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My Recent Posts · Nov 7 08 5:54 PM

Tags : alkene, synthesis, alkane, butane, ethane, halogen

I was wondering if anyone could help me get started with some synthesis problems. I'd prefer to try to work them out myself - but I can't seem to get started.

On the first one, I'm stuck at the idea that I'm starting out with an alkane, and if I halogenate it - I'll end up with a secondary halogen. It's functionalized, but it's still secondary (Markovnikov). I have to come up with the anti-Markovnikov from an alkane.

I'm thinking I halogenate the butane, react it with OH- to form but-2-ene. Then, react a peroxide and HBr with the but-2-ene? I'm kind of lost.

A) butan-1-ol from butane

B) 2-ethoxy-2-methylpropane from methylpropane and ethane

C) 1-methylcyclohexane-1,2-diol from methylcyclohexane

Thanks!

My Recent Posts · Nov 7 08 7:41 PM

I'm not sure what you are thinking nor do I know what reactions you know. I will give a set of reagents and you can see if you can follow the reactions.

A) Br2, heat or light; KOtBu; BH3; NaOH, H2O2/H2O.

B) Br2, heat or light; H2O; NaH, BrCH2CH3

C) Br2, heat or light; NaOEt, EtOH; OsO4, HOO-t-Bu, KOtBu

My Recent Posts · Nov 8 08 5:22 AM

A)

Br2 + hv -> secondary alkyl halide
secondary alkyl halide + t-butoxide (E2 Hoffman) -> but-1-ene
but-1-ene + BH3 (splits the double-bond forming the H-BH2 bond intermediate) -> butylborane
butylborane + NaOH + H2O2 -> butan-1-ol

I don't follow where you're adding NaOH then H2O2 and H2O?

My Recent Posts · Nov 8 08 5:43 AM

B)

Br2 + hv -> 2-bromo-2-methylpropane + bromoethane

2-bromo-2-methylpropane + bromoethane + H2O -> ???

I think I missed something in lecture, or he didn't explain it very well....

My Recent Posts · Nov 8 08 6:01 AM

You did get the 1-butene correct, then you start with 2-butene?

Hydroboration/oxidaton
You have it listed correctly. The hydroboration product is tributylborane. That isn't what you are trying to synthesize. How do you convert tributylborane to butanol? You need this rearrangement reaction, see http://orgo.curvedarrow.c...iewtopic.php?pid=363#p363 Oops, this is being compressed by the board and breaking the link. Try these options, go to http://www.curvedarrow.com and go to the orgoforum and topic "Mechanism of borane oxidation in hydroboration-oxidation of propene"

My Recent Posts · Nov 8 08 7:10 AM

orgopete wrote:
You did get the 1-butene correct, then you start with 2-butene?

Gah, oops. I did get 1-butene.

My Recent Posts · Nov 8 08 7:11 AM

orgopete wrote:
Hydroboration/oxidaton
You have it listed correctly. The hydroboration product is tributylborane. That isn't what you are trying to synthesize. How do you convert tributylborane to butanol? You need this rearrangement reaction, see http://orgo.curvedarrow.c...iewtopic.php?pid=363#p363

For some reason, Norton here at work keeps blocking this link. I'll have to check it out when I get home.

I'm trying to figure out how the product is tributylborane...

My Recent Posts · Nov 8 08 8:32 AM

I'm lost on the tributylborane. I thought it'd just be butylborane?

My Recent Posts · Nov 8 08 9:03 AM

3 CH3CH2CH=CH2 + BH3 -> (CH3CH2CH2CH2)3B

This is the step before the oxidation/rearrangement. Draw the mechanism and you will see.

My Recent Posts · Nov 8 08 12:41 PM

Hmm. I'll have to look this up when I get home this evening. I guess I'm wrong about what tributylborane actually looks like - because it makes no sense to me.

My Recent Posts · Nov 8 08 3:46 PM

I still keep coming up with this as a product.. I'm not sure where I'm going wrong even after researching.

My Recent Posts · Nov 9 08 10:31 AM

I see the product you have come up with. How did it form? Was 1-butene the nucleophile and boron the electrophile? If so, how can tributylborane form? It is the same reaction mechanism. Fundamentally, all of the electrophilic reactions of an alkene are the same.

