bereal511
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Determining percentage of alcohol mixtures.
Hello,
I've been racking my brain over this problem for a few weeks. I was wondering if there was a way to determine the mass percent composition of an
unknown mixture between different low-mass alcohols (methanol, ethanol, butanol, etc. to possibly decanol) without expensive equipment such as a
analytical spectrometer or the sort. Any suggestions would be greatly appreciated.
As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life -- so I became a
scientist. This is like becoming an archbishop so you can meet girls.
-- Matt Cartmill
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neutrino
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Mix the alcohols with another inert chemical with a boiling point much higher (at least 80*C higher) than that of the highest boiling alcohol present.
Then fractionally distill and measure the fractions (weigh or determine volume), discarding the last fraction (the chemical you added). Record the
boiling point of each fraction while distilling to figure out what it is.
Of course, this won’t help much with isomers or contaminants. This procedure assumes that all the alcohols can be easily identified from their
boiling points alone.
Note that the added chemical is for raising the temperature of the fractionating column to expel the last portion of alcohol.
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leu
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The phenomenon of azeotropism is going to complicate any procedure using distillation 
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neutrino
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Oh yes, I'd forgotten about that. Thinking doesn't work so well at 3 AM. Not
bad for something I pulled off the top of my head, though.
Maybe chromatography could work. I don't have as much knowledge about that topic; do some research on it. Find a copy of Vogel's organic chemistry
book. There are ~7 editions with slightly different names.
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bereal511
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Ah thank you, this will help a lot. My sister has a copy of Vogel's.
As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life -- so I became a
scientist. This is like becoming an archbishop so you can meet girls.
-- Matt Cartmill
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leu
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In the past derivatives of 3,5 dinitrobenzoyl chloride were used to identify alcohols. Scientific papers were published explaining how to do this
using paper chromatography. A flat bed scanner, Igor Pro and thin layer chromatography can be used together to create a procedure that will enable
quantitative analysis to be performed. This technique was based on the use of a charge couple detector to quantify the results of thin layer
chromatography 
The synthesis of 3, 5 dinitrobenzoic acid, from Organic Syntheses Collective Vol III 337-8
[Edited on 21-6-2006 by leu]
[Edited on 21-6-2006 by leu]
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leu
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The article in which charge coupled chromatography was used:
Attachment: liang.zip (137kB)
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leu
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The following examples illustrate the preparation of several 3,5-dinitrobenzoates andp-nitrobenzoates. If the derivatizing
reagent is not available, it is prepared according to the directions given in Example 13.05.
Example 13.01: Derivatization of Ethanol: Ethyl 3,5-Dinitrobenzoate
Place in a 6-in. tube 400 mg of pure 3,5-dinitrobenzoyl chloride and 0.12 ml of 95 per cent ethanol. Heat for about 5 minutes by means of a microflame
so that the melt at the bottom of the tube does not solidify. Avoid a hot flame. If there is much evidence of condensation on the sides of the tube 20
to 30 mm above the reaction mixture, the flame should be reduced or the tube raised.
Allow the melt to solidify. By means of a glass rod or a microspatula break and thoroughly pulverize the crystalline mass, so that no lumps remain.
Add to the tube 5 ml of 2 per cent sodium carbonate and continue the grinding of crystals against the walls of the tube. Heat the mixture gradually to
50 to 60°, place a solid rubber stopper on the mouth of the tube, and shake for about 15 seconds. Filter the mixture (page 65) and wash 3 times with
3 to 4 ml of water.
Place the crystals in the tube in which the derivative was prepared, add 15 ml of ethanol or methanol, and heat until solution is effected. Filter and
add water to the filtrate until cloudiness appears; reheat until. the cloudiness disappears. If the cloudiness persists near the boiling point of the
solution, add alcohol dropwise. Cool.for 10 to 15 minutes and filter. Wash twice with 3-ml portions of equal parts of alcohol and water, and dry on a
clay plate. About 250 to 300 mg of pure ethyl 3,5-dinitrobenzoate, melting at 93°, are obtained.
NOTE. Good results are obtained with 100 mg of 3,5-dinitrobenzoyl chloride and
0.05 ml of the alcohol. For example, 40 mg of pure n-propyl 3,5-dinitrobenzoate melting at 73.5 to 74° were obtained after one crystallization from
0.05 ml of 1-propanol.
In the case of alcohols having 6 or more carbon atoms, the heating of the reaction mixture should be prolonged to 10 minutes and, if the results are
poor, the procedure
described for the preparation of fl-naphthyl 3,5-dinitrobenzoate (page 486) should be used. When the quantity of the alcohol available is 1 drop or
less, the procedure
described for isobutyl 3,5-dinitrobenzoate or cyclohexyl 3,5-dinitrobenzoate is used. If the melting point of the dinitrobenzoate after
crystallization is more than 2 to 4°
below that recorded in the literature, proceed as follows : Dissolve the dinitrobenzoate (it need not be dry) in 5 ml of ethyl or isopropyl ether and
wash the ethereal solution
first with 3 ml of 2 per cent sodium hydroxide solution and then with 3 ml of water. Evaporate the ether and crystallize the residue once from an
alcohol-water mixture.
If this method is applied to a crude sample of ethyl 3,5-dinitrobenzoate melting at 84 to 86°, a product is obtained melting at 92 to 93° without
further crystallization.
The 3,5-dinitrobenzoyl chloride should be pure if it is to be used in semimicro work.
Derivatives of Alcohols and Phenols 471
The method of preparation and purification is given on page 472. Commercially available chloride should be recrystallized from carbon tetrachloride
unless the purity is specified. The stopper of the bottle in which the chloride is kept should be sealed with paraffin wax and exposure to air should
be kept at a minimum.
