Sciencemadness Discussion Board

grignard reaction

nelsonB - 17-11-2013 at 12:22

Hi


i was looking for the grignard reaction with co2
that give a Carboxylic acid
i wonder if the following reaction is possible
Isopropyl chloride + magnesium >> isopropylmagnesium chloride + co2 = Isobutyric acid

vulture - 17-11-2013 at 12:27

EDIT: Ignore, I made a dumb comment below.

Depends on which isomer of isopropyl chloride you use...



[Edited on 17-11-2013 by vulture]

[Edited on 18-11-2013 by vulture]

PHILOU Zrealone - 17-11-2013 at 12:55

Isopropyl chloride is simply another name for 2-chloropropane.
So it should work to make isobutyric acid (or 2-methyl-propanoïc acid).

nelsonB - 17-11-2013 at 13:25

do we should need to acidify the final product ?
cause the acid could react with magnesium to make magnesium isobutyrate

edit:i was thinking adding dry ice as a co2 source and lightly pressurize the set up


[Edited on 17-11-2013 by nelsonB]

Asepsis - 17-11-2013 at 13:47

I'd recommend just pouring the prepared Grignard onto the dry ice with vigorous agitation; no additional pressurization needed. Let it sit until all the dry ice has sublimed. Also, to maximize the isobutyrate, be sure to keep the dry ice 'dry' by not letting it be exposed to atmospheric water until use. This reaction will form the magnesium salt. Adding aqueous mineral acid will render it isobutyric acid (which I imagine to be very stinky). You can extract that into the organic phase easily for purification.
Cheers.

UnintentionalChaos - 17-11-2013 at 14:27

Quote: Originally posted by nelsonB  
do we should need to acidify the final product ?
cause the acid could react with magnesium to make magnesium isobutyrate

edit:i was thinking adding dry ice as a co2 source and lightly pressurize the set up


[Edited on 17-11-2013 by nelsonB]


I don't mean to be condescending, but I dont think you're going to have much luck running a grignard reaction if you cant answer these questions for yourself. It is famously difficult to start and sensitive to trace moisture. The ether can be rather dangerous if mishandled as well. I would start with something easier and more reliable, and teach yourself mechanisms and technique along the way. I'd suggest fisher esterification or an alkyl bromide prep (less hazardous and cheaper than iodides, easier to work with than highly volatile chlorides).

vulture - 17-11-2013 at 14:31

Whoopsie, I was thinking about chloropropane. Indeed, with isopropyl chloride it's theoretically possible.

However, the boiling point of isopropyl chloride is 36C, which is going to complicate things when your grignard reaction starts heating up.

DJF90 - 17-11-2013 at 14:35

Should be fine if you conduct it in diethyl ether, Vulture. It'll just start refluxing with the solvent, so have an efficient condenser in place. It'll probably be better behaved than most other Grignard formations.

vulture - 17-11-2013 at 14:49

I'm not sure, I expect this reaction to show oscillating behavior.

iPrMgCl is made in large amounts on an industrial scale and is commercially available, so a patent search should provide some clues.

Anyway, I'm not sure this is an economical method of producing isobutyric acid. Biochemical synthesis or synthesis from other OTC precursors might be more viable.

nelsonB - 17-11-2013 at 14:57

yeah i imagine using dry ice as a source of carbon dioxide also double as a method to cool down the Isopropyl chloride
that have a low boiling point

deltaH - 17-11-2013 at 15:29

? 2iPrOH(l) + 3Mg(s) + 4CO2(s) => Mg(iBuO2)2(s) + 2MgCO3(s) + H2(g) ?

Any chance in hell?

[Edited on 17-11-2013 by deltaH]

UnintentionalChaos - 17-11-2013 at 16:37

Quote: Originally posted by vulture  
I'm not sure, I expect this reaction to show oscillating behavior.
...
Anyway, I'm not sure this is an economical method of producing isobutyric acid. Biochemical synthesis or synthesis from other OTC precursors might be more viable.


1) wat?

