Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
malachite green
This report tells of my adventures making malachite green (MG) following the procedure of Brewster, circa 1962. This was a small scale experiment
using 4mL each of benzaldehyde and N,N-dimethylaniline (NDA). Also required was 3g of PbO2. All of these reagents were homemade.
The benzaldehyde and NDA, along with 3g of anhydrous ZnCl2 were placed in the bottom of a 250mL RBF and heated to 130-140C for 10 minutes. This
formed the leuco base of MG, a gummy mass that just sat glued to the bottom of the RBF. Then 150mL of water was added and I set up for
direct steam distillation to remove the residual benzaldehyde and NDA. This is where the misadventure began.
Because of the gummy leuco base on the bottom, heat transfer was bad and I had a surge into the condenser. I turned off the heat and decided to (1)
add a Claisen head, and (2) add a stir bar for magnetic stirring. I removed the glass stopper in the top of the stillhead. Now being impatient I did
not let it cool down properly: I just dropped the stirbar down the hatch. This resulted in a violent discharge of superheat with some leuco base in
water shooting out the port all over the place. So a lot of things got spattered green, especially once the leuco base had gotten oxidized to the
deep blue-green of malachite.
Eventually I continued with the synthesis and only experienced one more surge, and it never made it to the condenser.
So I made about 200mL of a water solution with about 2g of dissolved chloride salt of malachite green. This can be seen in the test tube on the right
in the picture below. Next to it is a 1:10,000 dilution, and on the end is malachite green in conc HCl where it turns yellow at pH<2.
Entropy will especially get a chuckle out of this as the opening paragraph of the procedure tells how you needn't spill so much as a drop. It's a
good thing that Brewster is probably gone to his reward or I would be required to report to a University in Kansas for retraining.
   
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
entropy51
Gone, but not forgotten
Posts: 1612
Registered: 30-5-2009
Member Is Offline
Mood: Fissile
|
|
When you said you were making dimethylaniline, I could immediately visualize the mutli-colored palette on the roof of your fume hood.
I knew a chemist who once said that anyone who thought he wasn't being exposed to chemicals had never synthesized a dye. It soon becomes apparent
that everything you weigh, pour, filter, evaporate or whatever gets on everything in the lab.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
Quote: Originally posted by entropy51  |
I knew a chemist who once said that anyone who thought he wasn't being exposed to chemicals had never synthesized a dye. It soon becomes apparent
that everything you weigh, pour, filter, evaporate or whatever gets on everything in the lab. |
Amen.
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
RiP057
Harmless
Posts: 29
Registered: 26-10-2010
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by entropy51 |
I knew a chemist who once said that anyone who thought he wasn't being exposed to chemicals had never synthesized a dye. It soon becomes apparent
that everything you weigh, pour, filter, evaporate or whatever gets on everything in the lab. |
hear here again
after working in the lab go to a mirror and turn on a black light... everytime I can see the ring of my goggles cause all of the indoles would
luminesce and they were everywhere that wasnt protected
and sorry nico no references.... 
|
|
|
benzylchloride1
Hazard to Others
Posts: 299
Registered: 16-3-2007
Member Is Offline
Mood: Pushing the envelope of synthetic chemistry in one's basement
|
|
Interesting, I have not prepared any triphenylmethane type dyes, but my experience with azo dyes verifies this statement, the stuff gets everywhere. I
once coupled 2-naphthol with diazotized sulfanilic acid to produce the azo dye which was subsequently converted to 1,2-naphthoquinone. Needless to
say, my hands and my fume hood were red in color after the experiment.
Amateur NMR spectroscopist
|
|
|
Sandmeyer
National Hazard
Posts: 784
Registered: 9-1-2005
Location: Internet
Member Is Offline
Mood: abbastanza bene
|
|
There is a really easy solution - wear gloves and don't be sloppy...
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
