Sciencemadness Discussion Board - Making a 70% Ethylamine Solution

Making a 70% Ethylamine Solution

johnames - 19-1-2012 at 09:00

I currently have some Ethylamine HCL that I'd like to turn into a 70% Ethylamine solution for the Henry Reaction but have not been able to find a decent way to do it.

I thought of dissolving the Ethylamine HCL in a minimum of water and adding solid NaOH but that would give me less than a 70% solution plus NaCl contamination. Distillation from this solution would result in a lot of ethylamine becoming "stuck" in the solution, just like trying to distill ammonia.

Are there any quantitative (or near quantitative) methods of producing a 70% Ethylamine solution from Ethylamine HCL? Can Ethylamine HCL be used as is in the Henry Reaction?

Adas - 19-1-2012 at 10:06

Don't add water but finely powder the reagents.

johnames - 19-1-2012 at 11:21

Quote: Originally posted by Adas

Don't add water but finely powder the reagents.

So finely powder stoichiometric amounts of Ethylamine HCL and NaOH? That should create roughly 18ml of water and 1 mol of NaCl. How would I get rid of the NaCl at this point?

Seems like NaCl will dissolve in the produced water and Ethylamine will precipitate.

Adas - 19-1-2012 at 11:54

Isn't Ethylamine a gas??? How could it percip.?

unionised - 19-1-2012 at 11:57

Quote: Originally posted by johnames

Quote: Originally posted by Adas

Don't add water but finely powder the reagents.

As Adas pointed out, ethylamine is a gas.
However, with the right equipment you can dissolve that gas into cooled water.

johnames - 19-1-2012 at 12:49

I would have thought that the Ethylamine would dissolve into the formed water.

I guess due to the heat caused by the neutralization the Ethylamine wouldn't dissolve and would instead leave the flask?

I don't see an easy way of finely powdering them together while at the same time condensing the Ethylamine gas evolving from the reaction. The only way I can see it happening is with a strong mechanical stirrer but all I have is magnetic at the moment.

Any other ideas? As a last resort I guess I could drip a saturated solution of Ethylamine HCL into a saturated solution of NaOH and condense the gas. Only problem is the losses incurred but I guess that can't be helped.

EDIT: BTW, boiling point of ethylamine is approximately 62 degrees fahrenheit so condensing isn't an issue.

[Edited on 19-1-2012 by johnames]

johnames - 19-1-2012 at 13:44

Instead of the above I am going to dissolve necessary amount of Ethylamine HCL for the Henry Reaction into isopropanol, neutralize with stoichiometric NaOH, and filter. Hopefully the ethylamine will dissolve in the large excess of isopropanol without any problems. I have looked for solubility of ethylamine in isopropanol but haven't found anything, just that it is soluble in alcohol.

[Edited on 19-1-2012 by johnames]

Sedit - 19-1-2012 at 19:32

Its boiling point is 16 degrees C. Why can't you just distill pure Ethylamine and make the solution from that?

johnames - 20-1-2012 at 10:34

Yes, 16C 62F.

I do not have a mechanical stirrer for the dry mixing of Ethylamine HCl and NaOH and dropping a saturated solution of Ethylamine HCl into a saturated solution of NaOH will lead to losses.

johnames - 20-1-2012 at 11:20

Well...added 10mmol Ethylamine HCL to 20ml Isopropanol, all dissolved with a little heating. Added 10mmol NaOH beads with stirring and most dissolved over 30 minutes. Slight ethylamine smell coming from flask. Solution was decanted and was extremely cloudy.

Currently running a Henry Reaction with the above solution, will let you know how it turns out. I think distilling is a much better method and will try dropping a saturated solution of Ethylamine HCL into a saturated solution of NaOH tomorrow.

EDIT: Question: Why are acetate salts of primary amines preferred over the HCL salts in a Henry Reaction? I always see Methylamine Acetate used instead of Methylamine HCL. Would Methylamine/Ethylamine HCL work just as well as the acetate salts?

