H. B. THOMPS~N, L. EBERSON, AND J. V. DAHLEN
1634
cerned largely with the full composition range from one pure component to the other. Little direct information is presently available for dilute solutions (below a few tenths molar), wherein it is commonly assumed in solvent extraction studies that activity coefficients of solute species are constant. The isopiestic method can readily be used to test this assumption. It seems clear from the present results and from eq. 5 , based on the treatment of Hildebrand and Scott,20 that such an
V O ~66 ,
assumption often is not justified. For example, it can be predicted that for 0.1, 0,2, and 0.3 771 TPM in octane, YTPM = 0.84, 0.71, and 0.60 by calculation I1 and 0.91,0.83, and 0.76 by eq. 5, respectively, These values are significantly below unity for a system in which no specific chemical effects have been assumed. Acknowledgment.-It is a pleasure to ackno.tv1edge the valuable technical assistance of W. E. Oxedine in this investigation.
ELECTRIC MOXEKTS OF SUBSTITUTED SUCCINIC ACIDS. THE LOW ELECTRIC MOMENT OF SUCCISIC ACID' BY H. BI~ADFORD THONPSOS, LENNARTEBERSOX, AND JEANNE V. DAIILEN Uepurtinent of Chemistry, Gustavus Adolphus College, St. Peter, Minnesota, and the Dtvisim of Organic C/umistry, Draco, Ilunds Farmacevtiska, Lund, Sweden Recezvsd February 18, 1861
The electric monicnts of substituted succinic acids have been determined in ordcr to explain the rclatively low rnomcnt of succinic acid. Contrary to previous speculations, a low moment is associated with conforniations in which carboxyl groups are separated, while structures involving internal hydrogen bonding show high moments.
Rogers2 noted that the electric moment of succinic acid was 0.4 D. lower t>han that of other aliphatic dicarboxylic acids, and proposed that '(a ring structure involving both carboxyl groups" might be responsible. He also not'ed that a similar low moment for diethyl succinate had been reported by Smyth and Walls.3 This would appear to rule out hydrogen bonding as the basis for any such cyclic conformation. Similar low moments for the four-carbon mcmhers have been reported in other series of @,adisubstit'uted and recently have been e ~ p l a i n e dwithout ~,~ recourse to cyclic conformation. It, seems advisable to consider more closely, t)hen, the case of succinic acid. Accordingly, we report here electric moment sttidies of 2,3-disubstitutcd succinic acids, in mmc of which cyclic st,ructurcs arc stmically most unlikely. Experimental
Preparation and purification of the substituted acids have been described previously.1° Oxalic acid was sublimed a t about 130" in vucuo. The remaining unsubstitutcd acids (Eastman) were recrystallized and dried in vacuo a t 55-69' for at least, 24 hr. At least four solutions of each acid in dioxane were prepared, the most concentra.ted being in every case less than 0.005 mole fraction acid. Dioxane was purified by reflux with sodiuin for at least 24 hr.; reflux was continued until no further dulling of the shiny surface of the molten sodium fipheres occurred. The dioxane then was fractionally distilled, and the fraction between 100.0 and 100.4' (at 730 mm.) collected and used within 24 hr. Less than 0.04% volatile impurity could be detected by vapor chrornatoyraphy.
Results and Discussion The Unsubstituted Acids.-T;hble I s i i n 1 i i i : t r i x w oiu' resu1t:s and tl:osc OC Rogers for t,he unsub~:titubed dibasic acids. We, too, find a lorn moment for succinic acid. However, our rnorncrrt~s and those of Rogers differ significmtly, our values f~;lcc.fric: nroinrnts xwre detcrrnirrctl I ) p Giiggenlicini'fi agreeing more closely with .those of 13egniii aitd iiiot,hotls: the qwirtity ( r : - n 2 ) / ( e + 2)(rLz -4.- 2) WRH c:tlcii- Gaumann.ll It appeared wort'hwhilc to determine latcd for cacli of four or ~ I V Psolut,ions, aud plot,lcd against, whether t,he discrepancy lics in the met8hod,siiicc we concenimtiori in rnoles/cc. The dope ( S )of tjhc bcet straight cmployed the procedure of Guggenheim8 whilc line WRS taken equal to 4 ~ N p ~ / 2 2'. 7 k Thc dielectric conRogers used that of Halverstadt and l
