There are thousands of toxic chemicals that could be used in chemical weapons. Depending on the type of agent to be produced, there can be technical hurdles that must be overcome. Classic agents can be manufactured using existing chemical infrastructure, and most have legitimate commercial uses. Likewise, vesicants are not technologically complicated. The production of the nerve agents, however, requires significantly more sophisticated chemical processing.
Some production processes require strict temperature control.
Containment of toxic substances and gases can pose problems. Depending on the immediacy of use, purity of product can add a difficult dimension to production. These hurdles can be overcome. If sufficient purity cannot be attained, an agent can be manufactured and used immediately. This presupposes the capability to manufacture a sufficient quantity in the time allotted.