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Topic: photometrics  (Read 3895 times)

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rob

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photometrics
« on: April 01, 2006, 05:08:11 PM »
I have done a spectrophotometric study of the kinetics of iodination of aniline  but was told that to obtain good results freshly distilled aniline should be used. Please can you explain me why, how would it affect my result if not so?
thnx
« Last Edit: April 03, 2006, 06:04:32 PM by rob »

Offline pantone159

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Re:please help with spectrophotometrics
« Reply #1 on: April 01, 2006, 11:35:03 PM »
If it isn't freshly distilled, it probably has impurities, which messes it up.

Offline lemonoman

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Re:photometrics
« Reply #2 on: April 08, 2006, 02:53:15 AM »
Mark's right.  Aniline is NOTORIOUS for containing impurities, because it's a somewhat-easily-oxidized primary amine, when exposed to air (among other things).

How will it affect your results?  I'm not expert, but my 3rd-year-University guess is that the overall concentration of aniline won't be what you think it is.  You'll assume you have 1 mL of pure aniline but you'll really only have like, 0.8 mL and 0.2 mL of impurity (not sure of the numbers...because they will vary based on how much your aniline is oxidized!!).  Anyways, you'll have to figure out what the result of air oxidation of amines is...and then see if that increases or decreases iodination (electrophilic aromaic substitution?).

I personally think that it'll make the amine-substitutent LESS activating, and DECREASE the overall rate of iodination.

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Re:photometrics
« Reply #3 on: April 08, 2006, 02:59:48 AM »
Just take a mass spec of freshly distiled aniline and come pare it with the undistilled batch, to see if impurities are problematic. Anyway, its always a good idea to use "clean" reagents anyways. Speaking of which, I should practise what I preach.
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