J . Chrm. SOC., Faraday Trans. I, 1982, 78, 2297-2302 Magneto-optical Rotation Studies of Liquid Mixtures Part 6.-Specific Interactions in Mixtures of CCl, with Aliphatic and Aromatic Ketones and Esters BY J. GRAHAM DAWBER Department of Chemistry and Biology, North Staffordshire Polytechnic, Stoke-on-Trent ST4 2DE Received 18th November, 198 1 Measurements have been made of the magneto-optical rotations at 435.8 nm of binary mixtures of CCl, with 35 aliphatic and aromatic ketones and esters. The departure from ideality of each binary mixture was treated in terms of an excess magnetic rotation, aE ; for many systems, particularly the aromatic compounds, the variation of a E with composition gave indications of interaction between the CCl, and the other component. The results for the longer-chain aliphatic compounds indicated that their liquids contain orientational order which was broken up by addition of the CCl,.The molar magnetic rotations, Am, were calculated from the results and compared with the values calculated from a set of partial magnetic rotation parameters obtained previously. In most cases the agreement was quite good thus confirming the approximate additivity of the Faraday effect. Previous studies'. on the magneto-optical rotations of binary mixtures of miscible liquids have shown that the departures from ideality of the systems could be expressed in terms of an excess magnetic rotation, aE. The variations of aE with liquid composition were used to give an indication of the overall changes occurring in the liquid state. In some mixtures in which CCl, was one of the components there were indications that weak charge-transfer complexes were formed, particularly when the other component was an aromatic compound, although this also occurred, albeit to a lesser extent, with aliphatic amines, ethers and alcohols.For some mixtures the changes in aE could be interpreted in terms of a breakdown of order in the liquid structure of the second component by the addition of CCl,. Many of the systems previously studied1* had been investigated by other workers using a variety of techniques and the magneto-optical studies complemented their findings. In the work presented here we have extended these studies to mixtures of compounds which have not been studied by other techniques, and have included in the investigation aliphatic and aromatic ketones and esters in order to study the possible interaction of the carbonyl group with CC1,.EXPERIMENTAL The magnetic rotation apparatus has been described previ~usly.l-~ The measurements of magnetic rotation were made at the 435.8 nm line of the Hg emission spectrum with the sample in a 1 cm path-length cell placed in a magnetic flux density of 0.54 T. The wavelength used was well outside the electronic absorption bands of all the substances studied. The compounds were of laboratory reagent grade and were dried with common drying agents. Mixtures of CCl, + the second component were made up to cover the whole composition range. The temperature of the liquids was nominally 20 O C . Readings of angular rotation could be estimated to 0.001*.22972298 MAGNETO-OPTICAL ROTATION STUDIES OF LIQUID MIXTURES RESULTS The results were first of all calculated as magnetic rotation, a,, defined as (1) a, = 8,/1 where 8, is the magnetic rotation of the solution in a magnetic flux density of 1 T and 1 is the path-length of the solution in metres. The units of a, are thus deg m-' T-'. TABLE 1 .