PURIFICATION OF TETRAHYDRODIBENZO[B,D]PYRANS FROM CRUDE SYNTHETIC MIXTURES

Abstract: (-)-6a, 10a-Trans-1-hydroxy-3-n-pentyl-6,6,9-trimethyl-6a,7,8,10a-tetrahydrodibenzo[b,d]pyran or any of its related pyrans in which the n-pentyl group is replaced by hydrogen or C1-C10 alkyl is isolated from a crude synthetic mixture by a process which comprises esterifying the mixture to form perfluorinated alkanoic acid esters, removing low-boiling and non-volatile components, passing the mixture through a first gas chromatographic column with a packing whose liquid phase consists of a slightly polar phenyl-substituted silicone oil and recovering a fraction rich in the desired component, passing the recovered fraction through a second gas chromatographic column with a packing whose liquid phase consists of a non-phenyl-substituted silicone oil and recovering a fraction rich in the desired component, hydrolyzing the fraction recovered from the second stage, and recovering the desired product from the hydrolysis mixture.

Description: PURIFICATION OF TETRAHYDRODIBENZO[B,D]PYRANS FROM CRUDE SYNTHETIC MIXTURES Funding for the research to support this invention was supplied by the National Cancer Institute. Background of the Invention The crude resin obtained from the flowering tops of female plants of several varieties of Cannabis sativa L. has been known for its psychotomimetic activity since antiquity. Common names assigned to some of these varieties include marijuana, hashish, charas, dagga, and bhang. With the advent of advanced analytical techniques, it has been determined that the resin contains a variety of ingredients varying in molecular configuration, with both the components and their proportions varying from one source to the next. In general, the active compounds have the following formula where R is hydrogen or alkyl containing from one to ten carbon atoms. They are useful as psycho¬ tomimetic agents, sedatives, and analgesics. Extensive studies have led to the identification of a single component as the one primarily responsible for the psychotomimetic activity. Although its complicated ring structure gives rise to differing nomenclature depending upon the numbering system used, the active component is most commonly referred to as (-)-6a,10a-trans-l-hydroxy-3-n- pentyl-6,6,9-trimethyl-6a,7,8,lOa-tetrahydrodi- benzo[b,d]pyran, in which R in the formula above is n-pentyl and occupies the meta position with respect to the hydroxyl group. This component is also known by the simplified names "trans-Δ 9 -tetrahydrocannabinol" and "trans-Δ 9 -THC." Following the identification of this ingredient, a variety of synthetic preparation methods were developed, in order to eliminate the need to extract the material from natural sources. A survey of these techniques can be found in the comprehensive article by Mechoulam et al., entitled "Recent Advances in the Chemistry and Biochemistry of Cannabis," Chemical Reviews, 76 (1), pp. 75-112 (1976). Two notable techniques are. those described by Petrzilka et al. in Helv. Chim. Acta, 52, 1102 (1969), and by Razdan et al. in J. Am. Chem. Soc, 96, 5860 (1974). In addition to its psychotomimetic properties, the active ingredient has also been found to be a beneficial adjunct to cancer treatment in view of its ability to sup¬ press the unpleasant side-effects which accompany che o- therapy. "For this reason as well as its psychotomimetic activity, there is a serious need for comprehensive testing of the material in order to determine in full detail its pharmacological effects. For reliable and reproducible results, test samples of the material must be obtained in a highly pure state. Unfortunately, synthetic procedures tend to produce a mixture containing a broad variety of geometric isomers, optical isomers, intermediates, unreacted starting materials, and products of assorted side-reactions. Many of these can be separated from the active component by conven- tional separation techniques. A certain number, however, particularly the isomers, are extremely difficult to remove. The only process developed to date which has been effective in supplying a product of sufficient purity is a low pressure liquid chromatography process. This process has several disadvantages. First, there are practical --- limitations on the scale-up of liquid chromotography equip¬ ment in terms of the diameter and length of the columns due to the need to avoid certain undesirable effects. Such limitations, together with considerations of packing effi- ciencies and absorbent weights, impose a severe limitation on the column through-put rate. As a result, a practical liquid chromatography system requires a tank farm containing several columns. Second, a solvent recovery system is ' necessary in order to separate out the product and recycle the solvent, entailing extensive processing equipment and the frequent attention of plant operators. This. dds great¬ ly to the expense. Third, the large number of vessels and 5 transfer lines tends to increase the danger of handling losses and potential theft. A serious need thus exists for a simplified purification system with a lower capital investment, a lesser need for operator attention, a higher through-put rate, and better product accountability. ° Summary of th Invention It has now been discovered that a compound of the above formula in which R is hydrogen or C.