Here is another boron reaction, www.curvedarrow.com (orgoforum, topic: boron trifluoride-ether complex).
Is the boron in that example different than BH3 or butylborane? Are the electrons of dimethyl ether different than the electrons of butene (except being shared)? That example is from Chapter 2 of "A Guide to Organic Chemistry Mechanisms" (Amazon.com, Barnes and Noble or Curved Arrow Press). However, it is just as important in this example. If you are still having trouble, contact me and I'll show you the complete mechanism.

My Recent Posts · Nov 9 08 1:01 PM

I'm really confused..

Is there any way you could show me through the rest of the synthesis? I'd really appreciate it. I feel like such a retard.

My Recent Posts · Nov 9 08 5:28 PM

For the second synthesis:

methylpropane and ethane + Br2 and hV -> 2-bromo-2-methyl-propane and bromoethane
2-bromo-2-methyl-propane and bromoethane + H2O -> ethanol and 2-methylpropan-2-ol
ethanol and 2-methylpropan-2-ol + NaH -> ???

Is the NaH used to abstract the extra hydrogen (producing the alcohols above)? I'm confused about what happens when the H2O is added (I think I'd understand the NaH, then). I really don't see how we're going to get the ether.

My Recent Posts · Nov 9 08 5:40 PM

For the third synthesis:

methylcyclohexane + Br2 + hV -> 1-bromo-1-methyl-cyclohexane
1-bromo-1-methyl-cyclohexane + NaOEt -> 1-methylcyclohex-1-ene
1-methylcyclohex-1-ene + OsO4 + H2O2 -> 1-methylcyclohexane-1,2-diol

Wouldn't adding the OsO4 and H2O2 to the 1-methylcyclohex-1-ene give me the vicinal diol product? Assuming the NaOEt gave a Zaitsev elimination...

My Recent Posts · Nov 9 08 8:24 PM

methylpropane and ethane + Br2 and hV -> 2-bromo-2-methyl-propane and bromoethane
2-bromo-2-methyl-propane and bromoethane + H2O -> ethanol and 2-methylpropan-2-ol

Just not together, separate reactions each.
2-bromo-2-methyl-propane + H2O -> 2-methylpropan-2-ol
2-methylpropan-2-ol + NaH -> NaO-t-Bu + H2
NaO-t-Bu + BrCH2CH3 -> ethyl t-butyl ether + NaBr

Wouldn't adding the OsO4 and H2O2 to the 1-methylcyclohex-1-ene give me the vicinal diol product?

I hope so as that is C.

My Recent Posts · Nov 9 08 8:52 PM

What happens to the ethanol formed after adding water?

My Recent Posts · Nov 9 08 9:00 PM

What ethanol?

My Recent Posts · Nov 9 08 9:08 PM

Ohhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh.............. I was thinking about these in a mixture! I think I just had an epiphany. We're reacting them separately then combining them....

I've got it now. It makes a ton more sense thinking about it the correct way.

I see where you're going in that first synthesis. Does that imply it'll make 3 moles of the alcohol in the mechanism?

My Recent Posts · Nov 9 08 10:02 PM

1 mole propene -> 1 mole propanol, but it only requires 1/3 mole BH3.

My Recent Posts · Nov 10 08 5:23 AM

Ahhh, okay. I get it then. Well, everything seems to make sense to me so hopefully I've done them all right when I go to class today.

