324 SPENCE AND VA%HRMA4K : QUASI-QUANTITATIVE [AwaZyyst, VOl. 91 Quasi-quantitative Separation of Paraffins and Olefins BY J. A, SPENCE AND M. VAHRMAN (Northampton College of Advanced Technology, St. John Street, London, E.C. 1) By the addition of iodine monochloride to a mixture of paraffins and olefins, an easy chromatographic separation on silica gel of the two is made possible by virtue of the olefin adduct being much more strongly adsorbed. The olefins are regenerated by refluxing the halogenated derivative with ethanol and excess sodium iodide. The efficacy of the method has been proved on the total aliphatics of low temperature tars and on pairs of pure n-paraffins and 1-olefins of the same carbon number. The small losses incurred are almost entirely in the olefins. THE problem of the quantitative separation of paraffins from olefins, and retention of the identity of the latter, arises in the examination of their mixtures in fractions from petroleum and coal tars.In the latter, saturated and unsaturated aliphatic hydrocarbons exist in quantity in low temperature tars and in those of a type intermediate between low and high temperature tars.l Adsorption chromatography is well established as a method of determining hydrocarbon types, especially in lower boiling mixtures, e.g., the fluorescent-indicator adsorption method.2 Liquid chromatography has been used for the separation of paraffins and olefins, from C, or C,, up to C,,, from the lower boiling neutral portion of low temperature That the total neutral components in such tars could also be separated by this method was shown by Boyer et u Z ., ~ if three fractional distillation cuts were separately chromatographed. In the higher molecular weight hydrocarbons, where the lone double bond of the olefins was considerably “diluted” in the long chains, not more than 5 per cent. of paraffins contaminated the separated olefin fractions. Hydrocarbons up to about C,, were then determined by gas chromatography. The original aim of the work reported here was the quantitative separation of paraffins and olefins from the total aliphatic hydrocarbons of low temperature tars, without prior frac- tionation of these hydrocarbons. The method devised, however, is applicable to such mixtures of hydrocarbons from a wide variety of sources. For example, we have applied it successfully to the analysis of hydrocarbons from coal extracts and to waxes from plants and soils.EXPERIMENTAL The total aliphatic hydrocarbons were first prepared by liquid chromatography on silica gel (column length, 20 cm; diameter, 2 cm; weight of charge, 2 g) of the neutral, light petroleum-soluble oil of a low temperature tar1 from the carbonisation of Thoresby coal (Sational Coal Board classification KO. 801) by internal heating of the charge with hot gas. The soft wax thus obtained contained n-, iso- and cyclo-paraffins and a corresponding series of olefins, the range being from C,, to &. In all subsequent chromatographic separations, the same ratios of column length to diameter were used, the actual dimensions being appro- priate to the weight of charge.The bulk of the solvent was removed each time by atmospheric distillation on a steam-bath, the small amount remaining being eliminated by vacuum desiccation (5 mm of mercury) to constant weight of the cooled flask. The basis of the method of separation of the paraffins from the olefins was the selective addition of iodine monochloride to the latter, the subsequent easy separation of the paraffins from these addition compounds by liquid chromatography, and the regeneration of the olefins. A 70 to 90 per cent. molar excess of Wijs’ reagent (0.2 N iodine monochloride in glacial acetic acid) was added to a 2 per cent. solution in carbon tetrachloride of the whole aliphatic hydrocarbon fraction in a stoppered, brown glass bottle, and the whole allowed to stand for 30 minutes.The scheme of analysis is shown in Fig. 1.May, 1!166] SEPARATIOX OF PA%RA%FFINS AND OLEFINS TOTAL ALIPHATIC HYDROCARBONS lodrrie monochloride i Unreacted paraffins Halogenated olefin derivatives + Liquid chrornotography on silica gel 1 + TOTAL PARAFFINS Vtc todo-chloro olefin derivatives Sodium iodide in boiling ethonol 1 Crude regenet-ated olefins 325 I TOTAL OLEFINS Fig. 1 . Scheme for the separation of olefins and paraffins At the end of the reaction period, excess of 15 per cent. potassium iodide solution was added to convert the unconsumed iodine monochloride reagent to iodine and potassium chloride; a large volume of distilled water was also added. The liberated iodine was finally titrated with sodium thiosulphate solution.The carbon tetrachloride layer was separated from the aqueous acid, which was then further extracted with carbon tetrachloride to ensure complete removal of the sample. The combined carbon tetrachloride solutions were washed with distilled water until free of acid, dried over anhydrous sodium sulphate, and the solvent distilled off. The residual brown wax, a mixture of paraffins and halogenated olefins, was dissolved in sufficient light petroleum (40" to 60" C) to make a 10 per cent. solution; this was then poured on to an activated silica gel (100 to 200 mesh) chromatographic column. Elution was continued with light petroleum until the faint purple-brown colour, the front of the halogenated olefin derivatives, approached the bottom of the column. The colourless first eluate contained the total paraffins, which were recovered by evaporation of the solvent.The coloured, halogenated olefins were completely eluted with ethanol and the original olefins regenerated by boiling the solution gently under reflux with excess sodium iodide. Most of the