JP3907449B2 - Method for purifying fluorine-containing benzoic acid - Google Patents
Method for purifying fluorine-containing benzoic acid Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は含フッ素安息香酸の精製方法に関する。
【０００２】
【従来の技術】
含フッ素安息香酸の精製に関しては、例えば、特開平３−１６１４５０号公報、特開平５−８６０００号公報、特開平９−０６７３０３号公報、特開平９−０６７３０４号公報および特許第２８８６９０８号公報の実施例に記載されている。 これら精製方法は、ヘキサン、トルエンなどの有機溶媒を使用して、再結晶法により目的とする含フッ素安息香酸を精製するというものである。
【０００３】
【発明が解決しようとする課題】
本発明者らの研究によれば、（１）含フッ素安息香酸を前記有機溶媒を用いた再結晶法により精製する場合、有機溶媒に対して含フッ素安息香酸の溶解度が比較的高いため、精製工程での含フッ素安息香酸の歩留まりが低下する、（２）含フッ素安息香酸が、例えば、硫酸などの酸性物質の存在下で加水分解により製造された場合、含フッ素安息香酸に含有される硫酸や硫酸アンモニウムは、有機溶媒を用いた再結晶法によっては効率よく除去することができず、十分に高い純度の含フッ素安息香酸を得ることができない、（３）再結晶後、乾燥により有機溶媒を蒸発除去する場合、飛散する有機溶媒の量が多く、有機溶媒の回収率が低下し、また有機溶媒の回収率を上げようとすると、高価な設備が必要になり、工業的あるいは経済的に不利となる、ことがわかった。
【０００４】
本発明の目的は、従来のヘキサン、トルエンなどの有機溶媒を用いた再結晶法に代わる、新規な含フッ素安息香酸の精製方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明者らの研究によれば、（１）含フッ素安息香酸を水の存在下に加熱すると、含フッ素安息香酸が油状（液体状）になる、（２）これを攪拌すると、含フッ素安息香酸が水中に分散される、（３）この分散状態で冷却すると、高純度の含フッ素安息香酸が析出して、効率よく分離できることがわかった。すなわち、トルエン、キシレンなどの有機溶媒の代わりに、含フッ素安息香酸の溶解度が小さい水を用いるので精製収率が高く、また含フッ素安息香酸を水中に分散させることにより、含フッ素安息香酸中の不純物が水に抽出されるので、高純度の含フッ素安息香酸が得られるのである。
【０００６】
すなわち、本発明は、一般式（１）
【０００７】
【化２】
（式中、Ｆはフッ素原子であり、ｍは１〜５の整数である。）で表される含フッ素安息香酸を水の存在下に、加熱、攪拌して、水に分散させた後、水から分離することを特徴とする含フッ素安息香酸の精製方法である。
【０００９】
詳しくは、粗製状態の含フッ素安息香酸を、水を配合し、水に分散させて、酸成分などの水に溶解する不純物を洗い、目的である含フッ素安息香酸を、純度よく得るための、含フッ素安息香酸の精製方法である。
【００１０】
さらに詳しくは、上記の粗製状態の含フッ素安息香酸を水に分散させた後、冷却して含フッ素安息香酸を析出させて分離する含フッ素安息香酸の精製方法である。さらに詳しくは、本発明の上記含フッ素安息香酸の精製方法は、含フッ素安息香酸を水の存在下に、４０〜１００℃の温度範囲で加熱する工程を含んでいる。
【００１１】
なお、本発明における粗製の含フッ素安息香酸とは、例えば、酸成分が１％以上含まれる粗製の含フッ素安息香酸を精製の対象とする形態が好ましい。また、本発明の粗製含フッ素安息香酸の精製方法によって得られる、精製された含フッ素安息香酸における酸成分の含有量としては、１％未満が好ましい。より好ましくは０．８％以下である。さらに好ましくは０．５％以下である。
【００１２】
