How to confirm Grignard Reagent before step up to next reaction. I am facing problem for the synthesis of dithiobezoic acid derivative through Gringard reagent with Carbon disulphide.
Any useful suggestion highly appreciated.
Nadeem, check out the following URL: https://www.reddit.com/r/chemistry/comments/31vhpo/how_do_you_verify_how_much_grignard_reagent_you/
Essentially, you can use a small sample of your solution and titrate it.
I agree, a titration would tell you the how much Grignard reagent you have formed and is therefore worth doing.
However, in your case, it is likely that your desired product can be easily separated from the starting materials (carbon disulphide has a boiling point of about 46C and is easily removed under vacuum, and the dithiobenzoic acid product is likely to have a very different solubility to your starting material - I presume you are using an aryl halide).
So, you could just assume you have made *some* Grignard and simply carry on with the reaction, adding at least one equivalent of carbondisulphide. After separating the product from the starting materials you should then be able to take any unreacted aryl halide and use it to form some more Grignard and repeat the reaction.
There is a caveat to this, if you are using wet reagents or solvents, you may very well end up de-halogenating some of your starting material, and this by-product may be difficult to remove when you go to recycle your unreacted starting material.
... its probably worth mentioning that you should filter off any un-reacted magnesium (dry filter cannula, or decanting) before adding the carbon disulphide.
To confirm Grignard Reagent before step up to next reaction add Iodine solution . The decolorization of iodine indicates the reagent has been formed.
You can use GC. First run a GC of your starting material (RX). Add a sample of your grignard solution onto ammonium chloride solution or dilute acid then run GC of the organic layer . If the grignard has formed completely your starting material will be gone and you will have a new peak corresponding to the dehalogented starting material, from the reactions RX + Mg ---> RMgX + H2O ---> RH .
R(=S)-S-H synthesis routes (also non-Grignard !) see in attached file
In addition to colleagues recommendation, quenching with Me3SiCl is useful method for detection of RLi or RMgBr presence (with NMR analysis).
doi:10.1021/ja01684a032 A QUALITATIVE COLOR TEST FOR THE GRIGNARD REAGENT
Richard Bryan what if both peaks are undiscovered? Does it mean that the formation of the Grignard reagent was unsuccessful? However, if the Grignard solution was not initially dissolved in the dilute acid (a direct measurement in GC), the new peak which is a different peak from the starting material was observed. Thank you
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