Blackout - 29-11-2004 at 19:28
Does someone know how to synthetize pinacolyl alcohol?
[Edited on 10-12-2004 by chemoleo]
Marvin - 30-11-2004 at 00:54
This one is more obvious than it looks from the structure.
Acetone -> Pinacol -> Pinacolone -> Pinacolyl Alcohol.
I suspect this is a set question, but if you are remotly interested in doing this I suggest you use the Magnesium/Magnesium iodide method to make the
pinacol rather than the magnesium amalgam method. Mercuric chloride has toxicity problems of its own but trace organo mercury compounds with much
nastier properties in the product are a big risk.
chemoleo - 30-11-2004 at 10:01
Isn't the pinacol reaction done with acetone and isopropanol as starting reagents, and a strong light source to facilitate the reaction?
I always thought it's an interesting reaction, given that it is hv-catalysed, and has easily available reactants...
[Edited on 30-11-2004 by chemoleo]
Marvin - 1-12-2004 at 02:55
That sounds interesting and plausible. Ive never heard of it though. If you have more information I would be interested. The Mg/MgI2 method is the
only one Ive found apart from electrolytic processes that requires no mercury.
Classically Pinacol coupling is done by adding a small amount of mercuric chloride to magnesium filings, producing amalgamated magnesium. This then
reduces acetone with a reasonable yeild of pinacol after hydrolysis (considering how cheap acetone and magnesium are). A random webpage suggests 40%.
Orgsyn on checking uses the same method claiming a 43-50% yeild based on magnesium.
Pinacol synthesis with light:
chemoleo - 10-12-2004 at 12:57
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325 ml of a 1:1 mixture of acetone and isopropanol by volume are reacted in a vessel into which a quartz lamp is dipped (it gives type, but no
wattage). The temperature is kept at 50 deg C for 3 days (!!), and it needs water cooling, or the dipping needs to be adjusted, and done outside at
cold temperatures (winter must be perfect for it!).
This is destilled, and the fractions distilling over between 75 and 80 deg C at 12 torr (you'll have to look up yourself what pressure in bar
that is) are collected.
These fractions, when weighed, are mixed with 90% of its weight with water.
Pinacol hexahydrate crystallises in plates, and is separated from the above solution. This is dried on air, and after weighing one obtains 50-60 g
(15% of the theoretical yield) of pinakol, MP 46 deg C.
(CH3)2C=O + (CH3)2HCOH ---hv---> (CH3)2HCOH-HCOH(CH3)2
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I really like this method, as it involves minimal amounts of reagents, and something quite unusual - light!!!
Regarding the light source, it should be pointed out that ketones adsorb at 280-290 nm, so a lamp with a high blue content is desired. I should think
that a plain UV lamp would be even better, and facilitate a faster reaction.
Nice prep, huh?
By the way, all sorts of additional reactions can be done with pinacol, i.e. very strong acids convert this to the keto derivative pinacon (sp),
which, when reduced, forms the 2,2 dimethyl 3 butanol. This, with H2SO4, forms tetramethylethylen.
PS: If anyone is interested, the reaction mechanism proceeds by raising the non-bonding 1 p electrons to the pi* state. This then converts to the
triplett state, which is highly reactive and can react with isopropanol while hydrogen is being transferred. The resulting hydroxypropyl radicals then
combine to form pinacol.
PS2 Taken in part from Gattermann, die Praxis des organischen Chemikers.
alchemie - 16-12-2004 at 10:30
Voguel has a procedure for benzopinacol wich is somewhat similar to the one above but uses sun light instead and is done at room temperature.
The stated yields are close to quantitative, but, in practice, high yields can only be reached by letting the mixture stand in a sunny place for a
couple of months.
I don´t know how it applies to isopropanol though.
Blackout - 10-5-2005 at 19:39
After a long search,
Pinacole chemical formula: HOC(CH3)2C(CH3)2OH or C6H14O2
then, for the synthesis of pinacolone (C6H12O):
C6H14O2 + CaO ---> C6H12O + Ca(OH)2 ?
Blackout - 11-5-2005 at 04:30
Nice chemoleo!
Since informations on pinacolyl alcohol and his precursors are mostly unavailable, I don't know if pinacolone would react with an acid (for
example, HI) to produce the PA.
C6H12O + 2 HI ---> C6H14O + I2
I didn't found if iodine was soluble in pinacolyl alcohol...
[Edited on 11-5-2005 by Blackout]
[Edited on 11-5-2005 by Blackout]
Marvin - 11-5-2005 at 07:36
"After a long search, "
Don't you just hate it when a webpage takes 6 months to load?
The time has come the walrus said, to tell us exactly what you want this for. We are attempting to explain chemistry, you apear to be playing
scrabble and the only uses for this compound that suggest themselves do not bear thinking about in relation to someone of your level of cluelessness.