【発明の実施の形態】
本発明の精製方法によれば、一般式（１）で表される含フッ素安息香酸のいずれについても、極めて高純度の含フッ素安息香酸を得ることができる。一般式（１）で表される含フッ素安息香酸のなかでも、ｍが５であるペンタフルオロ安息香酸が好適に用いられる。そこで、ペンタフルオロ安息香酸を例に挙げて本発明を詳しく説明する。なお、水の使用量などの各種条件は、他の含フッ素安息香酸の場合についても同じである。
【００１３】
ペンタフルオロ安息香酸は一般に知られた、常温で固体の化合物であり、例えば、ペンタフルオロベンゾニトリルを酸性物質、代表的には硫酸の水溶液で加水分解することにより製造することができる。
【００１４】
ペンタフルオロ安息香酸の融点は１００〜１０２℃程度であるが、ペンタフルオロ安息香酸を水の存在下に４０℃を超える温度で加熱すると、融点以下の温度で油状となり、水層と分離する。しかも、ペンタフルオロ安息香酸の水に対する溶解度は１〜２質量％程度と比較的小さいので、油層と水層とを攪拌すると、油層が水層中に分散された状態になり、ペンタフルオロ安息香酸中の無機あるいは有機の不純物が水中に抽出されることになる。
【００１５】
ペンタフルオロ安息香酸を水の存在下で加熱すると、その融点以下の温度で油状になって分散した状態になる理由は明らかではないが、ペンタフルオロ安息香酸層に少量の水が溶解することやペンタフルオロ安息香酸中のフッ素原子の存在による静電的な性質によるものと考えられている。
【００１６】
本発明の精製の際に使用する水の量は、ペンタフルオロ安息香酸に対し、０．５〜２０質量倍、好ましくは１〜１５質量倍、更に好ましくは１．５〜１０質量倍である。０．５質量倍より少ないと十分な精製効果が得られないだけではなく、冷却によって析出したペンタフルオロ安息香酸のスラリー濃度が高すぎて取り扱いが困難となる。一方、２０質量倍より多いと、ペンタフルオロ安息香酸の水への溶解による損失が多くなって歩留まりが低下する。
【００１７】
加熱する温度は、通常、４０〜１００℃であり、好ましくは４５〜９５℃、更に好ましくは５０〜９０℃である。４０℃より低い温度ではペンタフルオロ安息香酸が油状とならないので、油状の分散状態を形成することができない。
【００１８】
本発明の方法によれば、通常、ペンタフルオロ安息香酸に前記量の水を添加し、攪拌下に前記温度範囲で加熱し、ペンタフルオロ安息香酸を水に分散させる。
【００１９】
前記温度範囲での保持時間は、ペンタフルオロ安息香酸中に含まれる無機あるいは有機の不純物を十分除去できる時間、具体的には、１〜１５０分、好ましくは１０〜１２０分、更に好ましくは２０〜９０分とすればよい。
【００２０】
上記ペンタフルオロ安息香酸を水中に分散させる操作は、常圧、加圧あるいは減圧のいずれでもよいが、通常、常圧下に行う。なお、前記温度範囲は常圧下のものである。
【００２１】
前記攪拌は、ペンタフルオロ安息香酸中の不純物の水中への抽出に好適な分散状態が形成されるように行えばよい。具体的には、Ｐｖ値（攪拌機の動力（ｋｗ）／反応液の総量（ｍ３））が０．０５〜３ｋｗ／ｍ３、好ましくは１〜２ｋｗ／ｍ３となるようにするのがよい。
水中に分散されたペンタフルオロ安息香酸を水から分離する方法の一つは、分散液を冷却してペンタフルオロ安息香酸を析出させ、析出物をろ過などの手段により分離する方法である。そのほか、ペンタフルオロ安息香酸を水に分散させた後、静置すると油層と水層とに容易に分離するので、油層を水層から分離して精製ペンタフルオロ安息香酸を得てもよい。
【００２２】
