Author Topic: Synthesis of 4-methyl-3-hydroxy-benzaldehyde  (Read 1889 times)

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Bandil

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Synthesis of 4-methyl-3-hydroxy-benzaldehyde
« on: April 30, 2004, 10:07:00 AM »
The following presents a practical test of

this

(https://www.thevespiary.org/rhodium/Rhodium/chemistry/mma.html) preparation of 4-methyl-3-methoxy-benzaldehyde, from the corresponding nitro compound.

45 g's of SnCl2.2H2O was dissolved in 60 mL 30% aq. HCl and stirred violently in a 500 mL erlenmeyer flask. To this mixture, 11 g's 4-methyl-3-nitrobenzaldehyde was added in one portion. The reaction temperature climbed very very slowly. It was suspected that the low reaction volume would cause too much heat loss to allow the the internal reaction temperature to go up. A little heat was applied, till the internal temperature hit 40oC. The flask was removed from the heat source while still stirring. Within 1-2 minutes, the temperature reached 100 degrees, and the lask was sumberged in water to cool the reaction to slightly below 100 oC. After five minutes, the reaction subsided, and the entire mix cooled down. This was placed in an ice/salt/water bath, and stirred for 1½ hour. The Mixture had taken on a very reddish tint. Unfortunately no precipitate was observed. The flask was loosely stoppered with toilet paper and placed in the freezer for 48 hrs.

After this period the flask was full of a very reddish precipitate, which was suction filtered. The filtercake was suspended in 60 mL 30% HCl. This was cooled to 5 degrees on an ice bath. While maintaining this temperature, 4,6 g's NaNO2 in 5 mL's water, was added over 5 minutes. The mixture was stirred for 1 hour at 5 oC. The precipitates where suction filtered off.

The filtercake was added in small portions to a 170 mL's boiling water. This caused very heavy gas evolution, so it had to be added really slowly. After 20 mins the addition was complete, and no more gas evolved. The solution was cooled and extracted with 3*20 mL's DCM The DCM was stripped at atmospherical pressure, and the resulting oil was placed in the freezer over night. The next day, it had crystallized into browning "flowery-looking" crystals. These where recrystallized from a minimum amount of benzene two times, to give 5.4 g's pretty crystals with a brown tint(GC-MS showed 98% purity). This corresponds to a 60% yield, exactly as described

here

(https://www.thevespiary.org/rhodium/Rhodium/chemistry/mma.html).

The hydroxy group was methylated with trimethylphosphate, but a fuckup (molten phase methylation was used) caused the yield to go piss poor (20%). A methylation reaction will be attempted again ASAP.

But the nitro to hydroxy reaction worked like a charm!

Regards
Bandil