FR2689506A1 - Elimination of prim amine(s) from commercial di:phenylamine - by treatment with a sulphonic acid cation exchange resin - Google Patents

Abstract

Prim. amines, such as aniline, 4-amino biphenyl (4-ABP) and 2-amino biphenyl (2-ABP) are eliminated from commercial grade diphenylamine (I) by the following process: (a) a soln. of (I) in an organic solvent is contacted with a cationic ion exchange resin carrying sulphonic acid gps., in the presence of up to 3% water, (b) the resin and the soln. are sepd., the purified (I) remaining in the soln. USE - (I) is used as an antioxidant to protect fruits such as apples and pears during storage against scald and fungal attack. The commercial grades of (I) may contain carcinogenic and suspected carcinogenic impurities at levels above those deemed acceptable by the World Health Organisation.

Description

The present invention relates to ion exchange purification of diphenylamine ("DPA") which is a secondary amine, and the resulting purified product. More specifically, it relates to the purification of technical grade DPA (including formulations containing
Technical grade DPA) contaminated with various by-products, including primary amines such as aniline, 4-aminobiphenyl ("4-ABP") and 2-aminobiphenyl ("2
ABP ").

 DPA is widely used in post-harvest treatments as an antioxidant to protect fruits such as apples and pears during a long cold storage life from the physiological disease called scald. DPA is also endowed with fungicidal activity. It is often formulated as an emulsifiable concentrate which, after dilution with water, can be used as it is or in combination with waxes, the fruits being immersed in the liquid so that they are covered with a protective layer.

The commercially available "Technical Quality" DPA contains a number of byproducts (such as acridine, aniline, quinoline, indole, 4-ABP and 2-ABP) that are inherent in production process. Processes for producing DPA are taught in the literature; for example, see Kirk-Othmer Encyclopedia of Chemical Technology for an overview of these processes in the section describing the production of aromatic diarylamines. Several of the by-products mentioned above pose a toxicological problem, in particular 4
ABP which is a recognized carcinogenic compound. Aniline and 2-ABP are also suspected in this respect, so it is important to remove these impurities to as low a level as possible to reduce the danger to human health when consumed fruits thus treated with DPA.

Although the purification of technical grade DPA can be carried out by well known techniques such as distillation or recrystallization, these methods involve great expenditure of energy for heating and cooling. The object of the present invention is to find a more efficient method for the selective removal of impurities posing a toxicological problem. The guidelines for these impurities are being reviewed with the organization
World Health, but regulatory limits for impurities are expected to be set at a maximum of 0.5 milligrams / kilogram ("mg / kg") for 4-ABP and at a maximum of 2 mg / kg both for 2-ABP and for aniline. Another aim of the present invention is therefore to find a process for producing a purified DPA, of quality for food, including the levels of aniline, of 2
ABP and 4-ABP are well below regulatory limits.

 To the knowledge of the Applicant, there is no literature revealing the use of ion exchange resins for the purification of DPA.

 The invention provides a process for the selective removal of primary amines from DPA, wherein (1) a solution containing DPA and an organic solvent is contacted with a cation exchange resin carrying sulfonic acid groups functional in the presence of up to about 3 percent water, based on the weight of the solution, and (2) the resulting purified solution is then separated from the resin. This operation can be carried out according to a continuous procedure by passing the DPA solution over a column containing the resin or according to a discontinuous mode by stirring the DPA solution with the resin, then removal of the resin by decantation or filtration. Preference is given to the continuous procedure. Suitable solvents include ethanol or acetone.

It is advantageous, when preparing an emulsifiable concentrate of DPA, to use as an initial solution for the purification process an emulsifiable concentrate of
Technical grade DPA.

The Applicant has just found that primary amines present a toxicological problem (aniline, 2
ABP and 4-ABP) could be removed from technical grade DPA to the degree of purity for food by contacting a solution of technical grade DPA in an organic solvent with acid cation exchangers resins, continuous or discontinuous as indicated above, in the presence of 0 to about 3.0 percent by weight of water, based on the weight of the solution.

In one form of implementation, the starting solution consists of DPA of technical quality and of the organic solvent. In this embodiment, the purified DPA solution can be treated in any of several ways. Thus, the solvent can be removed for possible reuse by distillation, and the
DPA obtained can be formulated, for example, as an emulsifiable concentrate; or the purified DPA solution can be cooled until part of the DPA crystallizes and, after filtration, the DPA obtained can be formulated and the filtrate can be kept for reuse; or the solution of purified DPA can be used as it is in the preparation of a formulation. Solvents which are appreciated for this embodiment are those which have a good capacity for dissolving DPA and which are polar in nature in order to allow the reaction between impurities and resin. Examples of these solvents include acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, methyl formamide, acetonitrile, ethyl formate, (poly) alkylene glycol ethers and their esters, alkylphenylpoly (alkylene glycol) ethers, or mixtures of these solvents. The final choice of solvent can be dictated by the way one chooses to process the purified DPA solution. The amount of solvent used varies greatly depending on the nature of the solvent; with such polar solvents it is sufficient that a small amount of water is present, or else water may be absent. However, when non-polar solvents are used such as a paraffin oil (white mineral oil, consisting of a mixture of branched alkanes) or other hydrocarbon oils, the purification is usually carried out in the presence of a proportion of up to to 3.0 percent by weight of water, preferably 1.0 to 2.0%, especially 1.5%. Water can be added to the solution, but it is best to add it to the resin, as this results in more efficient activation of the resin.