上記冷却分離方法において、分散液を冷却するにあたっては、分散液を０．０１℃／分〜５℃／分の速度で冷却するか、あるいはペンタフルオロ安息香酸の析出が開始した時、この析出開始温度を基準として、分散液の温度を、析出開始温度±５℃の温度範囲に、必要時間、具体的には１〜１５０分、好ましくは１０〜１２０分、更に好ましくは２０〜９０分保持するか、もしくは分散液を０．０１℃／分〜５℃／分の速度で冷却するとともに、ペンタフルオロ安息香酸の析出が開始した時、この析出開始温度を基準として、分散液の温度を、析出開始温度±５℃の温度範囲に、必要時間、具体的には１〜１５０分、好ましくは１０〜１２０分、更に好ましくは２０〜９０分保持するのがよい。これにより、析出物のろ過効率が向上し、また析出物の含液率（析出物に含まれる硫酸などの不純物の割合）が低くなり、高純度の精製ペンタフルオロ安息香酸を得ることができる。冷却速度が５℃／分を超えるとペンタフルオロ安息香酸の結晶が十分成長せずに析出する結果、ろ過後の析出物の含液率が高くなり、不純物の含有率が高くなる。このため、ろ過効率が低下するとともに精製ペンタフルオロ安息香酸の純度が低下する。冷却速度が０．０１℃／分より低いと、ペンタフルオロ安息香酸の析出に必要以上の時間を要することになり経済的でない。
【００２３】
本発明で使用する水としては、工業的に利用できる、いわゆる工業用純水を使用することができる。一方、精製後の水は、本発明の精製方法によって除去される、前述の有機物あるいは無機物などの不純物を含有しているほか、前述のように、ペンタフルオロ安息香酸が、水に対して約１〜２質量％溶解するため、ペンタフルオロ安息香酸をこの程度の濃度で含有している。
【００２４】
したがって、精製後の水は、所望の純度が達成できる範囲において、ペンタフルオロ安息香酸の精製に繰り返して使用するのが、ペンタフルオロ安息香酸の溶解損失を抑制でき、また歩留まりが向上して、工業的に有利であって好ましい。この場合、精製に繰り返し使用する水に含まれる有機物や無機物の濃度は、通常２０％以下であり、好ましくは１５％以下であり、更に好ましくは１０％以下である。
【００２５】
また、ペンタフルオロ安息香酸を分離した後の少量のペンタフルオロ安息香酸を含む水は、ペンタフルオロ安息香酸を製造する場合の加水分解工程における、酸性物質水溶液を調製する際の水として再利用することができる。
【００２６】
【発明の効果】
本発明は、上記含フッ素安息香酸を水の存在下に、加熱、攪拌して、水に分散させた後、水から分離することを特徴とする含フッ素安息香酸の精製方法である。
【００２７】
言い換えると、上記、本発明の含フッ素安息香酸の精製方法は、含フッ素安息香酸を、水を使用して再結晶する工程を含み、水の存在下に、加熱、攪拌して、水に分散させた後、水から分離することを特徴とする含フッ素安息香酸の精製方法である。
【００２８】
本発明の精製方法によれば、高純度の精製含フッ素安息香酸を高い歩留まりで得ることができる。特に、含フッ素安息香酸を水に分散させた後、冷却によって析出させて分離する場合には、高いろ過効率をもって水と分離することができる。
【００２９】
【実施例】
以下、実施例を挙げて本発明を更に具体的に説明する。
【００３０】
＜参考例１＞
攪拌機、冷却器および温度計を備えた容量５００ｍｌのセパラブルフラスコに７０質量％硫酸２５９ｇを仕込んだ後、攪拌しながらペンタフルオロベンゾニトリル１４０ｇ（０．７２５モル）を仕込み、内温を１６０℃に昇温して、４００ｒｐｍで攪拌しながら、還流下に１２時間反応させた。
【００３１】
反応終了後、反応液の温度が１５５℃になった時点で、攪拌下に水１９３ｇを反応液に投入した。水投入終了後、反応液を１℃／分の速度で冷却したところ、反応液の温度が７２℃になったところで結晶が析出し始めた。結晶析出開始後、反応液を７１〜７５℃に３０分保持した後、１℃／分の冷却速度で２５℃にまで冷却した。
【００３２】
反応液をろ紙（Ｎｏ．２）を使用し、ヌッツェで減圧下にろ過して、粗製のペンタフルオロ安息香酸の結晶（ろ過ケーキ）１６７ｇを得た。粗製ペンタフルオロ安息香酸の純度を液体クロマトグラフィーで分析したところ、純度９０．０％、含液率１０．０％（硫酸３．３％、硫酸アンモニウム１．１％、水５．６％）であった。
【００３３】
＜実施例１＞
