Patent Description:
Perfluorooctyl bromide (abbreviated as "PFOB"), of the formula C<NUM>F<NUM>Br, is known as a compound having X-ray contrast ability and MR contrast ability. It is also known that PFOB can be used as an active pharmaceutical ingredient of a diagnostic drug, a medicinal intermediate, and the like.

It is known that PFOB can be produced by various methods. Examples of known methods of obtaining PFOB include a method of reacting a compound of the formula C<NUM>F<NUM>I (n-perfluorooctyl iodide, abbreviated as "PFOI") with a brominating agent, such as bromine, in a gas phase (e.g., <CIT>); and a method of obtaining PFOB by performing photochemical bromination of PFOI (e.g., <CIT>).

<CIT> discloses a process for the preparation of compounds of the formula CnF2n+<NUM>Br (n = <NUM>-<NUM>) by reacting a compound of the formula CnF2n+<NUM>I with bromine at a molar ratio of <NUM>: (<NUM>-<NUM>), without further additives and without using high-energy artificial electromagnetic radiation, at <NUM>-<NUM>.

<CIT> relates to a method for producing perfluoroalkyl bromides by reacting a perfluoroalkyl iodide of the formula CnF2n+<NUM>I or I (CF<NUM>)mI (n = <NUM>-<NUM>, m = <NUM>-<NUM>) with bromine in the presence of a radical initiator at <NUM>-<NUM>.

However, as a result of a detailed analysis of the production of PFOB using PFOI as a starting material, the present inventors found that under conditions in which at least water and/or oxygen are present, PFOI used as a starting material undergoes decomposition due to the action of light or heat, and undesirably forms perfluoro-octanoic acid (PFOA; C<NUM>F<NUM>COOH). When PFOB is produced using such a starting material containing PFOA, PFOA is easily incorporated in the reaction product, and the purity of PFOB is easily reduced. To minimize the amount of PFOA in PFOB, for example, an additional step is required for separately purifying PFOI; or strict control is required for the storage method or storage time for PFOI used as a starting material. Furthermore, since PFOA is known as a compound that is likely to have an adverse effect on the environment, it is considered significantly important to provide PFOB containing a smaller amount of PFOA.

The present invention has been accomplished in view of the above. An object of the present invention is to provide a method for producing a composition containing PFOB with a small amount of PFOA as an impurity.

In order to achieve the above object, the present inventors conducted extensive research, and consequently found that the above object can be achieved by a washing process by which PFOA is efficiently removed from PFOB. The present invention has been accomplished based on this finding.

More specifically, the present invention provides a method for producing a composition containing C<NUM>F<NUM>Br, and further containing C<NUM>F<NUM>COOH, comprising reacting C<NUM>F<NUM>I and a brominating agent to obtain C<NUM>F<NUM>Br; and alkali-washing the obtained C<NUM>F<NUM>Br to reduce the C<NUM>F<NUM>COOH content to ≤ <NUM> ppb based on the total weight of C<NUM>F<NUM>Br, wherein the alkali-washing is repeatedly performed until the alkali layer after alkali-washing has a pH of ≥ <NUM>.

The composition containing C<NUM>F<NUM>Br (PFOB) obtained by the method of the present invention ("the present composition" hereinafter) contains a small amount of C<NUM>F<NUM>COOH (PFOA), and the purity of PFOB is high; therefore, the present composition is less likely to have an adverse effect on the environment.

According to the method for producing PFOB of the present invention ("the present method" hereinafter), the PFOA content is easily reduced to ≤ <NUM> ppb based on the total weight of PFOB, and high-purity PFOB is produced with a simple process.

Specific embodiments of the present invention are described in detail below. In this specification, the expressions "comprise" and "contain" encompass the concepts of "comprise," "contain," "consist essentially of," and "consist of.

The present composition containing C<NUM>F<NUM>Br further contains C<NUM>F<NUM>COOH, and the C<NUM>F<NUM>COOH content is ≤ <NUM> ppb based on the total weight of C<NUM>F<NUM>Br. As stated later, C<NUM>F<NUM>COOH can serve as an impurity component in the composition. Otherwise, C<NUM>F<NUM>COOH may be, for example, a by-product during the production of C<NUM>F<NUM>Br. Alternatively, C<NUM>F<NUM>COOH may be, for example, a component intentionally added to the composition.

