Hofmann rearrangement: Methylamine

[Cyrax]

Reaction:

  CH₃CONH₂ + Br₂ + 2 NaOH  -->  CH₃NH₂ + CO₂ + 2 NaBr + H₂O


Procedure:

Place 25 g (0.42 mol) of dry acetamide in a 500 mL conical flask, and add 69 g (23 mL, 0.43 mol) of bromine (CAUTION): a deep red liquid is produced.  Cool the flask in ice-water and add 10 % NaOH solution (about 210 mL) in small portions and with vigorous shaking until the solution acquires a pale yellow colour.  At this stage the bromoacetamide is present in the alkaline solution.  If any solid should crystallise out, add a little water.
 Place a solution of 60 g (1.5 mol) of NaOH in 150 mL of water in a 1 litre, three necked round-bottomed fitted with a dropping funnel, a thermometer reaching to within 1 cm of the bottom of the flask and a reflux condenser.  Connect the top of the latter to an inverted funnel type of gas absorption trap; charge the beaker with 100 mL of dilute (1:1) chloric acid.  Introduce a few fragments of porous pot and warm the solution to 60 - 70 °C.  Run the bromoacetamide solution slowly into the flask at such a rate that the temperature does not rise above about 70 °C; heat is evolved in the reaction and if the temperature rises above 75 °C the flask should be surrounded momentarily by a bath of cold water.  Wen all the sloution has been added, maintain the temperature of the mixture in the flask for about 15 minutes at 65 - 70 °C; by this time the solution should be clear and colourless.  Gently boil the solution and thus drive off the methylamine vapour into the dillute hydrochloric acid.  As soon as the distillate is no longer alkaline (40 - 60 minutes), evaporate the hydrochloric acid solution on a rotary evaporater and dry the solid residue in an oven held at 100 - 105 °C.  The yield of crude dry produce (which is contaminated with some NH₄Cl) is about 24 g.  Transfer the finely powdered, dry solid to a 250 mL round-bottomed flask fitted with a reflux condenser and CaCl₂ guard-tube.  Add about 120 mL of absolute EtOH (which dissolves only the methylamine hydrochloride) and boil the mixture for 10 minutes.  Filter through a hot water funnel.  Extract the residue with a further 50 mL of boiling absolute EtOH and filter again.  Cool the combined ethanolic extracts when colourless crystalls of methylamine hydrochloride will separate out.  Filter rapidly at the pump, and transfer the crystalls (which are deliquescent) to a stoppered bottle.  Evaporate the filtrate to about 1 / 3 of the original volume, when a further crop of crystalls will be obtained.  Dry all the crystalls in a desiccator.  The yield is about 18 g (64 %).

ref.: Vogel's Textbook of practical organic chemistry, 4 th ed., p 573 - 574.

Don't try to search this procedure in the new, 5 th edition.  You will be disappointed because it isn't included.  It is my impression that they have omited all the goodies from the old editions ...  

[foxy2]

Hmmm
To many Hive and Rhodium linkages?  

Edit: Sorry I don't have a clue what I was talking about here.
Did you change this post?
Those who give up essential liberties for temporary safety deserve neither liberty nor safety

[Chromic]

Why not use the hypohalites to do the oxidation (either NaOCl or Ca(OCl)2) as they're OTC, easier to handle, less suspicious and do the same job?

[hellman]

Yes, just exchange the bromine for HTH, from the pool supplier, Eleusis has the mole'ige for this in Rhod's site under Rambling and ravings from zwitt/Eleusis,.
There are no formal changes that need to be made, when substituting HTH, for bromine, or chlorine,

Goodluck, this is one of my favourite reactions,
\I have written a write-up for for this and FORMIC ACID, it will be available this month,
Also in what is exciting, is the fact that you can make acetamide, in a somewhat perfect reaction, with no side products, no recrystallization. from Just Urea and Glacial Acetic acid,.
Urea is sold at any pharmacy, and from most ag. suppliers,.

This is a beautiful way to make Methylamine, from only urea and Acetic acid,.
This is the direction you guys should be heading for OTC large or small scale methylamine,.

Less solvents, less by products, Fanatasically improvisable equipment,
Just make sure you watch the temp when doing the above reaction, keeping the reaction cool, is the secret,.
Sorry to be so vague, out of time,
But if any body is truly desperate,
the Acetamide prep is on Page 2?? in vogels 3rd.
Must be third. Damn it!!!

helski                      
IQ is the rate of logic, as Wisdom increases logic, fear & compromise decrease to reveal objectivity

[terbium]

This is a beautiful way to make Methylamine, from only urea and Acetic acid,.
This is the direction you guys should be heading for OTC large or small scale methylamine,.
Why do you think that this is better than methylamine from ammonium chloride and formaldehyde? Seems to me like a lot of trouble.

[Cyrax]

Chromic, I agree: it is more convenient to use a NaOCl solution.  I only posted this so that there would be a good writeup for this reaction, I realize that there are few bees that have Br₂ (yukk) lying around in their kitchen.  

However, it is a good procedure (since it is a good factual report: the lab procedure is well described).  But not good from clandistine point of view ... you are right.

In order to integrate the knowledge at The Hive, check out

Post 330710 (missing)

(foxy2: "Preparation of Acetamide", Chemistry Discourse).

P.S.: Yup, Foxy2: I first posted the reaction, and then I found the courage to type in the lab procedure - I was a bit lazy last night    .

[hellman]

Simply because it doesn't use those chemicals you mention,.
Everything is easily obtainable,.


IQ is the rate of logic, as Wisdom increases logic, fear & compromise decrease to reveal objectivity

[raffike]

Been cleaning up raf's dad's former cland. lab and found some(about 15 liters) of 85% Acetic acid.Could that be used or is GAA needed?Raf told him about AmCl and formalin reaction for methylamine,but dad said it's not for big amounts.Instead he recommended "Hoffmann 'something'".There's some Urea too(about 10 kgs of lab grade).What the heck,i'll better UTFSE than bother you with my newbee questions.
A friend with speed is a friend indeed

[Rhodium]

Check Eleusis' Methylamine document at my page. You react that 85% acetic acid with urea, forming acetamide, which upon treatment with some hypochlorite (chlorox or pool shock) under basic conditions undergoes Hoffmann Rearrangement, forming methylamine.