2) It really isn't very economical. Isobutyraldehyde is made on a massive industrial scale by hydroformylation of propylene. Most of this is probably hydrogenated to isobutanol (which is available online if you look hard enough). Oxidation with acidic dichromate would produce the desired acid. PMMA (poly(methylmethacrylate)) can be thermally cracked to methyl acrylate and hydrogenated to methyl isobutyrate though this is probably not a great approach either.
Quote: Originally posted by nelsonB  
yeah i imagine using dry ice as a source of carbon dioxide also double as a method to cool down the Isopropyl chloride
that have a low boiling point


The isopropyl magnesium chloride would have to be formed in ether with exclusion of air, reactive gases (CO2, SO2, etc.) or proton sources (alcohols, water, etc.) prior to addition of CO2 in any form. By the time you add dry ice, there is no iPrCl left.
Quote: Originally posted by deltaH  
? 2iPrOH(l) + 3Mg(s) + 4CO2(s) => Mg(iBuO2)2(s) + 2MgCO3(s) + H2(g) ?

Any chance in hell?

[Edited on 17-11-2013 by deltaH]


No. Just because you can balance an equation doesn't mean it happens. If you knew anything about the mechanism of a grignard reaction, you would know that this is impossible.

Furthermore, isobutyrate would be iPrCO2-1 not iBuO2-1.

[Edited on 11-18-13 by UnintentionalChaos]

nelsonB - 17-11-2013 at 16:51

yeah Asepsis
that stuff must stink but as ester usualy are fruity
as ethyl butyrate has a odor that is close to pineapple
i wonder what would be the smell of ethyl 2-methyl-propanoate
here some description
Quote:

ethyl 2-methylpropanoate Organoleptic Properties Odor Type : fruity Odor Strength : high , recommend smelling in a 10.00 % solution or less Odor Description: at 10.00 % in dipropylene glycol. sweet ethereal fruity alcoholic fusel rummy Odor Description: Sweet, etherial and fruity with pungent, alcoholic, fusel and rummy nuances Mosciano, Gerard P&F 22, No. 2, 69, (1997) Taste Description: at 12.50 ppm. Pungent, etherial and fruity with a rum-and egg nog-like nuance Mosciano, Gerard P&F 22, No. 2, 69, (1997) Substantivity : 4 Hour(s)



[Edited on 18-11-2013 by nelsonB]

deltaH - 17-11-2013 at 17:07

Quote:
If you knew anything about the mechanism of a grignard reaction, you would know that this is impossible.
What exactly in the Grignard mechanism prevents this from happening with iPrOH please, I had a look at it and cannot decide why this is a problem? I'm not saying that this is possible, I am simply trying to understand, if not, why not.

As for the iPrCO2, good point!

[Edited on 18-11-2013 by deltaH]

nelsonB - 17-11-2013 at 18:44

if the isopropylmagnesium chloride react with water
would not it make propane ?

Crowfjord - 17-11-2013 at 19:01

@deltaH: magnesium reacts with alcohols to give the alcoxide, i.e., it reduces the hydroxyl hydrogen rather than the ipso-carbon.

@nelsonB: reacting Grignard reagents with water gives the alcohol.

BTW, Wikipedia has a good article on the Grignard reaction, check it out

nelsonB - 17-11-2013 at 20:03
Quote:

Reactions of Grignard reagents Grignard reagents and water Grignard reagents react with water to produce alkanes. This is the reason that everything has to be very dry during the preparation above. For example:


Quote:

The inorganic product, Mg(OH)Br, is referred to as a "basic bromide". You can think of it as a sort of half-way stage between magnesium bromide and magnesium hydroxide.

http://www.chemguide.co.uk/organicprops/haloalkanes/grignard...


[Edited on 18-11-2013 by nelsonB]

Crowfjord - 17-11-2013 at 20:26

Whoops, my mistake! I was thinking of reaction with oxygen for some reason...

nelsonB - 17-11-2013 at 20:37

when reading on grignard its support lot of chemical reaction i wonder why i din't study more on this
Victor Grignard have done an amazing job

zenosx - 19-11-2013 at 17:09

I found these video's helpful when first studying grignard reagents. I will also say again from above that they are Incredibly difficult to get started sometimes and Incredibly sensitive to moisture. The I2 crystal trick is handy however...

Introduction to Grignards.

Pickardjr - 20-11-2013 at 09:59

the mag chlorides aren't prepaid like the mag bromides. I read that chlorobenzene is added directly to magnesium and heated in a sealed tube without solvent. don't know about chloropropane but I bet its a bastard to get going under ordinary conditions like other grignards.

zed - 25-11-2013 at 17:09

Umm. Are you trying to produce a specific molecule? If so, the production of (CH3)2- CH-COOH, MIGHT be more easily achieved by the hydrogenation of Methyl Methacrylate, followed by hydrolysis. Methyl Methacrylate itself, can be produced by the pyrolysis of Lucite.