参考例１で得られた粗製ペンタフルオロ安息香酸１６７ｇを攪拌機、冷却器および温度計を備えた容量５００ｍｌのセパラブルフラスコに仕込み、純水３７０ｇを添加して、４００ｒｐｍで攪拌しながら、７０℃に昇温し、６５〜７５℃の温度範囲に７０分間保持した。これによりペンタフルオロ安息香酸は油状となって水中に分散された状態となった。
【００３４】
その後、１℃／分の冷却速度で冷却したところ、３６℃で結晶が析出し始めた。そこで、内温３５〜３７℃で１時間保持した後、１℃／分の冷却速度で２０℃まで冷却した。その後、この液を、ろ紙（Ｎｏ．２）を使用し、ヌッツェで減圧下にろ過してペンタフルオロ安息香酸の結晶（ろ過ケーキ）１５３ｇを得た。得られた精製ペンタフルオロ安息香酸を液体クロマトグラフィーで分析したところ、精製ペンタフルオロ安息香酸含有量９６．０％、含液率４．０％（硫酸０．０７％、硫酸アンモニウム０．０２％、水３．９％）であった。上記の含液率４％の精製ペンタフルオロ安息香酸を減圧下、４０℃で乾燥することにより純度９９．８％のペンタフルオロ安息香酸を得た。
【００３５】
＜実施例２、３＞
実施例１において、粗製ペンタフルオロ安息香酸を水中に分散させるための加熱温度範囲を５０℃±５℃（実施例２）および９０℃±５℃（実施例３）に変更した以外は実施例１と同様にして精製ペンタフルオロ安息香酸を得た。得られた精製ペンタフルオロ安息香酸の含有量（組成）、含液率および乾燥後の純度を表１に示す。
【００３６】
＜参考例２、実施例４、５＞実施例１において、添加する水の量を１００ｇ（参考例２）、２５０ｇ（実施例４）および５００ｇ（実施例５）に変更した以外は実施例１と同様にして精製ペンタフルオロ安息香酸を得た。得られた精製ペンタフルオロ安息香酸の含有量、含液率および乾燥後の純度を表１に示す。
【００３７】
＜実施例６＞実施例１において、冷却速度を変更した以外は実施例１と同様にして精製ペンタフルオロ安息香酸を得た。得られた精製ペンタフルオロ安息香酸の含有量、含液率および乾燥後の純度を表１に示す。
【００３８】
＜実施例７＞実施例１で得た精製後のろ液を再使用して、参考例１で得られたと同じ粗製ペンタフルオロ安息香酸の精製を実施例１と同様の方法で行った。
【００３９】
すなわち、参考例１で得られた粗製ペンタフルオロ安息香酸１６７ｇを攪拌機、冷却器および温度計を備えた容量５００ｍｌのセパラブルフラスコに仕込み、実施例１で得た精製後のろ液３８０ｇを添加して、４００ｒｐｍで攪拌しながら７０℃に昇温し、６５〜７５℃の温度範囲に７０分間保持した。これによりペンタフルオロ安息香酸は液体状態となって、水中に分散された状態となった。
【００４０】
その後、１℃／分の冷却速度で冷却したところ、３６℃で結晶が析出し始めた。そこで、内温３５〜３７℃で１時間保持した後、１℃／分の冷却速度で２０℃まで冷却した。その後、この液をろ紙（Ｎｏ．２）を使用し、ヌッチェで減圧下にろ過して、ペンタフルオロ安息香酸の結晶（ろ過ケーキ）１５６ｇを得た。液体クロマトグラフィーで分析したところ、ペンタフルオロ安息香酸含有量９５．７６％、含液率４．２４％（硫酸０．１８％、硫酸アンモニウム０．０５％、水４．０１％）であり、実施例１で純水を使用した場合に得られた精製ペンタフルオロ安息香酸含有量とほぼ同等であり、精製ろ液の再使用が可能であることがわかった。
【００４１】
＜比較例１＞
参考例１で得た粗製のペンタフルオロ安息香酸ケーキを攪拌しないで３７０ｇの水をかけて洗浄した。結果を表１に示す。
【００４２】
＜比較例２＞参考例１で得た粗製のペンタフルオロ安息香酸ケーキをトルエン４００ｍｌで再結晶して精製を行った。結果を表１に示す。
参考例３
実施例１において、精製時の加熱温度範囲を２８〜３２℃とした以外は、同様の方法で精製を行った。結果を表１に示す。ペンタフルオロ安息香酸は油状にならなかったが精製は可能であった。
【００４３】
【表１】
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying fluorine-containing benzoic acid.