[Edited on 20-1-2012 by johnames]

[Edited on 20-1-2012 by johnames]

Sedit - 20-1-2012 at 11:29

There would be no need to use two saturated solutions, you would be much better to drip saturated ethylamine onto NaOH prills in excess as it would aid in drying the ethylamine gas produced which could be feed through a drying tube of CaO or CaOH. Think of it along the same lines of producing dry ammonia gas except it would be much easier to liquify the resulting ethylamine.

johnames - 20-1-2012 at 12:04

Quote: Originally posted by Sedit

There would be no need to use two saturated solutions, you would be much better to drip saturated ethylamine onto NaOH prills in excess as it would aid in drying the ethylamine gas produced which could be feed through a drying tube of CaO or CaOH. Think of it along the same lines of producing dry ammonia gas except it would be much easier to liquify the resulting ethylamine.

Thanks Sedit. I'll try that tomorrow, I won't use a drying tube though since I'll be making a 70% solution anyway. The small amount of water shouldn't hurt in a Henry Reaction.

Sedit - 20-1-2012 at 13:13

A drying tube would still make it easier to determine the concentration as you could just check for weight gain but even so I guess Titration could still give you the figures you need to know before proceeding to further reactions.

johnames - 20-1-2012 at 17:48

Well...looks like I may have made a nice solution of benzoic acid but won't know for sure until tomorrow.

10mmol Ethylamine solution prepared by adding 10mmol Ethylamine HCl in 20ml isopropanol followed by addition of 10mmol NaOH and decantation leaving a cloudy solution

Dissolved 100mmol Benzaldehyde and 2.5ml GAA in 20ml isopropanol followed by addition of 10mmol Ethylamine solution and finally 120mmol Nitromethane.

Refluxed for 3hrs obtaining a yellow solution with white precipitate (hopefully NaCl from neutralization of Ethylamine HCl). Decanted solution from the precipitate and placed in refrigerator.

Most writeups I have seen have ended in two distinct layers after reflux while I had a homogeneous solution. I will update this thread with results tomorrow, hopefully with good news.

[Edited on 21-1-2012 by johnames]

[Edited on 21-1-2012 by johnames]

entropy51 - 20-1-2012 at 18:26

@johnames, could you please elaborate and perhaps give a reference for what you are calling the Henry reaction?

The reactants you are talking about do not compute in the context of the Henry reaction as I learned it back in the Dark Ages.

The Henry reaction I learned goes something like this: http://orgchem.chem.uconn.edu/namereact/henry.html
which seems quite at odds with what you describe. What am I missing?

johnames - 21-1-2012 at 05:35

The Henry Reaction also known as the nitro-aldol reaction. The link you gave is exactly what I'm doing, not sure what you mean.

Aldehyde + nitroalkane + catalyst (ethylamine in my case) = b-nitro alcohol + dehydration = nitroalkene

Is the Nitromethane throwing you off? Using benzaldehyde and nitromethane will result in phenylethylamine after reduction of the double bond and nitro group which is what I am after.

[Edited on 21-1-2012 by johnames]

[Edited on 21-1-2012 by johnames]

johnames - 21-1-2012 at 11:02

Checked the refrigerator today and no crystallization had occurred so I decided to distill Ethylamine instead.

Set up for distillation, filled flask with 1mol of NaOH beads, made saturated solution of .5mol Ethylamine HCL and put it into a pressure equalized addition funnel. Addition commenced at approximately 1 drop per second and approximately 18ml of distillate was collected in a chilled receiver over 1 hour.

Some was lost to the atmosphere and some remained in the NaOH solution. I made a 70% Ethylamine solution by adding water until specific gravity of .800 was met.

I decided to add .5ml of this Ethylamine solution to my presumed failed Henry Reaction and stirred the solution for 1 hour. I placed the solution into the refrigerator and set up for a new Henry Reaction with my freshly made 70% Ethylamine solution.

While the second Henry Reaction ran I got impatient and took the first Henry Reaction beaker out of the refrigerator, still no separation or crystallization. I decided I would heat and stir it for awhile on the hotplate. I cleaned and rinsed off a stir bar (didn't dry it) and dropped the stir bar into the solution. Immediately the flask was full of crystalline material.

I'm not sure if adding the additional 70% Ethylamine solution did anything or not. I will run another experiment on another day with my original method of producing Ethylamine in situ and try a little harder to induce crystallization.