| Overview |
| Instructions |
| Operating scheme |
| Substances |
| Equipment |
| Evaluation |
| Analytics |
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; Side reactions |
Acid catalyzed acetalisation of 3-nitrobenzaldehyde with ethanediol to the correspondent 1,3-dioxolane |
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Synthesis instructions as PDF file for printing |
ReactionFor the set up of the reaction apparatus in the microwave see the article Microwave: Reflux Setup. The used apparatus, compared to the standard refluxing apparatus, is slightly modified: A three-neck round-bottom flask is used instead of a two-neck round-bottom flask, and the reflux condenser is exchanged with a distillation bridge with a collection round-bottom flask. A temperature sensor is placed into one of the side openings in the three-neck round-bottom flask. In the second side opening a PTFE tube is connected via a ground glass joint adapter. This tube passes through an opening in the microwave system and is connected to a bubble counter and a stop-cock that is connected to the air pressure or nitrogen line. The flow rate of the cooling water in the distillation bridge can be reduced to a minimum during the course of the experiment. The stop-cock is closed to begin with.
15.1 g (100 mmol) 3-Nitrobenzaldehyde, 9.32 g (8.4 mL, 150 mmol) ethanediol and 1.0 g (5.3 mmol) p-toluenesulfonic acid monohydrate 
are placed in a 100 mL three-neck round-bottom flask fitted with a stir bar or
a cross stirrer. The reaction mixture is irradiated for 50 minutes with 900 W
at a set temperature of 130 °C.
The stop-cock remains closed during the first 25 minutes. Thereby a weak reflux
is established in the glass connecting tube. The volatile components of the
reaction mixture are mainly water and ethanediol. As the absorption of the
microwaves in the gas phase is much less than in the liquid phase, neither
water nor ethanediol is distilled over.
After 25 minutes reaction time under reflux whilst the microwave program
continues to run, an air or nitrogen flow is introduced with such a flow rate
that no single gas bubbles are visible in the bubble counter (if a flow rate
meter is present, 5 L/h). A mixture (3-8 mL) of water, ethanediol and small
amounts of product are collected in the collection round-bottom flask.
Work upOnce the program is completed, the reaction flask is placed in a water bath and the oily contents, which tends to crystallization, is allowed to stir for 5 minutes. One then adds 80 mL water and allows to stir intensively for a further 15 minutes.
The water is separated from the ivory coloured solid product with a folded
filter paper. The crystallized product traces in the condenser and in the
collection round-bottom flask are also rinsed out with water and filtered.
Crude product yield: 18.6 g; melting point 50-52 °C; Purity according to GC: 98% In order to remove the not converted aldehyde with sodium hydrogensulfite, the crude product (which can still be wet) is dissolved in 200 mL tert-butyl methyl ether and extracted with 20 mL saturated aqueous sodium hydrogensulfite solution. The organic phase is dried over sodium sulfate. Once the drying agent has been filtered off, the solvent is completely evaporated on the rotary evaporator with a bath temperature of 40 °C. The bath temperature should not be higher due to the low melting point of the product. A pale yellow, fine crystalline solid remains. Yield: 17.7 g; melting point 52-54 °C; Purity according to GC: 99.8% The product can be recrystallized from a solvent mixture of tert-butyl methyl ether/ petroleum ether: The product is placed into a 250 mL two-neck round-bottom flask contanining a magnetic stir bar. A solvent mixture of 40 mL tert-butyl methyl ether and 50 mL petroleum ether (40-60 °C) is added. The flask is set up in the microwave, as described for the standard reflux apparatus, and allowed to stir under reflux for 2 minutes at 500 W and 55 °C. The clear solution is cooled in a water bath during the 5 minute ventilation period in the microwave .
The semi-solid crystalline slurry is then allowed to stand for at least a
further 15 minutes at room temperature and then a further 1 hour in the
refrigerator. The crystals are filtered off using a suction filter. The
crystallization flask is washed 2 times with 10 mL petroleum ether, thereby
washing the residue onto the filter. The recrystallized product is dried in the
desiccator at reduced pressure.
Yield: 16.4 g; melting point 53-55 °C; After evaporating the solvent of the mother liquor from the recrystallization, a residue of 1.2 g, consisting of 95% product, is obtained. Duration of the experimentIsolation of the crude product 2 hoursWork up to the pure product 1 hour Recrystallization with drying about 2 hours Where can I stop the experiment?After stirring the reaction mixture with waterRecyclingThe tert-butyl methyl ether evaporated during the work up of the crude product can be used for the recrystallization. The leftover ether is collected and redistilled. |
Suggestions for waste disposal |
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