HBr / H2O2 bromination of vanillin - 87%

[psyloxy]

Patent US4551557

... mentioned but unrevealed 6 years ago by Osmium :

Post 165556 (missing)

(Osmium: "A better Br2 generation method", Chemistry Discourse)

Example 1

Vanillin (15.2 g; 0.1 mole) was dissolved at ambient temperature in HBr at a concentration of 48% by weight (180 ml) in a 500 ml round glass flask equipped with a stirring system, thermometer, a dropping funnel and cooled with a cold water bath. The mixture was cooled to approximately 5°C. H₂O₂ at a concentration of 30% by weight (11.4 g; 0.1 mole) was then added dropwise. The solution, which turned red in color where the H₂O₂ dropped into the mixture, became colorless in a few seconds. The reaction mass became heterogeneous very quickly. When the addition was complete the mixture was maintained under stirring for 6 hours at 5°C, after which ice water (150 mL) was added to the reaction mixture. The precipitate was filtered off and washed on the filter with ice water.

After drying under vacuum at approximately 60°C, a dry precipitate was obtained which weighed 21.28 g and had a melting point of 160°C. The composition , determined by high pressure liquid chromatography, was 95% 5-bromovanillin and 3% vanillin.

The results obtained were as follows:
Gegree of conversion of vanillin: 96.2%
Yield of 5-bromovanillin/vanillin converted: 91.1%
Yield of 5-bromovanillin/vanillin employed: 87.6%

Example 2

The procedure of Example 1 was repeated, but 70 mL of hydrobromic acid were employed instead of 180 mL. The reaction medium was heterogeneous, the vanillin being incompletely dissolved. The results obtained were the same as in Example 1.

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