Halogenation in flow: a safe an sustainable alternative to the use of chlorine gas and elemental bromine in batch.

The time of big industrial installations spewing clouds of smoke and carbon dioxide into the
atmosphere is over. Nowadays, the main issues in industrial processes are safety, sustainability
and efficiency. Quality wins the favour over quantity. A possible way of achieving this is by
replacing hazardous chemical batch processes by microreactor processes. Microreactor and
mesoreactor technology consist of pumping the reagents through narrow tubes (10- 5000 μm) on
demand instead of reacting them in one big batch and storing them afterwards. This has several
advantages, i.a. a better control over the reaction parameters, resulting in a better reaction and a
lower risk of a runaway reaction and a subsequent explosion. It also facilitates the transition from
the laboratory to industrial processes. But the biggest advantage only shows when things do go
wrong: when a batch reactor explodes, tons of toxic intermediates can escape and cause harm.
When a microreactor explodes, only a few millilitres escape.
This will be put into practice with chlorination reactions: even though organochlorides are badly
needed in today’s chemistry, mostly as intermediate products, their production with chlorine gas
is a dangerous process. By producing chlorine gas inside the microreactor from hydrochloric acid
(the main component of gastric acid) and sodium hypochlorite (common household bleach) and
reacting it directly with organics, the risk for chlorine gas-related accidents will be eliminated.