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description=3 posts published by milkshake during September 2010;

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september, 2010, org, prep, daily, 29, 17, 15, oxindole, carboxylic, acid, carboxy, dimethylpyrrole, carboxaldehyde, knorr, pyrrole, synthesis,

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september 2010 org prep daily org prep daily september 29 2010 oxindole 5 carboxylic acid filed under procedures milkshake 12 42 pm indole 5 carboxylic acid 5 00g combiblocks 31 0 mmol solution in ethanol 99 120ml and tert butanol 180ml in a 1l rb flask was cooled on ice bath to 5 c meanwhile a solution of lithium bromide 9 0g 103 6 mmol in neat acetic acid 60ml was placed into an addition funnel neat bromine 5 0ml 16 0g 100 1 mmol was then charged to this libr solution and the addition funnel was briefly swirled by hand to mix the reagents the resulting bromine libr solution was dropwise added into the vigorously stirred indolecarboxylic acid solution at 5 c over a 90 min period after a complete addition the addition funnel was then washed with etoh 2 x 5 ml and the washings were added to the reaction mix at the end of the bromine addition the cooling bath was let to expire and the reaction mix was stirred at 5 to 15 c bath for 1 hour and at 15 c for additional 15 min the reaction mixture was then diluted with additional acetic acid 100ml zn dust 20g aldrich 10 micron 306 mmol was added in one portion gas evolution and the mixture was stirred in an open flask on ambient water bath overnight 16 hours the next day the precipitated solids were collected by filtration washed with ethanol and dried by suction the solid containing a mix of the product unreacted zn metal and zn salts was transferred into a large beaker on a hotplate suspended in boiling methanol 300ml and filtered the extraction with boiling methanol was repeated twice more to separate the unreacted zn metal from the product the combined methanolic filtrates were evaporated to dryness separately the acetic acid libr containing filtrates from the reaction mix were concentrated to a small volume on rotovap and the produced salt rich residue was diluted with water 0 6l and acidified with 6m hcl to about ph 1 5 this mixture was then combined with the evaporation residue obtained from the methanolic filtrates the solids in the flask were re suspended by a brief sonication 5 min and the slurry was cooled down on ice bath then placed into a freezer 20c for 4 hours the precipitated product was collected by filtration washed with ice cold water dried by suction and on highvac y 5 23g 95 of a light tan solid 1h d6 dmso 400mhz 12 58 br s 1h 10 72 s 1h 7 82 dd 8 3hz 1 6hz 1h 7 75 s 1h 6 88 d 8 3hz 1h 3 54 s 2h note skin contact with bromine produces excruciating burns heavy duty protective gloves with extended sleeves are required make sure that the used syringe does not leak work in the hood do not wash bromine contaminated glassware with acetone use water or alcohol comments 28 september 17 2010 4 carboxy 3 5 dimethylpyrrole 2 carboxaldehyde filed under procedures milkshake 7 27 pm 4 carbethoxy 3 5 dimethylpyrrole 2 carboxylic acid tert bu ester 16 35g was dissolved in neat trifluoroacetic acid 85 ml and the solution was stirred at room temperature for 30 min the mix turned burgundy red with gas evolution note 1 then cooled to 5 c on ice water bath neat triethyl orthoformate 16 5 ml 1 6 eq was added and the mix was stirred at 5 c for 35 min then concentrated on rotovap from ambient water bath to a small volume the residue was diluted gradually with water addition 300ml the resulting slurry was shaken for 5 min and the precipitated ethyl ester intermediate was collected by filtration washed thoroughly with water and dried by suction this intermediate ethyl ester was suspended in ethanol 150 ml placed on a 120 c oil bath and stirred to complete dissolution a solution of koh 20g pellets 85 in water 200ml was then added to the mix the flask was equipped with a short path distillation adaptor and the reaction mixture was distilled under a stream of nitrogen gas on a 120c oil bath for 90 min only water distilled at this point and the ethyl ester hydrolysis was complete by hplc note 2 the reaction mixture was cooled charcoal 5 spoons was added and the reaction mix was then stirred on ambient water bath for 30 min and filtered the charcoal was thoroughly washed on buchner funnel with water the combined filtrates were acidified with addition of 6m hcl the precipitated product was collected by filtration on a large buchner funnel washed thoroughly with water and semi dried by suction note 3 the crude product