July, 1956
EXTRACTIOK OF FERRIC CHLORIDE BY ISOPROPYL ETHER
Some interesting observations may be made on the effect of adding a second hydrophilic group to a long hydrophobic chain. The solubility of disodium a-sulfostearate and the c.m.c. of disodium 2sulfoethyl a-sulfostearate are not what one might expect from half the number of carbon atoms attached t o one hydrophilic group but rather theii ion solubilities are about midway between those reported'3 for sodium dodecyl sulfate and sodium tetradecyl sulfate. Likewise, disodium a-sulfopalmitate and disodium 2-sulfoethyl a-sulfopalmitate have a little higher ion solubility than sodium dodecyl sulfate. Disodium 2-sulfoethyl a-sulfostearate has been found to have good detergency and shows a response to building4 similar to that of surfactants with twelve and fourteen carbon atoms. The c.m.c. values given here are only slightly lower than those reported by Shinoda14 for corresponding alkyl malonates: Cl2H2&H(COOK)2, 1.7%; CMHW CH(COOK)2,0.7'%; CiaH&H(COOK)2,0.2-0.49;',. (13) J. Powney and C. C. Addison, Trans. Faraday SOC.,38, 1243 (1937). 69, 432 (1955). (14) K.Shinoda, THISJOURNAL,
90 1
Conclusions The conductance method is preferred for measurement of critical micelle concentrations of asulfonated acids and esters when the value obtained is above 0.05% (0.001 M ) . The surface tension and dye titration methods were used for those having lower c.m.c. values. a-Sulfonated acids and their alkyl esters have c.m.c. values in the same region as other surfactants of equal carbon chain length. Disodium 2sulfoethyl a-sulfostearate has a c.m.c. between that of sodium dodecyl sulfate and sodium tetradecyl sulfate. Simple monosodium and disodium salts of a-sulfonated acids do not form micelles a t room temperature but have solubilities which are very close to the c.m.c. values of other materials having the same length of alkyl chain and the same number of hydrophilic groups. Acknowledgment.-The authors wish t o express their appreciation to Serge N. Timasheff for his helpful suggestions in carrying out this work and to Raymond G. Bistline, Jr., for making some of the surface tension measurements.
THE EXTRACTION OF FERRIC CHLORIDE BY ISOPROPYL ETHER. PART I. THE SIGNIFICANCE OF WATER I N THE EXTRACTED IROX COMPLEX BY A. H. LAURENE,D. E. CAMPBELL, S. E. WIBERLEYAND H. M. CLARK Department of Chemistry, Walker Laboratory, Rensselaer Polytechnic Institute, Troy, New York Received December 9 , 1966
The crystalline anhydrous dietherate of tetrachloroferric acid has been prepared and its behavior with water has been studied. The hydrated acid was shown by spectro-chemical means to be identical with the complex which is extracted.by isopropyl ether from hydrochloric acid containing ferric chloride. It has been found that wat8eris essential for the extraction of the ferric chloride complex and that water is the controlling factor in the formation of a third phase in the extraction system.
Introduction Several in~estigatorsl-~ have displayed interest in the possible significance of the water found in the ether layer when ferric chloride is extracted from hydrochloric acid solution by ether. It is generally believed that most of this water is associated with the extracted material. 1*2,6-7 By means of analyses for hydrogen, iron, chloride and water in the ether layer, previous workers's2 have assigned the empirical formula HFeC14.4-5H20 to the material which extracts. Hydrogen chloride and water are normally distributed between isopropyl ether and hydrochloric acid.3~~It may be expected that these compounds will also exist in the ether layer of the ferric chloride extraction system apart from that associated with the extracted material. The amounts of free hy(1) S. Kato and R. Ishii, Sei. Papers Inat. Phys. Chem. Research, Tokyo, $6, 82 (1939). (2) J. Axelrod and E. H. Swift, J . Am. Chen. Soc., 62, 33 (1940). (3) N. H.Nachtrieb and J. G. Conway. ibkd.. 70, 3547 (1948). (4) N. H. Nachtrieb and R. E. Fryxell, ibid., '70, 3552 (1946). (5) R. J. Myera and D. E. Metzler, ibid., 72, 3772 (1950). (6) R. J. Myera, D. E. Meteler and E. H. Swift, ibid., 72, 3767
(1950). (7) H. L. Friedman, ibid., IC, 5 (1952).