-C- Q alkyl can be purified from a crude synthetic mixture by a relatively simple and highly efficient process which comprises (a) esterifying at least a portion of the mixture to form perfluorinated alkanoic acid esters, (b) removing low-boiling and non-volatile components, (c) passing the mixture through a first prepara- tive gas chromatographic column containing a packing con¬ sisting essentially of a slightly polar phenyl-substituted silicone oil on a porous, inert, solid support to separate the mixture into a plurality of substantially discrete portions, and recovering therefrom the portion containing the highest proportion of the perfluorinated alkanoic acid ester of the desired component, or a substantial fraction of that portion, . (d) passing the recovered portion or fraction . .through a second preparative gas chromatographic column containing a packing consisting essentially of a non- phenyl-substituted silicone oil on a porous, inert, solid support to further separate the portion or fraction into a plurality of substantially discrete εubportions, and recovering therefrom the εubportion containing the highest proportion of the perfluorinated alkanoic acid ester of the desired component, or a substantial subfraction of that subportion, OMPI (e) hydrolyzing the recovered εubportion or subfraction to convert the esterified components back to their original form, and (f) recovering the desired component. By virtue of its unique column staging arrange¬ ment, this process provides a composition of unusually high purity with an ease of operation and through-put capacity not heretofore seen in industrial scale attempts at prepar¬ ing such materials. Whereas perfluorinated alkanoic acid esters are known in the art as a means of enhancing the volatility of the components for chromatographic purposes (see Mechoulam et al., ibid, at p...93), the nature of the liquid phases described above and their use in this par¬ ticular combination are novel and unique in their ability to separate the desired material from the other components in the mixture. Description of the Preferred Embodiments The process of the present invention is applicable to the preparation of p * urified forms of all compounds of the general formula in which R is hydrogen or alkyl containing from one to ten carbon atoms: R ■ The term "alkyl" is used herein to designate both "• ' straight- and branched-chain alkyl groups within the stated range of carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-pentyl, isopentyl, n-hexyl, n-octyl, and n-decyl. In one preferred embodiment of the formula, R occupies the meta-position on the ring relative to the hydroxyl group. Straight chains are par- OMPI ticularly preferred, particularly those of two to eight carbon atoms in length. The synthesis of (-)-6a,10a-trans-l-hydroxy-3- alkyl-6,6,9-trimethyl-6 ,7,8,lOa-tetrahydrodi- benzo[b,d]pyrans, hereinafter referred to as "the trans-Δ 9 isomer," can be accomplished in a variety of ways well documented in the literature. Most of the synthetic routes involve the reaction between a resorcinol (a 1,3-dihydroxy benzene) containing an alkyl substituent (or a hydrogen atom) corresponding to the R shown in the above formula (l,3-dihydroxy-5-n-pentylbenzene is known by the common name "olivetol") with a menthadienol- or a closely related struc¬ tural analog of the latter such as a menthadiene-ol or a menthenediol. An extensive list of synthetic routes is offered by Mechoulam et al., in "Recent Advances in the Chemistry and Biochemistry of Cannabis," Chem. Rev. 76 (1), 75-112 (1976). Each route produces a mixture of isomers, intermediates, unreacted starting material, and side- reaction products. Variations in the identity and propor- tion of the components in the product mixture occur from one route to the next. Many of the same impurities, however, are common to all synthetic routes. Any synthetic route, therefore, which produces the desired product indicated above is suitable for the present invention, and those which produce this material as a major component are preferred. Particularly preferred processes are those involv¬ ing the use of resorcinol or olivetol (or its alkyl analogs) and (+)-p-mentha-2,8-dien-l-ol. Notable in this regard are the processes developed by Petrzilka (U.S. Patent Nos. 3,560,528, 3,668,224, 3,833,616, and 3,920,705) and Razdan et al. (U.S. Patent No. 4,116,979). The disclosures of these patents are incorporated herein by reference. The most preferred process is that disclosed by Razdan et al. in the indicated patent, which offers a comprehensive descrip- tion thereof. This process basically involves reacting (+)-p-mentha-2,8-dien-l-ol with resorcinol or its alkyl- εubεtituted analogs in the presence of a Lewis acid catalyst in an inert organic solvent under anhydrous conditions. The preferred Lewis acid is boron trifluoride etherate, and the anhydrous conditions are preferably maintained by the pres¬ ence of a non-alkaline dehydrating agent such as magnesium sulfate. The product mixture components are of low volatil¬ ity and thus not conducive to vapor phase chromatographic separation. In order to convert them to a more volatile form, the mixture is esterified, whereby the hydroxyl groups are replaced by perfluorinated alkanoic acid ester moieties. . Any perfluorinated alkanoic acid can be used, including εtraight-and branched-chain groups, with no critical limi¬ tation on the chain length. Straight chains are preferred, however, and chains of excessive length will be impractical since the volatility of the ester eventually begins to decrease as the chain continues to lengthen. Most conven¬ iently, the ester moiety will contain from two.to six carbon atoms. Examples include trifluoroacetate, pentafluoro- propionate, heptafluorobutyrate, etc. The esterifying agent itself can assume any con¬ ventional form, notably an acid anhydride, an acid halide, and an acyl imidazole, in addition to the acid itself. The acid itself is less preferred, since it has a greater tendency to isomerize the active trans-Δ 9 component to the corresponding and less active trans-Δ 8 isomer. " The quantity of esterifying agent used is not critical. It is generally • preferred, however, that an excess be used to insure a complete reaction. An excess in this context refers to the number of acyl moieties in the esterifying agent in compari- son to the number of available hydroxyl groups in the product mixture. The amount of excess will most convenient¬ ly fall within the range of approximately fifty percent up to several thousand percent. Although not essential, the eεterification re- action is uεually conducted in the presence of an inert organic solvent. It will be particularly convenient to use the same solvent used in the synthesis step. This elimi¬ nates the need to separate the products, isomers, inter- mediates, etc., from the solvent prior to treatment of the mixture with the esterifying agent. Useful solvents include conventional inert organic solvents such as aromatics, ethers, ketones, esters, and aliphatic hydrocarbons option- ally