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Synthesis of 4-methylpropiophenone from 4-methylbenzaldehyde with diazoalkanes

William Dampier

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Diazoalkanes synthesis:
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1. Diazoethane can be synthesized from ethylamine hydrochloride, which, when reacted with urea, is converted to ethylurea. It reacts directly with sodium nitrite, NaNO2, and then in an acidic environment to form nitrosoethylurea. Eventually, this nitrosourea reacts with potassium hydroxide and, removing one equivalent of potassium cyanate, KCNO, forms diazoethane, and nitrosoethylurea forms diazomethane.


Propiophenone synthesis:
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1. A solution of diazoethane (6.7 g in 150 ml dry ether) was added to a solution of benzaldehyde (10g) in a small volume of ether, cooled in ice.
2. When nitrogen evolution had ceased (24 hours), ether and the excess of diazoethane were removed by distillation, and the colourless residue shaken with sulphuric acid to acid pH for 8 hours.
3. After neutralisation with sodium hydroxide, steam distillation, extraction with ether, and drying over sodium sulphate, the product was recovered by evaporation and shaken with saturated sodium bisulphite solution for 5 hours.
4. The unchanged oil, separated in the usual manner, yielded propiophenone (12 g).
 
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ASheSChem

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the final result is 4-methylpropiophenone ?
 

WundaBearz41

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I've been researching these 4-methylpropiophenone syntheses' and came to the conclusion there is no way to make 4-methylpropiophenone with OTC reagants. Some are very protected, is that correct?
 

woohoo

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Please note that diazoalkanes is extremely dangerous.
"In one instance a laboratory worker consumed a hamburger near a fumehood where he was generating a large quantity of diazomethane, and died four days later from fulminating pneumonia."
From wikipedia.

This chemical is only for very skilled chemists, don't work with it at home.

This also an explosive too.
"The compound explodes when heated beyond 100 °C, exposed to intense light, alkali metals, or calcium sulfate. Use of a blast shield is highly recommended while using this compound. "

quotes from wiki

Carcinogenic too, but wiki says it has much higher acute toxicity, than carcinogenic.
Better use fluid reactor, than make it in a flask.
 

William Dampier

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I've been researching these 4-methylpropiophenone syntheses' and came to the conclusion there is no way to make 4-methylpropiophenone with OTC reagants. Some are very protected, is that correct?
There are legal ones, but for vapor-phase synthesis.
 

William Dampier

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Please note that diazoalkanes is extremely dangerous.
Yes, the substance is very dangerous (poisonous and explosive), requires careful handling and experience, you are right.
 

serialz

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Hello,

Wouldn't it be easier to prepare ethyl bromide? Add it to the benzaldehyde via a grignard reaction and then oxidize it with NaClO + Acetic acid. (Or KMnO4 - NaCr2O7)

I think that Propiophenone can be obtained "more easily" in this way?
 

Sitr1x

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I'm really hoping there is a safer method that is "known and tested" that I can try to get some 4-Methylpropiophenone...
 

G.Patton

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serialz

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Would this be a viable route for a new chemist to try does anyone know?

https://chemistry.mdma.ch/hiveboard/novel/000423945.html
The beginning of the synthesis is a Friedel Craft acylation. (the part with aluminium chloride)

Nothing is "complicated" in organic chemistry. But experience and study of this discipline helps to avoid the danger of synthesis.

In the Friedel Craft alcylation step, hydrogen chloride in quantity escapes from the reaction medium. Therefore, it should be done with either a gas trap or a fume hood.

So if you follow the "recipe" (God, I hate writing this as an organicist.) it should not be complicated.
 

Sitr1x

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Thanks G and serialz for replying.

Lol, yes the word "recipe" is very strange when you use it in such context as Chemistry, sounds like your cooking up some big dinner 🥣

Plan on using a gas trap for sure when I get to that part. Am going to try to nail the 2-iodo-methylpropiophenone bit first then proceed from there. Will keep everyone posted on how I go.
 

William Dampier

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Hello,

Wouldn't it be easier to prepare ethyl bromide? Add it to the benzaldehyde via a grignard reaction and then oxidize it with NaClO + Acetic acid. (Or KMnO4 - NaCr2O7)

I think that Propiophenone can be obtained "more easily" in this way?
The industrial method is a cross-gas phase synthesis. Here we do not publish because of the requirements for specific equipment. The synthesis of this topic for informing.
 
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