drogen chloride and water in the ether layer depend on the concentration of hydrochloric acid in the aqueous layer and on the effect of ferric chloride on their distribution. Because the latter effect has not been determined, it is difficult to establish the exact amount of water which is associated with the extracted iron complex from analyses alone. The problem has been approached, therefore, by studying the action of water on anhydrous HFeC14and ether. Experimental Materials.-The isopropyl ether, ferric chloride and hydrogen chloride used in the preparation of tetrachloroferric acid, HFeCL, were anhydrous. All operations were carried out in a dry box which was charged with phosphoric anhydride. The drying agent was stirred frequently to expose a fresh surface and waa replaced as soon as its efficiency appeared doubtful. The isopropyl ether was purified by treatment with acidified, saturated ferrous sulfate solution followed by sodium hydroxide solution. It was rinsed with distilled water, dried with silica gel and distilled twice over calcium hydride. The fraction of the purified ether which boiled between 67.4 and 67.9" (uncor.) was collected for use. Commercial C.P. anhydrous ferric chloride was found to be entirely satisfactory for this preparation. The hydrogen chloride was taken from a cylinder of the anhydrous gas.
902
A. H. LAURENE,D. E. CAMPBELL, S. E. WIBERLEY AND H. M. CLARK
Analyses.-Iron was determined on the aqueous extracts of the samples after the ether had been removed by evaporation. The aqueous solutions were made two molar in hydrochloric acid, passed through a silver reductor and titrated with standard ceric sulfate to the ferrous-o-phenanthroline end-point. Chlorine was determined by the Volhard method (the silver chloride precipitate being filtered off). -4nalysis for hydrogen was carried out on aqueous extracts of the samples without removal of the ether. The aqueous solution was titrated with standard sodium hydroxide solution to the phenolphthalein end-point. The hydrogen was computed by subtracting the volume of reagent required for the known quantity of iron present from the total volume of reagent used. The isopropyl ether content of solid etherate samples was determined by difference after the amounts of all other constituents had been determined. Spectra.-A Beckman model D.U. quartz spectrophotometer, equipped with a Beckman hydrogen discharge lamp and a constant voltage power pack, was used to obtain ultraviolet absorption spectra. A Model B Beckman spectrophotometer was employed for obtaining spectra in the visible region. Matched glass-sto pered cells with quartz windows and ten millimeter inside tkckness served to contain the samples for both of these instruments. Infrared absorption spectra were run on a Model 12B Perkin-Elmer Infrared Spectrometer using a rock salt prism and cells with fixed and demountable rock salt windows. The spectroscopic nomenclature recommended by Hughes* was used in reporting data. The Preparation of Anhydrous Tetrachloroferric Acid Dietherate.-Isopropyl ether was dried by allowing it to react for two days with extruded sodium. It was then filtered into a large bottle and a few grams of calcium hydride added. The bottle was fitted with a syphon so that ether could be removed by increasing the air pressure within the apparatus. A h e sintered glass filter was sealed to the lower end of the siphon to prevent small particles of calcium hydride from being withdrawn along with ether. This dispensing apparatus was kept in the dry box throughout its use.