In a second embodiment, in which the starting solution is an emulsifiable concentrate of technical grade DPA, it is preferable to use non-polar solvents in the presence of water, as mentioned above. Such concentrates also normally contain emulsifiers such as polyethylene glycol esters, ethoxylated fatty acids or alcohols and ethoxylated alkylarylphenols and, usually, an anti-foaming agent. In the formulation, the emulsifiers or detergents act as co-solvents. In this embodiment, the resin can be separated from the purified concentrate by decantation and filtration or, preferably, by means of an apparatus of the type
D-Canter (centrifuge).

 The cation exchange resin is advantageously a resin formed from a copolymer of styrene and of divinylbenzene sulfonated in particles of 0.030 to 2 mm (preferably 0.297 to 0.84 mm) with a crosslinking rate of 1 to 30 (preferably from 20 to 25%). Such resins are commercially available. The resin must carry the sulfonic acid group in its acid form or must be converted to this form (if it is in the salt form) before its use by treatment of the resin with, for example, a hydrochloric acid solution.

Temperatures are not critical and are normally maintained in the range of about 15 to 50 C. It is desirable to avoid very low temperatures because they increase the viscosity and lower the solubility of DPA in the solvent and the rate of absorption of impurities by the resin. Very high temperatures lead in some cases to a darkening of the solution of
DPA.

 The contact times or the flow rates are dependent variables which vary with the temperature, the solvent, the type and quantity of resin, the level of impurities in the technical APD, etc. Analysis of samples can be performed during the process, for example by high performance liquid chromatography ("HPLC") to indicate when removal of impurities to the desired level has been achieved.

Example 1 - Batch process with acetone: 25 grams ("g") of technical grade DPA (impurities indicated below) were loaded into a 150 ml flask equipped with a stirrer and a reflux condenser in Table 1) and 50 milliliters ("ml") of acetone. The flask was placed in a water bath at 40 "C and its contents were stirred until all of the DPA had dissolved. Then, a styrene copolymer resin was added as the cation exchange resin. and divinylbenzene sulfonated into particles of 0.297 to 0.84 mm carrying the sulfonic acid group in the acid form and continued stirring at 40 ° C for 5.5 hours. The resin was separated from the DPA solution by filtration and the purified DPA was isolated by evaporation.

23.5 g of DPA were collected (yield 94%). Quantitative analysis by CHIP of the starting material and the purified product gave the following values for aniline, 2-ABP and 4-ABP
Table 1
Aniline 2-ABP 4-ABP
Starting material 1.45 mg / kg 22.29 mg / kg 6.77 mg / kg
Purified matter 0.08 mg / kg 0.56 mg / kg <0.01 mg / kg
Quantity eliminated
born,% 95 97> 99
Example 2 - Batch process with methanol
250 g of technical DPA and 1000 ml of ethanol (95%) were loaded into a 2 liter flask fitted with an agitator. The mixture was stirred at 20 "C until all of the DPA had dissolved and then the same resin was added as in Example 1. Stirring was continued for 6 hours after which the clear solution was separated from the resin by decantation, the ethanol was distilled off from the solution on a rotary evaporator and 242 g of purified DPA were obtained (yield 97%).
HPLC has given the following results
Table 2
Aniline 2-ABP 4-ABP
Starting material 1.45 mg / kg 22.29 mg / kg 6.77 mg / kg
Purified matter 0.45 mg / kg 0.57 mg / kg <0.01 mg / kg
Quantity eliminated
born,% 69 97> 99
Example 3 Continuous Process with Methanol
A solution of 12.5 g of technical DPA in 50 ml of ethanol (95%) was passed in an hour at 20 ° C. over a column 72 mm long and 10 mm in internal diameter packed with 5, 5 g of resin of example 1. The DPA was isolated from the eluate obtained by evaporation of the solvent. 11.5 g of purified DPA were obtained (yield 92%). Analysis by HPLC gave the results following
Table 3
Aniline 2-ABP 4-ABP
Starting material 1.45 mg / kg 22.29 mg / kg 6.77 mg / kg
Purified matter 0.11 mg / kg 0.46 mg / kg <0.01 mg / kg
Quantity eliminated
born,% 92 99> 99
Example 4 - Batch process with concentrate
emulsifiable
Six batches of 9000 kg of emulsifiable concentrate were prepared from technical DPA with average purity levels of approximately 40 mg / kg of aniline, 7 mg / kg of 4-ABP and 18 mg / kg of 2-ABP . The medium concentrate contained about 31% (by weight) of diphenylamine; a solvent consisting of white mineral oil; an emulsifying composition consisting of a polyglycol ester, an ethoxylated fatty acid and an ethoxylated ankylarylphenol; and an anti-foaming agent. Each batch was prepared in a closed reactor equipped with a stirrer and heated to 37-40 "C. The same resin was then added as in Example 1 containing approximately 1.5% water (based on the batch weight), the mixture was stirred at about 3740 ° C for at least 4 hours and the resin was separated.

HPLC analysis of the purified batches gave the mean values (in mg / kg) of 0.039 for aniline, less than 0.01 for 4-ABP and 0.32 for 2-ABP.

Claims (4)

 1. Method for selectively eliminating primary amines from diphenylamine, characterized in that it consists in (a) bringing in a solution containing diphenylamine and an organic solvent in contact with a cation exchange resin carrying functional sulfonic acid groups in the presence of up to about 3% by weight of water, based on the weight of said solution, and (b) separating the resulting solution from said resin.  2. Method according to claim 1, characterized in that the diphenylamine solution is passed continuously over a column of cation exchange resin.  3. Method according to claim 1, characterized in that the solvent is acetone or ethanol.  4. Diphenylamine solution characterized in that it is purified according to the process according to claim 1.