I would like to make dry DMA. I found that you can dried it with BaO and distilled it under reduced pressure and store it in the presence of molecular sieves 4A, but unfortunately our lab does not have BaO. Do you have any experience on drying DMA? What method are you using?
CaH2 is good drying agent for DMA (with following distillation). If you have 2-3 days, simply allow to stay over 3A-molecular sieves, shaking one time per day.
See for inspiration Burfield
and Smithers J Org Chem 43 3966 1978, and for a review on purification, tests of purity and physical
properties, see Juillard Pure Appl Chem 49 885 1977
In my experience reagent of choice for drying DMF is phosphorous pentoxide. Its just adding and distillation of homogeneous mixture (unlike CaO, CaH2 and BaO). Another advantage is removing basic impurities like dimethylamine. May be it will work in case of DMA as well.
Hi Maria,
if your lab is unable to offer chemical for drying ,you can do fractional distillation using long columns. if there is high acetic acid conc. with your sample first try to neutralize the acid then do fractional distillation.
The definition of dry reagent depends upon the extent of dryness (water content) expressed in terms of %, ppm or still less. This, as a classical organic chemist, I learned in a hard way while carrying out some polymerisation reactions with ethylene. In essence, the method of making a dry solvent will depend essentially on the level of dryness we are looking for.
I hope DMA can be dried in a similar manner as used for drying of DMF. DMA can be distilled with dry benzene (2x100 ml per litre of DMA) to remove the water as azeotropic mixture . It is to be followed by shaking (once) with activated neutral alumina, filtration and distillation (under reduced pressure) with calcium hydride. The DMA thus obtained can be stored over 3A-Molecular sieve. It can be preserved and used for a long period.
Dear Mrs. Koyoni, all these methods will work. You have to decide about the dryness you want to get. To my experience the best drying results can be reached by using molecular sieves. Nevertheless, a two step-drying process (Drying with a hydride disitillation and drying with molecular sieve) is necessary in this case.
This will give DMA in super dry condition. Super dry aprotic solvents show nearly no evolution of hydrogen if combined with pure sodium hydride. Molecular sieve technique will give DMA that can be used instantly. On the other hand handling of Molecular sieves need some special equipment: a drying flask, an oven that can be heated up to 300 °C dry Nitrogen or better Argon. Please note all procedures must be carried out under a blanket otherwise DMA will discolourise after several days. And store the flask in a dark place.
Dear all, To my experience 3A-molceular sieves are more convenient - if one has the equipment to dry them at 300 °C and to cool them under Argon to room-temperature. If CaH2 is used it has to be ground and stirred for a certain time. Care must be taken not to transfer turbid material to your reaction-batch. DMA and DMF have to be stored in darkness. Furthermore I would recommend not to store these upon molecular sieves for more than 3 weeks. Or you have to transfer them from one vessel to another with a new portion. Strictly omit oxygen! I found that DMF i.e. will show only very slight hydrogen evolution if dried this way when sodiumhydride is added at room-temperature. Chemical reactions using sodiumhydride can be done in DMF if the mineral oil is removed previously by pentane and dried in vaccuo. This effect can be used to find out when it is dry enough - take a small volume, add a pinch of sodiumhydride (90% in mineral oil) - the hydride will sediment very rapidly . And keep in mind to throw away this type of solvent if there is a smell of "amine"! Amine (dimethylamine) can be removed by distillation (with water) but I think nowadays it is more comfortable to buy a new bottle.
Best regards, Dr. Wolfram Eichinger
Shaken with BaO for several days, refluxed with BaO for 1 h, then distd under reduced pressure, and stored over 3A-molceular sieve.
Ali Moghadam , about the amount of CaH2 needed to dry 1L dimethylacetamide (DMA), i can roughly say that 3 to 5 lab spoons of CaH2 can do the job. Just after mixing CaH2 and DMA, let it stands at overnight (~10 h) under stirring at ambient temperature before distillation under reduced pressure.
Methods for drying N,N-Dimethylacetamide (DMA) :; It is hygroscopic compd. wash it twice with ether and dry under vacuum using Abderhalden drying apparatus.
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