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Author Topic: How I can distinguish....  (Read 5149 times)

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Farid

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How I can distinguish....
« on: April 11, 2007, 04:20:54 AM »

How I can distinguish one substance from the other.

a) Phenol (benzenol) from Toluene (methylbenzene )
b) Phenol from  Benzoic acid
c) Glucose from pentan-3-one  [C2H5C(=O)H]
d) propanone from pentanal  [ C2H5-C(=O)C2H5   ]
e) but-1-ene from but-1-yne
f)  pentan-2-one from pentan-3-one
g) phenylyethene from phenylyethane.

I haven't got any ideas....

In a) it could be reaction with,for examle chlorine, because i think phenol react with chlorine without catalyst in contrast to toluene.

In b) it may be sth like that: "When we obtain the phenol solution in a high temperature, It will be dim (i mean-cloudy, dull etc. i think you will understand :) ) when we cool down that solution.

in d) i think the answer is: "Tollens' reagent"

in e) it migh be a quantity of chlorine, brom or KMnO4 used in reaction with alkene /alkyne

and in g the same as in e.

So, am i right? What about c and f ? .
« Last Edit: April 11, 2007, 07:30:22 AM by Farid »
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Dan

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Re: How I can distinguish....
« Reply #1 on: April 11, 2007, 07:09:02 AM »

c) Glucose from acetone [C2H5C(=O)H]

C2H5C(=O)H is propanal
CH3C(=O)CH3 is acetone

Quote
d) propanone from pentanal  [ C2H5-C(=O)C2H5   ]

C2H5-C(=O)C2H5 is pentan-3-one
C4H9C(=O)H is pentanal

Rememer, aldehydes are -C(=O)H
ketones are R-C(=O)-R (where R is a carbon chain)

For f) pentan-2-al and pentan-3-al do not make any sense. Do you mean pentan-2-one and pentan-3-one?

For chemical tests, here[/b][/u] is a decent website, here[/b][/u] is a .pdf you may also find useful. Google "chemical test" if there's not enough.

So, what do you reckon now?

Note: a and c are in fact very simple.
a) hint: just add water
c) hint: you could instantly tell just by looking at the samples (assuming they are pure, ie not in solution)
« Last Edit: April 11, 2007, 07:18:50 AM by Dan »
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Yggdrasil

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Re: How I can distinguish....
« Reply #2 on: April 11, 2007, 07:44:12 AM »

Here's a hint for f.  Pentan-2-one is a methyl ketone but pentan-3-one is not.  There is a very simple chemical test for methyl ketones.
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Farid

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Re: How I can distinguish....
« Reply #3 on: April 11, 2007, 08:24:09 AM »

Thanks,

a) Phenol is more soluble than Toluene / or reaction with iron (III) chloride
b) Add  iron (III) chloride ( phenol solution will  change color)
c) Glucose is more soluble / or add Tollen's reagent
d) add Tollen's reagent
e) quantity of chlorine, brom or KMnO4 used in reaction with alkene /alkyne
    I need more for but-1-yne solution
f) reaction iodine in base environment.
g) chlorine, brom or KMnO4 solution changes color under the influence of phenylyethene

Is it better?
 
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Dan

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Re: How I can distinguish....
« Reply #4 on: April 11, 2007, 10:21:03 AM »

c) Glucose is more soluble / or add Tollen's reagent

Yes, and even simpler, glucose is solid at room temperature, acetone is a liquid.

Quote
e) quantity of chlorine, brom or KMnO4 used in reaction with alkene /alkyne
    I need more for but-1-yne solution

That should work. The disadvantage being that you have to measure things out and be somewhat precise (a sort of slap-dash titration). Another way would be to treat them with silver nitrate in aqueous ammonia (see the 2nd link in my first post). That would be easier to confirm, but your suggestion is by no means wrong.

Quote
f) reaction iodine in base environment.

Yep, this is called the iodoform test.

g) permanganate can oxidise phenylethane (= ethylbenzene) to acetophenone. Br2 is probably the way to go on this one.

a,b,d are fine too.

It's worth mentioning that where you have suggested the use of halogens, Br2 is better for these tests (provided they are the limiting reagents) because it is intensely coloured (dark brown/orange) , and the discolouration on reaction is more obvious than with Cl2 which only has a comparatively pale colour to start with.
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Abhinav

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Re: How I can distinguish....
« Reply #5 on: April 11, 2007, 07:59:45 PM »

How I can distinguish one substance from the other.

a) Phenol (benzenol) from Toluene (methylbenzene )
b) Phenol from  Benzoic acid
c) Glucose from pentan-3-one  [C2H5C(=O)H]
d) propanone from pentanal  [ C2H5-C(=O)C2H5   ]
e) but-1-ene from but-1-yne
f)  pentan-2-one from pentan-3-one
g) phenylyethene from phenylyethane.

a) Use neutral FeCl3 solution, works with all enols.

b) Use Cacodyl Oxide test, sure shot for all carboxylic acids, or sodalime decarboxylation and test for CO2.

c) Tollen/Benedict/Fehling

d) Tollen/Benedict/Fehling (aldehyde)

e) Ammonical silver nitrate

f) Haloform reaction

g) I doubt KMnO4 or Br2 would work, Bromine water reacts with Benzene. Maybe a longer method would be using NBS to add a benzyl halogen in phenyl ethane (shouldn't add in phenyl ethene), and then testing for the halogen group?
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Farid

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Re: How I can distinguish....
« Reply #6 on: April 11, 2007, 10:39:09 PM »

How I can distinguish one substance from the other.

g) I doubt KMnO4 or Br2 would work, Bromine water reacts with Benzene. Maybe a longer method would be using NBS to add a benzyl halogen in phenyl ethane (shouldn't add in phenyl ethene), and then testing for the halogen group?

Do you think the reaction of phenylyethane and bromine look like that:


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Abhinav

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Re: How I can distinguish....
« Reply #7 on: April 13, 2007, 04:14:32 AM »

I would think so, the attack is electrophilic. Look on this page for "bromine"

http://mooni.fccj.org/~ethall/benzene/benzene.htm
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Dan

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Re: How I can distinguish....
« Reply #8 on: April 13, 2007, 06:46:52 AM »

You make a valid point, but I think the addition reaction of bromine with phenylethene will be alot faster than the substitution reaction with phenylethane (in the absence of a catalyst).

So I think the bromine test would work, decolourisation will be very fast with phenylethene.
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Abhinav

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Re: How I can distinguish....
« Reply #9 on: April 13, 2007, 09:23:37 PM »

You make a valid point, but I think the addition reaction of bromine with phenylethene will be alot faster than the substitution reaction with phenylethane (in the absence of a catalyst).

So I think the bromine test would work, decolourisation will be very fast with phenylethene.

Considering that, yes things should be fine. I'm starting out with Organic, so I really dont look that deeply into catalysts and rate yet, but I hope get better soon.
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