Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Plumbum on July 01, 2015, 05:06:52 AM
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hi
I have to analyzes an unknown mixture consisting of two liquids in my oc labrotory.
I have the following clues :
Ph: 5
No color
Absolute no smell
And the IR.
I don't really know what I can do now cut my if doesn't show so much. Do I have an alcohol ? Thank u
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I have the following clues :
Ph: 5
No color
Absolute no smell
And the IR.
I don't really know what I can do now cut my if doesn't show so much. Do I have an alcohol ? Thank u
There is not enough information here to identify two unknowns. But I suppose you could suggest a composition that is consistent with the data.
What does the pH suggest?
Side point: Did you measure the pH yourself or was it given to you? If you measured it yourself, how did you do it - neat or in aqueous solution?
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By a first view, this IR spectrum indicates an alcohol or an amine that contain both methyl and methylene/methyne groups. Amine must be excluded due to the low pH. The strong hydoxyl peak indicates a small molecule but small alcohols have a characteristic odor.Thus, the absence of odor indicates a small polyol (diol or triol). Besides, the content ratio of methyl and methylene groups as it figures, might be due a mixture with another liquid. In other words, information is not enough for the safe determination of the structure.
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i have some further information maybe u can tell me how i should continue cuz i am absolutely clueless at this point.
My solution dissolves in water, 5% Hcl,5% NaOH and 5% Sodium bicarbonate solution.
It doesnt dissolve in Diethyl ether, whereas my solution in the bottom and Diethyl ether above.
I tried to distill it, my solution became kinda yellow...it didnt work though.My temperature didnt raise higher than 60 °C for some reason. So the boiling point from both solutions mustbe above 60 °C.
help :(
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Which small alcohol or polyol is insoluble or slightly soluble in diethyl ether and do not smell? There must not be too many.
Are you sure that your sample does not decompose during distillation?
Which small alcohol or polyol decomposes during (quick) distillation? There must not be too many.
Which might be the potential decomposition product that boils near 60oC?
Did you run an IR spectrum of the distillate? (Do not smell it because it might be toxic).
Did you compare the given IR spectrum with other IR ones of small alcohols or polyols, which can be found in the web?
PS: Given that information is still not enough, all above might not be to the right direction but they must be explored.
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The pH 5 is difficult to account for.
This is why I asked:
Side point: Did you measure the pH yourself or was it given to you? If you measured it yourself, how did you do it - neat or in aqueous solution?
because the result will be misleading if it was not measured in aqueous solution.
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I measured it myself in aqueous solution.
Do you agree with me that I can pretty much exclude the other functional groups excecpt for alcohol and amine due to the IR? If so, I could simply test for amine
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You do not have carbonyls, nor unsymmetrical triple bonds or allenes, neither aromatics. Apart these, you cannot exclude other functional groups because the IR spectrum is not an absolute criterion of the structure, except if it coincides with the one of a known compound (even so, it is not 100% safe). But before excluding anything, try to answer the above questions.
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Does it react with FeCl3 solution?
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Does it react with FeCl3 solution?
Didnt try that. What does it mean if it does?
@pgk I'll get to your questions later, i gotta do some research.
thanks fo helping me, though!
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Does it react with FeCl3 solution?
Didnt try that. What does it mean if it does?
Try google
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DO you think i might have a phenole?
Right now I suppose I may have an alcohol and an ether.
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Let me tell you what I did today.:
I gave FeCl3 to my solution -> negative , no phenole.
No Ether, cuz it doesnt dissolve in Diethylether.
Rojahn was negative
Test for aromate was negative as well..
my test for alcohol was positiv though but that was obvious.
So I came to the coclusion that both of my solutions must be alcohol with a very high boiling point!
I also made a vacuum destillation. It boiled finally at 150 °C, and the IR looks like that:
Im pretty desperate at this point and have no idea what to do next.
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You can infer symmetry from the CH/CH2/CH3 peaks in the spectrum. If possible the first step which is missing is to take a mass spec and narrow down the formula, so we have something easier to work with.
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It was mentioned above that you do not have aromatics (that appear near 1600 cm-1).
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I am not allowed to do mass spectrum or NMR unfortanely.
I suppose one of the substances is glycerol.
-The IR is similar
-its a colorless liqour and viscous
-it odorless
-it dissolves in water
-boiling point is very high ( does anyone know when glycerol boils at 50 bar?)
what do you think?
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What you can conclude abbout the OH peak, it is likely that it is intermolecularly bonded because the peak is more <-- than usual. There are 2 C-O stretches. Saturated primary should be higher than secondary and more intesne 1054 ∆t
= 0.00012 (760 - p) (t + 273) t in kelvin, p in bar.
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So...you think I might have a double bond?
( Sorry- my english is not so good)
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Double bond appears at ≈1550-1600cm-1. So, you do not have a double bond in the first IR spectrum.
