US2926197A - Production of benzene hexachloride - Google Patents

Description

Feb. 23, 1960 FREDERICK E. KUNG 2,926,197

PRODUCTION OF BENZENE HEXACHLORIDE Filed March 16. 1953 F'iGJ OUT B FlChZ FIG. 3

IN V EN TOR. FQ'AER/CK E: KU/VG United States Patent PRODUCTION OF BENZENE HEXACHLGRIDE Frederick E. Kung, Akron, Ohio, assignor to Columbia- Southern Chemical Corporation Application March 16, 1953, Serial No. 342,348

3 Claims. (Cl. 260-648) This invention relates to a novel method of providing benzene hexachloride compositions containing high gamma isomer concentrations thereof. It relates to a novel method of selectively separating isomers of benzene hexachloride. Moreover, it concerns a novel method whereby the gamma isomer of benzene hexachloride may be separated from other isomers of benzene hexachloride.

The conventional methods of preparing benzene hexachloride described in the literature involve the additive chlorination of benzene with elemental chlorine in the presence of an appropriate catalytic 'means, such as actinic irradiation. By recourse to the processes described in the literature, it has been possible to manufacture benzene hexachloride containing a maximum of from about 12 to 16 percent by weight of the gamma isomer thereof. Frequentlyythe gamma isomer concentrations are as low as 7 percent, or less, in the operation of such processes.

Additive chlorination of benzene in the preparation of benzene hexachloride results in the formation of at least five isomers thereof. These isomers have been designated as alpha, beta, gamma, delta, and epsilon. It has been universally recognized that the gamma isomer is useful, notably in the insecticidal field. Although some uses have been suggested for isomers other than the gamma isomer, it is the gamma isomer which appears to be of most commercial significance.

Because only a minor percentage of the benzene hexachloride produced in the normal manufacture thereof is the gamma isomer, considerable import has been attached to the development of various methods for separating the gamma isomer from the isomeric mixture. Preparation of compositions containing larger percentages of the gamma isomer of benzene hexachloride than is provided by the chlorination .of benzene has many advantages. It avoids the shipment of the insecticidally inert isomers. It makes it possible to formulate more concentrated preparations for use in the field by the farmer. It further allows for the recoveryof the ,insecticidally inert isomers so that they may be utilized, such .as by conversion to other more useful compounds, notably trichlorobenzene by dehydrohalogenation of the benzene hexachloride. It also permits other isomers to be concentrated and used for purposes otherthan insecticides, e.g., the delta isomer has been suggested to be a suitable herbicidal material.

According to the present invention, it is possible to prepare compositions of benzene heXaChloride which contain more gamma isomer than is normally present in benzene hexachloride manufactured by additive chlorination. Moreover, this invention is simply and conveniently performed. T hus, recourse to the'instant invention obviates the disadvantages attendant to the use of isomeric mixtures of benzene hexachloride containing low gamma isomer concentrations. Y 4 a The instant invention also. provides a suitable and convenient process for preparing compositions containing more of one isomer than is normally present in theadditive chlorination product. For example, it is possible 0 to prepare compositions containing extremely high porn centrations of the delta isomer. Delta isomer concentrations on the order of percent orrnore by weight of benzene hexachloride are often attained by recourse to the instant invention. In view of. suggestions that the delta isomer has value as a herbicide, the present inven-' tion makes it possible to prepare valuable herbicidal compositions.

It h been discovered sum n to th nvea ion that when a mixture of two or more isomers of benzene hexachloride is dissolved in a pair of immiscible solvents and the immiscible solvents are thereafter separated, the solute in each solvent will contain a higher percentage of one of the isomers based on the total benzene hexachloride dissolved in said solvent than the percentage of that isomer in the initial mixture. Thus, for example, if a mixture of gamma and delta isomers containing {50 percent by weight of each isomer is dissolved in a 'pair of immiscible solvents and the solvents are then separated, one solvent will contain an isomeric mixture of benzene hexachlorides containing over 50 percent by weight Qof the gamma isomer based on the total benzene hexachloride present as solute therein. Likewise, the other solvent will contain a solpte having over 50 percent by weight of the delta isomer.

The above-described phenomenon is also observed when various isomeric mixtures of benzene hexachloride are dissolved in a pair of immiscible solvents. However,

the exact distribution of each isomer in each solvent comprising the pair of immiscible solvents depends on the particular solvent pair and the relative volumes of the respective solvents. Thus,--the prediction of which solvent will contain the solute enriched in one or more isomers requires a knowledge of the particular solvent pair, and to a certain extent, the relative volumes in which each component solvent of the pair is utilized.

In this regard, it has been discovered that reference to the distribution coeflicients of the various isomers in benzene hexachloride for any given pair of immiscible solvents permits the judicious selection of a suitable solvent system for selectively separating one or more isomers from one or more other isomers; This distribution coefiicient is defined as the concentration of a given isomer in the less polar phase divided by the concentration of that isomer in the more polar phase for a given immiscible solvent pair when the isomer is dissolved in the solvent pair and the system is at equilibrium. Moreover, the constant is apparently not noticeably influenced by 'the'presence of other -isomersin thesystem.

Thus, the coefficient may be determined by dissolving The following table lists a series of illustrative solvent pairs and the respective distribution coeflicients for the major isomers, alpha, gamma, delta, and epsilon:

may be predicted to be 49.5 percent by weight of the solute.

If the volume of pentane is only one half that of Solvent pair Distribution coeflictent (k) No.

