[xshadow]

I have a doubt....

I have an exercise where I have a double bond and an esteric group on the same molecule (NOT conjugated)...and I have HCl (aq) as reagent.


What is the  reaction that I can have???

A) hydrolysis of esteric group -COOR giving a -COOH group
B) HCl addition to C=C bond getting an alkyl alide
C) Both A e B




My reasoning is that  IF I add HCl in catalytic condition I have only a small amount of H⁺ so the  acid catalysed hydrolisis of ester is favoured while If I add much more HCl I can also get the addition of HCL at C=C (here H⁺ is needed as ""reagent" (huge  HCl/H⁺ amount ) and  not as catalyst (small amount)

May have it sense? thanks

[Orcio_87]

My reasoning is that  IF I add HCl in catalytic condition I have only a small amount of H+ so the  acid catalysed hydrolisis of ester is favoured while If I add much more HCl I can also get the addition of HCL at C=C (here H+ is needed as ""reagent" (huge  HCl/H+ amount ) and  not as catalyst (small amount)

May have it sense?

There are no reasons why the first reaction (hydrolysis) will be catalyzed by small amounts of HCl, while second (addition to C=C) will be favoured with larger concentration. Both reactions depends strictly on the concentration of HCl.

Still - one of them can be faster than the other.

[xshadow]

My reasoning is that  IF I add HCl in catalytic condition I have only a small amount of H+ so the  acid catalysed hydrolisis of ester is favoured while If I add much more HCl I can also get the addition of HCL at C=C (here H+ is needed as ""reagent" (huge  HCl/H+ amount ) and  not as catalyst (small amount)

May have it sense?

There are no reasons why the first reaction (hydrolysis) will be catalyzed by small amounts of HCl, while second (addition to C=C) will be favoured with larger concentration. Both reactions depends strictly on the concentration of HCl.

Still - one of them can be faster than the other.

why not?

In the ester acid hydrolysis  the proton H⁺ is always "recycled" ( so a small amount is enough) while in HCl addition to  a C=C  the H⁺ is added irreversibly to the double bond ,so it's a reagent (and a small-catalytic amount is not enough)
According to me it can make sense.


Also If I read HCl/H2O I think that HCl is usually in excess compared to the substrate so even if the ester hydrolisis is faster than  I get  a product with the C=C (that did not react)  + some HCl not reacted  (excess)with the -COOR group...at this point why I can't have the HCl addition to an alkene??

[Orcio_87]

In the ester acid hydrolysis  the proton H+ is always "recycled" ( so a small amount is enough) while in HCl addition to  a C=C  the H+ is added irreversibly to the double bond ,so it's a reagent (and a small amount is not enough)
According to me it can make sense.

First reaction (hydrolysis) depends on concentration of HCl, but HCl is recovered with lapse of time.

Second reaction (addition to C=C) depends on concentration of HCl but HCl (as a reagent) is consumed, so reaction rate will drop over time.

But - reactions goes separetely, so with progress of second reaction (addition), rate of first reaction (hydrolysis) will also drop.

[xshadow]

In the ester acid hydrolysis  the proton H+ is always "recycled" ( so a small amount is enough) while in HCl addition to  a C=C  the H+ is added irreversibly to the double bond ,so it's a reagent (and a small amount is not enough)
According to me it can make sense.

First reaction (hydrolysis) depends on concentration of HCl, but HCl is recovered with lapse of time.

Second reaction (addition to C=C) depends on concentration of HCl but HCl (as a reagent) is consumed, so reaction rate will drop over time.

But - reactions goes separetely, so with progress of second reaction (addition), rate of first reaction (hydrolysis) will also drop.

I've seen the exercise solution and the - COOR group  has been hydrolyzed  while the C=C is remained the same.
So  I don't understand why HCl + water (no other info on the amount) will only give hydrolysis and not also addition to C=C ,after some time...

[Orcio_87]

I've seen the exercise solution and the - COOR group  has been hydrolyzed  while the C=C is remained the same.
So  I don't understand why HCl + water (no other info on the amount) will only give hydrolysis and not also addition to C=C ,after some time...

What you tell is that hydrolysis of -COOR is faster than addition to C=C.

This means that both reaction can be completed (first hydrolysis then addition).

If addition will be faster reaction, then hydrolysis can't be done.

[xshadow]

I've seen the exercise solution and the - COOR group  has been hydrolyzed  while the C=C is remained the same.
So  I don't understand why HCl + water (no other info on the amount) will only give hydrolysis and not also addition to C=C ,after some time...

What you tell is that hydrolysis of -COOR is faster than addition to C=C.

This means that both reaction can be completed (first hydrolysis then addition).

If addition will be faster reaction, then hydrolysis can't be done.

OK
But  why the  solution says that I get only the esteric group hydrolysis while the C=C doesn't react...

[Orcio_87]

Probably C=C reacts slower than -COOR group.

