5-Br-Vanillin

[methymouse]

30 grams of vanillin (USP) were dissolved in 150ml GAA (homemade from vinegar).  This process is endothermic, and it took ~10 min for the vanillin to finish dissolving, even with heavy magnetic stirring.  The mixture turned slightly yellow.  48 grams NaBr (pool supply >99%) are dissolved in 75ml dH2O in another flask, and is then added to the GAA/vanillin flask.  11ml 95% H2SO4 is diluted with 20ml GAA in a beaker.  The temperature quickly rises, and the beaker is placed in a refrigerator for 20 minutes until it is somewhat below room temperature.  The GAA/H2SO4 and GAA/vanillin mixtures are then poured into a mason jar in a water bath with magnetic stirring, and allowed to sit for several minutes. 

22ml 30% cold H2O2 is then measured out, and added in 1ml portions every 3 minutes.  After each addition, a column of reddish-brown fluid formed in the vortex caused by the stirring, and it took a few seconds to dissolve.  Ice was added to the water bath during the addition so as to keep the temperature between 15 and 25C.  After approximately 30 minutes of the addition (~10ml H2O2), a yellow precipitate started to form.  After the addition was finished, the mixture was stirred for 90 minutes, and then diluted with 400ml cold water.  By this point, the mixture had become too thick to stir magnetically, and so was stirred manually at approximately 1 minute intervals for 20 minutes.  The mixture was filtered, and the yellow filtrate washed with 100ml cold dH2O.

The liquid was placed in the refrigerator for 24 hours, but nothing else precipitated.  The filtrate was dried over calcium chloride to constant
weight.  Yield:  27.27g (60%)

A melting-point test was not performed.

This reaction was a precise halving of Uemura’s wonderful writeup

Post 297806

(uemura: "How to prepare hydroxyvanillin", Methods Discourse), with the exception of the NaBr.  The experimenter spaced out whilst weighing the NaBr, by measuring precisely half of Uemura’s value for KBr.  The substitution should have been equimolar, not equimassive.  The H2O2 may have been added too quickly, since the color of the solution oscillated from brownish-red to yellow in between additions.  The high bromine concentration (both from adding H2O2 too quickly and using too much NaBr) probably accounts for the lower yield.

Even with these mistakes, the reaction went very smoothly, and exactly as Uemura wrote--the Br-vanillin didn’t even gum the filter paper.  If only everything was this easy.

Complete writeup on the rest of the mescaline synthesis to follow, probably next week.

- MethyMouse

[Vitus_Verdegast]

The mixture was filtered, and the yellow filtrate washed with 100ml cold dH2O

Did you wash the precipitate with H₂O, or do you mean diluting the filtrate with water?

BTW, recrystallize your product before attempting the next step.

[methymouse]

SWIM washed the precipitate with H2O.  Sorry; I had thought of filtrate as meaning roughly "the portion you want to keep" (in this case, the solids) in a filtration, but I see this belief was in error. 

Uemura didn't recrystalize the product in making hydroxy-vanillin (the next step), but I suppose it couldn't hurt, and would probably help.  I imagine that if if there is any residual bromine in the product (likely causing the yellow color), that it might lead to the formation of sodium hypobromite in the next step.  Oxidizers are certainly to be avoided.   

SWIM just placed the product in 200ml water, and heated the water to boiling.  None of the Br-vanillin dissolved, though the water turned brown, and this seemed to wash the Br-vanillin very well.  The crystals now appear much less yellow, almost white.  I suppose I'll have to do more reading about what would be a good recrystalization solvent

[methymouse]

The following worked well:

To the crude product is added 75ml acetone, and boiled until all the crystals dissolve.  The beaker is then removed from heat, 125ml dH2O is added,  and it is placed in an ice bath for a few minutes.  The liquid is then decanted off.  Repeat two more times, to yield cream colored cubic crystals, somewhat resembling sodium chloride.  SWIM will try to perform a melting point test after they are dry.

Added later:  Final weight:  22.28g

[Saddam_Hussein]

Recrystallization usually doesn't hurt the purity of your compounds, but if you just wash the precipitated 5-bromovanillin with an abundance of cold water, its purity (and further: safety) should be OK.

[methymouse]

"Recrystallization usually doesn't hurt the purity of your compounds"

Ye gods, I should hope not!  It's supposed to increase the purity.

"if you just wash the precipitated 5-bromovanillin with an abundance of cold water, its purity (and further: safety) should be OK"

The safety wasn't a serious concern.  Later products are going to be purified.  The method you suggest does not work nearly as well as a recrystalization.  SWIM washed it with boiling water, but after the first recrystalization, the waste solvent was dark brown, yet the crystals had become more yellow!  Presumably the water treatment was only cleaning the surface.

But it's not that big an issue anyway, Uemura didn't bother to recrystalize, and got acceptable yields.