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Alt 26.07.2006, 21:40   #14   Druckbare Version zeigen
lindan Männlich
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AW: Wie rein ist Baumarkt-Aceton?


zur Reinheit / Reinigung von Aceton gibt es einen guten Eintrag in "Purification of Labority Chemicals" 5th Edition.

Ich zitiere :

Acetone [67-6&1] M 58.1, b 56.2O, d 0.791, n 1.35880, pK125 -6.1 (basic, monoprotonated), pK2 20.0 (acidic) The commercial preparation of acetone by catalytic dehydrogenation of isopropyl alcohol gives relatively pure material. Analytical reagent quality generally contains less than 1 % organic impurities but may have up to about 1% H20. Dry acetone is appreciably hygroscopic. The main organic impurity in acetone is mesityl oxide, formed by the aldol condensation. It can be dried with anhydrous CaS04, K2CO3 or type 4A Linde molecular sieves, and then distd. Silica gel and alumina, or mildly acidic or basic desiccants cause acetone to undergo the aldol condensation, so that its water content is increased by passage through these reagents. This also occurs to some extent when P2O5 or sodium amalgam is used. Anhydrous MgS04 is an inefficient drying agent, and CaC12 forms an addition compound. Drierite (anhydrous CaS04)offers the minimum acid and base catalysis of aldol formation and is the recommended drying agent for this solvent [Coetzee and Siao Znorg Chem 14v 2 1987; Riddick and Bunger Organic Solvents Wiley-Interscience, N.Y., 3rd edn, 19701. Acetone was shaken with Drierite (25gL) for several hours before it was decanted and distd from fresh Drierite (10gk) through an efficient column, maintaining atmospheric contact through a
Drierite drying tube. The equilibrium water content is about 10-2M. Anhydrous Mg(C104)2 should not be used as drying agent because of the risk of EXPLOSION with acetone vapour.
Organic impurities have been removed from acetone by adding 4g of AgN03 in 3OmL of water to 1L of acetone, followed by lOmL of M NaOH, shaking for lOmin, filtering, drying with anhydrous Cas04 and distilling [Werner Analyst (London) 58 335 19331. Alternatively, successive small portions of KMnO4 have been added to acetone at reflux, until the violet colour persists, followed by drying and distn. Refluxing with chromium trioxide (CrO3) has also been used. Methanol has been removed from acetone by azeotropic distn (at 350) with methyl bromide, and treatment with acetyl chloride. Small amounts of acetone can be purified as the NaI addition compound, by dissolving l00g of finely powdered NaI in 400g of boiling acetone, then cooling in ice and salt to -8O. Crystals of NaI.3Me2CO are filtered off and, on warming in a flask, acetone distils off readily. [This method is more convenient than the one using the bisulfite addition compound.] Also purified by gas chromatography on a 20% free fatty acid phthalate (on Chromosorb P) column at looo. For efficiency of desiccants in drying acetone see Burfield and Smithers [J Org Chem 43 3966 19781. The water content of acetone can be determined by a modified Karl Fischer titration [Koupparis and Malmstadt Anal Chem
54 1914 19821.]

Rapid procedure: Dry over anhydrous CaS04 and distil."

Gruß Lindan

Geändert von lindan (26.07.2006 um 21:46 Uhr)
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