Tempo Oxidations Part II

I've previously mentioned the TEMPO/BAIB combo for oxidising alcohols to carboxylic acid. A very smooth and mild oxidation. Back when we discussed this particular reaction we had a brief discussion about stopping this reaction at the aldehyde stage. This is indeed what this particular reaction type was developed for originally and so when I recently had to oxidise a primary alcohol to an aldehyde I thought I'd give it a go. By chance Delfourne et al. (DOI: 10.1021/jm0308702) had previously made the same compound using a TEMPO oxidation. Too easy! According to the procedure the product was obtained in quantitative yield and purification wasn't required! This particular procedure involves a crazy cocktail of reagents. This is what I did:Fortunately, all the ingredients are reasonably affordable. Mixing it all up and adding the alcohol gives a biphasic reaction mixture that looks a bit like Schweppes Orange:
However, unlike Delfourne et al. my final product wasn't clean after a simple work up. Succinimide was simply precipitating everywhere and hence some silica was required. In the end a filtration through a silica plug proved sufficient to give clean product on a reasonably large scale (18 grams) in excellent yield (97%). So despite the fact that a simple work up wasn't sufficient to clean the product up this is an easy to do reaction that I would recommend to anyone who's tired of stinky old Swern. D!

Fun with singlet oxygen

So finally I'm back fresh and invigorated after numerous bottles of awesome South Australian Wine. I'd like to recommend Primo Estate/Joseph, Kay Brothers, Pertaringa and Leconfield/Richard Hamilton in McLaren Vale and Langmeil, Rockford and Richmond Grove in Barossa Valley. Anyway, first day back at work I did a photolysis as we often do were I work. In other words a diene is irradiated in the presence of oxygen and a triplet sensitiser (in this case Rose Bengal). I love this reaction because it's absolutely beautiful. Check it out man:
Now the above reaction is obviously totally irresponsible and was only on for less than a minute so that I could take the picture. We are dealing with a fancy piece of glassware that has oxygen bubbling through it whilst two flood lamps are hammering photons away generating singlet oxygen and in the process heating the fume hood up big time. Hence, aluminium foil on the bottom of the hood is required to literally avoid a melt down and I'll be hooking a pump up that sends ice water through the cooling jacket. Moreover, I'm synthesising an endoperoxide - AAaARRRrGGGHhHh PEROXIDE - yeah I know but they are really quite stable. In fact our friends at the defence force haven't been able to blow them up so we aren't too worried. However, to avoid any nasty surprises we try not to make more than 5-10 grams of endoperoxides at any time. So as I said totally irresponsible hence I proceed to wrap this beautiful reaction up in two blasts shields covered in aluminum foil, pull the sash down and hook a cooling box/pump up to the glass ware and the final set up looks like this:
Well at least I know it's beautiful behind all that plastic and aluminium foil. This particular day I was doing the following photolysis:

Reactions of this type generally work quite well giving yields in the 40-70% range and since dienes are easily accessible using classic Wittig chemistry we consider making endoperoxides quite trivial. So why was I making this particular endoperoxide? Well if I told you I would have to kill you. There should be a paper coming out later this year featuring amongst others this particular endoperoxide turning into a supa cool cyclopropane in one (yes one) synthetic step so keep your eyes open for that paper. Some of you are probably wondering what Rose Bengal is. Behold the halogenated beast:We tend to use the bis-triethyl ammonium salt (as shown) because it is nicely soluble in organic solvents such as dichloromethane. D!

Off to McLaren Vale (and Barossa Valley)

As someone pointed out I'm a slacker. I'm off to McLaren Vale for a bit of a wine adventure returning on Thursday and departing the same day for another little wine adventure in Barossa Valley. I expect to tune my brain to chemistry again in a weeks time. I really have to talk a bit about some TEMPO oxidations and Mannich reactions I've been messing around with lately. So come back in a week or so for the lowdown. D!

Off to Chicago

Gone Fishing

Penfolds Koonunga Hill - 30th Anniversary

I was looking for a Penfolds Bin 51 Riesling in the local liquor store the other day but couldn't find it so I decided to ask the staff if they had any. The proprietor told me that he generally didn't stock Penfolds wines which struck me as odd since Penfolds is the most iconic Australian winery and located only a short drive from where we where. Anyway, a long discussion on the quality of Penfolds wines before and after the acquisition by Southcorp and more recently by Fosters ensued (as you would expect the quality hasn't exactly improved). Anyway, why am I writing all this here? Well as it turned out he did have some special release Penfolds Koonunga Hill to commemorate the 30th Anniversary of the first release. The bottles have had special sleeves designed for them making it virtually impossible to sell the stuff since they look ridiculous. However, the sleeve on the Chardonnay was so funny I ended up buying a bottle (Check out the photo). The bottle is "decorated" with the periodic table of the elements and the structure of what seems to be cyclopentyl-methyl-carbonate (or something?). What have the marketing guys at Penfolds been smoking recently? Unfortunately, the stuff tastes terrible so I wouldn't recommend buying it. D!

How (not) to get rid of old diethyl ether

These darn old containers of diethyl ether that you need to get rid of... have you ever considered opening them with an axe and then pour them down the sink?

"A University of Washington pharmacology professor pleaded guilty in federal court today to charges of illegally dumping a chemical down a laboratory sink.

Daniel Storm, 62, last June broke open five containers of ethyl ether with an ax and dumped the contents, according to a release by the U.S. Department of Justice. UW health and safety inspectors had surveyed Storm's lab and determined that five containers of ethyl ether, which is highly flammable, needed to be disposed, but Storm didn't want to pay $15,000 out of a lab operations account to get rid of the substance properly. Storm then concealed the dumping, according to the Justice Department.

Under the terms of the plea agreement, prosecutors have recommended Storm be given probation when he is sentenced June 18. He faces a maximum five years in prison and a $250,000 fine.

Storm continues to work at the UW, where he faces an internal disciplinary process."

Well, as this post in The Seattle Times illustrates, it is - quite surprisingly - not too good an idea!

C!

Gurrs Microscopical Stains and Reagents

Don't you just love the way they used to store chemicals back in the day when men where men and women were women? We use a fair bit of Rose Bengal as a triplet sensitiser for the photochemical synthesis of 1,2-dioxines from dienes and oxygen. At the moment we are using some top-quality Rose Bengal from the world renowned chemical supplier Gurr:

Chemicals just don't come in containers like this anymore. If Sherlock Holmes ever used Rose Bengal he would most certainly have been a Gurr-man. Unfortunately, I haven't been able to get a new catalogue from George T. Gurr. I did however find this add for his products in Journal of Physiology (March 1953, Vol. 119, No. 4):

I wonder what happened to goode olde George and his microscopical reagents. D!

Quinine

Flipping through C&EN brought my attention to a recent review published in Angewandte Chemie (DOI:10.1002/anie.200601551) about the history of quinine synthesis. If you like (somewhat lengthy) stories about the history of chemistry and natural product synthesis, you might want to print this one out for bedtime reading.

And don't forget to drink a gin and tonic now and then to keep the malaria away! C!

A Column Apart

It's quiz time. Check out the flash column below. I may look like any other flash column but it is a truly unusual little fella. This is the first chromatography column of this kind I have ever put eyes on. I admired it for quite a while together with the other guys in the lab. We were all there for the packing and loading. Amazing stuff...our presence really freaked the guy running the column out. I don't think he grasped the significance of what he was doing. Anyway, what do you think is so special about it? D!