TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): Producing the compound (III) involves: heat-decomposing substituted 2-trifluoromethyl-(1,3)dioxolane-2-carbonyl fluoride compound of formula (II). Preferred Definitions:    -Rf1-SO2F and -Rf 2-SO2F=perfluorinated 2-fluorosulfonyl ethoxy group-substituted 1-3C alkylene.    SPECIFIC COMPOUNDS - 1 Compound i.e. 2-((2-difluoromethylene-5-(difluoro-(1,1,2,2-tetrafluoro-2-fluorosulfonyl-ethoxy)-methyl)-4,5-difluoro-(1,3)dioxolan-4-yl)-difluoro-methoxy)-1,1,2,2-tetrafluoro-ethanesulfonyl fluoride (III') is specifically claimed as (III).    EXAMPLE - Into a tube reactor an inner diameter of 1.6 cm, glass beads (central particle size of 105-125 microns, glass bead number 150) were filled until the filled height reached 40 cm, and then the tube reactor was heated to 325 degrees C. While continuously heating the tube reactor, a gas mixture comprising 99 mol.% of nitrogen gas and 1 mol.% of vaporized gas of 4,5-bis-(difluoro-(1,1,2,2-tetrafluoro-2-fluorosulfonyl-ethoxy)-methyl)-4,5-difluoro-2-trifluoromethyl-(1,3)dioxolane-2-carbonyl fluoride preliminary (II) heated in the raw material line, was introduced from the bottom of the tube reactor in such a manner that the linear speed of the gas mixture in the tube reactor was 2.65 cm/second. Further, at the top end of the tube reactor, a dry ice trap was set up. In such a state, the above gas mixture was supplied for 2 hours, and then only nitrogen gas was let flow through for 1 hour. The amount of the compound (II) introduced in the tube reactor was 3.96 g. As a result, liquid (2.45 g) recovered in the dry ice trap, and the presence of the product having a purity of 85.5% was produced. The actual yield of the compound 2-((2-difluoromethylene-5-(difluoro-(1,1,2,2-tetrafluoro-2-fluorosulfonyl-ethoxy)-methyl)-4,5-difluoro-(1,3)dioxolan-4-yl)-difluoro-methoxy)-1,1,2,2-tetrafluoro-ethanesulfonyl fluoride (III') was 60%. By distilling the heat-decomposition crude liquid obtained in the same manner, the objective compound (III') (a mixture of anti-form and syn-form) having boiling point of 99-102 degrees C/0.40-0.53 kPa was obtained.