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Preparation of a 10% Methylamine solution in Methanol

by Sunlight

This is a convenient way of making a 10% methanolic solution of methylamine freebase from the commercially available 40% aqueous solution.

Put in a 2-neck flask 700 grams of commercial dry NaOH, and using a compensating pressure separatory funnel attached to one of the necks, add slowly over one hour 350 cc of aq. methylamine to the NaOH. In the other neck attach a rubber stopper with a teflon tube and to it a glass tube with a gas diffusor ( a tiny glasfunnel with a glasfilter glued in it with 6 seconds glue or two component glue or just melt it tight with a torch ), and bubble the MA-gas in 1000 cc of methanol in a flask in a methanol- or water/ice bath. Reaction is endothermic, finally you can heat a bit the NaOH containing flask to force the liberation of the last gas, but it's not really necessary, just shake it to see a homogeneus paste. The compensation of pressure can be done using a regular separatory funel if you attach a 1-hole rubber stopper with a teflon tube connecting to the NaOH flask, if you use a 3-neck flask you can use the other neck, and if you use a two neck flask, you can use in one of the necks a 2-hole rubber stopper, 1 hole connecting to the stopper in the neck of the separatory funel and one to the ... dripping hole of it (excuse my english...)

You can refill your sep. funnel with aq. methylamine if it's not enough big to complete the whole liberation of all the gas, close the valve and close the other tube, open it and put the aq. solution in, then stop it and free the other tube. The absortion of methylamine in methanol at 0-5 C is perfect, you don't even need to redirect possible fumes from the methanol, there aren't, but stop the flask with some papertissue to prevent the entry of humidity. The gas diffusor can be done with a regular glass tube, try to enlarge a bit one of the ends, and then try to weld inside it a piece of fine filterglass for the gas bubbles feed, it will act as a diffusor, not very good, but enough, and it won't heighten the pressure too much (one stopper could jump and you would have a toxic ambient atmosphere of methylamine in your viginity). Probably using a pipette will work, absortion is very good.

You can weight finally the 10% methanolic solution of methylamine to know the exact weight of gas you have in it (you weighted it before). You will have a bit of water, but don't worry, mix it with the ketone (350 grams), add silica gel (160 gr) and shake and let stand, shake and so on... during an hour, filter and wash the silica with 200-300 cc of methanol, add the NaBH4 at +7 C (an ice/salt bath works fine) to get from 75-87% of the desired product depending on the purity of your ketone. You can dehydrate the methylamine gas by passing it through a flask with NaOH, but it's not necessary due to the addition of silica gel.

Addendum by KrZ:

The mix {MeNH2 + 2H2O (The product of catalytic hydrogenation of methylamine) in methanol with Na2SO4} was split in half and each half sat with 1500g of Na2SO4 for an hour, with occasional stirring. The Na2SO4 (sodium sulfate) was filtered off for a long time, until it was quite dry in appearance, the mix halves were combined and washed 2x with 1L of CH3OH (methanol), which was filtered off and added back to the solution.

Addendum by Sunlight:

We did something similar with MgSO4, trying to dry a mixture of 40% MeNH2 and methanol, and the end product was titrated and it was about 3 % instead of 10 % w/w (weight/weight), the MgSO4 had a strong smell of methylamine, so we thought most of the gas was ended in the water and in the magnesiumsulfate, and we tried the above procedure, that works fine. But we are not God or the Queen of England. They use "we" as a pluriform all the time.