PROCESS FOR THE PRODUCTION OF PEROXYACIDS

Abstract: Poorly soluble peroxyacids obtained by reacting a solid carboxylic acid substrate with an Caro's acide solution can suffer from impaired purity. The purity of the product can be improved by preparing the Caro's acid solution in two stages, the first stage having an intermediate acidity (A value) of below 0.5 and thereafter in the second stage, by the introduction of further sulphuric acid, its A value is increased to the operating value that is often between 0.7 and 0.8. The second stage can be effected immediately prior to contact or in the presence of the carboxylic acid substrate.

Description: Process for the production of peroxyacids The present invention relates to a process for the production of peroxyacids, particularly to the production of solid peroxyacids and more particularly to a process employing a particulate feedstock and acidic hydrogen peroxide. Peroxyacids as a class have a wide range of attractive properties, including being powerful oxidants, effective wide-spectrum biocides and effective bleaches under appropriately selected conditions, both for industrial applications and in the domestic environment. They are increasingly popular as their "green" qualities are recognised, such as being effective stain removers and biocides at low concentrations and at low temperatures. In a number of applications, for example in particulate compositions or as a dispersion in liquid formulations, it is desirable to employ the peroxyacids in solid form and consequently there remains a need for production processes that can yield solid peroxyacids. There have been a number of processes suggested for producing solid peroxyacids in which a suitably chosen substrate, such as in particular the corresponding carboxylic acid or less commonly related classes of compounds like anhydrides or acid halides, is reacted with an acidic solution of hydrogen peroxide. In some of them, the substrate is pre-dissolved in an acidic substrate. Early processes such as by W E Parker et al in a series of papers published in J Am Chem Soc, including JACS vol77, p 4037-41 (1955) and JACS vol 77, p1929-31 (1 957) predissolved the substrate in sulphuric or an organosulphonic acid into which aqueous hydrogen peroxide is introduced. Such processes are acceptable on a laboratory scale, but the evolution of heat in situ by either in situ formation of permonosulphuric acid or simply by the in situ dilution of the acid/peroxide mixture means that they are less acceptable on an industrial scale. The solubility of many, if not most, of the carboxylic acid substrates diminishes rapidly as the acid strength diminishes, so that it has been recommended and in practice adopted to employ concentrated acid as solvent, often of around 90% or higher w/w. Some other proposed processes have suggested the use of carboxylic acid substrate as a solid. Hutchins, in USP 41 19660 discloses a process for making aliphatic diperoxyacids of C1 2 to C20, which in fact are very poorly soluble even in acidic media, by preforming a mixture of hydrogen peroxide and sulphuric acid into which mixture is introduced powdered dicarboxylic acid. He advocates a sulphuric acid content which others have called an A value, of 69 to 82%. Bettle in a later USP 4314949 draws attention to the need to operate the peroxidation process safely to prevent it becoming uncontrollable and suggests using a particulate carboxylic acid and a liquid medium in a liquids to solid ratio of greater than 1 5: 1 and preferably greater than 30: 1 or 40: 1 . In a high shear mixer operated in a particular manner a ratio of 10: 1 can be operated, but even there a ratio of over 1 5: 1 is recommended. He too advocates a high sulphuric acid content of form 60 to 80%, preferably 70 to 77%. This is also apparent from Krimm, USP 2813896, who advocates using conditions and reaction mixtures such that at least 1 mol sulphuric acid remains at the end of the reaction to 6 mols of water. His examples disclose from 1 mol to 1 .5 - 3 mols. When this is translated into weight proportions, Krimm's lowest exemplified A value occurs in Example 3 at 60.3% and his highest in Example 4 is at 75.5%. The use of high concentrations of sulphuric acid to catalyse the peroxidation reaction of carboxylic acids is described by Y L Zherebin et al in Zorka, Vol 8, An, p41 -44 ( 1 972) where concentrated peroxide is employed to shift the equilibrium towards high degrees of conversion. A 20 fold molar excess of sulphuric acid over the carboxylic acid is stated to be optimum for dicarboxylic acids. In his experimental section, the weight proportion of sulphuric acid in his reaction mixture is about 70.8% (excluding the substrate). Subsequently, there have been other disclosures which have followed the earlier teaching to use high concentrations of sulphuric acid, but have introduced additional control requirements. Thus, for example Interox Chemicals Limited (now known as Solvay Interox Limited) N A Troughton et al describe a process in which the A value of the reaction mixture is kept at least constant or is increased during progressive addition of a solution of the carboxylic acid substrate to the reaction