Abstract:
Methods of preparing a polyaniline homopolymer or copolymer comprising at least one carboxylic acid group, and homopolymers or copolymers arising therefrom, the methods comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group (eg. 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid) in a solvent selected from aqueous methanesulfonic acid or aqueous ammonia and optionally one or more additional polyaniline precursors (such as aniline); and oxidatively polymerising the polyaniline precursor or precursors.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to processes for preparing polymers that include aminobenzoic acid monomers, and to copolymers and homopolymers prepared by those processes. 
       BACKGROUND ART 
       [0002]    Polymers of aniline and its derivatives are useful as antimicrobial agents and have good antistatic and free radical scavenging properties. These properties make them useful for the manufacture of antimicrobial, antistatic and antioxidant objects, and suitable for use in, for example, the health, food, packaging, water, paint, wood, textile, poultry, glass, paper, rubber, ceramic, seafood, sports, plastic and agricultural industries. 
         [0003]    Adding substituents to polyaniline (PANI) is one way in which the various properties of the polymer can be improved. However, the synthesis of substituted PANIs is not always a straightforward matter. Any substituent introduced to the aniline building block needs to be compatible with the reagents used, which is not always possible under the traditionally robust oxidative polymerisation conditions used to form PANIs. 
         [0004]    Carboxylated PANIs are one type of PANI derivative of particular interest due to their good antibacterial properties. Carboxylated PANIs can either be homopolymers, which could also be described as a poly(aminobenzoic acid) (poly ABAs) or copolymers, which could be considered as a PANI backbone bearing carboxylic acid groups on some of the aromatic rings. FIG. 1 shows the probable structure of poly(2-aminobenzoic acid) and poly(3- aminobenzoic acid). FIG. 2 shows the probable structure of copolymers of aniline and 2-aminobenzoic acid or 3-aminobenzoic acid, where X and Y are the numbers of repeat units. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0005]    However, producing PANI homopolymers and copolymers from aminobenzoic acid (ABA) monomers in good yield and purity is not a simple procedure. There are significant problems with the solubilities of ABAs. ABAs tend to be solids, unlike aniline itself or many substituted anilines (alkyl anilines like toluidine, alkoxy anilines like anisidine etc) which can be used directly in their liquid form. This low solubility impacts upon the cost of synthesis and the quality of the resultant polymers. 
         [0006]    There thus exists a need to produce poly-ABAs (carboxylated PANIs) in high yield and in a cost effective manner, with high conversion of monomer units, short production time and high molecular weights. 
         [0007]    It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. 
       SUMMARY 
       [0008]    In a broad aspect, the invention provides a method of preparing a polyaniline homopolymer or copolymer comprising at least one carboxylic acid group; the method comprising:
   preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in a solvent selected from aqueous methanesulfonic acid or aqueous ammonia and optionally one or more additional polyaniline precursors; and   oxidatively polymerising the polyaniline precursor or precursors.   
 
         [0011]    Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. 
         [0012]    In one aspect, the invention provides a method of preparing a polyaniline homopolymer comprising carboxylic acid groups; the method comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous methanesulfonic acid; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group. 
         [0013]    In one aspect, the invention provides a method of preparing a polyaniline homopolymer comprising carboxylic acid groups; the method comprising: 
         [0014]    preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous ammonia; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group. 
         [0015]    The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group may be any aromatic ring bearing —NH 2  and —COOH moieties in any position, with or without other substituents. In certain preferred embodiments, the substance being polymerised is selected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid.
   Monomers other than amino benzoic acids can be used, for example aniline or pyrrole, or derivatives thereof may be used.   
 
         [0017]    In one aspect, the invention provides a method of preparing a polyaniline copolymer comprising at least one carboxylic acid group; the method comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous methanesulfonic acid and one or more additional polyaniline precursors; and
   oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group and the one or more additional polyaniline precursors.   
 
         [0019]    In one aspect, the invention provides a method of preparing a polyaniline copolymer comprising at least one carboxylic acid group; the method comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous ammonia and one or more additional polyaniline precursors; and
   oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group and the one or more additional polyaniline precursors.   
 