-MAGNETO-OPTICAL PARAMETERS OF PURE LIQUIDS (Or: AND Am) AND MAXIMUM EXCESS MAGNETIC ROTATIONS (a:,,.) OF THEIR MIXTURES WITH CC1, AT 436 nm AND 20 "C compound acetaldehyde propan-2-one (acetone) butan-2-one 4-methylpentan-2-one nonan-5-one 2,6-dimethylheptan-4-one heptan-2-one acetophenone 1 -phenylpropan- 1 -one p-me thy lace tophenone 1 -phenylpropan-2-one propanal methyl formate ethyl formate methyl ethanoate ethyl ethanoate n-propyl ethanoate isopropyl ethanoate n-butyl ethanoate n-pentyl ethanoate isopentyl ethanoate ethyl propionate ethyl n-butyrate n-butyl n-butyrate isobutyl n-butyrate glyceryl tributyrate methyl benzoate ethyl benzoate isopropyl benzoate n-butyl benzoate benzyl ethanoate benzyl benzoate diethyl phthalate ethyl acetoace ta te pentane-2,4-dione (acetyl acetone) 336.1 335.9 356.6 382.5 385.2 402.7 38 1 .O 781.0 755.1 744.1 788.0 347.9 284.7 330.4 305.1 320.3 338.7 336.3 346.4 366.7 378.7 352.2 345.3 360.6 365.1 371.2 752.4 720.7 684.0 665.3 754.6 962.1 617.2 360.8 512.2 18.9 24.7 31.9 47.9 66.6 71.1 53.4 91.5 100.3 99.4 105.7 25.0 17.6 26.6 24.2 31.4 38.9 39.3 45.8 54.6 56.6 40.4 45.7 60.0 60.2 108.5 94.1 107.9 110.4 118.6 107.5 183.0 122.8 45.7 52.6 17.0 17.5 24.5 10.2 32.0 3.0 47.0 -9.5 69.5 -14.4 69.5 -12.6 54.5 - 7.2 100.5 28.0 108.0 27.8 104.5 31.2 108.0 32.0 24.5 - 17.0 23.4 24.5 4.4 24.5 5.3 4.7 32.0 -2.2 39.5 -10.0 39.5 -10.6 47.0 -14.3 54.5 -20.4 54.5 -12.6 39.5 - 9.0 47.0 -14.4 62.0 -19.8 62.0 -16.8 136.0 -35.0 100.5 24.0 24.0 108.0 30.3 115.5 31.0 123.5 31.5 108.0 32.6 183.0 87.0 128.0 26.8 48.0 -7.5 40.5 11.1 0.38 0.48 0.35 0.62 0.56 0.55 0.58 0.55 0.52 0.60 0.60 0.50 0.48 0.36 0.68 0.52 0.50 0.54 0.58 0.52 0.54 0.54 0.54 0.54 0.55 0.67 0.37 0.65 0.55 0.54 0.55 0.57 0.65 0.55 0.43 0.50 - Ai for 0 in OR of R'COOR = 0.0.J .G. DAWBER 2299 The values of aO, for the single liquids are given in table 1. The molar magnetic rotations, A,, defined as A, = aO,M/d were calculated, where d is density (kg mP3) and M is molecular weight, and these are also given in table 1 as Am(obs.).The non-ideality of the liquid mixtures was expressed in terms of the excess magnetic rotation, a E , which is defined as (2) aE = a,-(X,aO,,+X,aO,,) (3) where X , and X , are the mole fractions of components 1 and 2 in the mixture, and a;, and a;, are the magnetic rotations of the pure components. The values of aE for 6 4 2 - 0 F E d I Do - 2 a il . - 4 - 6 -8 -1 0 -12 -14 mole fraction of CC14 FIG. 1 .-Excess magnetic rotations of binary mixtures of CCl, with aliphatic ketones. (a) Propan-2-one, (b) butan-2-one, ( c ) heptan-2-one, ( d ) 4-methylpentan-2-one, (e) 2,6-dimethylheptan-4-one, (f) nonan- 5-one.2300 MAGNETO-OPTICAL ROTATION STUDIES OF LIQUID MIXTURES the various binary mixtures were plotted as a function of XCcl4 and the maximum values of aE and the corresponding values of XCcl4 are given in table 1.A typical set of graphs for a selection of ketones in binary mixtures with CC1, are shown in There are several possible reasons for the changes in aE as the liquid composition is changed. These include the association or depolymerisation (i.e. breakdown of structure) of the components, or specific molecular interactions between the two components in the mixture. From previous work1. 2 y it was found that the aE results can best be interpreted if CCl, is regarded as an unassociated liquid, and that depolymerisation of the other component by the CCl, is accompanied by negative aE values. On the other hand, specific interaction between the CCl, and the other component will be accompanied by positive aE values.fig. 1. DISCUSSION ADDITIVITY OF THE MOLAR MAGNETIC ROTATION, Am In a previous paper6 a set of partial magnetic rotation parameters, Ai, were deduced empirically from measurements made on 72 compounds. Using these partial parameters, values of Am were calculated for the compounds used in this work, and these are presented as in table 1. An additional partial parameter was used in the calculation, namely, Ai for the oxygen atom in the acyl group of esters was given a value of 0.0 rather