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chapter thirteen
Large-scale reactions
13.1 Introduction
This chapter deals with some of the techniques required when work-
ing with larger scale reactions. For the purposes of this chapter, we
will dene a larger scale reaction as one involving reaction volumes
between 1 and 5 L. Working on reaction volumes in excess of this usu-
ally requires the use of specialist equipment and is beyond the scope
of this book.
Compared with small scale, there are additional issues that must be
considered when moving to large scale work. Safety is the main concern
because on a larger scale, all the hazards associated with a reaction are
increased. It is, therefore, essential to test the reaction on a small scale
before attempting it on a larger scale and always limit any scale up to
10-fold.
Some of the main issues that need to be considered when working on
a larger scale are as follows:
1. Everything will tend to take longer. Because of the larger volumes
involved, reagent addition, evaporation of solvent, phase separation
during work-up, and so on, will all take longer than they did on a
smaller scale, so make sure that you have enough time available to
complete the experiment. The reaction apparatus will also be signi-
cantly heavier, so make sure that it is held securely.
2. Effective agitation can be a problem. Mechanical stirring is usually
necessary as magnetic stirring is ineffective in larger equipment.
It can also be benecial to include a bafe in the reaction vessel
as this will improve the effectiveness of the agitation. Something
as simple as a thermometer dipping into the reaction mixture
will cause signicant turbulence and have a benecial effect on
mixing.
3. Addition of reagents will require careful planning. Manual addition
via a syringe can be used for smaller quantities (<50 cm
3
), but syringe
pumps are more useful for addition of larger quantities, particularly
when slow, controlled addition is required. Addition of solutions via
pressure-equalized dropping funnels can also be used, but these do

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