There is no alternative to change in this particular case, I do tihnk that its not optimal to use DCM becase the reaction is too long, while we do use methylamine HCL which leads to more impurities, however reaction has its pro that it can be even done as " 1st job".
DCM preferably with other solvents preferably dmso or nmp is reaction that rarely exceeds 40 mins.
The precise dosage of methylamine aq is the key, combined with speed of stirring we can control exhotermic reaction. I suggest to start from 20g of 2b4m, 45-55 m of dcm at 20c and 12-16 ml of dmso/nmp. Nmp is added to DCM, then 2b4m is dissolved.
Recommended equipment is mechanical stirrer with precise regulatoin of the stirring, three necked flask, thermometer probe (glass).
We can add methylamine all at once (35ml), but using the funnel, and dropping on the glass walll!! the stirring speedis minimum for several minutes, after 10-15 mins we can try to speed it up a little, and obtain the control of 36c. when temp will be "slowly not incrashing" stirrin is adjusted to keep 36c, usually it can be about 700-900 RPM using 2 leaf stirrer. Flask size is 250 ml for that scale.
TLC is performed to check of remains of 2b4m, if cant be performed the best sign is "deep yellow" is a sign that reaction is over, 4x volumetric amount of used dmso/nmp is added to the flask to stop the reaction.
Now its time to get rid of methylamine by 3x wash with cold h2o and begin to acidfiication using h2o and acid. After that solvent is evaporated.
