Synthesis

[rtkt01]

 Outline all steps in the synthesis of each of the following compounds using only the organic starting material given, plus any needed organic/inorganic reagents.

 1. 1-bromopropane from 2-bromopropane.
 2. 2,3-dimethylbutane from 1-propene.
 3. 2-bromo-2-iodopropane from 1-chloropropane.

 Here's what I tried.
                            Zn                 Br2
 1. 2-bromopropane ----> propane ---> 1-bromopropane
                            H+                light

                   H2               Br2                         
 2. 1-propene----> propane---> 2-bromopropane
                   Pt                light                       
                             2Na
     2 2-bromopropane ---> 2,3-dimethylbutane
                             Boil
                             Zn              I2                        Br2
 3. 1-chloropropane ---> propane ---> 2-iodopropane ---> 2-bromo-2-iodopropane.
                            H+                                         light

 It's first time ever I'm solving these types of questions, and I'm really confused with these.  Am I on the right track ?

 

[azmanam]

step 2 in #1 will predominantly give bromination at the 2 position, regenerating starting material.  You should think about what ways you know to introduce a halide to a primary carbon, and then how you could form that intermediate from the given starting material

[rtkt01]

step 2 in #1 will predominantly give bromination at the 2 position, regenerating starting material.  You should think about what ways you know to introduce a halide to a primary carbon, and then how you could form that intermediate from the given starting material

How does this look?

2-bromopropane + KOH ----> propene

propene + HBr (peroxide present) -----> 1-bromopropane

and did I get question 2 and 3 correctly ?

[orgopete]

#2, that would work, soft of. I don't think that was the intended answer for that question though.

#3, like #2, but since that wasn't intended, it now falls off into definitely wrong.

Review your alkene reactions, you probably don't have that many. Do any of them give a halide as a product? Do any of them have a dihalide as a product? A dibromide could be changed into a bromo-iodo compound by stepwise reactions.

[mehc201]

Hmm you must be in my orgchemistry class because I have these exact same questions for hw due tmrw... HCC?

But yeah I got that for #1 and you'll find the answer for #3 on 19A of the practice exam in the back of our notes

[mehc201]

But what about #2?

2,3-dimethylbutane from 1-propene

I've tried hydrogenation to propane followed by addition, but I'm not sure how that extra methyl was added. Does anyone have any suggestions?

[rtkt01]

But what about #2?

2,3-dimethylbutane from 1-propene

I've tried hydrogenation to propane followed by addition, but I'm not sure how that extra methyl was added. Does anyone have any suggestions?

I could not get #2 either.  I don't know if I'm missing something, but it's just not shown anywhere.
 

[rtkt01]

                            KOH
 1. 2-bromopropane -----> Propene
                 HBr
     Propene -----> 1-bromopropane
                ROOR

                 HBr
 2. Propene ------->  2-bromopropane
                                                           
                                                            Li
                                    diethylether         l
    2-bromopropane + 2 Li --------->    CH3-C-CH3 + LiBr
                                                            H
              Li
    2         l
       CH3-C-CH3  + CuI ---------->  ( CH3-C-CH3 )2 CuLi   +   LiI
                                                           H

     ( CH3-C-CH3 )2 CuLi   +   Cl-CH-CH3 -------> 2,3-dimethylbutane
              H                             l
                                            CH3

                                KOH                         Br2                                      3NaNH2              _   -    +      NH4Cl
 3. 1-chloropropane ----------> H-C=C-CH3 -------->  1,2-dibromopropane -----------> CH3C =   C : Na  --------->
                              alcohol                       CCl4 

         _
 CH3C = CH   +    NH3    +  NaCl

         _           HBr
 CH3C = CH   -------->  CH3C = CH2
                                       l
                                       Br
                 HI
 CH3C=CH2 --------> 2-bromo-2-iodopropane
       l
      Br

Can anyone check if there's anything wrong with these?
Thank you.