N,N-dimethylaniline

As requested, here is the first synthesis using my homemade autoclave.

Preparation of N,N-dimetylaniline

This synthesis followed the procedure in Fundamental Processes of Dye Chemistry by Fierz-David and Blangey, 1949, p.133. This can be found in the SM library.

Special Equipment
This synthesis requires the use of an autoclave capable of 60atm. I used my homemade autoclave, construction of which is documented in the Prepublication section of this forum.

Reagents
Methanol was Drygas gasoline de-icer. It tested negative for ethanol and acetone in an iodoform test. Sulfuric acid (96%) was Rooto drain cleaner. The aniline, which was amber, was from Daigger. All reagents were used “as received.”

Procedure
Due to the highly poisonous nature of aniline and N,N-dimethylaniline, all procedures were conducted in my hood using gloves.

A. 1st Heating Period (6hrs at 215C)
133mL of methanol and 91mL of aniline were mixed in a 400mL beaker using a magnetic stirrer. One mL (of 5mL) of sulfuric acid was added to the stirring solution. This resulted in a small but violent reaction. The rest of the acid was added by the drop. The solution turned an opaque creme color, presumably due to the formation of aniline acid sulfate. Resulting pH was 5.

The autoclave had been sealed shut, except for the fill port, using a Garlock Graph-Lock 3123 gasket. This is a 1/16” gasket made of graphite. It was then backfilled with argon, which was probably unnecessary. The reactants were introduced at the bottom of the autoclave through the fill port using a ¼” OD x 0.170” ID Tygon tube attached to a glass funnel. The fill port plug was then installed using Ace TFE thread sealant.

The heaters were turned on. The silicone oil bath was set at 225C. The aux heater was set at 30% (330w). Forty-five minutes later the pressure (P) = 40 psig. At 2 hrs heating P= 460psig. At 2.5 hrs heating the thermowell temperature (Tw) = 220C. The indicated pressure was very close to that of the procedure, ie, 30atm. At 8 hrs heating the heaters were turned off and the autoclave allowed to cool overnight.

B. 2nd Heating Period (5hrs at 170C)
The next day the fill port was opened and a 5mm glass rod was inserted to the bottom of the autoclave through the fill port. This assured that this passage was open, and provided a minimal amount of vertical stirring. Then 18.8mL of 30% NaOH was added to the autoclave via a small screw-on funnel made of pipe fittings.

The oil bath was set at 195C. Aux heater was set at 20% (192w). After 1 hr of heating P=55 psig and Tw = 120C. After 2.75 hr heating P = 200psig, Tw = 176C. After 5 hours of heating the heaters were turned off, the insulation removed, and the autoclave allowed to cool overnight.


C. Steam Distillation
Set-up for steam distillation using a 1000mL 3-neck RBF as pot. Both live steam and direct heating would be used simultaneously.

Opened up the autoclave. The product was a clear liquid with about 4mL of black particles which settled upon standing. This was assumed to be carbon. The solution pH was 11. The product was transferred to the pot using a turkey baster. The small amount of carbon sludge and water was discarded. There was some noticeable vapor pressure in the pot, most likely due to unreacted methanol.

The steam distillation proceeded without incident. The product was placed in a separatory funnel. NaCl was added to saturate the water layer and the organic layer was separated. It weighed 104.4g and had a napthalenic smell. I did my best not to smell it due to its highly poisonous nature.

D. Simple Distillation
I then set up for simple distillation using a 250mL RBF as pot. The procedure called for use of a small bulb column, which I did not have. Expecting that the forerun would be off-spec a 25mL RBF was used as receiver. Expected boiling point would be 192C so ptfe joint clamps and an insulating blanket were used. Distillation quickly proved problematic due to foam generation causing a carryover surge of pot contents into the condenser. I then shutdown and added a Claisen head to lengthen the distillation path and impinge the foam. By careful manipution of the insulating blanket to control the temperature of the Claisen head I managed to just keep the foam out of the condenser.

The distillate came over at a rock steady 192C and therefore was considered sufficiently pure. The net product weighed 91.4g. I probably lost about 10g due to the carryover during the foam surge. This could have been recovered but I chose not to.

Yield
The procedure expected yield was 117g. My net was 91.4g. This is a 75.5% yield based on the amount of aniline charged.

Cleanup
The small amount of sludge was not resinous, ie, not sticky and was easily removed from the autoclave. The autoclave was then sprayed down with WD-40 for storage.

Conclusions
I like this procedure as it is relatively straightforward in terms of chemistry and workup. Also it delivers the product in good yield. The long heating times are a downside, however.

I am pleased with this performance of my autoclave. This was its first use.




[Edited on 14-10-2010 by Magpie]

[Edited on 15-10-2010 by Magpie]

Quote: Originally posted by smuv

Nice work. Can you post more pictures of the autoclave? In the picture you posted I can only see the flange. What is the max pressure rating of that flange? class 900? [Edited on 10-15-2010 by smuv]

I am planning to repeat this reaction ,but on para-aminophenol(from paracetamol) instead as I don't have aniline lying around

so here is my question: Is there a chance of ether formation between the phenolic OH and the methanol ?

http://www.masterorganicchemistry.com/2014/11/14/ether-synth...

http://en.wikipedia.org/wiki/Ether#Dehydration_of_alcohols

[Edited on 26-12-2014 by CuReUS]

Quote: Originally posted by CuReUS

I am planning to repeat this reaction ,but on para-aminophenol(from paracetamol) instead as I don't have aniline lying around so here is my question: Is there a chance of ether formation between the phenolic OH and the methanol ?

I think the quinone formation can be prevented if the pH of the solution is kept low enough
I have done the same thing while i was making dyes using 2,4 diaminonaphthol and it worked.When the 2,4 diamino was put in a beaker with 20ml conc HCl,the oxidation was prevented

This seems like too much work

Tertiary methyl amines can be more easily prepared by the Eschweiler–Clarke reaction. Atmospheric pressure + formic acid + formaldehyde + aniline. Might want to reconsider the pressure vessel if I am not too late. In the end a pressure vessel is never a useless piece of equipment if you already committed.

Quote: Originally posted by Yugen

@CuReUS 1. Doubtful, esters can be hydrolyzed (maybe under anhydrous conditions it'd work...)

because in the reaction mechanism of Ho-Ma rearrangement ,methyl carbocation is produced,which might alkylate the OH instead of attacking the ring.I am not scared that It will get removed

Quote: Originally posted by Yugen

Tertiary methyl amines can be more easily prepared by the Eschweiler–Clarke reaction. Atmospheric pressure + formic acid + formaldehyde + aniline. Might want to reconsider the pressure vessel if I am not too late. In the end a pressure vessel is never a useless piece of equipment if you already committed.