medium, final A values of 70 to 80% being contemplated and exemplified. In the course of studies leading to the present invention, the inventors have tried many variations on the general theme of reacting carboxylic acids with hydrogen peroxide in an acid catalysed environment. Hardly surprisingly, they found that some of the variations were more attractive than others, as shown for example by the yield or purity of the product. One aspect that had not hitherto been highlighted was that the purity of the resultant product, at least of certain diperacids was better if the substrate were introduced into the reaction medium in solution and worse if the same substrate were introduced in particulate form. When the carboxylic acid substrate is introduced as a solid into a liquid phase, the hydrogen peroxide and sulphuric acid components of the reaction mixture are typically pre-mixed, forming a Caro's acid solution. Such a solution contains peroxy-derivatives, primarily peroxymonosulphuric acid, water and residual concentrations of hydrogen peroxide and sulphuric acid. In accordance with known technology, the reaction forming the peroxy- derivatives tends towards equilibration at a rate determined by the prevailing conditions. The derivative-forming reaction is strongly exothermic and can be rapid and the ability to control it at point in the overall process separate from the reaction peroxidising the carboxylic acid has been seen as beneficial. In general, literature to date has paid regard merely to the total content of hydrogen peroxide and total content of sulphuric acid in the reaction mixture and has not sought to distinguish between hydrogen peroxide and any derivatives such as peroxymonosulphuric acid in the subsequent peroxidation of the carboxylic acid. Surprisingly, it has now been found that the manner in which a Caro's acid solution is produced can influence to a significant extent the resultant percarboxylic acid product. It is an object of the present invention to devise a process for the production of peroxyacids which can ameliorate the disadvantage of impaired purity that arises when a particulate substrate feedstock is employed . It is a further object of at least some preferred embodiments of the present invention to devise a process for producing peroxyacids employing a particulate substrate which can achieve a product purity similar to that obtainable from using a solution of the carboxylic acid substrate as feedstock. In accordance with the present invention there is provided a process for the production of a poorly soluble percarboxylic acid from a poorly soluble carboxylic acid in which i) a particulate carboxylic acid and a liquid reaction medium comprising a mixture of sulphuric acid, hydrogen peroxide and water having an A value of at least 0.6 are brought into contact with each other forming a reaction mixture, ii) the reaction mixture is agitated at a temperature of not greater than 50°C until at least some peroxycarboxylic acid has been formed, iii) where necessary at least a fraction of the percarboxylic acid is precipitated from the reaction mixture and optionally thereafter separated from the reaction mixture characterised in that the reaction medium is prepared in two stages, in the first stage of which the medium is produced having an A value of less than 0.6 and in the second stage in the presence of or immediately prior to contact with the particulate carboxylic acid further sulphuric acid is added to increase the A value of the medium by at least 0.05 A value units and attain an A value selected in the aforesaid range of at least 0.6. In the context of the present invention, poorly soluble indicates poor solubility in water at ambient temperature. A value is indicated as a proportion as an alternative to a percentage, eg 0.6 corresponding to 60%. By the operation of a two stage process for the preparation of the reaction medium, it has been found possible to improve the purity of the resultant percarboxylic acid product. It is believed that the two stage preparation method enables a reaction medium to be obtained, which, at the time when it takes part in the peroxidation reaction contains a higher proportion of sulphuric acid and hydrogen peroxide and a lower proportion of peroxymonosulphuric acid than would be the case in an equilibrium composition formed from the same amounts of sulphuric acid and hydrogen peroxide in a single stage. Notwithstanding the fact that peroxymonosulphuric acid is a more powerful oxidising agent than hydrogen peroxide, we believe that a higher proportion of hydrogen peroxide remains as such in the invention two stage method, and this appears to contribute to an improved extent of peroxidation of the carboxylic acid. It will be understood, however, that this explanation of our beliefs is given to assist the implementation of the invention without in any way limiting the invention, and successful operation of the present invention is not dependent upon the accuracy of the beliefs or explanation. The principle of the present invention is that in the first stage of preparing the reaction medium, the A value is chosen to be significantly lower than when the reaction with