http://www.sci.tamucc.edu/pals/morvant/orglab/orglab2/iodinationvanillin.pdf (http://www.sci.tamucc.edu/pals/morvant/orglab/orglab2/iodinationvanillin.pdf)
Easy procedure scalable for the iodination of vanillin.
Transformation of 5-bromovanillin into syringaldehyde
5-bromovanillin (5 mmol) is refluxed with EtOAc (3 mmol) and CuBr (1 mmol) in 5 M MeONa/MeOH (10 ml) for 14 h; classical work-up leads to pure syringaldehyde (95%).
Reference: https://www.thevespiary.org/rhodium/Rhodium/chemistry/arylhalide.methanolysis.cu-etoac.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/arylhalide.methanolysis.cu-etoac.html)
Important details regarding this synthesis are discussed in this thread: Post 275171 (https://www.thevespiary.org/talk/index.php?topic=6626.msg27517100#msg27517100)
(uemura: "Re: Vanillin", Chemistry Discourse)
Inert atmosphere is not required: Post 474077 (https://www.thevespiary.org/talk/index.php?topic=8829.msg47407700#msg47407700)
(Rhodium: "Substituted Vanillins are Resistant to Oxidation", Methods Discourse)
Theroretical discussions:
Post 530151 (https://www.thevespiary.org/talk/index.php?topic=9947.msg53015100#msg53015100)
(Kinetic: "Cu catalysed nucleophilic aromatic substitutions", Methods Discourse)
Post 528896 (https://www.thevespiary.org/talk/index.php?topic=9947.msg52889600#msg52889600)
(Kinetic: "Bromination", Methods Discourse)
Pablos, if you are going to try this prep for syringaldehyde, try using activated copper instad of Cu(I)X as catalyst during the methoxide swap stage. Would also bee nice if you could report back.
From Post 198873 (https://www.thevespiary.org/talk/index.php?topic=7503.msg19887300#msg19887300)
(ZyGoat: "Re: Iodination of Vanillin", Chemistry Discourse) I quote:
Example 3 was also repeated using from 5 to 10 mole % of cuprous oxide, cuprous chloride, cuprous iodide and copper dust, as the catalyst for conversion of the iodovanillin to hydroxyvanillin. Recovery of 5-hydroxyvanillin was 80-85% (remainder vanillin) with copper dust, from 70-80% with the copper oxide or salts.
They compare different Cu (I) salts as catalysts for the swap, but notice that it is optimal to use copper dust making it a bit more OTC. Use of activated copper* might bee lead to better results. Should work equally well or most probably even better with OMe than OH as the former is more powerful nucleophile.
*Active copper preparation:
An active copper powder can be prepared from copper sulfate. One hundred grams (0.4 mole) of copper sulfate (CuSO4·5H2O) is dissolved in 350 cc. of hot water in a 1-l. beaker. After cooling to room temperature 35 g. (0.53 gram atom) of zinc dust (more if necessary) is gradually added until the solution is decolorized. The precipitated copper is washed by decantation with water. Dilute hydrochloric acid (5 per cent) is added to the precipitate to remove the excess of the zinc, and agitation is continued until the escape of hydrogen ceases. The copper powder is filtered, washed with water, and kept in a moist condition in a carefully stoppered bottle.