the process of this invention for preparing 2 - amino - 6 - chloropurine comprises the step of reacting guanine with hexamethyldisilazane in the presence of ammonium sulfate . in a preferred embodiment , the process of this invention for preparing 2 - amino - 6 - chloropurine comprises the steps of : ( a ) reacting guanine with hexamethyldisilazane in the presence of ammonium sulphate ; ( b ) reacting the product from step ( a ) with an inorganic acid chloride ; ( c ) adding the product from step ( b ) to an aqueous alkaline solution ; ( e ) isolating 2 - amino - 6 - chloropurine from the hydrolysed reaction mixture produced in step ( d ). in other preferred embodiments , this process comprises the steps of reacting guanine in the presence of ammonium sulphate with hexamethyldisilazane in a polar solvent , preferably n , n - dimethylacetamide , at elevated temperature , preferably under reflux conditions , until a clear reaction mixture is obtained . the solvent and the unreacted hexamethyldisilazane are then distilled off under reduced pressure and the residue remaining is cooled , combined with an inorganic acid chloride -- such as phosphorus pentachloride , phosphorus trichloride , thionyl chloride and preferably phosphorus oxychloride , and a solvent , preferably acetonitrile , and a phase transfer catalyst , preferably triethylbenzylammonium chloride , and reacted at elevated temperature , preferably under reflux conditions , whilst any low boiling reaction products such as trimethylchlorosilane are distilled off . subsequently , the solvent and excess phosphorus oxychloride are distilled off under reduced pressure and the evaporation residue is added to an aqueous solution of an alkali metal hydroxide , preferably to dilute sodium or potassium hydroxide solution . the resulting reaction mixture is hydrolysed as completely as possible at a ph greater than 3 , preferably in the range from 5 to 8 and most preferably in the range from 6 to 7 , at elevated temperature , preferably boiling temperature , whilst any components of the reaction mixture which are volatile under these conditions are distilled off . after the hydrolysis mixture has been cooled , preferably to ambient temperature , and after seeding , if necessary , the 2 - amino - 6 - chloropurine crystallises out in the form of yellowish crystals . after conventional isolation procedures , a 2 - amino - 6 - chloropurine is thus obtained in good yields , containing less than one percent of unreacted guanine ( hplc ). a particularly preferred process for preparing 2 - amino - 6 - chloropurine according to this invention comprises the steps of : ( a ) reacting guanine with hexamethyldisilazane in the presence of ammonium sulphate in a solvent ; ( b ) removing the solvent and the unreacted hexamethyldisilazane from the reaction mixture produced in step ( a ) to produce a residue ; ( c ) combining the residue produced in step ( b ) with an inorganic acid chloride and a solvent ; ( d ) heating the reaction mixture produced in step ( c ) and distilling off the low boiling components to produce a residue ; ( e ) adding the residue produced in step ( d ) to an aqueous alkaline solution ; ( f ) hydrolysing the reaction mixture produced in step ( e ) at a ph of greater than about 3 at elevated temperature ; ( g ) distilling off the volatile components from the reaction mixture produced in step ( f ); ( i ) precipitating and isolating 2 - amino - 6chloropurine from the cooled solution produced in step ( h ). a more preferred process for preparing 2 - amino - 6chloropurine according to this invention comprises the steps of : ( a ) reacting guanine with hexamethyldisilazane in the presence of ammonium sulphate in a polar solvent at elevated temperature ; ( b ) distilling off the polar solvent and the unreacted hexamethyldisilazane from the reaction mixture produced in step ( a ) under reduced pressure to produce a residue ; ( c ) combining the residue produced in step ( b ) with phosphorus oxychloride and a phase transfer catalyst in a solvent ; ( d ) heating the reaction mixture produced in step ( c ), distilling off the low boiling components , distilling off the solvent from step ( c ) and excess phosphorus oxychloride under reduced pressure to produce a residue ; ( e ) adding the residue produced in step ( d ) to an aqueous solution of an alkali metal hydroxide ; ( f ) hydrolysing the reaction mixture produced in step ( e ) at a ph in the range from about 5 to about 8 at elevated temperature ; ( g ) distilling off the volatile components from the reaction mixture produced in step ( f ); ( i ) precipitating and isolating 2 - amino - 6 - chloropurine from the cooled solution produced in step ( h ). the most preferred process for preparing 2 - amino - 6 - chloropurine according to this invention comprises the steps of : ( a ) reacting guanine with hexamethyldisilazane in the presence of ammonium sulphate in n , n - dimethylacetamide under reflux conditions ; ( b ) distilling off the n , n - dimethylacetamide and the unreacted hexamethyldisilazane from the reaction mixture produced in step ( a ) under reduced pressure to produce a residue ; ( c ) combining the residue produced in step ( b ) with phosphorus oxychloride , acetonitrile and triethylbenzyl - ammonium chloride ; ( d ) heating the reaction mixture produced in step ( c ) to reflux temperature , distilling off the low boiling components and distilling off the acetonitrile and excess phosphorus oxychloride under reduced pressure to produce a residue ; ( e ) adding the residue produced in step ( d ) to an aqueous sodium or potassium hydroxide solution ; ( f ) hydrolyzing the reaction mixture produced in step ( e ) at a ph in the range from about 6 to about 7 at boiling temperature ; ( g ) distilling off the volatile components from the reaction mixture produced in step ( f ); ( i ) precipitating and isolating 2 - amino - 6 - chloropurine from the cooled solution produced in step ( h ). the objectives described above are achieved by means of the processes outlined above and further illustrated in the examples . various other embodiments of the process will be apparent to anyone skilled in the art from the descriptions provided . however , it is expressly pointed out that the examples and the associated description are provided purely as an exemplification and illustration and should not be regarded as restricting the invention . 121 g ( 0 . 8 mol ) of guanine and 1 . 6 g of ammonium sulphate were suspended in 800 ml of n , n - dimethylacetamide , 864 ml of hexamethyldisilazane were added and the mixture was refluxed for 4 hours . excess hexamethyldisilazane and the solvent were distilled off in vacuo . the residue was combined with 450 ml of phosphorus oxychloride , 280 g of triethylbenzylammonium chloride and 320 ml of acetonitrile and boiled for about 1 hours , whilst any low boiling fractions , predominantly trimethylchlorosilane , were distilled off through a short vigreux column . then the solvent and excess phosphorus oxychloride were distilled off under reduced pressure and the evaporation residue was added dropwise without cooling to a supply of sodium hydroxide solution . the hot solution was boiled at ph 6 - 7 in order to complete the hydrolysis , during which organic components were distilled off . then it was cooled , seeded ( if necessary ) and left to crystallise at ambient temperature for a period of about 12 hours . the precipitate was suction filtered , washed thoroughly with water and dried . 108 g ( 79 . 8 % of theory ) of yellowish crystals of 2 - amino - 6 - chloropurine were obtained , with a guanine content ( hplc ) of 0 . 2 - 0 . 3 %. 30 . 3 kg ( 200 mol ) of guanine , 0 . 4 kg of ammonium sulphate , 235 kg of n , n - dimethylacetamide and 211 kg of hexamethyldisilazane were refluxed in a 500 litre enamel stirring apparatus until a clear solution was obtained . excess hexamethylsilazane and the solvent were distilled off completely with the gradual application of vacuum . 113 liters of phosphorus oxychloride were carefully added to the residue , then 80 liters of acetonitrile and 70 kg of triethylbenzylammonium chloride were added and the mixture was brought to the boil again . after about 1 hour when about 65 liters had been distilled off , distillation was continued with gradual lowering of the pressure until a viscous residue was obtained . this was added slowly and with cooling to 900 liters of 13 % potassium hydroxide solution which had been placed in a 1200 liter enamel stirring apparatus . the solution was neutralised , heated to boiling whilst the ph was monitored and distilled until a sump temperature of 100 ° c . was achieved . after cooling and , seeding the product was stirred until it had crystallised out completely , the crystals were then centrifuged , washed and dried . 30 . 6 kg ( 90 . 5 % of theory ) of ochre - coloured finely crystalline 2 - amino - 6 - chloropurine were obtained with a guanine content ( hplc ) of about 0 . 9 %.