(Seek help) Separation of 345-trichlorotrifluorotoluene series

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Background: The raw material contains 3,4-dichlorotrifluorotoluene； 3,4,5-Trichlorotrifluorotoluene ； 2,4,5-Trichlorotrifluorotoluene ； There are also some other impurities. The boiling point of 34 is 173°C, that of 345 is 202°C, and that of 245 is above 210°C. Question: In intermittent distillation, during the distillation process, logically speaking, since 34 has a lower boiling point, it should emerge first. However, during the separation process, both the 345 product and the 245 product also contain 34, and the higher the degree of distillation, the greater the amount of 34 – rising from 0.5% at the beginning to 3%. I would like to ask whether this substance decomposes Is it possible for one of the components in the recombined impurities to break down into 34? The image below is the test report for the residue after steaming. I need an expert to help answer this.