11-04-03 09:41
No 468713
Cub wants to use PB(para-benzoquinone) Wacker for preparation of some ketone.He used to prepare ketone via Peracid methods but these methods doesn't satisfy cub.Yields of PB wacker are on the high side,now cub is little worried about Wacker impurities.When O2 is used as reoxidant then safrole oxidises to PMK with some aldehyde being major impurity(about 15% of final product is aldehyde other 85% is ketone).Rhodium says that benzoquinone wacker is very ketone selective.Has anyone ever analysed PMK prepared via PB wacker?Is purity of wacker ketone comparable to purity of peracid ketone?Does vacuum distillation of PB ketone yield reasonably pure ketone?Some refs say propiophenone is major impurity in Wacker oxidation of allylbenzene.How about when safrole is used?Cub couldn't find any info on this subject but cub wants his ketone pure as pure ketone gives better yields and purer final product.
Thanks,
Cublium
(Chief Bee)
11-04-03 18:28
No 468824
Post 438347 (Rhodium: "3-(3,4-Methylenedioxyphenyl)-propyl-met
(Hive Bee)
11-04-03 21:31
No 468859
Is there a way to easily detect this impurity in final product?Cub thinks rextal from acetonitrile should remove it.Does this aldehyde react with hydroxylamine to produce corresponding oxime?
(Chief Bee)
11-05-03 05:54
No 468913
Is there a way to easily detect this impurity in final product?
Yes, a quick TLC will tell you that you have more than one product in your mix.
Cub thinks rextal from acetonitrile should remove it.
As long as you use enough acetonitrile so that the weight loss upon recrystallization is ~20% (the byproduct aldehyde is usually formed in around 15% yield in the case of safrole, and 5% other impurities, such as dimers, aren't unreasonable to expect). I believe it is smarter to remove it prior to amination though, as per the link I gave you.
Does this aldehyde react with hydroxylamine to produce corresponding oxime?
Yes.
(Hive Bee)
11-05-03 07:53
No 468931
Yes, a quick TLC will tell you that you have more than one product in your mix.
Someone should run one like that on some ketone.
As long as you use enough acetonitrile so that the weight loss upon recrystallization is ~20% (the byproduct aldehyde is usually formed in around 15% yield in the case of safrole, and 5% other impurities, such as dimers, aren't unreasonable to expect). I believe it is smarter to remove it prior to amination though, as per the link I gave you.
This sounds like a mandatory step before consuming or giving away the final product,why i haven't a single report on someone doing such thing?Are you sure benzo wacker also gives 85/15 ratio of ketone/aldehyde?I think benzo wacker differs pretty much from 02 wacker,for example in latter,oxidiser(oxygen in that case) is constantly added to reaction mix while in benzo wacker, substance that is to be oxidised,is added durign the reaction.This thing definitely has to be checked and if it turns out to be true,solution to this problem has to be worked out,IMO.
(Chief Bee)
11-05-03 08:27
No 468939
This sounds like a mandatory step before consuming or giving away the final product, why i haven't a single report on someone doing such thing?
People are in general not aware of this aldehyde impurity, as it reacts just like the ketone (and have almost the same boiling point). The final amines both forms nice white crystals, and can hence not be seen. Also, reports tell that the impurity isn't strongly psychoactive, and is thus not easily detected by any taste test as it is present in a relatively small amount.
Are you sure benzo wacker also gives 85/15 ratio of ketone/aldehyde?
It may be more or it may be less, I am only aware of the O2 Wacker being tested. I am completely sure of the fact that it is present though.
(Hive Bee)
11-05-03 08:31
No 468943
Seems like KrZ has run a TLC on benzo wacker ketone and says it's clean.
Post 67760 (KrZ: "Re: O2 Wacker Nightmares", Methods Discourse)
Maybe aldehyde gets oxidised during the reaction and is washed away with bicarb?Or maybe it's never formed in significant quantities?Cub will run few benzos and hopefully he gets a chanche to analyze some PMK from this reaction.
(Chief Bee)
11-05-03 09:32
No 468950
KrZ is not usually a reputable source of information unless duplicated by another researcher: Post 72730 (psychokitty: "Re: O2 Wacker Nightmares", Methods Discourse)