carboxylic acid occurs. Thus, in an alternative or additional characterisation of the invention process, the A value of the reaction medium in the second stage is often at least 0.10 and in a number of instances between 0.015 and 0.5 higher than in the first stage, and in many suitable embodiments is selected in the range of from 0.2 to 0.4. This can be achieved readily by selecting a sulphuric acid concentration in stage 1 (ignoring any derivative formation with hydrogen peroxide) of from about 40% to about 50% w/w, ie an A value of 0.4 to 0.5, and by separate addition of a concentrated sulphuric acid solution, normally greater than 80% w/w and often from 94 to 98% w/w into the reaction vessel the A value of the medium is increased in stage 2, preferably to the range of from 0.7 to 0.8 A value. The concentrated sulphuric acid solution can conveniently be added just prior to the introduction of the carboxylic acid substrate or alternatively at least a fraction of the sulphuric acid can be added in stage 2 simultaneously with the substrate during its the period of addition or even after all the substrate has been introduced. In practice, the process operator will so arrange his orders of addition of and instantaneous contents of reagents and organic substrate that the instantaneous composition does not pass inadvertantly into a hazadous range of compositions containing high substrate, high hydrogen peroxide and insufficient diluent (eg water). The proportion of hydrogen peroxide in the reaction medium at stage 2 is often selected within the range of from 5 to 25% w/w, and in many suitable embodiments is selected in the range of from 7 to 1 5 % w/w. In some embodiments, it is convenient for all of the hydrogen peroxide to be present in the reaction medium in stage 1 , in which case that the proportions of hydrogen peroxide in the medium will be proportionately higher in stage 1 than in eventual stage 2. The actual proportions of hydrogen peroxide in stage 1 self-evldently take into account the desired increase in A value in stage 2,, but for guidance purposes, in stage 1 the hydrogen peroxide content is often chosen in the range of 10 to 35% w/w, and particularly from 14 to 25% w/w. The total amount of hydrogen peroxide employed in practice is often calculated in order to provide a significant excess above the stoichiometric requirement of 1 mole per mole equivalent of carboxylic acid. In some embodiments, all of the hydrogen peroxide can be introduced in a single stage addition. In other embodiments, a fraction such as at least 40% and particularly from 40 to 75% of the desired total amount of hydrogen peroxide is introduced into the reaction medium at stage 1 and the remainder is introduced into the reaction mixture at a later stage. The introduction of the remainder or the hydrogen peroxide can precede, be concurrent with or even follow the introduction of the substrate or the second addition of sulphuric acid. In some desirable embodiments, the second fraction of peroxide addition is concurrent with or after the final stage of sulphuric acid addition. Hydrogen peroxide is preferably introduced at an equivalent mole ratio to the carboxylic acid, such as those listed hereinafter, of at least 1 .5: 1 , usually not more than 6:1 and more preferably from about 2: 1 to about 5: 1 . For dicarboxylic acid compounds, it will be recognised that the actual mole ratios are double those indicated herein above for diperoxidation of the compound, and as the mole ratio falls towards the lower preferred limit or lower end of the range, the extent of the unreacted carboxylic acid and monoperoxidised product each increases. The balance of the reaction medium is usually water or a dilute solution of the carboxylic acid substrate and/or of the percarboxylic acid product. The medium can contain, optionally, a small concentration of process additives, typically up to about 2% w/w, that can assist in the reaction or subsequent precipitation of product. The present invention is applicable to poorly soluble carboxylic acids with the formation of poorly soluble peroxyacids. Such compounds may be aliphatic, optionally substituted by or containing an embedded or terminal aromatic group and may also be aromatic and may contain embedded heteroelements, including specifically nitrogen. The carboxylic acids can be mono or dicarboxylic acids and generally contain from 8 to 30 carbon and heteroatoms (excluding the oxygen atoms in the carboxylic acid group or groups). Suitable aliphatic carboxylic acid substrates include linear or branched aliphatic monocarboxylic acids containing at least 10 and often not more than 18 carbons such as lauric acid, and α - ω dicarboxylic acids, usually linear, containing from 8 to 16 carbons such as dodecanedioic acid. Particularly suitable carboxylic acid substrates include the class obeying the general formula R-L-A-CO2H or R-(L-A-CO2H>2 in which R represents an aromatic group optionally substituted by an unreactive substituent, L represents an optional link group comprising an amido, imido or sulphonimido group, and A represents an aliphatic moiety optionally substituted by an unreactive substituent. The aromatic group R is conveniently