Non-polar Polar a 1 A Benzene Ethylene glycoL. 16. 7 13. 3 5. 5 13. Pcrchloroethylene. do 12. 8 7. 9 0. 9 1. Ethylene dichlorid do 6. 1 5.0 1.2 2. 4 Carbon tetrachloridedo 8.6 6.0 0. 6 1.6 M do 12. 0 8. 4 1. 2 2. 1 M do 13. 2 13. 3 3.0 5. 5 Ethyl ether do 8. 4 5.2 2.5 2.3 n-Hexane (comm) -do 3. 0 1. 9 0.26 0. 30 Pentane do 3.0 1. 1 0. 10 0. 18 Decalindo. 7. 1 3. 7 0.8 1. 2 Cyclohexane Methylcellosolve 0.42 0. 29 0. 17 0. 10 do Butanediol-1.3 1. 7 1. 5 0. 17 0. 27 do Polyglycol-400. 0. 0. 14 0. 009 0. 031 chloroform- 11.5 6. 6 2.0 3.4 Benzene-.- o 17.5 11. 1 16.7 n-Heptane Ethylene glycol 2. 3 1. 46 0. 15 0. 29 Cyclohexana o. 3. 4 2. 4 0.22 0.35 do Polyglycol-400. 0. 5 0. 3 0. 036 0. 063 Pentane. Dlethylene glycol. 0. 41 0. 17 0. 0145 0. 006 Cyclohexane. do 0. 61 0.27 0.032 0.043

Carbon tetrachlorlde do 0.70 0.42 0. 046 0. 14 Perchlorocthylene o- 1. 75 0.9 0. 09 0. 12 Trichloroethylene Ethylene glycol 15. 6 10. 3 1. 08 1. 7 Dinentene do 3.4 3.6 1.4 3.3 25. Toluene do 28 16 7. 5 16 26.-- n-Butyl bromide do 20. 6 16.0 3. 3 3. 6 27..- Cyclohexane- Propylene glycol 2.0 1. 14 0. 096 0. 10 28 ---do Trimethylene glyc 2. 7 1. 0.18 0.26 29 do Acetonitrile 2. 8 0. 17 0. 082 0, 064

Varying the ratio of the volumes of pentane and ethylene glycol will permit the attainment of varying degrees of resolution. The following example is intended to illustrate the value of this data. Assuming an isomeric mixture of 100 grams, containing the four isomers in equal proportions and equal volumes of solvent, the following mixture will comprise the solute in the pentane.

Concentration alpha in pentane Concentration alpha in ethylene glycol l (3) (2) weight alpha in ethylene glycol By following these calculations, the respective amounts of the isomers in the solute of the pentane phase may be anticipated as:

ot=15 grams =8.95 grams A=1.19 grams e=2.06 grams This represents an alpha concentration of percent by If a=grams alpha in pentane, 25 -a=grams alpha in ethylene glycol. Then by substitution:

a=18.75 grams alpha a 13.1 grams a =2.3 grams ae=3.8 grams The concentration of alpha isomer in the pentane phase weight of the solute in the pentane.

Accordingly, the present invention may be practiced by dissolving an isomeric mixture of benzene hexachloride containing all the known isomers thereof into a pair of immiscible solvents and separating respective liquid phases thus formed.

Usually, the dissolved benzene hexachloride present in each of the separated phases is recovered by known expedients, notably distillation, crystallization, etc. with the solvent being collected and reused. Under certain circumstances, the phases need not be subjected to further treatment, but may be suitable for direct use as a liquid formulation. Normally, however, it is more economical to separate the solvents and benzene hexachloride.

Although the description of this invention will be made with specific reference to providing compositionscontaining enhanced gamma isomer concentrations, e.g., the selective separation of the gamma isomer from other isomers, it should be understood that the process may be utilized to separate orconcentrate-any given isomer of benzene hexachloride with respect, to a mixture of any two or more isomers,

A specific embodiment of this invention Comprises introducing a mixture of at least alpha, gamma, and'delta isomers into a pair of immiscible solvents and recovering the benzene hexachloride present in the less polar solvent, notably the alpha and gamma isomers.

It is also possible to introduce a mixture of isomers containing alpha and gamma isomers, but not containing any appreciable percentage of delta isomer, and recover the benzene hexachloride in each solvent toseparate the alpha and gamma isomers from one another. This procedure is of particular utility because many of the solvent pairs readily permit a separation of the delta isomer from the alpha and gamma isomers, but with the delta isomer present satisfactory separation of the alpha and gamma. isomers is difiicult-or economically unattractive in the same separation. It will be understood that this particular procedure may have particular utility in combination with a process wherein the delta isomer is removed from the alpha and gamma isomers and a second step is utilized to separate gamma and alpha isomer. Such process, for example, would comprise treating the less polar solvent phase which contains essentially no delta isomer obtained from a prior separation with a fresh polar solvent to separate the alpha and gamma isomers, the gamma isomer selectively distributing in the more polar solvent. The more polar solvent comprising the fresh polar solvent may be even the same solvent ,employed in the delta separation so long as it has been freed of delta isomer. It may be a different solvent (different chemical structure) entirely.l

Practice of this invention is predicated upon employing a pair of immiscible solvents. By fpair," it is to be understood that two or more components 1s meant,;

as will hereinafter be explained.

It has been found that a suitable pair of immiscible solvents comprises one or more polar and non-polar solvents. In this regard, polarity is a relative term and the system may be characterized as containing a more polar and less polar solvent. As a practical matter, immiscible solvents normally differ in dielectric constant by at least about 25 to 30 or more. Thus, by stipulating that the solvents are immiscible usually inherently defines solvents which have substantially different polarities. Moreover, immiscible solvent pairs are generally comprised by a non-polar solvent and polar solvent. For the purposes of explaining the invention, the terms polar and non-polar solvent-will be employed, although it is to be understood that such expression will refer to the relative polarity of the solvents rather than absolute polarity.

Besides evidencing the above-described immiscibility, the solvent pair should comprise liquids which have different densities such that it is possible to separate them when they contain solute (benzene hexachloride) by centrifugation, phase separation, or equivalent expedients. For practical purposes, solvents comprising the pair which have density diiferences at atmospheric conditions, e.g. room temperature, are most suitable. In some instances, it may be possible to employ solvents which have different densities only within a specific temperature range by effecting the separation of the solvents within such range.

Manifestly, the solvents employed should be chemically inert under the conditions at which the invention is practiced. That is, they should not react with each other, benzene hexachloride or any other materialthat may be present in the system to produce a compound or compounds not originally present. Under certain special circumstances wherein a new material is produced that has marketable value, chemical reaction may be permissible. Even then, if considerable chemical reaction is encountered, it is preferable to select conditions .and solvents which avoid or minimize such reaction.

The .instantinvention makes it possible to selectively separate one isomer from other isomers. The degree 6 to which the selective separation is accomplished, and also the isomers which may be separated depend on the particular solvent pair that is utilized. Thus, the particular objective of the separation governs to some extent the solvent pair which is employed, although beneficial results will accrue from the use of any solvent pair which satisfies the hereinbeforedescribed requirements. Optimum results for a specific separation are, therefore, ob-

.tained by recourse to selected solvent pairs. 7

The elficiency of a particular solvent pair in providing the desired objective, to Wit, the ease with which the resolution of certain mixtures of isomers into its component isomers or'into mixtures which contain larger amounts of one isomer thanthe .initial. mixture, may be predicted by reference to the separationcoefiicient of the solvent pair. This separation coefficient is not always the same value for separation of different isomersl Thus, one solvent pair often will provide an easier separation of the gamma and delta isomers, whereas an other solvent pair will provide a rnore'eflicient separation of the gamma and alpha isomers. However, it is em phasized that any immiscible solvent pair which otherwise fulfills the outlined requisites will provide a beneficial separation.