[0002]
[Prior art]
With regard to the purification of fluorine-containing benzoic acid, for example, implementation of JP-A-3-161450, JP-A-5-86000, JP-A-9-066733, JP-A-9-0667304, and Japanese Patent No. 2886908. It is described in the example. These purification methods purify the target fluorine-containing benzoic acid by a recrystallization method using an organic solvent such as hexane and toluene.
[0003]
[Problems to be solved by the invention]
According to the studies by the present inventors, (1) when purifying fluorinated benzoic acid by a recrystallization method using the organic solvent, the solubility of the fluorinated benzoic acid in the organic solvent is relatively high. The yield of fluorine-containing benzoic acid in the process is reduced. (2) When fluorine-containing benzoic acid is produced by hydrolysis in the presence of an acidic substance such as sulfuric acid, sulfuric acid contained in fluorine-containing benzoic acid And ammonium sulfate cannot be efficiently removed by a recrystallization method using an organic solvent, and sufficiently high purity fluorine-containing benzoic acid cannot be obtained. (3) After recrystallization, the organic solvent is removed by drying. When evaporating and removing, the amount of scattered organic solvent is large, the recovery rate of the organic solvent is reduced, and an attempt to increase the recovery rate of the organic solvent requires expensive equipment, which is not industrially or economically effective. To become, it was found.
[0004]
An object of the present invention is to provide a novel method for purifying fluorine-containing benzoic acid in place of the conventional recrystallization method using an organic solvent such as hexane and toluene.
[0005]
[Means for Solving the Problems]
According to the study by the present inventors, (1) when fluorine-containing benzoic acid is heated in the presence of water, the fluorine-containing benzoic acid becomes oily (liquid form). (2) When this is stirred, fluorine-containing benzoic acid is obtained. It was found that the acid is dispersed in water. (3) When cooled in this dispersed state, high-purity fluorine-containing benzoic acid is precipitated and can be separated efficiently. That is, instead of an organic solvent such as toluene and xylene, water having a low solubility of fluorine-containing benzoic acid is used, so that the purification yield is high, and by dispersing fluorine-containing benzoic acid in water, Since impurities are extracted into water, a high-purity fluorine-containing benzoic acid is obtained.
[0006]
That is, the present invention relates to the general formula (1)
[0007]
[Chemical 2]
(In the formula, F is a fluorine atom, and m is an integer of 1 to 5.) After the fluorine-containing benzoic acid represented by heating and stirring in the presence of water and dispersing in water, This is a method for purifying fluorine-containing benzoic acid, characterized by being separated from water.
[0009]
Specifically, in order to obtain the target fluorine-containing benzoic acid with high purity, the crude fluorine-containing benzoic acid is blended with water, dispersed in water, and washed with impurities dissolved in water such as acid components. This is a method for purifying fluorine-containing benzoic acid.
[0010]
More specifically, this is a method for purifying fluorine-containing benzoic acid, in which the crude fluorine-containing benzoic acid is dispersed in water and then cooled to precipitate fluorine-containing benzoic acid. More specifically, the method for purifying the fluorine-containing benzoic acid of the present invention includes a step of heating the fluorine-containing benzoic acid in the temperature range of 40 to 100 ° C. in the presence of water.
[0011]
The crude fluorine-containing benzoic acid in the present invention is preferably in the form of, for example, a crude fluorine-containing benzoic acid containing 1% or more of an acid component for purification. Moreover, as content of the acid component in the refine | purified fluorine-containing benzoic acid obtained by the purification method of the crude fluorine-containing benzoic acid of this invention, less than 1% is preferable. More preferably, it is 0.8% or less. More preferably, it is 0.5% or less.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the purification method of the present invention, extremely high purity fluorine-containing benzoic acid can be obtained for any of the fluorine-containing benzoic acids represented by the general formula (1). Among the fluorine-containing benzoic acids represented by the general formula (1), pentafluorobenzoic acid having m of 5 is preferably used. Therefore, the present invention will be described in detail by taking pentafluorobenzoic acid as an example. Various conditions such as the amount of water used are the same for other fluorine-containing benzoic acids.
[0013]
Pentafluorobenzoic acid is a generally known compound that is solid at room temperature, and can be produced, for example, by hydrolyzing pentafluorobenzonitrile with an acidic substance, typically an aqueous solution of sulfuric acid.
