THE OPTICAL ROTATORY POWER, ETC. 4 9MI.-The Optical Rotatory Power of Dwivatives ofSuccinic Acid in A queous Solutions of InorganicSalts. Part I.By GEORGE WILLIAM CLOUGH.WORKERS on thO Walden inversion have been confronted by thefundamental difficulty that there are a t present no means ofascertaining whether, when a group attached to an asymmetriccarbon atom of an optically active compound has been displacedby another group, a change of configuration has or has notoccurred. For example, in the transformation I-malic acid 2d-chlorosuccinic acid -+ &malic acid it is impossible to statewhich of the two reactions is accompanied by a change of con-figuration. The various hypotheses that have been advanced inexplanation of the phenomenon are concerned with the mechanismof the reaction, but, its Frankland stated in his PresidentialAddress, (‘ unfortunately all the attempts which have hitherto beenmade to apply these explanations to specific cases have been singu-larly unfruitful ” (T., 1913, 103, 726).In his investigation of therelative effects of the various reagents that have been employed,Frankland makeis the tentative hypothesis that the change of signwhich almost invariably accompanies the action of phosphoruspentachloride o r phosphorus pentabromide is, in the absence ofevidence to the contrary, to be regarded as betraying a change ofAg20VOL. cv. 50 CLOUGH: OPTICAL ROTATORY POWER OF DERIVATIVES OFconfiguration. The same author, however, emphasises the possibilitythat, notwithstanding the usual change in sign, the action ofphosphorus pentachloride may be a ‘‘ normal ” action.It is evident,therefore, that, until confirmatory evidence is forthcoming, thissuggestion can only be accepted with the greate& reserve.The present investigation has been undertaken in the hope thata study of the influence of solvent, concentration, and temperaturerespectively on the rotation of certain similarly constituted com-pounds of the same configuration will reveal regularities which maybe subsequently utilised for the dgtermination of configurativerelations in doubtful cases. The large amount of experimentalmaterial already accumulated in this field exhibits few regularitieswhich may be justifiably employed for this purpose.Frankland,however, has used the method in order to prove that the esters ofaj3-dichloropropionic acid obtained by the action of phmphoruspentachloride on the lzevorotatory esters of glyceric acid haveidentical configurations. Ahhough the higher esters obtained areoptically opposite t o the methyl ester, they are configurativelysimilar to the latter, inasmuch as rise of temperature diminishestheir lzvorotation, but increases the dextrorotation of the methylester (Zoc. cit., p. 718).The present author proposes t o make a comparative study of therotation of optically active derivatives of succinic acid in the purecondition, in aqueous solution and in aqueous solutions of certaininorganic salts. The rotatory power of many derivatives of succinicacid is particularly msceptible to the influence of solvent, concen-tration and temperature, and it appears to be more than a coinci-dence that compounds which exhibit the phenomenon of anomalousrotatory dispersion usually possess rotations which vary widelywith the conditions under which they are measured.The influenceof a large number of electrolytes on the rotation o€ aqueous 2-malicacid a t a constant temperature has been investigated by Stubbs(T., 1911, 99, 2265), whilst Patterson and Anderson have studiedthe effect of inorganic salts on the rotatory power of ethyld-tartrate (T., 1912, 101, 1833).I n the present paper the effects produced by sodium and bariumhaloids on the rotation of aqumus solutions of d-tartaric acid,methyl d-tartrate, ethyl d-tartrate, and d-tartramide respectively a tvarious temperatures are described.The results bear a strikingresemblance to those obtained by Stubbs and by Patterson andAnderson. The salts employed cause a relatively large depressioiiof the dextrorotation of theBe compounds in aqueous solution, andin some instances they cause a reversal of the sign of rotation.The curves in Fig. 1 represent the rotation of tartaric acid iSUCCINIC ACID IN AQUEOUS SOLUTIONS OF INORGANIC SALTS. 