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Thread: Need Help. Lowering bond enthalpy

  1. #1 Need Help. Lowering bond enthalpy 
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    Hello,

    I want to do cracking. I have an idea to make biodiesel using mediated electrochemical oxydation. But to do cracking with MEO, bond energy of C=C bond that i want to crack has to be lower than C=O and C-O bond. What i want to ask is, is it possible to lowering bond enthalpy of C=C bond in carboxylic acid system?

    Thanks in advance.


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    Hi,

    I don`t think so. The bond energy is given by overlap of respective wavefunctions and these are roughly the same for all molecules. For example C-C bond in C2H6 will have, with error of few percent, same energy as C-C bond in say C3H8. The error is smaller the bigger molecules is. Of course this is naive way to "calculate" binding energies but has very good results and is widely used by chemists. For more exact solutions you would have to use some quantum chemistry methods like Hartree-Fock, coupled cluster or configurational interaction.


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  4. #3  
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    Quote Originally Posted by aharra View Post
    Hello,

    I want to do cracking. I have an idea to make biodiesel using mediated electrochemical oxydation. But to do cracking with MEO, bond energy of C=C bond that i want to crack has to be lower than C=O and C-O bond. What i want to ask is, is it possible to lowering bond enthalpy of C=C bond in carboxylic acid system?

    Thanks in advance.
    I must confess I'm not very familiar with MEO. As I understand it, the principle is to use a metal cation in a high oxidation state, e.g. Ce IV, as an oxidising agent, which is reduced by reacting with the organic molecule that it oxidises and is itself then reoxidised electrochemically.

    If this is so, how do you use this process to crack a hydrocarbon? As I understand it, cracking is the process of splitting longer chain hydrocarbons into shorter ones, without oxidising them. With hydrocracking, hydrogen is added to "book-end" the free carbons at each end of the newly split chain. With thermal cracking the C:H ratio is fixed, so what happens is you get rearrangments to include more secondary and tertiary carbon, as the molecules get smaller. So I'm having trouble seeing how MEO can do this.

    Perhaps you could explain what type of reaction do you envisage, in terms of typical reactant and typical product?

    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Last edited by exchemist; September 25th, 2013 at 12:01 PM. Reason: Added extra para
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    Quote Originally Posted by exchemist View Post
    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Wow, really? I mean I`m not a chemist but I would not expect that. By how much can you lower it? Did I miss something in my reasoning? By what mechanism does this happen? I mean it must pull C atoms wider apart lowering overlap but how?
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  6. #5  
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    Quote Originally Posted by Gere View Post
    Quote Originally Posted by exchemist View Post
    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Wow, really? I mean I`m not a chemist but I would not expect that. By how much can you lower it? Did I miss something in my reasoning? By what mechanism does this happen? I mean it must pull C atoms wider apart lowering overlap but how?
    Sorry, I was speaking far too lazily - blame old age! In fact what it does is reduce the activation energy for the reaction, rather than radically altering the bond energy. There is an explanation of the process here:

    http://www2.chemistry.msu.edu/facult...ene2.htm#add4a
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    Oh I see, thanks. I will look at that ASAP. It seems they have some trouble with server now.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by aharra View Post
    Hello,

    I want to do cracking. I have an idea to make biodiesel using mediated electrochemical oxydation. But to do cracking with MEO, bond energy of C=C bond that i want to crack has to be lower than C=O and C-O bond. What i want to ask is, is it possible to lowering bond enthalpy of C=C bond in carboxylic acid system?

    Thanks in advance.
    I must confess I'm not very familiar with MEO. As I understand it, the principle is to use a metal cation in a high oxidation state, e.g. Ce IV, as an oxidising agent, which is reduced by reacting with the organic molecule that it oxidises and is itself then reoxidised electrochemically.

    If this is so, how do you use this process to crack a hydrocarbon? As I understand it, cracking is the process of splitting longer chain hydrocarbons into shorter ones, without oxidising them. With hydrocracking, hydrogen is added to "book-end" the free carbons at each end of the newly split chain. With thermal cracking the C:H ratio is fixed, so what happens is you get rearrangments to include more secondary and tertiary carbon, as the molecules get smaller. So I'm having trouble seeing how MEO can do this.

