Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-03-14
2002-03-26
Solola, T. A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06362347
ABSTRACT:
The present invention relates to a process for recovering phthalides from as-obtained phthalide synthesis reaction mixtures.
Phthalides, i.e., substituted lactones of 2-(hydroxymethyl)benzoic acid, and phthalide itself (isobenzofuran-1(3H)-one) are required especially as intermediates for the synthesis of crop protection agents or drugs.
Various processes for preparing phthalides are known. Phthalides are predominantly prepared by means of electrochemical processes, by homogeneously or heterogeneously catalyzed hydrogenation.
DE-A 21 44 419 describes a process for the electrochemical preparation of phthalide. An aqueous solution of ammonium phthalamate is cathodic ally reduced at electrolysis temperatures of up to 65° C. over metals having a hydrogen overpotential greater than that of copper. High purity lead in particular is used as cathode material. To work up, any excess ammonia and solvent and some of the water are distilled off. A solution of the primary reaction product, the ammonium salt of o-aminomethylbenzoic acid, is left behind and is treated with a strong acid to precipitate phthalide. The phthalide is isolated by filtration. Product still in solution can be extracted with benzene. The product obtained can be further purified by recrystallization from hot water.
DE-A 25 10 920 describes a process for electrochemical preparation of phthalide. An ammoniacal aqueous solution of phthalic anhydride or acid is cathodically reduced at up to 100° C. over metals having a hydrogen overpotential greater than that of copper. The reaction mixture is worked up by distilling any excess ammonia and/or water out of the electrolysis mixture to separate off the phthalide and acidifying the residue at from 35 to 100° C.
Prior DE-A 196 18 854, unpublished at the priority date of the present invention, describes a process for preparing phthalides by cathodic reduction of phthalic acid derivatives. Reduction is carried out in an organic solvent comprising less than 50% by weight of water in an undivided electrolysis cell. It is stated that the workup can be effected by distillation, precipitation or recrystallization. In addition, the phthalides can be dissolved in ammoniacal aqueous solutions, then the aqueous phase separated off and the phthalide reprecipitated by acidification of the aqueous phase. The exemplified workup involves distillative removal of the solvent mixture and vacuum distillation of the phthalide.
The distillation has to be carried out at a high temperature level in the region of the boiling point of the phthalides, so that the product is subjected to considerable thermal stress for a prolonged period. In addition, distillation is not in all cases suitable for obtaining a pure phthalide. Specifically in the case of the electrochemical preparation of phthalides starting from methyl phthalates, unconverted methyl phthalates and phthalide form an azeotrope which cannot be separated by distillation. If the proportion of methyl phthalate remaining in the product is to be minimized by the way the reaction is conducted, the phthalide yield decreases and other, secondary products can appear.
Recrystallizing the phthalides involves dissolving them in a solvent and cooling the solution to crystallize them out again. It is thus necessary to provide a solvent and to separate it again from the pure phthalide at some inconvenience. Handling the solvent in a closed-loop system requires complex processing technology. After the crystallizate has been separated from the mother liquor, the mother liquor has to be concentrated in order that it may be further processed. The product obtained may include residual solvent, which has to be removed by drying.
It is an object of the present invention to provide a process for recovering phthalides from as-obtained phthalide synthesis reaction mixtures without the disadvantages of existing workups. More particularly, the process shall not require the use of solvents or of other assistants, shall keep the thermal stress on the phthalides to a minimum and shall be economical to carry out in energy terms.
We have found that this object is achieved according to the invention by a process for recovering phthalide from an as-obtained phthalide synthesis reaction mixture by
(a) distilling compounds having a boiling point below the boiling point of the phthalide from the reaction mixture, provided such compounds are present in the reaction mixture, to obtain a crude phthalide as bottom product,
(b) crystallizing the phthalide from a melt of the crude phthalide.
The phthalide is crystallized from a melt of the crude phthalide, i.e., without use of other solvents or other assistants, as required, for example, for a recrystallization.
The solvent-free crude phthalide is in turn obtained from the reaction mixture by distillative removal of compounds having a lower boiling point than the desired phthalides. If such compounds are present in the reaction mixtures, they are thus removed by distillation prior to the crystallization. The bottom product of the distillation is a crude phthalide, and the thermal stress involved in removing the low boiling compounds is considerably less than the thermal stress that would be involved in an additional, subsequent distillation of the phthalide. The crude phthalide used for the crystallization is thus substantially or, preferably, completely free from solvents or lower boiling compounds.
In one embodiment of the invention, the crystallizing is effected on a cooled surface on which the crystals grow.
So the liquid crude phthalide is brought into contact with a cooling surface, and phthalide crystals are formed thereon. On completion of the crystallization phase, the remaining liquid (mother liquor) is removed. The purity of the phthalide crystals remaining on the cooling surface can be increased by partially melting off (sweating) comparatively impurer portions of the crystals. In addition, the purity of the crystals on the cooling surface can be increased by washing, for example with the crude phthalide feed or with liquid phthalide of higher purity. Finally, the purified crystals are liquefied by heating, and the resulting melt of the pure phthalide is removed from the cooling surface.
The cooling surface where the crystallization is carried out is not subject to any restriction; it may have any desired suitable shape. The temperature of the melt during the crystallization is preferably within the range from −10 to 75° C., particularly preferably within the range from 20 to 70° C. The solids content in the crystallizer is customarily within the range from 10 to 90 g, preferably within the range from 30 to 80 g, per 100 g of crude phthalide feed.
The crystallization can be carried out continuously or batchwise, in one stage or in a plurality of stages.
The crystallization on the cooled surface can be carried out as a static crystallization or as a dynamic layer crystallization. In the first case, the crude phthalide melt used is stationary. Such a static crystallization process is available for example from BEFS/Prokem (France) or from Sulzer Chemtech (Switzerland). In a dynamic layer crystallization, the melt of the crude phthalide is subjected to forced convection. Such a process is available for example from Sulzer Chemtech (Switzerland). In both process variants, the cooled surfaces are disposed inside the crystallization apparatus, so that the crystals which form are immobilized inside the apparatus. Preference is given to the use of a static crystallization, where the melt of the crude phthalide is stationary and only natural convection occurs.
The advantage of this process is that the product is subjected to only a very low thermal stress and that the temperature level required is low, keeping the energy requirement relatively low. The separation of crystals from the mother liquor can be effected without additional equipment requirements.
The crystallization on a cooled surface is preferably effected in multiple stages as a fractional crystallization. Fractional crystallization can also be employed in the ca
Baumann Dieter
Hannebaum Heinz
Pütter Hermann
BASF - Aktiengesellschaft
Keil & Weinkauf
Solola T. A.
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