As has been indicated, the separation coefficient of any solvent pair may vary depending on the isomer separation involved. The separation coeflicient of a solvent .pair for any two isomers of benzene hexachlorideis dewherein Wi represents the weight of isomer x in solvent A, W? the weight of isomer y in solvent B, We the weight of isomer y in solvent A and W}? the weight of isomer x in solvent B. A coefi'icient of 1 indicates no separation whereas the greater the difference of the value for K from 1, the easier the separation of x and y may be expected to be. Thus, small coeflicients, e.g., less than 0.8 or coefficients larger than about 1.2 indicate suitable solvent system. This coefficient is indicative of the maximum effectiveness of the solvent pair in resolving a mixture containing x and y into separate components x and y.

The separation coefiicient K as defined above, it will be appreciated, also represents the ratio of the distribution coefficients of the two isomers in question. Thus, K in the above equation is equal to is indicative ofthe number of steps or stages that may be required to provide a complete or essentially complete separation of x and y. With a comparatively small coefficient, say of about 1.5 to 3, a considerable number of steps or stages are indicated. As the coefiicient increases, the number of these steps or stages should decrease.

This coefficient for a given temperature may be ascertained by dissolving given amounts of x andy isomers in the selected solvent pair intimately mixing the pair to achieve equilibrium, and thereafter analyzing the x and y isomer content in' one or both of the resulting phases at the temperature.

Some of the polar solvents which may be employed to comprise the more polar solvent in the solvent pair used to perform the instant invention include normally liquid aliphatic alcohols such as methanol, ethanol, isopropanol, propanol, butanol and the like, liquid polyhydroxy compounds including glycerine, glycols such as ethylene glycol, 1,3-butyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and higher polyethylene ,glycols, glycol ethers, acetonitrile, formamide, formic acid, aniline, and various other compounds including methyl Cellosolve, ethylene carbonate, nitromethane, and methyl 7 Carbitols. In general, materials in which benzene hexachloride will dissolve and which have a dielectric contant of above about 10 are suitable.

The polar solvent portion of the solvent system contemplated by this invention are not limited to the use of any one of the above-enumerated solvents, but may constitute a plurality of such solvents so long as they are completely miscible. In this regard, aqueous solutions of the water-soluble solvents recited are also useful. Mainly, aqueous solutions of the aliphatic alcohols and glycols are found most suitable. Aqueous methanol, ethanol, isopropanol solutions are of particular importance for reasons that will become apparent.

Solvents which are suitable for providing the nonpolar (less polar) solvent for the immiscible solvent pair employed in the practice of this invention include the normally liquid aliphatic and cycloaliphatic hydrocarbons, such as n-hexane, cyclopentane, pentane, heptane,

cyclohexane, alkyl .cyclohexanes such as methyl cyclohexane, dimethyl cyclohexane; benzene, decalin, indane, Skellysolves, petroleum fractions, and the like. Halogenated hydrocarbons, and notably chlorinated hydrocarbons, which are normally liquid, such as carbon tetrachloride, chloroform, methyl chloroform, ethylene dichloride, trichloroethylene, tetrachleroethane, perchloroethylene, methyl chloride, methyl iodide, hexachlorobutadiene, hexachlorocyclopentadiene, and the like are also suitable. Generally, halogenated hydrocarbons containing up to and including four carbon atoms are satisfactory. Ethers, such as ethyl ether are also useful. The invention, however, is not limited to the use of but one of these non-polar solvents to comprise the non-polar phase of the solvent pair. Mixtures of miscible non-polar solvents are contemplated, subject to the limitation that in admixture with the polar solvent, they provide a solvent pair having the requisite immiscibility and other physical properties.

In the event recourse to multi-component polar and non-polar phase, e.g. when two or more solvents are employed to provide either one or both of the respective phases, it is, necessary to consider certain factors to insure satisfactory performance of the invention. Notably, the miscibility of the various members of one phase must be such that, during the course of carrying out the invention, there is no tendency for more than two phases to be formed. Thus, the possibility that one of the several solventsmay disrupt the normal miscibility (or immiscibility) of the system, particularly in a multistep process, should be considered. However, such situations are the exception rather than the rule.

Typical solvent pairs which are used in the instant invention include among others cyclohexane-ethylene glycol; perchloroethylene-ethylene glycol; ethylene dichloride-ethylene glycol; carbon tetrachloride-diethylene glycol; cyclohexane-diethylene glycol; perchloroethylenediethylene glycol; methyl chloroform-ethylene glycol; methanol-cyclohexane; benzene-ethylene glycol; methyl iodide-ethylene glycol; ethylene glycol-carbon tetrachloride; ethylether-ethylene glycol; aqueous methanol-cyclohexane; nitromethane-n-hexane; ethylene glycol-pentane, ethylene glycol-cyclohexane; cyclohexane-methyl Cellosolve; cyclohexane-butanediol-1,3; cyclohexane-polyethylene glycol (polyglycol 400Union Carbide and Carbon); chloroform formamide.

Some of these solvent pairs are especially suitable for separating specific pairs of isomers. Thus, ethylene glycol-carbon tetrachloride; diethylene glycol-carbon tetrachloride; diethylene glycol-pentane; diethylene glycolperchloroethylene; pentane-ethylene glycol; and cyclohexane-polyethylene glycol apparently provide the highest separation coefficient for the gamma-delta isomers and normally offer an optimum solvent system for separating the gamma and delta isomers. Similarly, per chloroethylene-ethylene glycol; pentane-ethylene glycol;

carbon tetrachloride-diethylene glycol; pentane-diethylene glycol; cyclohexane-polyethylene glycol; chloroformformamide; decalin-ethylene glycol appear to be the more suitable pairs for separating the gamma and alpha isomers.