was dissolved in etoh 900ml at reflux the solution was allowed to crystallize at ambient temperature overnight 14 hours the product was collected by filtration washed with etoh dried by suction and on highvac concentrating the supernatants to a small volume but not to dryness diluting the slurry with ethanol 100ml and refluxing the mix for 30 min then letting the mix to crystallize at rt overnight provided a second crop of a pure product the combined yield was 8 32g 81 th overall y of a light tan crystalline solid 1h d6 dmso 400mhz 12 12 s 1h 12 10 very br s 1h 9 61 s 1h 2 46 s 3h 2 42 s 3h note 1 the original procedure calls for the tbu ester deprotection acid promoted decarboxylation to be performed at 45c 15 min in my hands running this step at ambient temperature 23 c for 30 min provided a cleaner reaction mixture and a less colorful final product note 2 performing the hydrolysis under a nitrogen blanket seems to improve the final product purity also 3 5 dimethylpyrrole 4 carboxylic acids esters are rather sluggish to hydrolyze probably because of the steric hinderance and pyrrole nh deprotonation distilling ethanol from the reaction mixture accelerates the hydrolysis by increasing the mixture boiling point note 3 the crude material is static and rather hard to crush when completely dry it is best handled moist comments 6 september 15 2010 knorr pyrrole synthesis filed under procedures milkshake 1 31 pm a solution of tert butyl acetoacetate 31 65g 200mmol in acetic acid 40 ml was cooled on ice bath to 5c and a solution of nano2 14 00g 1 eq in water 20ml was injected slowly under the level of the reaction mix with cooling and vigorous stirring over a 20 min period so that the internal temperature did not exceed 15c the syringe was washed with water 2 x 3 ml and the washings also added to the mix the reaction mix was stirred on melting ice bath to rt in an open flask overnight 16 hours separately in a 3 necked 1l round bottom flask with a large egg shaped stirbar and internal thermometer and an addition funnel anhydrous sodium acetate 20g and ethyl acetoacetate 29 0g 1 1 eq were dissolved in acetic acid 100ml on a 60c oil bath with vigorous stirring zn dust 10g aldrich 10micrometer was then added followed by dropwise addition of the nitrosated mixture from tbu acetoacetate and sodium nitrite this addition was carried out over a 45 min period while an additional zn dust 40g was simultaneously added to the mix in approx 5 g portions few minutes apart each zn addition was accompanied by a temperature spike the internal temperature in the flask was kept below 85c the bath temperature was 60c and the the internal temperature in the flask was controlled by the rate of addition of zn dust and the nitrosation mix the total quantity of used zn dust was 50g at the end the addition funnel was washed with additional acetic acid 3 x 10 ml and this was added to the mix and continued for 1 more hour at 60c the resulting foamy reaction mixture was finally diluted by addition of water 100ml and the mixture was stirred for one more hour at 60c the reaction mix was then poured into a large beaker diluted with water 0 5l some crushed ice was added total mix volume was 1 5l and the slurry was placed on ice bath and stirred for 1 hour the precipitate was collected by filtration washed thoroughly with water and dried by suction the obtained crude product was dissolved in a 1 1 mix of ethanol ethyl acetate 0 5l with gentle heating the solution was filtered from the leftover zn dust zn washed with etoac on buchner and the filtrates were evaporated to dryness the solid residue was suspended in acetonitrile 60ml and the slurry was placed into a freezer 20c overnight the precipitate was collected by filtration washed with cold acetonitrile dried by suction and on highvac y 35 55g 66 5 of a white sugar like crystalline solid 1h cdcl3 400mhz 8 93 br s 1h 4 29 q 7 1hz 2h 2 53 s 3h 2 50 s 3h 1 57 s 9h 1 36 t 7 1hz 3h note there were couple more grams of the product left in the supernatants that could be likely isolated on a column or doing a fractional crystallization from mecn but it was not worth the trouble comments 5 pages about milkshake about org prep daily bug report chemistry resources chemistry chemjobber in the pipeline med chemist open flask org chem portal practical fragments stellen fuer chemiker edible links serious eats links to behold idle words categories chris douglas industry life krest17 lab destruction lit highlights mechanisms procedures questions uncategorized search archives january 2026 december 2025 november 2025 october 2025 september 2025 april 2019 march 2019 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