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Topic: Synthesis of Isopentyl Acetate (posted procedure)  (Read 4106 times)

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Offline duubs

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Synthesis of Isopentyl Acetate (posted procedure)
« on: October 19, 2013, 03:18:38 PM »
So I was in the lab, synthesizing some Isopentyl Acetate. It smelled like bananas and had a very strong smell, a nice dark tint of yellow, which seemed like quite pure product. I neutralized the acid properly but when I put a drying agent in the finished product before distillation, I noticed that it dissolved right away and that the colour of my ester darkened a little. When attempting to distill the impurities out, the thermometer didn't go past 95 Celsius (very strange) and I tried it with a different thermometer as well, same outcome. The aqueous layer (tested for refractive index: 1.3400) distilled out with the ester (tested for refractive index: 1.3980) while the thermometer reached equilibrium at 96 Celsius. What went wrong? I just can't figure out what I did wrong.
-sulfuric acid as catalyst
-isopentyl alcohol used in excess. Refractive index of 1.3776
-Isopentyl Acetate has a refractive index of 1.4040
-acetic acid has a refractive index of 1.3716
« Last Edit: October 19, 2013, 05:37:57 PM by duubs »

Offline duubs

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Re: Synthesis of Isopentyl Acetate
« Reply #1 on: October 19, 2013, 05:20:15 PM »
To make it a little easier, here's my procedure:
Part A: Reaction
1.   Reactants (11.53g or 10.99mL Acetic Acid and 6.771g or 8.37mL Isopropyl Alcohol) were mixed in a 250 mL round bottomed flask and 2.5 mL of sulfuric acid was added.
2.   The beaker was heated for an hour making sure the vapours only got one third of the way up the reflux tube so as to not lose any product or reactants.
Part B: Extraction
1.   The solution was poured into a 250mL separatory funnel using a little bit of water (10 mL) to rinse the reaction chamber and ensure all products made it out of the reaction chamber.
2.   Once the solution separated, the aqueous layer was drained and NaOH was added to it. The aqueous layer was added back to the organic layer in the separatory funnel.
3.   Repeated step 1-2 except tested both the organic and aqueous solutions with pink litmus paper to check when the acid had been neutralized.

Part C: simple distillation to separate products didn't work properly.

Offline Archer

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Re: Synthesis of Isopentyl Acetate (posted procedure)
« Reply #2 on: October 19, 2013, 05:51:15 PM »
You don't seem to have a water wash to remove the excess base (NaOH). You also don't seem to dry it so you are distilling the product in the presence of hydroxide.

This may have hydrolysed some of your product.
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

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Offline duubs

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Re: Synthesis of Isopentyl Acetate (posted procedure)
« Reply #3 on: October 19, 2013, 06:08:01 PM »
I put the drying agent in and it instantly dissolved. Should I have put more?  Also before distilling, I had an aqueous layer which tested 1.3400 for refractive index, but the refractive index of water is 1.333.

Offline Archer

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Re: Synthesis of Isopentyl Acetate (posted procedure)
« Reply #4 on: October 20, 2013, 03:20:56 AM »
I put the drying agent in and it instantly dissolved. Should I have put more?  Also before distilling, I had an aqueous layer....

Drying agents are to remove traces of water if you had an aqueous layer then this should have been removed prior to distillation.
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline duubs

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Re: Synthesis of Isopentyl Acetate (posted procedure)
« Reply #5 on: October 21, 2013, 02:20:15 PM »
So I actually used sodium bicarbonate to neutralize the acids present in the solution. Do you think that I had too much aqueous layer and it prevented the temperature of the vapours from passing 96 Celsius? I think that sodium bicarbonate is quite unreactive after neutralizing the acids

Offline duubs

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Re: Synthesis of Isopentyl Acetate (posted procedure)
« Reply #6 on: October 21, 2013, 08:07:17 PM »
*Ignore me, I am impatient*... really need help

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