It isnot intended that the inference should be drawn that because a solvent pair is eminently suited for separation of a given pair of isomers that it is not suitable for separating other groups of isomers. On the contrary, it may be noted that cyclohexane-polyethyleneglycol appears to be among those classified as suitable for resolution of gamma-delta and gamma-alpha. It appears that all solvent pairs possessing the requisite physical characteristics provide a desirable result, with some being more suitable for a specific task.

Various expedients may be employed to effectively practice the process of this invention. They all, however, perform certain basic steps which comprise dissolving the isomer mixture of benzene hexachloride in a solvent pair having the afore-described characteristics, and thereafter separating the immiscible phases of the resulting mixture. Normally, the respective phases, after being separated are subjected to separate further treatment to recover the solute therein, namely, the benzene hexachloride, as by distillation, precipitation or equivalent operation.

The temperature of the system, e.g. the solvent pair, at which the invention is performed may be widely varied. It is preferable to perform the invention at convenient temperatures, e.g. about 25 C. It does not appear that the temperature is critical. Since many of the solvents are relatively volatile, the lower temperatures are favored.

However, as longas the temperature provides the liquid solvent system (does not permit the formation of a solid phase due to freezing) and does not volatilize any solvent appreciably, it is suitable. Temperatures from about 0 C. to about C. generally satisfy these requirements. At temperatures of between 15 C. and 40 C., the process appears to operate at or near optimum overall efliciency.

Generally, each solvent comprising the pair should be present in at least sufficient quantities to dissolve the respective portion of the benzene hexachloride feed which is expected to selectively dissolve therein. It will be recognizedthat such quantities will vary depending on the temperature, since solubility of benzene hexachlorides in these solvents increases with higher temperatures. At higher temperature less volume of solvent will normally be required to perform the same job.

In many instances, one such contact with the solvent pair, as outlined above, does not provide as complete a separation of isomers as may be desired. Accordingly, it is often advantageous to repeat such steps employing the respective phase to form one of the phases in the next operation. For example, the polar phase containing the selectively dissolved mixture of isomers may be treated with a fresh non-polar solvent to further selectively concentrate one or more isomers in the polar solvent. In a similar fashion, the non-polar phase may be admixed with a fresh polar solvent.

One of the operations which embodies this procedure is a pseudo-countercurrent batch process. In such process, a plurality of mixing chambers and settling chambers are provided. Benzene hexachloride (isomeric mixture) is added to one such mixing chamber as a feed. The same procedure is followed in each pair of chambers comprising a mixing and settling chamber. The non-polar and polar solvents are mixed, preferably vigorously, and then separated by settling and decanting. One phase is then moved to the next adjacent pair of chambers, while the other phase is moved in an opposite direction to the other adjacent pair of chambers.

Fresh solvents are introduced suitably at each end of the line of pairs of chambers, the non-polar solvent from a different end than the polar solvent. Similarly, the

isomeric mixture of benzene hexachloride to be fractionated is added at one stage, usually an intermediate stager The product, that is, solvent plus benzene hexachloride, is ultimately removed at the respective ends of the line. Removal of the non-polar solvent containing the selectively removed benzene hexachloride takes placenormally at the end of the line of chambers whereinthe fresh polar solvent is introduced into the system.

Quite a variety of apparatus may be used to provide a means for providing acontinuous countercurrent process. Generally, apparatus such as towers which have alternating agitating and settling zones whereby theresults achieved in the settling and mixing chambers are simulated may be used. One such tower, for example, provides alternating zones, one set of such zones having an agitating means therein while the other set of zones serves as a settling area and is not subjected to: agitation. Another provides packed zones to achieve.- a suitable alternate set of settling areas to operate conjunctly with the agitating zones.

Other such equipment for accomplishing results similar to this will be apparent to those familiar therewith, including bafiied towers, and towers packed with inert materials such as Raschig rings and Berl saddles. Often a means for jetting one of the solvents down through various portions of the tower is utilized.

These towers are operable in a multitude of ways which depend, to a major extent, on the objective of the selective separation. In countercurrent operation, the heavier solvent is fed into or adjacent the; top of the tower and the lighter solvent enters the tower at its lower portion. By virtue of their respective densities, downward and upward flow of the solvents occurs and the lighter solvent is withdrawn from the upper portion of the tower; the heavier solvent is removed from the lower section.

The isomeric mixture of benzene hexachloride (feed benzene hexachloride) may be introduced into the tower at any point. In one type of operation, the feed benzene hexachloride is introduced at one end of the tower. In another, it is introduced intermediate the extremities of the tower. I

When the benzene hexachloride is introduced into the tower at one end thereof, it may be conveniently dissolved in the solvent that is introduced at that end.- Thus one feed stream to the tower may contain a solution of the benzene hexachloride. Since benzene. hexachloride is normally solid, this avoids difiiculties attendant to the introduction of a solid into a liquid system.

if benzene hexachloride is introduced into the tower intermediates the feed points of the solvents, the problem of addition is somewhat more complicated. It may be advisable to introduce molten benzene. hexachloride. Alternatively or in conjunction with molten feed, the feed of benzene hexachloride may be facilitated by dissolving it in a small quantity of one of the solvents. Generally, the volume of solvent added to the system in this manner should be kept at a minimum; for satisfactory performance of the tower the solvent introduced thusly should be less than 25 percent of the total amount of that solvent added to the system.

Still another expedient is available to enhance the efficiency of the tower. The material issuing out of any given end of the tower may be partially recycled to the tower at a point above or below the respective end, as the case may be. For example, the heavier solution which is ithdrawn from the lowermost point of the tower may be recycled .to a higher point in the tower than the point of withdrawal. The recycled material may comprise a portion, but not all, of the withdrawn solution, with or without partial or total removal of the solvent. Similarly, it is possible to recycle a portion of the lighter solution leaving the upper section of the tower to a point below its removal point, with or without partial or complete removal of the solvent.

The towers herein described and their equivalents may be used in combination-with one another depending again on the particular. ends to be accomplished. One convenient combination of towers utilizes. at least three towers. The solvents issuing out of the respective ends of the first tower provide one solvent feed for each of the other two towers. Fresh solvent is employed as the other feed in each of these two towers. Other combinations of towers and feeds will be apparent to. one acquainted with the use of such extraction equipment.

Ultimately, whether one or more towers are employed, the respective streams emerging from the final step are treated to recover the solvents, which recovered solvents are conveniently reintroduced to the system as fresh feed.