    Perhaps you could explain what type of reaction do you envisage, in terms of typical reactant and typical product?

    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Thank you for the answer, it really helped.

    Yup, MEO is based on oxidation reaction. In this experiment, i want to make biodiesel from plant oil that has long carbon chain (fatty acid). So with MEO, i expect to cut C=C bond in this fatty acid to become shortener carboxylic acid. My "senior" has try to cut C=C bond with ozonitation, it is also based on oxidation reaction. So i think it is possible to do it with MEO, but i don't know it is really possible or no.

    Can i use protective agent in specific C=C bond in fatty acid, so i can add a halida to it. Because i think adding a halida can lower the bond enthalpy of C-C bond. It is just my imagination. I'm not really good at organic chemistry
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  9. #8  
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    Quote Originally Posted by Gere View Post
    Hi,

    I don`t think so. The bond energy is given by overlap of respective wavefunctions and these are roughly the same for all molecules. For example C-C bond in C2H6 will have, with error of few percent, same energy as C-C bond in say C3H8. The error is smaller the bigger molecules is. Of course this is naive way to "calculate" binding energies but has very good results and is widely used by chemists. For more exact solutions you would have to use some quantum chemistry methods like Hartree-Fock, coupled cluster or configurational interaction.
    Thank you Gere

    I will try to learn about the method that you mentioned.
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  10. #9  
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    Quote Originally Posted by aharra View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by aharra View Post
    Hello,

    I want to do cracking. I have an idea to make biodiesel using mediated electrochemical oxydation. But to do cracking with MEO, bond energy of C=C bond that i want to crack has to be lower than C=O and C-O bond. What i want to ask is, is it possible to lowering bond enthalpy of C=C bond in carboxylic acid system?

    Thanks in advance.
    I must confess I'm not very familiar with MEO. As I understand it, the principle is to use a metal cation in a high oxidation state, e.g. Ce IV, as an oxidising agent, which is reduced by reacting with the organic molecule that it oxidises and is itself then reoxidised electrochemically.

    If this is so, how do you use this process to crack a hydrocarbon? As I understand it, cracking is the process of splitting longer chain hydrocarbons into shorter ones, without oxidising them. With hydrocracking, hydrogen is added to "book-end" the free carbons at each end of the newly split chain. With thermal cracking the C:H ratio is fixed, so what happens is you get rearrangments to include more secondary and tertiary carbon, as the molecules get smaller. So I'm having trouble seeing how MEO can do this.

    Perhaps you could explain what type of reaction do you envisage, in terms of typical reactant and typical product?

    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Thank you for the answer, it really helped.

    Yup, MEO is based on oxidation reaction. In this experiment, i want to make biodiesel from plant oil that has long carbon chain (fatty acid). So with MEO, i expect to cut C=C bond in this fatty acid to become shortener carboxylic acid. My "senior" has try to cut C=C bond with ozonitation, it is also based on oxidation reaction. So i think it is possible to do it with MEO, but i don't know it is really possible or no.

    Can i use protective agent in specific C=C bond in fatty acid, so i can add a halida to it. Because i think adding a halida can lower the bond enthalpy of C-C bond. It is just my imagination. I'm not really good at organic chemistry
    Ah OK, so presumably the idea is an alternative way of making biodiesel to today's transesterification of palm oil, right?

    I am not an expert in this field. The best I can suggest is to do some reading on the reactions of known MEO agents, (Ce IV etc), with hydrocarbons. Because as I understand it in MEO, it is this high oxidation state metal cation that you want to make the attack on C=C.

    I'm not sure that "adding a halide" will be a good idea. If you do that, you saturate the C=C to C-C, which makes it more like all the other C-C bonds in the chain. The last thing you want, presumably, is an uncontrolled cutting of the chain at any old C-C bond. I suspect it is best to exploit the unique reactivity of C=C in some way. The good news is that oxidation involves removing electrons, and many saturation reactions of C=C proceed by a +ve species attracting the pi=bond electrons of the double bond. So you could be in with a chance, it seems to me. But it's 40 years since I was last in an organic chemistry lab, so you may well be able to get better advice from someone else.