chlorinated. Examples include petroleum ether, diethyl ether, benzene, toluene, tetrahydrofur n, dioxane, methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, ethylene dichloride, and isopropyl ether. Chlorinated hydrocarbons are preferred. The temperature of the esterification reaction is not limited to any critical range and can vary widely. For considerations of efficiency and .optimal product recovery, however, elevated temperatures are less preferred, since high temperatures promote the isomerization of the trans-Δ 9 isomer to its less active isomers (notably the trans-Δ 8 isomer). Thus, the preferred temperature range is from about -20°C to about +25 β C, with about 0°C to about 10°C particularly preferred. Cooling can be accomplished by conventional externally applied cooling techniques, such as ice-water bathε, dry ice-acetone baths, and cooling coils, and can be aided by appropriate agitation. Once the esterification reaction is complete, or has been permitted to proceed to the desired degree, it will be beneficial to quench the reaction, since prolonged expo- sure to the acid produced as a by-product from the reaction will promote isomerization of the trans-Δ 9 component to the tranε-Δ 8 . Quenching can be accomplished by any conventional acid quenching agent, notably alkaline metal or alkaline earth metal carbonates or bicarbonates. Sodium or potassium bicarbonates are particularly useful in this regard. Again, this is not an eεεential feature of the process, but will be generally beneficial toward achieving the optimum yield of active ingredient. Following the ester formation, high boiling and low boiling components are removed from the product mixture in order to provide efficient operation of the gas chroma¬ tographic columns and to prolong the useful life of the column packings. The low boilers include the solvent, any unreacted resorcinol and menthadienol (or whatever starting material is used), plus products of side-reactions * involving the latter. The high boilers include impurities of high viscosity whose presence would impair the efficiency of the chromatographic columns. With this in mind, any conventional separation method can be used. The preferred techniques are any of the various known forms of distillation. The primary concern in this portion of the process is the minimization of any opportunity for isomerization in the product mixture. Note that isomerization in this mixture, which occurs at increas¬ ing rates as the temperature rises, generally results in a decreasing proportion of the active trans-Δ 9 isomer. Thus, short contact times and moderate operating temperatures are preferred. To achieve the most useful results, distillation under reduced pressure is preferred such that the operating ' temperature is maintained below about 250°C, with a practi¬ cal operating range being from about 180°C to about 220°C. To achieve this result, a column operating at a pressure of less than about 0.10 torr is preferred, with a pressure between about 0.005 and about 0.05 torr particularly pre¬ ferred. A single stage distillation is generally sufficient although multiple stages can also be used. A particularly useful piece of equipment for this step is a wiped-film distillation apparatus. Once the low-boiling components and non-volatiles have been removed, the product mixture is ready for the first stage of its separation by gas chromatography. The object of this stage as well as the second stage chromato- graphic separation is to divide the mixture into subεtan- ' tially discrete portions (or "peaks") which can be isolated from each other by a simple valve switching mechanism. The columns for each of the two stages are packed columns, the packing comprising particulate material consisting of an inert porous solid support wetted with an absorptive liquid phase. The liquid phase in the first column consists of a silicone oil characterized by a slight polarity due to the presence, of phenyl groups on the εilicone molecule, and further characterized by the general absence of polar groups such as eεterε, cyano groups, trifluoro ethyl groups, and ethers. Substituents other than phenyl groups can be present on the εilicone backbone provided that they do not substantially alter the slightly polar character afforded by the phenyl groups. In addition, the phenyl groups them¬ selves are optionally substituted with conventional sub¬ stituents which are not highly polar, e.g., lower alkyl groups, halogens, etc., but preferably not nitro groups, cyano groups, trifluoromethyl groups, etc. Any conventional support,material can be used, provided that it is sufficiently porous to provide a high surface area for the liquid phase, and sufficiently inert that it does not promote decomposition of any of the com¬ ponents of the product mixture sought to be separated. A suitably inert support material will be essentially free of metal ions and acids, and will contain few or no acid sites. It is advisable that the support be silanized or otherwise passivated prior to being wetted with the liquid phase. Particularly suitable packing materials are calcined diatomite aggregates which have been acid washed and treated with dimethyldichloroεilane. Such materials are available from the Johns Manville Corporation under the trade name "Chromosorb ® ." The packing material as a whole is generally characterized by a maximum operating temperature, as a guide for prevention against loss of liquid phase by volatiliza¬ tion and against chemical degradation of the liquid phase. For the purposes of the present invention, there are no critical limits on the maximum operating temperature. It will be most convenient, however, to use a packing whose maximum operating temperature is 250°C or greater. The physical dimensions of the column itself are not critical and can vary over a wide range. They are generally limited by the range of equipment on the market as well as the deεired through-put rate. Increaεed column lengthε will generally promote more favorable "cr" values, where the a value for a given impurity peak is the ratio of the retention time for that peak to the retention time of the peak containing the desired tranε-Δ 9 component. Al¬ though no particular range of a