Okay, I copy and pasted from another forum. Like I said, this is nothing anyone doesn't already know, here anyway. There will be a short addendum to be added regarding some hypotheses I have. I will add them when I have time.
Background
It has been noted by many over the years that the aluminum amalgamation can be a difficult route to obtain consistent yields of amine when making methylamine in situ from nitromethane. Many reaction parameters have been suggested and a sort of folklore surrounds the issue as to how much of of each reactant is to be used as well as substrate. The issue is so confused that debate about how much Hg++ salt is needed and addition time, amongst other factors, is a constant source of debate. It is likely that the amalgamation favors the reduction of nitromethane over imine reduction and that addition time is probably not much of a factor. However, the following two (2) amalgamations were only devised to determine two (2) factor: One, that 400-500mg of Hg++ salt is more than what is needed for a good yield; and two that external heat is probably not necessary for this reaction.
An amalgamation was formed in a 2-liter flat bottomed flask using the following parameters:
The Parameters
-950ml of methanol
-90-100mg HgCl2
-37.6 grams of aluminum
-30.9 grams nitromethane
-50 grams of a ketone that is estimated 77% MD-whatever and 23% some alkene, so the estimated ketone is 38.5 grams)
-An additional portion of methanol is added to the ketone/nitromethane mixture until a volume of 150ml is obtained
Experiment #1
In a 2-liter flat bottomed flask was added 90-100mg HgCl2 and then 950ml methanol. It was allowed to stir for 1 minute and then, as stirring was continued, 37.6 grams of aluminum foil that was prepared by grinding in a coffee grinder was added. This was allowed to stir for another minute. The stirring was then stopped and the amalgamation allowed to form for 30 minutes. Stirring was begun and addition was started. At this point external heat was added immediately. The dial on the hotplate was set to a setting similar to what is required for mild reflux of methanol. Addition was completed withing 30 minutes. The mixture was allowed to stir. An additional 200ml methanol was dropped as fast as it could so as if to wash the aluminum sludge that had climbed up the flask during the peak of the reaction back into the mother liquor. Mild reflux was maintained for 5 hours. The external heat was discontinued and the flask allowed to cool. The reaction flask was flooded slowly with ~30% NaOH. Little heat was noticed as the NaOH was added. It was allowed to cool then extracted with three (3) portions of xylene that were 250ml each. An additional extraction with 50ml of xylene was done. These extractions were combined and added to a 4-liter separation funnel. The xylene and amine solution was ~850ml. The xylene/amine was washed three (3) times with 1000ml distilled water and once more with 1000ml of a saturated NaCl solution. The organic layer was then dried with 40 grams of CaCl2. It was dried for 10 minutes and then filtered. The CaCl2 was caked at the bottom of the flask used for drying and another 25ml of xylene was added. After 5 minutes that was filtered and added to the extraction. Anhydrous HCl gas was used to form the organic salt. The amine was filtered and residual xylene was removed by three (3) acetone washes that were decanted. The organic salt was then dried. A yield of 32 to 36 grams is generally obtained without any scrapping of beakers and drying plates.
Yield: 31.7 grams of a fluffy white powder
Experiment #2
In a 2-liter flat bottomed flask was added 90-100mg HgCl2 and then 950ml methanol. It was allowed to stir for 1 minute and then, as stirring was continued, 37.6 grams of aluminum foil that was prepared by grinding in a coffee grinder was added. This was allowed to stir for another minute. The stirring was then stopped and the amalgamation allowed to form for 30 minutes. Stirring was begun and addition was started. Addition was completed withing 30 minutes. The mixture was allowed to stir. An additional 200ml methanol was dropped as fast as it could so as if to wash the aluminum sludge that had climbed up the flask during the peak of the reaction back into the mother liquor. The reaction was allowed to continue for 5 hours with no external heat. The reaction flask was flooded slowly with ~30% NaOH. Little heat was noticed as the NaOH was added. It was allowed to cool and then was extracted with three (3) portions of xylene that were 250ml each. An additional extraction with 50ml of xylene was done. These extractions were combined and added to a 4-liter separation funnel. The xylene and amine solution was ~850ml. The xylene/amine was washed three (3) times with 1000ml distilled water and once more with 1000ml of a saturated NaCl solution. The organic layer was then dried with 40 grams of CaCl2. It was dried for 10 minutes and then filtered. The CaCl2 was caked at the bottom of the flask used for drying and another 25ml of xylene was added. After 5 minutes that was filtered and added to the extraction. Anhydrous HCl gas was used to form the organic salt. The amine was filtered and residual xylene was removed by three (3) acetone washes that were decanted. The organic salt was then dried. A yield of 32 to 36 grams is generally obtained without any scrapping of beakers and drying plates.
Yield: 31.9 grams of fluffy white powder
Notes: Originally the idea was to use 30 grams of nitromethane but 30.9 was accidentally measured into the ketone. The aluminum and nothing else was adjusted as the reduction of nitromethane is believed to be more favorable than the imine. At the very least we know it happens first. So 36 grams of aluminum became 37.6. These aren't accurate yields as extraction and distillation of the freebase oil is best for getting all the amine and not losing it to all those washes. It might be noted that 3 or 4 DH2O washes followed by a saturated NaCl wash can probably be substituted with just two (2) saturated NaCl washes (brine).
Conclusion
The results show that a good yield to amine can be had utilizing the aluminum amalgamation, where methylamine is made in situation, with as little as 100mg of HgCl2 if note less and that external heating is probably not necessary.
