How Is Benzylamine Prepared from Benzamide Using LiAlH4?

[Chirostudent]

I need to answer a assignment question about how one can prepare benzylamine by reducing benzamide with LiAlH4. I read that LiAlH4 is a good reducing agent, and I understand that, but can someone explain how benzamide gets reduced?

And in the other half of the question, it says that this reaction does not go to completion, and that there is still a substantial amount of benzamide still in the product (but that it is mostly benzylamine). I need to explain with the aid of a flow diagram, how I would separate the pure benzylamine. Can anyone help me?

Please post it here, or send me a mail on: Kenneth_toerlen@hotmail.com ! Need it as soon as possible :)

thanks

 

[as_phoenix]

Hi kenneth,

I am looking for the same thing (I am betting we are both in the same course). Not sure if we're supposed to do this though, I find the easiest way to trawl for related info in Wikipedia or chemistry websites, and piece it together.

Good luck.

 

[Blueshift5]

I can explain the process of preparing benzylamine by reducing benzamide with LiAlH4. LiAlH4 is a strong reducing agent that is commonly used in organic synthesis to reduce carbonyl compounds, such as benzamide, to their corresponding alcohols.

When LiAlH4 is added to benzamide in a solvent, such as ether or tetrahydrofuran, it reacts with the carbonyl group of benzamide, breaking the carbon-oxygen double bond and replacing it with a carbon-hydrogen bond. This results in the formation of benzylamine, as well as a byproduct of lithium aluminum oxide.

However, this reaction does not go to completion, meaning that not all of the benzamide is converted to benzylamine. There is still a significant amount of benzamide present in the reaction mixture. To separate the pure benzylamine from the remaining benzamide, a purification process is necessary.

One method of purifying the benzylamine is by using a separation funnel. The reaction mixture is first transferred to the separation funnel and allowed to settle into two layers - an organic layer containing the benzylamine and a water layer containing the remaining benzamide. The organic layer is then carefully drained into a separate container, leaving behind the water layer.

The organic layer is then washed with a dilute acid solution, such as hydrochloric acid, to remove any traces of the byproduct and other impurities. The resulting solution is then dried using a drying agent, such as anhydrous sodium sulfate, to remove any remaining water.

The purified benzylamine can then be isolated by evaporating the solvent, leaving behind solid benzylamine. This solid can be further purified by recrystallization, in which the solid is dissolved in a hot solvent and then allowed to slowly cool, causing pure benzylamine crystals to form.

In summary, the reduction of benzamide with LiAlH4 results in the formation of benzylamine, but the reaction does not go to completion. To obtain pure benzylamine, a separation and purification process is necessary, such as using a separation funnel and performing recrystallization.