Ritter
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Aldol (3-hydroxybutyraldehyde)
Anyone have any experience with making or using this? The Merck Index states that it is a sedative/hypnotic. One step from acetaldehyde seems
simple enough.
Ritter
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Karl Marx
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garage chemist
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This substance would be more interesting, I think, as an intermediate for the production of crotonaldehyde, which forms from it by dehydration.
The dehydration happens easily, but the proper catalyst has to be used, as e.g. strong acids would cause immediate irreversible polymerization and
resinification.
Self-addition of acetaldehyde forming aldol is done using sodium sulfite (a weak base) as the catalyst.
The dehydration to crotonaldehyde is then done by distilling the isolated aldol with a small amount of iodine.
Here's a preparation of aldol and crotonaldehyde: http://www.lambdasyn.org/synfiles/crotonaldehyd.htm
If aldol is the desired product, just leave away the iodine distillation step and stop after evaporation of the Et2O.
The Organikum also contains a lab synthesis of aldol.
As to the sedative properties of aldol: Paraldehyde, the trimer of acetaldehyde, is a sedative as well, and is easier to prepare (look in Rhodium
under acetaldehyde).
Maybe aldol undergoes the retro-aldol reaction in the organism, forming acetaldehyde back which acts as the actual sedative, just as paraldehyde forms
acetaldehyde in vivo as well?
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Ritter
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| Quote: | Originally posted by garage chemist
This substance would be more interesting, I think, as an intermediate for the production of crotonaldehyde, which forms from it by dehydration.
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I am primarily interested in its biological properties rather than its use as an intermediate.
| Quote: | | The Organikum also contains a lab synthesis of aldol. |
Unfortunately I do not have access to this.
| Quote: | As to the sedative properties of aldol: Paraldehyde, the trimer of acetaldehyde, is a sedative as well, and is easier to prepare (look in Rhodium
under acetaldehyde).
Maybe aldol undergoes the retro-aldol reaction in the organism, forming acetaldehyde back which acts as the actual sedative, just as paraldehyde forms
acetaldehyde in vivo as well? |
Interesting theory. Acetaldehyde is the metabolite of ethanol.
Ritter
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Karl Marx
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Ritter
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| Quote: | J Phys Chem A. 2008 Apr 3;112(13):2827-37. Epub 2008 Mar 4.
A kinetic and mechanistic study of the amino acid catalyzed aldol condensation of acetaldehyde in aqueous and salt solutions.
Nozière B, Córdova A.
Department of Meteorology, Stockholm University, SE-106 91 Stockholm, Sweden. barbara.noziere@misu.su.se
The amino acid catalyzed aldol condensation is of great interest in organic synthesis and natural environments such as atmospheric particles. However,
kinetic and mechanistic information on these reactions is limited. In this work the kinetics of the aldol condensation of acetaldehyde in water and
aqueous salt solutions (NaCl, CaCl2, Na2SO4, MgSO4) catalyzed by five amino acids (glycine, alanine, serine, arginine, and proline) at room
temperature (295 +/- 2 K) has been studied. Monitoring the formation of three products, crotonaldehyde, 2,4-hexadienal, and 2,4,6-octatrienal, by
UV-vis absorption over 200-1100 nm revealed two distinct kinetic regimes: at low amino acid concentrations (in all cases, below 0.1 M), the overall
reaction was first-order with respect to acetaldehyde and kinetically limited by the formation of the enamine intermediate. At larger amino acid
concentrations (at least 0.3 M), the kinetics was second order and controlled by the C-C bond-forming step. The first-order rate constants increased
linearly with amino acid concentration consistent with the enamine formation. Inorganic salts further accelerated the enamine formation according to
their pKb plausibly by facilitating the iminium or enamine formation. The rate constant of the C-C bond-forming step varied with the square of amino
acid concentration suggesting the involvement of two amino acid molecules. Thus, the reaction proceeded via a Mannich pathway. However, the
contribution of an aldol pathway, first-order in amino acid, could not be excluded.
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Ritter
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Ritter
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From Organic Reactions vol. 16:
| Quote: | Aldol (Self-Condensation of Acetaldehyde).
Acetaldehyde (1 kg, 22.7 moles) contained in a 2-l. flask is cooled below 5 deg. Over a 20-minute period 25 ml. of 10% aq. NaOH is added dropwise with
vigorous stirring while the temperature of the reaction mixture is maintained at 4-5 deg After the mixture has been stirred for 1 hour at 4-5 deg., it
is made slightly acidic with tartaric acid The mixture is filtered to remove sodium tartrate (addition of diethyl ether facilitates the filtration).
The filtrate is distilled under reduced pressure from an oil bath by raising the temperature slowly. Acetaldehyde and aldol distil together as the
aldoxan dissociates. Redistillation of the aldol fraction yields about 500 g (50%) of aldol, bp 72 deg/12 mm. Aldol should be distilled immediately
before use since it dimerizes to paraldol on standing |
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Aldoxans are unstable trimers of aldol. Paraldol is a crystalline dimer.
This problem of dimerization on standing could limit interest in this compound unless there is a way to stabilize the monomer.
[Edited on 30-6-2008 by Ritter]
Ritter
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\"The production of too many useful things results in too many useless people.\"
Karl Marx
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Sauron
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It's kind of a very old fashioned sedative, and at least some of its relatives like paraldehyde, are controlled substances. From the Merck entry on
paraldehyde:
Caution: May be habit forming. This is a controlled substance (depressant) listed in the U.S. Code of Federal Regu lations, Title 21 Parts 329.1 and
1308.14 (1995).
Sic gorgeamus a los subjectatus nunc.
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