Physical Properties of Triglycerides IV. Dielectric Constant By Dr. Ir. T. H. GOUW"and Prof. Dr. Ir. J. C. Vlugter"" L)e~iur&meri~of Chentical Engineering, Technological University, DelfL. The Netherlands Dielectric constants at 200 and at 40OC of a number of trigly- Propridtds physiques des triglycdrides IV: Constante didlectrique cerides in the liquid state have been measured. A molar additive La constante dielectrique a 20 ou 40°C a ete trouvee suru function of the dielectric constant, based on a relation derived un nombre de triglycerides a I'etat liquide. A l'aide d'une by J. van Elk, was used in combination with a previously derived equation precedemment derives pour les triglycerides, conjointe- equation for triglycerides to give an equation whicfi relates the ment avec une fonction additive molaire de la constante dielec- dielectric constant of a triglyceride or triglyceride mixture to trique, qui est basee sur une relation obtenue par J. van Elk, its refractive index, density, and iodine value. Quantification of on a etabli une equation qui fournit les relations entre la con- this relation was based on prime data obtained from these model stante dielectrique d'un triglyceride ou d'un melange de trigly- triglycerides and from previously published data on fatty acid cerides et leur indice de refraction, densite et indice d'iode. methyl esters. +MwqeciiMe cBoi4crr3a TpMrJMqepiiAoB. CooBqeiiue 4: Ati- xiewpMaeclcaa nucwmwax. Physikalishe Eigenschaften von Triglyceriden IV: DielektrizitPts- konstante &TSI PSIAa TPMr~7MqepM~OBU XMAKOM COCTOSIHMH OIlpe- jenerw AM~.~~KTPMWCKM~IIocTonHHbxe npx 20 M 40° C. Bei einer in flussigem Anzahl von Triglyceriden Zustand wurde c IIOMOqbIO PaHee Bbll3eAeHHOI'O YpaBHeHMJi AJSI TpMPJIM- die Dielektrizitatskonstante bei 200 bzw. 400 C ermittelt. Unter lJ,epMAOB M MOJISIPHOU aAAUTMBHOfi (PYHICqHIi JM3.TeWrpH- Zuhilfenahme einer fruher ahgeleiteten Gleichung fur die Tri- ~IeCKOnnOCTOSIHHO8, Ga3~py101qeflc~Ha IIOJI>'qeHHOM RaH. glyceride zusammen mit einer molaren additiven Funktion der D.1bKOM COOTHOLUeHMM, IIOlIyYeHO ypaBHel1Me J.1.R COOTHO- Dielektrizitatskonstante, die auf einer von J. van Elk erhaltenen LLIeHMR MeXAy j&MMIeICTpMqeCKOfi IIOCTORHHOfi TpMFJIHqe- Beziehung beruht, wurde eine Gleidmng aufgestellt, die die Be- p~firtM cMecM TpwmiqepMAoB M MX Kox])(PMqMewrw npe- ziehungen zwiscfien der Dielektrizitatskonstante eines Triglycerids .10MJleHUR, nJIOTHOCTbI0 M fiOJHblM YMCJIOM. nPMBOASITCR oder Triglycerid-Gemiscfies und deren Brecfiungsindex, Dihte und lcOJIMYeCTBeHIlbIe AaHHhIe 8TOrO COOTHOLUCHMSI Ila OCHOBB- Jodzahl ergibt. Quantitative Aussagen dieser Beziehung wurden HUN AaHHbIX J.rlSI hIOxe.lbHbIX TpMrJlMqepMAOB M pallee auf Grundlage der Daten bei Modell-Triglyceriden und aus bereits OIIy6JIMKORallHbIX AaHHbIX A.7R Mf?TN.'IOBbIX 3CbUpOII 5KNP- veroffentlihten Werten fur Fettsaure-methylester gemacfit. HIJX KMC;IOT. Introduction In this relation z stands for the increment of the The dielectric constant of a material, E, is defined atom i, and c is the number of the atoms i in the mole- as the ratio of the capacitance of a condenser with the cule. M stands for the molecular weight and d is the investigated substance between the plates, C, and the density. capacitance when a vacuum separates the plates, C,. Additive behaviour was ascribed to this function and C. B. Hence, Thwing obtained excellent results for many compounds. Other investigators have, however, noted significant differences be- E = c/c, (1) tween predicted ahd observed values. P. Waldene mentions and the dielectric constant thus defined is dimensionless. tetranitromethane for which 104.3 is predicted whereas a This value, also called the static or the quasi-static value of only 2.1 is observed. To obtain improved predictions P. Walden assumed atomic groups to contribute to the dielectric constant, is measured in a static field or in dielectric behaviour. A distinction is made between dielec- an alternating electric field of low frequency. trophoric and dielectrogenic groups. The high contribution of The first systematic measurements on the dielectric constant a dielectrophoric group is only noticeable in the presence of of fatty acids and triglycerides were carried out more than a dielectrogenic group in the same chain. half a century ago; L. Kahlenberg 1 observed that the dielectric H. Kauffmann7 made a further study on the influence of constant of natural fatty oils with a high percentage of oleic these groups in different positions in the molecule. He ob- acid was quite similar to the dielectric constant of the acid served the general trend in homologous series, the influence itself. In the following years only a small number of studies of branching, unsaturation, and substitution on the value of