Sciencemadness Discussion Board - Assistance Needed to Balance Equation to Determine Theoretical Yield

Assistance Needed to Balance Equation to Determine Theoretical Yield

RelativeEffectiveness - 16-2-2015 at 09:14

I am new to this forum but not new to amateur experimentalism. I took college chemistry once upon a time and but much of the more basic material eludes me. I have a synthesis that I would like to evaluate the efficacy of, which I already know to be poor, so that I may attempt to improve upon its' values. More importantly, I want to UNDERSTAND exactly what is taking place. I am not asking simply for the solution (no pun intended) but an explanation of the processes (what are the reaction products and how I would balance it) leading up to it alongside this answer. Any help would be greatly appreciated. And before anyone gets upset, I did make a solid attempt at figuring this out myself and I feel that I need someone to explain it to me. Much like a student might have a textbook with all the answers but a teacher is also present because oftentimes a different perspective is required.

In the synthesis, solution A is added dropwise to solution B allowing for an ether to transform into an ester to for use of the 1deg alcohol oxidation into a lactone.

Solution A: (CH2)4O + CH3CN + CH3CO2H
Solution B: Ca(ClO)2 + H2O

If you understand this equation then you'll almost certainly understand its ultimate purpose as it has limited use for anything else. However, it bears no importance to my inquiry. I am seeking a complete understanding of the chemistry involved here. Thank you! :-D

[Edited on 16-2-2015 by RelativeEffectiveness]

gdflp - 16-2-2015 at 09:27

No one will help you make drugs. There are plenty of other substrates for this reaction if you are interested in the chemistry, choose one of them. There seem to be a lot of people trying to synth GBL recently.

RelativeEffectiveness - 16-2-2015 at 10:06

I know how to make it. I can make it. That is not the point. I want to know more intimately the actual chemistry taking place because it interests me. I am asking for help solving and balancing the equation. I dont "need anyones help making drugs." I need someones help better understanding chemistry. If it is better for your conscience, provide me with a similar substrate with similar or identical reactants and go through it for me.
Lets use tetrahydropyran instead then.
[Edited on 16-2-2015 by RelativeEffectiveness]

[Edited on 16-2-2015 by RelativeEffectiveness]

gdflp - 16-2-2015 at 10:12

Then why choose this substrate if you are just interested in the chemistry? If you really want to know, search, hypochlorite oxidation of legal substrates is a common lab experiment.

RelativeEffectiveness - 16-2-2015 at 10:19

Because I did not know enough about chemistry to know that this was such a common reaction. I apologize. I was simply using that reaction because I was familiar with it. If you could attempt to look past the idea that i am trying to make drugs and replace it with your new understanding of my desire to comprehend solving and balancing this type of reaction I would still appreciate an explanation from anyone will.

[Edited on 16-2-2015 by RelativeEffectiveness]

Nicodem - 16-2-2015 at 14:21

Quote: Originally posted by RelativeEffectiveness

If you could attempt to look past the idea that i am trying to make drugs and replace it with your new understanding of my desire to comprehend solving and balancing this type of reaction I would still appreciate an explanation from anyone will.

And how is anybody to do that? You forgot to give the reference and without it there can be no reasonable answer.

turd - 16-2-2015 at 16:26

Quote: Originally posted by RelativeEffectiveness

Assistance Needed to Balance Equation to Determine Theoretical Yield

This question makes no sense - you have to specify what you want the yield based on. THF or Ca(ClO)2?

There are many things wrong with your post. Don't beat around the bush. Give references (https://www.erowid.org/archive/rhodium/chemistry/ether2ester...). Give a clear title (e.g. Stoichiometry of calcium hypochloride oxidation of THF to gamma-butyrolactone). Ask your question clearly and succinctly. Sensitivities go to Whimsy.

Anyway, the classic high-school solution to the question would be:

(1) THF + H₂O ---> GBL + 4H⁺ + 4e^-
(2) Ca(ClO)₂ + 4H⁺ + 4e^- ---> CaCl₂ + 2H₂O
(1) + (2) ==> THF + Ca(ClO)₂ ---> GBL + CaCl₂ + H₂O

PS: GHB sucks. IMHO it's on the same level as alcohol. Wasting acetonitrile on this reaction is a bit of a sacrilege.

Quote:

No one will help you make drugs

Who gives you the authority to speak for everyone? Stop being a prick.

[Edited on 17-2-2015 by turd]

gdflp - 16-2-2015 at 17:09

Quote: Originally posted by turd

Quote:

No one will help you make drugs

Who gives you the authority to speak for everyone? Stop being a prick.

[Edited on 17-2-2015 by turd]

You're right, I phrased that wrong. Everyone who values their equipment and doesn't want to face the small chance of being charged as an accomplice will not help you make drugs. I apologize.

