After spending way too much time dealing with separating Methylamine and Ammonium Chloride, dealing with formaldehyde fumes, and recrystalizing, I've began looking for alternate routes to Methylamine. In digging around yesterday I came across the metal-assisted reduction of nitroalkanes. It's been discussed on this board and other places around the net, but I've yet to see a full runthrough from nitromethane to methylamine. I'd like to start off by talking a bit about the procedure. Maybe get some input on it. Then, in the next couple weeks, I'll plan on trying it out.
Here are the references I'm running off of:
1) Chemical Abstracts 11, page 1650 Synthesis of Alkylamines -- Chemiker Zeitung 40, 810 (1916
Ratios:
2) Vogel 5th Ed, p. 892
Ratios:
Note: Vogel uses Tin. I vaguely recall seeing somewhere that when tin is used, more acid is necessary. That would explain the higher HCl ratio in this procedure.
3) Johnson and Degering
Ratios:
4) Eluesis
Note: I don't think Eleusis actually tried this procedure. Notice the emphasized "should" above. Also, I think the reaction would be done in much less than 14 hours with the addition of FeCl3.
Ratios:
5) Hudlicky, "Reductions in Organic Chemistry" p. 213
Ratios:
Now one very interesting thing in the last reference is that they don't use any acid at all. Apparently the catalyst is enough to keep the reaction going. In fact, they say earlier in the book:
By the way, the listed amounts of water take into account any other water present -- such as in conc. HCl or ferric chloride solution.
Imagine, 1 gallon of nitromethane, 16 kg Fe (assuming 4 molar excess) (or 7 kg going by Hudlicky's procedure), and a few grams FeCl3 you could get 4.7 kg Methylamine HCl!
I know, that looks like a lot of iron, but filings can be found for pretty cheap.
I have all the supplies on the way. Thoughts?
Here are the references I'm running off of:
1) Chemical Abstracts 11, page 1650 Synthesis of Alkylamines -- Chemiker Zeitung 40, 810 (1916
Quote
EtNO2 and MeNO2, which are readily prepared by a process recently patented (ref. not given) served as the mother substances for the corresponding alkylamines (RNH2). The latter were formed by reducing RNO2 in HCl with Fe. When 2.13 g. EtNO2 in 8 g. H2O, 7 g. Fe filings and 0.8 g. HCl were heated together at 50-60 degrees for 6 hrs. in a flask from which air was excluded, 0.96 g. EtNH2 (about 75% of the theoretical amount) was obtained.
In a similar experiment, in which the reaction mixture was heated for only 3 hours, the yield was materially decreased. In these experiments only 1/36 of the amt. of acid required by the following equation was used: RNO2 + 3Fe + 7HCl = RNH2.HCl + 3FeCl2 + 2H2O. Furthermore, the mixtures became alkaline long before the reduction was complete, and Fe(OH)2 was pptd. and rapidly oxidized to Fe(OH)3 by the excess of EtNO2.
In another experiment, RNO2 which remained unchanged when treated with Fe and H2O alone was reduced when small amounts of RNH2.HCl were added to the mixture It is evident, therefore, that the above equation does not accurately represent the mechanism of the reduction. Apparently Fe reacts further with the RNH2.HCl formed earlier in the reduction, according to the equations 2RNH2, HCl + Fe = 2RNH2 + FeCl2 + 2H. 2RNH2 + FeCl2 + 2H2O = 2RNH2.HCl + Fe(OH)2, and H and Fe(OH)2 are the active reducing agents. Very nearly quantitative yields of MeNH2 and EtNH2 were obtained by using 1.5 mols. of HCl per mol. of RNO2 in the reduction, and heating the reaction mixture at 70 degrees for about 1 hr.
Ratios:
- Nitroalkane: 1.30 mol
- HCl: 1.00 mol
- Iron: 5.71 mol
- Water: 366 ml
2) Vogel 5th Ed, p. 892
Quote
Cognate procedure: Setup a flask with reflux condenser in which .25 mol of nitromethane, .38 mol of granulated tin metal and a stirrer magnet have been added. Carefully pour 115mL of 31.45% hydrochloric acid (muriatic acid) down the reflux condenser in 10-15mL increments, waiting for the reaction to settle down before pouring the next aliquot. If the reaction seems to get out of hand (excessive frothing, vapor escaping the reflux condenser, etc...) then quickly slide an ice bath in place until it slackens back down. Once all the HCl has been added, heat the mixture to reflux with an electric mantle for 1hr. At the end of this time, allow to cool, preferably in an ice bath, then add, carefully, a chilled solution of 75g sodium hydroxide in 125mL of water. If the flask contents start to bubble violently you will watch your yield go out the window, so add slowly! Since methylamine readily dissolves in water, you will need to distill the reaction contents carefully to first liberate the 40% constant boiling solution (bp: 53°C) and then the gas itself. The product is best captured by bubbling the distillation vapor into a beaker of hydrochloric acid (use a slight molar excess of HCl to insure no loss). Proceed as above by evaporating the bubbler solution to yield the crystals (take care when evaporating HCl solutions, as the excess acid will vaporize into the air, corroding ovens, lungs, etc...)