values is critical, it will be most convenient to obtain a separation in which all α values differ from that of the desired peak by a minimum of 0.10. Different column lengths will provide varying degrees of peak resolution. Excessive lengths produce peak broaden¬ ing, which detracts from a clean separation. The optimum column length can be selected with these considerations in mind. With a high degree peak of resolution and favorable retention times, injection batches can be overlapped in order to increase the through-put rate while still maintain¬ ing a clean separation of the desired peak. With these considerations in mind, it will be most convenient to use a column with a diameter of up to approximately 600mm and a length ranging from approximately 0.5 to approximately 6.0 meters. Particularly preferred columns are those with a diameter ranging from approximately 20 to approximately 250mm and a length ranging from approximately 1.0 to approx¬ imately 4.0 meters. Any carrier gas can be used provided that it is inert and gaseous under the operating conditions of the column. The most useful carrier gases will be those with a high degree of disperεibility throughout the pores of the packing material. With this in mind, any conventional carrier gas used in either analytical or preparative gas chromatography can be used. This includes nitrogen, carbon dioxide, hydrogen, and helium, as well as other materials meeting the above description. In general, carrier gases " with a low molecular weight are preferred, and helium is particularly preferred. The flow rate of the carrier gas through the column, although not critical, should be fast enough to promote separation of the system components and to minimize the contact time and possible isomerization, yet slow enough to permit proper contact and permeability between the liquid and vapor phaεeε and to prevent excessive pressure drop. Clearly, such features as peak resolution and broadening will be affected by the carrier gas flow rate. The flow rate will further depend on the column diameter, the density of the packing material, etc. Although no critical range exists, it will be most convenient to operate the column with a carrier gas flow rate of about 0.1 to about 2.0 liters per minute per square centimeter of column cross- section, preferably from about 0.2 to about 1.0 liters per minute per square centimeter. The column temperature can also be varied widely . with no critical range, although it is generally.limited by the quoted maximum operating temperature of the packing material and by the desire to avoid isomerization of the trans-Δ 9 isomer. Clearly, a shorter contact time will permit the use of a higher temperature in the column, since there will be less time for the product to convert to its isomers. With these considerations in mind, it will be most convenient to operate the column at a temperature within the range of approximately 100°C to approximately 300°C, most preferably from about 150°C to about 260°C. A constant and uniform temperature can be readily maintained by preheating the carrier gas to the same temperature as the column pack¬ ing. The product manifold at the exit of the column should be maintained at approximately the same temperature. The primary considerations here are to prevent condensation of the product components in the manifold and yet to avoid isomerization. The manifold will consist of an array of automatically operated valves directing the gases to any one of a series of condensers where the separated products are - condensed out from the carrier gas. In order to determine the proper timing of the valves, the column exit line can be equipped with any conventional type of chromatograph detec¬ tor to determine the retention times and magnitudes of the peaks. The most useful detectors are those which cause no physical or chemical change in the stream being measured, so that the entire exit stream can be routed through the detec¬ tor. Thermal conductivity detectors are particularly useful in this regard. The detector will enable one to identify the elution times of any particular component as well as the shape and breadth of the peak containing this component. Once this information has been obtained, the collection 5 manifold can be set up with a timer and automatic switching circuit to direct portions of the eluted material as desired to any of a series condensers arranged in parallel to pro¬ vide individual fractions. When peak overlapping occurs on the product peak, recycling a portion of the peak can be 10 beneficial in providing a higher purity product. The optimum portion of the peak for recycle and the amount of that portion will vary with the composition of the original mixture and are readily determined by routine experimenta¬ tion. Condensation of the various components from the 15 carrier gas can be achieved by any conventional condensation technique at any convenient temperature. Due to the high viscosity of the product materials, very low condensation temperatures are best avoided. Once the desired peak or portion of the peak has 20 been selected, and isolated from the effluent of the first column and condensed out from the carrier gas, the resulting material is directed to the second stage of the gas chroma¬ tographic separation. The second column is similar to the first although it is characterized by a liquid phase con- 25 sisting essentially of a silicone oil which is essentially non-phenyl-εubstituted. The oil will thus contain at most minor amounts of phenyl substituents sufficiently low in number that they have little or no effect on the behavior of the oil itself. In place of phenyl εubstituentε, εuitable 30 . oils will ' preferably have polar substituents. Examples . - "' include cyanoalkyl groups, fluorinated alkyl groups, etc. Particularly preferred are alkyl-substituted εilicones where the alkyl groups have a minimum of three carbon atoms and are fully fluorinated from the third carbon outward. There 35 is no critical upper limit on the length of the carbon chain, although as the chain length continues to increase, access of the carrier gas to the liquid phase will begin to diminish. With these conεiderationε in mind, preferred alkyl groups are