Diluting vitride (red-al)

[Vaaguh]

According to various reports it is written that in order to  obtain good yields the vitride has to bee diluted with an equal ammount of toluene.

Could equal ammounts of dry THF bee used instead of toluene for this dilution?

[Barium]

Yes

[Vaaguh]

Thanks,

I just wanted to back report that diluting with THF worked well.

40 mmol 10% solution of 2,5DMNS in THF was succesfully dissolved and reduced using 350 mmol 3.5M red-al/toluene solution diluted with 100 ml THF.

However another reaction where 40mmol of 3,4,5-trimethoxy substrate was dissolved in 100 ml THF and added to 100 ml 3.5M red-al/toluene diluted with 100 ml THF slowly over the course of 10 minutes made the whiteish solution turn deep red 30 minutes after the addition had completed another 25 ml vitride was added  and things are refluxing for about 18 hours now. taking a drop of the reaction mixture and adding it to water causes some fizzing, perhaps the reduction requires a long reaction time ? (in pihkal the lah reduction took 48 hours).

As for the purity, tlc on the nitrostyrene gave a single spot at Rf 0,62 using ethylacetate with a mp of 117-118 Celcius

[starlight]

Is it possible to use methylene chloride for solubilizing the nitrostyrene to be introduced into the reaction?

[Vaaguh]

While dichloromethane and toluene are miscible the volatility and low bolingpoint will probally not bee appreciated seeing as this reaction is quite exothermic.

[starlight]

Of course. Maybe dibromomethane bp. 98C then? Any danger this could react with the Red-Al under the conditions here?

[Rhodium]

Dibromomethane is expensive, and may react with the Red-Al.

[starlight]

Knew it wasn't cheap, but was interested owing to the high solubility of nitrostyrenes in halogenated solvents and their water immiscible properties. Thought there may be some danger of reaction with the Red-Al. but wasn't sure how harsh the conditions would have to be. Best to leave the Dibromomethane for methylenations then.

[Vaaguh]

In my experience THF dissolves nitrostyrene's very well

[starlight]

Does the presence of THF create a need for change in workup due to its water miscibility. Does it interfere with the phase separation at all or the phase distribution of the product?

BTW. I have heard of a 1-(2,5-DimethoxyPhenyl)-2-nitropropane reduction with Red-Al going bright red without terrrible consequences. Upon basification during workup the color apparently returned to clear. No THF was involved.

[Vaaguh]

That is great information.

The workupplan is to hydrolize the mixture with plain H2O and then to filter off the solids with celite.

From there distilling off the thf/h2o/toluene/2-methoxyethanol, an a/b followed by vacuum distillation of the freebase amine.

I will post more details when the workup is performed

update:
Hmm after H2O addition the filtering proceeds utterly slow  and leaves dark black tar in the filter, hopefully there is something that can bee recovered.

[Vaaguh]

After the workup nothing interesting was recovered   .

The reaction shall bee repeated another time.

[Barium]

When hydrolysing a Vitride reduction use 180 ml 5% aq NaOH/mol Vitride instead of water. This gives a saturated solution of sodium aluminate as the bottom layer. The toluene layer containing the product is easily isolated using a sep funnel.

Reducing nitrostyrenes directly to amines with Vitride will give good to great yields with only a few nitrostyrenes. A much better way is to reduce the nitrostyrene to the nitroalkane and then use Vitride. Nitrostyrenes gives the oximes as intermediates when reacted with Vitride. This should theoretically not be a problem at all since the literature teaches that oximes are easily reduced by Vitride. Practice shows that large excess of Vitride must be used to get good yields. Roughly 8 mols Vitride/mol nitrostyrene if the reduction takes place at room temp or close to. If prolonged reflux is applied less Vitride is needed.

My experience is that good yields are obtained as long as the reaction mixture is colorless. As soon as there is coloration more Vitride must be added.

[Vaaguh]

Hydrozling using diltue NaOH to keep the sodium aluminate in solution would make the workup easier but the problem is that the THF that is used as a cosolvent is miscible both with toluene and H2O.

That is why plain H2O was used to hydrolize in order to filter off the aluminium sludge and then to evap the solvents.

It really makes me wonder why the 3,4,5-trimethoxybetanitrostyrene is such a hard candidate to reduce compared to 2,5-dimethoxybetanitrostyrene.

[Barium]

Saturate with NaCl then when the hydrolysis is over. Then extract the aueous layer twice with toluene.

[Vaaguh]

Seeing that some of the 2-methoxyethanol would most likeley go into the organic layer, is it possible to wash away the 2-methoxyethanol using brine?

Washing the toluene with plain H2O might give problems here because of the moderateley soluble nature of 3,4,5-trimethoxyphenylethylamine freebase in H2O.

[starlight]

I wondered this too, as a result of experiencing low yields when using 2,4,5 Trimethoxynitropropane as a substrate. Never tried it though as I assumed the brine would decrease the water solubility of 2-methoxyethanol too (salt it out).