Author	Comment
chrisf	A few synthesis problems...	Lead	[-]
Posts: 55 Nov 7 08 5:54 PM Reply Quote More My Recent Posts	Tags : alkene, synthesis, alkane, butane, ethane, halogen I was wondering if anyone could help me get started with some synthesis problems. I'd prefer to try to work them out myself - but I can't seem to get started. On the first one, I'm stuck at the idea that I'm starting out with an alkane, and if I halogenate it - I'll end up with a secondary halogen. It's functionalized, but it's still secondary (Markovnikov). I have to come up with the anti-Markovnikov from an alkane. I'm thinking I halogenate the butane, react it with OH- to form but-2-ene. Then, react a peroxide and HBr with the but-2-ene? I'm kind of lost. A) butan-1-ol from butane B) 2-ethoxy-2-methylpropane from methylpropane and ethane C) 1-methylcyclohexane-1,2-diol from methylcyclohexane Thanks!
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orgopete		#1	[-]
Posts: 977 Nov 7 08 7:41 PM Reply Quote More My Recent Posts	I'm not sure what you are thinking nor do I know what reactions you know. I will give a set of reagents and you can see if you can follow the reactions. A) Br2, heat or light; KOtBu; BH3; NaOH, H2O2/H2O. B) Br2, heat or light; H2O; NaH, BrCH2CH3 C) Br2, heat or light; NaOEt, EtOH; OsO4, HOO-t-Bu, KOtBu Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press
chrisf		#2	[-]
Posts: 55 Nov 8 08 5:22 AM Reply Quote More My Recent Posts	A) Br2 + hv -> secondary alkyl halide secondary alkyl halide + t-butoxide (E2 Hoffman) -> but-1-ene but-1-ene + BH3 (splits the double-bond forming the H-BH2 bond intermediate) -> butylborane butylborane + NaOH + H2O2 -> butan-1-ol I don't follow where you're adding NaOH then H2O2 and H2O? Last Edited By: chrisf Nov 8 08 8:32 AM. Edited 2 times.
chrisf		#3	[-]
Posts: 55 Nov 8 08 5:43 AM Reply Quote More My Recent Posts	B) Br2 + hv -> 2-bromo-2-methylpropane + bromoethane 2-bromo-2-methylpropane + bromoethane + H2O -> ??? I think I missed something in lecture, or he didn't explain it very well....
orgopete		#4	[-]
Posts: 977 Nov 8 08 6:01 AM Reply Quote More My Recent Posts	You did get the 1-butene correct, then you start with 2-butene? Hydroboration/oxidaton You have it listed correctly. The hydroboration product is tributylborane. That isn't what you are trying to synthesize. How do you convert tributylborane to butanol? You need this rearrangement reaction, see http://orgo.curvedarrow.c...iewtopic.php?pid=363#p363 Oops, this is being compressed by the board and breaking the link. Try these options, go to http://www.curvedarrow.com and go to the orgoforum and topic "Mechanism of borane oxidation in hydroboration-oxidation of propene" Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press Last Edited By: orgopete Nov 8 08 7:48 AM. Edited 1 times.
chrisf		#5	[-]
Posts: 55 Nov 8 08 7:10 AM Reply Quote More My Recent Posts	orgopete wrote: You did get the 1-butene correct, then you start with 2-butene? Gah, oops. I did get 1-butene. Last Edited By: chrisf Nov 8 08 7:26 AM. Edited 1 times.
chrisf		#6	[-]
Posts: 55 Nov 8 08 7:11 AM Reply Quote More My Recent Posts	orgopete wrote: Hydroboration/oxidaton You have it listed correctly. The hydroboration product is tributylborane. That isn't what you are trying to synthesize. How do you convert tributylborane to butanol? You need this rearrangement reaction, see http://orgo.curvedarrow.c...iewtopic.php?pid=363#p363 For some reason, Norton here at work keeps blocking this link. I'll have to check it out when I get home. I'm trying to figure out how the product is tributylborane... Last Edited By: chrisf Nov 8 08 7:26 AM. Edited 1 times.
chrisf		#7	[-]
Posts: 55 Nov 8 08 8:32 AM Reply Quote More My Recent Posts	I'm lost on the tributylborane. I thought it'd just be butylborane?
orgopete		#8	[-]
Posts: 977 Nov 8 08 9:03 AM Reply Quote More My Recent Posts	3 CH3CH2CH=CH2 + BH3 -> (CH3CH2CH2CH2)3B This is the step before the oxidation/rearrangement. Draw the mechanism and you will see. Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press Last Edited By: orgopete Nov 8 08 1:37 PM. Edited 1 times.
chrisf		#9	[-]
Posts: 55 Nov 8 08 12:41 PM Reply Quote More My Recent Posts	Hmm. I'll have to look this up when I get home this evening. I guess I'm wrong about what tributylborane actually looks like - because it makes no sense to me.
chrisf		#10	[-]
Posts: 55 Nov 8 08 3:46 PM Reply Quote More My Recent Posts	I still keep coming up with this as a product.. I'm not sure where I'm going wrong even after researching.
