If the liquid comes as a solution in solvent, simply add it via syringe.
For highly exothermic reactions, or other reactions
requiring slow addition, dilute neat liquids with reaction solvent
before adding it via syringe or addition funnel.
For slow reactions (hours to completion), neat liquids may be added via
For corrosive, reactive, or viscous liquids, see also: How to handle difficult compounds.
Atmospheric pressure of hydrogen, carbon monoxide, or carbon
dioxide: Addition is accomplished by replacing the
atmosphere of the reaction
mixture with the gas using a balloon. First, the gas is bubbled through the
solution (via pipette/tubing or needle/luer lock/tubing) for a few minutes to
achieve saturation. Then, the balloon is left connected to the flask for the
duration of the reaction, providing ~1 atm (aka "positive pressure") of gas.
When a procedure requires "dropwise addition" of a reagent.
By hand: You stand with the reaction and manually control the rate of
addition by syringe.
By syringe pump:
If one is available, this is the most precise method
for slow addition, and works well for addition of a range
of solvent volumes.
By addition funnel: The addition funnel works
best for large scale reactions,
when >15 or 20 mL of solvent must be added over a long time period.
Round-bottom flask: All purpose vessel for standard reactions.
Flasks with two or three necks are useful for reactions...
Test tube: Septa fit nicely on the tops of test tubes-
this reaction vessel is
useful for screening reaction conditions and for smaller
scale procedures. Best
for reactions run in the zero degrees to room temperature range.
Heavy-wall conical vial: These are good for
small scale reactions that must be
run at high temperature. The vials are sealed, so solvent cannot escape, and
allow stirring of small volumes of solvent. Obviously, the contents develop
pressure as they are heated.
Erlenmeyer flask: These are not used for air-sensitive
reactions, but allow
good stirring of heterogeneous mixtures of 50 mL or more.
They are also useful
for stirring biphasic mixtures if necessary during aqueous workup.
Pear-shaped flask: Just like a round-bottom flask, but elongated.
Sometimes useful for reactions run in baths. The elongated flask
can allow more efficient stirring, because the stir bar is closer
to the stir plate.
Heart-shaped, or "recovery" flask: These flasks have a
pointed end, and are
not used for reactions (stirring is not efficient). However, upon
rotoevaporation, a small amount of oil will become concentrated in the point,
making it easy to dissolve and remove by syringe or pipette. Similarly, it is
easy to scrape solids off the walls of the flask and into the point for easy