It is not safe to use Teflon-lined stainless steel autoclaves for reactions involving toluene at high temperatures. Teflon is not compatible with toluene at temperatures above 121°C (250°F) and can degrade and release toxic fumes that can lead to health hazards. Additionally, Teflon-lined vessels are not designed for high-temperature and pressure applications.
In your specific case, exposing toluene to a temperature of 200°C for 5 hours in a Teflon-lined stainless steel autoclave is likely to cause the Teflon lining to degrade and release toxic fumes, which is extremely hazardous. The reaction conditions can also cause the Teflon lining to crack or blister, which can lead to the release of toxic and corrosive chemicals.
It is important to use vessels that are specifically designed and rated for the specific reaction conditions and chemicals being used. In this case, an alternate vessel material such as glass or Hastelloy® would be more suitable for the reaction conditions you have described. It is also important to ensure that proper safety measures are in place, such as personal protective equipment, ventilation, and emergency procedures, before conducting any chemical reactions.