Process for brominating unsaturated organic compounds with removal of quaternary ammonium or quaternary phosphonium monochlorides
Unsaturated organic compounds are brominated with a quaternary ammonium tribromide or a quaternary phosphonium tribromide, especially when the bromination is conducted in a chlorinated solvent. A quaternary ammonium or quaternary phosphonium monobromide salt is produced in the reaction, together with some amount of quaternary ammonium or quaternary phosphonium monochloride salt. The monochloride salt is converted to the corresponding quaternary ammonium monobromide salt by reacting it with a source of bromide ions. The monobromide salt is then reacted with bromine to regenerate the quaternary ammonium or phosphonium tribromide, which is recycled into the bromination reaction. This process reduces the amount of chlorine that is incorporated into the brominated product.
1. A process comprising
a) contacting an unsaturated compound containing aliphatic carbon-carbon double bonds with a quaternary ammonium tribromide or a quaternary phosphonium tribromide in the presence of at least one solvent for the unsaturated compound under conditions such that the unsaturated compound becomes brominated and, as a by-product, (1) a mixture of a quaternary ammonium monobromide salt and a quaternary ammonium monochloride salt or (2) a mixture of a quaternary phosphonium monobromide salt and a quaternary phosphonium monochloride salt is formed,
b) separating the quaternary ammonium monochloride salt or quaternary phosphonium monochloride salt from the brominated unsaturated compound, then
c) contacting a solution of said separated quaternary ammonium or quaternary phosphonium monochloride salt with a source of bromide ions under conditions that at least a portion of the quaternary ammonium or quaternary phosphonium monochloride salt reacts with said source of bromide ions to regenerate a quaternary ammonium monobromide salt or quaternary phosphonium monobromide salt and a chloride by-product;
d) contacting the regenerated quaternary ammonium monobromide salt or regenerated quaternary phosphonium monobromide salt with bromine to form the corresponding quaternary ammonium tribromide or quaternary phosphonium tribromide; and then
e) before, during or after step d), separating the chloride by-product from the regenerated quaternary ammonium or quaternary phosphonium monobromide salt or quaternary ammonium or quaternary phosphonium tribromide and then
f) recycling quaternary ammonium tribromide or quaternary phosphonium tribromide obtained in step d) back into step a).
2. The process of claim 1 , wherein the solvent for the unsaturated compound is chlorinated.
3. The process of claim 1 , wherein the source of bromide ions is an alkali metal bromide, an alkaline earth metal bromide; hydrogen bromide, a hydrobromic acid solution; an organic amine hydrobromide salt or an organic phosphine hydrobromide salt.
4. The process of claim 1 , wherein step e) is performed before step d).
5. The process of claim 1 , wherein the unsaturated compound is a homopolymer or copolymer of butadiene.
6. The process of claim 1 , wherein the brominated unsaturated compound contains 500 ppm or less of chlorine.
7. The process of claim 2 , wherein the source of bromide ions is an alkali metal bromide, an alkaline earth metal bromide; hydrogen bromide, a hydrobromic acid solution; an organic amine hydrobromide salt or an organic phosphine hydrobromide salt.
8. The process of claim 7 , wherein step e) is performed before step d).
9. The process of claim 8 , wherein the unsaturated compound is a homopolymer or copolymer of butadiene.
10. The process of claim 9 , wherein the brominated unsaturated compound contains 500 ppm or less of chlorine.