[Edited on 2-17-2015 by gdflp]

Etaoin Shrdlu - 16-2-2015 at 17:17

Quote: Originally posted by RelativeEffectiveness

I took college chemistry once upon a time and but much of the more basic material eludes me.

Luckily, there are many college chemistry textbooks, study guides, and lecture series readily available online. Read them.

j_sum1 - 16-2-2015 at 18:33

Balancing equations and determination of yield are pretty fundamental skills.
Generally this is learned in simple experiments like acid-base neutralisation, simple redox, electrolysis of water, combustion and that kind of thing.

If you are refreshing on these skills and require help, I have no idea why you would choose this as an example.
If you are investigating a reaction mechanism then I am not sure why you would ask about yield nor again why you would choose this particular example.
If you are wanting a leg-up in your new enterprise as a drug cook, I am not sure why you would ask here. This is not the focus of this board.

So, I am confused by your question.

Chemosynthesis - 16-2-2015 at 20:40

Quote: Originally posted by turd

Quote: Originally posted by RelativeEffectiveness

Assistance Needed to Balance Equation to Determine Theoretical Yield

This question makes no sense - you have to specify what you want the yield based on. THF or Ca(ClO)2

Hardly. The question may not make sense for reasons others have stated, but your comment here is not one of them. Obviously in a balanced equation, the theoretical yield is 100%. In practice, unless otherwise stated, absolute yield is generally understood to be by mass (rather than molar yield) and percent yield is in terms of the limiting reagent unless specified. This does make experimental yield determination without quantified data meaningless, but that isn't what the poster asked and not for the reason you're stating while you're calling members unnecessary names instead of just disagreeing with them which is pretty clearly against forum decorum, you can look it up or ask a chemist if you disagree.
http://orgchem.colorado.edu/Technique/Procedures/Notebook/Yi...

turd - 16-2-2015 at 23:00

Quote:

The question may not make sense for reasons others have stated, but your comment here is not one of them.

Yes, actually it is - if the yield is supposed to be on THF there is no need to "balance" an equation for determining yield:
THF + x oxidizer ---> GBL + y something
If the yield is supposed to be on the oxidizer things may get more hairy, because oxidizers may behave differently in different conditions.

Quote:

In practice, unless otherwise stated, absolute yield is generally understood to be by mass (rather than molar yield) and percent yield is in terms of the limiting reagent unless specified.

Thank you Mr. Wikipedia-Chemist. Now can you also post something useful and help OP?

[Edited on 17-2-2015 by turd]

Chemosynthesis - 17-2-2015 at 01:32

Quote: Originally posted by turd

You are making the assumption that your x coefficient is in excess of the understood '1' in front of THF for some reason, assuming one molecule of oxidizer per THF molecule in the balanced equation (necessary to normalize to). This assumption is a mistake.

A percent yield only makes sense with regard to a theoretical yield, which is what the OP asked about. Read what he said. You need a limiting reagent from a balanced equation to determine this, end of story. If you disagree, you are obviously just completely ignorant or trolling.

How exactly do you propose someone determine the limiting reagent without a balanced equation, then? This is part of what the OP wants as far as I understand "I have a synthesis that I would like to evaluate the efficacy of, which I already know to be poor" and then asking for... a balanced equation, presumably so they can determine the denominator of their percent yield for comparative purposes under what are presumably different reaction conditions for comparative optimization in a method oriented synthesis in synthetic methodology, as opposed to something like total synthesis. I know I haven't been in a chemistry class in awhile, but it appears to still be taught the way it was in every course I ever took, and how I had to keep logs for experiments in bound notebooks in research and in publication. I guess I just lack all the experience tard here has, er, turd. My apologies, your calling me an armchair chemist doesn't mean I should insult you back, so now that we have exchanged barbs, how about address what the poster said, or the content of my post rather than making wild assumptions and ignoring how yield conventions work.. and/or why don't you go brush up on how a yield is determined like I suggested.

Determining "yield on the oxidizer" when your limiting reagent is THF is meaningless in terms of theoretical yield. No one publishes yields like this. Feel free to find me a peer-reviewed article where someone has just to show me wrong. Your theoretical yield is limited by the limiting reagent, hence the name. The limitation is stoichiometric, which requires some form of equation balancing. No one determines a theoretical yield by a reagent in excess, regardless of whether that excess increases percent yield.

Quote:

Thank you Mr. Wikipedia-Chemist. Now can you also post something useful and help OP?