benzene or may less commonly comprise a heterocyclic group, and the unreactive substituent can conveniently comprise an alkyl group such as methyl or t-butyl or a halo group such as chloro. The linking group L is conveniently an amido, (N in or N outwards pointing) imido or sulphonimido group. The aliphatic moiety A often contains from 1 to 10 carbons, and in a number of instances from 2 to 6 carbons and suitable non- reactive substituents include phenyl groups, optionally further substituted by an alkyl or halo group as for R. The invention is especially suited for reaction of carboxylic acids obeying the formula Ph-(CO-NX-A'-CO2)n in which n is either 1 or preferably 2, X represents preferably hydrogen or alternatively can be alkyl C1 to C1 2 or phenyl and A' represents a linear alkylene group containing from 2 to 10 and preferably 5 carbons. The amidoaliphatic acid substituents are preferably para to each other around the benzene nucleus and can alternatively be meta to each other. An especially suitable substrate comprises HO-CO-(CH 2 )5-NH-CO-C 6 H4-CO-NH-(CH 2 )5-CO-OH in which the substituents are meta or para to each other. The invention process is of particular applicability to the preparation of peracids that are substantially soluble under the prevailing conditions, in the selected sulphuric acid reaction medium such as one having an A value of between 0.7 and 0.75 at a carboxylic acid substrate to reaction medium weight ratio of about 1 :6 to about 1 :9, including the amido peracids in the immediately preceding paragraph. The process is correspondingly applicable to aliphatic diperoxyacids such as DPDDA at reaction temperatures encouraging substantial solubility in the reaction mixture. Such conditions can include reaction temperatures selected at the higher end of the range such as from 40 to 45°C, and liquor to substrate ratios of around 7.5: 1 to about 0: 1 . To the extent that the peroxyacid becomes less soluble under the prevailing selected reaction conditions, so that an increasing proportion of the product present as a solid phase in the reaction mixture before any quenching is undertaken, the advantages of the instant process become less marked by comparison with a conventional solid feed process. The peroxidation reaction is preferably conducted at a temperature of from about 5 to about 50°C and in many embodiments between about 10 and 35°C. The reaction is usually conducted by introducing the particulate substrate with agitation into the reaction mixture over a period of at least 5 minutes and in many instances up to 40 minutes. By the end of the period of introduction, we have found that a fraction of the carboxylic acid has reacted to produce percarboxylic acid product. Thereafter, the reaction is usually permitted to continue, to provide an overall reaction period, including the period of introduction of the substrate of at least 20 minutes and often up to about 4 hours. The overall reaction period is preferably chosen in the range of from about 30 minutes to about 2 hours. The reaction can be monitored by taking samples, analysing them for peroxyacid content and purity. It has been observed that the purity of the product will tend to reach a maximum as the reaction period lengthens and thereafter decline, though the point at which this reversal occurs will depend on the other operating conditions in the reaction mixture. Such monitoring permits product at or near optimum purity to be recovered. A further variable under the control of the process user is the weight ratio of liquids to solids in the reaction mixture, a ratio that is sometimes alternatively referred to herein as the liquor to substrate ratio. In many embodiments according to the present invention the ratio is chosen in the range of from about 4: 1 to 10: 1 and often is from about 6: 1 to about 8: 1 . A higher ratio than 10: 1 is usable at the discretion of the producer, though normally not more than about 20: 1 and indeed may be desirable in order to produce a reaction mixture with little or no residual solids, under conditions that relatively adverse to solubility, such as a substrate having relatively poor solubility and/or a lower reaction temperature and/or a medium with lower A value within the aforesaid ranges. At the end of the reaction, the physical state of the product depends on the inherent solubility of the peroxyacid, its concentration and the temperature and acidity of the reaction mixture. At least a fraction remains in solution, and in some instances, particularly ata selected A value in the range of about 0.7 to about 0.8 for the aforementioned preferred peroxyacids of formula Hθ3C-(CH )5-NH-CO-C6H4-CO-NH-(CH2)5-Cθ3H in which the substituents are meta or para to each other, all the product is in solution. The process of the present invention is particularly applicable to those combinations of substrate/product selection and concentration and reaction mixture conditions selected within the ranges disclosed herein before in which there are no discernible solids in the reaction mixture. In order to form solid product or increase the proportion of solid product, it is often convenient to induce further precipitation. This can