Process for purifying phthalimidoperoxycaproic acid (PAP) which removes chlorinated solvent impurities from it

Abstract: Process for purifying phthalimido-peroxycaproic acid (PAP) from chlorinated solvents, by dissolving it in a polar and volatile solvent selected from alcohols, ketones and aliphatic esters, and a following crystallization thereof and solvent stripping. Preferred solvents are aliphatic esters, in particular ethyl acetate.

Description: The present invention relates to a process for purifying phthalimido-peroxycaproic acid (PAP) from the impurity constituted by the chlorinated solvents used in the synthesis and entrapped inside PAP crystal lattice. More in particular, the present invention relates to a process for purifying PAP in which the chlorinated solvents, which constitute the impurity, are removed by means of a solvent showing particular characteristics. FR-A-2385697 describes an improved process for preparing peroxycarboxylic acids by oxidation of the corresponding carboxylic acids with oxygen peroxide in a strong acid. The improvement consists in reducing the reaction time by adding to the reaction mixture an inert solvent, which is not soluble in water and has a scarce solvent capacity for the starting acid, while it is a good solvent for the peroxyacid. For this purpose, methylene chloride is particularly suitable. The process for preparing PAP is known from European Patent Application No. 490,409. According to this process, phthalimido-caproic acid (PAC) is converted into peroxy acid, by means of H₂O₂ , in the presence of a strong acid, in a double phase system, in the presence of an organic solvent constituted by a halogenated aliphatic hydrocarbon selected from dichloromethane and trichloromethane The resulting PAP is recovered from the organic phase by low-temperature crystallization, or solvent removal under vacuum (stripping). By means of analyses of the end products (PAP) (gaschromatography, x-ray fluorescence), the presence of the chlorinated solvents used for the synthesis, was determined. PAP crystals contain such entrapped solvents in an amount comprised within the range of from 500 to 2,500 ppm. It is known that the halogenated aliphatic compounds are toxic and potentially carcinogenic; they may consequently create pollution problems. Therefore, the content of chlorinated solvents entrapped inside PAP should advisably be reduced down to an extremely low level in all products designed for consumers' usage. Such a reduction or removal is recommended in the case of industrial use of PAP as a bleaching agent in medium-low temperature detergent compositions. The purpose of the present invention is hence of providing a process which can be performed at an industrial level, in order to eliminate the impurities constituted by the chlorinated solvents entrapped inside the crystal lattice of PAP, obtained according to the process as disclosed in European Patent Application No. 490,409. The present Applicant found now that the use of a solvent, used after the synthesis of PAP and showing particular characteristics, makes it possible the chlorinated solvents present inside PAP's crystal lattice, also at an industrial level. Therefore, the subject-matter of the present invention is a process for purifying phthalimido-peroxycaproic acid (PAP) from chlorinated solvents, by dissolving said PAP and subsequent crystallization and evaporation of the solvents (stripping), characterized in that said PAP is dissolved in a polar and volatile solvent, selected from the group consisting of alcohols, ketones and aliphatic esters. More in particular, an object of the present invention is a process for purifying PAP from chlorinated solvents by means of a dissolution thereof and subsequent crystallization or evaporation of solvents (stripping), characterized in that said PAP is dissolved in a solvent belonging to the class of aliphatic esters. The choice of the solvent used for PAP purification according to the present process is critical. The solvents suitable for the purposes of the present invention must meet the following requisites: -- they should be good solvents for PAP and for the chlorinated solvent used in the synthesis and entrapped inside the crystals of the obtained PAP; -- they should display good volatility, in order to facilitate the removal of the solvent from the peracid, which volatility however should be not excessively high, in order to jeopardize a possible industrial use teherof; -- they should be not toxic, in order to prevent that a further toxic solvent is entrapped inside PAP crystal; -- they should be completely inert towards the peracid, and display an extremely good oxidation resistance, because the residual traces of solvent used (from 100 to 800 ppm) remaining inside the end product, or of its oxidation products, could, besides creating safety problems, remain inside the peracid crystals, reducing the stability thereof (for example, esters, when into contact with oxygen, form peroxides). The used solvents, which meet the above mentioned requisites, required by the process according to the present invention, are polar and volatile solvents. In particular, these solvents are aliphatic esters, such as methylacetate and ethylacetate. Preferred solvent is ethylacetate. The ratio, by weight, of the peracid and the solvent used in order to dissolve it according to the process of the present invention is determined by the solubility of the peracid in the solvent, and preferably is comprised within the range of from 1:2 to 1:8. When aliphatic esters are used as solvents, this ratio is