Sciencemadness Discussion Board

My Phenylethylhydrazine Extraction Mystery..

Maui3 - 23-3-2025 at 06:45

I am currently in the process of making 2-phenylethylhydrazine from hydrazine hydrate! :-)

I tried a few different ways, but I am still a bit lost, since the melting point of my product (the hydrochloride) is not at all like phenylethylhydrazine hydrochloride.

I was hoping to get some advice.

I first mixed 1,5 g Phenethylbromide in ethanol with a mixture of 8 g Hydrazinesulfate and 2 g KOH in water. Then I refluxed it for 4 hours, cooled to room temperature, slowly added HCl to make the hydrochloride. The mixture produced white fumes and heated up quite a lot. Possibly the phenethylhydrazine could have evaporated in the process? Then I evaporated all of the ethanol, freebased the phenylethylhydrazine with KOH, extracted with ethylacetate (in which I do not know if it is soluble), added 30% HCl, as I can't produce anhydrous HCl, and boiled it down. I was left with a white to yellowish powder that is soluble in water.

I freebased the powder with KOH + water, assuming it is something that can actually be freebased. It did not seperate into layers.

The freebase did not react with hypochlorite, or at least not very rapidly like hydrazine hydrate.

I couldn't melt it, though it might have been because of impurities or my poor way to heat it.

I do not see what else it could be that can be extracted this way? I know I am missing something obvious..

bnull - 23-3-2025 at 16:50

It is more messy than mysterious but, since you didn't mention the source of the procedure (it wasn't you yourself who devised it, was it?), there's not much I can do except to give some references and perhaps a little poking around*.

What published procedure did you follow? How much alcohol did you use? How much water? What temperature? You know, that kind of thing.

According to at least two sources (1, 2), the less water, the better. 2 has a pretty neat procedure in page 273. It uses phenethyl chloride and hydrazine hydrate, but you probably can get away with the bromide.
Quote:
Then I evaporated all of the ethanol, freebased the phenylethylhydrazine with KOH, extracted with ethylacetate (in which I do not know if it is soluble), added 30% HCl, as I can't produce anhydrous HCl, and boiled it down.

Why did you do that? If you don't know if it is soluble in ethyl acetate, why do you suppose it was extracted with ethyl acetate?

[1] GB 695513, Manufacture of New Monoalkyl-Hydrazine Sulphates, https://worldwide.espacenet.com/patent/search/family/0045296...

[2] E. Votoček, O. Leminger, Sur la β-phenoéthylhydrazine, Collect. Czech. Chem. Commun. 1932, 4, 271-281, https://doi.org/10.1135/cccc19320271

[3] Robert A. Moss, Clois E. Powell, Alkane diazotates. XIX. Hydrazinolysis of 1-phenylethane diazotate. New synthesis of 1-phenylethylhydrazine (mebanazine), J. Org. Chem. 1975, 40, 9, 1213–1216, https://doi.org/10.1021/jo00897a007

[4] K. A. Jensen, H. R. Baccaro, O. Buchardt, G. E. Olsen, C. Pedersen and
J. Toft, Studies of Thioacids and Their Derivatives. V. N-Substituted Thiohydrazides, Acta Chem. Scand., 15, 1109 (1961), http://actachemscand.org/doi/10.3891/acta.chem.scand.15-1109


*: English is not my first language and I'm not that good with it anyway. Add that to a splitting headache the whole day and you'll see why I seem a bit more cheesed off than usual.

Maui3 - 24-3-2025 at 00:36

Yeah, I agree. It was also mostly mysterious for me - not for you guys :P

I tried some different procedures, like the one you listed: https://doi.org/10.1135/cccc19320271, though using a molar equivalant of phenylethyl bromide instead of the chloride.

I extracted with ethyl acetate, because I was sure I read somewhere that it was soluble.. but then later I started doubting it.. I of course cannot find the source to where I read it now :/

Thank you for the help bnull!

Dr.Bob - 24-3-2025 at 11:01

The desired product should be soluble in ethyl acetate, but you might TLC the extracts to check. I have made other hydrazines before and used either ethyl acetate or DCM as the solvent. They are useful for making pyrazoles.

bnull - 24-3-2025 at 14:56

Quote:
I extracted with ethyl acetate, because I was sure I read somewhere that it was soluble.. but then later I started doubting it.. I of course cannot find the source to where I read it now

If you knew how many times I had to search the same information again and again...

Anyway. Use alcoholic hydrazine hydrate. Lerner (p.114, quoted below) has a procedure that yields 73% starting from 101.5 g of hydrazine sulfate. Scale it down to one-tenth and use 10 g of hydrazine sulfate and 10 g of KOH. I think you can use mortar and pestle in place of the electric grinder and a 100-mL flask with stopper because of the quantities involved.
Quote:
Alcoholic hydrazine hydrate from Lerner's Small Scale Synthesis of Laboratory Reagents

To start, 114 g of 90% KOH flakes (about 1.8 mol) is ground to a fine powder in an electric grinder and added slowly, in a fume hood, with intermittent shaking to 101.5 g N2H6SO4 (0.78 mol) in a 500-mL, glass-stoppered flask. The reaction generates its own moisture by Reaction 11.9, and the addition is slow, ~5 g at a time in the initial stages, with shaking regularly halted to let out any pressure buildup. Should caking occur, as evidenced by lack of substantial heating on the addition of KOH, the contents of the flask are well stirred with a glass rod and the addition continued. When all KOH has been added, 120 mL of absolute ethanol is poured into the flask, the contents are well shaken, and stirring of the now fluid mixture in the stoppered flask is continued magnetically for about 30 min. The precipitate of K2SO4 is filtered and washed together with the reaction vessel several times with fresh absolute ethanol until 240 mL of the latter has been added.


Edit: Missing word.

[Edited on 25-3-2025 by bnull]

Maui3 - 26-3-2025 at 07:35

Thank you both!