hereinafter , the present invention is described in more detail with reference to examples . γ - alumina ( al 2 o 3 ) a ( pore volume of 0 . 45 ml / g ) ( average particle size of 3 mm ) that was not fluorinated was used as a catalyst . the catalyst was placed in a tubular hastelloy reactor with an inner diameter of 15 mm and a length of 650 mm . the reactor was heated to 200 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . table 1 shows the contact time : w / f ( g · sec / cc ), i . e ., the ratio of the amount of the catalyst w ( g ) relative to the supply rate f ( cc / sec ) of the starting material . the outlet gas from the reaction tube was analyzed using gas chromatography . table 1 shows the analysis results . the numerical values shown in table 1 are the component proportions ( mol %) determined by multiplying the area ratio of each peak obtained by the gas chromatography by a coefficient for correcting a sensitivity to each gas . the low - boiling - point component containing ch 3 f and the high - boiling - point component containing fluoride were separately analyzed . the analysis results in table 1 show the ratio , expressed as a percentage , of each of them to all of the components . as is clear from the above results , the two desired compounds , i . e ., fluoromethane ( ch 3 f ) and 3 , 3 , 3 - trifluoro - 2 -( trifluoromethyl ) propanoyl fluoride (( cf 3 ) 2 chcof ), can be obtained as main components by a pyrolysis reaction of 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether . the yields of these compounds were both 91 % or more , and impurities were suppressed to 0 . 8 % to 2 . 1 %. the gas obtained after the pyrolysis in example 4 was passed through a 5 wt % koh aqueous solution , so that ch 3 f accounted for 99 . 5 % of the gas component . this result confirms that 3 , 3 , 3 - trifluoro - 2 -( trifluoromethyl ) propanoyl fluoride can be separated and removed by bringing the produced gas after pyrolysis into contact with an aqueous alkaline solution . further , the gas obtained after the separation was cooled , collected , and subjected to rectification , thereby obtaining ch 3 f with a purity of 99 . 99 %. under the same conditions as those of examples 1 to 5 , the reactor was heated to 150 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . under the same conditions as those of examples 1 to 5 , the reactor was heated to 250 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . table 2 below shows the results obtained by analyzing the outlet gas from the reactor using gas chromatography . as is clear from the above results , when the temperature of the pyrolysis was 150 ° c . ( example 7 ), the conversion was nearly 100 %, and the yield of the product was high . when the temperature of the pyrolysis was 250 ° c . ( example 8 ), the conversion slightly decreased , but the yield of ch 3 f was maintained at a high value of 92 %. α - alumina ( example 9 ), tio 2 ( example 10 ), or cro 2 ( example 11 ) was used as a catalyst . under the same conditions as those of examples 1 to 5 , the reactor was heated to 150 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . when α - alumina ( example 9 ) or cro 2 ( example 11 ) was used , the conversion decreased , but the selectivity of ch 3 f and fluoride was high . since the selectivity is high , ch 3 f and fluoride can be obtained with high yields if the unreacted starting material is returned to the reactor . under the same conditions as those of examples 1 to 5 , the reactor was heated to 200 ° c . 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether in an amount of 15 cc / min , which is a starting material , was mixed with nitrogen in an amount of 15 cc / min , and the mixture was supplied to the reactor . a catalyst that was not fluorinated and had a different pore volume , i . e ., γ - alumina ( al 2 o 3 ) b ( pore volume of 0 . 38 ml / g ), c ( pore volume of 0 . 43 ml / g ), or d ( pore volume of 0 . 64 ml / g ) was used . γ - alumina b , c , and d had an average particle size of 3 mm . table 4 shows the results of example 12 obtained when a reaction was performed using b , the results of example 13 obtained when a reaction was performed using c , and the results of example 14 obtained when a reaction was performed using d . when c and d , which had larger pore volumes , were used , the yields of ch 3 f and fluoride were 99 %. further , these reactions were continuously carried out for 100 hours . the results of example 15 were obtained using b in the reaction for 100 hours , the results of example 16 were obtained using c in the reaction for 100 hours , and the results of example 17 were obtained using d in the reaction for 100 hours . as shown in examples 15 to 17 , the larger the pore volume , the smaller the decrease in the conversion and selectivity regarding ch 3 f and fluoride , and the longer the catalyst can be used even without regeneration . under the same conditions as those of examples 1 to 5 , the reactor was heated to 150 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . as a catalyst , γ - alumina ( al 2 o 3 ) d ( pore volume of 0 . 64 ml / g ) ( average particle size of 3 mm ) that was not fluorinated was used . the results of example 18 were obtained when a reaction was continuously carried out for 370 hours . the conversion regarding ch 3 f and fluoride decreased , but the selectivity remained high . the results of example 19 were obtained when a reaction was performed in the same manner as in example 17 except that w / f was changed from 5 ( g · sec / cc ) to 10 ( g · sec / cc ). the conversion was restored by increasing w / f , showing 98 %. then , the catalyst was removed , and composition analysis of the surface thereof was performed by xps ( esca ). the composition of the outermost surface was as follows : 25 wt % of fluorine , 8 wt % of carbon , 26 wt % of oxygen , and 41 wt % of aluminum . the results of example 20 were obtained when a reaction was continuously carried out at w / f = 30 ( g · sec / cc ) for 700 hours . the conversion and selectivity regarding ch 3 f and fluoride remained high . when w / f was increased and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether was sufficiently contacted with the catalyst , the conversion and selectivity were high even if the reaction was performed for a long period of time . under the same conditions as those of examples 1 to 5 , the reactor was heated to 150 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . as a catalyst , silica alumina a ( sio 2 / al 2 o 3 = 68 wt %/ 26 wt %) or silica alumina a ( sio 2 / al 2 o 3 = 83 wt %/ 13 wt %) was used . the conversion and selectivity regarding ch 3 f and fluoride were high . 3 . 6 g of γ - alumina ( al 2 o 3 ) d ( pore volume of 0 . 64 ml / g ) ( average particle size of 3 mm ) that was not fluorinated was placed in a tubular hastelloy reactor with an inner diameter of 15 mm and a length of 650 mm . the reactor was heated to 350 ° c . while nitrogen was supplied in an amount of 50 cc / min . trifluoromethane was then supplied thereto in an amount of 50 cc / min , and the mixed gas of nitrogen and trifluoromethane was allowed to flow at a trifluoromethane concentration of 50 vol % for 30 minutes to fluorinate the γ - alumina . composition analysis of the surface of the catalyst was performed by xps ( esca ). the composition of the outermost surface was as follows : 25 wt % of fluorine , 5 wt % of carbon , 29 wt % of oxygen , and 41 wt % of aluminum . using the thus - obtained fluorinated γ - alumina catalyst , the reactor was heated to 150 ° c ., and 1 , 1 , 3 , 3 , 3 - pentafluoro - 2 - trifluoromethylpropyl methyl ether , which is a starting material , was supplied to the reactor . the conversion was 100 %, and the yield of ch 3 f and the yield of fluoride were 96 % and 100 %, respectively .