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description=2 posts published by milkshake during February 2008;

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february 2008 org prep daily org prep daily february 24 2008 arnold salt filed under procedures milkshake 5 33 pm anhydrous dmf 160ml in a 0 5l round flask was cooled on ice bath and neat pocl3 40 ml 436mmol was added greadually over 10 min period exothermic the mixture was warmed up to rt bromoacetic acid solid 19 00g 136 7 mmol aldrich 99 was added quickly in one portion hygroscopic wear gloves bromoacetic acid and pocl3 are nasty the flask was equipped with a reflux condenser and the mixture was stirred under ar on oil bath at 90c for 9 hours the mixture turned orange with a slow co2 evolution the mixture was cooled to rt dmf was distilled out on highvac rt to 90c at 0 5 torr and the obtained thick residue was treated with ice cold water 100ml on a sonicator bath an exothermic hydrolysis commenced when all residue dissolved and the mixture cooled to rt solid sodium hexafluorophosphate 46 2g 275 mmol was added in one portion followed by some additional water 50 ml the mixture was shaken vigorously for 10 min the precipitated product was collected using a large buchner funnel the solid cake was compressed on the frit washed with ice cold water 5x20ml dried by suction and then on highvac y 61 05g 94 of a yellowish white solid 1h d6 dmso 400mhz 8 439 s 3h 3 535 s 9h 3 376 s 9h note 1 the formylation is complete in 6 hours at 90c kpf6 is probably a better source of hexafluorophosphate because unlike the sodium salt it does not hydrolyse readily does not etch glass and is non hygroscopic aqueous hpf6 can be also used it is important to remove most dmf from the reaction mixture this takes some time i used a rotovap hooked to oil pump note 2 the product can be re crystallised to analytical purity from mecn some antisolvent thf but the crude material is suitable for most purposes note 3 bromoacetic acid can be replaced with bromoacetyl chloride or bromide in such case the pocl3 amount can be reduced by one equivalent comments 13 february 21 2008 5 n pyrazolyl 3 nitrobenzoic acid filed under procedures milkshake 7 14 pm 3 hydrazinobenzoic acid 13 95g 91 68 mmol suspension in water 100ml was diluted with acetic acid 100ml and 1 1 3 3 tetramethoxypropane 15 5ml 15 11g 92mmol was added to the mixture followed by conc hcl 10ml the mixture was stirred under reflux on a 100c oil bath for 45 min the condensation was complete in less than 30 min the dark reaction mixture was poured into a large beaker and the stirred mixture was diluted with gradual water addition up to 1l total volume after 30 min stirring the obtained slurry was allowed to crystallize in a fridge 1c overnight the precipitated m n pyrazolyl benzoic acid was collected by filtration washed with ice cold water 100ml dried by suction and on highvac y 15 38g of a light tan powder 89 th 1h d6 dmso 400mhz 13 217 br s 1h 8 609 dd 2 5hz 0 4hz 1h 8 377 t 1 9hz 1h 8 095 ddd 8 1hz 2 4hz 1 0hz 1h 7 861 ddd 7 7hz 1 4hz 1 0hz 1h 7 784 dd 1 7hz 0 4hz 1h 7 627 t 7 9hz 1h 6 572 dd 2 5hz 1 8hz 1h 15 11g of m n pyrazolyl benzoic acid from the previous step 80 29mmol was gradually added to conc sulfuric acid 96 55ml with cooling on ambient water bath after 20 min stirring when the starting material mostly dissolved in sulfuric acid 8 0 ml of 70 nitric acid was added dropwise and the mixture was stirred on ambient water bath for 75min then poured on ice 200g the total volume of the slurry was adjusted to 0 5l with water and the mixture was stirred for 15 min the precipitated crude product was collected by filtration washed thoroughly with water and dried by suction the crude product was dissolved in a mixture of ethanol 500ml and water 100ml at reflux the hot solution was diluted with hot water 400ml and the mixture was allowed to crystallise at rt overnight the precipitated product was collected by filtration washed with 1 1 ethanol water mixture 300ml dried by suction and on highvac y 13 85g of a pale yellow fluffy crystalline solid 73 5 th containing 4 5 of a nitropyrazole impurity 1h d6 dmso 400mhz 14 076 br s 1h 8 775 dd 2 5hz 0 3hz 1h 8 251 t 1 4hz 1h 8 200 d 0 4hz 2h 7 891 d 1 5hz 1h 6 661 dd 2 6hz 1 7hz 1h note even though pyrazole is a fairly electron rich ring in conc sulfuric acid it becomes fully protonated so the bezoic acid portion of the molecule nitrates faster the nitration is rather messy but the desired 1 3 5 substituted product crystallizes well to obtain the isomeric meta 4 nitropyrazol 1 yl benzoic acid one can nitrate by very slow addition of 2 5 equivs of 90 white fuming nitric acid dissolved in ac2o 4 equivs into acoh slurry of the substrate at 60c a very dangerous system comments 9 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 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