In this specification, C<NUM>F<NUM>Br (perfluorooctyl bromide) is abbreviated as "PFOB," and C<NUM>F<NUM>COOH (perfluoro-octanoic acid) is abbreviated as "PFOA. " Further, a compound of the formula C<NUM>F<NUM>I (n-perfluorooctyl iodide) mentioned later is abbreviated as "PFOI.

In the present composition, the upper limit of the PFOA content based on the total weight of PFOB is preferably <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, <NUM> ppb, and <NUM> ppb, in descending order of preference. Furthermore, in the present composition, the upper limit of the PFOA content based on the total weight of PFOB can be <NUM> ppb.

In the present composition, if the PFOA content exceeds <NUM> ppb based on the total weight of PFOB, PFOA may possibly have an adverse effect on the environment, and the usage of PFOB is restricted; therefore, a PFOA content exceeding <NUM> ppb is not preferable.

There are believed to be various reasons why PFOA can be present as an impurity in PFOB. In particular, when PFOI is used as a starting material to produce PFOB, the produced PFOB is likely to contain a large amount of PFOA. This is because PFOI is a compound unstable to light and heat; and, due to the action of either light or heat, or both light and heat, PFOI undergoes a reaction with oxygen or oxygen present in the air and/or water, and easily decomposes into PFOA. In the presence of oxygen and/or water, in particular, PFOI is liable to decompose into PFOA.

As long as the effects of the present invention are not impaired, the present composition may contain a compound other than PFOB, such as known additives. When the present composition contains a compound other than PFOB, it can contain PFOB in an amount of ≥ <NUM> wt%, preferably ≥ <NUM> wt%, more preferably ≥ <NUM> wt%, and particularly preferably ≥ <NUM> wt%, based on the total weight of the composition. The present composition may consist only of PFOB containing ≤ <NUM> ppb of PFOA.

The method for producing C<NUM>F<NUM>Br (PFOB) of the present invention comprises reacting C<NUM>F<NUM>I and a brominating agent to obtain C<NUM>F<NUM>Br; and
alkali-washing the obtained C<NUM>F<NUM>Br to reduce the C<NUM>F<NUM>COOH content to ≤ <NUM> ppb based on the total weight of C<NUM>F<NUM>Br. The reaction product obtained through this production method is PFOB (C<NUM>F<NUM>Br) containing PFOA (C<NUM>F<NUM>COOH) as an impurity, and the PFOA content, in particular, is ≤ <NUM> ppb based on the total weight of PFOB.

Hereinafter, the step of reacting C<NUM>F<NUM>I (PFOI) and a brominating agent to obtain C<NUM>F<NUM>Br is referred to as "the reaction step," and the step of alkali-washing the obtained C<NUM>F<NUM>Br to reduce the C<NUM>F<NUM>COOH content to ≤ <NUM> ppb based on the total weight of C<NUM>F<NUM>Br is referred to as "the purification step.

In the reaction step, PFOI is reacted with a brominating agent to produce PFOB.

The brominating agent is not limited, and bromine, for example, can be used. Additionally, a compound that releases bromine can also be used. Examples of the compound that releases bromine include IBr and IBr<NUM>, N-bromosuccinimide, N-bromophthalimide, dibromoisocyanuric acid, <NUM>,<NUM>-dibromo-<NUM>,<NUM>-dimethylhydantoin, N-bromoacetamide and N-bromosaccharin. The brominating agent is preferably bromine.

The PFOI used in the reaction step may be produced, for example, by using known methods; or may be commercially available PFOI. As described above, PFOI contains PFOA as an impurity. Thus, for example, PFOI can be purified in advance before use. In the production method of the present invention, however, PFOA as an impurity is easily removable in the purification step after the reaction step. Therefore, PFOI can be subjected to the reaction step without purifying the PFOI in advance. This can make the entire production process simpler.

