Sciencemadness Discussion Board - Making t-butanol

Making t-butanol

vmelkon - 4-1-2012 at 07:22

hi, I am a noob when it comes to organic chemistry but I'm willing to learn.

I was looking at wikipedia and also a organic chem textbook.
Wikipedia doesn't provide a recipe and I don't have those startup chemicals.
And as for my textbook, I don't know if it is a theoretical exercise or not.

According to my book, you can use a grignard reagent.
You need 2-propanol. You need methanol.

I'm guessing you need to do
methanol + HBr => CH3Br (bromomethane)

and then to make the grignard reagent :
CH3Br + Mg => CH3MgBr

and then add grignard reagent to 2-propanol :
2-propanol => t-butanol

Does any of that make sense (the CH3 would attach itself to the 2nd carbon on 2-propanol)? Are the steps above documented somewhere properly?

The 2-propanol route sounds interesting since I have it in 99% form.

[Edited on 4-1-2012 by vmelkon]

Lambda-Eyde - 4-1-2012 at 07:32

The grignard reagent would react with 2-propanone, acetone. Also, methyl bromide is a gas. Methyl iodide would be a much better choice. If you are a "noob" to organic chemistry, maybe the Grignard reaction isn't the best place to start.

entropy51 - 4-1-2012 at 07:43

Quote: Originally posted by Lambda-Eyde

The grignard reagent would react with 2-propanone, acetone. Also, methyl bromide is a gas. Methyl iodide would be a much better choice. If you are a "noob" to organic chemistry, maybe the Grignard reaction isn't the best place to start.

Methyl bromide is a gas at room temperature, but it can be dissolved in ether as its being generated and then dripped into a Grignard. The gas stream has to be dried before it enters the ether of course. The starting materials for methyl bromide are easier to find than the ingredients for methyl iodide.

When I worked in industry we ran Grignards with methyl bromide all the time. We ran the liquid out of a tank into the addition funnel and dripped it into the reaction. It was strange to see it boiling in the addition funnel, but since the funnel was stoppered the vapor boiling off went into the reaction as well.

Lambda-Eyde - 4-1-2012 at 07:50

Quote: Originally posted by entropy51

When I worked in industry we ran Grignards with methyl bromide all the time. We ran the liquid out of a tank into the addition funnel and dripped it into the reaction. It was strange to see it boiling in the addition funnel, but since the funnel was stoppered the vapor boiling off went into the reaction as well.

Yes, in industry that might be the case. In industrial settings, handling gases is much easier and more focus is on the economical aspects and feasability of scaling up. When doing a small-scale reaction however, convencience often decides what reagents to use. Example: high-pressure hydrogenation with Pt catalysts vs. atmospheric reduction with LAH. Surely you agree with me.

Not saying that MeBr (or even MeCl) can't be used in a laboratory setting, though. I might even do it myself one day. But for most people, handling a liquid over a dissolved gas is often the preferred solution (pun intended

turd - 4-1-2012 at 08:31

Quote: Originally posted by Lambda-Eyde

Not saying that MeBr (or even MeCl) can't be used in a laboratory setting, though. I might even do it myself one day.

*cough* https://www.sciencemadness.org/whisper/viewthread.php?tid=10... *cough*

vmelkon - 4-1-2012 at 10:35

Quote: Originally posted by Lambda-Eyde

Why 2-propanone? The text book describes it with 2-propanol since the OH groups doesn't participate in the reaction.