those with a chain length ranging from three to ten carbon atoms, with three to five carbon atoms particularly preferred. Examples of such alkyl groups are -CH 2 CH 2 CF 3 , -CH 2 CH 2 CF 2 CF 3 , -CH 2 CH 2 CF 2 CF 2 CF 3 , etc. The column diameter and length, type of carrier gas, carrier gas flow rate, and operating temperature, are subject to the same considerations as those expressed above for the first stage. Considerations for the selection of product and recycle fractions are also the same, except that these two fractions will frequently be in the reverse order of that used for the first stage. Product purity can be further enhanced by using multiple passes through each chromatographic separation stage. It will be readily apparent to those skilled in the art that variations in the column packing material, the carrier gas, and the composition of the crude mixture will affect the optimum operating parameters such as the tempera¬ tures of the two columns, the carrier gas flow rate, the column lengths, the recycle portions and sizes, etc. Ana¬ lytical scale columns containing the same packing material are highly useful for the screening of packing material candidateε, since they offer a good approximation of the behavior of a preparative scale column with the same packing material. Analytical scale columns can be obtained from numerous suppliers, while preparative scale columns can be obtained from Elf Aquitaine Development, 9 West 57th Street, New York, New York 10019. Once the final cut is obtained from the second stage of the ^ chromatographic separation, it is hydrolyzed to -convert the eεterified components back to their original hydroxylated form. The reεult will be a composition of a high purity with regard to the trans-Δ 9 iεomer. Hydrolysis can be accomplished by any conventional technique. The variety of reagents and operating conditions which can be used are well within the knowledge of those skilled in the art. Typical reagents include alkali and alkaline earth metal hydroxides, preferably in aqueous solution. Examples are sodium, potaεsium, calcium and barium hydroxides, with sodium hydroxide particularly preferred. In view of its relatively low expense, together with the desirability of achieving a complete hydrolysis in a short amount of time, 5 the hydrolyzing agent is preferably used in large excess, and the hydrolysis reaction iε generally performed in the preεence of a water immiscible solvent. This permits a convenient separation of the product from any unreacted caustic or other hydrolysis agent present as well as from 10 the by-product alkanoic acid, thus enhancing the reaction rate. Suitable solvents include ethers-, ketones, aromatics, hydrocarbons, and chlorinated hydrocarbons. The organic solvents recited above in connection with the esterification reaction are useful examples. 15 Once the hydrolysis has been completed, the product can be recovered from the solvent by any conven¬ tional recovery technique. Distillation will be partic¬ ularly appropriate owing to the large difference in boiling points between the solvents and the product. As in all 20 stages of the process, isomerization of the product and the consequent loss of itε psychotomimetic properties can be minimized by avoiding the use of elevated temperatures. It should be noted, however, that the non-esterified material is more susceptible to isomerization than its esterified 25 counterparts. Thus, preferred temperatures are those fall¬ ing below about 150°C. The type of distillation apparatus which will accomplish this and the pressure under which the column operates will depend on the type of solvent used, and can be readily determined by routine experimentation. 30. The following examples are offered ^ to illustrate the process of the present invention, and are intended neither to limit nor define the invention in any manner. EXAMPLE 1 This example illuεtrateε the preparation, puri- 35 fication, and recovery of (-)-6a,10a-tranε-l-hydroxy-3-n- pentyl-6,6, -trimethyl-6a,7,8,lOa-tetrahydrodibenzo[b,d]- pyran, hereinafter referred to as trans-Δ 9 -tetrahydro- cannabinol or "tranε-Δ 9 -THC," according to the process of the invention, uεing trifluoroacetyl esters. A. Preparation of Synthetic Crude Mixture A 12-liter flask maintained under a nitrogen atmosphere was charged with 8.0 liters of methylene chloride, 720g (4.00mol) of olivetol, 608g (4.00mol) of (+)-cis/trans-p-roentha~2,8-dien-l-ol, and 400g (3.33mol) of anhydrous magnesium sulfate. While the mixture was main¬ tained at a temperature of 0-5 β C by use of an ice-water bath, two portions of freshly distilled boron trifluoride etherate totaling 160ml (1.28mol) wre added as follows: an initial 5-ml portion was added over a period of 10 minutes and an exo-herm was observed up to 12°C, and the remainder was added approximately thirty minutes later when the reac- tion mixture had cooled back down to 5°C. The mixture was then stirred at 0-5°C until analysis by analytical gas chromatography indicated that the reaction was complete (about 3-4 hours). Then 800g (9.25mol) of solid εodiu bicarbonate was added and the resulting mixture was stirred for thirty minutes at 0-5°C. The solids were then filtered off and washed with 1.0 liter of methylene chloride. B. Esterification The solution from above was transferred to a 12 liter flask, cooled to 0-5 β C in an ice-water bath, and treated with 1260g (6.00mol) of trifluoroacetic anhydride over thirty minutes. ' After stirring for 1 hour at 0-5°C, the solution was siphoned over a thirty-minute period into a vigorously stirred mixture of 1600g (16.0mol) of potassium bicarbonate in 5 liters of water in a 5-gal (19-liter) glass bottle. This mixture was stirred vigorously for 1 hour at ambient temperature. The phases were then separated and the aqueous phase was washed with 1.0 liter of methylene chloride. The combined methylene chloride phases were washed with 1.0 liter of water and dried over 400g of anhydrous magnesium sulfate. The magnesium sulfate was filtered off and the methylene chloride was removed under reduced preεεure to give 1.6kg of crude product of which about 40% was the desired trifluoroacetyl (hereinafter referred to as "TFA") derivative of Δ 9 -THC. C. High- and