    P.S. I may be quite wrong about halogenation: see this patent, which I've just found on the web: Mediated electrochemical oxidation of halogenated hydrocarbon waste materials - Scimist, Inc.

    I'd definitely do a literature search, if I were you - there does seem to be some stuff out there on treatment of waste organic materials by MEO.
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  11. #10  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by aharra View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by aharra View Post
    Hello,

    I want to do cracking. I have an idea to make biodiesel using mediated electrochemical oxydation. But to do cracking with MEO, bond energy of C=C bond that i want to crack has to be lower than C=O and C-O bond. What i want to ask is, is it possible to lowering bond enthalpy of C=C bond in carboxylic acid system?

    Thanks in advance.
    I must confess I'm not very familiar with MEO. As I understand it, the principle is to use a metal cation in a high oxidation state, e.g. Ce IV, as an oxidising agent, which is reduced by reacting with the organic molecule that it oxidises and is itself then reoxidised electrochemically.

    If this is so, how do you use this process to crack a hydrocarbon? As I understand it, cracking is the process of splitting longer chain hydrocarbons into shorter ones, without oxidising them. With hydrocracking, hydrogen is added to "book-end" the free carbons at each end of the newly split chain. With thermal cracking the C:H ratio is fixed, so what happens is you get rearrangments to include more secondary and tertiary carbon, as the molecules get smaller. So I'm having trouble seeing how MEO can do this.

    Perhaps you could explain what type of reaction do you envisage, in terms of typical reactant and typical product?

    By the way, you can lower the effective bond energy of C=C by adsorption onto the surface of a metal catalyst. Indeed this sort of thing is the basis of a lot of catalysts used for things such as cracking. But that's not in an aqueous phase.
    Thank you for the answer, it really helped.

    Yup, MEO is based on oxidation reaction. In this experiment, i want to make biodiesel from plant oil that has long carbon chain (fatty acid). So with MEO, i expect to cut C=C bond in this fatty acid to become shortener carboxylic acid. My "senior" has try to cut C=C bond with ozonitation, it is also based on oxidation reaction. So i think it is possible to do it with MEO, but i don't know it is really possible or no.

    Can i use protective agent in specific C=C bond in fatty acid, so i can add a halida to it. Because i think adding a halida can lower the bond enthalpy of C-C bond. It is just my imagination. I'm not really good at organic chemistry
    Ah OK, so presumably the idea is an alternative way of making biodiesel to today's transesterification of palm oil, right?

    I am not an expert in this field. The best I can suggest is to do some reading on the reactions of known MEO agents, (Ce IV etc), with hydrocarbons. Because as I understand it in MEO, it is this high oxidation state metal cation that you want to make the attack on C=C.

    I'm not sure that "adding a halide" will be a good idea. If you do that, you saturate the C=C to C-C, which makes it more like all the other C-C bonds in the chain. The last thing you want, presumably, is an uncontrolled cutting of the chain at any old C-C bond. I suspect it is best to exploit the unique reactivity of C=C in some way. The good news is that oxidation involves removing electrons, and many saturation reactions of C=C proceed by a +ve species attracting the pi=bond electrons of the double bond. So you could be in with a chance, it seems to me. But it's 40 years since I was last in an organic chemistry lab, so you may well be able to get better advice from someone else.

    P.S. I may be quite wrong about halogenation: see this patent, which I've just found on the web: Mediated electrochemical oxidation of halogenated hydrocarbon waste materials - Scimist, Inc.

    I'd definitely do a literature search, if I were you - there does seem to be some stuff out there on treatment of waste organic materials by MEO.
    Thank you so much exchemist.
    Yes, i already done some literature search, but i haven't got a good one.
    I will try to search on other source my friend mentioned. Hope i get what i need.

    Your answer really helped me. Thank you so much
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