, Thus, the stream emerging from one end of the tower may be subjected todistillation with the distillate being appropriately cooled-"and returned to the tower. The residue from such distillation will be benzene hexachloride having an enhanced concentration of at least one isomer thereof as compared with the benzene hexachloride feed.

Instead of recourse to a distillation step, comparable expedients may be employed. The solute may be precipitated by cooling the solution, by addition of a liquid which is miscible with the solvent to provide a solution in which the solute is lesssoluble, partial distillation of the solvent followed by cooling to precipitate asolid phase, or the like. Thereafter, filtration, centrifugation, settling and decanting, or other means for separating solid and liquid phases may be utilized.

instead of relying on gravity to cause the two solvents to rise or fall in atower, it is possible to use centrifugal force to provide the intimate contact :between the two solvents. Thus, the instant invention may be practiced by recourse to a Pobielniak centrifugal extractor, or other such apparatus. In such extractions, the heaviersolvent is fed into the center of a cylindrical chamber and by rotating the chamber centrifugal force causes the heavier solvent to move to the outermost portion of the chamber. The lighter solvent is fed'under pressure at the outermost portion of the chamber and effectively moves toward the center thereof. Thus, the outward movement of the heavier solvent coupled with the inward movement of the lighter solvent, due to rotation of the chamber causes the respective solvents comprising the solvent pair to move in countercurrent flow.

A plurality of extractors which utilize centrifugal force to perform the extraction in such manner are known. They all are basically the same. Some, however, employ mechanical expedients to increase the efficiency of the extraction, notably, by increasing the flow paths of the respective solvents. This provides longer contact between the solvents. All sorts of bafiie arrangements, perforated baffles, etc. are used to enhance the operation of centrifugal extractors.

Inthese extractors (towers or centrifugal extractors), benzene hexachloride feed may be accomplished by dissolving the isomeric mixture in one of the respective solvents which is introduced into the column. Under certain circumstances, it is also possible to add the benzene hexachloride as a molten mass to the extractor, provided precautions are taken to minimize or avoid clogging due to solidification. Often, heating means may be employed to maintain the feed molten until it has entered the ex-- tractor and has been dissolved. Sometimes it may be desirable to add a small portion of one solvent to the feed to enhance its flow and dissolving in the extractor.

Essentially all isomeric mixtures of benzene hexachloride may be treated in accordance with this invention with beneficial results. Certain mixtures, however, are most usually encountered in the commercial manufacture of benzene hexachloride and such isomeric mixtures are the ones which may be expected to be employed in practice of the instant invention. One such mixture is the benzene additive chlorination product prepared by reaction of benzene and chlorine inthe presence of an appropriate catalytic means, notably actinic irradiation.

The exact isomer distribution in this product varies somewhat, depending on the exact process employed. A typi-- Isomeric mixture prepared by additive chlorination mixtures wherein other catalytic means besides actinic light is employed such as organic peroxides are also useful. Similarly, the additive chlorination product prepared in accordance with the process described in application, Serial No. 225,854, filed May 11, 1951, now abandoned, in the names of Joseph A. Neubauer, Franklin Strain, and Frederick E. Kung may be used.

. Another isomeric mixture that is frequently encountered in the commercial manufacture of benzene hexachloride is one that results from the filtration of the additive chlorination slurry and recovery of the soluble isomers. This isomeric mixture may likewise be employed in the present process. US. Patent No. 2.569,677, granted October 2, 1951, describes one typical method of obtaining such isomeric mixture. Other processes which provide somewhat better separation of the alpha isomer than the one described in the aforedesignated patent may also be used to provide an isomeric mixture which is suitable for carrying out the present invention.

The present invention has also been found to have particular utility when employed in cooperation with other techniques for resolving isomeric benzene hexachloride mixtures into its components, and notably providing essentially pure gamma isomer, e.g. lindane. One technique for obtaining lindane involves the extraction of solid benzene hexachloride containing from 12 to 55 percent by weight of the gamma isomer with a lower aliphatic alcohol, notably methanol or ethanol. The resulting extract, containing an enriched gamma isomer content is thereafter selectively precipitated by addition of water to the extract or by cooling the extract. A pure gamma isomer precipitate may be obtained in this manner, or alternatively, a product containing upwards of 70 percent of the gamma isomer may be prepared.

Unfortunately, the process outline in the preceding paragraph has certain limitations, namely, that the higher the gamma isomer concentration is in the precipitate, the less efiicient the process. That is, if lindane (99 percent or more gamma) is precipitated, a substantial portion of the total amount of gamma isomer remains unprecipitated. Being satisfied to produce a less concentrated gamma product as the precipitate decreases the amount of gamma that remains in solution, but it is economically impossible to waste the soluble gamma isomer since it still represents a considerable portion of the total amount that is treated.

Attempts to recycle the contents of the aqueous methanol solution, such that recovery of the unprecipitated gamma isomer is efiected, have been relatively unsuccessful. It seems that a considerable amount of delta isomer builds up by such recycling and eventually makes the processes inefiicient and often unsuccessful.

However, in accordance with this invention, it is possible to selectively separate the gamma and delta isomers present in an aqueous methanol solution. 'It has been found that by extracting the aqueous methanol solution with a non-polar solvent such as hexane or others hereinbefore enumerated, the delta isomer tends to concentrate in the solute of the polar material whereas the gamma isomer remains predominately in the non-polar phase. By recourse to the present invention, it is, therefore, possible to treat the aqueous methanol solution to recover the gamma isomer present therein while simultaneously effecting a separation of the troublesome delta isomer from the gamma isomer.

Thus, when this invention is practiced in cooperation with the afore-described process for preparing lindane or other high gamma isomer containing products, no interference in the continuous operation of such process is encountered due to a buildup in delta isomer concentrations. Moreover, the instant invention increases the efiiciency of such processes by permitting the unprecipitated gamma isomer to be recovered and, if desired, to be recycled for further treatment in the process.

The following examples illustrate the instant invention:

Example I The apparatus used in this example comprised five SOO-milliliter flasks individually fitted with agitators and drain plugs. Reference to Figure l of the drawings will illustrate diagrammatically how the five flasks were disposed relative to one another.

