August, 1963
THERMODYSAMIC PROPERTIES OF ETHYLENE GLYCOL-~IETHASOL SYSTEM
tlensity of the solution was also determined with aliquot3 of the solution. The pH of the remaining solution was decreased by clropwise addition of concentrated hydrochloric acid with stirring. Aliquots were taken a t appropriate pH values (Beckman Model ( i pH meter with Beckman glass and caloniel electrodes) and placed in n.m.r. tubes which were immediately sealed and immersed in a Dry Ice-isopropyl akohol slurry until crpectra were recorded. Spectra of the water-proton resonance were recorded under fastpassage conditions1’using the “saw-tooth” sweep unit of the spectrometer. Care was taken to ensure reproducible homogeneity of the field. All samples were run consecutively and npectra of a sample of pure Tmter were run between each pair of
1665
determinat,ions to ensure that the field remained constant. Results for the pure water samplewere 1/72‘ = 2.04 i: 0.06 set."' for six determinations. Cancentrated Sulfuric Acid Solutions.--The compositions of the HL304-HzO and D2S04-D20 mixtures were determined by titration of weighed amounts with standardized aqueous sodium hydroxide. Values of Ho and DOwere determined from data of Paul and Long.l6* Bigelei~en’5~ has shown that data for HzSOa apply equally well for DaSO, in the composition range involved. Solutions of 3 were prepared with cooling, transferred to n.1n.r. tubes, imniediately sealed, and immersed in a Dry Ice-isopropyl alcohol slurry until the spectra were recorded.
EXCESS THERMODYNAMIC PROPERTIES OF THE BINARY LIQUID SYSTEM ETHYLENE GLYCOL-METHATL’OL BY P. D. CRATIN~ AND J. K. GLADDEK Chenzistry Department, T h e Agricultural and Xechanical College of Texas, College Station, Texas Received February .2, 1963 The excess thermodynamic properties of the binary liquid system ethylene glycol-methanol have been determined at 25’. This system shows small positive deviations from Raoult’s law. The mixing process is slightly endothermic. The entropy of mixing is negative. There is a small contraction in volume upon mixing. The n.m.r. spectrum of this system shows some very unusual properties. An attempt is made to offer a plausible explanation for the observed behavior of this system.
Introduction Interest in the ethylene glycol-methanol system was aroused by statements in the literat’ure concerning binary mixtures of monohydric alcohols. I n 1924 Parks and Schwenk2 reported that mixtures of ethanol and 1propanol formed ideal solutions throughout t,he entire composition range at 39.90’. I n 1953, Mitchell and Wynne-Jones3 stated that from available literature data, the systems et,hanol-methanol and ethanol-lpropanol “form ideal solutioiis with zero values for all excess fuiictioiis.” Furthermore, these authors seem to imply that all mixtures of monohydric alcohols should exhibit ideal behavior. A recent Americari Petroleum Institute compilation of the results from thirty-four laboratories4 on the vapor pressure of methanol brought out some inconsistencies. These findings, further substantiated in this Laboratory, show the vapor pressure of niethaiiol to be 2 to 4y0 higher than the previously accepted value.5 If the more recent data are correct, then it is doubtful whether the reported excess free energies for methanol solutions are correct. It has been found6that methanol in contact with boron-containing glass produces trimethyl borate in subst,antial quantities (as high as 12 mole Yo). Thus, it, is conceivable t’hat some of the reported values for the vapor pressure of methanol mere low due to the trinietliyl borate present. Some inconsistencies exist iii the literat’ureconcerning aqueous solut’ions of et’liylene glycol. Curme’ has reported a volunie contraction of 1.47, at 50% volume (1) Abstracted from t,he P h . D . Dissertation submitted b y P. D. Cratin t o the Agricultural and Mechanical College of Texas, 1962. (2) G. S. Parks and J. R. Bchwenk, J . Phys. Chem., 28, 720 (1924). (3) A. G. Mitchell a n d W. 17. K. Wynne-Jones, Discussions Faraday Soe., 16, 161 (1953). (4) “Selected Values of Properties of Hydrocarbons and Relat.ed Compounds,” American Petroleum Institute Research Project 44, Vol. I. (5) T. E. Jordan, “Vapor Presaures of Organic Compounds,” Interscience Publishers, Inc., New York, N. Y., 1954, p. 65. (6) R. P . Porter, J . Phys. Chem., 61, 1260 (1957). (7) G. 0. Curme, “Glycols,” A. C. S. Monograph Series Number 114, Reinhold Pubi. Corp., New York, N. Y., 1952, p. 36.
conceiitratioii whereas a recent publication by Fogg8 stated that there is almost a h e a r relationship between the composition and density of aqueous ethylene glycol solutions. Experimental Chemicals.-The methanol used in this research was Fisher’s reagent grade (“suitable for Karl Fischer reagent”). The methanol was purified by the method outlined by VogeLg The fraction distilling between 64.45 atid 64.55’ was collected and used in this investigation. The reCractive index, n%, of this fraction was 1.3269, and the density a t the same temperature was 0.78G7 g. ml.-’. The methanol used for the vapor pressure determinations in this research had been stored no longer than a month in a Pyrex container; a flame test as outlined by Scottlo confirmed the absence of borates in the methanol. The ethylene glycol used in this work was Matheson, Coleman and B d l reagent grad? material, whose normal boiling point bad a range of 195 to 197”. Four different methods were employed to purify this reagent grade material. (1) Distillation of the glycol under reduced pressure. The middle fraction which distilled a t 110” (28.5 mm.) was collected. (2) Distillation of the glycol at atmospheric pressure. The middle fraction having a boiling point rang. of ca. 0.3” was collected. (3) Water and other low boiling materials were removed by prolonged heating at 110’ and 50 mm. pressure, and the pot charge was saved. (4) The water and other low boiling materials were removed by maintaining a temperature of 25” and a pressure of 5 mm. for a period of 10 to 12 hr. The pot charge was saved and used for this investigation. KO diffei-ence could be detected in the refractive index of the products obtained from the above four methods. The refractive index, n%, was 1.4302; the density a t 25” was 1.1103 g. rnI.-’. Temperature Control.-The temperature control was achieved by means of a Sargent 8-83805 Thermostatic, 0.01”, mercurial regulator, reactor controller water bath. A Beckmann differential thermometer, previously calibrated at 20 and 25” with Bureau of Standards thermometers, was immersed in the bath to facilitate temperature readings. The temperature was controlled to &0.02” for all the refractive index, density, and vapor pressure measurements. (8) E. T . Fogg, A. N. Hixson, and A. R. Thompson, Anal. Chem., 2T, 1609 (1955). (9) A. I. Vogel, “.4 Textbook of Practical Organic Chemistry,” Longmans Green and Co., London, 19.51, pp. 167-168. (10) W. W. Scott, “Standard lLIethods of Chemical Analysis,“ D. Van Yostrand Go., Inc., New York, X. Y., T70l. I, p. 162.
1'. D. GRATINA N D J. I