51FIU. 1.Tartaric Acid.--4T.11.1x1.IV.V.0 10 20 30 40 50 60l'emnperattere.I. Watcr (p=16'67).11. Water (~'50).111. Aqz~eous sodium chloride (~~13.95).1V. AqzLeous sodiwm chtoride (p = 44.76).V. Tmrtaric acid.The aqueous sodium chloride contains 11.7 grams of sodium chloride in50 grams of water52 CLOUGH: OPTICAL ROTATORY POWER OF DERIVATIVES OFaqueous solution and in aqueous sodium chloride.The dextro-rotation of an aqueous solution of tartaric acid increases consider-ably both with dilution and with rise of temperature. Althoughthe specific rotation of sodium hydrogen tartrate in aqueous solutionis higher than that of tartaric acid, the rotation of tartaric acid inaqueous sodium chloride is much less than in aqueous solution.It is again obvious from the curves that the more dilute solutionof tartaric acid in aqueous sodium chloride has a greater rotationthan the more concentrated solution, and that the temperature-coefficients for all the solutions are positive. For the sake ofcomparison, the values calculated by Winther by extrapolationfor the rotation of tartaric acid in the pure state are representedby the dotted curve (Zeitsch.physikal. Clhem., 1902, 41, 161). Thedepression of rotation caused by sodium bromide is greater thanthat caused by sodium chloride, but less than that caused bysodium iodide. These salts thus exert the same relative effects onaqueous tartaric acid as on aqueous ethyl tartrate (Patterson andAnderson, Zoc. cit.). Stubbs similarly observed that potassiumiodide influenced the rotation of malic acid to a greater extentthan potassium bromide, which in turn had a greater effect thanpotassium chloride. Moreover, these regularities extend to theinfluence of barium haloids, which cause a greater alteration inthe rotation than equivalent quantities of the correspondingsodium salts.The rotation curves for methyl tartrate in the pure condition,in aqueous solution, and in aqueous sodium chloride, are drawn inFig.2. The curves for the pure ester and for the aqueous solutionsare drawn from the valuable data given by Patterson. The dissolu-tion of methyl tartrate in water considerably raises the rotation ofthe ester, and whilst the temperature-coefficient for the pure esteris positive, that for the aqueous solution is negative. The presenceof sodium chloride in the aqueous solution has a remarkable effect,for not only is the rotation greatly reduced, but rise of temperatureis now accompanied by an increase of rotation. The influence ofbarium bromide on the rotation of aqueous methyl tartrate is againmuch greater than that of sodium chloride.The curvea for ethyltartrate are very similar to those for the methyl ester. Patterson’scurves for the pure ester and for the aqueous solution, which arereproduced in Fig. 3, show that the rotation of the ester is muchgreater in aqueous solution than in the pure condition. The specificrotation in aqueous sodium chloride, however, is lower than thatof the pure ester, but the temperature-coefficients are now similar.The relative effects of barium bromide and sodium chloride on therotation of ethyl tartrate are of the same order as those of thesSUCCINIC ACID IN AQUEOUS SOLUTIONS OF lNORGANIC SALTS. 532220i a1614.$ 12uu 2 s u” 1c0ae440FIG.2.Methyl tartrate.710 20 30 40 50 00 70Temperature.I. Water (p=5-17).11. Water (p=49-8).111. Aqueozu sodiicm chloride ( ~ ~ 4 . 0 4 4 ) .IV. Methyl tartrate.V. Aqueous sodium chloride ( p = 43‘02).The aqueous sodium chloride contains 5 *85 grams of sodium chloridein 20 grams of water,I I.1x1.I v.1754 CLOUGH: OPTICAL ROTATORY POWER O F DERIVATIVES OFsalts on tartaric acid and methyl tartrate. The comparatively large1zvorota.tion of methyl and ethyl tartrates in aqueous bariumbromide at low temperature is particularly noticeable.The other derivative of tartaric acid which has been examinedFIG. 