Keras
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Crystal Violet Synthesis (Alternative Route?)
Folks,
As a preliminary disclaimer, I was unable to locate any thread about Crystal violet. Can’t seem to be able to look for a combination of two words
together.
So, I plan – much like Apoptosis on his YouTube™ channel – to synthesis a few azo/triarylmethane dyes. I have received 500 mL of N,N
dimethylaniline, which is the basic block of many of these compounds. Anyways. One of them is Crystal violet.
Traditionally, Crystal violet is made from ‘Michler's ketone', the analogue of benzophenone but with N,N dimethylaniline. Unfortunately Michler's
ketone is synthesised from N,N dimethylaniline and … phosgene using a Friedel-Craft reaction, which doesn’t make it friendly at all. Worse, the
final step entails the use of phosphorus oxychloride, which I don’t have (I have phosphorus pentachloride, but I don’t plan to use it to make
oxychloride).
So I'd like to use a somewhat safer way to synthesise C.V. Of course, I’m sure that using a Friedel-Craft alkylation between N,N-dimethylaniline and
chloroform wouldn't work, although patent US 3,689,495 seems to suggest it can. Has anyone already tried?
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bnull
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Kirk-Othmer's chapter on triphenylmethane dyes has a section on synthesis using aldehydes, formaldehyde in the case of crystal violet, which yields
the dye on oxidation. Ullmann's has something similar.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Keras
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Thanks for the pointer. is somewhat useful, though (at least in K-O) the process is not clearly disclosed.
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bnull
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Ullmann's gives an example (based on patent DE 2334918, "Verfahren zur herstellung basischer farbstoffe durch katalytische oxidation", reference 188):
| Quote: |
Production Example. A mixture of 1089 parts dimethylaniline, 90 parts paraformaldehyde, and 1391 parts glacial acetic acid is heated to 70 °C for 1
h. The solution is cooled to 50 °C, treated with 15 parts chloranil and 15 parts (dihydrodibenzotetraaza[14]annulene)iron,
and the mixture aerated for 20 h with vigorous stirring. Ca. 800 parts glacial acetic acid are distilled off at reduced pressure and the residue is
dissolved in 16000 parts water at 95 °C. The solution is filtered hot and the dye is precipitated from the filtrate with 3000 parts sodium
chloride at pH 1.5. The crystalline dye is collected by suction filtration and washed with 3000 parts dilute sodium chloride solution. Yield: 1050
parts. |
The first reaction produces the leuco form of crystal violet, which is subsequently oxidised by air in the presence of the funny catalysts. You can
use the other usual oxidisers and forget those catalysts, of course, and modify the section in blue to suit your oxidiser. Even electrooxidation will
do.
The German patents below (in German) are references from Ullmann's.
DE2334918 Organic iron complex catalysts for preparation of basic dyes by oxidation of diamino diphenyl methane derivatives
DE2152703 Basic dyes preparation from their leuco derivatives by catalytic oxidation of diamino diphenylmethanes
DE2138931 Basic dyes preparation by catalytic oxidation of corresponding compounds using complex catalysts containing heavy metals
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Keras
National Hazard
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Registered: 20-8-2018
Location: (48, 2)
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Thank you! As far as I know, a mild oxidiser must be used lest the molecule be broken (HClO won’t do, maybe diluted hydrogen peroxide? Benzoquinone?
Manganese dioxide?)
Anyways, thanks a lot again. Will try that when I have the time.
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