2 4 6 trichloro 5 methylthio pyrimidine are introduced into a 5 liter autoclave and heated at 100 u00b0 c for 2 hours the solution obtained is concentrated under reduced pressure and ether is added to the residue obtained the part insoluble in the ether is separated washed with water and dried 153 7 grams of a mixture of isomers a and b in which isomer a is predominant are thus obtained this mixture melts at 145 u00b0 c and is characterized by its ir and nmr spectra 100 grams of toluene 23 g of 2 4 6 trichloro 5 methylthio pyrimidine and 10 1 g of triethylamine are heated at the boiling point for 3 hours in a round bottomed flask of 500 ml provided with a cooling device the solution obtained is concentrated under reduced pressure and the residue is introduced into a 500 ml autoclave with 350 ml of methanol and 50 g of ammonia the solution obtained after 2 hours reaction at 130 u00b0 c is concentrated again under reduced pressure a residue is obtained which is washed with water and recrystallized from a water alcohol mixture 17 5 grams of 4 amino 6 chloro 2 diethylamino 5 methylthio pyrimidine melting at 68 u00b0 c are thus obtained which product is characterized by its ir and nmr spectra this compound is obtained by the method of operation of example 1 with the exception that in the first stage the ethylamine is replaced by methylamine it melts at 205 u00b0 c and is characterized by its ir and nmr spectra this mixture is obtained by the method of operation.