than a value of 4.0 which was used for alcohols.6 The values of Am(,bs.) and Am(calc.) are compared in table 1. For the 35 compounds studied in this work the majority of the A,(obs.) and Am(c?lc.) agree quite well, thus confirming the additive property of the molar magnetic rotation.The poorest agreement was for acetophenone, propiophenone,p-methyl acetophenone, glyceryl tributyrate, ethyl acetoacetate and pentane-2,4-dione (acetyl acetone). In the case of the phenone group of compounds the possible conjugation of the carbonyl group with the phenyl ring may account for the discrepancy between the calculated and observed Am values. Ethyl acetoacetate and pentane-2,4-dione exist partially in the enol form and this would certainly influence the value of Am(,bs.). The large molar magnetic rotation. A,/deg m2 mol T-' kg-' FIG. 2.-Relationship between [R] and A, for aliphatic compounds. 0, this work; x , ref. ( 6 ) .J. G .DAWBER 230 1 discrepancy for glyceryl tributyrate may be due to the large inter- and intra-molecular interaction in the liquid state. Molar refraction, [R], defined as (n2 - 1) M/(n2 + 2) d, has additive properties and values of [R] were calculated from the refractive indices, n; at the sodium D-line.' The values of [R] for the aliphatic compounds of this work are plotted against Am(obs.) in fig. 2. Also plotted for comparison are the values for the aliphatic compounds from the previous study.6 The correlation between Am(obs.) and [R] for both sets of data is reasonable. (N.B. the [R] scales in fig. 2 and 3 of ref. (6) are incorrect by a factor of 2, i.e. the [R] scale should read 0 to 60 cm3 and not 0 to 30 cm3 as shown.) MIXTURES OF CCl,+KETONES The interaction between CCl, and aliphatic ketones in a binary mixture, as judged by the aE values, seems to be markedly influenced by the substituents around the carbonyl group (table 1 and fig.1). The largest effect amongst the aliphatic compounds is with acetaldehyde but this interaction may involve hydrogen bonding with a chlorine atom in CCl, in addition to interaction of the carbonyl group in charge transfer from the n-electrons to a vacant d-orbital of a second chlorine atom. The interaction with CC1, decreases going from propan-2-one (acetone) to butan-2-one, probably owing to the slight loss of accessibility of the carbonyl group. For the remainder of the aliphatic ketones the values of aE are negative. These negative values are indicative of structure breaking of the liquid structure of the ketone by the CC1,.Thermodynamic studies of linear- and branched-chain alkanes indicate that there is orientational order among the long chains of a n-alkane and that this can be disturbed by addition of a more spherical mo1ecule.8-11 These observations were confirmed by our magneto-optical studies.2 It seems from the present work that a similar effect is observed for ketones and that the longer-chain members have some orientational order in the liquid state which is broken up by the addition of the CCl,, and that this masks any interaction which may occur between the carbonyl group and the CCl, molecule. For all of the mixtures of aromatic ketones with CCl,, aE was strongly positive indicating interaction of the ketone with the CCl,. There is a variety of evidence which suggests that aromatic hydrocarbons form charge-transfer complexes with CCl,.12-22 From previous experience with aromatic hydrocarbons and aminesly 2 v we conclude that these effects are also observed in magneto-optical studies and that the interaction of aromatic compounds with CCI, is via a charge-transfer complex involving the aromatic n-electrons acting as the donor.The results of this work (the aE values in table 1) also suggest that this is the principal interaction of the aromatic