[0014]
Although the melting point of pentafluorobenzoic acid is about 100 to 102 ° C., when pentafluorobenzoic acid is heated at a temperature exceeding 40 ° C. in the presence of water, it becomes an oil at a temperature below the melting point and separates from the aqueous layer. In addition, since the solubility of pentafluorobenzoic acid in water is relatively small, about 1-2% by mass, when the oil layer and the aqueous layer are stirred, the oil layer is dispersed in the aqueous layer, and the pentafluorobenzoic acid in Inorganic or organic impurities are extracted into water.
[0015]
When pentafluorobenzoic acid is heated in the presence of water, the reason why it becomes oily and dispersed at a temperature below its melting point is not clear, but a small amount of water is dissolved in the pentafluorobenzoic acid layer. It is thought to be due to electrostatic properties due to the presence of fluorine atoms in fluorobenzoic acid.
[0016]
The amount of water used in the purification of the present invention is 0.5 to 20 times, preferably 1 to 15 times, more preferably 1.5 to 10 times the amount of pentafluorobenzoic acid. If the amount is less than 0.5 times by mass, not only a sufficient purification effect cannot be obtained, but the slurry concentration of pentafluorobenzoic acid deposited by cooling is too high, and handling becomes difficult. On the other hand, when it is more than 20 times by mass, the loss due to the dissolution of pentafluorobenzoic acid in water increases and the yield decreases.
[0017]
The temperature to heat is 40-40 degreeC normally, Preferably it is 45-95 degreeC, More preferably, it is 50-90 degreeC. At temperatures lower than 40 ° C., pentafluorobenzoic acid does not become oily, so an oily dispersion cannot be formed.
[0018]
According to the method of the present invention, usually, the above amount of water is added to pentafluorobenzoic acid, and the mixture is heated in the temperature range with stirring to disperse the pentafluorobenzoic acid in water.
[0019]
The holding time in the temperature range is a time that can sufficiently remove inorganic or organic impurities contained in pentafluorobenzoic acid, specifically, 1 to 150 minutes, preferably 10 to 120 minutes, more preferably 20 to 20 minutes. 90 minutes is sufficient.
[0020]
The operation of dispersing the pentafluorobenzoic acid in water may be normal pressure, increased pressure, or reduced pressure, but is usually performed under normal pressure. The temperature range is under normal pressure.
[0021]
The stirring may be performed so that a dispersion state suitable for extraction of impurities in pentafluorobenzoic acid into water is formed. Specifically, the Pv value (power of the stirrer (kw) / total amount of reaction solution (m 3 )) is 0.05 to 3 kw / m 3 , preferably 1 to 2 kw / m 3. .
One method for separating pentafluorobenzoic acid dispersed in water from water is a method in which the dispersion is cooled to precipitate pentafluorobenzoic acid, and the precipitate is separated by means such as filtration. In addition, since pentafluorobenzoic acid is dispersed in water and then allowed to stand, it is easily separated into an oil layer and an aqueous layer. Thus, purified pentafluorobenzoic acid may be obtained by separating the oil layer from the aqueous layer.
[0022]
In the cooling separation method, in cooling the dispersion, when the dispersion is cooled at a rate of 0.01 ° C./min to 5 ° C./min, or when precipitation of pentafluorobenzoic acid starts, this precipitation starts. Based on the temperature, the temperature of the dispersion is maintained in the temperature range of the precipitation start temperature ± 5 ° C. for the necessary time, specifically 1 to 150 minutes, preferably 10 to 120 minutes, more preferably 20 to 90 minutes. Or when the dispersion is cooled at a rate of 0.01 ° C./min to 5 ° C./min, and when precipitation of pentafluorobenzoic acid starts, the temperature of the dispersion is determined based on this precipitation start temperature. The required temperature, specifically 1 to 150 minutes, preferably 10 to 120 minutes, more preferably 20 to 90 minutes, should be maintained in the temperature range of the starting temperature ± 5 ° C. As a result, the filtration efficiency of the precipitate is improved, the liquid content of the precipitate (ratio of impurities such as sulfuric acid contained in the precipitate) is reduced, and high-purity purified pentafluorobenzoic acid can be obtained. When the cooling rate exceeds 5 ° C./min, pentafluorobenzoic acid crystals are not sufficiently grown, and as a result, the liquid content of the precipitate after filtration is increased, and the content of impurities is increased. For this reason, the filtration efficiency is lowered and the purity of the purified pentafluorobenzoic acid is lowered. When the cooling rate is lower than 0.01 ° C./min, it takes more time than necessary for precipitation of pentafluorobenzoic acid, which is not economical.
