Sciencemadness Discussion Board

Calcium oxide and alcohols/ethers

Rattata2 - 9-8-2009 at 15:58

I know that Calcium oxide, basically being an anhydride reacts with water to form calcium hydroxide according to the formula CaO + H2O -> Ca(OH)2 which of course can be turned to NaOH by reacting with Na2CO3

I am wondering however if calcium oxide would react with dialkyl ethers or alcohols to form the corresponding alkoxides, and if not then why not?

Seems like it would be quite a convenient way to obtain alkoxides if that were the case...CaO + Et2O -> Ca(OEt)2

12AX7 - 9-8-2009 at 18:58

Hmm, could very well be. I recall CaCl2 also forms alcoholates, in analogy to the hydrates it's usually used for. The question here essentially becomes, is it basic enough? In water, it isn't very basic, but under anhydrous conditions, it has something else going for it.

Try it and see!

Edit: whoa whoa whoa, you typed Et2O, not EtOH ;)

Tim

[Edited on 8-10-2009 by 12AX7]

Sedit - 9-8-2009 at 19:56

But he ment Et2O Tim.

I was under the impression that CaO underwent hydrolysis at a very slow rate in H2O.

12AX7 - 9-8-2009 at 23:25

Well, he said ethers, but I don't get why... what the hell do ethers do, they form peroxides and that's about it, isn't it? They're peculiarly difficult to cleave (actually, I don't know of an ether cleavage reaction off the top of my head, aromatic ethers don't count). The reaction is actually balanced, which makes it possible, but I don't see that ether opening up. As for alcohol, it would leave an extra H2O, which would go with another CaO, cutting yield in half and potentially requiring purification.

CaO does react with water exothermically. A sack of fresh CaO dropped into just enough water and stirred around heats the water to boiling as it forms slaked lime (Ca(OH)2).

Tim

DJF90 - 10-8-2009 at 00:23

Hydroiodic and hydrobromic acids are used to cleave ethers, although the latter requires boiling of the reaction mixture. I also seem to recall an oxidising agent that cleaved methyl ethers (I think), it might have been Fetizon's reagent. Calcium oxide is listed as a drying agent for alcohols so I dont think it will react appreciably with them. And yes, the reaction water with CaO is fairly fast and exothermic.

Rattata2 - 10-8-2009 at 07:14

Yeah perhaps ethers wouldn't be the way to go since they're so stable...perhaps alcohols would react in this way but again I'm not really 100% sure on that...I think if an alcohol were to work though it would only produce the mono-alkoxide. Which could be alright but means upon conversion to the sodium salt would yield 50% NaOH and 50% of the alkoxide...

But as you said DJF90, CaO apparently finds use as a drying agent for alcohols so that might not happen either.

Shucks, thought I'd might have found a convenient way to get to those alkoxides!

All well at least this general process can be used to generate hydroxides...thinking about building a setup for calcining CaCO3 to get CaO, so I can use that to produce decently high-purity NaOH in a recyclable manner.

Tis a shame alkoxides are so hard to get at, they'd be useful if there was a somewhat viable path (ie: not reacting alkali metals with alcohols :p)

edit: When I obtain some CaO I will give this a try just to be sure (with both ethers and alcohols) but I doubt the results will be significant...if they are I'll post back :)

[Edited on 10-8-2009 by Rattata2]

12AX7 - 10-8-2009 at 13:14

What about EtCl or EtBr, might that etherate CaO? Hah, something of a Grignard approach there... the result would have to be Cl-Ca-OEt. If that in turn precipitates CaCl2 then you'd be left with Ca(OEt)2.

If CaO is good for drying those, too, then to hell with any of it. :D

Tim

DJF90 - 10-8-2009 at 13:56

I think this is probably the wrong way to go about an alternate prep. of alkoxides. Aluminium alkoxides are relatively simple to prepare, and aluminium is very available. Then perhaps an alcoholic solution of this could be added to an alcoholic solution of NaOH, with Al(OH)3 precipitating? I dont know if this would work - its pure speculation. But its a possibility until proven otherwise.

chloric1 - 10-8-2009 at 17:59

Quote: Originally posted by DJF90  
I think this is probably the wrong way to go about an alternate prep. of alkoxides. Aluminium alkoxides are relatively simple to prepare, and aluminium is very available. Then perhaps an alcoholic solution of this could be added to an alcoholic solution of NaOH, with Al(OH)3 precipitating? I dont know if this would work - its pure speculation. But its a possibility until proven otherwise.


I think the aluminum alkoxides need mercuric chloride as a catalyst. The mercuric salt removes the oxide film exposing extremely reactive Aluminum to the alcohol molecules.

Theophrastus - 13-8-2009 at 05:13

Quote:
[quote=chloric1]
I think the aluminum alkoxides need mercuric chloride as a catalyst. The mercuric salt removes the oxide film exposing extremely reactive Aluminum to the alcohol molecules.


I suppose with a little initial heat, you could also use a smidge of iodine. I've done a similar sort of thing, only with a layer of wax as well, to inscribe some lovely wording into an aluminium plate.

[Edited on 13-8-2009 by Theophrastus]

DJF90 - 13-8-2009 at 06:17

Yes it probably requires a catalytic quantity of HgCl2; All preps I have seen so far use the mercury salt to activate the aluminium. I would think if you "wash" the aluminium with conc. HCl before adding straight into the alcohol them this need of catalyst is bypassed - there should be very little oxide layer if you're quick about the transfer. Iodine could also be a good activator - I'm fairly certain I've seen its use with mercury chloride (i.e. used simultaneously) in an aluminium alkoxide prep.

stoichiometric_steve - 13-8-2009 at 08:26

Quote: Originally posted by Rattata2  
Calcium oxide, basically being an anhydride


Although this is off topic, i think CaO is not an anhydride.

unionised - 13-8-2009 at 10:12

Quote: Originally posted by Sedit  
But he ment Et2O Tim.

I was under the impression that CaO underwent hydrolysis at a very slow rate in H2O.

The slaking of quicklime is farily fast and vigorous.