preferably comprised within the range of from 1:3 to 1:6. The temperature at which the subject process is carried out, is lower than 40°C, in order to prevent peracid decomposition. In the process according to the present invention, the crystallization or the solvents evaporation (stripping) may take place both in the precence and in the absence of demineralized water. The peracid is separated in crystal form. The PAP obtained according to the process of the present invention contains less than 3 ppm of chlorinated solvents. PAP deprived of the chlorinated solvents is stable, in particular when as the solvent in the process according to the present invention, aliphatic esters are used. According to a preferred embodiment, PAP containing the impurity constituted by a chlorinated solvent is dissolved in a solvent belonging to the class of aliphatic esters, and the purification is carried out by using methodologies known in the art, at a temperature lower than +40°C. In order to better understand the present invention and to practice it, some illustrative, examples are reported in the following. EXAMPLES 1 - 4 50 g of PAP was dissolved in each of the solvents reported in following Table 1, at a temperature lower than +40°C. So dissolved PAP was treated by means of well-known methodologies [(a) and (b)] in order to recover PAP practically free from chlorinated solvents. (a) According to the crystallization methodology, dissolved PAP was recrystallized at the temperature of 0°C. The resulting crystals were filtered off from the suspension, and were subsequently dried in a desicator (CaCl₂) for 24 hours at the temperature of +25°C, under vacuum. (b) According to the stripping methodology, dissolved PAP was fed, either continuously or batchwise, to a reactor, or to the kettle of a rotary evaporator, at a temperature lower than +40°C. PAP solution was kept at this temperature under such a residual pressure as to cause the evaporation of the solvent. The peracid was subsequently filtered off, was dried inside a desiccator (CaCl₂) under vacuum for 24/48 hours at room temperature. The operations carried out with the above disclosed [(a) and (b)] methodologies were carried out both in the presence (Examples 2 and 4) and in the absence of demineralized water (Examples 1 and 3). The process conditions and the results obtained are reported in Table 1. EXAMPLES 5 - 6 The operating modalities of Examples 1-4 were repeated, however using, as the solvent in PAP purification, an alcohol (ethanol) and a ketone (acetone). Stripping and crystallization were carried out in the absence of H₂O. The operating conditions and the results obtained are reported in Table 2. Stability of purified PAP The thermal stability of purified PAP was determined by DSC (differential scanning calorimetry) according to ASTM method No. E-537-84 using a PERKIN-ELMER DSC-2C instrument, as well as the loss of peroxide content (%) of said purified peroxid acid. In order to determine this loss, the tests (A) and (B) were carried out. According to test (A), 10 g of purified PAP were stored inside a tightly ceiled container, for 30 days at +25°C. According to test (B), 0.3 g of purified PAP were stored as a suspension in an inert hydrocarbon (diisopropylbenzene) for 1 hour at +70°C. The results obtained by examining PAP purified according to Examples 1-6 are reported in following Table 3. The data reported in Table 1, 2 and 3 demonstrate that the process according to the present invention removes the impurity constituted by dichloromethane from PAP. The PAP obtained by using the aliphatic esters as the solvent of the process according to the present invention, is very stable. EXAMPLE 7 (comparison example) The hexane used for comparison purposes would be capable of dissolving the chlorohydrocarbon impurity entrapped inside PAP crystals, but does not dissolve said PAP and therefore does not meet the requisites required by the solvent to be used in the process according to the invention. The operating modalities of Examples 1-4 were repeated using n-hexane as the solvent, and separating PAP by stripping at the temperature of +37°C. The residual pressure was of 20 mm Hg . The operating conditions and the results obtained are reported in Table 4. The data shown in Table 4 demonstrate that dichloromethane was not removed from PAP, therefore the purification did not occur.

Claims: Process for purifying phthalimido-peroxycaproic acid (PAP) from chlorinated solvents, by dissolving said PAP and subsequent crystallization and evaporation of the solvents (stripping), characterized in that said PAP is dissolved in a polar and volatile solvent, selected from the group consisting of alcohols, ketones and aliphatic esters. Process according to claim 1, characterized in that said solvent is an aliphatic ester. Process according to claim 1 or 2, characterized in that said solvent is ethyl acetate. Process according to any of the preceding claims, characterized in that the ratio of the peracid to the solvent is comprised within the range of from 1:2 to 1:8 by weight. Process according to claim 4, characterized in that the ratio of the peracid to the solvent is comprised within the range of from 1:3 to 1:6 by weight. Process according to any of the preceding claims, characterized in that the temperature at which the process is carried out is lower than +40°C.

Inventors: CAVALLOTTI CLAUDIO, GARAFFA ROBERTO, TROGLIA CLAUDIO, CAVALLOTTI, CLAUDIO, GARAFFA, ROBERTO, TROGLIA, CLAUDIO
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1993
Main classification: C07D209
IPC codes: C07D209, B01D11