3.Ethyl tartrate.10 20 30 40 50 60Temperature.I. Water (p = 50).11. Ethyl tartrate.111.Aqueozcs sodium chloride (p=43%2),IV. Aqueous barium bromide (p=36.45).The aqueous sodium chloride contains 5.85 grams of sodium chloride in 20 gramsof water and the aqueous barium bromide contains 14.86 grams of barium bromidein 20 grams of water.is tartramide. This compound is only sparingly soluble in water,but the aqueous solution is strongly dextrorotatory. The dextro-rotation is diminished by sodium chloride, and still more eo bybarium bromide. Increase of temperature slightly reduces thSUCCINIC ACID IN AQUEOUS SOLUTIONS OF INORGANIC SALTS. 55specific rotation, both in aqueous solution and in aqueous sodiumchloride.In order to account for the results obtained in the case of malicacid Stubbs advanced the view that the influence of the salts ismainly due to a direct and distinctive power possessed by theinactive molecules in solution to affect the asymmetry of the activeones within their sphere of influence without actual chemicalcombination.Patterson and Anderson maintain that the influence of inorganicsalts is of the same order ag that of organic solvents.Some yearsago Patterson suggested that there was a relation between therotatory power of a substance in a given solvent and the internalpressure of that solvent. This pressure, it was pointed out, wouldchange the volume and also the shape of an asymmetric molecule,but as the shape of the molecule conditions the value of therotation, alteration of volume would be accompanied by changeof rotation (T., 1901, 79, 189).It would thus appear that thereis little difference between the explanation put forward by Stubbsand that previously advanced by Patterson for the more generalcase. In a recent paper Patterson expresses the belief “that thepotentialities of the asymmetric carbon atom and of the most simplephysical conceptions of those inter-molecular forces to which lique-faction is due are ample to account for all the observed behaviour ”(T., 1913, 103, 173).This conception implies that a gradual alteration of temperatureor concentration, o r the gradual addition of an inactive substanceproduces a corresponding gradual alteration in the shape or asym-metry of the molecules, and consequently a change of rotation.Although this hypothesis may explain the changes of rotation inmany cases, i t appears to be inadequate to account for the greatvariations in the rotation of such compounds as tartaric acid andits esters, or for the phenomenon of anomalous rotatory dispersion.More than sixty years ago Biot showed that a substance whichexhibits anomalous rotatory dispersion behaves in this respect inprecisely the same way as a mixture of two substances havingopposite rotations and different dispersive powers (Ann.Chim.Phys., 1852, [iii], 36, 405). This interesting suggestion has beenrecently elaborated by Armstrong and Walker (Proc. Roy. SOL,1913, A , 88, 388), who advance the hypothesis that substancespossessing anom alouz rotatory dispersive power consist of iso-dynamic forms having different rotatory powers ; for example, anaqueous solution of d-tartaric acid contains an equilibrium mixtureof a dextrorotatory form and a lzevorotatory form, the formerpreponderating at high temperatures and in dilute solution56 CLOUGH: OPTICAL ROTATORY POWER OF DERIVATIVES OFInasmuch as the equilibrium is conditioned by solvent, concentra-tion, and temperature, change of rotation is also dependent ont h a e factors.The present author believes that this is the mostsatisfactory explanation that can be advanced a t present to accountfor the large variations of rotation described in this paper. It isevident that the presence of certain inorganic salts in aqueoussolution profoundly alters the equilibrium of the two isodynamicforms. The reason for the great difference between water andaqueous salt solutiom is not a t present clear.The influence ofthe salts is certainly opposite to that of dilution, but the rotationof ethyl tartrate in aqueous sodium chloride may be less than thatof the ester in the pure condition. The rotation curves of theesters of tartaric acid indicate that the influence of temperature isnot always the same, for in some solvents the temperature-coefficientis positive, whilst