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Testing For Alcohols!!

I was just wondering, what are the conditions required when you do the test for an alcohol using PCl5 and then testing that the gas evolved turns blue litmus paper red?? I have looked but can't find it anywhere in my notes or on t'internet!! Which seems unusual!!

Reply 1

sal33m

i think pcl5 will produce steamy white fumes which turns damp blue litmus red. Another test if its a methyl alchohol is the iodoform test, dont know if youve learnt that yet.

Reply 2

Raspy

cheers. but do you need to heat and reflux it or anything like that, or can you literally just add one to the other (in a fume cupboard of course!!).

Reply 3

henryt

Na + Alcohol --> Hydrogen + Alkoxide (Test for the Hydrogen given off)

Very good test!

Reply 4

Raspy

Cheers that's superb!! For our coursework we have to design a series of tests on an organic chemical. we know it is one of aldehyde, ketone, prim. alc., tert. alc., ester, alkene, phenol, carboxylic acid. would the attached flowchart fit the bill?? cheers.

flowchart.JPG68.6KB

Reply 5

Eau

I don't see why you won't use PCl5 for alcohol test. You just need to make sure the conditions are anhydrous.

Reply 6

RyanY

perhaps because it is dangerous to carry out, it releases toxic gases. Best test for an alcohol is the addition of sodium and it'll bubble and release h2.

Reply 7

charco

Study Forum Helper

both tests are used (although they are both bollox as a little water impurity will also give the same test)
PCl5 is a white powder that gives white fumes of HCl on addition of a little alcohol.. (not at all dangerous by the way - just don't breath in large amounts... or any at all for that matter!)
Na is a metal that releases H2 from alcohol... (once again without peril)
Water impurity is a colourless liquid that gives positive to both of the above...

Reply 8

Raspy

yes, and since we know what we will be testing is a pure organic liquid then any positive result indicates the presence of a hydroxyl group found in alcohols! so really either test could be used, but for a college lab purposes, although there's nowt wrong with the PCl5 test, the Na one is much easier!!

Reply 9

Eau

RyanY

perhaps because it is dangerous to carry out, it releases toxic gases. Best test for an alcohol is the addition of sodium and it'll bubble and release h2.

Well I've done it a dozen of times. Just wear a glove and do it in a fume cupboard.

Reply 10

Revd. Mike

Seeing as those are fooled by presence of water, couldn't you try oxidising them and observing for the presence of ketones/aldehydes/carboxylic acids?

Reply 11

Eau

Revd. Mike

Seeing as those are fooled by presence of water, couldn't you try oxidising them and observing for the presence of ketones/aldehydes/carboxylic acids?

That wouldn't work for teritiary alcohols.

Just use the god damn PCl5 test!

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