Useful like you're being as you level insults at everyone while ignoring the original poster's actual questions and being arrogant in... what, speaking for the OP? Didn't you just criticize someone for speaking for others? Gee, if an .edu domain website on organic chemistry lab notebooks and yields, like the OP mentioned in their post, isn't helpful I don't know what is. Then again, you clearly ignored it, then went to wikipedia and found that it too says what every textbook on chemistry says and ignored that too, so I guess that's indicative of something. If someone asks for a total yield, it's assumed they mean by mass unless they state "molar yield." Similarly, it's understood that a percent yield is with respect to a limiting reagent, which you implicitly determine relative a balanced reaction equation. This doesn't have to be specified, but it does have to be done.

Maybe if you were educated in the subject you could use the proper terms such as "limiting reagent" or distinguish theoretical from percent yield while you go calling people 'wikipedia chemist' and citing solely from erowid mirrors. In fact, take said article. Your source. Note how the comparative yields per oxidizer are listed? Those are percent yields with a denominator of the theoretical yield given a limiting reagent, tabulated solely for comparative purposes across substrate. The percent yields are still normalized based on the theoretical yield, which is based off the limiting reagent. If they weren't done in this manner, how would you compare them? The hubris is matched only by your ignorance. I would expect someone working from wikipedia, or the academic educational source I cited, to know the difference between a percent and theoretical yield, which is more than I can say for your posting at the moment. Maybe you can cite your own source that disputes how a theoretical yield is determined, and enlighten us all, or stop insulting people and admit you made a mistake.

turd - 17-2-2015 at 01:48

Serious question: Have you been diagnosed with autism / Asperger's? That would explain your incoherent rants on complete trivialities.

Chemosynthesis - 17-2-2015 at 02:00

Quote: Originally posted by turd

Serious question: Have you been diagnosed with autism / Asperger's? That would explain your incoherent rants on complete trivialities.

Nah, but I play autism spectrum on the internet. By the way, claiming that balancing a reaction is not necessary to calculate a theoretical yield is the kind of triviality that fails students straight out of chemistry, and (autism mode) is against the Sciencemadness Guidelines (TM).

Serious question back at you: are you trolling, or just prone to making what you feel are completely trivial mistakes (dyslexia?) while insulting people? Honest question. Because that would explain how much difficulty you express at simple, reiterative English making sense.

turd - 17-2-2015 at 02:34

I may be dyslexic, but you clearly lack in even the most basic understanding how reaction equations work. E.g.:

Quote:

This makes no sense. x is determined by the reaction. It cannot be in excess of something. You don't write unreacted reagent to the right of the equation. And that was only the first sentence of your rant!

And no, in many cases a chemist does not have to balance equations to calculate yields. It's not uncommon to have different reactions at the same time. Example: You oxidize a substrate with KMnO4. As long as you use an obvious excess of KMnO4, it's irrelevant whether it goes down to MnO2 or Mn2+ or some crazy mixture, if you calculate the yield on the substrate.

turd - 17-2-2015 at 03:18

Quote: Originally posted by Chemosynthesis

You have 'x' as a reactant coefficient for your oxidizer on the LEFT of your equation. It absolutely can be in excess of the limiting reagent if this is not a balanced equation.

Again: you don't understand what an equation is.
x is defined in what I have written above. It cannot be in excess.

Quote:

Your entire argument was based on not needing to balance equations for determining yields, when the poster was very specific about percent yield. I already explained percent yield does require a balanced equation.

No, it doesn't and in some cases there is no well defined equation. You will find many papers without equations, yet calculated yields.

Quote:

Now we're getting into semantics. How does a chemist know what an excess is unless they mentally ballpark a balanced equation to some arbitrary order of magnitude?

From experience. E.g. you cook phenylacetone from phenylacetic acid in acetic anhydride. You use a huge excess of acetic anhydride, because you know that you will get biaryl product otherwise. Say 20 g PAA in 800 ml AA. You can calculate yield based on PAA without knowing how much AA reacts with PAA.

Quote:

As for multiple reactions occurring at once, that's irrelevant.

Absolutely not. Your oxidizer can have different pathways to different oxidation states.
You cannot determine what you get in the end, therefore you cannot balance your equation, still you can determine your yield based on substrate. QED.

Chemosynthesis - 17-2-2015 at 03:20

Quote: Originally posted by turd

I may be dyslexic, but you clearly lack in even the most basic understanding how reaction equations work. E.g.:

Hardly close to reality with that assumption about my understanding. Balanced reaction equations have nothing to do with unreacted reactants... those are equilibrium constants. You seem to be conflating the two, or assuming I was discussing them. I was not.

Quote:

This isn't relevant to anything I said. Maybe you didn't understand what I said, but I am not under the impression you write unreacted reactants on the right of a balanced equation, nor did I state one should.

You have 'x' as a reactant coefficient for your oxidizer on the LEFT of your equation. It absolutely can be in excess of the limiting reagent if this is not a balanced equation. Your entire argument was based on not needing to balance equations for determining yields, when the poster was very specific about comparing reactions, which requires percent yield. I already explained percent yield does require a balanced equation, and theoretical yield (hence why the original poster is asking, I presume).