be achieved by either cooling the reaction mixture, preferably by at least 5 to 20°C or by reducing the A value of the reaction mixture by dilution. Both methods can be combined by quenching the mixture with cold water or preferably iced water or ice, often adding at least half the weight of the reaction mixture. In some especially preferred embodiments, the amount of quench water/ice is selected such that the A value of the quenched reaction mixture is within the range of about 0.4 to about 0.6, whereby after the introduction of the desired amount of hydrogen peroxide, the resultant solution accords with the compositions prepared in stage 1 of the Caro's acid solution. Advantageously, in these embodiments, the maximum amount of the spent sulphuric acid phase can be recycled with consequential minimum loss or need for sulphate recovery from the spent liquor. The present invention process is particularly suited for batch operation, though continuous operation, for example, in a flow-through reactor equipped with multiple inlet injection points can be contemplated. The solid peroxycarboxylic acids that are produced by the invention process are suitable for a wide range of applications, including incorporation in particulate washing compositions or dispersed in liquid formulations to impart stain bleaching and disinfectant properties at low wash temperatures or in disinfectant compositions. Having described the invention in general terms, specific embodiments thereof will herein be described more fully by way of example. Comparison 1 In this comparison, a particulate carboxylic acid substrate, terephaloyl- diamidocaproic acid, TOCAP, was reacted with a Caro's acid reaction medium produced in one stage by mixing and cooling concentrated sulphuric acid (98% w/w, 45.4) and aqueous hydrogen peroxide (35% w/w, 21 .9g) for 20 minutes at about ambient temperature. The resultant solution had an A value of 0.727 and a temperature of 24°C. The particulate substrate ( 10.01 g) was introduced into the reaction medium with continued stirring over a period of 1 7 minutes providing a liquid:solid ratio of 6.86: 1 and a mole ratio of hydrogen peroxide:substrate of 8.8: 1 . The reaction was allowed to continue for a further 2 hours with continuous stirring at about 20°C and samples of product were taken at half hourly intervals. Each sample comprised withdrawing a small volume of the reaction mixture, quenching it with iced water and washing the solids to pH 3. Samples of the product were taken at intervals and analysed for peracid avox content by a standard method in which a sample is dispersed in methanol/glacial acetic acid containing iron, sodium iodide solution is added and the liberated iodine is titrated against sodium thiosulphate. Immediately after addition of the substrate was completed, extracted sample of the resultant peracid had a purity of 69.9%, ie a peracid avox content that was 69.9% of the theoretical avox of 1005 pure diperoxyacid. Later taken samples were analysed as 69.3% after 1 hour and 61 .3% after 2 hours. A solid product was recovered from the reaction mixture by quenching to an A value of below 0.5. The yield of recovered, washed and dried solid product was 10.21 g. Example 2 In this Example, a further sample of the substrate TOCAP employed in Comparison 2 was reacted with a reaction medium having a similar A value and using the same amounts of reaction medium and of substrate, but using a reaction medium that had been produced in two stages. In the first stage, concentrated sulphuric acid (98% w/w, 30.8g) and aqueous hydrogen peroxide (35% w/w, 43.8g) were mixed together plus ice (3.12g), with cooling to produce a liquid medium having an A value of 0.486 and a final temperature of 1 5°C. This was transferred into a reaction vessel together with additional sulphuric acid (98% w/w, 60. Og) over 10 minutes to produce a reaction medium having an A value of 0.725 at approximately ambient temperature, between about 20 and 25°C. The particulate substrate (20g) as immediately introduced into the reaction medium with stirring over a period of 20 minutes, whilst maintaining approximately the same temperature. The reaction mixture had a weight ratio for liquids:solids of 6.86: 1 and the mole ratio of hydrogen peroxide:substrate of 8.8: 1 . A sample of the product was withdrawn from the reaction mixture 30 minutes after the addition of the substrate was complete when the reaction mixture was a clear solution and solids were obtained and analysed in the same way as for Comparison 1 . It was found that resultant product had a purity of 80.4%. The reaction continued to be stirred at ambient temperature for a further 2 1 /2 hours, and samples taken at regular intervals. The purity of the product remained similar initially, measuring 80.8% after a further hour but then declined gradually. It will be seen by comparing the product of Example 2 with that of Comparison 1 , that the invention process resulted in a markedly purer product. Example 3 In this Example, the process of Example 2 was followed using the same amount of substrate TOCAP, except that in the first stage of reaction medium preparation, the amount of sulphuric acid (98%) was 