[rolnor]

Can the molecule form a ring, the carboxylic group adding to the double bond, like water can hydrate a alkene?

[xshadow]

Can the molecule form a ring, the carboxylic group adding to the double bond, like water can hydrate a alkene?

I have already a ring in that molecule.
the molecule is a derivate of this:
Ethyl cyclohexane propionate
https://chem.nlm.nih.gov/chemidplus/structure/10094-36-7


Where I  have also a double bond on the left side of the ring (1,3 distance   with the substituent on the ring)


And the exercise solution -after reaction with HCl + H2O- says  I get  the same molecule but with the COOR group converted in COOH group.The C=C bond doesn't  react with HCl, is always there.

I wonder why....can the  -COOH group formed inhibit the C=C protonation (that is the first ,important  step of HCl addition to  a C=C)??
 I mean the protonation will always  be at the oxygen (much faster) ,also when  the esteric group is all converted in the carboxylic one :  the equilibrium is actually something dynamic so I can imagine that at every moment  the COOH protonation will always occur ,than H₂O will attack the COOH protonated group  and obviously I'll get always the same COOH group, as the leaving group and the nucleophile are the same)

But this loop prevents protonation of  C=C (that I know is a slower process than oxygen protonation since  C=C protonation   creates a carbocation and also C has to change hybridization (it takes some time...)

While if I do a -COOH reduction with BH₃ I suppose that HCl will now reduce the C=C .

Can it make sense??
thanks

[Orcio_87]

Also If I read HCl/H2O I think that HCl is usually in excess compared to the substrate so even if the ester hydrolisis is faster than  I get  a product with the C=C (that did not react)  + some HCl not reacted  (excess)with the -COOR group...at this point why I can't have the HCl addition to an alkene??

Sorry, I did misdirect you.

Both reactions (hydrolysis and addition) are catalyzed by HCl, but concentration of HCl will not change as the H₂O (not HCl) will attach to C=C.

That is why A) is the correct answer.

[xshadow]

Also If I read HCl/H2O I think that HCl is usually in excess compared to the substrate so even if the ester hydrolisis is faster than  I get  a product with the C=C (that did not react)  + some HCl not reacted  (excess)with the -COOR group...at this point why I can't have the HCl addition to an alkene??

Sorry, I did misdirect you.

Both reactions (hydrolysis and addition) are catalyzed by HCl, but concentration of HCl will not change as the H₂O (not HCl) will attach to C=C.

That is why A) is the correct answer.

But I don't get an alcoholic group in the product (as happens if H₂O attacks the C=C . And then an  alcoholic group in HCl  environment  should give a Sn2 substition)
The C=C is not touched,

PS: In the HCl addition  H⁺ is not a catalyst but a reagent that is consumed.
In water addition ok,right. But for alkene hydratation my textbook uses H2SO4 instead of HCl (perhaps to avoid  some competition with Cl- )

Anyway my textbook says that only the esteric group reacts with HCl/H₂O but don't understand why C=C can't react with HCl or also with water as you said.
Ok C=C reaction is slower but should happen affter a while.... but instead .

[rolnor]

I think it would be good if you draw the reactions you suggest, its getting very complicated.

[xshadow]

I think it would be good if you draw the reactions you suggest, its getting very complicated.

[

I mean that since I have always a C=O group also after all the COOR group is converted to COOH  the protomation
(much more faster than the competitive protonatipn at C=C) should occour again on the COOH group and then H₂O (the nucleophile) can attacck.

I get an intermediate instable that rigenerates the COOH group with the leaving of a water molecule

This reaction can occour , obviously the nucleophile  and the leaving group are the same (H₂O) so nothing seems to happen , but actually this reaction should always occour(the chemical equilibrium is something dynamic,reactions always happen but at the same rate) and prevents the competitive protonation at C=C. (Less reactive/slower)

This is the only  explanatipn I can give to explain whyC=C can't react with HCl/H2O after a while...
In literature I don't fine many examples of acid hydrolysis of a C=O group with also a C=C bond(NOT conjugated) on that substrate ...

[OrganicH2O]

Although your mechanism makes sense, and is likely actually happening, it doesn't actually explain why the alkene doesn't react. After all, the equilibrium constant for forming the tetrahedral intermediate you draw is very small.

In order for the alkene to react, it would likely have to occur via a secondary carbocation. Early in the class, you draw many mechanisms and chemical reactions that occur via secondary carbocations. But in terms of big picture reactivity, secondary carbocations are pretty darn unstable, and difficult to form. Many acid catalyzed processes occur through more stable cation intermediates. With sufficient time, maybe the alkene could react. Then it would be a big mess, probably with some rearrangements. A competing functional group that is only able to form a secondary carbocation can't compete with many other functional groups that form more stable reactive intermediates. Examples of more reactive functional groups include many acid derivatives, acetals, imines, enamines, enol ethers etc.