Quote:

And no, in many cases a chemist does not have to balance equations to calculate yields. It's not uncommon to have different reactions at the same time. Example: You oxidize a substrate with KMnO4. As long as you use an obvious excess of KMnO4, it's irrelevant whether it goes down to MnO2 or Mn2+ or some crazy mixture, if you calculate the yield on the substrate.

Now we're getting into semantics. How does a chemist know what an excess is unless they mentally ballpark a balanced equation to some arbitrary order of magnitude? Nowhere did I state balancing couldn't be mentally estimated, or that one needed a certain number of significant figure: just that it had to be done. Now it would seem we're agreeing in principle, but seemingly conflicted about methodology.

As for multiple reactions occurring at once, that's irrelevant. You can have all kinds of spectator ions on both sides of an equation if you wanted, though it's not simplified, and ping-pong kinetics in reactions are also possible to write, but the level of specificity has to allow you to balance your product and reactant to determine a theoretical yield, which is what the poster was asking about!

Chemosynthesis - 17-2-2015 at 03:28

Oops. Deleted my post trying to reply. Hit back and posted out of sequence above.

Quote: Originally posted by turd

Again: you don't understand what an equation is.
x is defined in what I have written above. It cannot be in excess.

I beg to differ. You don't seem to understand what a variable is, and you're questioning my grasp of equations. Nowhere did you define x that I see. Please point that out explicitly for me in case I missed it. In your original post there, which I quoted, you have:
"Yes, actually it is - if the yield is supposed to be on THF there is no need to "balance" an equation for determining yield:
THF + x oxidizer ---> GBL + y something
If the yield is supposed to be on the oxidizer things may get more hairy, because oxidizers may behave differently in different conditions."

Where is x defined? There is no mathematical (or physical, more importantly) reason that x can't be between 0 and 1, which makes the oxidizer the limiting reagent if it is only capable of oxidizing one equivalent of THF each, which makes a theoretical yield in terms of THF meaningless. If you said x>=1, x= some number greater than or equal to one, or even (1+x), there would be clear excess regardless of whether your oxidizer oxidized 1 or 20 equivalents of THF. You went back and edited in a balanced set of half reactions in your earlier post now, without mentioning, I see. This wasn't there originally. Why do it if it were completely unnecessary for the poster?

Quote:

Pathways aren't shown in a balanced equation, nor are transition states or a lot of other irrelevant things to theoretical yield calculation. And yes, you can determine what you get in the end of a reaction. It's called characterization, and it honestly kind of sucks. HPLC, UHPLC, GC/MS, and various other chromatographic separations and spec techniques give a very good idea of what you get in a reaction. You might not 'know' it before your experiment, but that is not relevant to theoretical yield, which is the only yield in the thread title/original post!

A pathway doesn't affect a theoretical yield for identical limiting reagent molar quantities.

Different pathways to a reaction, or papers without balanced equations written, still presumptively balance the equation the authors want to happen, or expect, in terms of calculating percent yields from limiting reagents and theoretical yields. That is where the "theory" portion of the yield comes from. The actual equation might not be printed in the paper or the supplementals, but it's discernible from the reaction schemes and molar equivalences. Published scientists don't generally post every little calculation or bit of data they did when it's common knowledge and can be determined from what they do write, even though it may have been done. Ask anyone you can verify has published and trust, since clearly you want to pretend I just don't understand equations without linking to anything that supports where you were taught your paradigm with regard to theoretical yield.

Now you're discussing how efficient or clean a reaction is, as side reactions or intermediates may form. Again, this is actually irrelevant to determining theoretical, though as I said earlier, may affect the percent yield. I was very specific about this. Look at any complete combustion reaction of fuel and oxygen to CO2, H2O. That is an idealized scenario, yet it is still used for calculation of BTUs. I have personally synthesized and painstakingly characterized reactions under various conditions where yields improved, but side products increased. In one reaction condition, very pure products and unreacted substrate were separated. In a second condition, more product, less reactants, and various additional side products were made. As you said, not uncommon. Yield was determined identically for comparisons.

As for experience, that is still mentally ballparking a balanced equation. You have to have some comprehension of what the limiting reagent is. This is a mental calculation. If you don't like my terminology, fine. You don't consider it a calculation, even if instinctual, to determine the limiting reagent. Clearly an experienced chemist working from memory or intuition has enough of a grasp of the relative molar quantities of two reactants interacting to get a known product and balance an equation in their heads. It might not be simplified, but it was done at some point, even if instinctually. The OP is obviously not there, nor is that what they asked. Changing topics to "cooking" P2P might be an entirely different matter, as I don't necessarily expect a "cook" to even care about yields, waste disposal, etc.

