Sciencemadness Discussion Board

Making alkyl halides from denatured ethanol is just really shit

theAngryLittleBunny - 7-2-2018 at 07:28

So, I just needed an ethyl halide for a grignard reagent, and I decided to use denatured ethanol and NaBr, I used about 200g of NaBr, 120g of ethanol, 330g of H2SO4 and 120g of water. Ethyl bromide boils at 38°C, but the flask content was barely boiling at a oil bath temperature of 100°C, it only really distilled at 120°C to 130°C. The yield was about 45% based on NaBr, which is rather disappointing, because normally the yield is more like 90%. I did this reaction before with denatured ethanol, and it was kinda the same. But when I did it with undenatured ethanol, and n-propanol, it always worked just fine with yields around 80 to 90%.

I also tried ethyl iodide, by reacting the ethanol with phosphorus and iodine, which gives me a yield around 75%. But since iodine is rather expensive, I would still love to improve that.

So my question is, could the 1% methyl ethyl ketone in the ethanol have a significant effect? The other things which are in the ethanol are 1% isopropanol, and 10ppm denatonium benzoate, but I don't think they have much of an impact on that.

DraconicAcid - 7-2-2018 at 11:38

Water? Why would you add water to what is essentially a dehydration reaction?

SWIM - 7-2-2018 at 12:50

Quote: Originally posted by DraconicAcid  
Water? Why would you add water to what is essentially a dehydration reaction?


It's been awhile since I did that reaction but I think it required some water to mitigate the oxidizing effect off the H2SO4 on the bromide.

I think you could do it without water with phosphoric acid.

Haven't seen this done, but I'm sure somebody must have tried it.

theAngryLittleBunny - 7-2-2018 at 14:17

Quote: Originally posted by DraconicAcid  
Water? Why would you add water to what is essentially a dehydration reaction?


The "oxidizing" properties of H2SO4 are really exaggerated, even when you mix dry NaBr with 95% H2SO4, it barely oxidizes anything, it turns slightly orange. Anyway, the water is more like a solvent for the NaBr, and I noticed it keeps foaming down. I initially added only 80mL of water, and it foamed like crazy, and when I added another 40mL, the foam immediately just completely vanished.

Corrosive Joeseph - 7-2-2018 at 15:42

Quote: Originally posted by theAngryLittleBunny  

So my question is, could the 1% methyl ethyl ketone in the ethanol have a significant effect? The other things which are in the ethanol are 1% isopropanol, and 10ppm denatonium benzoate, but I don't think they have much of an impact on that.


From what I have read 'denured alcohol' can be a mix of ethanol and any old cheap crap left over at the factory.

They gotta get rid of it some how. Over the years, people have reported occassional random changes of formulations in different locations worldwide.

Refux in excess NaOH to polymerize the crap, cool, add activated carbon and distill.

You are good to go. If you are really fussy, distill a second time.


/CJ

Crowfjord - 7-2-2018 at 16:16

Water is part of the typical reaction forming haloalkanes from alcohols, bromide salts, and sulfuric acid. It keeps the HBr from escaping the reaction as a gas.

Angrylittlebunny, did you reflux the mixture or go straight to distillation? Yields improve significantly with a one hour reflux prior to distillation.

theAngryLittleBunny - 7-2-2018 at 18:32

Quote: Originally posted by Crowfjord  
Water is part of the typical reaction forming haloalkanes from alcohols, bromide salts, and sulfuric acid. It keeps the HBr from escaping the reaction as a gas.

Angrylittlebunny, did you reflux the mixture or go straight to distillation? Yields improve significantly with a one hour reflux prior to distillation.


No I didn't, and honestly making alkyl halides is just so boring that I wouldn't have the motivation to do that additional step. For alkyl iodides mayyybe I'll think about it, but I honestly can't be bothered with alkyl bromides. I also don't think it's needed for alkyl bromides, since with pure alcohols, it works just fine, so I'll have to buy the undenatured alcohol, which kinda pisses me off because it's 3 to 4 times as expensive as any other alcohol.
Quote: Originally posted by Corrosive Joeseph  
Quote: Originally posted by theAngryLittleBunny  

So my question is, could the 1% methyl ethyl ketone in the ethanol have a significant effect? The other things which are in the ethanol are 1% isopropanol, and 10ppm denatonium benzoate, but I don't think they have much of an impact on that.


From what I have read 'denured alcohol' can be a mix of ethanol and any old cheap crap left over at the factory.

They gotta get rid of it some how. Over the years, people have reported occassional random changes of formulations in different locations worldwide.

Refux in excess NaOH to polymerize the crap, cool, add activated carbon and distill.

You are good to go. If you are really fussy, distill a second time.


/CJ


I actually used sodium to dry the alcohol, the resulting sodium hydroxide condensed the methyl ethyl ketone and it turned dark orange after a day, and the I distilled it. The distillate was clear, but it still smelled a little funky. And the formulars are defined where I live, it's 1% methyl ethyl ketone, 1% isopropanol and 10ppm denatonium benzoate. They used these 2 substances because their boiling points are really close to that of ethanol, so it's aĺmost impossible to seperate them by destillation.