Low-Boiler Removal The crude TFA derivative was "separated from vola¬ tile and non-volatile impurities by double distillation through a 17x2cm Vigreaux column. The product distilled at 160-170°C (head temperature) and 0.3 Torr. The distillation data, with a rough analysis of the fraction collected in this temperature range obtained by analytical gas chroma¬ tography, is shown in Table 1. ' TABLE 1.1 Reduced Pressure Diεtillation of Crude TFA Product gc Assay, Area Percent Distillation Weight, kg Δ 9 -TFA High-Boilers 1 0.85 57.3 14.1 2 0.71 60.1 2.4 The balance of the distillate in each case consisted of isomers and other impurities with boiling points very close to that of Δ 9 -TFA. The final product fraction was a pale yellow liquid and was passed through the industrial scale chromatographic column without further treatment. D. Chromatographic Separation - First Stage The final TFA derivative of the preceding step was diluted with 0.14kg of methylene chloride and the solution passed through a preparative gas chromatography column of the following specifications: TABLE 1.2 First Stage Column Specifications Diameter: 40mm Length: 3.0m ^ y iϊE f Packing: 10% (by weight) 0V-17 - 0 . (a phenylmethyl- silicone of the general formula [OSi(C 6 H 5 )(CH 3 )3 manufactured by Ohio Valley Specialty Co.) on Chromoεorb W HP (a diato ite support manufactured by Johns-Manville Products Corp., Denver, Colorado) Injector Temperature 250°C Column Temperature 245°C Detector (thermal , conductivity) Temperature: 245°C Collector Temperature: • - 160°C Carrier Gas: Helium at 7.5 1/min Column Supplier: Elf A uitaine Development, 9 West 57th St., New York, N.Y. 10019 The eluting material was separated by collection manifold into four fractions and condensed with atmospheric steam. The third fraction was selected as the product fraction and the second was selected for recycle. Each of these frac¬ tions as well as the feedstock mixture was analyzed on a 25 meter by 0.3mm capillary column of fused silica with a 5% phenyl/1% vinyl dimethylsilicone liquid phase designated as SE-54 , obtained from Hewlett-Packard Company, Palo Alto, California (Model 5720A) with a flame ionization detector, to give the following composition: TABLE 1.3 First Stage, First Pass Analysis by Capillary GC . Peak No. and Area Percent • Stream 3 4 5_ 8 _ 10 Feedstock 15.9 2.2 43.1 0.5 6.6 0.4 0.5 Product (Trap 3) 2.9 0.3 2.8 66.9 0.8 0.2 0.4 13.4 1.1 1.1 Recycle (Trap 2) 26.0 0.3 3.5 56.3 1.2 5.1 0.2 From prior use of the same column on mixtures of known composition, the major peaks were identified as fol¬ lows: Peak 1 iεo-TΞC and trans-Δ 8 -THC Peak 3 cis-Δ 9 -THC Peak 4 tranε-Δ 9 -THC and abnormal-iεo-THC Peak 8: abnormal-THC The product (trap 3) fraction shown above was combined with corresponding product fractions from similar runs as well aε product fractions from recycle passes, and then fed back through the same column for a second pass. The capillary column analysis gave the following results: TABLE ' i.4 First Stage, Second Pass Analyisis by Capillary GC Peak No . and Area Percent Stream 1 2 3 4 5_ 6_ 7 _ _ 10 Feedstock 7.3 0.9 5.1 69.2 1.8 0.5 0.2 9.6 1.0 1.4 Product (Trap 3) 0.4 0.4 1.9 71.1 0.4 0.8 0.6 15.2 2.4 2.9 Trap 2 -4.2 1.1 5.0 75.1 1.5 0.2 0.2 9.3 0.9 0.7 E. Chromatographic Separation - Second Stage The product stream from the second pass above was passed through a second stage column of the following specifications: TABLE 1.5 Second Stage Column Specifications Diameter: 40mm Length: 2m Packing: 15% OV-202 ,«" (a trifluoropropylsilicone of the general formula £OSi(CH 3 ) (CH 2 CH 2 CF 3 )3_ manufactured by Ohio Valley Specialty Co.,) on Chromosorb § W HP Injector Temperature 225°C Column Temperature 220°C Detector Temperature: 220 β C Collector Temperature: 160°C Carrier Gas: Helium at 7.5 Ji/ in Column Supplier: Elf Aquitaine Development Four fractions were again collected. This time, however, the second fraction (trap 2) was selected as the product fraction and the third (trap 3) was recycled. Analysis on the capillary column gave the following results: TABLE 1.6 Second Stage, First Pass Analysis by Capillary GC Peak No. and Area Percent Stream 1 2 3 £ ' ' 5. i . 2 £ 2 12 Feedstock 0.4 0.4 1.9 71.1 0.4 0.8 0.6 15.3 2.4 2.9 Product •- (Trap 2) 1.4 0.6 3.1 93.4 - 0.2 - 0.4 - 0.9 Recycle (Trap 3) 0.5 0.4 0.5 69.5 1.1 1.8 0.2 13.1 3.0 7.7 As with the first stage, the product fraction was combined with corresponding product fractions from similar runs and from recycle passes, and then fed back through the same column for a εecond pass to give the following results: TABLE 1.7 Second Stage, Second Pass Analysis by Capillary GC Peak No. . and Areai Percent Stream 1 2 3_ 4 5 6 7 8 9 10 Feedstock 1.3 0.6 2.6 92.8 - 0.3 - 0.6 ( D.2 1.2 Trap 2 2.0 0.6 3.0 93.8 - - - 2.0 0.2 Trap 3 1.0 0.4 0.9 96.2 - - - 0.3 - 0.1 Each of the'two fractions shown above indicate a high purity product. Attempts to do the εame type of sepa- ration using different liquid phases outside the scope of the invention were not as successful. Liquid phases of the type used in thiε example are therefore unique. OMPI F. Hydrolysiε and Product Recovery A 5.0 liter flaεk was charged with 3.0 liters of diethyl ether and 300g (0.732mol) of a product fraction obtained as described in the previous step. To this solu- tion at ambient temperature was added 500ml (l.SOmol) of 3M aqueous εodium hydroxide. This mixture was stirred vigor- ouεly for one hour at ambient temperature. The phaεes were then separated and the ether phase was washed with water (three 500ml portions) until neutral. After drying over MgSO., the ether was removed by rotary evaporation. The tranε-Δ 9 -THC was then distilled in two passes through a wiped-film still to remove any εolventε and non-volatile impurities. The first pass was made at about 110°C and 5-7 Torr to remove solvent and the εecond pass at about 200°C and 0.5-1.0 Torr to distill the Δ 9 -THC. EXAMPLE 2 This example illustrates the use of pentafluoro- propionyl esters of the synthetic crude mixture in gas chromatographic separation. The esterε were prepared and distilled in a manner analogous to that described in Example 1. Although analytical scale packed columns were used rather than