[Edited on 18-2-2015 by Chemosynthesis]

Darkstar - 17-2-2015 at 03:43

Quote: Originally posted by RelativeEffectiveness

I am seeking a complete understanding of the chemistry involved here.

I had some time to waste and felt like playing around in ChemDraw anyway. If you really are interested in the actual chemistry involved in that reaction, I'm guessing this is how it probably works. The THF gets oxidized twice, with the second oxidation proceeding through either a hydroxyaldehyde or a cyclic hemiacetal (probably both). Any input from others is welcome.

mech1.bmp - 2.3MB

[Edited on 2-17-2015 by Darkstar]

RelativeEffectiveness - 17-2-2015 at 09:49

Thank you everyone for your input. This is the actual reference. I had chosen this reaction because I am familiar with it and it interests me. Can I not choose to practice and relearn the fundamentals of chemistry on a substance that has value as a recreational drug? You all assume that mynintent is to use this knowledge to pursue clandestine and illicit experiments. The isn't the case. Been there done that. Im genuinely interested in understanding a reaction that I have performed in the past as my interests have become more fixated on the chemistry itself rather than the drug. I would hope someone can understand that without an immediate bias against drug synthesis and the connotations they elicit.
I am also aware of the existence of chemistry textbooks. After looking through much of auch information I opted to ask the opinions and look to see the insight of like-minded chemists with substantially more knowledge and experience than myself. I assumes this was a community of chemists interested in the chemistry of all organic and inorganic materials. If you do not wish to help me, than abstain from doing so. But please do not patronize me with sarcastic remarks about textbooks and how I would have been better off never asking this question or for help in this forum. This is counterproductive. For those who have not misinterpreted my intent, I thank you for your input.

"A general procedure is outlined for the oxidation of l-menthol to l-menthone. Thus l-menthol (3g, 19mmol) was dissolved in acetonitrile : acetic acid (3:2 25ml) and added dropwise over a period of ten minutes to a cooled (0degC) and stirred solution of Ca(OC1)2 (1.84g, 12.7 mmol) in water (40ml). Stirring was continued for 1 hr after which water (40 ml) was added. The solution was extracted with CH2Cl2 (4 x 30ml) and the organic layers washed with 10% NaHCO3 followed by an aqueous wash. After drying with MgSO4 and evaporating the CH2Cl2 the crude product was distilled affording l-menthone (2.89 g, 98%). The spectra (ir and nmr) were identical with those of authentic material{9,10}.

Oxidation of primary alcohols under identical conditions gave an aldehyde only in the case of benzyl alcohol{11}. Other primary alcohols gave esters as tabulated in table 2. This table also includes our results on the oxidation of of ethers to esters. Though the yields were not nearly as good as for the alcohols, the data is reported because of the unusual and potentially useful transformation{12}. The ethers were oxidized under similar conditions as the alcohols except that the reactions were carried out at room temperature for from 4-16 hrs. Heating does not seem to increase the yield.

We are presently carrying out studies to improve the yields on the ether to ester transformation and to utilize the 1deg alcohol oxidation for the preparation of lactones from a-w diols.

______________________________________________________________________________

Table 2. Oxidation of 1 deg-Alcohols and Ethers Using Calcium and Sodium Hypochlorite.

Run Substrate Product %Yield(a) (Ca(OCl)2 NaOCl) Reference

--------------------------------------------------------------------------------------------------------

1 benzyl alcohol -> benzaldehyde 98 98 10

2 1-pentanol -> pentyl pentanoate 83 91 10

3 l-hexanol -> hexyl hexanoate 98 98 9e

4 3-methyl butanol -> 3-methyl butyl isovalerate 76 87 10

5 ethyl alcohol -> ethyl acetate -- (b) 9b, 10

6 ethyl alcohol -> ethyl acetate (b) -- --

7 butyl ether -> butyl butanoate 40 -- 10

8 tetrahydrofuran -> g-butyrolactone 68 -- 9b, 10

9 tetrahydropyran -> d-valerolactone 56(c) -- 9b, 10

(a) Isolated yield

(b) Yield not calculated due to the volatility of the products but significant conversion was indicated by IR and NMR analysis.

(c) Yield obtained by GC analysis."

I am very busy at the moment but I am very grateful for everyones help and will be on later to analyze all this new information.

[Edited on 17-2-2015 by RelativeEffectiveness]

[Edited on 17-2-2015 by RelativeEffectiveness]

Etaoin Shrdlu - 17-2-2015 at 10:58

Could you two stop insulting each other? Chemo's calculating percent theoretical yield based on mass product per expected mass product from limiting reagent, turd's calculating practical yield based on mass product per mass substrate assuming excess other reagents. Neither of you two is a "wikipedia chemist" nor completely lacking practical experience, for the love of common sense.

