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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: maximh on June 15, 2020, 05:04:53 AM

Title: Is this reaction is possible?
Post by: maximh on June 15, 2020, 05:04:53 AM
Hello,
I'm trying to get a specific product, will this reaction work? (this was a question in my exam):

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fup419.siz.co.il%2Fup1%2Fxzjgyzumgty4.jpg&hash=cc43f6a7b2c5f297d380fb17a6fccf8864f2a5dd) (http://www.siz.co.il/)
Title: Re: Is this reaction is possible?
Post by: Babcock_Hall on June 15, 2020, 06:37:55 AM
What are your thoughts?
Title: Re: Is this reaction is possible?
Post by: maximh on June 15, 2020, 06:40:28 AM
that is possible
Title: Re: Is this reaction is possible?
Post by: rolnor on June 15, 2020, 07:08:20 AM
What about the first step, how will you control that you only get one HBr adding and not two? Also, is there any risk for side-reactions, you have strong acid and two reactive groups?
Title: Re: Is this reaction is possible?
Post by: maximh on June 15, 2020, 09:18:18 AM
Quote from: rolnor on June 15, 2020, 07:08:20 AM
What about the first step, how will you control that you only get one HBr adding and not two? Also, is there any risk for side-reactions, you have strong acid and two reactive groups?

maybe use only one equivalent of hbr?
Title: Re: Is this reaction is possible?
Post by: rolnor on June 15, 2020, 12:29:12 PM
But the mono-brominated compound will react as fast as the non-brominated, how will you get this selectivity?
Title: Re: Is this reaction is possible?
Post by: Enthalpy on June 15, 2020, 05:34:10 PM
Quote from: rolnor on June 15, 2020, 12:29:12 PM
But the mono-brominated compound will react as fast as the non-brominated, how will you get this selectivity?

Could the sought mono-alcohol leave the reaction medium as soon as it's formed? Apparently not usual in a lab, but with adequate setup maybe. React among gases, let the mono-alcohol rain down but choosing the temperature pressure.  The prediction software Mpbpvp imagines that the mono-alcohol boils at 41K warmer than the diene under 1atm, and at +25°C its vapour pressure is 20 times smaller.

Bromine makes a much smaller difference. So the process would begin with water addition, which can be stopped at the mono-alcohol, and continue with HBr addition.

Would that be conceivable?
Title: Re: Is this reaction is possible?
Post by: Babcock_Hall on June 16, 2020, 08:44:35 AM
Enthalpy wrote, "Bromine makes a much smaller difference. So the process would begin with water addition, which can be stopped at the mono-alcohol, and continue with HBr addition.

Would that be conceivable?"
I see a potential problem with two reactions possible for HBr.  @OP, what do you think?
Title: Re: Is this reaction is possible?
Post by: Enthalpy on June 17, 2020, 04:15:22 PM
OK, probably a bad attempt. Unless some special conditions lead to HBr addition.
Title: Re: Is this reaction is possible?
Post by: AWK on June 26, 2020, 06:11:22 AM
Have you considered the reverse order of reaction?.
The yield of dibromo derivative can be significantly increased by exchange of OH for Br by exchange using PBr3