At the outset, each flask was charged with 200 milliliters of ethylene glycol, 50 milliliters of carbon tetrachloride, and 5 grams of benzene hexachloride. This benzene hexachloride analyzed as follows:

Each fiasks contents was thereupon stirred for onehalf hour at room temperature (e.g. 25 C.). The phases therein were then drained into separate vessels and reintroduced into extractors so that the glycol phase moved one extractor to the right and the carbon tetrachloride phase moved one extractor to the left. In the drawing, A represents ethylene glycol and B designates carbon tetrachloride. New solvent was added at extractors 1 and 5; fresh glycol (200 milliliters) was added at 1 and fresh carbon tetrachloride (50 milliliters) was introduced at 5. Benzene hexachloride of the same composition was added at extractor 3. Stirring for 30 minutes followed by separation of the phases plus movement of the phases to the respective adjacent extractor was effected. Fresh additions to the system were made in the manner already described. Each addition of the two solvents and benzene hexachloride constituted a separation-addition step. The terminal efiluents are removed from the system.

This procedure was repeated until ten (10) separationaddition steps were performed. The ethylene glycol phase I removed from extractor 5 and the carbon tetrachloride phase emanating from extractor 1 were then treated to remove the benzene hexachloride solute therein and submitted to infrared spectroanalysis to determine the isomer distribution.

Benzene Isomer analysis, percent Phase exachloride,

grams Alpha Beta Gamma Delta Epsilon Example II 90 percent methanol, and 10.0 grams of benzene hexachloride were employed. The procedure in this example differed from Example I in that the benzene hexachloride was fed at extractor in a methanol solution, e.g., terminal feed as distinguished from intermediate feed was employed.

The following are the analyses of hexachloride compositions:

the respective benzene The large diflference in the contents of the respective phase with respect to the gamma and delta isomers is apparent. The delta isomer tends to accumulate in the methanol phase and a product containing 59.5 percent delta isomer was attained. Conversely, a gamma isomer content of 48.5 percent was achieved in 'the'hexane phase.

By continuing the extraction employing more than extractions, even greater resolution of theisomersmay be achieved. 1

Example 111 In order to demonstrate the applicability of the present process to commercial liquid-liquid extraction of the isomers, the following process was performed in a Scheibel column. l

Reference to Figure 2 of the drawings will permit more complete descriptionof the column employed. It included glass tube 4 which was four feet high and had an inner diameter of one inch. End plates land 2, through which shaft 3 was centrally disposed, provided the closures at the respective ends of tube 4. The upper end of shaft 3 was connected to drive means (motor) 5 whereby shaft 3 could be rotated at any desired rate.

This column consisted of eleven (11) stages disposed equally along the length thereof. Each-stage consisted of a settling zone 6 and an agitating zone 7. Each settling zone was provided by loose metallic mesh 8 which filled the entire diameter of the tube and was approximately three inches deep. The agitating zone was provided by a zone about /2 inch deep wherein agitator 9 was disposed.

Agitator 9 consisted of a four-finned element anchored to shaft 3. Figure 3 which isa cross section taken at A-A of Figure 2 of the drawings depicts the configuration of this element and fins 10. I

For end feed, the heavier solvent is tube 12 into the uppermost settling zone while the lighter solvent is charged via tube 13 into the lowermost setting zone. The heavier solvent is withdrawn from the tower through tube 14 while the lighter solvent leaves the system by way of tube 15. The feeds are pumped by appropriate means (not illustrated) into the column While heavier solvent comprising the continuous phase through out the entire length of the column. This was achieved by regulating the highest point of inverted U 16 which was adjustably connected to take-0E tube 14 through a rubber tube element.

introduced via 1 An aqueous methanolsolution containing percent by volume of methanol was fed viatube 12 to the highest settling zone. This solution'contained 8 grams of henzene hexachloride per 160 milliliters thereof and was introduced at the rate of 368 milliliters per hour. The benzene hexachloride in solution had an isomer distribu tion as follows as determined by infra-red spectroanalysis:

Alpha= 16.1 Beta=4.9 Gamma== 17.6 Beta=4.9 Epsilon: 12.1

The other solvent employed was n-hexane (commercial grade comprising 70 percent n-hexane and the balance other hexane isomers) and it was introduced into the system via tube 13 at the rate of 222 milliliters per hour.

With the feeds being introduced as described, drive means 5 was operated at 900 revolutions per minute to rotate agitator element 9. The operation was performed at room temperature, 25 C.i3 C.

After the column had been in operation for Phree hours, samples of each phase leaving the column were treated to recover the residual benzene hexachloride therein by distillation of the solvents. 'The respective compositions were subjected to an infra-red spectroanalysis to ascertain their isomer distribution. Thereafter, during the course of the run, samples were taken periodically and analyzed.

The residual benzene hexachloride in the methanolic liquor leaving the tower, when recovered from the solvent, was a tan, crystalline material. It was extremely rich in delta isomer. The product recovered from the hexane stream emanating from the column'was an oily mass which crystallized slowly on standing at room temperatures.

The feed containing the benzene hexachloride in this example was obtained by taking the additive chlorination product prepared by adding elemental; chlorine to benzene which is irradiated with actinic light and removing the solid phase that forms during the reaction. Thereafter, the benzene hexachloride (.700 grams) recovered Benzone Percent isomer distribution Source hexa- ,7 s

. chloride weight,

grams a {3 'y A e 1. Additive chlorination product minus alpha cake formed during chlorination 700 21.0 2.0 42. 5 20. 5 8.0 Isomer weight (grams)- 147 14 298 144 56 2. Cake left alter methanol extraction 62 64.0 0 28. 5 1.0 1. 5 Isorner weight (grams)- 40 0 18 1 1 3. Precipitate formed by Water addition to methanol solution 17.5 0 76.0 0 2.0 Isomer weight (grams) 275 48 0 209 0 6 4. Aqueous methanol solution after removing (3)- Feed to column 360 16.1 4. 9 17. 6 40. 2 12.1 Isomer weight (grams)- 58 18 63 145 44 5. Aqueous methanol stream from tower 144 1. 5 5.0 5.0 70. 5 12. 5 Isomer weight (grams). 2 7 7 102 18 6. Hexane stream from tower. 216 22. 5 3. 5 23. 0 23.0 10.5 isomer weight (grams)- 49 8 50 50 23 15 Reference to items 5 and 6 in thetable makes it evident that resolution of the delta and gamma isomers may be achieved by recourse to the instant invention. The process including the methanol extraction, precipi-.