preparative scale, the separations achieved give an accurate indication of the separation which will be achieved in a preparative scale unit. The columns were as follows: First stage: 10% OV-17 ® on Chromosorb ® W HP, length 10 feet (3.0m), outer diameter 1/8 inch (3.2mm), carrier gas helium at 28ml/min, temperature 250°C. '* Second stage: 5% A -600 (a cyanoethylmethyl- silicone oil) on Chromosorb W HP, length 6 feet (1.8m), outer diameter 2mm, carrier gas helium at 20ml/min, temperature 180 β C. The following table (Table 2.1) shows the reten- tion times of the various peaks eluting from each of these columns expressed in terms of the "cr value," where α is the ratio of the retention time of the peak (as measured from the solvent peak) to that of the peak correεponding to the tranε-Δ δ component. The SE-54 capillary column of Exam¬ ple 1 iε alεo included to show the compoεition of the crude mixture. TABLE 2.1 Peak Retention Times for Pentaflυoropropionyl Ester Mixture SE-54 * Capillary OV-17 8 AN-600 ® _ Area % .Area % _ Area % . .9900 5 5 .90 26 .88 25 .92 15 . 96 10 1.00 47 1.00 57 1.00 63 1.05 ' 12 1.17 4 11..0088 77 1.20 14 1.21 5 1.12 4 1.51 2 1.31 3 Since a peak separation satisfactory for pre¬ parative purposes is one where all impurity peaks are sepa¬ rated from the product peak by at least a 0.10 difference in σ value, it is clear that the product peak in each case can be properly isolated. EXAMPLE 3 This example illuεtrateε the uεe of heptafluoro- butyryl esters. The esterε were prepared and diεtilled in a manner analogouε to that deεcribed in Example 1. Uεing the εame columnε deεcribed in Example 2, the following results were obtained: TABLE 35.1 Peak Retention Timeε for Heptafluorobutyryl Eεter Mixture SE-54® Capillary OV- -17 β AN-600® Area % Area % or Area % .91 10 .90 43 .88 43 .93 32 - - - .96 4 - - - 1.00 45 1.00 50 1.00 53 1.13 5 1.05 6 1.28 1 - - - 1.31 3 — 1.45 4 Using the columnε in εequence will clearly provide for adequate εeparation. EXAMPLE 4 This example illustrateε the collection and analysis of discrete fractions from packed columns using the same heptafluorobutyryl 1 esters used in Example 3. Columns representing each of the two stages were used, each column measuring 10 feet (3.05m) in length and 1/8 inch (0.32cm) in outer diameter. Each column was equipped with a thermal conductivity detector in whose output line the eluting material condensed. Samples of the condensate were taken with a capillary-size collection tube over discrete periods of time designated as ranges of α-values. Each of these samples was then analyzed on the SE-54 capillary column used in the previous examples. A. First Stage Column A column with OV-17 packing was operated at 250°C with helium as the carrier gas at a flow rate of 15ml/min. Four fractions were collected, at c-value ranges of <.88, .88-.95, .96-1.02, and 1.04-1.10 (measured with respect to the trans-Δ 9 peak). Capillary column analyεeε of each of theεe fractionε are shown in Table 4.1. With thiε informa- tion plus the chromatogram trace from the thermal conductiv- ity detector on the OV-17 column, α-values for each of the mixture components were determined. These are also shown in the table. All α values refer to the chromatogram trace from the OV-17 column, and all area percents refer to the 5 chromatogram trace from the capillary column. TABLE 4.1 Heptafluorobutyryl Ester Separation on OV-17 a ranges of fractions: Fraction A: < .88 0 Fraction B: .88-.95 Fraction C: -.96-1.02 Fraction D: 1.04-1.10 Area Percents by Capillary GC α Value on Component Feed A B C D OV-17 abn-iso 12 4 19 3 5 >.88 iso 19 50 35 - 8 <.88 abn 11 1 - - 17 1.05 cis-Δ 9 2 - 2 8 5 -1.0 trans-Δ 8 12 37 35 3 9 .88 trans-Δ 9 31 4 3 82 50 1.0 dimers 6 - - - - >1.3 dimers 6 — _ — — >1.3 It iε clear from the above that all components except the abnormal and cis-Δ 9 iεomers are adequately εepa- rated (by "adequate separation" iε intended a separation with an r value removed from the product peak by approxi¬ mately 0.10 or greater). The following section demonstrates that these two iεomerε are readily separated in the second - .- • stage. B. Second Stage Column A column with OV-210 packing (a 10% trifluoro- propylεilicone on Chromoεorb W HP) waε operated at 225°C with helium aε the carrier gas at a flow rate of 20ml/min. Three fractions were collected and analyzed on the capillary column, and or values were determined as in the first stage. The results are shown in Table 4.2. TABLE 4.2 • Heptafluorobutyryl Ester Separate .on on OV-210 cr Ranges of Fractions: Fraction A: .87-. 92 Fraction B: .99-1 .01 - Fraction C: 1.05-1 .30 Area Percents by Capillary GC a Value on Component Feed A B C OV-210 abn-iso 11 - 2 ' 77 1.2 iso 18 46 - 6 .88 abn 10 - 3 - 1.4 cis-Δ 9 1 4 - - -.9 trans-Δ 8 13 7 - 4 .91 trans-Δ 9 35 40 89 9 1.0 It iε clear from thiε table that iεomerε which are not adequately εeparated from the trans-Δ 9 peak in the first stage will be adequately εeparated on thiε column. To further show the efficacy of this type of liquid phase in the εecond stage column packing, an addi¬ tional liquid phase outside the scope of the present inven¬ tion waε used. Thiε material is designated OV-225, and is a phenylcyanopropylsilicone of the general formula [OSi(C 6 H 5 )(CH 3 )] I1 [OSi(CH 3 )(CH 2 CH 2 CH 2 CN)3 11 on Chromosorb W AW support (10% by weight). The latter is another diatomite support similar to Chromosorb W HP. The operating condi- - tionε were otherwise identical to those used on the OV-210, except that four fractions were taken rather than three. The results are shown in Table 4.3. TABLE 4.3 He tafluorob tyry1 Ester Separation on OV-225 cr ranges of fractions: Fraction A: .84-.90 Fraction B: .99-1.01 Fraction C: 1.04-1.08 Fraction D: 1.10-1.30 Area Percents by Capillary GC cr Value on Component Feed A B C D OV-225 abn-iso 11 80 4 1.06 iso 18 55 1 - .86 abn 10 3 ' ; .. - 89 1.22 cis-Δ 9 1 1 - - <1.00 ^ trans-Δ 8 13 39 - - .86 trans-Δ 9 35 4 87 3 2 1.00 Clearly, the separation of cis-Δ 9 isomer from the product peak is inadequate. It is also clear that the εeparations of both the abn and abn-iso peaks from the product peak are inferior. The trifluoropropyl silicone is clearly a superior liquid phase for the second stage.

