suitable pipework to other pieces of specialized plant such as filtration, crystal-
lization and drying equipment. A variety of methods are used to transfer the
product from the reaction vessel to these additional pieces of equipment. They
include the use of pumps, nitrogen gas under pressure, screw and conveyor
systems. Separations are usually carried out using the reaction vessel as the
separator and running the lower liquid phase out of the bottom of the reaction
vessel. Control of the reaction and, if required, a subsequent operations are
achieved by the use of appropriate sensor systems and small armoured glass
windows known as sight-glasses, which enable the plant operators to view the
contents of the vessel and/or pipework.
The reactions selected for pilot and manufacturing processes must take into
account the limitations of the available plant, for example the reaction vessel
and the ancillary equipment required for isolation and purification of the
product. Reaction vessels usually have an operating range of between about
15 and aboutþ 140 C. Consequently, as both heating and cooling are expen-
sive, the reactions selected should give a satisfactory yield as near to room
temperature as possible and certainly within the temperature control limits of
the vessel. Furthermore, large scale reactions require longer processing times,
because they take longer to reach their working temperature, produce a satis-
factory yield and cool down than laboratory preparations. This means that the
reagents, products, solvents and catalysts used must have an adequate degree of
stability under the prevailing operating conditions.
11.2.2 Chemical plant, health and safety considerations
Health and safety is of paramount importance when selecting the reactions
for either the pilot or manufacturing processes. A full chemical hazard assess-
ment should be carried out before commencing the reaction on a large scale.
This should cover the chemistry of the process, the safety of the plant operatives,
waste disposal and its impact on the environment. The chemical and biological
hazards associated with all the chemicals and solvents used in the reactions
should be documented, together with protocols for dealing with accidents, leaks
and spillages. Even in the best regulated chemical plants there will be some
leakage of compounds, such as solvent vapour and chemical dust into the
atmosphere, and so monitoring equipment must be appropriate for the sub-
stances being used. Reactions that involve handling highly toxic substances
should not be used unless there is no alternative. In this case a stringent protocol
governing their use must be drawn up and enforced. One important consider-
ation for all health and safety protocols is the nature of the thermochemistry of
226 DRUG DEVELOPMENT AND PRODUCTION