I wanted to ask what's the temperature required for carrying out elimination reactions?
Wherever I read about elimination reactions, they just mention that elimination reactions occur at high temperature and substitution reactions are favoured at low temperatures.
So how do I decide which is high temperature and which is low, because we always talk in relative terms
Does it mean room temperature? If so, then will elimination reaction be favoured at $40^{\circ}$C for instance?
This is a question that is answered by careful experimentation [Possibly the experiment has been done already]. Primary and secondary require high T to dehydrate usually about 150-200C, intermediate temperature can give ether formation especially for primary; Usually conversion to a halide or sulfonate followed by base E2 reaction is superior. Tertiary or benzyl will dehydrate more easily. My experience with reacting substituted benzyl alcohols to make chlorides and bromides [more difficult] with thionyl chloride and PBr3, both very acidic reagents, gave very little E1 reaction at room temperature for most compounds. However, methoxy substituted phenyl compounds would eliminate almost immediately; I made some but they were thermally unstable probably because I couldn't purify them. My point is that one doesn't know until one tries. The text book pat answers are guides.
25°C (approx) is considered to be low (room temperature). Substitution reactions are favoured. And we consider 50°C (approx) to be high and elimination reactions are favoured at this temperatures.