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was noted a t this stage. When it was ap arent that all thc ferric chloride had been precipitated bye!t reaction taking place, continued passage of gas through the solution caused a sharp rise in temperature. The Aow of hydrogen chloride was stop ed at this point, the hose connections clamped off, and the $ask with its gas bubbler removed to the dry box. The solid material was separated, first by decanting the bulk of the ether, and finally by suction filtering. While on the sintered glass filter, the solid was washed several times with dry ether from the dispensing bottle. After a brief drying by suction, the crystalline material was collected and samples were taken for analysis. The solid is light yellow-green in color, crystalline, voluminous in bulk and adheres to glass and metal even after thorough drying between pieces of filter paper. It is extremely hygroscopic and forms a dark green sirupy liquid immediately upon exposure to atmospheric moisture. It is only very slightly soluble in isopropyl ether (0.0025 mole per liter, obtained by iron and chloride analysis). The composition of the crystalline solid was found to be 14.25% iron, 36.09% chlorine, 0.255% hydrogen and 49.4% isopropyl ether. The atomic ratios of the constituents are 1.OO Fe: 3.98 C1; 1.00 H:1.89 i-PrzO giving the empirical formula HFeC14.2isopropyl ether. The Action of Water on Anhydrous HFeCt.24-Pr204.-As stated previously, anhydrous tetrachloroferTic acid is extremely hygroscopic. When hydrated, the ac:d becomes soluble in isopropyl ether. In order to determine quantitatively the amount of water necessary to make the anhydrous material soluble in ether, the compound, in the presence of isopropyl ether, was titrated with water. Arbitrary amounts of the anhydrous acid were placed in 100-ml. volumetric Aasks. About 75 ml. of dry isopropyl ether was added to each fiask which was then stoppered and removed from the dry box. Each mixture was titrated with water from a micro-buret. During the titration two ether phases formed and the denser phase, containing most of the iron, was observed to grow at the expense of the light phase. In the systems which contained small amounts of tetrachloroferric acid the dense ether layer reached a maximum
TABLE I THEDEGREEOF HYDRATION OF ETHER-SOLUBLE TETRACHLOROFERRIC ACID No.
Type of soh.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Light ether phase Heavy ether phase Heavy ether phase Heavy ether phase Heavy ether phase
Fe
0.0130 .1544 ,0980 .0483 ,0439 ,0211 ,0202 .0111 ,00854 ,00569 ,00261 ,2381 ,2463 .2829 ,3116
One liter of the dry isopropyl ether was saturated with anhydrous ferric chloride and the solution filtered into a oneliter Aask provided with a male 24/40 ground joint. Samples of this solution were taken for iron analysis. The ether solution was found to be 0.367 molar in ferric chloride. The flask containing the anhydrous solution of isopropyl ether and ferric chloride was fitted with a bubbling device which consisted of a female 24/40 joint with a side arm and a ring-sealed tube. A coarse, sintered lass, gas bubbler was sealed to the bottom of the tube. h i s apparatus was removed from the dry box and connected via a Dry Ice-acetone cold trap to a cylinder of hydrogen chloride gas. Care was taken to prevent the introduction of atmospheric moisture. Hydrogen chloride gas was passed sIowly through the Fystem and a solid began to separate from the solution immediately. No increase i s the temperature of the solution (8) H. K. Hughes, Anal. Chem., 24, 1349 (1952).
Molar conan. of c1
0.0529 0.609
... ... ... ... ... ... ...
... ... 0.957 0.973 1.126 1.239
Ratios of constituents
HzO
0.0655 .749 ,493 ,252 ,221 ,103 ,105 ,0595 .0481 .0262 ,0135 1,067 1.106 1.265 1.363
Fe C1
HzO
1:4.06:5.04 1:3.94:4.85 1: . . . :5.03 1: . . . :5.22 1: . . . :5.02 1 : . , , :4.88 1 : , . , :5.19 1: . . . :5.37 1: . . . :5.63 1: . . . : 4 . 6 1 1: . . . :5.18 1 :4.02:4.48 1:3.96:4.49 1 :3 . 9 9 :4.47 1:3.98:4.37
volume which then began to decrease as the titration proceeded and suddenly disappeared. The disappearance of the two layers which produced a clear homogeneous solution, was considered the “end-point’’ of the titration. The SYStems containing large quantities of the acid exhibited a continuous expansion of the dense phase a t the expense of the light ether layer above it. The “end-point’’ in these cases was the disappearance of opalescence in the solution which indicated that no more light ether layer existed. It was noted that just a t the end-point each solution foamed very readily. Following the preliminary titrations with water, each flask was returned to the dry box and filled to the mark with dry ether. The solutions which contained large amounts of the tetrachloroferric acid again formed two liquid phases. These were titrated to homogeneous solutions by a few drops of water.