ethanol was removed by evaporation under reduced pressure, and the regeneration mixture partitioned between light petroleum (40" to 60" C ) and dilute aqueous sodium thiosulphate solution: the latter removed the iodine which had been liberated, while the regenerated olefins passed into the light petroleum phase. After washing the light petroleum solution with distilled water and drying over anhydrous sodium sulphate, the solvent was evaporated off if a determination of the crude olefins was required.To obtain the pure product, a 10 per cent. solution of the crude olefins in light petroleum (40" to 60" C) was chromatographcd on silica gel with the same solvent as eluant. The olefins were recovered by distilling off the light petroleum from the total eluate. For comparison, paraffin contents were also determined by sulphuric acid extraction. A 20 per cent. w/v solution of the sample in cyclohexane was extracted repeatedly at room temperature with equal volumes of 98 per cent. sulphuric acid until no further colouration was imparted to the acid layer (about 10 extractions). The acid extracts were combined, washed twice with cyclohexane, and then discarded. The combined cyclohexane solution and washings were evaporated to give an approximately 10 per cent.solution of paraffins and then chromatographed on silica gel with cyclohexane as eluant. The pure paraffins were then recovered from the total eluate by evaporation of the solvent. Infrared absorption spectroscopy was used throughout as a guide to the completeness of separation of the olefins from the paraffins.326 SPENCE AND VAHRMAK QUASI-QUANTITATIVE [Analyst, VOl. 91 The results of a separation by the iodine monochloride method of 10 g of the aliphatic hydrocarbon fraction from the tar are given in Table I. TABLE I RESULTS FOR THE SEPARATION INTO ITS PARAFFINIC AND OLEFINIC COMPONENTS OF THE ALIPHATIC HYDROCARBON FRACTION FROM A LOW TEMPERATURE TAR Percentage by weight Paraffins . . .. .. . . .. . . .. 49-1 Purified olefins .. .. . . . . .. . . 43-9 Losses . . . . . . . . .. . . . . .. 7.0 Paraffins (by removal of olefins with sulphuric acid) 51.1 . . G. Clubb and M. Vahrman, in this laboratory, working on a different aliphatic fraction from a low temperature tar, investigated the effect on the separation by this method of using different amounts of iodine monochloride, and ascertained the reproducibility of the results with the optimum excess of reagent (Table 11). TABLE I1 RESULTS OF SEPARATIONS OF ALIPHATIC HYDROCARBONS FROM TAR BY IODINE MONOCHLORIDE METHOD Molar excess Weight of Weight of Weight of monochloride, material, recovered, recovered, per cent. per cent. of iodine starting paraffin olefin Paraffin, Olefin, per cent. g 6 10* 2.4916 1.8070 0.4760 72.4 19.1 30* 2.5085 1.6872 0.5637 67.2 22-4 50 2.5110 1.5138 0.6088 60.4 24.2 67 2-4751 1.5732 0.6366 63.6 25.8 80 2.4936 1.5757 0.7069 63-2 28.4 80 2.4694 1.5536 0,6232 63.2 25.2 80 2.4957 1.5632 0.6845 62.8 27.4 80 2.5299 1.5983 0.6942 63.1 27.4 80 2.4863 1.5572 0.6489 62.5 26.0 80 2.5138 1.5802 0.661 1 62.9 26.3 80 2.4588 1.5480 0.6552 63-0 26.7 so 2-4688 1.5602 0.6509 63.2 26.4 THE Recovery, per cent. 91.5 89-6 84.6 89.4 91.6 88.4 90.2 90.5 88.5 89.2 89.7 89.6 * The infrared spectra of the recovered unreactcd materials showed the presence of olefinic unsaturation.Paraffin content (by extraction with 98 per cent. sulphuric acid): 63.0 per cent. w/w. The iodine monochloride addition method, with 80 per cent. excess of reagent, was tested on binary mixtures of n-paraffins and 1-olefins of the same carbon number (Table 111).TABLE I11 RESULTS OF SEPARATIONS BY THE IODINE MONOCHLORIDE METHOD OF BINARY MIXTURES O F PURE PAKAFFINS AND OLEFINS Percentage by Percentage by 20 weight of paraffin or Hydrocarbons mixture nD olefin recovered nL, 'LO weight in synthetic n-Tetradecane . . . . 52.3 1.4272 61.9 1.4269 1.4341 Tetradec-1-enc . . . . 47.7 1.4342 45.3 n-Eicosane . . . . 72.1 1.4306 72.0 1.4308 Eicos-1-ene . . .. 27.9 1-4363 25.8 1.4362 DISCUSSION A minimum of 50 per cent. excess of iodine monochloride was necessary to effect complete separations of olefins from paraffins: 80 per cent. excess is considered to give a safe margin. The recovery of paraffins is virtually complete; the losses, mainly in the olefinic fraction, are probably due to irreversible substitution reactions with the halogen reagent, together with the retention of olefins on the column during purification.Losses diminish with increase in weight of original sample. No further yields of olefins could be obtained with ethanol and sodium iodide from the material left on the chromatographic column after removal of the pure olefins.May, 19661 SEPARATION OF PARAFFINS AND OLEFINS 327 As both the addition and elimination of halogens in. ethylenic compounds are specifically trans, and result in the regeneration of the original isomers, the method can be used if the structures of the olefins are to be investigated. That no isomerisation of the olefins occurred by the method described was confirmed from the infrared absorption spectra of the original aliphatic material and of the separated, regenerated olefins. The authors are grateful to Rexco Research and Development Company Ltd., for a grant to one of them (J.A.S.), and for samples of their tar. REFERENCES 1. 2. 3. Coppens, L., Bricteaux, J., and Ncuray, M., Annls Mines Belg., 1961, 121, 1156. 4, Lewis, H. R., Chem. & Ind., 1959, 1049. 5. Boyer, A. F., Ferrand, R., Ladam, X., and Payen, P., Chim. Ind., 1961, 86, 523. Blunt, G, V., and Vahrman, M., J . Inst. Fuel, 1960, 33, 522. A.S.T.M. Designation D 1319-61T, A .S.T.M. Special Technical Publication, No. 332, 1963. Received April 6th, 1965