Ratios:
- Nitroalkane: 1.00 mol
- HCl: 4.68 mol
- Tin: 1.52 mol
- Water: 390 ml
Note: Vogel uses Tin. I vaguely recall seeing somewhere that when tin is used, more acid is necessary. That would explain the higher HCl ratio in this procedure.
3) Johnson and Degering
Quote
To 35g of 40-mesh iron filings are added 75 ml of water and 10 ml of concd. hydrochloric acid . After the evolution of hydrogen has stopped , one-sixth of a mole of nitroparaffin is added and , with rapid stirring , the mass is heated at 100 ºC for thirteen to fifteen hours.
2-Nitro-2-methylpropane and other nitroalkanes were reduced to the corresponding aliphatic amines in 82–94% yields . The yields were 93–97% “in the presence of ferric chloride
Ratios:
- Nitroalkane: 1.37 mol
- HCl: 1.00 mol
- Iron: 5.14 mol
- Water: 667 ml
4) Eluesis
Quote
The lower nitroalkanes (sometimes refered to as nitroparaffins) are easily reduced by a multitude of systems, but by far the easiest, and also the highest yielding, is the Iron/Hydrochloric acid system. The reaction is:
4 RNO2 + 9 Fe + 4 H2O =HCl=> 4 RNH2 + 3 Fe3O4
First, your Nitromethane *may* require purification, especially if it was for "fuel" use. In this case, it needs to be vacuum distilled at a vacuum of better than 100mm Hg. At that pressure, it will come off at ~47°C. Distillation at atmospheric pressure is possible, but I do not recommend it due to the highly flammable nature of the compound and because it's flash point is 42°C. It's your choice.
*CAUTION*
The lower nitroalkanes form shock and/or temperature sensitive EXPLOSIVE compounds with amines and hydroxides. BE CAREFUL, DAMNIT! You have been warned.
Assemble a 500mL RB flask with claisen adapter, thermometer down the center to read the liquid temperature, and reflux condenser with a cork and tube leading to a beaker of 1M Hydrochloric acid. Drop a stirrer magnet in, then add 105g of 40 Mesh Iron filings, 225mL of water and 1g of Ferric Chloride. Next, add 35mL of concentrated Hydrochloric Acid ("muriatic acid" is ok). When the bubbling ceases, add 31g of Nitromethane.
Heat the reaction mixture to 100°C and hold for 14 hours. A temperature regulator is necessary if using a heating mantle, else use a large boiling water bath (if you will be doing it overnight, so it doesn't run out).
At the end of this time, allow to cool then add enough 25% Sodium Hydroxide solution to to get the pH above 11. Heat on a water bath or with gentle electric heat to drive the Methylamine off as a gas into the same beaker of Hydrochloric acid used as a trap during the reaction.
Evaporate the beaker contents to dryness on a glass plate in the oven to collect the crystals of Methylamine HCl (hygroscopic!). The yield should be approximately 15g (95%).
Note: I don't think Eleusis actually tried this procedure. Notice the emphasized "should" above. Also, I think the reaction would be done in much less than 14 hours with the addition of FeCl3.
Ratios:
- Nitroalkane: 1.19 mol
- HCl: 1.00 mol
- Iron: 4.41 mol
- Water: 588 ml
5) Hudlicky, "Reductions in Organic Chemistry" p. 213
Quote
A 500 ml three-necked rbf fitted with a robust mechanical stirrer, a reflux condenser, and an inlet is charged with 50g (0.3mol) of m-dinitrobenzene, 14g of 80 mesh iron filings, 45 ml of water, and 7.5ml of a 33% solution of ferric chloride (or 50 ml of water and 3.7g of sodium chloride). The flask is immersed in a preheated water bath, stirring is started at 35 rpm, and additional iron filings are added to the mixture in two 13g portions after 30 minutes and 1 hours. After 2.5 hours of stirring and heating the reaction mixture is cooled and extracted with ether, giving an essentially quantitative yield of m-nitroaniline.
Ratios:
- Nitroalkane: 1.00 mol
- Iron: 1.77 mol
- Water: 173 ml
Now one very interesting thing in the last reference is that they don't use any acid at all. Apparently the catalyst is enough to keep the reaction going. In fact, they say earlier in the book:
Quote
Iron was one of the first metals employed for the reduction of organic compounds over 130 years ago. it is used in the form of filings. best results are obtained with 80 mesh grain [165]. Although some reductions are carried out in dilute or concentrated acetic acid, the majority are performed in water in the presence of small amounts of HCl, acetic acid, or salts such as ferric chloride (as little as 1.5-3%) [165], ferrous sulfate [166] and others. Under these conditions iron is converted to iron oxide, Fe3O4. Methanol or ethanol are used to increase the solubility of the organic material in the aqueous medium [166].
4RNO2 + 9Fe + 4H2O --> 4 RNH2 + Fe3O4
By the way, the listed amounts of water take into account any other water present -- such as in conc. HCl or ferric chloride solution.
Imagine, 1 gallon of nitromethane, 16 kg Fe (assuming 4 molar excess) (or 7 kg going by Hudlicky's procedure), and a few grams FeCl3 you could get 4.7 kg Methylamine HCl!
I know, that looks like a lot of iron, but filings can be found for pretty cheap.
I have all the supplies on the way. Thoughts?