Patent Application: US-17896298-D

Abstract:
a method of preparing tetrahydrocannabinol using extraction of plant material with a non - polar solvent followed by vacuum distillation and collection of a constant boiling fraction . additional distillation steps and chromatographic steps , including hplc reversed phase hplc and flash chromatography , may be performed .

Description:
the present invention relates to a process for providing an efficient and economic method for isolating thc from cannabis plant material . the plant material is extracted with a non - polar organic solvent . useful solvents include lower alkanes , such as , for example , hexane , heptane or iso - octane . the extract containing thc , after solvent removal , is subjected to fractional distillation under reduced pressure and a first distillate is collected . in one embodiment of the present invention , the first distillate is again subjected to fractional distillation at reduced pressure and a second distillate is collected . the second distillate has a thc content of greater than 90 % by wt . in another embodiment of the invention the crude extract from the plant material is first subjected to column chromatography . one possible method by which the material can be placed on the column is by mixing the extract residue in an organic solvent with a portion of the column packing material and transferring the dried slurry onto the top of a packed column . direct application of the extract residue in the initial elution solvent ( minimum volume ) directly to the top of the packed column is also possible . the column is eluted with an organic solvent in a manner such that the column is eluted with a solvent or a solvent mixture with progressively increasing polarity . the fraction or fractions containing the major portion of thc from the column elution is subjected to fractional distillation at reduced pressure . distillate is collected in the substantially constant boiling temperature range and this distillate was found to contain greater than 90 % by weight thc . thc with purity of greater than 95 %, preferably greater than 98 % can be obtained by further purification of the distillate from the fractional distillation by column chromatography or by normal or reversed phase hplc . the column chromatography can be carried out using any known packing material including , for example , silica or alumina for normal phase operation or c 18 or c 8 bonded phase silica for reversed phase operation . elution of the normal phase chromatography column is carried out with solvents having an increasing polarity . non - polar solvents include the lower straight chain and branched chain alkanes , including , for example , pentane , hexane , isooctane and petroleum ether . more polar solvents include various organic ethers , alcohols , esters or ketones , including , for example dialkyl ethers , lower alkyl acetates , lower dialkyl ketones and lower alkanols . illustrative polar solvents include , for example , acetone , ethylacetate , diethylether and isopropyl alcohol . the ratio of non - polar solvent to polar solvent can vary between 100 : 0 to 80 : 20 . elution chromatography under the reversed phase conditions is carried out with solvents having decreasing polarities . these solvents include water or acidic buffer as the polar portion and lower alkanol ( such as methanol , ethanol and isopropanol ) or acetonitrile as the less polar portion , in mixtures ranging from 50 : 50 to 0 : 100 aqueous to organic . the chromatographic process can also be carried out under hplc conditions in much the same way as described above under either normal or reversed phase operation using a preparative scale column . flash distillation is carried out under reduced pressure , i . e . under vacuum at pressures below 1 mm hg , preferably close to 0 . 