vmelkon
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Making t-butanol
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]
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Lambda-Eyde
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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. 
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entropy51
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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.
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Lambda-Eyde
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| 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  ).
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turd
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*cough* https://www.sciencemadness.org/whisper/viewthread.php?tid=10... *cough*
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vmelkon
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| 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. |
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?
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kavu
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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]
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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entropy51
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| Quote: Originally posted by Lambda-Eyde | 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.
|
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!
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[Edited on 5-1-2012 by entropy51]
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vmelkon
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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.
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kavu
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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.
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symboom
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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]
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Lambda-Eyde
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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.
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