10.85g, and the amount of hydrogen peroxide solution (70%w/w) was 9.91 g, producing with ice (10.85g) a solution having an A value of 0.431 . In stage 2, the amount of sulphuric acid (98% w/w) added was 28.39g, producing an A value of 0.725. Immediately afterwards, the TOCAP was mixed into the stirred reaction mixture over a period of about 5 minutes providing a liquid:solids ratio of 6: 1 and a peroxide:substrate mole ratio of 8: 1 . The mixture was allowed to react for a further 45 minutes. A sample of product was then obtained and analysed in the same way as for the Comparison. The product had a purity of 88.2%. By comparing this result with that of Example 2, it can be seen that a product of even higher purity than that of Example 2 can be obtained, despite a reduction from 8.8: 1 to 8: 1 of peroxide:substrate mole ratio, a reduction which would have been expected to reduce purity. It indicates that the additional reaction period was beneficial. Example 4 In this Example, the process of Example 3 was followed, except that the order of the reaction was changed. The substrate TOCAP was added to the first stage reaction medium at 12°C and immediately afterwards the second stage addition of sulphuric acid then occurred . The product sample was taken 20 minutes after all the reagents had been added . The resultant product had a purity of 88.6%, which is extremely similar to the purity in Example 3, indicating that the relative timing of addition of the substrate and the second addition of sulphuric acid is not crucial, but confirming that the benefit is maintained by separating the Caro's acid preparation into two stages. Example 5 In this Example, the process of Example 4 was modified in that the addition of hydrogen peroxide was divided into two equal fractions, half being employed in the first stage preparation of the reaction medium and half being introduced into the reaction mixture after the second stage addition of sulphuric acid. Throughout the additions of substrate TOCAP, sulphuric acid and hydrogen peroxide into the reaction mixture, the temperature was maintained at about 23 - 25°C. Although the total amounts of reagents were the same as in Example 4, the delayed introduction of half of the hydrogen peroxide meant that the A values of the reaction medium differed in the first stage, being 45.9 and immediately after the second stage sulphuric acid addition, being 74.6, but after the second half of the peroxide had been added , the A value was 72.5, ie substantially the same as in Example 4. The reaction mixture was allowed to react for a further 30 minutes after the hydrogen peroxide had been added, and the product sampled had a purity of 88.3%. By comparison with the preceding Examples, it can be seen that benefit of preparing the reaction medium in two stages was confirmed. Example 6 In this Example, the process of Example 4 was followed, but employing a different ratio of liquor to solids. The starting Caro's acid solution employed was made using 1 9.41 g 98% sulphuric acid, 5.64g water and 9.91 g 70% hydrogen peroxide. This meant that the liquor to solid ratio in the reaction mixture was 4: 1 . A sample taken about 30 minutes after the end of the substrate addition had a purity between 83 and 84%. By comparison with Example 4, it will be observed that the purity is assisted by a higher liquor to solid ratio, but the result is still markedly higher than for a conventional solid feed process of comparison 1 . Example 7 In this Example, the process sequence followed the sequence described in Example 4, but using slightly different liquor to solid ratio , peroxide to substrate ratio and a different substrate. The initial Caro's acid solution was made from water, (7.2g) sulphuric acid (98%w/w, 7.7g) and H2O2 (85% w/w, 4.5g) . The substrate that was introduced into the Caro's acid solution was 5g of ground, particulate meta- phthaioyl diamidocaproic acid, and in the subsequent addition of sulphuric acid, 1 5g 98% acid was added. A sample taken at the end of the addition of the sulphuric acid was analysed as approximately 91 % pure. This Example confirms that the invention process is applicable to the formation of metaphthaloyl diamidopercaproic acid. Example 8 In this Example, the invention process was employed in respect of the preparation of an aliphatic diperoxyacid. The reaction sequence followed was similar to that employed in Example 4. A Caro's acid solution was obtained from sulphuric acid (98%, 21 .4g), hydrogen peroxide, (85% w/w, 6.05g) and water (9.79g) and heated to about 45°C. Dodecanedioic acid (5g) that had been ground to below 125μ diameter was introduced into the reaction mixture within seconds and stirred, then sulphuric acid (98%, 15g) was introduced slowly over a period of 15 minutes with constant stirring, the reaction temperature being maintained at 45°C. A sample of product was taken for analysis straightaway and after a further 30 minutes reaction at the same temperature. The first sample had a purity of nearly 95% and the sample after 30 minutes had a purity of over 98%. This demonstrates that the present process has made most acceptable diperoxydodecandioic product under the conditions of the Example.