1 mm hg . it will be understood by those skilled in the art that various modifications and substitutions may be made to the invention as described above without departing from the spirit and scope of the invention . accordingly , it is understood that the present invention has been described by way of illustration and not limitation . 200 g of the air - dried and powdered buds ( 7 . 82 % thc ) and 270 g of the air - dried and powdered buds ( 6 . 61 % thc ) were mixed and extracted by maceration at room temperature with hexane for 24 hours ( 2 . 2 l hexane × 4 ). the hexane extracts were combined and evaporated under vacuo to give 76 . 5 g ( 16 . 3 % extractives ). 56 g of the hexane extract ( 40 % thc ) was mixed with 100 g silica gel ( silica gel 60 , e . merck ) and 50 ml hexane . the dried slurry was transferred onto the top of a silica gel column ( 850 g silica gel 60 , dimensions : 10 × 60 cm ). elution was carried out with petroleum ether and ether in a manner of increasing polarities . twelve fractions were collected and tlc screened . identical fractions were pooled together . the fraction eluted with pet . ether - ether ( 9 : 1 ) was evaporated to give 37 . 3g of residue which showed thc content of 55 . 87 % using gas chromatography ( gc ) analysis . this fraction contained the majority of thc ( 93 %) in the material applied onto the column . a portion ( 7 . 1 g ) of the collected fraction was subjected to fractional distillation under vacuum ( between 0 . 08 - 0 . 1 mmhg ) to get two major fractions , one collected between 170 - 175 ° c . ( 2 . 34 g @ 90 % thc ) and one between 175 - 180 ° c . ( 1 . 32 g @ 88 . 2 % thc ). the air - dried and powdered buds ( 380g , 2 . 20 % thc ) were extracted with hexane by maceration at room temperature for 24 hours ( 1 . 8 l hexane x 3 ). the total weight of the hexane extracts was 29 . 1 g ( 7 . 7 % extractives ). the % of thc in the hexane extract was 28 . 76 %. the hexane extract ( 29 . 1 g ) was mixed with 100 g of silica gel ( silica gel 60 , e . merck ) and 50 ml hexane . the dried slurry was transferred on to the top of silica gel column ( 850 g silica gel 60 , dimensions : 10 × 60 cm ). elution was carried out with petroleum ether - ether mixtures in a manner of increasing polarities . nine fractions were collected and tlc screened . identical fractions were pooled together to give 4 fractions . the fraction collected with petroleum ether - ether ( 9 : 1 ) was evaporated to yield 13 . 3g of residue . gc analysis of this fraction showed a concentration of thc of 58 . 98 %, again representing & gt ; 93 % recovery of all thc in the material applied to the column . a portion ( 7 . 3 g ) of the fraction collected above was subjected to fractional distillation at vacuum ( 0 . 08 - 0 . 1 . mmhg ). the major fraction ( 3 . 738 g ) was collected between 172 - 180 ° c . and was found to contain 89 % thc by weight . one kg of the fine powdered marijuana plant material [ average % of thc was about 5 . 21 %] was macerated with 6l hexanes ( hexanes gr from em sciences ) in a percolator ( 9 ″ in diameter from the top and 20 ″ long , cone shaped ) for 24 hours at room temperature and filtered . the macerate was reextracted with 5l hexanes for another 24 hours . the hexane extracts were combined and evaporated under reduced pressure at low temperature to give 110 . 7 g residue ( 11 . 07 % extractives ). the % of thc in the hexane extract was 41 . 21 %. the hexane extract ( 110 . 7 g ) was mixed with 150 g silica gel ( silica gel 60 , art .# 9385 - 3 ) and 50 ml hexane . the air dried slurry was transferred to the top of a silica gel column ( 800 g silica gel 60 , particle size 0 . 04 - 0 . 063 mm , from em science , art . # 9385 - 3 ). the column was eluted with hexane : ether mixtures in a manner of increasing polarities . fractions were collected and tlc screened ( analytical silica gel plates , developing system : hexane : ether ( 80 : 20 ), visualizing agent : fast blue ). the fractions collected with hexane ( 3 l .) and hexane - ether ( 95 : 5 , 2 l .) were discarded . the following fractions collected with hexane - ether ( 95 : 5 , 3 l .) and hexane - ether ( 9 : 1 , 5 l .) were combined and evaporated to yield 77 . 