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orgopete		#11	[-]
Posts: 977 Nov 9 08 10:31 AM Reply Quote More My Recent Posts	I see the product you have come up with. How did it form? Was 1-butene the nucleophile and boron the electrophile? If so, how can tributylborane form? It is the same reaction mechanism. Fundamentally, all of the electrophilic reactions of an alkene are the same. Here is another boron reaction, www.curvedarrow.com (orgoforum, topic: boron trifluoride-ether complex). Is the boron in that example different than BH3 or butylborane? Are the electrons of dimethyl ether different than the electrons of butene (except being shared)? That example is from Chapter 2 of "A Guide to Organic Chemistry Mechanisms" (Amazon.com, Barnes and Noble or Curved Arrow Press). However, it is just as important in this example. If you are still having trouble, contact me and I'll show you the complete mechanism. Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press Last Edited By: orgopete Nov 9 08 10:36 AM. Edited 1 times.
chrisf		#12	[-]
Posts: 55 Nov 9 08 1:01 PM Reply Quote More My Recent Posts	I'm really confused.. Is there any way you could show me through the rest of the synthesis? I'd really appreciate it. I feel like such a retard.
chrisf		#13	[-]
Posts: 55 Nov 9 08 5:28 PM Reply Quote More My Recent Posts	For the second synthesis: methylpropane and ethane + Br2 and hV -> 2-bromo-2-methyl-propane and bromoethane 2-bromo-2-methyl-propane and bromoethane + H2O -> ethanol and 2-methylpropan-2-ol ethanol and 2-methylpropan-2-ol + NaH -> ??? Is the NaH used to abstract the extra hydrogen (producing the alcohols above)? I'm confused about what happens when the H2O is added (I think I'd understand the NaH, then). I really don't see how we're going to get the ether. Last Edited By: chrisf Nov 9 08 6:33 PM. Edited 1 times.
chrisf		#14	[-]
Posts: 55 Nov 9 08 5:40 PM Reply Quote More My Recent Posts	For the third synthesis: methylcyclohexane + Br2 + hV -> 1-bromo-1-methyl-cyclohexane 1-bromo-1-methyl-cyclohexane + NaOEt -> 1-methylcyclohex-1-ene 1-methylcyclohex-1-ene + OsO4 + H2O2 -> 1-methylcyclohexane-1,2-diol Wouldn't adding the OsO4 and H2O2 to the 1-methylcyclohex-1-ene give me the vicinal diol product? Assuming the NaOEt gave a Zaitsev elimination...
orgopete		#15	[-]
Posts: 977 Nov 9 08 8:24 PM Reply Quote More My Recent Posts	methylpropane and ethane + Br2 and hV -> 2-bromo-2-methyl-propane and bromoethane 2-bromo-2-methyl-propane and bromoethane + H2O -> ethanol and 2-methylpropan-2-ol Just not together, separate reactions each. 2-bromo-2-methyl-propane + H2O -> 2-methylpropan-2-ol 2-methylpropan-2-ol + NaH -> NaO-t-Bu + H2 NaO-t-Bu + BrCH2CH3 -> ethyl t-butyl ether + NaBr Wouldn't adding the OsO4 and H2O2 to the 1-methylcyclohex-1-ene give me the vicinal diol product? I hope so as that is C. Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press Last Edited By: orgopete Nov 9 08 10:01 PM. Edited 2 times.
chrisf		#16	[-]
Posts: 55 Nov 9 08 8:52 PM Reply Quote More My Recent Posts	What happens to the ethanol formed after adding water? Last Edited By: chrisf Nov 9 08 8:56 PM. Edited 1 times.
orgopete		#17	[-]
Posts: 977 Nov 9 08 9:00 PM Reply Quote More My Recent Posts	What ethanol? Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press
chrisf		#18	[-]
Posts: 55 Nov 9 08 9:08 PM Reply Quote More My Recent Posts	Ohhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh.............. I was thinking about these in a mixture! I think I just had an epiphany. We're reacting them separately then combining them.... I've got it now. It makes a ton more sense thinking about it the correct way. I see where you're going in that first synthesis. Does that imply it'll make 3 moles of the alcohol in the mechanism? Last Edited By: chrisf Nov 9 08 9:19 PM. Edited 1 times.
orgopete		#19	[-]
Posts: 977 Nov 9 08 10:02 PM Reply Quote More My Recent Posts	1 mole propene -> 1 mole propanol, but it only requires 1/3 mole BH3. Disclaimer, I am the author of the material found at Curved Arrow Press and curvedarrow.com. If you wish to leave me a comment, please find a link at Contact Curved Arrow Press
chrisf		#20	[-]
Posts: 55 Nov 10 08 5:23 AM Reply Quote More My Recent Posts	Ahhh, okay. I get it then. Well, everything seems to make sense to me so hopefully I've done them all right when I go to class today.
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A few synthesis problems...

A few synthesis problems...