Methyl iodide sounds easier to prepare (according to wikipedia it is methanol + iodine with present of red phosphorus (I guess from a match). Does it work?

kavu - 4-1-2012 at 11:28

If you wish to prepare t-BuOH with Grignard reaction you will need acetone and methylmagnesium reagent as stated. The gignard reagent is the nucleophile, attacking the carbonyl carbon. Look up the mechanism at http://www.organic-chemistry.org/namedreactions/grignard-rea.... You can see the big picture: R group from the organomagnesium halide gets attached to the carbon with a C=O. As this happens the C=O bond turns to a C-O bond, oxygen carrying the pi-electrons and thus having a negative charge. Once you toss in aqueous acid, the oxyanion gets protonated and an alcohol is produced. You see, grignard reagent + ketone = tertiary alcohol, grignard + aldehyde = secondary alcohol, gignard + formaldehyde = primary alcohol. If you draw the stucture of acetone and methylmagnesium iodide and then the mechanism as shown in the link, you will see that t-BuOH should form. Gignard reagents are not stable in the presence of water and dry diethyl ether of THF is needed to produce them. Also MeI is a rather nasty chemical and should be handled with care. There is no problem using methylmagnesium iodide though, it's a general source of Me⁻ for synthetic purposes.

[Edited on 4-1-2012 by kavu]

Magpie - 4-1-2012 at 12:16

Quote: Originally posted by vmelkon

The text book describes it with 2-propanol since the OH groups doesn't participate in the reaction.

This is an error.

Grignard reagents will abstract the H from the -OH group of an alcohol to produce an alkane. This will also occur with the following:

HOH, ROH, NH3, R2NH, ArOH, RCO2H, RSH, and terminal alkynes.

entropy51 - 4-1-2012 at 17:37

Quote: Originally posted by Lambda-Eyde

I don't agree that MeBr is not a good methyl source for Grignards in the amateur setting. I've used in many times downstairs in the basement. I prefer it to methyl iodide actually.

I've also used it in other reactions in place of MeI. MeBr is much under appreciated.

Good chemists can work with gases just as easily as liquids.

Quote: Originally posted by Nicodem

Excellent job!

For years I was wondering why nobody reports using this method for methylating phenols while it is the most obvious choice for those who don't have any dimethyl sulfate or methyl iodide. I often considered trying it myself, but then picking up the bottle of dimethyl sulfate off the shelve is so much easier, so I never bothered. I'm glad someone else finally did it. You really should write down a full report for the Prepublication section!

[Edited on 5-1-2012 by entropy51]

vmelkon - 5-1-2012 at 02:18

Looks like I was wrong. The chapter is called "Multistep Syntheses".
Looks like 2-popanol can be converted to acetone with a Cr(6+) ion and I have no idea what that means in terms of actual conditions

This chapter doesn't specifically mention making t-butanol. I'm just looking at tables with general chem equations with "R" all over the place.

kavu - 5-1-2012 at 02:55

Reading books on practical organic chemistry gives you an idea on what the chemistry looks like in lab. Vogel's textbooks are freely available online and cover many useful preparations, including Gignard reactions.

symboom - 5-1-2012 at 11:08

that would sound great methyl iodide is a liquid

Methyl iodide can also be prepared by the reaction of methanol with potassium iodide, catalyzed by acid:

CH3OH + KI + H2SO4 → CH3I + K2SO4 + H2O
then purification by distilling at boiling point 108 °F

oh and this probally also forms

Alternatively, it is prepared from the reaction of dimethyl sulfate with potassium iodide in the presence of calcium carbonate:[4]

(CH3O)2SO2 + KI → CH3I + CH3OSO2OK
2 CH3OH + H2SO4 → (CH3)2SO4 + 2 H2O

then reacting it with magnesium turnings

forming the reagent

then reacting that with absolute isopropanol (rubbing alcohol) alcohol

Like many organoiodide compounds, methyl iodide is typically stored in dark bottles (amber dark bottles"clean hydrogen peroxide bottle) to inhibit degradation cause by light to give iodine

excerp from http://en.wikipedia.org/wiki/Methyl_iodide

and http://en.wikipedia.org/wiki/Dimethyl_sulfate#Production

[Edited on 5-1-2012 by symboom]

Lambda-Eyde - 5-1-2012 at 11:11

The reaction doesn't work with sulfuric acid. It will oxidize the iodide to iodine. If you look in the prepublications forum, Peach even did an experiment on it (which of course failed).

Phosphoric acid and p-toluenesulfonic acids are both non-oxidizing and suitable.