parrshaker

parrshaker, biotransformation

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168
Chem. Educator
2001,
6,
168Î171
A Simple and Inexpensive Alternative to a Medium-Pressure
Hydrogenation Shaker-Type Apparatus
Douglas C. Smith,* John H. Craig, and Stanley E. Hill, III
Department of Chemistry, California State University, San Bernardino, San Bernardino, CA 92407,
dcsmith@csusb.edu
Received September 25, 2000. Accepted November 15, 2000
Abstract:
Materials and directions for the assembly of a safe and low-cost medium-pressure hydrogenator are
provided. Most items required for the construction of this apparatus were readily available at local home
improvement stores. The apparatus was tested at a pressure of 60 psi, and typical experiments were performed at
60 psi.
Introduction
suggested pressure for these borosilicate-glass bottles, as
suggested by Parr, is 60 psig; thus, the maximum pressure for
leak tests and reactions should not exceed these manufacturer's
recommendations. Finally, it is strongly advised that the entire
reaction-vessel-containment system be enclosed behind a
safety shield for additional protection.
For sample preparation, all reaction mixtures should be
degassed prior to use. This is most efficiently accomplished
using one of the following two methods: (1) Bubble a stream
of nitrogen gas through the solution for approximately fifteen
minutes prior to attaching the borosilicate-glass bottle, see
below, to the containment system or (2) Evacuate the flask
containing the reaction mixture and subsequently refill the
flask with an inert gas, such as argon or nitrogen. Repeating
this procedure three times should minimize any exposure of
the reaction mixture to oxygen.
Recently, this laboratory had the need to perform medium-
pressure catalytic hydrogenations at ambient temperature, but
did not have the resources to purchase a costly commercial
shaker-type apparatus. To meet this need, a new and cost
effective (total cost ca
.
$30.00) bottle-containment system was
designed to be used in conjunction with the Parr 250-mL
borosilicate-glass bottle, a hydrogen-gas cylinder, and a
hydrogen-gas regulator. Shown below is a schematic (Figure
1) and a photographic (Figure 2) representation of the reaction-
vessel-containment system designed in this laboratory. It
should be noted that this bottle-containment system was used
routinely at pressures of 60 psi without leaks or stress upon
this system. (Note: All pressure tests were conducted over a 30
min period using an inert gas, nitrogen, prior to using
hydrogen gas in this system.)
Construction Procedure
Preliminary Remarks
The bottom assembly is fashioned as follows. Each threaded
zinc rod is fitted with one 1/4-in nylon locking hex nut. The
four rods are inserted through the equidistant holes of the 1-in
floor flange [4] such that the flat surface of the flange faces
upwards and the lock nuts rest against its contoured surface.
The threaded rods are then fixed into place against the floor
flange using 1/4-in SAE washers and a regular 1/4-in hex nut.
The taped borosilicate bottle, containing the reaction
mixture and a magnetic stir bar, is placed against the flat
portion of the first floor flange inside of the four upright
treaded rods, and this partial assembly is placed on top of a
magnetic stirrer.
The upper portion of this assembly is then prepared as
follows. A 1-in bushing is screwed into the central hole of the
contoured face of the second floor flange. The copper tubing
(1/4-in) is inserted into the central hole of the flange/bushing
assembly and a number 6 rubber stopper is affixed to this
tubing such that the stopper rests next to the bushing with the
tapered portion of the stopper facing away from the bushing.
The stopper is fitted into the neck of the bottle and the upper
portion of this assembly is placed against the stopper, such that
the threaded rods pass through the four equidistant holes of
this plate. Each rod is then fitted with a second SAE washer
The hydrogenation apparatus presented herein has been used
in an undergraduate research setting by well-trained
undergraduate research students (usually at the junior or senior
levels),
with proper faculty supervision
. It is essential that the
supervising faculty member be knowledgeable about and
experienced in performing catalytic hydrogenations [1].
Moreover, the supervising faculty member should be
conversant in working with compressed gasses [2], particularly
hydrogen gas [3].
Safety.
