Re: organic question

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DC - 30 Jul 2003 19:53 GMT

To begin with, your professor is right - an acid catalyzed alkene hydroamination
just isn't going to happen in the way you propose. As an alternative, check out
the Ritter reaction. As for your observations, if I am correct in my assumption
that the 1% ammonia solution you used is of the household cleaning product
variety, then I bet you can attribute the variations in color to reactions
involving the other components of that product - surfactants and such.

D

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Paul J. Franklin(moderator - sci.chem.organic.synthesis)
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Steve Turner - 30 Jul 2003 19:55 GMT

Corwin Joy <cjoy@houston.rr.com> wrote:

>Experiment 1. 100ml 93% sulphuric was combined with 100 ml 91% isopropyl
>alcohol and allowed to react with vigorous stirring with the flask in a
>water bath at 25C for 5 minutes.
>(1) C-C-OH + H2SO4 --> C-C-OSO3H (I assume)

Not a good assumption. Although combining these two will generate
heat, it is heat of solvation of the sulfuric acid, just as if you had
added it to water. The amount of ester formed is probably small.

>To this clear solution was then slowly added 100ml 1% ammonia solution.
>(2) C-C-OSO3H + NH3 --> ???
> RESULT: A vigorous exothermic reaction ocurred and immediately a pink
>solution was formed. The reaction proceeded with the solution slowly
>becoming a darker red over the next hour.

The vigorous exotherm is expected. You are mixing a strong acid and a
pretty decent base. I doubt the red color is significant. None of
the reactions simply predicted would generate colors.

>Experiment 2. 100ml 91% isopropyl alcohol was combined with 100ml 1%
>ammonia. RESULT: No discernable reaction occured. Solution remained clear.

As expected.

>Experiment 3. 100ml 93% sulphuric was combined with 100ml 1% ammonia.
>RESULT: Exothermic reaction, BUT no color change.

As expected. Strong acid + base --> salt and lots of heat.

>Experiment 4. 100ml 93% sulphuric was combined with 100ml 91% isopropyl
>alcohol and allowed to react at 25C for an hour. RESULT: Exothermic
[quoted text clipped - 6 lines]
>here? Am I getting an amine salt? Something more complicated? Why does
>experiment 1 give a different result than experiment 3 and 4?

How did you determine the quantity of heat evolved? Remember that
relating "quantity of heat" with temperature is not necessarily a
trivial thing to do.

Bottom line -- the instructor was correct. You will get proton
transfer faster than anything else, and that will kill the reaction
you're trying to do.

Steve Turner

Real address contains worldnet instead of spamnet

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Paul J. Franklin(moderator - sci.chem.organic.synthesis)
http://organicworldwide.net/sci.chem.organic.synthesis
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Steve Turner - 30 Jul 2003 19:56 GMT

Corwin Joy <cjoy@houston.rr.com> wrote:

The vigorous exotherm is expected. You are mixing a strong acid and a
pretty decent base. I doubt the red color is significant. None of
the reactions simply predicted would generate colors.

>Experiment 2. 100ml 91% isopropyl alcohol was combined with 100ml 1%
>ammonia. RESULT: No discernable reaction occured. Solution remained clear.

As expected.

>Experiment 3. 100ml 93% sulphuric was combined with 100ml 1% ammonia.
>RESULT: Exothermic reaction, BUT no color change.

As expected. Strong acid + base --> salt and lots of heat.

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Ivana Fleischer - 30 Jul 2003 19:59 GMT

Hi,

I cannot explain your problem,but I can give you some hints.

>I'm a beginning organic chemistry student and I was wondering if someone
>would be willing to help me understand a puzzling reaction I observed.
[quoted text clipped - 3 lines]
>(1) C=C + H2SO4 (80% conc) --> C-C-OSO3H
>(2) C-C-OSO3H + H2O --> C-C-OH

Here, the ester is formed only if the acid is concentrated. Water reacts
with the carbocation, not HSO4-.

>In step (2) water acts as a nucleophile to substitute for OSO3H and form an
>alcohol. So, my thought was, maybe one could use a nucleophile other than
>water in step (2) and perhaps this would be a way to use acid as a catalyst
>to substitute groups that would normally not react with an alkene. One
>classic example of a nucleophile other than water would be ether synthesis:

>(1) C-C-OH + H2SO4 (80% conc) --> C-C-OSO3H
>(2) C-C-OSO3H + C-C-OH --> C-C-O-C-C (ethanol acts as a nucleophile)

This is more complicated, because it depends on the temperature what
happens. At first, ROH2+ is formed. If the temperature is <50°C (if the
alcohol is ethanol), the mono- or diethylester is formed. At T>50°C, the
monoester reacts with another nucleophile and at higher temperature an
elimination occurs (is always a side reaction). NH3 isn't good nucleophile
for this substitution.

>So my thought was, what happens in step (2) if, for example, NH3 is
>used?? It is a
>stronger nucleophile than water and might form an amine salt:

>(2) C-C-OSO3H + NH3 --> C-C-NH4+ HSO4- ???

And what is this? A 5-bonding nitrogene cation???

>This was quickly shot down by my professor since he told me that the

ammonia

>would simply form a salt with the acid and I would get no amine since the
>NH3 would be completely tied up as a salt and not be able to act as a
>nucleophile:
>NH3+ H2SO4 -- > NH4+ HSO4-

I think your professor is right, no substitution can occur. I cannot
understand your experiment. Why took you these amounts of compounds? What is
the 9% impurity in your alcohol?

Ivana Fleischer.

>At this point I must confess that I am sadly stubborn and had to try the
>reaction for myself.
>So, I tried the following experiments:

>Experiment 1. 100ml 93% sulphuric was combined with 100 ml 91% isopropyl
>alcohol and allowed to react with vigorous stirring with the flask in a
[quoted text clipped - 5 lines]
>solution was formed. The reaction proceeded with the solution slowly
>becoming a darker red over the next hour.

>Experiment 2. 100ml 91% isopropyl alcohol was combined with 100ml 1%
>ammonia. RESULT: No discernable reaction occured. Solution remained

clear.

>Experiment 3. 100ml 93% sulphuric was combined with 100ml 1% ammonia.
>RESULT: Exothermic reaction, BUT no color change.

>Experiment 4. 100ml 93% sulphuric was combined with 100ml 91% isopropyl
>alcohol and allowed to react at 25C for an hour. RESULT: Exothermic
>reaction, BUT no color change.

>So, if the ammonia is really all tied up as a salt, I would have expected
>experiment 1 (acid+alcohol+ammonia) to produce the same result as

experiment

>3 (acid+ammonia). Instead, in experiment 1 I get a much more exothermic
>reaction than experiment 3 and a pink/red solution. So what is happening
>here? Am I getting an amine salt? Something more complicated? Why does
>experiment 1 give a different result than experiment 3 and 4?

>Anyway, sorry to bother folks here but I was just hoping someone would be
>willing to explain what is happening since I'm really puzzled now.

>Thanks in advance for any help,
>
>Corwin

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Paul J. Franklin(moderator - sci.chem.organic.synthesis)
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Georgia State University <chepjf@panther.gsu.edu>
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Natural Science Forum / Chemistry / Organic Synthesis / July 2003

Re: organic question