         [0021]    The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group may be any aromatic ring bearing —NH 2  and —COOH moieties in any position, with or without other substituents. In certain preferred embodiments, the substance being polymerised is selected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid. The one or more additional polyaniline precursors may be any amino substituted aromatic ring, which is in some cases preferably comprises aniline. 
         [0022]    FIG. 3 shows a possible structure of poly(4-aminobenzoic acid). 
         [0000]    
       
                 
         
             
             
         
       
     
         [0023]    Monomers other than amino benzoic acids can be used, for example aniline and other derivatives thereof or pyrrole and derivatives thereof may be used. 
         [0024]    The most preferred copolymers are those formed from mixtures of aniline and 2-aminobenzoic acid, aniline and 3-aminobenzoic acid or aniline and 4-aminobenzoic acid. FIG. 4 shows a possible structure of copolymers of aniline and 4-aminobenzoic acid. Y and Z are the numbers of repeat units. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0025]    The ratio of the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group: the one or more additional polyaniline precursors is from 99:1 to 1:99. Alternatively, ratios in the range 72:25 to 25:75 may be used. 
         [0026]    If aqueous methane sulfonic acid is used, it is preferably in a concentration of 0.1 to 10 M in water. It is generally preferred if the ratio of concentration of ABA to methanesulfonic acid is from 2:1 to 1:2. For example, it is preferred to use a solution of methanesulfonic acid of around 1 M and an ABA concentration of around 0.5 M. 
         [0027]    The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group is preferably dissolved in the aqueous methane sulfonic acid and oxidising agent is added. If a copolymer is desired, additional polyaniline precursors may be added in a suitable compatible solvent, which may include water or aqueous methane sulfonic acid. 
         [0028]    If ammonia is used, the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group is suspended in water and ammonia is added to dissolve it. The amount and concentration required can be readily determined. Typically, commercial strength ammonia is added to a suspension of the ABA in water until the monomer is dissolved. The pH is readily maintained at around neutral to slightly alkaline pHs, for example around pH 7-8. 
         [0029]    The reaction of aminobenzoic acid and/or aniline to synthesize the homopolymer or copolymer is carried out in an acidic or near neutral medium in the presence of an oxidizing agent. Any suitable oxidizing agent may be used. Suitable oxidizing agents include, although are not limited to ammonium persulphate, potassium ferricyanide, potassium iodate, hydrogen peroxide, cerium (IV) sulphate, potassium dichromate and sodium vanadate. For neutral/alkaline based reaction, preferably the oxidizing agent is ammonium persulphate or hydrogen peroxide. 
         [0030]    The methods of the present invention will also usually further include the step of collecting the precipitated poly aminobenzoic acid homopolymer or copolymer by filtration. 
     
