Wednesday, November 21, 2007

Low Vacuum Manifold

I couldn't believe my eyes when I saw this. The glass blower who made the manifold has missed the point. Five excellent high vacuum taps combined with a rubbish Teflon tap to produce a nice a shiny low vacuum manifold. Speaking of missing the point check this set up out using the same manifold. Spot 5 mistakes. D!

Tuesday, November 20, 2007

Sleeping with the stirring bars

Speaking of grease it appears that the spider mob has been busy again and sent one of their own to a greasy death. I'm sure that I'll have nightmares about falling into the massive silicon oil bath from hell for a while. D!

Monday, November 12, 2007


Some time ago I received an email from a reader regarding some problems keeping a constant vacuum during a distillation:
"...What type of grease (if any) do you use for the ground glass joints during high (oil pump) vacuum distillation? I use the 'regular' Dow Corning High Vacuum Grease that comes in a funky aqua colored tube. Sometimes when I am carrying this out, all of the sudden partway through the distillation, the pressure will suddenly go from about 0.06-0.1 Torr (where it normally is) to maybe 0.6-1.0 Torr. It doesn't always happen but the effect on keeping track of the boiling point is irritating with the pressure all over the place..."
This is a common problem and it's not necessarily a problem associated with the grease. Let's talk grease first. I have never used the grease mentioned above but I'm sure that there are many excellent greases available and this particular grease may also be good. However, I do know that if you stick to the correct Apiezon grease for your application you won't have any grease related problems. There is a whole range of Apiezon grease and for a high vacuum distillation I would recommend either Apiezon T or H. All the information you need to select the correct Apiezon grease is available here. Don't overdo it when you apply your grease otherwise you'll contaminate your material during distillation.
Interestingly, I recently had a similar problem to that described above when setting up a high vacuum manifold. However, in this case the problem was not the grease but the use of inappropriate vacuum tubing. The vacuum I was operating at was much lower than that described above but the same vacuum surge phenomenon was observed. The solution to this problem is to buy Tygon tubing. It's expensive but it's worth all the money and you usually don't need more than a few meters anyway. Aldrich sell 10 foot pieces of Tygon. It's transparent, nonreactive, flexible, not brittle and doesn't leak. It's simply the best. There's a good post at Wikipedia on grease. Notice the smart way of applying grease using a syringe. Also if you are setting up a high vacuum manifold you should consider reading this post at Org Prep Daily. D!

Saturday, November 10, 2007

Curly Arrow update

Apologies for the infrequent posting. I'm very happy to see that people keep coming to the blog despite this. So what's my excuse this time? Well I just started a new job. I have left academia (for now) and I'm working in a medium size biotech company doing some traditional medicinal chemistry to cure the world etc. However, I have been made an adjunct research fellow at the university and continue to supervise some students so I still have a foot inside the academia door. Also I have become a regular writer for the chemistry magazine published by the Danish Chemical Society which is quite exiting. Unfortunately this only gets published in danish so it won't be of interest to most of you guys. What's even more cool is that they have agreed to set up a blog on the magazines web page where the articles will also be published.
I'd like to thank people for the many emails I get with interesting questions and requests for paper reprints. Thanks for taking an interest. Curly Arrow has now been running for 1 year and seems to be a fairly popular blog (see some stats below). I've even reached the point where people are offering me money to place adds on the blog (You have to pay a lot more guys if you even want me to reply to those emails) and I have been blessed with lots of spam comments linking to porn sites (the pinnacle of my career). I almost clicked on cucumber sex to see what cucumber variety would be employed. D!
From 18th October 2006 to 9th November 2007
Absolute unique visitors: 13,369
Total visits: 34,820 (89.47 Visits/Day)
Average time on site: 1:06 minute
The 10 most frequent visitors identifiable:
(1) Scripps Research Institute
(2) University of Cambridge
(3) Oxford University
(4) University of California
(5) Princeton University
(6) Columbia University
(7) University of Rochester
(8) Harvard University
(9) The Pennsylvania State University
(10) North Dakota State University