We performed isothermal pentachlorophenol synthesis experiments to obtain data useful for kinetics analysis and reaction pathway resolution. The rate of pentachlorophenol production was not a monotonic function of temperature, and no pentachlorophenol was ever observed before the tetrachlorophenol yield reached its maximum value. The results were consistent with a reaction network wherein trichlorophenol forms an intermediate product, which then forms tetrachlorophenol. Pentachlorophenol then forms from tetrachlorophenol through an autocatalytic pathway. Microcontaminants produced during pentachlorophenol synthesis included hexachlorobenzene and hexa, hepta, and octachlorodibenzodioxins. The total amount of microcontaminants at a given temperature initially increased with time, and at the higher temperatures reached a maximum and decreased. The total amount of microcontaminants was lower at a lower temperature, for a given pentachlorophenol yield. Finally, these experiments produced pentachlorophenol in roughly the same yield and with roughly the same microcontaminant level of commercially produced pentachlorophenol, which indicates a general correspondence between the laboratory experiments and the plant reactor, though the two systems operate differently.