It is important that proper precautions are taken
while employing this apparatus. This apparatus should be used
in a well-ventilated area. No flames or other possible ignition
sources should be used while working with hydrogen gas, as it
is very explosive. In addition, to further reduce explosion risk,
care should be exercised to prevent the exposure of hydrogen
gas to any incompatible oxidants (consult an MSDS form for
additional details).
All persons working with this equipment should wear
appropriate eye protection (goggles). In addition, it is also
suggested that all connections in this apparatus be tested for
leaks (a soapy water solution works well) using an inert gas,
such as nitrogen, prior to use. Moreover, the maximum
¨ 2001 Springer-Verlag New York, Inc., S1430-4171(01)03467-8, Published on Web 04/27/2001, 10.1007/s00897010467a, 630168ds.pdf
A Simple and Inexpensive Alternative to a Medium-Pressure Hydrogenation
Chem. Educator, Vol. 6, No. X, 2001
169
H
2
gas in
Wing Nut
1Ñ Floor Flange
1Ñ Bushing
Rubber Stopper
Copper Tubing
Threaded rod
Borosilicate
hydrogenation
bottle
Normal Hex-nut
1Ñ Floor Flange
Locking Hex-nut
Figure 1.
Schematic representation of reaction-vessel-containment system.
Ph
H
60 psi H
2
Ph
Ph
Cl
-
Cl
-
HO
N
and
HO
N
Ph
Pd on C
H
H
1
2
and the entire upper assembly is very tightly secured against
the rubber stopper using Đ-in wing nuts.
Finally, the entire cage is covered with carpenterÓs cloth, a
heavy gauge steel mesh, which is held in place using cable
ties. For additional safety, the entire bottle-containment system
is surrounded with a safety shield.
The second stage of a hydrogen gas regulator is used to
deliver the required pressure to the reaction vessel. The
regulator itself is connected to a three-way brass "T" joint
using
copper tubing. This same T joint is also attached to the
other end of the copper tubing fitted with the number 6 rubber
stopper. The third terminus of the T joint is connected to a
needle valve and the entire system can be readily vented to a
well-ventilated area through means of this valve (Figure 3).
Although a magnetic stir bar and a stir plate are used for the
agitation required for this reaction in place of a shaker-type
apparatus, it was found that reactions took place in a
satisfactory amount of time. Because we do not have a
commercial Parr apparatus available, comparative kinetic
studies of standard Parr equipment versus this inexpensive
model have not been performed. One of the authors prior
experience, however, is that hydrogenation with the
inexpensive equipment can actually proceed faster than with
commercial Parr equipment, because hydrogen entrainment
from cavitation of a rapidly spinning stir bar can effect more
efficient movement of hydrogen into the reaction solution than
can horizontal, vigorous shaking. Nevertheless, the actual rate
is strongly dependent on size and shape of the spin bar and its
rate of spin, something that we have not made an effort to hold
constant and quantitate.
A Typical Reaction Procedure
The above reaction is carried out according to the procedure
reported by Triggle [5]. Accordingly, 0.23 g of 5% Pd/C, 2.33
g (9.74 mmol) of the hydrochloride salt
1
, 25 mL of ethanol,
and a magnetic stir bar are placed in a 250-mL borosilicate-
glass bottle, and the resulting mixture is degassed by placing
the sample under vacuum, followed by purging with
anhydrous nitrogen gas. This flush and fill procedure is
repeated three times in order to ensure satisfactory removal of
dissolved oxygen. Subsequently, the reaction vessel is placed
inside of the apparatus and secured using the wing nuts,
carpenterÓs cloth and a safety shield; see above. The reaction
¨ 2001 Springer-Verlag New York, Inc., S1430-4171(01)03467-8, Published on Web 04/27/2001, 10.1007/s00897010467a, 630168ds.pdf
 170
Chem. Educator, Vol. 6, No. X, 2001
Smith et al.
Figure 2.
Photograph of reaction vessel containment system.
Relief valve
Relief tubing
to a well
ventilated
area
1/4Ñ Copper tubing
Hydrogenation
Apparatus
H
2
Gas
Cylinder
Brass T-joint
H
2
Gas
Regulator
Stir plate
Figure 3.