If the OP is genuinely interested in chemistry, Chemo's way is the one to understand first.

Molecular Manipulations - 17-2-2015 at 11:21

Quote: Originally posted by RelativeEffectiveness

Can I not choose to practice and relearn the fundamentals of chemistry on a substance that has value as a recreational drug?

Yes you can. Even if you had the intention of making the drug that wouldn't be against forum rules, as long as you're rather discussing it in a scientific manner and not just asking for a "recipe".

RelativeEffectiveness - 17-2-2015 at 13:33

I apologize for the bickering. You all have been extremely helpful. Im in search of a website (or any reference format) that would be ideal for helping me re-learn how to calculate the stoichiometry of chemical equations. As a few of you have already pointed out, this particular equation is not the ideal starting point. However, I had been dying to understand it for quite some time and now that Ive reverted from a life of persistent neurotransmitter disarray in my brain to one of pursuing the comprehension and application of chemistry, I can assure you that my intentions are genuine (not that this is a requirement). This is a great forum and I plan on sticking around for the copious amounts of applicable discussion that make this forum an excellent resource and an equally beneficial tool. If anyone knows of resource that might be of help in re-learning how to calculate the stoichiometry of equations I would be much obliged!

[Edited on 17-2-2015 by RelativeEffectiveness]

RelativeEffectiveness - 17-2-2015 at 13:39

Thank you especially to Chemosynthesis, turd and Darkstar. Darkstar, that was great of you to take the time to arrange that. That was amazingly insightful.

However, Im still at a loss as to what the stoichiometry would look like. Are the THF and the Ca(OCl)2 both 1 and 1? And I assume the limiting reagent is THF? Or would it depend on the intent of thr reaction and could also be Ca(OCl)2? Id like to understand and see how the acetonitrile and acetic acid play a role in the reaction.

[Edited on 17-2-2015 by RelativeEffectiveness]

[Edited on 17-2-2015 by RelativeEffectiveness]

Chemosynthesis - 17-2-2015 at 21:00

I think most people on the forum are happy to help you learn chemistry out of curiosity and genuine interest as long as we don't think it will harm others or contribute to regulations which would impact hobby chemistry, which the forum is based on. I am also pretty sure that at least most of us would enjoy having you as a member, and probably that within time, you can feel comfortable contributing. I think some of the confusion and suspicion is that you are trying to do many things at once that are not necessarily related, or taught as related.

You definitely posted in an appropriate subforum for learning or re-learning these things. I think you should seek out an introductory text or website to assist you as well, and the way courses are typically oriented in a highschool-to-college/university-to-graduate progression build on each other through much trial and error. You may have noticed this thread with additional resources: https://www.sciencemadness.org/whisper/viewthread.php?tid=66...

Where exactly are you stuck? There are two points of stoichiometry, and a bridge between them:
1. You have a theoretical, idealized, balanced equation. This has no limiting reagent because there is no waste. Everything reacts in the most efficient manner possible. This gives you theoretical yield, which is what you asked about. It's abstracted from how reality actually works, but we use it as a limitation or ceiling for how efficient a reaction can possibly be. Try and conceptually separate this from any experimentation. To reiterate, the theoretical yield, which is what you asked about, is built on a balanced equation. You have to have a concept of the equation first. This doesn't tell you about whether the equation is accurate for your reaction conditions, if it proceeds to the right or the left with a particular favorability, what the yield of an experiment is, etc. It doesn't show what happens in terms of energy or much in terms of three dimensional structure. These are all generally taught later, and build upon stoichiometry.

Bridge: You have data. You have data from the amount of reactants you started with, and then you have data on your reactants: the actual empirical/experimental yield. This is just a measurement. No stoichiometry necessary here.

2. Now, in theory, you could measure out exact, flawless amounts of reagent to match your balanced equation. In practice, this doesn't happen, and you have one reagent which limits your reaction, while the other(s) is/are in excess, and have zero bearing on the theoretical yield since they would be left unchanged when they ran out of partner reactants. This means you have to perform another round of stoichiometry to compare with the theoretical yield you already have.

Now you have percent yield. You determined how efficient your reaction was in reality versus how efficient it could possibly have been, taking into the real quantities of material you reacted.

Darkstar - 17-2-2015 at 22:13

Quote: Originally posted by RelativeEffectiveness

Darkstar, that was great of you to take the time to arrange that. That was amazingly insightful.

No problem. Just to make it clear, though, the exact mechanism for these hypochlorite oxidations isn't actually known. The only thing for certain is that they tend to work much better under acidic conditions, suggesting that it's actually hypochlorous acid that's doing the oxidizing (or at least playing a significant role in it), and don't appear to involve any sort of free-radical mechanism.