If experience in derivatizing milligram quantities of an alcohol is desired, cyclohexanol is useful. A microcone is constructed and charged (according
to the directions given in Examples 13.09 and 13.12) with 15 mg of finely pulverized 3,5-dinitrobenzoyl chloride and 0.01 ml of cyclohexanol. The
contents of the tube are heated as directed (Example 13.09), extracted with sodium carbonate solution and washed (Example 13.12), and then repeatedly
extracted with 0.5-ml portions of hot methanol, removing the hot solution in a 3-in. tube. Water is added dropwise until cloudiness appears and the
solution is cautiously heated until clear, then cooled. The crystals are separated and washed by centrifugation (page 71). About 10 mg of crystals,
melting at 112°, are obtained.
Example 13.02: Derivatization of Isobutyl Alcohol: Isobutyl3,5-Dinitrobenzoate
Place in a 6-in. tube 1 drop of isobutyl alcohol, 40 mg of 3,5-dinitrobenzoyl chloride, 5 ml of isopropyl ether (free from alcohol), and 1 drop of
pyridine. Place a microcondenser in the tube so as to permit refluxing and heat in a beaker containing water for 1 hour; adjust the flame of the
microburner so that the isopropyl ether boils gently (56°). Remove the tube from the water bath and cool in running water. Add 0.5 to 1 ml of dilute
sulfuric acid and 4 ml of water. Stopper the tube with a solid rubber stopper and shake to remove the pyridine. Transfer the ether layer into another
tube and wash it once with 1 ml of 10 per cent sodium hydroxide solution and twice with 4 ml of water to remove the dinitrobenzoic acid. Transfer the
ether layer to a small casserole or evaporating dish; wash the vessel from which the ether solution was transferred with 1 ml of fresh isopropyl
ether; and add the washings to the dish. Evaporate the ether carefully over a water bath; add to the residue 0.5 ml of alcohol and then 2 ml of water;
and transfer the liquid into a small test tube. Cool for about 5 minutes and then scrape the sides of the tube with a glass rod. Filter the crystals
and then wash them with 0.5 ml of water. The yield is 5 to 10 mg of crystals, melting at 85 to 86°.
NOTE. This procedure may be used whenever the quantity of hydroxy compound is small or the hydroxy compound is not very reactive. For example,
tertiary alcohols give good yields of dinitrobenzoates from 50 to 100 mg of the hydroxy compound.
Example 13.03: Preparation of a p-Nitrobenzoate: Methyl p-Nitrobenzoate
Place 0.2 ml of methanol and 100 mg of pure p-nitrobenzoyl chloride in a 6-in. tube and proceed as described in Example 13.01. Recrystallize the
crude product by dissolving in hot methanol and adding water to the hot filtered solution. The yield is 90 mg melting at 95 to 96°.
Example 13.04: Derivatization of Alcohols in Aqueous Solution
Use 5 to 10 ml of the aqueous solution containing 250 to 500 mg of the alcohol. Dissolve separately 1 g of 3,5-dinitrobenzoyl chloride or
p-nitrobenzoyl chloride in 2 ml of specially purified hexane or ligroin (washed with sulfuric acid, then with water, dried and distilled), and 8 ml of
dry benzene. Place the alcoholic solution in an 8-in. tube, cool to 0°, and add 5 ml of the acid chloride solution and 500 mg of sodium acetate.
Close the tube with a stopper, and shake for 2 minutes with cooling (ice bath) so that the temperature remains below 5°. Place the tube in the ice
bath for 30 minutes and shake it occasionally. Add 25 ml of ether, shake well, and separate the ether layer. Wash first with water, then with 5 ml of
5 per cent sodium hydroxide, then with 5 ml of 5 per cent hydrochloric acid solution and, finally, with water again. Evaporate the ether solution and
crystallize as in the Note on page 470.
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leu
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In toxicology laboratories, thin-layer chromatography (TLC) provides a quick and accurate method for qualitative identification of unknown biotoxins
that may be present in a fluid or tissue sample. These varied samples are presented to the toxicologist for analysis on a routine basis and also
during emergency situations or after a death. The ability of TLC to identify or rule out hundreds of compounds in a single analytical run makes it
amenable to emergency toxicology and forensic chemistry. However, the ability to decipher the various reactions and elicit meaningful results from the
raw data can take years of experience. It would be useful therefore, for analysts to obtain a firm background in TLC while still in academic training.
This analytical laboratory experiment demonstrates the methodology of TLC in its relation to toxicology and forensic chemistry. It is easily adapted
for high school seniors or undergraduates and employs experimental techniques associated with TLC and post-lab data analysis with concomitant
introduction of concepts. The procedures are designed to introduce the student to the concepts, mechanisms, methodology, and reactions of TLC while
building skills in record keeping, data analysis, and deductive reasoning.
____ ___ __ _
Rapid, Simple Quantitation in Thin-Layer Chromatography Using a Flatbed Scanner
Johnson, Mitchell E.
J. Chem. Educ. 77, 368-372 (2000)
Attachment: siek.zip (178kB)
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leu
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The appropriate tables from CRC Handbook of tables for Organic Compound Identification
Attachment: crchanorcomidtabvi.zip (162kB)
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leu
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The needed supplementary materail for using Igor Pro:
Attachment: supp368.zip (29kB)
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leu
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JACS 54 3758-659 (1932) which covers the use of paper chromatography in the identification of alcohols, the zone on paper
can be extracted for positive identification:
Attachment: bryant.zip (92kB)
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leu
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JACS 42 599-611 (1920) which describes an alternate synthesis of 3,5 dinitrobenzoyl chloride:
Attachment: adams.zip (160kB)
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