:16 This data make it clear that even in a single-stage extraction, at least partial resolution of a gamma-delta isomer mixture into its components is possible. The experiments indicate that considerable latitude in temtation, and liquid-liquid extraction provides a commercial- 5 perature, volumes of solvent, and ratio of the volumes ly feasible process for recovering high gamma isomer of the solvent is permissible. containing products without undue waste of a significant portion of the total gamma isomer involved. Example VI def'tXas wgs aexxlpllalrilsdmgrevlloolz byl, f llgnf tlgg zggg ffi g A series of simple tests were studied to demonstrate 4 a tagbl a 5 11 unsuitable *0 rac the ability of other pairs of immiscible solvents to sepama 6 F 0th a rate the various isomers of benzene hexachloride. The g r0 g ggz i f of 5; t i zi g tests comprised dissolving at room temperature (25 C.- ii-act i/ith the esent li lid 1' uid ext iaction this rob 3 a mixture of 5 grams of gamma isomer and 5 lem overcomep q p grams of delta isomer in the pair of. solvents, agitating the S 15 liquid mixture, separating the phases and determining the weight and isomer content of the solute in each phase. Example IV e In some instances, the analysls of the solute from only Employmg the column described 111 Example In and one of the two phases was performed; the content of followmg the a procedure. several r r made the other phase may be determined by simple weight balvary the relatlve volumes of the respectlve feed ance. streams. Except for variation in the relative feed vol- Th sult were; umes and operation of the agitating means at 1,000 revolutions per minute, the procedure in this example dupli- Gated Bemene isomer content The following table summarizes the variable operat- S l t a vfillilfillle l l exz a (pe c ing conditions and results: p fla t ig;

Re ti e n-Hexane 300 3. 7 54. 0 34. 5 volumes Benzene hexachloridelsomer analysis Nitromethane 50 5.8 42.0 50.0 (milliliters) eight nexane 500 4.5 76.3 22.5

(grams) Ethylene glycol 400 Cyclohexane. 400 7. 9 Aqueous na fl 7 A e Methanol 50 1.6 35.5 62.0 meth exane CYclohexane- 400 2.0 53.5 37.5 Methanol 200 6.9 45.0 54.0 Cycl0hexane 400 4.6 76.0 21.0 135 4.2 2.0 4.5 9.5 55.0, 12.5 Ethylene glycoL. 400

105 7.7 18.0 3.5 33.0 21.5 12.0 Cyclohexane 400 4.0 78.0 .5 144 4. 4 2. 0 4. 5 10. 0 68. 0 12. 5 Ethylene carbonate 5Q 104 7. 7 16. 0 3. 0 33. O 21. 0 13. O Cyglghgxane 400 6. 7 50, 5 48. 5

140 3. 4: 0 6. 5 4. 5 e 73. O 12. 5 Dlmgthylformam 5O 152 8.6 16.0 4.0 -32.0 23.0 10.0 Cyclghexaue 400 3 2 51 475 146 3.1 0 5.5 3.0 77.0 12.5 mmethyuormflm 100 158 8.9 18.0 2.6 32.0 22.8 10.7 40 g l h 400 7 9 5&0 42.5 Fried Analylsls (glgranls Formamlde" 75 enzene exac on e h. 4 0 56.0 41. perl00 milliliters) 11.5 4.0 25.5 30.0 13.0 8 7 6 5 :(F)ycloihexair(1]e.li 20g 7. 6 56. 0 41. 5 1 Leaving the tower per given unit of time. Volumes are those of the g fi f ig f i f 8 1 1 0 3 0 efiiuent p e Formlc acid (88%)- 400 3. 5 30.0 53. 0 Cyclohexane. 400 5.6 58.0 41.5 Example V Acetonitrile 3.8 41.5 57.0 Cyclphexane. 400 6.9 54.0 45.5 In this serles of experiments, the effectiveness of cyclo- Aniline 100 hexane and ethylene glycol as a solvent pair in separating gamma and delta isomers was investigated. The procedure consisted of dissolving 5 grams of delta isomer 50; Anothe et of simple one-stage extractions were carand 5 grams of gamma isomer in a mixture of the cycloried out using a mixture of isomers of benzene hexahexane-ethylene glycol solvent system, agitating the two chloride having the following composition: solutions, separating the phases, recovering the solute in each separated phase and analyzing by infra-red spectro- Alpha =16.5 analysis the respective products for isomer distribution. Beta 0 As will be clear from the following table, the effect Gamma =36.0 of varying the volume of solvent, temperature and ratio Delta =40.0 of volumes was considered in these experiments: Epsllon= 5.5

Products Analysis Volumes, milliliters T ergp. Cyclohexane phase Glycol phase 0H4 CzHgOz Weight '1 A Weight '7 A a 1 (grams) (percent) (percent) (grams) (percent) (percent) 100 100 1 Room 4. 6 81.0 21. 0 4. 9 27. 0 69. 5 400 400 iRoom 4.6 78.5 13.0 5.2 25.5 70.5 1,200 1,200 Room 4.5 75.0 20.5 5.0 24.0 74.0 400 400 7 3.9 81.0 15.5 .5.7 27.5 73.5 400 400 '25 4.5 78.5 18.0 52 25.5 70.5 400 400 5. s 54. 5 30. 0 3.9 23. 5 72. 0 25 25 70 5.5 53.0 35.5 3.2, 24.5 74.5 200 400 1 Room 3. 2 83.5 15. 0 3.3 32 0 54. 5 600 200 1 Room 0.5 65.5 32. 5 3.2 17.5 81. 5

.xzaoafieo.

. 1.7 The :procedure' wasrrthe 1 same mas described-in .Example except: that- 12 grams ft amixture 'having the abovercompositioniwasremployed. Results were .asatabulated:

. Benzene 'Isomer content, percent yolume, hexa- I V Bolventpair 'millichloride,

". .:liters weight .a '18 v A --e.

grams Benzenenuuru .100 8.1 :..19.5 0.0 40.5 33.0 .6. Ethylene glyeoh; '400 3.6 10.5 1.0 27.5 54.5 4. Perchloroethylene.. 100 5.4 26.0 0.0 53.0 15.5 3. Ethylene glycoL. 400 6.3 7.0 1.0 23.0 59.0 8. Ethylene dichloride 100 4.9 23.5 0.0 47.0 21.5 5. Ethylene glycol j; .400 6.9 113.0 0.5 26.5 52.5 6. Analysis of feed (12.grams) 16,5 .0.0 36.0 40.0 v 5.