PFOI as a starting material forms PFOA due to the action of light and/or heat during storage; thus, it is important to strictly control the storage conditions for PFOI. However, according to the purification step of the production method of the present invention, the PFOA content can be easily reduced, and thus the storage conditions for PFOI are not necessarily strictly controlled.

The ratio of PFOI to a brominating agent is not limited. For example, a brominating agent can be used in an amount of <NUM>-<NUM> mol, and preferably <NUM>-<NUM> mol, per mol of PFOI.

The reaction of PFOI and a brominating agent can be carried out, for example, in the presence of an inert gas, such as nitrogen.

The reaction of PFOI and a brominating agent can be carried out, for example, by a method of heating an optically transparent reactor containing PFOI, and adding a brominating agent thereto dropwise while being exposed to light. However, the method is not limited thereto; for example, it is also possible to use a method of heating without exposure to light. When heating is performed without exposure to light, the reaction proceeds even at a heating temperature of, for example, <NUM>. The brominating agent can be supplied in divided portions such that a portion of brominating agent is supplied to a reactor in advance, followed by a further addition of an additional amount. The reaction of PFOI and a brominating agent can also be carried out continuously. Examples of the optically transparent reactor include various glass reactors, such as a glass flask and a glass tube. The reaction of PFOI and a brominating agent can be carried out in a gas phase.

The temperature for heating the reactor, i.e., the reaction temperature, is not limited. The temperature is preferably a temperature at which PFOI is allowed to reflux, i.e., <NUM>-<NUM>, and particularly preferably <NUM>-<NUM>. The time for reacting PFOI and a brominating agent is not limited.

For exposure to light in the reaction of PFOI and a brominating agent, it is possible to use light with a wavelength of ≤ <NUM> or less (preferably <NUM>-<NUM>), such as visible light and ultraviolet light.

The reaction product obtained from the reaction of PFOI and a brominating agent contains PFOB, which is a target product. In the reaction product, e.g. IBr is also generated as by-product. Further, since PFOI contains PFOA as an impurity, as stated above, the reaction product obtained after the reaction can also contain PFOA. The reaction product obtained in the reaction step is subjected to the purification step.

In the purification step, PFOB obtained in the reaction step is alkali-washed. In this purification step, the PFOA content in the reaction product is reduced to ≤ <NUM> ppb based on the total weight of PFOB.

The method for alkali-washing is not limited. Examples include a method in which an alkali solution is added to the reaction product, the resulting mixture is stirred and then allowed to stand to separate it into two layers, i.e., a layer containing the reaction product, and a layer of the alkali solution (sometimes referred to as "the alkali layer"); and the layer containing the reaction product is collected by separation. In this manner, PFOB as a reaction product can be obtained. Alternatively, the layer containing PFOB, i.e., a reaction product, can also be obtained by adding an alkali solution to the reaction product, followed by distillation.

The series of operations from the operation of adding an alkali solution to the operation of collecting the layer containing the reaction product by separation is referred to as "alkali-washing.

The alkali-washing is repeated so that the alkali layer after alkali-washing has a pH of ≥ <NUM>, and preferably ≥ <NUM>.

The type of alkali used for alkali-washing is not limited, and known bases can be widely used. Examples include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, ammonia, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium bicarbonate, and other inorganic bases. Additionally, for alkali, it is also possible to use organic bases, such as organic amines, basic amino acids, and metal alkoxides.

When an alkali solution is used for alkali-washing, the solvent of the alkali solution may be water, an alcohol, or a mixed solvent thereof. Examples of alcohol include lower alcohols, such as methanol, ethanol, and isopropanol.

The concentration of the alkali solution used for alkali-washing is not limited. To more easily reduce the PFOA content in the reaction product, alkali-washing is performed using an alkali solution having a concentration of <NUM>-<NUM> wt%, and more preferably <NUM>-<NUM> wt%. The concentration of alkali solution is more preferably ≤ <NUM> wt%, still more preferably ≤ <NUM> wt%, particularly preferably ≤ <NUM> wt%, and most preferably ≤ <NUM> wt%. The concentration of alkali solution is more preferably ≥ <NUM> wt%, and particularly preferably ≥ <NUM> wt%.

