An Apparatus Permitting Constant Addition of Liquid ~mmoniain Preparative Scale Ammoniolysis Reactions Stephen J. Caflerl GTE Laboratories, Inc., 40 Sylvan Road, Waltham, MA 02254
Ammoniolysis is a common procedure in chemical synthesis and is usually achieved by bubbling the gas through a solution of the co-reactant. However, this process can he time-consuming and inconvenient on a large scale when certain aprotic solvents are used. Problems with this method can also arise when accurate quantities of ammonia are required to ensure stoichiometric additions. An alternative method involves the transfer of a known amount of liquid ammoniato the reaction vessel via a cannula. Unfortunately, slow, even addition of liquid ammonia is often difficult to achieve under these circumstances. The apparatus described here utilizes principles of ammonia distillation2 to enable a precise volume of liquid ammonia to be delivered a t a steady rate under an inert atmosphere. The use of grease is entirely avoided. I t consists of two Dewar-type condensers that terminate in extended glass tubing (see Fig. 1) and that are linked near the top by a Teflon valve. Provision is made in one condenser for an angled 24/40 ground glass joint. Figure 2 shows the twin condenser integrated in a typical experiment configuration. The Teflon line carrying the incoming ammonia gas is attached to a short piece of glass tubing that is positioned in the ground glass joint through the use of a Kontes Teflon adapter. The condensation and reaction flasks are connected similarly to the condenser "legs". A mechanical stirrer can be fitted into the center joint of the reaction flask if desired. orovided that a 500-mL or larger vessel is used (operation is greatly farilitated through the use of a flenihle stirrine shaft to enable relocation of the stirrer motor). In this case, the condenser "leg" is placed in an outer joint of the reaction vessel. A typical reaction sequence involves the following steps: (1) Establishment of an inert atmosphere within the apparatus. (2) Charge of the reaction vessel with reagents and solvent. This can be conveniently carried out in a glove box if required, in which case, the joint bearing the Teflon adapter is fitted with a sealed glass tube that serves as a plug until connection to the condenser is achieved under aflow of inert gas from both the reaction vessel and the condenser "leg". (3) Condensation of ammonia. This is accom~lishedby cooling the rondensation vessel and condenser to-760 OC, first making sure that the intercondenser valve is shut and that the condensation vessel's stopcock is open to the inert gas/ vacuum manifold. (4) Distillation. The other condenser and reactionvessel are now cooled to the desired temperature. (It has been found that the loss of ammonia on distillation is negligible with vessel temperatures as high as -20 OC.) The intercondenser valve is opened and the condensation vessel's stopcock is closed. It must be verified that there is a clear gas pathway from the reaction vessel to the manifold that can relieve pressure buildup. (The Teflon gas line should incorporate a valve that is reasonably close to the condenser which can be shut off a t this time.) The coolant
from the right-hand condenser is removed by an aspirator (acetoneldrv ice is sueeested as this mixture tends to be less .~~~~~ .... viscot~sthan isopropanol,dry ire at low temperatures) and the cooline Dewar is lowered free i f the condenintion vessel. As soon a\ the ammonia begins to boil, a reading of the volume in the condensation vessel should he taken. Within a ~
Figure 1. Schematic diagram of the apparatus: ail dimensions are In centimeters. (I) 0.5 a d . glass rod suppMt. (2) Dewar-type condenser, inner chamber 5 X 20: Outer 0.d. 7.5-8.5 (7.5 is beher if a mechanical stirrer isto be used). (3) Valve 1e.g.. Ace 8192-09). (4) $24140 female joint. (5) Glass tubing i.d. 0.75. 0.d. 1.0.
'
Present address: Dartco Manufacturing. Inc.. P.O. Box 5867. Augusta. GA 30906. Nicholls, D. Inorganic Chemishy in Liquid Ammonia; Elsevier: Amsterdam. 1979; Chapter 3.
Figure 2. The apparatus shown integrated in a typical experiment configuration.
Volume 64
Number 4 April 1987
365
few minutes the ammonia will distill into the reaction vessel at a rate of 1 drop every 3-4 seconds until the condensation flask is empty. Distillation can he temporarily halted by reimmersing the condensation flask in the Dewar, closing the intercondenser valve and opening the stopcock of the
366
Journal of Chemical Education
condensation flask. The distillation rate can also be varied by partially cooling or gently warming the same flask. The addition of Teflon granules to the condensation vessel is recommended to lessen bumping if fast distillation is required.
