Research Group Responsibilities (compiled by Samuel Huang)
Since most research groups operate under a commune-type relationship, it is necessary for each person in the laboratory to perform their respective duties. The following section attempts to outline the different types of responsibilities involved with maintaining a smooth running research group. Also included within this section is some information detailing what is involved with each of these responsibilities. It is worthwhile to attempt to gain experience with each of these chores so that you may become proficient, as you may be called upon to perform similar tasks in future employment (assuming that chemistry is in your future!).
1) Maintaining the Anhydrous Solvent Stills
If your research lab is involved with the handling of air and moisture sensitive reagents, it is necessary to maintain anhydrous solvents in order to run your reactions. Thus, ensuring a low water content in the solvents employed is absolutely necessary. The following are some instructions for handling the solvent stills. Note that all solvents are distilled under a stream of dry nitrogen or argon to ensure the anhydrous nature of the solvent, as well as to eliminate the exposure of these solvents to air (a necessity for performing air sensitive chemistry). Argon gas is somewhat superior to nitrogen in that it is heavier and is less prone to displacement by air.
Tetrahydrofuran*, Diethyl Ether* and Dimethoxyethane* are ethereal solvents, which are most effectively dried by refluxing over an appropriate drying agent; currently, this is a reactive species called a ketyl. This is formed by refluxing the solvent with 1-2g of sodium, sliced very thin to maximize its surface area, for about 30min; then, a small quantity (several grams; about a tablespoonful) of benzophenone (Ph2C=O) is added. Within only 5-10min at reflux, the mixture will take on a beautiful deep blue/purple color; this color indicates that the solvent is not only anhydrous, but oxygen-free. It is now ready for collection to be used in a reaction.
Quenching of a still is typically accomplished by cooling the pot of the distillation apparatus to 0 °C and slowly adding t-butyl- or isopropyl alcohol to the mixture with vigorous stirring, although we have been experimenting with quenches at higher temperatures. Students must be checked out by the experienced postgraduate students in order to be allowed to perform quenches; if the process is done incorrectly, fires and/or explosions can occur.
Dichloromethane*, Benzene**, and Toluene all have similar drying procedures as well. These solvents are most effectively dried by heating these solvents to reflux over calcium hydride (CaH2). Calcium hydride is a metal hydride which, relative to others (especially Group I) is of low reactivity (it is fairly selective for water). After these solvents are refluxed with calcium hydride for several hours, the pot will appear as a dark gray suspension); it is now time to distill the anhydrous solvent.
This type of still is quenched as above, except that 95% ethanol is used as the acid. Once again, I must check you out before you can do it on your own (but not alone, of course!).
The solvents listed above are among the ones more commonly in organic research. If you require other anhydrous solvents, two excellent sources of methods for the purification of chemicals is shown below.
Arnold J. Gordon and Richard A. Ford. The Chemists Companion. New York: John Wiley & Sons, 1972.
D. D. Perrin and W. L. F. Armarego. Purification of Laboratory Chemicals, 3 rd edition. Oxford: Pergamon Press, 1988.
* These solvents are most usually in our permanent stills in the left-most hood.
**Benzene is toxic and carcinogenic; it should be used only when absolutely necessary and only after checking with experienced postgraduate students first.
2) Group Supplies
This important job is to ensure that the group has a continuous supply of single-use items which researchers use daily; if we run out, things can come to a screeching halt! Some things we get from the stockroom; others we order. These items include acetone for cleaning glassware, anhydrous ethyl ether, paper towels, bulk solvents, disposable pipettes and small test tubes, concentrated acids, certain inorganic reagents, Kimwipes7, TLC plates, and the like.
Although there is a place on the board for people to write items that we need, part of this responsibility entails just being vigilant. It's nearly always possible, and an excellent idea, to have an item or two "in stock" in the lab, so that if we run out of something on a weekend, we won't run out (get it?). This would be particularly true for solvents.
3) Vacuum Pumps, Manifold, Rack, and Lines
This job is one that, if not done conscientiously, will have other group members screaming! The area around the vacuum rack must , as well as periodically cleaning the glassware associated with the line and occasionally re-greasing the ground glass joints of the vacuum line glassware. In addition, it is necessary to periodically drain the pump oil from these mechanisms, rinsing the inner chamber with organic solvent (usually with acetone or dichloromethane), and refilling the chamber with fresh pump oil. This needs to be done once every three months to ensure a long life of each vacuum pump. It is suggested that a maintenance log is kept for each individual vacuum pump describing problems with the pump, routine maintenance, oil changes, and the last measured operating pressure for each pump. If extended maintenance is required for a pump, the device in question should be taken down to the stockroom along with a tag explaining whose pump it is and what the problem is with the pump. A more detailed description for changing the pump oil is included in a later section of this manual.
