1420
FRANK S. FAWCETT
v ~ i 68 .
[CONTRIaCTIOV FROM SOCONY-\TACUUM 1,ABORATORIES ( D I V I S I O N O F SOCOSY-VACUUM OIL C O DEVELOPMEXT DEPARTMENT]
, INC.), RESEARCH
Physical Properties of 2- and 3-Methylthiophene BY FRANK S. FAWCETT Thiophene is produced from n-butane and sulfur by a process recently developed in this Laboratory.' The use of pentanes results in the production of methylthiophenes.2 The properties of thiophene from this process have been reported.$ The two methylthiophenes have now been purified and some of their physical properties measured. A number of physical properties of the methylthiophenes have been reported in the literature.4-g Purification of 1Methylthiophenes.-The two pilot plant products which served as the starting point for this work were examined by freezing point measurements and the preparation of chemical derivatives and each was found to contain approximately 95% of its respective isomer. Each of the two products was washed with dilute hydrochloric acid, sodium hydroxide, and distilled water and dried by distilling part of the material. Two liters of the resulting product was distilled a t atmospheric pressure with a rectifying column3 equivalent to approximately 95 theoretical plates. A reflux ratio of 50: 1 was used and the distillate was collected as 100-cc. fractions (57, of charge). Central portions were selected for use on the basis of time-temperature freezing curves, since most common properties are not very sensitive to changes in the proportions of the two isomers. For each isomer approximately 300 cc. of best material was obtained by combining three fractions having the same freezing point to 0.1'; fractions before and after those combined differed in freezing point by not more than 0.1'. 'The selected material was then evacuated to remove gases and, under reduced pressure, a portion was distilled and rejected and other portions were distilled into ampules, which were then sealed.l0 Determination of Properties.-The properties listed in Table I were determined using the same apparatus and procedures previously d e ~ c r i b e d , ~ (1) Rasmussen, Hansford a n d Sachanen, I n d . Eng. Chenr., 38, 376 (1946). (2) Rasinussen, t o be published. (3) Fawcett and Rasmussen, THISJOURNAL, 61, 3705 (1945). (4) Opolski, Forts. won Anz. A k a d . Wiss. K r a k a u , 318 (1905); Chem. Z e n f u . , 76, 11. 179ti (1905). (3) Auuers a n d Kohlhaas, J . prakt. Chem., (2) 108, 321 (1924). (F) Lowry a n d Nasini, Proc. Roy. SOC.(London), AlZ.9,688 (1929). (7) Midgley. Henne a n d Shepard, THISJOURNAL, 64, 2987 (1932). (8) Shepard, Henne and Midgley, i b i d . , 56, 1356 (1934). (9) Jurjew (Yur'ev), Bcr., 69B,1002 (1936). (10) T h e 3-methylthiophene sealed i n v a c w i n clear-glass vessels remained water-white after four months, while a portion similarly sealed and later opened t o t h e atmosphere became slightly yellow o n further standing for a few days. T h e freezing point of the colored T h e 2-methylthiophene sample h a a not changed by as much a s 0.1'. remained water-white under both conditions. Thiophene behaved a s 2-methylthiophene.
800 mm. 850 mm.
114.3 116.4
117.2 119.3
AND
Aug., 1946
PHYSICAL PROPERTIES O F
2- AND 3-METHYLTHIOPHENE
1421
TABLE I1 calculated as 2500 cal./mole for the higherfreezing form and 1900 cal./mole for the lowerFREEZING PO1N.r DEPRESSIONS OF METHTLTHIOPHENES freezing form. Thus the vapor pressure curves WITH L-ARIOUS SOLUTES
for the two crystalline modifications will intersect above the melting point of either. These are the 2-hfethylthiophcne Konc -63.5 characteristics of monotropic polyrnorphism.l2 -65.5 3-Methyl5.1 The phase diagram for the system 2-methylthiothiophene -67.9 9.9 phene-3-methylthiophene is complicated by the 19.6 -70.9 occurrence of the metastable lower-freezing form, -74.0 27.8 and only the data of Table I1 have been com5.5 -65.7 Thiophene pleted. The heat of fusion of 2-methylthiopliene -72.9 23 1 was calculated as 2200 cal./mole. d.2 -65,7 Toluene Viscosities and 20, 25 and 30' were determined 2 0 , -4 -72.8 as for t h i ~ p h e n e . ~Values a t 0' were determined 3-Methylthiophcne Soiie . . -68.9 in an ice-water-bath, using the extrapolated -69.7 Form Ia 2-Methyl3.3 values of the densities. The viscometer was G 7 t hiopheiic -71.3 calibrated with water and n-heptane a t that -72.9 12.0 temperature with the operating volume of charge. -73.8 14.9 A measurement was made a t 0' for the thiophene -75.8 18.3 previously ~ u r i f i e dand , ~ the value of qo was 0.873 -7$5.4 centipoise, The data for the three compounds 19.7 5.4c -70.7 Thiophene when plotted according to a Duhring-type rela22.0 -77.6 tionship gave nearly linear curves. Using vis- 7 0 . 