Background
It has been noted by many over the years that the aluminum amalgamation can be a difficult route to obtain consistent yields of amine when making methylamine in situ from nitromethane. Many reaction parameters have been suggested and a sort of folklore surrounds the issue as to how much of of each reactant is to be used as well as substrate. The issue is so confused that debate about how much Hg++ salt is needed and addition time, amongst other factors, is a constant source of debate. It is likely that the amalgamation favors the reduction of nitromethane over imine reduction and that addition time is probably not much of a factor. However, the following two (2) amalgamations were only devised to determine two (2) factor: One, that 400-500mg of Hg++ salt is more than what is needed for a good yield; and two that external heat is probably not necessary for this reaction.
An amalgamation was formed in a 2-liter flat bottomed flask using the following parameters:
The Parameters
-950ml of methanol
-90-100mg HgCl2
-37.6 grams of aluminum
-30.9 grams nitromethane
-50 grams of a ketone that is estimated 77% MD-whatever and 23% some alkene, so the estimated ketone is 38.5 grams)
-An additional portion of methanol is added to the ketone/nitromethane mixture until a volume of 150ml is obtained
Experiment #1
In a 2-liter flat bottomed flask was added 90-100mg HgCl2 and then 950ml methanol. It was allowed to stir for 1 minute and then, as stirring was continued, 37.6 grams of aluminum foil that was prepared by grinding in a coffee grinder was added. This was allowed to stir for another minute. The stirring was then stopped and the amalgamation allowed to form for 30 minutes. Stirring was begun and addition was started. At this point external heat was added immediately. The dial on the hotplate was set to a setting similar to what is required for mild reflux of methanol. Addition was completed withing 30 minutes. The mixture was allowed to stir. An additional 200ml methanol was dropped as fast as it could so as if to wash the aluminum sludge that had climbed up the flask during the peak of the reaction back into the mother liquor. Mild reflux was maintained for 5 hours. The external heat was discontinued and the flask allowed to cool. The reaction flask was flooded slowly with ~30% NaOH. Little heat was noticed as the NaOH was added. It was allowed to cool then extracted with three (3) portions of xylene that were 250ml each. An additional extraction with 50ml of xylene was done. These extractions were combined and added to a 4-liter separation funnel. The xylene and amine solution was ~850ml. The xylene/amine was washed three (3) times with 1000ml distilled water and once more with 1000ml of a saturated NaCl solution. The organic layer was then dried with 40 grams of CaCl2. It was dried for 10 minutes and then filtered. The CaCl2 was caked at the bottom of the flask used for drying and another 25ml of xylene was added. After 5 minutes that was filtered and added to the extraction. Anhydrous HCl gas was used to form the organic salt. The amine was filtered and residual xylene was removed by three (3) acetone washes that were decanted. The organic salt was then dried. A yield of 32 to 36 grams is generally obtained without any scrapping of beakers and drying plates.
Yield: 31.7 grams of a fluffy white powder
Experiment #2
In a 2-liter flat bottomed flask was added 90-100mg HgCl2 and then 950ml methanol. It was allowed to stir for 1 minute and then, as stirring was continued, 37.6 grams of aluminum foil that was prepared by grinding in a coffee grinder was added. This was allowed to stir for another minute. The stirring was then stopped and the amalgamation allowed to form for 30 minutes. Stirring was begun and addition was started. Addition was completed withing 30 minutes. The mixture was allowed to stir. An additional 200ml methanol was dropped as fast as it could so as if to wash the aluminum sludge that had climbed up the flask during the peak of the reaction back into the mother liquor. The reaction was allowed to continue for 5 hours with no external heat. The reaction flask was flooded slowly with ~30% NaOH. Little heat was noticed as the NaOH was added. It was allowed to cool and then was extracted with three (3) portions of xylene that were 250ml each. An additional extraction with 50ml of xylene was done. These extractions were combined and added to a 4-liter separation funnel. The xylene and amine solution was ~850ml. The xylene/amine was washed three (3) times with 1000ml distilled water and once more with 1000ml of a saturated NaCl solution. The organic layer was then dried with 40 grams of CaCl2. It was dried for 10 minutes and then filtered. The CaCl2 was caked at the bottom of the flask used for drying and another 25ml of xylene was added. After 5 minutes that was filtered and added to the extraction. Anhydrous HCl gas was used to form the organic salt. The amine was filtered and residual xylene was removed by three (3) acetone washes that were decanted. The organic salt was then dried. A yield of 32 to 36 grams is generally obtained without any scrapping of beakers and drying plates.
Yield: 31.9 grams of fluffy white powder
Notes: Originally the idea was to use 30 grams of nitromethane but 30.9 was accidentally measured into the ketone. The aluminum and nothing else was adjusted as the reduction of nitromethane is believed to be more favorable than the imine. At the very least we know it happens first. So 36 grams of aluminum became 37.6. These aren't accurate yields as extraction and distillation of the freebase oil is best for getting all the amine and not losing it to all those washes. It might be noted that 3 or 4 DH2O washes followed by a saturated NaCl wash can probably be substituted with just two (2) saturated NaCl washes (brine).
Conclusion
The results show that a good yield to amine can be had utilizing the aluminum amalgamation, where methylamine is made in situation, with as little as 100mg of HgCl2 if note less and that external heating is probably not necessary.
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