Quote:

However, Im still at a loss as to what the stoichiometry would look like. Are the THF and the Ca(OCl)2 both 1 and 1?

If you look back at Turd's original post, you'll see the balanced equation:

Quote: Originally posted by turd

THF + Ca(ClO)₂ ---> GBL + CaCl₂ + H₂O

According to this, in theory, one equivalent of Ca(ClO)₂ will oxidize one equivalent of THF, producing one equivalent of GBL, CaCl₂ and H₂O in the process. If you look at the mechanism I proposed, you'll see the same thing as well.

Quote:

Id like to understand and see how the acetonitrile and acetic acid play a role in the reaction.

The acetonitrile functions as a solvent and the acetic acid catalyzes the reaction by protonating hypochlorite and activating it for nucleophilic attack on its chlorine by THF's oxygen. The calcium acetate initially produced is eventually neutralized by the aqueous HCl, regenerating acetic acid and producing CaCl₂ instead.

Chemosynthesis - 18-2-2015 at 05:52

Yes, you may have missed that balanced equation because it wasn't there originally, RelativeEffectiveness. It's amazing what one can edit into a post after they claim to have defined variables and were asked to point it out.

I'd like to add another possible mechanism at play here as well, not to detract from Darkstar's post.

I don't have any chemical drawing software on this computer, but I might draw an alternative tomorrow. Luckily, it is very similar to Darkstar's first mechanism, and converges with the second oxidation.

What I would propose as also reasonable as a competing reaction mechanism is the protonation of THF at the oxygen (as opposed to the chlorination shown in Darkstar's first reaction), forming a different oxonium intermediate. Resonance structure of the oxygen withdrawing electrons from a proximate carbon, very similar to Darkstar's third step in the same mechanism, but instead of water, the attack is from hypochlorite. Ketone formation between the carbon and new oxygen, with loss of hydrogen and chlorine, respectively. Hydrogen joins free acetate anion deprotonated to activate the THF at the start of reaction, reforming the catalyst, and chlorine is evolved. Proceed with second oxidation in an identical fashion to Darkstar's proposal.

Edit-

Quote:

Are the THF and the Ca(OCl)2 both 1 and 1?

Oh, are you asking about how to balance the stoichiometry of the equation for theoretical yield calculation? Here is where you keep track of your atoms on both sides of the equation and use linear algebra so as not to violate conservation of matter. Empirical formulas make this simple to keep track of explicitly, but you can derive this from the mechanisms Darkstar drew since the bond line notation is understood to represent each atom, just with some more structural information. How much detail you show can vary, and it's important to figure out notation you prefer and what speaks to you. For example, if you take the dissociated hypochlorite as a reactant and ignore the calcium as a spectator ion, you will see 2 hypochlorite polyatomic ion for each molecule of THF. Adjust accordingly when necessary, as the valence and normality of reagents will not always follow.

You do need to keep track of your atoms. Once you hit aldol condensations, I see students mysteriously lose a carbon all the time. It's very easy to do, and it's also very wrong. Don't be that person! One of whole points of a mechanism is to be able to use pictures to represent the math for you, and also to give you a little more spatial information than an empirical formula, with more interactive information than a condensed formula.

It makes mathematical operation a bit more intuitive this way, but you still need to understand that what is on the left doesn't vanish from existence on the right. As with the equation 1+7, the commutative property shows you can also have 7+1 mean the same thing. THF+calcium hypochorite is indistinguishable from calcum chlorite+THF. In the real world, the rate of addition and order matter, but not here because it is using mathematical operation.

Subtraction is not commutative. 7-1=/=1-7. Similarly, Ca(OCl)₂- Ca²⁺ (dissociating) is not Ca²⁺-Ca(OCl)₂. Hopefully that doesn't warp anyone's brain reading this.

[Edited on 19-2-2015 by Chemosynthesis]

Darkstar - 18-2-2015 at 22:42

Quote: Originally posted by Chemosynthesis

I'd like to add another possible mechanism at play here as well, not to detract from Darkstar's post.

No problem at all. I'm completely open to alternative mechanisms. I welcome it, in fact. To be honest, I tend to believe there's more than one mechanism at play as well. I also suspect there's more than one active oxidizing species, too. While I'd like to think it's the hypochloronium ion, it could also be ClO-, HOCl, Cl₂, AcOCl or even something like a free chloronium ion. Since the reaction produces chloride ions that can be oxidized by H₂OCl+, Cl₂ may very well play some kind of role in the oxidation.

Which is why I've always found these hypochlorite oxidations rather interesting, as no one honestly knows how the hell they actually work.