July, 1956
EXTRACTION OF FERRIC CHLORIDE BY ISOPROPYL ETHER
After the titrations with water were complete, each solution was analyzed for iron and chloride. The results of the analyses, and the water titrations are summarized in Table I. The light ether layers .appeared to be entirely miscible with isopropyl ether while the heavy ether solutions were immiscible. As wss shown by this experiment, the immiscible layers could be made to dissolve isopropyl ether by adding small amounts of water. The average value (taken over all the solutions considered to be light ether phases) of the number of molecules of water necessary to make the anhydrous tetrachloroferric acid completely soluble in isopropyl ether is 5.09 with an average deviation of a single observation of f0.21. For the heavy ether solutions this ratio of water to iron appears W fall off with increasing iron concentration. Comparison of Spectra.-The solution indicated no. 1 in Table I was diluted with isopropyl ether to 1.3 X lo-* and its ultraviolet spectrum measured. The spectrum was found to be identical with that observed for an ether layer obtained by extracting iron from an aqueous solution of ferric chloride and hydrochloric acid with isopropyl ether. A markedly different ultraviolet spectrum was observed for an anhydrous solution of ferric chloride in isopropyl ether. Both the spectrum for the ether extract and that for the anhydrous solution were in agreement with those reported by bletaler and Me~e1.s.~ The visible spectrum of the solution indicated no. 14 in Table I was found to be identical with that of an ether layer from a ferric chloride-isopropyl ether extraction system and unlike that of anhydrous ether solution of ferric chloride. The latter two spectra were in agreement with those reported by Nachtrieh and Conway.8 Two bands appear a t 757 and 827 cm.-l in the infrared spectrum of the saturated anhydrous solution of ferric chloride and ieopropyl ether. These bands are not present in the isopropyl ether spectrum. A thin section (0.001 mm.) of the ether layer obtained by extracting with isopropyl ether from 7.0 M hydrochloric acid saturated with ferric chloride was run in the infrared. The 1015 cm.-' band of the isopropyl ether spectrum was shifted to 1000 cm.-l. The same shift was noted in the infrared spectrum of hydrated tetrachloroferric acid in isopropyl ether. A thin section (0.001 mm.) of this solution. which was 2.8 M in HFe-
'
The ultraviolet spectrum of an anhydrous solution of isopropyl ether, ferric chloride and hydrogen chloride was obtained. This solution was 1.38 X low4M in ferric chloride and 1.4 x 1 0 - 3 M in hydrogen chloride. The spectrum was identical with that of the hydrated tetrachloroferric acid in isopropyl ether.
Discussion The absorption spectrum of hydrated tetrachloroferric acid, from the ultraviolet through the infrared regions, is diffeient from the spectrum of anhydrous ferric chloride in isopropyl ether. It is identical with the spectrum of the ether layer from the ferric chloride-isopropyl ether extraction system. This is considered evidence that the complex in the ether layer of the ferric chloride extraction system is hydrated tetrachloroferric acid. The significance of associated water in the extracted complex is quite apparent from the fact that the anhydrous tetrachloroferric acid is insoluble in isopropyl ether. Moreover, when the mole ratio of water to iron in a solution of isopropyl ether and tetrachloroferric acid is less than five the solution is immiscible with dry ether. The complex becomes completely soluble in ether wheii sufficient water is present to form the pentahydrated acid. The manner in which water is associated with the complex acid in ethereal solution has not been determined. Results from studies of the electrolysis (9) D. E. Metsler and R. J. Meyers, J . Ani. Chem. Soc., 7 3 , 3776 (1950).
