old methylating agent: methyl nitrate

[otto]

in the last time some posts concerning methylation of phenols with reagents other than methyl sulphate occured. there was to my knowledge no mentioning of methyl nitrate, e.g. the ester one gets from reacting nitric acid with methanole. here is a short recipe of its preparation:

400 ml of nitric acid (65%), 30 g of ammonium nitrate and 100 ml of methanole are mixed in a 1 l RBF. the mixture was refluxed on a dean & stark apparatus. the lower phase in the dean-stark is to be collected. its methyl nitrate with about 15% methanole in it. this can be used without purification in the methylation of phenols instead of methyl sulphate. BP 65°C, methyl nitrate is highly flammable and explosive (thats why it isnt used anymore in industry since last century).

otto

[Rhodium]

Ouch! I would NOT play with that, it is almost as sensitive as nitroglycerin.

[Antoncho]

... and i guess it will have a tendency to oxidize as well as methylate some sensitive compd's - hydroquinone, aldehydes... whaddyathink?

Antoncho

[otto]

yes, it is a powerful explosive and gives good blasts.
no, it isnt as dangerous as nitroglycerine. its not sensitve to friction and nothing will happen if a bottle of it falls down. you can even hit it with a hammer on a metal plate without any reaction.
what you can't do is to heat it (or its vapours or mixtures with it) over 150°C. and its toxic of course.
otto has no acces to methyl sulfate and uses this stuff instead. the biggest problem with it is that its so volatile. otto tries to keep his nose off.

[Antoncho]

Hmmm... Now that looks much more interesting - but, pray tell me - what do you use it on, Otto? I'm concerned w/the possible oxidation problems, of course - what does your experience suggest, can you, say, methylate vanillin w/it? What kind of a yield one might expect to get?
And i'd like very much to know also if you ever tried the synthesis you describe - i've seen one, too, and it uses conc. nitric acid, not 65%.

Antoncho

[otto]

Hi Antoncho

currently I do an investigation on eugenol.
 82 g of eugenol (0.5 moles) and a solution of 30 g (0.54 moles) KOH in 200 ml of methanole are stirred in a 1 L RBF at room temperature. then 48 g of the raw 85% MeONO2 (0.5 moles) in 60 ml of methanole is added and stirring is continued for two hours. apparently there is no or little reaction as theres no precipitate at this time. heating in a water bath (never ever get over 150°C with methyl nitrate!) gives loouds of precipitate after half an hour. heating is continued for an additional hour.
after couling the red solution (of hopefully methyleugenol) is decanted from precipitate which is washed two times with methanol. combined washings and solution are heated on a waterbath to remove methanole and methyl nitrate.

I am right now to this point. the precipitate is KNO3. so the nitrate ion apparently wasnt altered in the reaction. there was no exothermic behavior of the reaction mixture, so things seamed to happen smoothly. I will report yield as soon as I finish the work up.

concerning preparation:
AFAIK conc. nitric acid means somewhere around 65%. there are recipies using fuming (nearly 100%) nitric acid and sulfuric. I decided to go for the destillation preparation. in the original recipe they add urea instead of ammoniumsalt to prevent oxidation of the alcohol (any nitrous acid promoting oxidations is destroyed this way), but ammoniumsalts also work. without it you get nitrous gases!
you can re-use the nitric acid remaining after preparation. just destill off the reaction water until 120 °C is reached. (nitric acid azeotrope with water is 121,5°C, containing 69% of nitric acid, so when you reach 121,5°C that means your acid will be of exactly that conc.)

methyl nitrate was used as a methylating agent in the last century even in industry. it also should methylate amines. AFAIK the homologous ethyl nitrate cannot be used in this manner.

otto

[otto]

so I finally worked on. the residue was poured into 300 ml of brine with 10 g of KOH added to get unreacted eugenol into the aqueous phase. after intensive shaking, the mixture needed an hour to separate. the organic phase (approx. 100 ml) was then steamdestilled. unfortunately at this point the 2-necked 2 l RBF broke, heating was done to harsh. all product was lost except 5 ml of an almost white oil, which already had been destilled over. the smell beeing different from eugenol (reminding of asarone) I assume that is methyleugenol and the reaction did take place in the desired manner.

otto

[otto]

in the houben-weyl encyclopedia i have read that it was possible to methylate NaI, NACN and NaSCN w/ nitrate esters. they give a ref Canad.J.Chem. 34,879(1956). unfortunately i am not able to get my hands on it. so i tried it myself in a micro-experiment:

300 mg (1,8 mmol) of KI were dissolved in 5 ml of methanole. then 0,5 ml of raw methylnitrate (85%, rest mainly methanol) were added. immidiately the mixture turned light brown (so some iodine was liberated).
after three days (!) white crystals appeared. the smell of a haloalkane was also there. the crystals were filtered, washed with methanole and tested. its KNO3! assuming the smell is from CH3I, this would be the analogous reaction to making Ch3I from dimethylsulfate.

otto