Process for preparing ammine salts of aluminum iodide
The present invention relates to a process for preparing ammine salts of aluminum iodide, in particular of hexamminealuminum iodide monoammoniate, of hexamminealuminum iodide and pentamminealuminum iodide, by reaction of aluminum, an iodine compound and ammonia. 
     Investigations on ammine salts of aluminum iodide have been described by G. W. Watt and J. H. Braun in J. Am. Chem. Soc. Volume 78 (1956), pages 5494-5496. It was found that AlI 3  ×2ONH 3  is unstable above -26° C. If AlI 3  ×2ONH 3  is heated at reduced pressure, white crystals of AlI 3  ×6NH 3  are eventually formed at 25° C. and 10 -3  bar. AlI 3  ×6NH 3  can be converted to AlI 3  ×5NH 3  in vacuo. 
     On page 5495 this article reports that aluminum, iodine and ammonia only react with each other if mercury is added as a catalyst. 
     It is an object of the present invention to report a process for preparing ammine salts of aluminum iodide from aluminum, an iodine compound and ammonia without a mercury catalyst in high purity and in crystalline form and also as a single crystal. 
     Surprisingly, it was possible to achieve this object by reacting aluminum, an iodine compound and ammonia in the liquid ammonia phase at a temperature from 20° to 600° C., in particular from 70° to 200° C. and at a pressure from 8 to 2000 bar, in particular 20 to 200 bar and evaporating excess ammonia after the reaction is completed. 
     Hexamminealuminum iodide monoammoniate is obtained from the reaction product by evaporating excess liquid ammonia at a temperature from 10° to 60° C., in particular 15° to 30° C. at atmospheric pressure. 
     Hexamminealuminum iodide is obtained from the reaction product by evaporating excess liquid ammonia at a temperature from 65° to 300° C., in particular 80° to 150° C., at atmospheric pressure or aspirating out excess liquid ammonia as a gas at room temperature up to a reduced pressure of 10 -3  bar or aspirating out excess liquid ammonia as a gas at a reduced pressure from 0.3 to 0.7 bar and a final temperature of 30° to 50° C. 
     Pentamminealuminum iodide is obtained from the reaction product by evaporating excess ammonia at a temperature from 305° to 380° C., in particular 310° to 330° C. at atmospheric pressure. 
     In a preferred embodiment, chlorine or an inorganic chloride, preferably aluminum chloride or ammonium chloride, is metered into the reactants as a reaction accelerator in an amount of 0.05 to 10% by weight, in particular 0.8 to 1.2% by weight, calculated as I used. 
     According to the invention, an atomic Al:I ratio of the reactants of 1:(2 to 3.1) is established. 
     Elemental iodine or ammonium iodide can be used as the iodine compound. 
     It has been found that in the case of an atomic Al excess with respect to iodine the unconverted aluminum can be separated off from the finished product by screening or the unconverted aluminum and undissolved impurities can be channeled out from the liquid ammonia phase by filtration or decantation. 
     The ammine salts of aluminum iodide can be incorporated into synthetic resins and synthetic paints as an expandable flameproofing agent. 
     The following examples serve to illustrate the invention without limiting it to these examples. 
    
    
     EXAMPLE 1 
     27 parts of aluminum shavings and 435 parts of ammonium iodide are initially introduced into an enameled heatable stirred autoclave under inert gas (N 2 , Ar). After evacuation, 561 parts of ammonia were condensed into the autoclave. After the autoclave had been closed, it was heated to 75° C. and kept at this temperature for 99 hours. A pressure of 35 bar was reached. The autoclave was then let down to atmospheric pressure at room temperature. The product gave the following analysis: 
     
         Al.sub.0.179 I.sub.0.573 N.sub.1.289 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.6 ] I.sub.3 (NH.sub.3)+0.201 NH.sub.4 I 
    
     The yield was 94% based on aluminum. 
     EXAMPLE 2 
     27 parts of aluminum shavings and 290 parts of ammonium iodide were initially introduced into the autoclave under inert gas (N 2 , Ar). After evacuation, 408 parts of ammonia were condensed in and the closed autoclave was heated to 400° C. and kept at 400° C. and 150 bar for 65 hours. The autoclave was let down to atmospheric pressure at 25° C. and the product obtained was removed from excess aluminum through a sieve having a clear mesh width of 0.20 mm. The conversion based on iodine was 100%. 
     The product gave the following analysis: 
     