During alkali-washing in the purification step, PFOA contained in the reaction product is removed; additionally, IBr as a by-product can also be removed.

After alkali-washing, the reaction product is optionally washed with a solution containing an inorganic salt. Examples of inorganic salts include sodium chloride and potassium chloride. By washing with a solution containing an inorganic salt, the pH of the reaction product after alkali-washing can be adjusted, and water can also be removed.

In the purification step, after the alkaline treatment, the reaction product may be further subjected to drying treatment and distillation treatment. The drying treatment can be performed by, for example, a method of adding a drying agent to the reaction product. The type of drying agent is not limited. Examples include anhydrous magnesium sulfate. The distillation treatment can be performed, for example, after the drying treatment. The method of distillation treatment is not limited, and known distillation methods can be widely used.

By performing the purification step, PFOB is purified, and high-purity PFOB containing ≤ <NUM> ppb of PFOA as an impurity is produced.

In particular, according to the present method, although PFOI containing PFOA is used as a starting material to produce PFOB, the resulting PFOB contains a small amount of PFOA, and high-purity PFOB can be obtained. Further, the amount of PFOA can be easily reduced by purification; thus, PFOI whose storage conditions are not strictly controlled can be used as a starting material.

The PFOB obtained by the present method is suitably used, for example, as a starting material for preparing the present composition containing PFOB. In particular, the PFOA content in the PFOB is less than that of known PFOB, and the PFOB of the present invention is less likely to have an adverse effect on the environment. Accordingly, the PFOB is less likely to be affected by environmental regulations etc..

The present composition containing PFOB obtained by the present method is suitably used for various applications, such as an active pharmaceutical ingredient of a diagnostic drug, a medicinal intermediate, etc., using the characteristics of PFOB, such as X-ray contrast ability and MR contrast ability.

The present invention is described in more detail below with reference to Examples.

PFOI (<NUM>) was supplied to a reaction vessel, the reaction vessel was heated to <NUM>-<NUM>, and the PFOI in the reaction vessel was stirred. Subsequently, <NUM>-<NUM> of bromine was supplied to this reaction vessel in several divided portions; and the mixture was heated to reflux, so that the PFOI was brominated.

After the completion of bromination, the reaction solution was cooled, and alkali-washed. In this alkali-washing, first, about <NUM> of a <NUM>-<NUM> wt% sodium hydroxide aqueous solution was added to the obtained reaction solution, followed by stirring. Thereafter, stirring was stopped, and the reaction vessel was allowed to stand to separate the mixture into a layer containing the reaction product and a layer of the sodium hydroxide aqueous solution. Then, the layer containing the reaction product was extracted by separation. This alkali-washing was repeated until the pH of the layer of the sodium hydroxide aqueous solution exceeded <NUM>.

Thereafter, the reaction product was washed by adding about <NUM> of brine whose concentration was adjusted to <NUM>-<NUM>%. Subsequently, the layer containing the reaction product was collected. About <NUM> of anhydrous magnesium sulfate was added to the collected layer containing the reaction product, and the mixture was stirred. Thereafter, the layer containing the reaction product was collected through filtration, followed by distillation to obtain <NUM> of PFOB.

The concentration of PFOA in the obtained PFOB was analyzed by LC-MS/MS. The concentration of PFOA was ≤ <NUM> ppb based on the total weight of PFOB.

PFOB (<NUM>) was obtained as in Example <NUM>, except that PFOI was changed to PFOI containing <NUM> ppm by weight of PFOA.

Claim 1:
A method for producing a composition containing C<NUM>F<NUM>Br, and further containing C<NUM>F<NUM>COOH, comprising reacting C<NUM>F<NUM>I and a brominating agent to obtain C<NUM>F<NUM>Br; and alkali-washing the obtained C<NUM>F<NUM>Br to reduce the C<NUM>F<NUM>COOH content to ≤ <NUM> ppb based on the total weight of C<NUM>F<NUM>Br, wherein the alkali-washing is repeatedly performed until the alkali layer after alkali-washing has a pH of ≥ <NUM>.