Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-10-05
2002-12-03
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06489525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods of preparing primary alkyl bromides, particularly methyl bromide. The invention also relates to methods of converting methyl chloride to methyl bromide and to methods of reducing the level of bromide salt in aqueous compositions.
BACKGROUND OF THE INVENTION
Primary alkyl bromides, such as methyl bromide, may be used as fumigants, alkylating agents, or intermediates in the synthesis of other chemical compounds, in particular pharmaceutical or agricultural chemicals.
Methyl bromide may be prepared by treating methanol with hydrobromic acid and sulfuric acid. Unfortunately, such processes required the handling and/or disposing noxious and/or dangerous compounds.
Salt exchange reactions include reactions wherein an alkyl halide is converted to another alkyl halide, such as, for example, the Finkelstein reaction wherein alkyl chlorides or bromides are converted to alkyl iodides using solid potassium or sodium iodide in acetone. Unfortunately, such reactions require the handling or large volumes of acetone, and the equilibrium constants for alkyl chloride/alkyl bromide exchanges in acetone often favor the alkyl chloride.
Hughes et al.,
J. Chem. Soc
., 3173-3175 (1955), teach that the displacement of bromine from alkyl bromides using lithium chloride in dry acetone is only mildly reversible. Starks and Liotta,
Phase Transfer Catalysis
”, Academic Press, New York, New York (1978), teach the use of phase transfer catalysts in halide exchange reactions in two-phase systems and in homogenous organic reactions, and disclose that the displacement of chloride ion on octyl bromide is faster than bromide ion displacement on octyl chloride.
Handling large volumes of acids may be difficult and/or costly. Additionally, processes using large amounts of sulfuric acid may generate an aqueous waste stream comprising NaSO
4
as well as residual sulfuric acid, and NaSO
4
generally causes more environmental problems than sodium salts such as NaCl or NaBr. Thus, there is a need for facile methods of producing primary alkyl bromides which do not require the use of large volumes of acids.
As handling large volumes of some organic solvents may be difficult and/or costly, there is a need for methods of producing primary alkyl bromides which do not require the use of large volumes of solvents such as acetone.
There is also a need for methods of reducing the level of bromide salts in aqueous compositions.
There is a need for methods of regenerating alkyl bromides from bromide salts which are formed when alkyl bromides, such as methyl bromide, are used as reactants.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to obviate problems of the prior art.
It is a further object of the present invention to provide methods of preparing alkyl bromides.
It is also an object of the present invention to provide methods of preparing alkyl bromides which do not require the handling, storage or disposal of large volumes of acetone, hydrobromic acid or sulfuric acid.
It is another object of the present invention to provide methods of removing bromide salts from liquid compositions.
It is a further object of the present invention to provide methods of regenerating alkyl bromides from bromide salts.
These and additional objects are provided by the methods of the invention.
In one embodiment the invention is directed to methods of converting methyl chloride to methyl bromide comprising:
(a) providing a composition comprising a bromide salt and water;
(b) contacting the composition with methyl chloride; and
(c) recovering a gaseous product comprising methyl bromide.
In another embodiment, the invention is directed to methods of preparing a primary alkyl bromide comprising:
(a) providing a composition comprising a bromide salt and water;
(b) contacting the composition with a primary alkyl chloride thereby forming a primary alkyl bromide; and
(c) recovering the primary alkyl bromide.
In a further embodiment, the invention is directed to methods of reducing the level of bromide salt in an aqueous composition comprising:
(a) providing an aqueous composition comprising bromide salt and water;
(b) reacting at least a portion of the bromide salt with a primary alkyl chloride to form a primary alkyl bromide; and
(c) recovering the primary alkyl bromide from the aqueous composition.
In yet another embodiment, the invention is directed to methods of converting methyl chloride to methyl bromide comprising:
a) providing a reaction column oriented substantially vertically along its axis and having an upper portion and a lower portion, wherein the reaction column contains packing suitable for continuous extractions;
(b) introducing an aqueous feed into the upper portion of the reaction column, wherein the aqueous feed comprises water and a bromide salt selected from the group consisting of the alkali metal bromides, alkaline earth metal bromides and combinations thereof;
(c) introducing methyl chloride gas into the lower portion of the reaction column; and
(d) allowing at least one portion of the aqueous feed and at least a portion of the methyl chloride to contact each other within the reaction column thereby converting at least a portion of the methyl chloride to methyl bromide.
These and additional aspects, objects and advantages of the invention are more fully described in the following detailed description.
DETAILED DESCRIPTION
The present invention is directed to the preparation of primary alkyl bromides in the presence of a liquid. The present invention is also directed to methods of reducing the level of bromide salts in an aqueous solution, and methods of regenerating alkyl bromides.
The primary alkyl bromides are prepared by providing a composition comprising bromide salt and a liquid, preferably water; contacting the composition with a primary alkyl chloride thereby forming a primary alkyl bromide; and recovering the primary alkyl bromide. In one embodiment the primary alkyl chloride is gaseous methyl chloride and/or methyl chloride dissolved in liquid. Methods in accordance with the invention may be used to regenerate alkyl bromides from bromide salts which are formed when alkyl bromides are used as reactants.
Methods in accordance with the invention avoid the use of large volumes of acids and/or organic solvents such as acetone. Thus any resulting aqueous waste stream may be easily handled and/or treated.
While not being bound by theory, it is believed that the reaction proceeds as set forth below:
R—X+ZBr→R—Br+ZX
wherein R is a primary alkyl, preferably a C
1
-C
20
primary alkyl, more preferably a C
1
-C
5
alkyl; even more preferably a C
1
-C
2
alkyl; X is a halogen, preferably a halogen other than Br, more preferably Cl; Z is a cation such hydrogen, sodium, potassium, lithium, magnesium, calcium or copper, preferably hydrogen, sodium, potassium or lithium.
Suitable bromide salts include hydrogen bromide, alkali metal bromides, alkaline earth metal bromides, organic quaternary bromides and combinations thereof, preferably the bromide salts are selected from the group consisting of alkali metal bromides, alkaline earth metal bromides and combinations thereof. In one embodiment the bromide salt is selected from the group consisting of sodium bromide, potassium bromide, lithium bromide, hydrogen bromide and combinations thereof. In another embodiment the bromide salt is an organic quaternary bromide, such as tetramethyl ammonium bromide or tetraethyl ammonium bromide.
The bromide salt may be present in a mixture with salts other than bromide salts, such as sodium sulfate and sodium chloride. The bromide salt may be present in the aqueous composition at a concentration of from about 1% to about 50%, preferably from about 5% to about 35%, by weight. The aqueous composition may further comprise water-miscible organic solvents.
The preparation of the primary alkyl bromide may occur in the substantial absence of water-immiscible organic solvent. As used herein “substantial absence of water-immiscible organic solvent” is intended
Cockrill David E.
Erdman David T.
Lamar Mary F.
Spicher Jonathan D.
Bayer Corporation
Gil Joseph C.
Mrozinski, Jr. John E.
Siegel Alan
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