Can someone help me with a suitable solvent system for the analysis of products from the malonic-ester synthesis?
Also, what sort of plate coating is suitable?
The reactions involve the mono & di alkylations fom methyl to hexyl.
Thanks
Frank.ziqquratu - 4-7-2010 at 18:00
Silica plates should work fine. For those compounds, I'd suspect hexane with either diethyl ether or ethyl acetate (whatever you have on hand) should
work fairly well.
I'd start with 3:1 hexane/ether (or about 9:1 hexane/EtOAc), and see how it goes. You can adjust the polarity from there once you see how your
compounds run.
Personally, I keep a few bottles of pre-mixed solvent which are appropriate to most of the compounds I work with (3:1 hexane/ether and 3:1
hexane/EtOAc being the main ones). Usually, I run the sample once with one of those, then adjust the solvent composition as required from the
information that gives me. Only exceptions are if I have been provided with a solvent system, or if I KNOW that my normal systems are going to be too
polar/not polar enough.FrankMartin - 4-7-2010 at 18:41
Thanks. I have been searching Merck and others for supply of plates and they're very expensive. I will try making my own from microscope slides and
a silica slurry. I suppose the slurry can be made with hexane? Will I need some sort of binder to adhere the silica to the plate?
Franknot_important - 4-7-2010 at 19:39
There's been other discussions on making LC plates, and I believe references were given for detailed instructions. If the site's search function
doesn't find them for you, use Google's avanced search restricted to this site,m or just do a Web search on 'making tlc plates'.
Those MIT lectures are incredible! I've seen them before and still watch them.FrankMartin - 8-10-2010 at 18:24
ziqquratu:
I have done as you suggested and used silca plates and a solvent mix of 25%tBuMeEther and 75% nHeptane to run them. I visualized the result with
iodine vapour. 254nm UV did not work.
The first trial was a prep of nButyl Malonic Ester (LHS) cf a sample of the Merck pure material (RHS).
The Second trial used smaller samples spotted on the plates.
Included are pictures, including the use of a trial edition densitometer program into which the plates images were just up-loaded digital photos.
I am new to all this and I need help in finding a simple inexpensive densitometer program for routine results. The one shown is very expensive.
Regards, Frankchemrox - 8-10-2010 at 20:53
Please re-post the pictures. They didn't show up in your post. I2 seems a very versatile visualization medium doesn't it? I use it for esters and
amines. I get most of the spots.Lambda-Eyde - 9-10-2010 at 02:10
Those MIT lectures are incredible! I've seen them before and still watch them.
Yeah, it's just too bad that the woman lecturing chemistry 5.301 has the most horrible, nagging, nasal, whining voice of all the MIT employees.
I recommend physics 1.01-1.03 with Walter Lewin. Mr. Lewin is without doubt one of the greatest pedagogic minds of the 20th century.
Reposted pictures of TLC plates.
FrankMartin - 9-10-2010 at 16:01
I upload the pictures (TLC plates) relevant to my post of the 9Oct10
peach - 11-10-2010 at 02:23
You can run semi-usable plates using proper lab filter papers if the TLCs are too much.
Filter papers are great for looking at solvents prior to using the plates. You can simply cut lots of strips, put a blob of the result on it, even
raw, and then dunk each and let it run. If you're getting careful, a dilute spotting solution is the way to go.
The resolution isn't as good, as the fibres are quite big and randomly dispersed, so you're more likely to get some streaking or blooming of the
spots. But, on developing them, the papers will give you a rough idea how it's responding to the different solvents and which might be a good idea.
Having the results a bit blurry will also encourage you to pick a solvent or pair that will produce a very fine split on the TLCs.
What's that software you're using to do the Rf's?
TLC Software.
FrankMartin - 11-10-2010 at 13:43
The one pictured is from the following site. http://www.sorbfil.com/en/index.htm
and it seems OK, but they want about 400Euros for it after the 30-day evaluation period.
Just the best for gel, tlc and densitometry, in my opinion, and free.
Cheers,
HBoffis - 21-2-2017 at 10:27
How do you use these pieces of software. Do you scan the plate on an ordinary flatbed scanner or photograph it (under UV light if you can) with a
digital camera or something and then open the image in the software and highlight the area to analyse? Even just the densitometry facility would be
useful.
@Harristotle. Do you have a bit more info on the TLC visualizer like a partial web address. I tried running "TLC visualizer" etc through google but I
mostly about various bits of hardware by CAMAG.
I found the gel analyser software though. Does anyone have any experience of it? Harristotle - 22-2-2017 at 03:07
Fantastic for citizen science and school level projects.
Cheers,
H.Boffis - 23-2-2017 at 11:40
@Harristotle, thank you very much for this. I will have a look at this.Boffis - 25-2-2017 at 10:33
This thread has reminded me of a project I looked into some years ago to make spot tests at least semi-quantitative using a scanner to scan them and
then use some kind of densitometry software to compare the test spot with standard ones. I got as far a buying the microlitre size automatic pipettes
and making up a large number of standard solutions but I couldn't find any suitable software. I vaguely remembered seeing a tool in a piece of image
processing software like Adobe or Photopaint but I can't remember where or exactly what it was designed for but thinking at the time it would do this
job. The piece of software above works with monochome images 8 bit TIFFs which would be OK for single component spots where optical density is OK but
for multi element spots or chromatographs you need to recognise the colour shift too. Any one out there got any suggestion.Harristotle - 25-2-2017 at 18:42
I am fairly sure that most lab imaging applications have been done. This was what many commercial bits of software developed from: being open source
and govt meant that it was a very good place to work out the math before commercialising.
Other plugins may also assist.
Cheers,
H.byko3y - 25-2-2017 at 19:05
Is manual analysis so hard? Usually errors are introduced during the chromatography itself, not during its analysis. You can use a simple straightedge
or any other measuring tool. Few dozens of marks might be hard to read carefully, but one or two spots are not a problem at all, unless I'm stupid and
don't understand something.