    
     DESCRIPTION 
       [0031]    Aminobenzoic acids have low solubility in water and in common acids used to carry out oxidative polymerization. For example, 3-ABA has only around 5 wt % solubility in 1 M HCl, which is typical for ABAs generally. Even if the aminobenzoic acids can be dissolved to some extent, it is difficult to get them into solution at sufficiently high concentrations to achieve good yields of the resultant polyaniline polymer or copolymer. The present inventors have developed solvent systems based around methanesulfonic acid or ammonia that enable the monomer to be dissolved in MSA or ammonia at high concentration (15% by weight or higher) 
         [0032]    The methods of the present invention enable the practical large scale production of PANIs, particularly those starting from amino benzoic acid derivatives, at room temperature. Because of the good solubility of the starting monomers, the reaction yield and starting monomer consumption is high and the reaction time is reduced, resulting in a less wasteful and more economic synthesis. Moreover, the products of the present invention have been found to have high molecular weight and, where copolymers are concerned, high incorporation of n-ABA in the resultant copolymer is observed. 
       COMPARATIVE EXAMPLES 
       [0033]    Oxidative polymerisation of 3-amino benzoic acid to the corresponding polycarboxylated PANI was carried out under standard conditions using 1M HCl as monomer solvent and APS as oxidant. 
         [0034]    From 150 ml 1 M HCl solution containing 2.2 g (16 mmol) 3-ABA, 0.0154 g polymer was obtained (0.7% yield*) when the reaction was performed at 10° C. for 7 days 
         [0035]    From 200 g 1 M HCl solution containing 10 g n-ABA monomer, 1 g polymer was obtained (10% yield*), when the reaction was performed at room temperature for 48 h *Yield:=100×[mass of the polymer]/[mass of the (co)monomer(s)] 
       INVENTIVE EXAMPLES 
     Methane Sulphonic Acid as Solvent 
       [0036]    Poly(n-amino benzoic acid) homopolymers, where n=2, 3 or 4 (P(n-ABA)) and poly(n-amino benzoic acid-co-aniline) copolymers (P(n-ABA-co-Ani)) were synthesised in 1 M methane sulfonic acid (MSA) at 25° C. (ambient temperature), with ammonium persulfate (APS) as the oxidizing agent. The monomer(s) concentration and the mole ratio of monomer(s) to APS were kept constant at 0.5 M and 1:1.25 respectively. The mole ratio of n-aminobenzoic acid (n-ABA) to aniline (Ani) in the comonomer mixtures was varied from 99:1 to 1:99, or more usually 75:25 to 25:75. 
         [0037]    The maximum concentration of n-aminobenzoic acid (n-ABA) in 1 M MSA is about 15%, which may be higher in more concentrated MSA. 
       Homopolymers 
       [0038]    Homopolymers of the present invention can be designated as follows: HpMn: Hp=Homopolymer, M=methane sulfonic acid (MSA), n=position of —COOH functional group (4 or 3 or 2) in n-ABA precursor. 
         [0039]    HpAn: Hp=Homopolymer, A=ammonia, n=position of —COOH functional group (4 or 3 or 2) in n-ABA precursor. 
         [0040]    Synthesis of PANI homopolymers of aminobenzoic acids P(n-ABA): 13.86 g of 4-ABA was dissolved in 100 mL of 1 M MSA. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50° C. From this process 7.2 g polymer HpM4 was obtained (52% yield). 
         [0041]    The yield can be seen to be significantly better than that obtained from the use of HCl as solvent. 
         [0042]    The use of 3-ABA and 2-ABA in an identical manner resulted in the synthesis of a homopolymer of 3-aminobenzoic HpM3 and a homopolymer of 2-aminobenzoic acid HpM2 respectively. 
         [0043]    Table 1 shows the properties of HpMn homopolymers synthesised using MSA as solvent. The yields are significantly better than using traditional solvents, such as HCl. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Antimicrobial 
                   
                   
               
               
                   
                 property 
               
               
                   
                 (Minimum 
               
               
                   
                 inhibitory 
                 Free radical scavenging 
               
               
                   
                 concentration) % 
                 (μmol DPPH scavenged/mg 
                 Conductivity 
               
             
          
           
               
                 Material 
                 Monomer 
                 Colour 
                 Yield (%) 
                 Mol wt. (g/mol) 
                 Gram +ve ( S. aureus ) 
                 Gram −ve ( E. coli ) 
                 of sample) % 
                 (S/cm) 
               
               
                   
               
             
          
           
               
                 HpM4 
                 4ABA 
                 Dark 
                 52 
                 19826 
                 0.5 
                 1 
                 64 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                 HpM3 
                 3ABA 
                 Dark 
                 18 
                 12947 
                 1 
                 &gt;2% 
                 60 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                 HpM2 
                 2ABA 
                 Dark 
                 30 
                 22200 
                 0.25 
                 1 
                 61 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                   
               
             
          
         
       