903
of ether extracts'O indicate that all of the water is combined with the hydrogen of the acid. Additional evidence for this is given by the work oi Friedman' who has shown that the absorbing species in tetrachloroferrate compounds is the anion and that the anhydrous compounds give spectra identical with the hydrated tetrachloroferric acid. Furthermore, the ultraviolet spectrum of the anhydrous isopropyl ether-tetrachloroferric acid solution in this study is the same as that of thc hydrated acid in ethereal solution. Ordinarily, when an absorbing complex becomes hydrated by coordinated water its spectrum is altered quite noticeably,"~12 The above evidence indicates that the material which is extracted by isopropyl ether from hydrochloric acid containing ferric chloride is (Ha0 +. 4HzO)FeC14-. A possible explanation for the occurrence of two ether phases in the ferric chloride extraction systeml3,l4is found in these studies. The two ether phases of this system are analogous to a heterogeneous HFeC14-ether system which has insufficient water to bring about a homogeneous ethereal solution. The two ether-phase extraction system occurs when the over-all concentration of hydrochloric acid is very high (above eight molar initial concentration). Stokes and R o b i n ~ o n 'indicate ~ that very little "free water'' exists in hydrochloric acid at a concentration of seven molar. Almost all the water present serves to hydrate the ions and very little, if any, acts as solvent. When the concentration exceeds seven molar a deficiency of water may be considered to exist. Thus, concentrated hvdrochlostance possessing looselyibound water. That some of the water associated with the extracted complex is loosely-bound is illustrated by the effect of sodium chloride on an ether extract. When the salt is added to the ether phase (separated from the aqueous phase) a layer of brine and two ether layers are formed. l6 Dehydrating agents stronger than sodium chloride will of course give the same effect. Under no circumstances have two ether phases been observed in the isopropyl ether-HC1-H20 ternary systems.17 A study of this system has, however, disclosed that when the initial hydrochloric acid concentration is increased the concentration of water in the ether layer decreases. When the over-all concentration of hydrochloric acid in the ferric chloride extraction system exceeds eight molar the aqueous layer may exert a dehydrating influence upon material in the ether layer. Part of the extracted tetrachloroferric acid may be deprived (10) J. E. Savolainen, unpublished results from this Laboratory. (11) W. R. Brode, THIS JOURNAL,SO, 56 (1926). (12) W. R. Brode, "Chemical Spectroscopy," John Wiley and Sons, Inc., New York, N. Y., 1943, p. 205, 240, 267. (13) R. W. Dodson, G . J. Forney and E. H. Swift, J . Am. Chem. Soc., 58, 2573 (1936). (14) N. H. Naohtrieb and R. E. Fryxell, ibid., 74, 897 (1952). (15) R. H. Stokes and R. A. Robinson, ibid., 70, 1870 (1948). (10) Unpublished results from this Laboratory. (17) D. E. Campbell, A. H. Laurene and H. M. Clark, J . A m . Chem. Soc., 76, 6193 (1952).
A. G. WHITTAKER, HARRYWILLIAMS AND P. M. RUST
904
of some associated water with the consequent formation of a heavy ether phase which has a water to iron mole ratio of less thanjive.
Vol. 60
Acknowledgment.-This work mas partially supported by the Atomic Energy Commission under Contract No. AT(30-1)-562.
BURNING RATE STUDIES. 4. EFFECT OF EXPERIMENTAL CONDITIONS ON THE COXSUMPTION RATE OF THE LIQUID SYSTEM 2-NITROPROPANE-NITRIC ACID BY A. GREENVILLE WHITTAKER, HARRY WILLIAMSAND PENNIMAN M. RUST Contribution f r o m the Chemistry Division, Research Department, U.S.Naval Ordnance Test Station, China Lake, California Received December 0. io66
An apparatus and experimental technique for measuring the consumption rate of burning liquid systems are described. The effect of such experimental parameters as pressure, igniter size, tube diameter and tube material on consumption rate was investigated. The consumption rate curve for the syst,em 2-nitropropane-nitric acid shows abrupt changes in slope at various pressures. Two of these regions of abrupt change in slope were studied in some detail by means of moderately high-speed motion-picture photography. The resolution obtained in these photographs was good enough to show many features of the burning process that could not be seen by direct observation.
