for 1 hour ( 5 ) . The solvents containing the dissolved hemicelluloses were filtered from the residues and the hemicelluloses were precipitated from each of the solutions by the addition of methyl alcohol, then filtered, washed with methyl alcohol and with acetone, and dried. The holocellulose residue remaining after tiltratiou of the hemicellulose solutions was made acid to litmus with hydrochloric acid, washed with water, air-dried, and weighed to ohtain the loss in weight due to the extraction. Approximately 20 grains of each holocellulose residue were reserved for analysis; the remainder was treated with the next consecutive hemicellulose solvent. Yields of the hemicelluloses dissolved and of the Corresponding holocellulose residue are shown in Table I.
TABLE I. YIELD AXD PERCENTAGE COMPOSITIONa OF MATERIALS Yield on Basis of ExtractiveFree Wood,
Uronic Acid Anhydride,
Pentosan,
Methoxyl,
Naterial 70 % % ’% Maple holocellulose 74.0 4.58 25.2 0.94 Hemicellulose A 3.0 16.4 52.7 2.5 Holocellulose residue A 71.0 4.32 24.0 0.75 Hemicellulose B 5.1 28.9 63.1 2.6 Holocellulose residue B 65.9 2.97 22.5 0.57 Hemicellulose C 9.6 12.2 82.7 2.1 Holocellulose residue C 56.3 1.92 11.7 0.44 Hemicellulose D 8.4 6.5 58.3 1.4 Holccellulose residue D 47.9 1.06 2.6 0.23 a Baaed on weight of ash-free, ovendry materials.
(I-
Acetyl,
% 2.95 9.3 2.06
.. .. .. .. .. ..
Cellulose, % ’ 70.3
..
72.3
..
77.1
..
89.3
..
94.5