in others the coefficient is negative.An interesting point which appears to have received little atten-tion is the phenomenon exhibited by some opticdly activecompounds of possessing, under certain conditions, no rotation. Ifthe asymmetry of the molecule is the cause of optical activity itis difficult to conceive how a solution of similar asymmetricmolecules could be optically inactive. The hypothesis of Armstrongand Walker, however, presents a ready solution of the difficulty.Under such conditions the rotations of the isodynamic formsexactly counterbalance one another.Armstrong and Walker suggest four possible formuls for theisodynamic forms of tartaric acid:C*OH C(OH),CH*OH/\\/YHooH 0 CH*OH Ho>C CH*CO,H p**" \/ co 0 C0,H C-OH(1.) (11.) (111.) UV.1but consider that the forms preponderating in aqueous solution arerepresented by the carboxylic formula (I) and the lactonic formula(111).There can be little doubt but that the dextrorotatory formof d-tartaric acid is represented by the carboxylic formula, butthere is little evidence in support of the lactonic formula for thelaevorotatory isodynamic form of d-tartaric acid.It seeme probablethat further work on the rotatory powers and rotatory dispersionsof similar compounds will throw some light on the constitutionof the latter form. The hypothesis should prove a useful guidein the investigation of the rotatory power of other derivatives ofsnccinic acid on which the author is at present engagedSUCCINIC ACID IN AQUEOUS SOLUTIONS OF INORGANIC SALTS. 57EXPERIMENTAL.In order that the results might be comparable with those ofother workers, the solutions have been prepared in such a mannerthat, whilst the weights of active substance and water are keptconstant, the weights of the salts added are equivalent; thus therotation of tartaric acid in water (p=16*667) should be comparedwith that in aqueous sodium chloride (p=13'95).Tartaric Acid i m Water.Tartaric acid (10 grams) in water (50 grams).t ..........14". 20.5". 29". 39". 50". 59". 69'. 80".(1?=4) ... +8'34 8.91 9.57 10'21 10.77 11'12 11'48 11.78[a]: ......... + 11-58 12.41 13.38 14.34 15.20 15.75 16-32 16.83Densities determined : t . . . ... 13". 23". 40". 55" 72"d...... 1.080 1.076 1.068 1-061 1'054p = 16.667 :dt ............ 1'080 1.077 . 1.073 1.068 1.063 1.059 1,055 1-050Tartaric acid (50 grams) in water (50 grams).t.... ........... 16.5". 30". 36". 48".d ............ 1'272 1.261 1.256 1.247a; (1=2) ... +8.76 10.95 11.90 13.50[alt ......... +6'89 8.68 9'47 10'83Densities determined : t ......23". 35". 55".d ... 1.266 1.257 1.243.p= 50.00 :Tartaric Acid in Aqueous Sodium Chloride.Tartaric acid (10 grams) and sodium chloride (11.7 grams,1 /5 gram-mol. weight) in water (50 grams),p= 13-95 :t ..................... 7". 15". 30". 46". 56". 64".cl ..................... 1.207 1-202 1.193 1.184 1.178 1.173a', (1=2) ........ - 0.08 +0'51 1.36 2.06 2-37 2-64[a]: .................. -0.24 +1*52 4.09 6'24 7'21 8.07Densities determined : 1 ...... i6". 31" 47". 64".d ...... 1.201 1.193 1.183 1'173Tartaric acid (50 grams) and sodium chloride (11.7 grams)in water (50 grams).p = 44.76 :t ..................... 16". 18". 27.5". 38". 54".d ..................... 1.333 1-332 1.327 1.320 1.309a', (Z=2) ...........- 0.20 i-0.22 2-26 4-22 6'52[a][, ................. - 0.17 f 0 . 1 8 1-90 3.58 5.56...... Densities determined : t 24". 40". 53".d ...... 1.329 1'318. 1.3058 CLOUGH: OPTICAL ROTATORY POWER OF DERIVATIVES OFTartaric Acid in Aqueous Sodium and Barium HaIoids.Tartaric acid (10 grams) and ths respective weights of anhydrousSalk in water (50 grams).Weiglr t Gram-mol.Salt. of salt. weight. p . d'f. a?(Z=2). [a]:?.Sodiumchloride ... 5%5 15'19 1.136 +2%3 + 7 ~ ...... 13.95 1.196 - 3.30'$ 9 13'43 1217 0 *67 1'90 .... 14.22 1.200 2 40 7-03,) 11 -70) ) 14-62)) bromide.. 10 *3 27J ,) 20% 12.41 1.309 0 70 2.159 ) 11.66 1.363 0 *07 0.22 ...... 1.71 5-11 ) ) iodide 15.0 cv 13'33 1.2579 7 )) ..... 37 5 10'26 1'482 -0.87 -2.88Barium chloride ......10.41 2n 14-20 1.223 -0'55 - 1.58,) bromide ..... 14-84 23 13.36 1.286 -0.80 -2'342 ) ,, ...... 