Claims: Claims:- 1 A process for the production of a poorly soluble percarboxylic acid from a poorly soluble carboxylic acid in which i) a particulate carboxylic acid and a liquid reaction medium comprising a mixture of sulphuric acid, hydrogen peroxide and water having an A value of at least 0.6 are brought into contact with each other forming a reaction mixture, ii) the reaction mixture is agitated at a temperature of not greater than 50°C until at least some peroxycarboxylic acid has been formed, iii) where necessary at least a fraction of the percarboxylic acid is precipitated from the reaction mixture and optionally thereafter separated from the reaction mixture characterised in that the reaction medium is prepared in two stages, in the first stage of which the medium is produced having an A value of less than 0.6 and in the second stage in the presence of or immediately prior to contact with the particulate carboxylic acid further sulphuric acid is added to increase the A value of the medium by at least 0.05 A value units and attain an A value selected in the aforesaid range of at least 0.6. 2 A process according to claim 1 characterised in that the reaction medium prepared in stage 1 has an A value of from 0.4 to 0.5. A process according to either claim 1 or claim 2 characterised in that the difference in A value for the reaction medium in stages 1 and 2 is from 0.1 5 to 0.30. A process according to any preceding claim characterised in that the second stage addition of sulphuric acid is made in the presence of at least part of the substrate. A process according to any preceding claim characterised in that the reaction takes place at a temperature in the range of 20 to 30°C. A process according to any preceding claim characterised in that the reaction mixture has an initial liquids:solids ratio of from 6: 1 to 8: 1 . A process according to any preceding claim characterised in that the hydrogen peroxide is introduced into the reaction mixture in two fractions, the first fraction of at least 40%, preferably from 40 to 75% in the first stage and the second fraction in a subsequent stage. A process according to claim 7 characterised in that the second fraction of hydrogen peroxide is added simultaneously with or after the final addition of sulphuric acid to the reaction mixture. A process according to any preceding claim characterised in that the carboxylic acid substrate satisfies the general formula R-L-A-CO 2 H or R-(L-A-CO 2 H) 2 in which R represents an aromatic group, L represents a group comprising an amido, imido or sulphonimido group, and A represents an aliphatic moiety. A process according to claim 9 characterised in that the carboxylic acid substrate satisfies the formula Ph-(CO-NH-A'-CO2)2 in which n is either 1 or preferably 2, and A' represents a linear alkylene group containing from 1 to 10 carbons. A process according to claim 10 characterised in that A' in the formula represents a pentamethylene group. A process according to any preceding claim characterised in that the hydrogen peroxide is employed in a mole ratio to the carboxylic acid substrate at a mole ratio of at least 1.5: 1 . A process according to claim 1 characterised in that the substrate is selected such that the resultant peroxyacid is substantially completely soluble in the reaction mixture at the prevailing reaction temperature and at the selected ratio of liquor to substrate when all the reaction medium has been introduced into the reaction mixture. A process according to claim 12 characterised in that the substrate is an aliphatic dicarboxylic acid, the reaction temperature is at least 40°C and the liquor to substrate weight ratio is about 7.5:1 to about 10:1. RECTIFIED SHEET (RULE 91) ISA/EP A process for producing a peroxyacid substantially as described herein with respect to any example or substantially as described herein with respect to any novel feature or novel combination of features. RECTIFIED SHEET (RULE 91) ISA/EP

Inventors: CARR GRAHAM, JAMES ALUN PRYCE, MCADAM JOHNATHAN, CARR, GRAHAM, JAMES, ALUN, PRYCE, MCADAM, JOHNATHAN
Applicants: CARR GRAHAM, JAMES ALUN PRYCE, MCADAM JOHNATHAN, SOLVAY INTEROX LTD, CARR, GRAHAM, JAMES, ALUN, PRYCE, MCADAM, JOHNATHAN, SOLVAY INTEROX LIMITED
Application year: 1995
Main classification: C07C409
IPC codes: C07C407, C07C409