     
       Copolymers 
       [0044]    Copolymers of the present invention can be designated as follows: CpMnYZ: Cp=Copolymer, M=methane sulfonic acid (MSA), n=position of —COOH functional group (4 or 3 or 2) in n-ABA precursor, YZ ratio Y:Z of n-ABA:aniline in feed. CpAnYZ: Cp=Copolymer, A=ammonia, n=position of —COOH functional group (4 or 3 or 2) in n-ABA precursor, YZ ratio Y:Z of n-ABA:aniline in feed. 
         [0045]    Synthesis of copolymers of aminobenzoic acids and aniline P(n-ABA-co-Ani): For a typical synthesis of P(n-ABA-co-Ani) (starting from a solution with equimolar proportions of comonomers, for example), 6.94 g of n-ABA was dissolved in 100 mL of 1 M MSA. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the solution of the monomers with constant stirring. Polymerisation was continued with stirring for 24 h. The polymer product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50° C. 
         [0046]    Oxidative synthesis of copolymer CpM411: 6.94 g of 4-ABA was dissolved in 100 mL of 1 M MSA. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the solution of the monomers with constant stirring. Polymerisation was continued with stirring for 24 h. The polymer product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50° C. From this process 11.6 g copolymer (CpM411) was obtained (100% yield). 
         [0047]    Under similar conditions, copolymers of 4-ABA and aniline, copolymers of 3-ABA and aniline, copolymers of 2-ABA and aniline at various monomer feed ratio (from 99:1 to 1:99) can be synthesized. 
         [0048]    Table 2 shows the properties of copolymers (CpMnYZ) synthesised in acidic medium. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Antimicrobial 
                   
                   
               
               
                   
                 property 
                 Free radical 
               
               
                   
                 (Minimum 
                 scavenging 
               
               
                   
                 inhibitory 
                 (micromoles 
               
               
                   
                 concentration) % 
                 of DPPH 
               
             
          
           
               
                   
                 Monomer ratio 
                   
                   
                 Gram +ve 
                 Gram −ve 
                 scavenged/mg 
                   
               
               
                 Material 
                 (n-ABA:Aniline) 
                 Colour 
                 Yield (%) 
                 ( S. aureus ) 
                 ( E. coli ) 
                 of sample) % 
                 Conductivity (S/cm) 
               
               
                   
               
             
          
           
               
                 CpM431 
                 4ABA:Aniline 
                 Dark 
                 78 
                 0.25 
                 2 
                 57 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpM411 
                 4ABA:Aniline 
                 Dark 
                 100 
                 0.5 
                 &gt;2 
                 59 
                 0.002 
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpM413 
                 4ABA:Aniline 
                 Dark 
                 112 
                 0.5 
                 &gt;2 
                 60 
                 1 
               
               
                   
                 (1:3) 
                 green 
               
               
                 CpM331 
                 3ABA:Aniline 
                 Dark 
                 85 
                 0.5 
                 2 
                 57 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpM311 
                 3ABA:Aniline 
                 Dark 
                 101 
                 2 
                 &gt;2 
                 54 
                 0.002 
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpM313 
                 3ABA:Aniline 
                 Dark 
                 114 
                 &gt;2 
                 &gt;2 
                 46 
                 0.6 
               
               
                   
                 (1:3) 
                 green 
               
               
                 CpM231 
                 2ABA:Aniline 
                 Dark 
                 78 
                 0.5 
                 2 
                 54 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpM211 
                 2ABA:Aniline 
                 Dark 
                 81 
                 0.5 
                 &gt;2 
                 47 
                 0.04 
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpM213 
                 2ABA:Aniline 
                 Dark 
                 121 
                 0.5 
                 &gt;2 
                 54 
                 2 
               
               
                   
                 (1:3) 
                 green 
               
               
                   
               
             
          
         
       
     
       Ammonia as Solvent 
     Homopolymers 
       [0049]    Synthesis of HpA4 in non-acidic medium (by neutralizing monomer with ammonia): 13.86 g monomer (4-ABA) was dissolved in 100 mL water by neutralizing with 7.5 mL of 28% ammonia. 28.52 g of APS was dissolved in 92.5 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated out from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50° C. From this process 11.37 g polymer HpA4 was obtained (82% yield). 
         [0050]    Again, the yield can be seen to be significantly better than that obtained from the use of HCl as solvent. Under the same conditions HpA3 and HpA2 can be synthesized in non-acidic medium (by neutralizing monomer with ammonia.) 
         [0051]    FIG. 5 below shows a possible reaction scheme for synthesis of poly(4-aminobenzoic acid). 
         [0000]    
       
                 
         
             
             
         
       
     
         [0052]    Table 3 shows the properties of HpAn homopolymers synthesised by pre-neutralization with ammonia 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                   
                 Free radical 
                   
               
               