ketones with CCl, rather than involving the carbonyl group. The aE values suggest that the extent of charge-transfer interaction is approximately related to the n-electron availability in the aromatic ring. MIXTURES OF CCl,+ESTERS The values of aE for mixtures of esters with CCl, (table 1) follow a similar pattern to those for the ketones. For the aliphatic esters positive values of aE for the lower members of the series indicate that the interaction with the CCl, falls off as the molecular size is increased.The interaction could be via the carbonyl group or the oxygen atom of the acyl group, but comparison with the ketones indicates that the interaction is likely to involve the carbonyl group. The longer-chain aliphatic members, like the ketones, have negative values of aE indicating an orientational order of the molecules in the liquid state which is broken up by the CCl,. The effect increases with chain length and is greatest for glyceryl tributyrate.2302 MAGNETO-OPTICAL ROTATION STUDIES OF LIQUID MIXTURES The aE values for the aromatic esters are all positive and indicate interactions of similar magnitude to other aromatic compounds, with aE being roughly correlated with the n-electron availability.In the case of benzyl benzoate the interaction is considerable. Again the interaction is likely to involve the n-electrons of the aromatic system as the donor and a vacant d-orbital ofa C1 atom in CCl, in a weak charge-transfer complex. The magneto-optical technique is not one of direct observation of complex formation. Although the method assumes that the departure from an ideal mixture law can be interpreted in terms of a chemical effect, it is possible to correlate the aE values in terms of structure breaking in the liquid mixture or in terms of the formation of weak complexes.In some cases both effects could be present (e.g. the aliphatic ketones and esters) but the magneto-optical method will in general only detect the effect which is predominant. The author acknowledges with thanks the financial assistance of the S.R.C. towards the cost of the polarimeter. J. G. Dawber, J . Chem. SOC., Faraday Trans. I , 1978, 74, 1702 and 1710. J. G. Dawber, J . Chem. Soc., Faraday Trans. I , 1979, 75, 370. J. G. Dawber, J . Chem. SOC., Faraday Trans. 2, 1974, 70, 597. J. G . Dawber, J . Chem. Sac., Faraday Trans. I , 1978, 74, 960. J. G. Dawber, J . Chem. Soc., Faraday Trans. 1, 1982, 78, 1127. J. G. Dawber, J . Chem. SOC., Faraday Trans. 2, 1980, 76, 1324. Handbook of Chemistry and Physics (The Chemical Rubber Co., Cleveland, Ohio, 60th edn, 1980). S. Turrell and G. Delmas, J . Chem. SOC., Faraday Trans. 1, 1974, 70, 572. V. Te Lam, P. Picker, D. Patterson and P. Tancrede, J. Chem. Soc., Faraday Trans. 2, 1974,70, 1465 and 1479. lo G. Delmas and Ng. T. Thank, J . Chem. SOC., Faraday Trans. I , 1975, 71, 1172. l 1 G. Delmas and P. Purves, J . Chem. SOC., Faraday Trans. 2, 1977, 73, 1828 and 1838. It G. H. Cheeseman and A. M. B. Whitaker, Proc. R . Soc. London, Ser. A, 1952, 212, 406. l3 L. A. K. Staveley, W. J. Tupman and K. B. Hert, Trans. Faraday SOC., 1955, 51, 328. l 4 M. L. McGlashan, Annu. Rev. Phys. Chem., 1962, 13, 409. l5 G. R. Coates, R. J. Sullivan and J. B. Ott, J . Phys. Chem., 1959, 63, 589. l6 R. Anderson and J. M. Prausnitz, J. Chem. Phys., 1963, 39, 1225. J. B. Ott, J. R. Coates and A. H. Budge, J. Phys. Chem., 1963, 67, 1225. R. P. Rastogi and R. K. Nigam, Trans. Faraday Soc., 1959, 55, 2005. l 9 J. B. Ott, J. R. Coates and A. H. Budge, J. Phys. Chem., 1962, 66, 1387. R. P. Rastogi, J. Nath and R. R. Misra, J. Chem. Thermodyn., 1971, 3, 307. 21 A. Ahmed, J . Chem. Soc., Faraday Trans. I , 1973, 59, 540. 22 M. L. McGlashan, D. Stubley and H. Watts, J . Chem. Soc. A , 1969, 673. (PAPER 1 / 1797)