5 cosity datal3 for water, the reference liquid, the Tolueiie 4.3 temperatures were plotted a t which the compound -76.5 20.4 and water have equal viscosities (fluidities). .. --74.1 3-Methylthioph(:tie Sone Such a plot yields an approximately linear curve Form IIb Thiophene 5.4' -76.4 a Higher-freezing form. * Lower-freezing form. :' The for wide temperature (viscosity) ranges for a two freezing points were observed for the same solution, as variety of materials, and is useful in extending was the case with 3-rnethylthiophene containing no solute. such data. The replacement of a hydrogen by a The freezing point was determined for several methyl group in thiophene causes an increase in mixtures of 2- and 3-methylthiophene in the same the viscosity a t a given temperature, as is the case manner as for the pure components, using a cop- with cy~lopentane.'~Such a change with ben, ~ ~ pyridine15 causes a deper-constantan thermocouple and a Rubicon Com- zene,14c y ~ l o h e x a n eand crease i n the viscosity. pany Type 13, No. 2780, potentiometer. ApFor the boiling points16the Rubicon potentiomproximately 3 5 - c ~ .samples were prepared by eter was used. The copper-constantan thermoweighing the two components. Freezing point depressions caused by toluene and by thiophene couple was calibrated against the resistance were also measured (Table 11). The thiophene thermometer in this range. A sample of the same used was a portion of that purified during other benzene previously prepared3 served as reference liquid. The values in Table I were obtained ironi work.3 J. T. Baker C.P. Analyzed toluene (%*OD 1.4962, d 2 0 4 0.8664) was distilled with the 95-plate Diihring plots of the observed corresponding column with a reflux ratio of 50: 1 and one of the boiling points and published data for b e n ~ e n e . ~ ' central portions was selected having n20D 1.4967. The calculated heats of vaporization are approsIn one instance, 5y0 thiophene in 3-methylthio- irnately 8500 cal./mole. The ratio of the x-apor phene, two freezing points were observed for the pressure of 2-methylthiophene to that of 3one solution. On undercooling the stirred solu- riiethyltliiophene a t the sanic teniperiit urc is 1 .On tion to -81' a lower freezing temperature was in the range 112-1 l(io. Vapor prcassurc (lata lor observed from which an abrupt, spontaneous the %methyl isomer over the range :3:i--9.jo have change occurred to a higher temperature. The been reported by Sasini.'s sample was melted and on refreezing the hi :her Derivatives of Methy1thiophenes.-The tribronio defreezing point was obtained. This behavior, here rivatives were prepared from the pilot plant products by and with the :;-metl-iyltliiophc~iealone, is evid;:nce (12) Findlay, "The Phase R u l e a n d its .\1>1~Iicatitr Reserve, Keconstriictiou I'insnce Corporation, iii connec.ioti with tlie Governmerit Synthetic Rubber Program. ( 2 ) (a) Ptory, THISJOTJKNAI., 69, 241 (1937); (b) Irany, i b i d . , 62, 2690 (1940). (3) Pri-e, Kell a n d Krebs, i b i d . , 64, 1103 (1942). (4) Sctulz a u d Xusemann, Z . p h y s i k . C h e m . , B39, 246 (1033).
ALLEN AND
R. J. DEARBORN
termination. Peroxide-catalyzed polymerizations of dienes differ from those of simple vinyl monomers in that the steps of initiation and propagation may consist in either 1,4-or 1,2-addition to the diene system, or both 1,4- and 1,2-addition may occur in random fashion. Ozonization studies of polybutadiene indicate that the polymer has a structure of the third type, resulting from both 1,4- and 1,2-additi0n.~-~ At the time of the beginning of the present work two theories were under general discussion as providing possible explanations for the action of modifying agents. I n one i t was supposed that the modifier acted as a catalyst for 1,4- addition to the diene, or as an inhibitor for 1,2-addition, so that its use resulted in the formation of polymer of essentially linear structurr. In the absence of a modifier the polyiiierization was supposed to yield a product in which a large proportion of the diene units were combined as vinylethylene residues CH-CH,
. The side-chain vinyl groups in
( 5 ) HIII, Lewis and Simonsen, Trans. Faraday Soc., 35,1067 (1939). ((i) Alekseeva and Belitzkaya, Rubber Chem. and Tech., 16, 693 11942).