         Al.sub.0.196 I.sub.0.568 N.sub.1.326 
    
     and therefore corresponded to the following formula 
     
         [Al(NH.sub.3).sub.6 ] I.sub.3 (NH.sub.3)+0.037 Al 
    
     EXAMPLE 3 
     Example 2 was repeated except that this time 705 parts of ammonia were condensed in. After a reaction time of 65 hours at 400° C., the autoclave was cooled to room temperature and the reaction mixture was removed from the autoclave using a pressure filter. The ammonia in the filtrate was evaporated at room temperature at atmospheric pressure. There remained 524 parts of crystals which gave the following analysis: 
     
         Al.sub.0.187 I.sub.0.570 N.sub.1.318 
    
     The analytical values therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.6 ] I.sub.3 (NH.sub.3)+0.048 NH.sub.4 I 
    
     0.44 part of residue remained on the pressure filter, 97% by weight of which was aluminum. 
     EXAMPLE 4 
     27 parts of aluminum shavings, 435 parts of ammonium iodide and 4 parts of ammonium chloride were initially introduced into the autoclave under inert gas (N 2 , Ar). After evacuation, 580 parts of ammonia were condensed in. After the autoclave had been closed, it was heated to 120° C. and kept at a pressure of 90 bar for 8 hours. It was then let down to atmospheric pressure at 120° C. The product gave the following analysis: 
     
         Al.sub.0.181 I.sub.0.591 N.sub.1.156 Cl.sub.0.015 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.6.04 ] I.sub.3 +0.240 NH.sub.4 I+0.075 NH.sub.4 Cl 
    
     The yield based on aluminum was 92%. 
     EXAMPLE 5 
     Example 1 was repeated except that after 90 hours the autoclave was kept at room temperature for 12 hours. The pressure of the autoclave was then first released at room temperature and ammonia was finally pumped off in an oil pump vacuum up to 10 -3  bar. The autoclave was kept at room temperature while the ammonia was being pumped off. The product gave the folowing analysis: 
     
         Al.sub.0.179 I.sub.0.597 N.sub.1.131 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.5.98 ] I.sub.3 +0.331 NH.sub.4 I 
    
     EXAMPLE 6 
     Example 1 was repeated except that after 90 hours the autoclave was cooled to 40° C. and was let down to atmospheric pressure at this temperature. The contents of the autoclave which was kept at 40° C. were then pumped off up to a pressure of 0.5 bar. The crystalline product gave the following analysis: 
     
         Al.sub.0.179 I.sub.0.594 N.sub.1.132 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.6 ] I.sub.3 +0.318 NH.sub.4 I 
    
     EXAMPLE 7 
     27 parts of aluminum shavings, 381 parts of iodine and 4 parts of ammonium chloride were initially introduced into the autoclave under inert gas (N 2 , Ar) and after evacuation 540 parts of ammonia were metered in. The autoclave was heated to 320° C. and kept at this temperature and a pressure of 180 bar for 7 hours. The autoclave was then let down to atmospheric pressure a temperature of 320° C. The product gave the following analysis: 
     
         Al.sub.0.182 I.sub.0.612 N.sub.0.985 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.5.05 ] I.sub.3 +0.363 NH.sub.4 I 
    
     The yield based on aluminum was 89%. 
     EXAMPLE 8 
     25 parts of aluminum shavings, 10 parts of aluminum chloride and 435 parts of ammonium iodide were initially introduced into the autoclave under inert gas (N 2 , Ar). After evacuation, 475 g of ammonia were condensed in. The autoclave was kept at 200° C. under a pressure of 140 bar for 7 hours. The autoclave was then heated to 310° C. and let down to atmospheric pressure. The product gave the following analysis: 
     
         Al.sub.0.186 I.sub.0.595 N.sub.1.025 Cl.sub.0.045 
    
     and therefore corresponded to the formula 
     
         [Al(NH.sub.3).sub.5.07 ] I.sub.3 +0.199 NH.sub.4 I+0.242 NH.sub.4 Cl.