Claims: WE CLAIM: 1. A process for the isolation of a compound of the formula: in which R iε hydrogen or C.-C 10 alkyl from a crude εyn- thetic mixture, compriεing the εteps of: .a) esterifying at least a portion of the com- ponents of said mixture to form perfluorinated alkanoic acid esterε thereof, (b) removing low-boiling components and non¬ volatile components from said mixture, (c) paεεing εaid mixture through a first pre- parative gas chromatographic column containing a packing consisting essentially of a slightly polar phenyl-substi¬ tuted silicone oil on a porous, inert solid support to separate εaid mixture into a plurality of εubεtantially diεcrete portionε, and recovering therefrom the portion containing the higheεt proportion of the perfluorinated alkanoic acid eεter of said compound, or a substantial fraction of said portion, (d) passing εaid recovered portion or fraction through a εecond preparative gaε chromatographic column containing a packing conεiεting eεεentially of a non- phenyl-εubεtituted εilicone oil on a porous, inert solid support to further separate said portion or fraction into a plurality of εubεtantially diεcrete subportionε, and recovering therefrom the subportion containing the higheεt proportion of the perfluorinated alkanoic acid eεter of εaid compound, or a subεtantial εubfraction of εaid subportion, (e) hydrolyzing εaid recovered subportion or εubfraction to convert the perfluorinated alkanoic ester moieties contained therein to hydroxyl groups, and (f) recovering εaid compound from εaid hydrolyzed εubportion or εubfraction. 2. A process according to claim 1 in which R is C.-C ; . 0 alkyl and occupies the meta-position relative to the hydroxyl group. 3. A process according to claim 1 in which R is n-pentyl and occupies the meta-position relative to the hydroxyl group. 4. A procesε according to claims 1, 2, or 3 in which the crude synthetic mixture is obtained by reacting an appropriately substituted resorcinol with (+)-p-mentha-2,8- dien-1-ol in the presence of a catalytic amount of a Lewis acid catalyst and an excess of a non-alkaline dehydrating agent, at a temperature of from about -20°C to about +25°C. 5. A process according to claims 1, 2, or 3 in which, the crude synthetic mixture is obtained by reacting 5-n-pentyl-resorcinol with (+)-p-mentha-2,8-dien-l-ol in the presence of a catalytic amount of boron trifluoride etherate and an excesε of anhydrouε magnesium sulfate, at a tempera¬ ture of from about -5°C to about +5°C, in the presence of an inert chlorinated hydrocarbon solvent. ' . 6. A process according to claims 1, 2, or 3 in which step (a) iε accomplished by treating the crude syn¬ thetic mixture with an exceεε of a member εelected from the group consisting of an acid anhydride, an acid halide, and an acyl imidazole of a perfluorinated alkanoic acid of from 2 to 6 carbon atoms, at a temperature of from about -20°C to about +25°C. OMPI " 7. A procesε according to claims 1, 2, or 3 in which step (a) iε accompliεhed by treating the crude syn¬ thetic mixture with at least a 50% excess of trifluoroacetic acid anhydride at a temperature of from about 0°C to about 10 β C in the presence of an inert chlorinated hydrocarbon solvent. 8. A process according to claims 1, 2, or 3 in which step (b) is accompliεhed by diεtilling εaid mixture at a temperature below about 250°C and a pressure below about 0.1 Torr. 9. A process according to claims 1, 2, or 3 in which step' (b) is accomplished by distilling said mixture at a temperature of from about 180 β C to about 220°C and a pressure of from about 0.005 to about 0.05 Torr. 10. A process according to claims ,1, 2, or 3 in which the packing of step (c) consiεtε eεεentially of a phenyl ethylsilicone on an acid-washed εilanized diatomite support, and occupies a space with a diameter of up to about 600mm and a height of from about 0.5m to about 6.0m, and the column is operated at a temperature of from about 100°C to about 300°C with a carrier gas flow rate of from about 0.1 tb about 2.0 liters per minute per square centimeter of column cross-section. 11. A process according to claims 1, 2 or 3 in which the packing of step (c) consiεtε eεεentially of a - . phenylmethylεilicone on an acid-waεhed εilanized diatomite εupport, and occupieε a space with a diameter of from about 20mm to about 250mm and a height of from about 1.0m to about 4.0m, and the column iε operated at a temperature of from about 150°C to about 260 β C with a carrier gas flow rate of from about 0.2 to about 1.0 literε per minute per εquare centimeter of column croεε-εection, and with a carrier gas selected from the group consisting of nitrogen, carbon dioxide, hydrogen, and helium. OMPI 12. A process according to claims 1, 2, or 3 in which the packing of step (d) consiεtε eεsentially of a member selected from the group conεiεting of cyanoalkyl εiliconeε and fluorinated alkyl εiliconeε on an acid-washed εilanized diatomite support, and occupies a space with a diameter of up to about 600mm and a height of from about 0.5m to about 6.0m, and the column iε operated at a tempera¬ ture of from about 100°C to about 300°C with a carrier gas flow rate of from about 0.1 to about 2.0 literε per minute per square centimeter of column cross-section. 13. A proceεε according to claims 1, 2, or 3 in which the packing of step (d) consiεtε eεsentially of C 3 -C 1Q alkyl εubεt ' ituted εilicones in which the alkyl groups are fully fluorinated from the third carbon outward, on an acid-washed εilanized diatomite support, and said packing occupies a space with a diameter of from about 20mm to about 250mm and a height of from about 1.0m to about 4.0m, and the column is operated at a temperature of from about 150°C to about 230°C with a carrier gas flow rate of from about 0.2 to about 1.0 liters per minute per square centimeter of column cross-section, and a carrier gaε εelected from the group conεisting of nitrogen, carbon dioxide, hydrogen, and helium. 14. A procesε according to claims 1, 2, or 3 in which the packing of step (c) consiεtε eεsentially of a phenylmethylsilicone on an acid-waεhed silanized diatomite support, and occupies a space with a diameter of from about 20mm to about 250mm and a height of from about 2.0m to about 4.0m, and the column iε operated at a temperature of from about 150°C to about 260°C, with helium aε the carrier gas at a flow rate of from about 0.2 to about 1.0 liters per minute per square centimeter of column cross-section; and the packing of step (d) conεiεtε eεsentially of a methyl- 3,3,3-trifluoropropylεilicone on an acid-waεhed silanized diatomite support, and occupies a space with a diameter of from about 20mm to -about 250mm and a height of from about OMP 1.0m to about 4.0m, and the column iε operated at a tempera¬ ture of from about 150*0 to about 230*0, with helium as the carrier gas at a flow rate of from about 0.2 to about 1.0 liters per minute per square centimeter of column cross-section. 15. A process according to claims 1, 2, or 3 in which step (e) accomplished by treating said recovered εubportion or εubfraction with an aqueouε εolution of an alkali or alkaline earth metal hydroxide in the presence of a water-immiscible solvent. 16. A process according to claims 1, 2, or 3 in which step (e) iε accomplished by treating said recovered subportion or subfraction with an excess of an aqueous εolution of εodium hydroxide in the preεence of diethyl ether.

Inventors: BACKLUND STEPHEN J, OLSEN ROBERT E, BACKLUND, STEPHEN, J., OLSEN, ROBERT, E.
Applicants: AEROJET GENERAL CO, AEROJET-GENERAL CORPORATION
Application year: 1982
Main classification: C07D311
IPC codes: C07D311