Introduction Studies of temperature profiles in burning liquidslJ were made after a study of the effect of experimental conditions on consumption rate had been completed. These results are given here along with a description of the liquid burning rate apparatus. This work was to test a method of measuring liquid consumption rate, and to determine how certain physical parameters affect the consumption rate. The apparatus might introduce spurious effects which would give rise to erroneous rate data. Therefore i t was desirable t o determine effects (if any) characteristic of the apparatus so that they could be distinguished from those characteristic of the burning liquid. A short study was made of the effect of bomb pressure, igniter energy, combustion tube size and combustion tube material since these factors most likely affect observed consumption rates. An effort was made t o determine the relationship between observed rate and fundamental burning rate. Many side observations were made. The more important ones are described. Although some 20 different combustible liquids (both single and two-component systems) were investigated to some extent, the system 2-nitropropane-nitric acid was chosen to illustrate the behavior of liquids burning under pressure because it was studied in most detail. Materials
obtained by either method was then analyzed and diluted to desired concentration with distilled water.
Commercial Solvents Corporation commercial grade 2nitropro ane was distilled once and the center constant boiling gaction was used in these studies. The starting material, however, gave consumption rates essentially identical with those obtained with the purified material. Nitric acid was obtained by two different methods. Anhydrous nitric acid was prepared from concentrated sulfuric arid and potassium nitrate. The anhydrous nitric acid was distilled from the mixture a t about 30’ and 1 mm. Larger quantities of anhvdrous nitric acid were prepared by distilling a mixture of C.P.white fuming nitric acid in the presence of a large excess of concentrated sulfuric acid a t a ressure of about 1 mm. This process also reduced the !TO* content to about 0.1% or less. The anhydrous acid
Apparatus and Procedure Description of Apparatus.-The apparatus used was fiimilar to that described by Crawford and co-workers,s t80measure the consumption rate of solid propellants. In this work the rate was measured according to a principle described by Muraour and Schumacherd in which a direct determination was made of the time required to burn a given length of combustible material of uniform cross section. The liquid was contained in Pyrex combustion tubes 4 mm. i d . , 6 mm. o.d., and 17.8 cm. long. The tubes were sealed a t the bottom end. Unless otherwise indicated all rates were measured in tubes of this size. The bomb was a stainless steel vessel having a concentric cavity approximately 23 cm. deep and 6.4 cm. in diameter. The bomb had two diametrically opposite windows of Lucite apprpximately 1.9 cm. wide, 17.8 cm. long, and 3.2 cm. thick. These windows showed no signs of failure after ronsiderable use up to pressures as high as 307 atm. The bomb head threaded into the top of the bomb and the seal was made by using the unsupported area principle. The combustion tube holder, which contained electric contacts for the igniter and fuse wires, was firmly fastened to the bomb head. Horizontal metal bars, spaced exactly 1 or 2 in. apart with respect to their top edges, were used to measure distances. Electric leads from the contact8 on the strand holder were brought out through the bomb head. Ignition of the liquid was achieved by. passing current through a short length of No. 30 iron wire with a small piece of ballistite threaded onto the wire. This wire was bent in a shar “U” around the ballistite bead so that it would fit insige the top of the combustion tube. The position of the ballistite was adjusted so that it just touched the surface of the liquid in the combustion tube. The bomb was pressurized by two methods. For pressures up to 125 atm. the bomb was pressurized from commercial cylinders of dry nitrogen; ressures above 125 atm. were obtained by means of a ttree-cylinder cascade system and a high-pressure reaction vessel. Liquid nitrogen was pumped into the reaction vesbel and permitted to vaporize which resulted in pressures of about 475 atm. This high-premure source WBR used to pressurize the bomb to 307 atm. During combustion a 3-liter surge tank maintained the ressure constant to within 3% in the low pressure range. Axjustable relief valves gave additional control. This combination permitted control to about 5% a t pressures above 70 atm. The bomb pressure was meamred on a 16-in. Heise gage of 410 atm. total range.
(1) D I,. Hildenbrand, A. G. Whittaker and C. B. Euston, Tme 1130 (1954). 9 ) 11, L. Hildenbrand and A. G Whittaher, ibid .,69, 1024 (1955).
(3) B. L. Crawford, Jr., C. Huggett, F. Daniels and R. E. Wilfong, Anal. Chem., 19, 630 (1947). (4) H. Muraour and W. Schumacher, Mbm. Poudrss. 81, 87 (1937).
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