on this subject was noted. A review by W. S. Singleton4 the dielectric constant. adequately covers this subject up to 1958. Of the more The chief deficiency in all these methods is the in- recent papers mention can be made of the investigations of ability to account for changes in configuration or for K. H. Ludde' on the dielectric and refractometric behaviour geometrical isomers, and it is in exactly these areas of fats on aging. Of interest is also the correlation between where dipole moment measurements have been very the dielectric constant and the iodine value, which R. R. Allen successful in resolving structural problems. The correct observed over the commercially important range of fatty oils. s additive formula should, therefore, contain vectorial Additive Functions of the Dielectric Constant terms to account for those molecular structures, whose contribution to E depends on its direction in space. One first attempts to predict the dielectric con- of the Existing additive functions are, however, still quite stant, E, from structural contributions was presented by adequate if one would only restrict the applicability C. B. Thwing5, who proposed the following relation: to a limited area. In our particular case, where we have limited ourselves to triglycerides with non-polymerized, non-conjugated, straight-chain component fatty acids, Present addresses: we have noted that good results are obtained by the '* Chevron Research Co., Richmond. Calif., U. S. A. 94 802. use of a semi-empirical additive function for homo- * Technische Hogeschool Twente, Enschede, The Netherlands. logous series recently derived by J. van Elk8. This func- 1 Trans. Amer. Electrochem. SOC.7, 167 [1905]. tion reads: 2 W.S. Singleton, in: Fatty Acids, Part. I, Editor K. S. Mark- ley, Interscience, New York 1960. 6 Z. physik. Chem. 70, 584 [1910]. Fette . Seifen . Anstrihmittel 61, 1156 [1959]. ' Beziehungen zwischen physikalischen Eigenschaf ten und che- J. Amer. &em. SOC.52, 671 [1955]. mischer Konstitution, Ferdinand Enke, Stuttgart 1920. 5 Z. physik. Chem. 14, 286 [1894]. * Thesis, Delft 1962. FETTE . SEIFEN . ANSTRICHMITTEL 69. Jahrgang Nr. 4 1967 223 Em = (~-1)"~M/d = Xqzi (3) Temperature In analogy to other molar quantities described in this Readings were taken with calibrated thermometers, series of communications we will term E,, the molar the control being better than 0.02O C at 20° C and 0.loC dielectric constant. It has the same dimensions as the at 40° C. molar volume and the molar refraction, i. e., ml/gmole. In our particular case E,, is not obtained by summation Products of atomic, but of group contributions. To ensure iin- The investigated products included all mono-acid proved accuracies we will consider the largest groups triglycerides with even-numbered component fatty acids possible in our area of study without the sacrifice of up to trilaurin, a number of mono-acid unsaturated versatility. triglycerides, and some mixed triglycerides. Their pre- paration and physical properties have already been Experimental described in previous communications I5-l7. Apparatus Measurements have been carried out on a commercial Results Multi-DK-meter (type DK 06-22 manufactured by Dr. With a single exception we could not ascertain any Slevogt, Weilheim). A description of the apparatus and comparable data in the literature. The observed dielec- the measuring procedure have already been published tric constants at 2OoC have been included in Table 1 in the literature O, lo. and those at 4OoC in Table 2. Em is the molar dielectric constant. The molar volume, M/d, has been obtained from a previous paper Is. XE is the sum of the molar Calibration ",' dielectric constants of the component fatty acid methyl The purification of calibration liquids for dielectric esters. Values of Em for the fatty acid methyl esters measurements has already been discussed in details by have already been published previously lo. The difference E. Oelimeo~lland by R. R. Mecke and coworkersIe. Al- most all standards used in these investigations have between En, of the triglyceride and the XE ",' of its been purified along the discussed lines. The compounds component fatty acids in the methyl ester form is called chosen as standards, viz., benzene, cyclohexane, di-n- r, the glyceride incrementt5. EF is the increment of the butyl ether, carbon tetrachloride, 1,i?-dichloroethane, and double bond. It has been obtained as one third the chlorobenzene, were already available in relatively high difference between the relative compounds. The E,,, of purity. Depending on the compound the final purifica- tristearin, included to facilitate comparison, has been tion of these products consisted of either a chemical computed by subtracting the average r from three times clean-up