11-26-02 00:57
No 383433
A practical and efficient epoxidation of aromatic olefins using Oxone in a two-phase system (ethyl acetate-water) is described. The reported method is suitable for large-scale synthesis and does not require phase transfer catalyst (PTC) or pH control.
Dioxiranes are highly clean and powerful oxidants and have been applied to a variety of oxidations.1 Recently Shi and co-workers reported a new method for epoxidation using trifluoroacetone in aqueous acetonitrile as solvent and hydrogen peroxide in place of Oxone (potassium peroxomonosulphate) generally used as dioxiranes generator. Though this method is practical and does not need large amounts of potassium carbonate to neutralize the consequently formed potassium hydrogen sulfate, several problematic features are still evident from the standpoint of large-scale manufactureability. For example, aqueous acetonitrile generally does not readily dissolve aromatic olefins due to their poor solubilities. A more fundamental problem is that toxic and rather expensive acetonitrile is unavoidable as an oxidizing mediator to ensure high conversion. Recycling of acetonitrile is also difficult mainly due to boiling point which is almost the same as that of water. In the last two decades, two-phase systems have been investigated in order to overcome these problems. These procedures in general used n-Bu4NHSO4 as the phase transfer catalyst (PTC). As a result, a tedious dropwise addition of base solution over a long time period under strict pH control was needed to avoid the oxidation of the PTC. From environmental and economical viewpoints, we sought a more practical and efficient procedure using an alternative solvent.
Reference
Org. Proc. Res. Dev., 6 (4), 405 -406, 2002. (../rhodium/pdf /two-phase.ox
(Hive Bee)
11-26-02 04:37
No 383479
...the file cannot be found on the server...
.I'd like to know where the author lives... AcCN is not expensive at all, slightly less than US$ 20 per 2.5 L. But all by all, it might be another useful oxone application. As you might have noticed, JOC and JACS are full of articles dealing with olefin epoxidation using oxone as oxidizing agent. However, not all of them are easy to practise, and others are a lab hazard if you don't have a well equiped laboratory.
Ave Hive, synthetisandi te salutant!
(Chief Bee)
11-26-02 05:05
No 383485
The file is now uploaded.
The reason I found this article to be of interest is that as good as every other article on the subject deals with the formation of the epoxide with as high ee (enantiomerical excess) as possible, using strange chiral ketones, amides and porphyrins, and none simply trying to get as high yield of epoxide as possible, using as simple reaction conditions as possible.
Why they say acetonitrile is expensive is because the article deals with industrial scale epoxidation, and by the metric ton, acetonitrile is a great deal more expensive than some ethyl acetate, which stays in a separate phase and everything.
(Stoni's sexual toy)
11-26-02 09:29
No 383563
> AcCN
MeCN?
> is not expensive at all, slightly less than US$ 20 per 2.5 L.
For industrial applications it is a good rule of thumb to divide those prices by 10 or 20 if you want to know the 'true' prices. If industry had to pay only half of what the lab suppliers charge us there wouldn't be any chemical industry.
Just an example: MeOH costs about €/$0.60 per liter from the big manufacturer when you order several barrels or a tank load of it. And guess what: they ship their industrial grade stuff to merck, Aldrich, Fluka etc too. if the quality is good enough it might end up in the reagent grade bottles without further distilling.
Aldrich is exceptionally greedy. It's true, they apparently keep huge inventories all over the world to be able to ship stuff without delay. But most of their products are nothing but cheap standard industrial chems which will be repackaged and sold for a HUGE premium. I've seen chemicals which appear to have a complicated structure, but they are mass produced and can be ordered for only a fraction of the price by the truckload from their original manufacturers. All you need to know is the brand name (which Aldrich of course will not mention to you!). I've seen 1L of such chems sold for $100 and more when in fact you can easily get bigger amounts for completely free (and shipping charges paid by them!) from industrial sources. And if they won't give you a free test sample you can easily buy a 20L barrel or more from them or other resellers for the same amount of money.
And then there are those stupid package prices. Like 5g $16.80, 50g $19.80. WTF is up with that? Their explanation is you save money by not having to store and properly dispose of all the leftovers. Thanks a lot for that good advice. Maybe I should simply send you the money and not expect anything in return, that way I can completely avoid having to pay for toxic waste disposal huh?
Shit sorry off-topic rant. Couldn't help it.
I'm not fat just horizontally disproportionate.
(Chief Bee)
11-26-02 10:03
No 383581
Another case in point is Aldrich 2,5-dimethoxybenzaldehyde ($50/100g) being amber to brown crumbs, while noname HongKong 2,5-dimethoxybenzaldehyde ($50/1000g) is sparkling white rhombic leaflets...
(Hive Bee)
11-26-02 11:14
No 383601
MeCN?
Yes, beat me now, spank me nice and hard
About the industrial scale thing... I'm aware of that, but the problem is that I can't just order solvents in enormous bulk quantities. Even don't have enough place to store them safely. When I was still at high school, the chem lab organizer ordered filters and other simple utilities at a company specialized in Biology laboratory materials. Price was 70% less. Only reason is the typical one: 'chemical industry'. You can see the same for pharmaceutical supplies... outrageous profit margins. Or specialized fields like GC supplies. I installed a new multiplier three weeks ago. It's half the size of my pink and costs US$ 1200...
And about Aldrich: yes, they stink
. I once ordered alpha-pinene from them, which was supposed to be 99+% pure. God bless GCs.... purity even wasn't 80%. Same for Merck's benzaldehydes. Some lots seem to be OK, others need some purification. Also, I don't understand why some catalogues seel a product at 5$/10 gram and at 10$/500 gram...Ave Hive, synthetisandi te salutant!
(Hive Bee)
11-26-02 11:54
No 383610
Also, I don't understand why some catalogues seel a product at 5$/10 gram and at 10$/500 gram
I noticed that too, why is that?
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