                   
                 Antimicrobial 
                 scavenging 
               
               
                   
                 property 
                 (μmol 
               
               
                   
                 (Minimum 
                 DPPH 
               
               
                   
                 inhibitory 
                 scavenged/ 
               
               
                   
                 concentration) % 
                 mg of 
                 Conductivity 
               
             
          
           
               
                 Material 
                 Monomer 
                 Colour 
                 Yield (%) 
                 Mol wt (g/mol) 
                 Gram +ve ( S. aureus ) 
                 Gram −ve ( E. coli ) 
                 sample) % 
                 (S/cm) 
               
               
                   
               
             
          
           
               
                 HPA4 
                 4ABA 
                 Dark 
                 82 
                 18362 
                 0.125 
                 &gt;2 
                 55 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                 HPA3 
                 3ABA 
                 Dark 
                 82 
                 62847 
                 1 
                 2 
                 61 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                 HPA2 
                 2ABA 
                 Dark 
                 71 
                 44645 
                 0.5 
                 1 
                 56 
                 &lt;10 −5   
               
               
                   
                   
                 brown 
               
               
                   
               
             
          
         
       
     
       Copolymers 
       [0053]    Oxidative synthesis of copolymer CpA411: 6.94 g monomer (4-ABA) was dissolved in 100 mL water by neutralizing with 4 mL of 28% ammonia. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 96 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated out from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50° C. From this process 10.2 g copolymer (CpA411) was obtained (88% yield). 
         [0054]    Under similar conditions, copolymers of (4-ABA) and aniline, (3-ABA) and aniline, and (2-ABA) and aniline at various monomer feed ratio (can be from 99:1 to 1:99) can be synthesized in acidic medium. 
         [0055]    Table 4 shows a property chart of copolymers (CpAnYZ) synthesised by pre-neutralization of monomer n-ABA with ammonia. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Antimicrobial 
                   
                   
               
               
                   
                 property 
                 Free radical 
               
               
                   
                 (Minimum 
                 scavenging 
               
               
                   
                 inhibitory 
                 (micromoles 
               
               
                   
                 concentration) % 
                 of DPPH 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Gram −ve 
                 scavenged/mg 
                   
               
               
                 Material 
                 Monomer ratio (n-ABA:Aniline) 
                 Colour 
                 Yield (%) 
                 Gram +ve ( S aureus ). 
                 ( E. coli ) 
                 of sample) % 
                 Conductivity (S/cm) 
               
               
                   
               
               
                 CpA431 
                 4ABA:Aniline 
                 Dark 
                 83 
                 0.06% 
                 &gt;2% 
                 60 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpA411 
                 4ABA:Aniline 
                 Dark 
                 88 
                 0.13% 
                 &gt;2% 
                 58 
                 &lt;10 −5   
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpA413 
                 4ABA:Aniline 
                 Dark 
                 90 
                 0.25% 
                 &gt;2% 
                 55 
                 0.0003 
               
               
                   
                 (1:3) 
                 green 
               
               
                 CpA331 
                 3ABA:Aniline 
                 Dark 
                 83 
                 0.125 
                 &gt;2 
                 58 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpA311 
                 3ABA:Aniline 
                 Dark 
                 87 
                 0.125 
                 &gt;2 
                 61 
                 &lt;10 −5   
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpA313 
                 3ABA:Aniline 
                 Dark 
                 85 
                 0.25 
                 &gt;2 
                 55 
                 0.00005 
               
               
                   
                 (1:3) 
                 green 
               
               
                 CpA231 
                 2ABA:Aniline 
                 Dark 
                 72 
                 0.125 
                 1 
                 53 
                 &lt;10 −5   
               
               
                   
                 (3:1) 
                 brown 
               
               
                 CpA211 
                 2ABA:Aniline 
                 Dark 
                 91 
                 0.125 
                 2 
                 52 
                 &lt;10 −5   
               
               
                   
                 (1:1) 
                 brown 
               
               
                 CpA213 
                 2ABA:Aniline 
                 Dark 
                 93 
                 0.25 
                 &gt;2 
                 56 
                 &lt;10 −5   
               
               
                   
                 (1:3) 
                 green