According both IR spectra, your product is probably glycerol that decomposes during fast distillation to acrolein which remains as an impurity. Thermal decomposition occurs through a dehydration mechanism, followed by enol-aldheyde tautomerism.
Acrolein (bp = 53oC): carbonyl at 1704 cm-1 and double bond at 1473 cm-1 in the new IR spectrum.
Note: Under normal conditions, glycerol decomposes to acrolein at 280oC. However, decomposition may starts near 50oC in small scale, fast distillation. In practice, distillation of glycerol without any decomposition is very difficult, in the lab. Besides, vacuum boosts the dehydrative decomposition, during distillation.
.
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so im starting to think thst my second Substance is methanole due to the perfect fitting IR. what do you think
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Methanol boils at 65 °C and it smells.
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Try to compare the first IR spectrum with the one of glycerol. Are there any differences, in regards of peaks or peak intensities?
Hint: Comparing IR spectra in absorbance scale instead of transmittance one, is more spectacular.
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So thats my current plan :
the following functional groups could be in my mixture:
-Ketone
-aldehyde
-acetale
-carboxylic acid
-ester
-Carboxamide
-Organic acid anhydride
-Acyl chloride
-nitrile
-Hydrocarbons
-alkylchloride/bromide/iodide/halide
-Polyhalides
-alcohole
-phenole
-ether
-primary und secunday amine
-tert amine
-Nitro compound
-sulfurous compounds
I can exlude al of them expect : Acetale, Nitrie, hydrocarbons, alkylchloride/bromide/iodide/halide, polyhalide compounds,alcohol or ether ( right??)
So I need to test for those functional groups.
Im pretty sure my first compound is glycerol but whats the second? I thought maybe another alcohol.
The following alochols can be in my mixture.
- 2-methyl 1 propanol
-methanol
-ethanol
-2-propanol
-2-methyl-2-propanol
-allyl alkohol
-1-propanol
-2-butanol
-2 methyl 2 butanol
-2 methyl 1 propanol
-3 methyl 2 butanol
-3 pentanol
-1 butanol
-2 pentanol
-trans 2 buten 1 ol (crotylalkohol)
-ethylen glycol monomethyl ether
-2-chlorethanol
-4-methyl 2 pentanol
-2 dimethylaminoethanol
-3 methyl 1 butanol
-3 methyl 2 pentanol
-2 ethoyalkohol
-1 pentanol
-cylopentanol
-2 ethyl 1 butanol
-2.2.2 trichlorethanol
-milchsäurethylester
-hexyl alcohol
-cyclohexanol
-4 hydroxy 4 methyl 2 pentanon
-furfuryl alkohol
-2-aminoethanol
-1 heptanol
-tetrahydrofurfuryl alcohl
-2-octanol
-2.3 butanediol
-1.2propanediol
-3.6 dioxa 1 heptanol
-1 octanol
-1.2 ethanediol
-3.3.5 trimethylcylohexanol
-1-phenylethanol
-benzyl alcohol
-1.3 propanediol
-1-nonaol
-phenethyl alcohol
-citronellol
-geraniol
-1-decaniol
-1.4 butanrdiol
-1.5 pentanediol
-2.2'-oxydiethanol
-1,3-glycerindiacetat
-4 methoxybenzylalkohol
-2.2' iminodiethanol
-glycerol
-3 hydroxypropionitrile
-lactic acid
pls help
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Please, read my replies more carefully.
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Sorry!
I only have an IR In transmittace, the IR Looks quite similar to the one from Glycerol, what do you think about my further approach ?
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There are not still enough data from IR, only. However, if there is no much difference in the IR spectra, think about another alcohol or a diol that does not smell. If an alcohol, it does not boils due to formation acrolein acetal during fast distillation and therfore, boiling point is not a safe criterion.
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Can I exclude Acetals, nitriles , hydrocarbons, alkylchloride/bromide/iodide/halide, polyhalide compounds, or ether ,though?
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No, because their peaks might be covered, if being in small amounts. As mentioned earlier, the IR only is not an absolute criterion for structural identification of mixtures.
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okay so I need to test for them. But I was told I can exclude the carbonyls they are very strong.
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Yes
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So at this point I'm pretty clueless how I should continue.
I am pretty sure with glycerol but I dint know how to find out the seconds substance. I can exclude a lot but that doesn't help me that much.
Tomorrow I am going to test for halides And work with the Lucas reagent. I don't know how I could test for nitriles. ( though I still think my second substance is an an alcohol as well)
What would you guys recommend me ?
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What would you guys recommend me ?
A suggestion, go back to you ridiculously space wasting post on the previous page, and actually trim that list: cross off the ones you know don't apply, and then begin to work on it. Looking at that list, you're not going to crack this problem, it just looks all the more daunting.
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Arkon is absolutely right.