in the formulae ( i ) and ( ii ), r 1 to r 9 independently of one another each preferably represent hydrogen , fluorine , chlorine , bromine , methoxy , ethoxy , methyl , ethyl , n - propyl , i - propyl , n - butyl or t - butyl . furthermore , up to 4 of the radicals r 1 to r 9 preferably represent one of the abovementioned substituents and the remaining radicals preferably represent hydrogen . particularly preferably , up to 2 of the radicals r 1 to r 9 represent one of the abovementioned substituents , and the remaining radicals particularly preferably represent hydrogen . very particularly preferably , unsubstituted anthracene is used . the process according to the invention can be carried out , for example , at 50 to 150 ° c ., preferably at 80 to 120 ° c . the process can be carried out at atmospheric pressure , elevated pressure or reduced pressure . it is preferably carried out at atmospheric pressure . for example 1 to 5 mol , preferably 1 to 2 . 5 mol of phosphoryl chloride and 1 to 5 mol , preferably 1 to 2 . 5 mol of dimethylformamide are employed per mole of the anthracene derivative of the formula ( i ). for example 0 . 2 to 1 . 5 mol , preferably 0 . 5 to 1 mol of dimethylformamide are employed per mole of phosphoryl chloride . the process according to the invention can be carried out , for example , by initially charging the anthracene derivative of the formula ( i ) and the phosphoryl chloride and metering in dimethylformamide at the desired reaction temperature , for example over a period of 0 . 5 to 48 hours . preference is given to metering in times of 2 to 18 hours . the reaction partners may also be added in a different order . it is advantageous to continue stirring the reaction mixture for some time in the temperature range from 50 to 150 ° c . after the addition of the last reactant has ended . the reaction mixture may be stirred , for example , for another 1 to 30 hours . in the most simple case , the hydrolysis is carried out by introducing the reaction mixture into water . hydrogen chloride evolves , and a dark red - brown solution is formed . the 9 - anthracenecarbaldehyde that is formed is finally precpitated by adding a base . suitable for this purpose are for example sodium hydroxide or aqueous sodium hydroxide solution . it is favorable to adjust the temperature of the water which is used for carrying out the hydrolysis initially to , for example , 30 to 70 ° c ., and to keep it at 35 to 90 ° c . during the hydrolysis . the addition of a base can be carried out for example in such a way that a ph of 0 . 5 to 7 , preferably of 1 to 5 . 5 , results . during the addition of the base , it is advantageous to keep the temperature in the range from 10 to 30 ° c ., and to increase the temperature subsequently to 20 to 90 ° c ., in particular to 30 to 80 ° c ., and to stir the reaction mixture for some more time , for example for 0 . 5 to 5 hours , in this temperature range . the 9 - anthracenecarbaldehyde of the formula ( i ) that has been prepared is then present as a precipitate and can be isolated by mechanical separation , for example by filtration . if the resulting 9 - anthracenecarbaldehyde is to be purified further , it can , for example , be stirred with water , and the suspension that has formed is , for example , stirred for 0 . 5 to 5 hours at 20 to 80 ° c ., filtered again and washed with water . in this manner , 9 - anthracenecarbaldehydes can be obtained in yields of , for example , more than 97 % and purities of more than 98 %. in comparison with the prior art , the process according to the invention affords 9 - anthracenecarbladehydes of the formula ( i ) in a more simple and more economic way and in better yields and purities . the amounts of byproducts , wastewaters contaminated with organic materials , and salts ( sodium chloride , phosphates , dimethylammonium salts ) are reduced to a minimum , and tedious work - up steps , for example steam distillation , recrystallization , recycling of reactants and recovering solvents , are not required . 520 g of phosphoryl chloride were initially charged in a vessel fitted with stirrer and reflux condenser , 300 g of anthracene were added , and 165 g of dimethylformamide were added dropwise with stirring at 85 to 90 ° c . over a period of 7 hours . the reaction mixture was subsequently stirred for another 19 hours at 85 to 90 ° c . after this time , the conversion was 99 . 8 %. the resulting hot dark - red to black reaction mixture was introduced into a recipient vessel containing 2 l of water which had been heated to 50 ° c . and was stirred , and the temperature was kept at 50 to 60 ° c . during this operation . violent evolution of hydrogen chloride gas occurred , and the gas was discharged via a reflux condenser . the resulting reaction mixture was cooled to room temperature . the ph was adjusted to 3 . 5 by adding solid sodium hydroxide ( about 240 g ) a little at a time , during which the temperature was kept at 30 ° c ., and the mixture was then stirred at 60 ° c . for 1 . 5 hours . the 9 - anthracenecarbaldehyde , together with a little unreacted anthracene , precipitated quantitatively . the precipitate was filtered off and freed from most of the mother liquor . the filter cake that remained was once again suspended in 2 l of water , stirred at 60 ° c . for 1 . 5 hours and filtered off , and the filter cake that was obtained was washed with 500 ml of water . the solid was dried at 60 ° c ., affording 340 g of 9 - anthracenecarbaldehyde corresponding to a yield of 98 %. the melting point of the product was 104 ° c ., the 9 - anthracenecarbaldehyde content was 99 . 7 % ( determined by gc ) and the anthracene content was 0 . 3 % ( determined by gc ). by elemental analysis , the following values were additionally determined :