do we not have to worry about the acid cleavage of the cyclic ether bonds?
It is an issue, and it is worse with the heavier halogens, since these are better nucleophiles and will more effectively attack and cleave the ether (thiolates will cleave it even in basic condition, being extremely nucleophilic), but it seems that hydrohalogenation occurs faster than ether cleavage, meaning that ether cleavage doesn't hurt yields too much, and probably not too much for the method to be viable.
Both HBr & HI with cleavage the cyclic ether bonds when REFLUXED as in
http://www.orgsyn.org/orgsyn/pdfs/CV4P0321.pdf However, when KEPT AT 0-1 Oc for 18 hours (max 24 hours) cleavage is negligible.
Why go through the extra steps of generating HI (and dealing with disposing of H2S) when HBr is so easy?
Just to clarify, are you saying HI is easier or HBr is easier?
The current procedure as written is...
Step 1. -CH=CH2 + HBr => -CHBrCH3
Step 2. -CHBrCH3 + NaI (or KI) => -CHICH3 (Finkelstein reaction
http://en.wikipedia.org/wiki/Finkelstein_reaction)
Since -CH=CH2 to -CHICH3 is the objective. Making HI and reacting with safrole will eliminate step 1 and give higher yields.
CV4P0321.pdf shows making 2 moles of HI in solution.
Tetrahydrofuran (36 g., 0.5 mole) is added to a mixture of potassium iodide (332 g., 2 moles), 85% orthophosphoric acid (231 g., 135 ml., 2 moles), and phosphoric anhydride (65 g.) (Note 2), (Note 3) in a 1-l. three-necked flask equipped with a sealed mechanical stirrer.
NOTES.
2. The specified mixture of commercial 85% orthophosphoric acid and phosphoric anhydride corresponds to a 95% orthophosphoric acid solution. The phosphoric anhydride is placed in the dry flask, and the 85% orthophosphoric acid is added with stirring. After the mixture has cooled to room temperature, solid potassium iodide is added. The solution should be cooled, before addition of the potassium iodide, to prevent evolution of hydrogen iodide and formation of iodine. After the tetrahydrofuran is added, the mixture can be heated as desired since the hydrogen iodide reacts as rapidly as it is formed.
3. Orthophosphoric acid of 95% concentration is most efficient for effecting cleavage of tetrahydrofuran. Commercial orthophosphoric acid (85%) may be used; however, the yield drops to 82% and approximately 10% of the tetrahydrofuran is recovered. Anhydrous orthophosphoric acid and tetraphosphoric acid cannot be employed conveniently because of the limited solubility of hydrogen iodide in these reagents.
0.5 moles of Tetrahydrofuran is substituted for 0.5-0.6 moles of Safrole. These are reacted at 0-1 oC for 18 hours (max 24 hours). GAA is added to increase the solubility of the Safrole into the concentrated HI solution and help keep the HI in solution.
Since WE ARE NOT CLEAVING ETHERS, BUT MAKING A CONCENTRATED HI SOLUTION, 85% orthophosphoric acid, OR 85% phosphoric acid solution can be used.
Topic: Yeee Haaah!! Jon's method DOES TOO work!! Bromosafrole... (Read 2846 times)