2 g of residue . gc analysis of the residue showed thc concentration to be 54 . 74 %. a portion ( 30 . 5 g ) of the residue collected above was subjected to fractional distillation under reduced pressure ( 0 . 1 - 0 . 15 mm / hg ). the temperature was slowly raised to 125 ° c . and the materials collected were kept separate . the temperature was then raised between 140 - 160 ° c . where the major fraction was collected ( 14 g ). gc analysis showed & gt ; 96 % thc . one kg of the fine powdered marijuana plant material [ average % of thc is 4 . 42 ] was macerated with 6 l hexanes and extracted by the same procedure followed in example 3 to yield 105 . 8 g residue ( 10 . 58 % extractives ). the % of thc in the hexane extract was 40 . 35 % by gc analysis . a portion ( 23 . 0 g ) of the hexane extract was subjected to fractional distillation under reduced pressure ( vacuum , 0 . 1 - 0 . 2 mm / hg ). the temperature was raised slowly to 160 ° c . where a small amount of material (& lt ; 1 g ) was collected and left separate . the major fraction ( 10 . 1 g ) was collected between 170 and 180 ° c . gc analysis of this fraction showed 72 . 66 % thc concentration . a second portion ( 25 . 0 g ) of the hexane extract was subjected to fractional distillation under similar conditions as the first portion . the major fraction collected between 170 - 180 ° c . weighed 11 . 6 g and had a thc concentration of 73 . 62 %. a third portion ( 25 . 0 g ) of the hexane extract was subjected to fractional distillation under similar conditions to the previous portions . the major fraction containing thc weighed 10 . 2 g and had a thc concentration of 73 . 72 %. the three major fractions obtained from the above three distillations were combined and analyzed . the analysis showed the concentration of thc to be 70 . 31 %. the mixture ( 28 . 9 g ) was subjected to fractional distillation , again under similar conditions . the temperature was raised slowly to 135 ° c . under vacuum ( 0 . 1 - 0 . 15 mmhg ) and the fractions collected were kept aside . the major thc containing fraction was collected at 140 - 160 ° c . and 0 . 05 - 0 . 06 mm / hg . the fraction weight was 18 . 4 g and the thc content was 92 . 15 %. a portion ( 0 . 8 g ) of the pure thc obtained in example no . 3 (% of thc was about 96 %) was mixed with one gram silica gel ( silica gel 60 ) and one ml hexane . the dried slurry was transferred on to the top of a silica gel column ( 12 silica gel 60 , dimensions : 1 × 50 cm ). elution was carried out with hexane : ether mixtures in a manner of increasing polarities . six fractions were collected and screened using tlc . fraction nos . 3 - 5 ( hexane : ether 98 : 2 ) were combined and yielded 0 . 63 g of residue (% of thc was 98 %). one gram of the thc prepared in example no . 4 ( purity was about 92 %) was mixed with one gram of silica gel ( silica gel 60 ) and one ml hexane . the dried slurry was transferred on to the top of a silica gel column ( 13 g silica gel 60 , dimensions : 1 × 50 cm ). elution was carried out under similar conditions as under example 5 . fraction nos . 3 - 5 yielded 0 . 78 g of residue (% of thc was 98 %). 1000 g of the air - dried and powdered cannabis buds % of thc by glc analysis was 6 . 49 %) were extracted by maceration at room temperature for 24 hours ( 5l × 3 , lot . no . 970424 ). the hexane extracts were combined and evaporated under vacuo to give 97 g residue . 67 g of the hexane extract was dissolved in 200 ml isooctane ( lot . no . 904038 ) and the solution was transferred onto the top of a silica gel column ( 280 g silica gel , 40 μm particle size , dimensions of column : 10 × 60 cm ). the column was eluted with iso - octane : methyl - t - butyl ether mixture 8 : 2 ( 3l , fraction 1 ) and then washed with methanol ( 1 l , fraction 2 ). glc analysis of fraction 1 ( 53 g ) showed a concentration of thc of 55 . 