Diagram of the hydrogen-gas delivery system.
¨ 2001 Springer-Verlag New York, Inc., S1430-4171(01)03467-8, Published on Web 04/27/2001, 10.1007/s00897010467a, 630168ds.pdf
 A Simple and Inexpensive Alternative to a Medium-Pressure Hydrogenation
Chem. Educator, Vol. 6, No. X, 2001
171
mixture is subjected to 60 psi of H
2
and stirred vigorously for
72 h. After this time interval, the pressure in the system is
released into a fume hood and the sample evacuated and
purged with N
2
in order to remove any residual hydrogen gas.
The catalyst is removed by filtration and the solvent is
removed under reduced pressure. The resulting mixture is
redissolved in 50 mL of methanol and extracted three times
with 25 mL of hexane. The resulting methanol solution is
concentrated in vacuo to afford 0.95 g (8.6 mmol) of the
ammonium salt
2
in 61% yield. This material gives physical
and spectral characteristics identical to those reported
previously [4].
4 threaded rods, 1-ft length and 1/4-in diameter with
standard 20-gauge threading
2 1-in Floor Flanges
1-in bushing
4 1/4-in hex nuts
4 1/4-in nylon lock nuts
8 1/4-in SAE washers
1-ft by 2-ft section of carpenters cloth
2 or 3 14-in cable ties
250-mL borosilicate-glass reaction bottle obtained from Parr
Acknowledgments.
We are grateful to the Henry and
Camille Dreyfus Foundation for funds with which to purchase
equipment and supplies (Award No. SL-96-02). We are also
grateful to Dr. Dennis Pederson of this institution, for his
assistance in the preparation of this manuscript.
Conclusion
This containment system, used in conjunction with a
magnetic stir plate, was capable of withstanding pressures of
60 psi for prolonged periods of time. The parts used in the
assembly of this reaction-vessel-containment system were
conveniently found at most home improvement stores and
were relatively inexpensive (total cost, ca.
$30.00).
This
reaction-vessel-containment system has been used safely and
routinely in this laboratory for carrying out medium-pressure
catalytic hydrogenations at ambient temperature. Again, it is
strongly advised that the individuals employing this apparatus
be experienced in performing catalytic hydrogenations and
knowledgeable in the use of compressed gases and medium-
pressure devices.
References and Notes
1.
Freifelder, M.
Practical Catalytic Hydrogenation, Techniques, and
Applications;
Wiley Interscience: New York, 1971. (b)
Organic
Syntheses,
Collective Volume I, 2nd ed.; Gilman, H.; Blatt, A.H.,
Eds Wiley & Sons: New York, 1964; pp 61Î67. (c) For a general
review of catalytic hydrogenation, refer to Rylander, P. N.
Catalytic
Hydrogenation in Organic Syntheses;
Academic Press: New York,
1979.
2.
(a) Matheson Gas Products Inc.
Guide to Safe Handling of
Compr
e
ssed Gases,
3rd ed.; Matheson Gas Products: Parsippany,
NJ, 1983. (b)
Prudent Practices in the Laboratory, Handling and
Disposal of Chemicals;
Committee on Prudent Practices for
Handling, Storage, and Disposal of Chemicals in Laboratories;
National Academy: Washington, D.C., 1995; pp 121Î128.
Itemized List of Parts
3.
Braker, W.; Mossman, A. L.
Gas Data Book, 6th Ed.
; Matheson Gas
Products: Secaucus, NJ, 1980; pp 366Î369.
1/4-in copper tubing
1/4-in brass three-way "T" joint with gas-tight fittings
1/4-in brass needle valve with gas tight fittings
hydrogen-gas regulator with gas-tight fittings for 1/4-in
copper tubing
4.
The floor flange is the name of a plumbing item, and it is referred to
by this name in home improvement stores. They are predrilled and
can be used without any modification.
5.
Chatterjee, S. S.; Triggle, D. J.
Chem. Commun.
1968,
93.
¨ 2001 Springer-Verlag New York, Inc., S1430-4171(01)03467-8, Published on Web 04/27/2001, 10.1007/s00897010467a, 630168ds.pdf
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