The Vespiary
The Hive => Newbee Forum => Topic started by: andromeda on December 05, 2003, 01:02:00 AM
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1) After the initial 4-5hrs 106deg reaction between 35-40% formaldehyde and am.cl, is there any advantage/disadvantages in using a rotavap in the following phases of the reaction?
2)In the me.am reaction photoessay on rhodium, it states to heat to 160deg to drive water out. I thought that going above 110deg produced di-me.am. Is this heating to 160deg ok because of its short time span?
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There is no formaldehyde in rx mix to react with methylamine to form dimethylamine when you heat it to 160.It's during the reaction when temp must be kept below 110C
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To elaborate a bit. In the preparation of methylamine from ammonium chloride and formaldehyde, excess ammonium chloride is used so that after the 5 hours at 104°C all of the formaldehyde gets used up. You can then heat the mixture much hottter without forming dimethylamine because there is no longer any formaldehyde available to react with the methylamine to produce dimethylamine.
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Why couldn't you initially heat the contents to 120, cool/filter, add more formalin and bring back to 120?
The post you reference is just following a published procedure by a trusted source.
Why couldn't you initially heat the contents to 120, cool/filter, add more formalin and bring back to 120?
Sure this would probably work too. But unless you are planning on producing dimethylamine in ton quantities and have the chemical analysis capabilities required to optimize a new procedure it is generally better just to follow a well established procdure.
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>why is it that in the preperation of dimethylamine, as outlined Chimimanie:
>"Dimethylamine from formaline" (Tryptamine Chemistry) the rxn proceeds the
>same as if one were to make methylamine, then, the rxn temp is raised?
Simple, because the steps are:
NH4Cl + HCHO -> CH2=NH.HCl + H2O
CH2=NH.HCl + HCHO + H2O -> CH3NH2 + HCOOH
Then, once the methylamine is made in good yield they go on to add more HCHO (that definitely should have caught your eye):
CH3NH2 + HCHO -> NH(CH3)2 + H2O
Right? The problem with high heat at the beginning with trying to form just methylamine is that the dimethylamine forming reaction takes place faster at higher temperatures. I imagine other reactions could place too that favor using a lower temp with this rxn. (that is, assuming anyone has taken the time to optimize this rxn)
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If I'm right, you can't use UV light to detect dimethylamine. You'd have to first develop the plates... (but, UV is good for aromatics)
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Does anyone know or could find out solubility of dimethylamine.HCl in chloroform?
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thx for the answers.
i have found that by doing the following procedure, i can produce more than enough meam.hcl easily:
1) the initial rxn at 104deg for 5 hrs, cooling and filtering,
2) reducing volume by 50% in a rotavap under vac, cooling and filtering,
3) rotavaping until evap flask is full of white crystals, cooling and filtering,
4) last rotavap of small amount remaining, cooling and filtering,
5) washing crystals with cold chloroform, filtering,
6) 1x recrystalization with meoh
For some reason, i have found it easier (and prefer the look of the crystal) when recrys from meoh.