56 %. fraction 1 ( 53g ) was subjected to fractional distillation at vacuum 0 . 1 - 0 . 6 mm / hg . the major fraction ( 20 . 0 g ) was collected between 160 - 170 ° c . and was found to contain 94 % thc by weight . 10 g of the major fraction ( purity about 94 %) was purified on hplc ( water delta prep 4000 ) connected to a waters 486 tunable absorbance detector and using column prep pak500 / silica . the eluent was iso - octane : methyl - t - butyl ether mixture ( 98 : 2 ). the flow rate was programmed to be 10 ml / minute for 10 minutes , 25 ml / minute for 60 minutes and finally 50 ml / minute for 200 minutes . time volume analysis fractions ( minutes ) ( ml ) weight ( g ) for thc 1 22 - 43 600 trace 2 67 - 72 300 0 . 3 g 3 72 - 74 100 0 . 9 g 4 74 - 81 450 2 . 7 g 96 . 6 % 5 81 - 97 800 4 . 0 g 99 . 0 % 6 97 - 100 1200 1 . 9 g 97 . 5 % purification of thc prepared by fractional distillation using flash column chromatography 2 . 1 g of thc ( 91 % purity ) were dissolved in 10 ml isooctane and the solution was transferred onto the top of a silica gel column ( 30 g silica gel , 40 μm particle size ; dimensions of the column : 2 . 5 cm × 40 cm ). the column was eluted with isooctane then a mixture of isooctane - acetone ( 99 : 1 ). seven fractions were collected and analyzed by glc . isooctane - acetone ( 99 : 1 ) fractions containing the bulk of the thc were contained and yielded 1 . 84 g of residue (% of thc was 97 %). 1 g of thc ( 91 % purity ) was dissolved in 5 ml isooctane and the solution was transferred onto the top of a silica gel column ( 15 g silica gel , 40 μm particle size , dimensions : 2 . 5 cm × 40 cm ). the column was eluted with isooctane - ethyl acetate mixture in a manner of increasing polarities and the fractions were collated . fraction no . 5 ( eluted with isooctane - ethylacetate 98 : 2 ) yielded 0 . 56 g of residue (% of thc was 97 %). fraction no . 4 ( eluted with iso - octane - ethylacetate 98 . 5 : 1 . 5 ) yield 0 . 32 g of residue (% of thc was 94 . 9 %). 1 . 1 g of thc ( 91 % purity ) was dissolved in 5 ml isooctane and the solution was transferred onto the top of a silica gel column ( 15 g silica gel , 40 μm particle size , dimensions : 2 . 5 cm × 40 cm ). the column was eluted with a mixture of isooctane : isopropyl alcohol in a manner of increasing polarities . five fractions were collected . fraction nos . 4 and 5 ( eluted with iso - octane - isopropyl alcohol ( 98 : 2 and 95 : 5 , respectively ) were combined and yielded lg of residue (% of thc was 94 %). 9 . 6 g of thc ( purity 92 . 8 %) was purified on hplc ( water delta prep 4000 ) connected to waters 486 tunable absorbance detector ( wave length used : 254 nm ) and using column prep pak c18 ( from waters , dimensions 46 mm × 30 cm , 55 - 105 , μm , lot no . t 72852 ). the eluent was a mixture of methanol : water ( 75 : 25 ). the flow rate was programmed to be 10 ml / minute for 10 minutes , 25 ml / minute for 50 minutes and finally 50 ml / minute for 140 minutes . the results are summarized in the following table : time volume weight analysis for fraction ( minutes ) ( ml ) ( g ) thc 1 69 - 96 1400 0 . 10 2 96 - 105 500 0 . 34 3 105 - 123 1000 6 . 00 99 % 4 123 - 135 600 1 . 98 98 % 5 135 - 155 1000 1 . 00 95 % 6 174 - 180 300 0 . 10 1 . thc can be prepared directly from a hexane extract of cannabis sativa l . by double fractional distillation . the purity of thc by glc analysis is about 90 - 92 %. further purification on a silica gel column gives thc with approximately 98 % purity . 2 . thc can be prepared directly from a hexane extract of cannabis sativa l . by column chromatography ( silica gel ) followed by fractional distillation . the purity of thc is about 95 - 96 %. further purification on a silica gel column gives thc with at least 98 % purity . 1 . elsohly , m . a . ; 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