Ensure that there are ample quantities of the most commonly employed solutions used during the aqueous work-ups of organic reactions. The common aqueous solutions employed our research lab are the following (all are saturated solutions unless otherwise specified):
Solution | Typical Uses |
Hydrochloric acid (1.5M) | used for removing amine reagents from reaction mixtures or for purifying amine products. |
Sodium Chloride | brine, used for removing water from organic solutions in an aqueous workup; it is usually the last solution the organic layer is washed with prior to using a drying agent. |
Sodium Bicarbonate | used for removing acid from the organic layer. |
Copper (II) Sulfate | for removing pyridine from reaction mixtures, esp. β-lactonizations.. |
Ammonium Chloride | commonly used as a mild acid for quenching mildly basic reactions, i.e. reductions and Grignard type reactions. |
Sodium Hydroxide(5% [w/v]) | used for removing acid and carboxylic acid reagents from reaction mixtures, as well as for removing phenols and thiophenols from reaction mixture |
To prepare saturated wash solutions, continue to add the inorganic salts to one gallon of distilled water until no more salt dissolves into solution and then add an additional quantity of the salt so that there is a layer of the salt about 1" deep at the bottom of the bottle. Doing this ensures that the wash solution will remain saturated.
A 5% aqueous solution of sodium hydroxide is prepared by dissolving 5 g of NaOH for every 100 mL of distilled water employed in preparing the solution. These are best stored in plastic bottles as highly alkaline (basic) solutions tend to etch glass upon standing for long periods of time.
A 1.5 M solution of hydrochloric acid may be prepared by diluting concentrated (12 M) HCl with distilled water. The ratio for such solutions is 125 mL of concentrated HCl and 875 mL of distilled water. This will prepare 1 L of the desired solution.
It is this person's responsibility to see to it that the balance area is being maintained in a clean fashion and to ensure that the balance is kept in working order. Should problems arise with the balance, it should be called in to either the stockroom or to Mr. Ramsey in the electronic shop down stairs. In addition to this, the person with this duty should also see to it that the refrigerator and other electronic or mechanical devices are in good working order. Also included in these items are the heating mantles, the hoods, light fixtures, the variable voltage transformers, the hoods, the rotary evaporator (Rotovap), and hot plates. Many of these items may be repaired by Terry Ramsey in the electronic shop on the first floor.
It is this person's responsibility to act as a liaison between the group and the chemical companies who supply the reagents and equipment employed within the lab. They are assigned to compile a list of chemicals required by the group, finding optimum prices for these chemicals, and ensuring a speedy delivery of these chemicals. In addition, they are responsible for checking with the chemical inventory person, to ensure we do not already possess this chemical, and with the research adviser for approval of the chemical order.
7) Chemical Inventory/Receiving
The person given this responsibility is entrusted to ensure that records are maintained for each chemical on hand. Ideally, these records should include the identity of the chemical, the quantity on hand, the date received and opened, the supplier of the chemical, and the location of this chemical within the research lab. This individual should attempt to make special note of any important storage requirements, and should file the necessary MSDS (Material Safety Data Sheets) of these chemicals for easy access within the group.
There are several reagents that are used fairly universally in our group, and this person's job is to be sure that we don't run out of distilled, pure reagents, stored in serum bottles to be used for syringe transfer. The reagents are, usually, the following:
Reagent | bp* | Dist'd. From | Stored Over | Comments |
Benzenesulfonyl chloride | 251 | nothing | 3Å sieves | Do in hood; nasty lachrymator |
Diisopropylamine | 84 | BaO | nothing | Can be off-color and still be OK |
Pyridine | 115 | BaO | nothing | Smelly; to some, it's unbearable |
Triethylamine | 89 | CaH | 3Å sieves | Stores very well, if pure |
*bp values are all in oC and at 760mm pressure.
The Waste Manager must ensure that log records are being maintained for each waste bottle and must act as a liaison between the stockroom and the research group for getting a timely schedule for waste collection. Forms for these waste bottles may be obtained from the stockroom and ideal containers for waste storage are 1 gallon glass bottles which are coated with a shatter resistant layer of polymer to prevent leakage if a breakage occurs. These bottles must also be properly labeled to ensure easy identification and content of these bottles.
沒有留言:
張貼留言