Chemosynthesis - 19-2-2015 at 02:13

Excellent points. It is fascinating to me how we can know so much about a product, yet so much less about how exactly it was produced, even with all the fancy equipment and techniques out there.

Kind of rambling for the rest of this.
I remember when I was first shown an attempt at reaction monitoring with a Raman spectroscope instead of TLC, or a transition state analog diagram, and how these were kind of hyped by the person showing me... And someone else in the lab or office or wherever chimes in with methodological critiques and signal-to-noise sensor limitations. Mental whiplash.
For related reasons, I can't help but get excited at things like tabletop NMRs and gel electrophoresis kits for home use. Kids of the future will be able to analyze their vinegar volcanoes in ways that would elicit my jealousy if it's all they can do!

CuReUS - 19-2-2015 at 03:05

Quote: Originally posted by gdflp

Quote: Originally posted by turd

Quote:

No one will help you make drugs

Who gives you the authority to speak for everyone? Stop being a prick.

[Edited on 17-2-2015 by turd]

You're right, I phrased that wrong. Everyone who values their equipment and doesn't want to face the small chance of being charged as an accomplice will not help you make drugs. I apologize.

surely you are not serious.So suppose someone makes a drug from the instructions in an article or journal,than the author of that article can be summoned to court and be charged as an accomplice ?
also,the accomplice could just say that he/she had no idea what the other guy was up to,because the OP has not clearly stated what chemical he is after.

Quote: Originally posted by RelativeEffectiveness

In the synthesis, solution A is added dropwise to solution B allowing for an ether to transform into an ester to for use of the 1deg alcohol oxidation into a lactone.

Solution A: (CH2)4O + CH3CN + CH3CO2H
Solution B: Ca(ClO)2 + H2O

If you understand this equation then you'll almost certainly understand its ultimate purpose as it has limited use for anything else.

I think what turd is trying to convey is right.Organic chemistry cannot be completely explained using equations,unlike inorganic(its like trying to give a reaction mechanism for say,a displacement reaction)
suppose there is a reaction,HCl +NaOH>>>NaCl+H₂O ,I am sure of the products formed,so I can now balance it and find out yields
but an organic reaction does not go like that
as turd gives an example:

Quote: Originally posted by turd

E.g. you cook phenylacetone from phenylacetic acid in acetic anhydride. You use a huge excess of acetic anhydride, because you know that you will get biaryl product otherwise. Say 20 g PAA in 800 ml AA. You can calculate yield based on PAA without knowing how much AA reacts with PAA.

like he says,along with phenylacetone,you will get other compounds.So you are not certain of your products
then how can you make an equation,when you don't even know all the different products that could form ?
anyways,the best thing to do would be to calculate the yield based on turd's and chemo's idea and check with this
http://winter.group.shef.ac.uk/chemputer/reaction-yields.htm...

Chemosynthesis - 19-2-2015 at 04:39

Quote: Originally posted by CuReUS

surely you are not serious.So suppose someone makes a drug from the instructions in an article or journal,than the author of that article can be summoned to court and be charged as an accomplice ?

I don't mean to speak for gdflip, Or what it takes to be considered an accomplice, accessory, civil asset forfeiture, etc. for any particular locale, but the law can be completely irrational. http://www.theverge.com/2014/11/11/7193391/italy-judges-clea...
published scientists scientists have actually discussed this very topic in relation to pharmacologically active compounds, potency, animal modeling, syntheses, etc. I doubt anyone quit their jobs over it, but I also thought this was a parody news story from The Onion. The law can be completely irrational in both how it is written and how it is interpreted/applied.
http://theweek.com/speedreads/443383/irs-seizes-womans-entir...

Some people even quit hobby chemistry for these underlying reasons. Everyone has to decide for themselves what is an appropriate level of concern for their own unique situation. I wear a seatbelt, but I don't strap on a trauma plate when I drive even though they are attributed dramatically increased car crash survivability odds in some circumstances.

Quote:

Organic chemistry cannot be completely explained using equations,unlike inorganic(its like trying to give a reaction mechanism for say,a displacement reaction)

I would be very careful about saying that as an absolute. From a reductionist approach, building a quantum model of anything requires approximations. From a larger scale perspective, no inorganic solid lattice is considered free of defects.

In terms of explaining the theoretical yield, like the thread title, yes, a theoretical equation of perfect efficiency is formulated and balanced. What else would we possibly use to normalize yield to in order to cross-compare samples?

The reaction equation itself never explains unreacted starting material to any degree of confidence without an empirical determination, just as real chemical byproducts must also be measured. And even then, measurements have associated error. You can never be 100% certain your reagents are pure down to the last molecule. Even if you assume them pure, UPLC solvents are not free from degradation over time, either. You have radioactive decay, which can transmute atoms and break bonds with recoil energy.