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Topic: organic chem:substitution reaction  (Read 3053 times)

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Offline jadelamlam

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organic chem:substitution reaction
« on: July 30, 2012, 04:51:38 AM »
In substitution reaction between bromine and hexane, why the bromine should be in organic solvent? Bromine is already a liquid!
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Offline discodermolide

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Re: organic chem:substitution reaction
« Reply #1 on: July 30, 2012, 05:15:07 AM »
Quote from: jadelamlam on July 30, 2012, 04:51:38 AM
In substitution reaction between bromine and hexane, why the bromine should be in organic solvent? Bromine is already a liquid!

Bromine and hexane do not react without something else being present.

I would imagine that they are not miscible, therefore you need a solvent.
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Offline jadelamlam

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Re: organic chem:substitution reaction
« Reply #2 on: July 30, 2012, 05:38:44 AM »
Thx for your reply.
I am not sure whether I can get what you mean.
Suppose oil is added to a cup of water.Obviouly there is no reaction between them.
Let A be a solvent which can dissolve both oil and water,
If A is added to the oil-water mixture,then oil will react with water?(Just assume that there is a reaction between oil and water)
Put this analogy into my case,the organic solvent provides a medium for hexane and bromine to react?
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Offline AWK

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Re: organic chem:substitution reaction
« Reply #3 on: July 30, 2012, 05:52:19 AM »
Bromine is soluble in hexane (both are nonpolar). Bromine in carbon tetrachloride is less dangerous then bromine itself.
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Offline jadelamlam

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Re: organic chem:substitution reaction
« Reply #4 on: July 30, 2012, 07:41:30 AM »
Thx for replying,
so the aim of adding organic solvent is just for safety?
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Offline fledarmus

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Re: organic chem:substitution reaction
« Reply #5 on: July 30, 2012, 08:57:15 AM »
What product are you trying to obtain when you react elemental bromine with hexane?

What other products are possible?

How does the concentration of bromine affect the proportions of the products formed?

How can you control the concentration of bromine in the reaction?

How much energy is released during the reaction?

How much will this increase the temperature of the reaction?

What will be the result on the vapor pressure of hexane and bromine, and their evaporation rate, of this increase in temperature?

All of these questions underlie the choice of solvents to be used during a reaction. In many cases, when you try to run a reaction without solvent, even if the reagents are mutually miscible, the concentrations are so high that you get very little selectivity between the reaction that you are trying to run and various side reactions leading to undesired products. You can also get runaway reactions with very rapid heat increases, outgassing of reagents and products, and explosions.

On the other hand, in some cases where you have very slow reaction rates or especially high activation energies, it can be very useful to run reactions without solvent, either as neat liquid mixtures or as melts.
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