RE: ORGLIST: question

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From: Ismail, Fyaz (F.M.Ismail$##$
Date: Thu Mar 17 2005 - 07:21:06 EST

The identification of compounds can be achieved by either spraying or =
dipping the plate using a number of reagents, a list of which is =
available in common textbooks of Organic Chemistry such as Vogel's =
Textbook of Organic Chemistry (various editions). A suitable choice =
depends on the nature of the compounds you are attempting to identify. =
The most general are phosphomolybdic acid (5% solution in ethanol) =
yields blue-green spots; Vanillin (3% solution in ethanol containing 1ml =
of sulfuric acid) also produces various colours. Similarly, =
anisaldehyde (2.5 % solution containing 1 ml of sulphuric acid) and =
ceric sulphate (15% aqueous sulfuric acid saturated with ceric sulfate) =
both produce various colours. A less satisfactory reagent is alkaline =
potassium permanganate that is suitable for detection of unsaturated =
compounds and alcohols (yellow spots) (see Advanced Practical Organic =
Chemistry by J. Leonard; B. Lygo and G. Procter, Blackie, Academic and =
Professional, Oxford, 2nd Edition, 1995). Using a glass backed plate =
allows one to heat the plate to a high temperature accelerating the =
development of the spots in question. Naturally you may scan using a =
densitometer to quantify your results.
If you are detecting specific types of compounds and are attempting to =
identify the functional Groups present, you can spray them with an =
appropriate reagent. A useful article is Functional Microanalysis by =
Chromato-Spectrometric Methods by Ya. L. Kostyukovski and D. B. Melamed: =
Russ. Chem. Rev, 54(2) 1985 pp 199- 213.
Dr. Fyaz M. D. Ismail,
Subject Leader,
Medicinal Chemistry,
Pharmacy and Chemistry
Liverpool John Moores University,
Liverpool L3 3AF
-----Original Message-----
From: everybody-bounces$##$ =
[mailto:everybody-bounces$##$]On Behalf Of madhav balakrishna =
Sent: 17 March 2005 08:49
To: everybody$##$
Subject: ORGLIST: question
TLC is the most common technique that we use for following reactions and =
identifying products. but there are instances when some of the =
reactants/reagents do not adsorb iodine or UV. do anyone know some other =
method than using conc. sulphuric acid spray (thus charing the compound) =
for identification of compounds in TLC?
Madhava B Mallia
Scientific Officer D


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