[0023]
As the water used in the present invention, so-called industrial pure water which can be used industrially can be used. On the other hand, the purified water contains impurities such as the aforementioned organic substances or inorganic substances that are removed by the purification method of the present invention, and as described above, pentafluorobenzoic acid is about 1 with respect to water. In order to dissolve -2% by mass, pentafluorobenzoic acid is contained at this level.
[0024]
Therefore, the purified water can be used repeatedly for the purification of pentafluorobenzoic acid within the range where the desired purity can be achieved, so that the dissolution loss of pentafluorobenzoic acid can be suppressed and the yield can be improved. It is advantageous and preferable. In this case, the concentration of organic or inorganic substances contained in water repeatedly used for purification is usually 20% or less, preferably 15% or less, and more preferably 10% or less.
[0025]
In addition, water containing a small amount of pentafluorobenzoic acid after separation of pentafluorobenzoic acid should be reused as water when preparing an acidic substance aqueous solution in the hydrolysis step when producing pentafluorobenzoic acid. Can do.
[0026]
【The invention's effect】
The present invention is a method for purifying fluorine-containing benzoic acid, characterized in that the fluorine-containing benzoic acid is heated and stirred in the presence of water, dispersed in water, and then separated from water.
[0027]
In other words, the above-described method for purifying fluorine-containing benzoic acid of the present invention includes a step of recrystallizing fluorine-containing benzoic acid using water, and is heated and stirred in the presence of water to be dispersed in water. And then purifying the fluorine-containing benzoic acid, which is separated from water.
[0028]
According to the purification method of the present invention, highly purified purified fluorine-containing benzoic acid can be obtained with a high yield. In particular, when fluorine-containing benzoic acid is dispersed in water and then separated by cooling, it can be separated from water with high filtration efficiency.
[0029]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0030]
<Reference Example 1>
A separable flask having a capacity of 500 ml equipped with a stirrer, a cooler and a thermometer was charged with 259 g of 70 mass% sulfuric acid, and then with stirring, 140 g (0.725 mol) of pentafluorobenzonitrile was added, and the internal temperature was adjusted to 160 ° C. The temperature was raised and the reaction was carried out for 12 hours under reflux with stirring at 400 rpm.
[0031]
After completion of the reaction, when the temperature of the reaction solution reached 155 ° C., 193 g of water was added to the reaction solution with stirring. When the reaction solution was cooled at a rate of 1 ° C./min after the addition of water, crystals began to precipitate when the temperature of the reaction solution reached 72 ° C. After the start of crystal precipitation, the reaction solution was held at 71 to 75 ° C. for 30 minutes and then cooled to 25 ° C. at a cooling rate of 1 ° C./min.
[0032]
The reaction liquid was filtered under reduced pressure using a filter paper (No. 2), and 167 g of crude pentafluorobenzoic acid crystals (filter cake) were obtained. When the purity of the crude pentafluorobenzoic acid was analyzed by liquid chromatography, the purity was 90.0% and the liquid content was 10.0% (sulfuric acid 3.3%, ammonium sulfate 1.1%, water 5.6%). It was.
[0033]
<Example 1>
167 g of the crude pentafluorobenzoic acid obtained in Reference Example 1 was charged into a separable flask having a capacity of 500 ml equipped with a stirrer, a cooler and a thermometer, 370 g of pure water was added, and the mixture was stirred at 400 rpm, and the temperature reached 70 ° C. The temperature was raised and held in the temperature range of 65 to 75 ° C. for 70 minutes. As a result, pentafluorobenzoic acid became oily and dispersed in water.
[0034]
Then, when it cooled at the cooling rate of 1 degree-C / min, the crystal | crystallization began to precipitate at 36 degreeC. Then, after hold | maintaining at 35-37 degreeC of internal temperature for 1 hour, it cooled to 20 degreeC with the cooling rate of 1 degree-C / min. Then, this liquid was filtered under reduced pressure using a filter paper (No. 2) to obtain 153 g of pentafluorobenzoic acid crystals (filter cake). The obtained purified pentafluorobenzoic acid was analyzed by liquid chromatography. As a result, the purified pentafluorobenzoic acid content was 96.0%, the liquid content was 4.0% (sulfuric acid 0.07%, ammonium sulfate 0.02%, water 3.9%). The purified pentafluorobenzoic acid having a liquid content of 4% was dried at 40 ° C. under reduced pressure to obtain pentafluorobenzoic acid having a purity of 99.8%.