37'2 n 10'29 1'564 -3'34 -10.88* Interpobted.) ? ...... !...... $ 9- ...... ,) 25-76 I2 9 ), ...... 29 72 2s 11.15 1.468 -2'89 - 8 831.................. + 12.98* None.. - I 16.67 1-075 -MethyI Tartrate in Aqueous Sodium Chloride.The methyl tartrate used gave a: ( I = 2 ) + 5.70°. Methyl tartrate(1.09 grams) in water (20 grams), p=5*17; weight of sodiumchloride added, 5.85 grams.p = 4'044 :t ....................... 18". 27". 35.5". 43".d ........................ 1'178 1.173 1'168 1.165a: (1 = 4) .............. + 1-16 1.31 1 '44 1.51[a] .................... +6'08 6'89 7'62 8 -33Densities deteimined : t ...... 17". 27". 41".d ...1.179 1'173 1.166Patterson's values for methyl tartrate in water (p=5-17) are:[ C Z ] ~ ' ~ + 21.10°, [a]E' 20*81°, 20.2a"(T., 1904, 85, 1150).Methyl tartratep=43*62 :(20 grams) and sodium chloride (5.85 grams)in water (20 grams).t ..................... 16". 18.5". 23". 35". 49".d .................... 1.254 1.252 1.249 1-240 1-229ak(Z=2) ............ +0'80 0'86 1-32 2'24 3'11Densities determined : t ...... 17". 29". 40".[u]: .................. +0.73 0.80 1-21 2-07 2.90d ... 1.253 1.245 1'23SUCCINIC ACID IN AQUEOUS SOLUTIONS OF INORGANIC SALTS. 59Methgl Tartrate in Aqueous Barium Bromide.Methyl tartrate (20 grams) and barium bromide (14.86 grams)in water (20 grams).p = 36-45 :t ......................... I f " . 29". 36".d ..........................1.473 1,464 1.468~4,(Z=2) .................. -12.69 -- 10*79 - 9.66[uJ; ........................ - 12-02 - 10.11 - 8-93Densities determined : t ...... 13". 24". 35".d .. 1476 1'468 1.459Patterson's values for pure methyl tartrate are:[a]E* + 1*83', [a]: 2 07", [a]:" 2 * 6 4 O , [a]$"s 3-60',and for aqueous methyl tartrate (p=49*77) :(T., 1904, 85, 766, 1150).+ 14.710, ~ ~ 1 ~ 3 14.590, [ . 1 ~ ' 7 14.130Ethyl Tartrate in Aqueous Sodiam Chloride.Ethyl tartrate (20 grams) and sodium chloride (5.85 grams)in water (20 grams).t ........................ 17". 28". 36". 50".d ........................ 1.202 1.193 1.187 1.176p=43*62:a4, (Z=2) .............. + 2.30 3'22 3-86 5-04[a]: ..................... +2*19 3-09 3.73 4-92Densities determined : t ......18". SO". 44".d ... 1.202 1-192 1.181Ethyl Tartrate in Aqueous Bariam Bromide.Ethyl tartrate (20 grams) and barium bromide (14.86 grams)in water (20 grams).t ..................... 15". 38". 45". 29".a? ................... 1-430 1.409 1-403 1-418p=36*45 :~E,(2=4) ............ -16'54 10.84 8-74 12-84[a]; .................. -7'93 5-03 4-27 6.21Densities determined : t ...... 15". 26.5". 41'.d ... 1'430 1.420 1'407ThO following are Patterson's values for the pure ester (T., 1913,103, 173):[a]", + 7-64', [ c c ] ~ ' . " 9*39', [a]:" 11 * 4 5 O ,whereas the ethyl tartrate used in the above experiments gaveu: + 18.92O (1=2). For aqueous ethyl tartrate (p=50) Pattersongives :[a]:' + 17-44', [a]?'' 17-34', [a]?'* 17.1'7', 16-91', [a]: 16-76'(T., 1901, 79, 201)60 CUNDALL :Tartramide in Water.Tartramide (0.5 gram) in water (50 grams).t ......................... 17". 27". 37".d ........................... 1.001 0 '999 0.998p = 0.99 :a; (I= 4 ) ............... + 4 *42 4 '40 4.38[a]: ........................ + 111.5 111.1 110 8Densities determined : t... ... 17". 31". 50".d ... 1,001 0.999 0.996.Tartramide in A p e o u s Sodium Chloride.Tartramide (0.5 gram) and sodium chloride (14.62 grams)in water (50 grams).t ........................... 16". 27". 40".d ........................... 1.176 1'170 1 -1 63as ( I = 4) .................. f 3 '20 3-12 3.02Densities determiiied : t ...... 17". 36". 46".d ... 1.175 1.165 1-159p = 0.768 :[aJt ....................... + 88'6 86.8 84.5 .The relative effects of sodium chloride and barium bromide areindicate 3 by the following values for solutions containing the saltsand tartramide (0.5 gram) in water (50 grams):Weight Gram-mol.Salt. of salt. weight. ~i42~. ~ 2 , ~ ( 2 = 4 ) . [a]:.Sodium chloride 11.7 B 1 '139 + 3.36 + 90'2Barium bromide. ..... 29.7 25 1'453 +1'97 +54'41 ......The author wishes to thank the Research Fund Committee of theChemical Society for a grant towards the expenses of this investi-gation.BIRKBECK OOLLEGE,LONDON, E.C