Example VII Employing the apparatus described in Example III, a solvent pair comprising carbon tetrachloride and diethylerr-e glycol was used to extract the isomers of benzene hexachloride. With this solvent pair, the-light phase, diethylene glycol, was the continuous phase and the liquid interface was at the bottom of the. column. Carbon tetrachloride was introduced via tube 12 into the top of the column, while diethylene glycol was fed via tube 13 into the lower part of the column. Apjfiroximately 3 times as much carbon tetrachloride was fed as diethylene glycol based on volume.

The isomeric mixture was introduced at the center of the column, e.g., midway between the liquid feed tubes 12 and 13, as a diethylene glycol solution containing 50 percent by weight of benzene hexachloride at between 60 and 80 C. to avoid any crystallization. Between 45 and 50 milliliters per hour of this solution was fed during the operation. The tower temperature, however, was about 25 C.

The rate of feed of carbon tetrachloride was such that the efiluent carbon tetrachloride phase was from 450 to 500 milliliters in volume per 45 minutes. Similarly, for 45-minute periods, the diethylene glycol effluent phase was between 153 and 172 milliliters in volume. The following table indicates the observed efiluent'volumes for 45-minute periods with the operational time indicating the length of time the tower was operating:

l Diethylene glycol.

Sample 5 (collection of which started after the tower was in operation 7 hours) was analyzed for isomer content in the respective eflluent phases with these results:

Benzene Isomer distribution, percent Efiluent hexa- 1 Diethyiene glycol.

Example VIII The same procedure and apparatus was employed as was in Example VII, with the exception that perchlorov ethylene." instead :ofrcar'bon. tetrachloride was employed.

, volume. Overa-periodof l /i -hours .of operation, the

perchloroethyleneeffluent was. 200 milliliters: and the diethylene glycol etlluent was between 102-105 milliliters for 30: minuteqefliuent volumes.

The. central feedof diethylene glycol solution of benzene. hexachloride (5 0 percentby weight); was introduced at a rate of 44-48mi1limeters.per. hour.

Analysis of. av sample of the-eflluent streams provided the following data:

1 Benzene Isomer distribution, percent .Efliuent hexachloride .lgrams): a B 1 .A e

9.6 29.0 1.5 58.0. 3:5 5.5 2.7 2.0 4.0 1.0 76.0 13.5 Feed 21.0 2.0 42.5 20.5 8.0

1 Diethylene glycol.

Example IX Employing the same procedure and apparatus described in Example VII, the solvent pair comprising carbon tetrachloride and ethylene glycol was employed to separate the isomers. Ethylene glycol was the lighter solvent in this system.

The benzene hexachloride was fed containing some carbon tetrachloride to avoid crystallization at C.

The following flow rates were observed:

Stream Milliliters I per hour Benzene hexachloride 22 182206 Ethylene glycol 550-560 The half-hour efiiuent pairs collected during the 3% to 4-hour period of operation were analyzed:

Volume, Benzene Isomer distribution, percent Stream millihexaliters chloride,

grams a B 'y A e 001. 91 9.5 29.5 1.5 50.5 13.0 5.5 Ethylene glyeoL- 275 2. 6 0 2 5 2. 5 79.0 13.0 Feed. 21. 0 2.0 42. 5 20. 5 8. 0

When the tower was opera-ted such that theratio of volumes of the effluentstreams'was increased to approximately 4 to 1, e.g.," about four times" as much ethylene glycol efiliient as carbontet'rachlorid e efiiuent was leaving the system per unit of time, the following results were observed:

Volume, Benzene Isomer distribution, percent Stream mlilihexaliters chloride,

grams a B 'y A e SO14 70 86 29.0 0.0 57.3 3.5 5.5 Ethylene glycoL- 255 3.1 0.5 4.1 5.0 72.7 15.1 Feed 21.0 2.0 42.5 20.5 8.0

' 19 chloride, forming two immiscible liquid phases Containing dissolved benzene hexachloride, glycol predominating in one phase and carbon tetrachloride predominating in the other, the gamma isomer selectively distributing in the carbon tetrachloride phase, and separating the liquid phases.

2. A method of preparing a benzene'hexachloride composition which comprises dissolving an isomeric benzene hexachloride mixture includingthe gamma and delta isomers in a pair of immiscible solvents for the benzene hexachloride, said pair comprising a liquid glycol and a halogenated hydrocarbon of up to 4 carbon atoms, forming two immiscible liquid phases containing dissolved benzene hexachloride, the glycol predominating in one phase and the halogenated hydrocarbon predominating in the other, the gamma isomer selectively distributing in the halogenated hydrocarbon phase, and separating the liquid phases.

3. A method of preparing a-benzene hexachloride composition which comprises dissolving 'an isomeric benzene hexachloride mixture including the gamma and delta isomers in a pair of immiscible solvents for the benzene hexachloride, said pair comprising a liquid glycol and a chlorinated hydrocarbon of up to 4 carbon atoms, forming two immiscible liquid phases containing dissolved benzene hexachloride, the glycol predominating in one phase and the chlorinated hydrocarbon predominating in the other, the gamma isomer selectively distributing in the chlorinated hydrocarbon phase, and separating the liquid phases.

References Cited in the file of this patent Scheibel Jan. 3, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF 'CORECTION Patent Nos 2 926 197 February 23 1960 Frederick Eo Kung It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 12, for "Beta=49" read De1ta=40.2 column 15, line 20 for "vary" read varying s Signed and sealed this 4th day of April 1961e 3323? ERNEST w. SWHDE ARTHUR w. CROCKER Attesting Ofiicer Acting Commissioner of Patents

Claims (1)

1. A METHOD OF PREPARING A BENZENE HEXACHLORIDE COMPOSITION WHICH COMPRISES DISSOLVING AN ISOMERIC BENZENE HEXACHLORIDE MIXTURE INCLUDING THE GAMMA AND DELTA ISOMERS IN A PAIR OF IMMISCIBLE SOLVENTS FOR BENZENE HEXACHLORIDE, SAID PAIR COMPRISING GLYCOL AND CARBON TETRACHLORIDE, FORMING TWO IMMISCIBLE LIQUID PHASES CONTAINING DISSOLVED BENZENE HEXACHLORIDE, GLYCOL PREDOMINATING IN ONE PHASE AND CARBON TETRACHLORIDE PREDOMINATING IN THE OTHER, THE GAMMA ISOMER SELECTIVELY DISTRIBUTING IN THE CARBON TETRACHLORIDE PHASE, AND SEPARATING THE LIQUID PHASES.

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