[0035]
<Examples 2 and 3>
Example 1 except that the heating temperature range for dispersing the crude pentafluorobenzoic acid in water was changed to 50 ° C. ± 5 ° C. (Example 2) and 90 ° C. ± 5 ° C. (Example 3). In the same manner, purified pentafluorobenzoic acid was obtained. Table 1 shows the content (composition), liquid content, and purity after drying of the purified pentafluorobenzoic acid obtained.
[0036]
< Reference Example 2, Examples 4 and 5 > Example 1 except that the amount of water added in Example 1 was changed to 100 g ( Reference Example 2 ), 250 g (Example 4 ) and 500 g (Example 5 ). In the same manner, purified pentafluorobenzoic acid was obtained. Table 1 shows the content, liquid content, and purity after drying of the obtained purified pentafluorobenzoic acid.
[0037]
Example 6 Purified pentafluorobenzoic acid was obtained in the same manner as in Example 1 except that the cooling rate was changed. Table 1 shows the content, liquid content, and purity after drying of the obtained purified pentafluorobenzoic acid.
[0038]
Example 7 The same purified pentafluorobenzoic acid as obtained in Reference Example 1 was purified in the same manner as in Example 1 by reusing the purified filtrate obtained in Example 1.
[0039]
That is, 167 g of the crude pentafluorobenzoic acid obtained in Reference Example 1 was charged into a 500 ml separable flask equipped with a stirrer, a cooler and a thermometer, and 380 g of the purified filtrate obtained in Example 1 was added. Then, the temperature was raised to 70 ° C. while stirring at 400 rpm, and kept in a temperature range of 65 to 75 ° C. for 70 minutes. As a result, pentafluorobenzoic acid was in a liquid state and dispersed in water.
[0040]
Then, when it cooled at the cooling rate of 1 degree-C / min, the crystal | crystallization began to precipitate at 36 degreeC. Then, after hold | maintaining at 35-37 degreeC of internal temperature for 1 hour, it cooled to 20 degreeC with the cooling rate of 1 degree-C / min. Then, this liquid was filtered under reduced pressure using a filter paper (No. 2), and 156 g of pentafluorobenzoic acid crystals (filter cake) were obtained. Analysis by liquid chromatography revealed that the content of pentafluorobenzoic acid was 95.76% and the liquid content was 4.24% (sulfuric acid 0.18%, ammonium sulfate 0.05%, water 4.01%). It was found that the purified pentafluorobenzoic acid content obtained when pure water was used in No. 1 was almost the same, and the purified filtrate could be reused.
[0041]
<Comparative Example 1>
The crude pentafluorobenzoic acid cake obtained in Reference Example 1 was washed with 370 g of water without stirring. The results are shown in Table 1.
[0042]
<Comparative Example 2> The crude pentafluorobenzoic acid cake obtained in Reference Example 1 was purified by recrystallization from 400 ml of toluene. The results are shown in Table 1.
Reference example 3
In Example 1, purification was performed in the same manner except that the heating temperature range during purification was 28 to 32 ° C. The results are shown in Table 1. Pentafluorobenzoic acid did not become oily but could be purified.
[0043]
[Table 1]
Claims (1)
該精製方法は、ペンタフルオロ安息香酸を油状として水に分散させて冷却して析出させ、水から分離して精製する方法であり、ペンタフルオロ安息香酸を水の存在下に４０〜９５℃の温度範囲で加熱し、
該温度範囲での保持時間を２０〜９０分とし、
該精製の際に使用する水の量をペンタフルオロ安息香酸に対し、１．５〜１０質量倍とする
ことを特徴とするペンタフルオロ安息香酸の精製方法。General formula (1)
The purification method is a method in which pentafluorobenzoic acid is dispersed in water as an oil, cooled and precipitated, separated from water and purified, and the pentafluorobenzoic acid is heated at a temperature of 40 to 95 ° C. in the presence of water. Heating in range,
The holding time in the temperature range is 20 to 90 minutes,
A method for purifying pentafluorobenzoic acid , wherein the amount of water used in the purification is 1.5 to 10 times by mass with respect to pentafluorobenzoic acid .
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