Abstract:
Described is the process of interconverting p-iodoaniline and o-iodoaniline, particularly converting p-iodoaniline to o-iodoaniline overall, by heating the former in the presence of aniline and, optionally, a mineral or organic acid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to, and has as its principal object the provision of, an isomerization of p-iodoaniline to o-iodoaniline. 
     2. Prior Art 
     Despite extensive search, no reference to isomerization of haloanilines has been found. 
     RELATED CASE 
     This application is related to my copending application, Ser. No. 382,844, filed July 26, 1973, which deals with the synthesis of o-, m- and p-phenylenediamines and the intermediate amination of haloanilines. The o-iodoaniline employed in Ser. No. 382,844 for the preparation of o-phenylenediamine can be made by the method of the present application. 
     STATEMENT OF THE INVENTION 
     This invention comprises the process of rearranging p-iodoaniline and o-iodoaniline, particularly the former to the latter, wherein a mixture of p-iodoaniline or o-iodoaniline, aniline, and, optionally, a mineral or organic acid is heated at 150°-250°C for 10 minutes to 4 hours or more. 
     DESCRIPTION OF THE INVENTION 
     The reaction requires merely the addition of 1-100 parts by weight of aniline to one part of p- or o-iodoaniline. It is, however, conveniently carried out in a solvent selected from aniline, decalin, prehnitene, tribromobenzenes, especially 1,3,5-tribromobenzene, benzene, dimethylsulfoxide and hexamethyl phosphoramide. The amount of solvent, if one is employed, ranges from 1-100 parts by weight per part of p-iodoaniline or o-iodoaniline. Aniline is essential to the reaction and, for economic reasons and ease of separability, is the preferred solvent. 
     Lower boiling solvents such as water, benzene, and hexane can be used when the reaction is run under pressure. 
     The acids employed in the practice of this invention are acids which retain their acidic properties under the reaction conditions. They serve as catalysts for the rearrangement of p-iodoaniline. Preferred catalysts are hydroiodic acid or anilinium iodide. Only small amounts are essential, i.e., the ratio of acid to p-iodoaniline can range from 1:1 to 1:10,000 and is preferably about 1:1000 parts by weight. 
     The rearrangement of p-iodoaniline is generally carried out at the boiling point of the solvent which may range from about 150° to about 250°C, preferably at 180°-200°C, and most preferred at about 190°C. 
     The reaction times range from 10 minutes for the hydroiodic acid-catalyzed reaction to 4 hours or more. 
     These reactions are generally carried out at ambient pressure but may be run under mild autogenous pressure, e.g., up to about 20 atmospheres. The latter is inferred from Examples 4 and 5. 
    
    
     EMBODIMENTS OF THE INVENTION 
     The following examples are meant as nonlimiting illustrations of specific methods of practice of the invention. 
     In these examples, all quantities are given in parts by weight unless otherwise specified and temperatures are in degrees centigrade. The reaction products were determined by gas-liquid partition chromatography (glpc) in a 6 feet × 1/8 inch column packed with 3% Hi Eff 8BP on Chromosorb cyclohexane dimethanolsuccinate, (Applied Science Laboratories, Inc., State College, Pa.) at 200°C and a helium flow of 40 ml/minute. The injection and detection temperatures were 220°C and the sample size was 0.5 μl. 
     EXAMPLE 1 
     A. A mixture of 10.0 g of p-iodoaniline, 0.5 g of o-iodoaniline and 40 ml of aniline was heated to 190° and kept at this temperature for 1 hour. The dark purple solution was heated to 210°C for 30 minutes and ca. 25 ml of liquid was distilled. Analysis showed that the distillate consisted of only o-iodoaniline and aniline, and the pot residue consisted of aniline and iodoanilines in the ortho and para isomer ratio of 9:1, respectively. 
     B. When the experiment was carried out in the presence of sodium carbonate little, if any, isomerization was observed. 
     EXAMPLE 2 
     This example demonstrates the use of hydroiodic acid as a catalyst. 
     A. A mixture of 10 g of p-iodoaniline, 40 ml of aniline and 0.5 ml of concentrated aqueous hydroiodic acid was heated for 20 minutes at 188°. No color change was observed. Analysis showed aniline and o-iodoaniline. 
     B. When m-iodoaniline was treated similarly to p-iodoaniline, no isomerization occurred. 
     EXAMPLE 3 
     A mixture of 25 g of p-iodoaniline, 40 ml of aniline and 0.5 ml of 48% aqueous hydroiodic acid was refluxed under nitrogen for 2 hours. The violet solution was cooled and the aniline partly evaporated. The oil was dissolved in methylene chloride, extracted in turn with aqueous sodium hydroxide and water, then treated with Darco activated carbon. The solvent was evaporated, hexane added, and the mixture cooled to -40°C. The crystals that formed were collected and dried. The yield was 12.6 g (50% theoretical). The analysis (glpc) and infrared spectrum were identical to authentic o-iodoaniline. 
     
         ______________________________________Anal. Calcd for C.sub.6 H.sub.6 IN:  C, 32.91;  H, 2.76;  N, 6.40;                               I, 57.90.Found: C, 31.96;  H, 2.58;  N, 6.26;                               I, 57.90    32.09      2,58      6.34    57.71______________________________________ 
    
     EXAMPLE 4 
     Each of fourteen 5-ml thick-walled, Pyrex ampoules was charged with 4 ml of a solution consisting of 15.17 g of p-iodoaniline, 7.20 g of 2-chlorobiphenyl, 101.64 g of freshly distilled aniline, and small amounts of the various acids listed in Table I. After briefly evacuating and sealing, the ampoules were kept in a 185° oil bath for 30 minutes. After cooling to 20°C, the dark purple contents of each ampoule were dissolved in 10 ml of methylene chloride, neutralized with 3 ml of 2N sodium hydroxide and the organic phase analyzed by glpc using the 2-chlorobiphenyl as the internal standard. The results are given as follows: 
     
                       TABLE I______________________________________               Iodoaniline*Amounts of Acid       % ortho   % para______________________________________None      None            13        740.05 ml   48% aq. HI      71        230.1 ml    48% aq. HI      67        250.2 ml    48% aq. HI      69        220.5 ml    48% aq. HI      61        210.2 ml    Conc. HCl       48        180.2 ml    Conc.HBr        10        30.1 ml    Conc. H.sub.2 SO.sub.4                     66        300.2 ml    Water           23        650.3 g     C.sub.6 H.sub.5 NH.sub.3 Cl                     67        230.2 g     Toluenesulfonic acid                     71        250.2 g     NH.sub.4 I      76        230.2 g     H.sub.3 PO.sub.4                     46        190.2 ml    CH.sub.3 CO.sub.2 H                     44        39______________________________________ *Based on total amount of p-iodoaniline charged; remainder decomposed. 
    
     EXAMPLE 5 
     Table II lists the results for the experiments when the ortho isomer was used instead of the para isomer. The same conditions and relative quantities were used as described in Example 4. 
     
                       TABLE II______________________________________             Iodoaniline*Amounts of Acid     % ortho    % para______________________________________None       None         99         None0.2 ml     48% aq. HI   34         170.2 ml     CH.sub.3 CO.sub.2 H                   96         Trace0.2 ml     Conc. HCl    10          2______________________________________ *Based on the total amount of 0-iodoaniline charged; remainder decomposed