Schlenk line

The successful polymerization of a, >-dienes via ADMET continually produces a small molecule, typically ethylene, and the removal of this small molecule drives the reaction. When Schrock s [W] and [Mo] alkylidenes (14) are used, care has to be taken in maintaining an inert atmosphere devoid of both moisture and air in order to avoid decomposition of the catalyst. For this reason, Schlenk line techniques such as those used to handle Ziegler-Natta or metallocene catalysts and high purity monomers are important. 

For oxidation by atmospheric oxygen a sample in an EPR tube may simply be opened to air and stirred. However, reaction with any other gas than air requires special handling of the sample on the manifold of a Schlenk line. Examples are oxidation by pure oxygen, reduction by hydrogen, and also the reaction by any gaseous substrate or inhibitor such as CO, C02, NO, N20, etc. Basically, there are two different experimental approaches mixing with a solution in which the gas is dissolved or mixing with a pressurized atmosphere of the gas. 

As noted, sol-gel syntheses for materials based on water-sensitive reagents, such as titanium isoproproxide, must be carried out under low pH20 conditions, which are typically achieved using either an inert atmosphere box (glove box) or under laboratory conditions using a Schlenk-line.73 The Schlenk-line, shown in Fig. 2.4,71 consists of a dual manifold arrangement with one line... 

Figure 2.4. (a) Typical Schlenk-line and (b) distillation/reflux apparatus used in sol-gel synthesis of film precursor solutions. [Reprinted from Ref. 71, with permission.]... 

N,N-Bis(2-mercaptoethyl)2-methylthioethylamine. In a flame-dried and argon-flushed tube (15 x 3.75 cm) fitted with a teflon needle valve, a solution of ethylene sulfide (4.40 g, 73 mmole) in toluene (13 mL) is added to a solution of 2-methylmercaptoethylamine (2.65 g, 29 mmole) in toluene (10 mL). The valve is then closed to seal the tube and the mixture is allowed to stand for 8 h at room temperature. The sealed tube containing the reaction mixture is then heated to 110-130°C for 30-40 h. After cooling to room temperature, the tube is attached to a Schlenk line and opened under N2. The product mixture is filtered to remove a white precipitate (ethylene sulfide polymer), and the solvent is removed under vacuum. The residual liquid is fractionally distilled at reduced pressure (1I4-II6°C 0.03 mm) to yield N,N-bis(2-mercaptoethyl)2-methylthioethylamine as a colorless liquid. Yield = 3.56 g (58%). 

The product is a colorless, air- and highly moisture-sensitive solid which has to be handled under an inert gas atmosphere (Schlenk line or glove box). It is soluble in ethers, chloroform, toluene, and acetone. The NMR spectrum (CDC13) exhibits two singlets at <5 0.33 (3H) and 0.62 (18H) (external tetra-methylsilane, TMS). 13C NMR (CDC13) <5 -13.4, 4.5. 

All operations are carried out in a protective atmosphere of high-purity dinitrogen using standard Schlenk line techniques to prevent oxidation of the molybdenum(III) compounds and to avoid hydrolysis of the compounds by reaction with water vapor. Tetrahydrofuran (THF) (HPLC grade) is dried with 3-A molecular sieves 48 h prior to use. 

All operations are carried out under an inert atmosphere using standard Schlenk line techniques.1 Either deionized or distilled water which has been... 

Fig. 4.3. Solvent storage tubes with Teflon valves, (a) The O-ring joint on the sidearm allows attachment to a vacuum line equipped with O-ring joints, (b) Same basic design as in (a) with a straight sidearm. This design is easily connected to a Schlenk line via Tygon or other flexible tubing that fits over the sidearm.

For forty years following the introduction of haloaluminate-based ionic liquids by Hurley and Wier, [44, 45] the majority of research in this field was carried out on systems which were reactive with air and, more specifically, with water. The difficulty of working with these materials, using elaborate Schlenk-line airless techniques or expensive and difficult-to-maintain controlled-atmosphere glove boxes, had the effect of limiting the research to four American-based research groups, mostly funded by the US Air Force [46]. Well aware of this limitation, John Wilkes and coworkers made the decision to substitute the reactive haloaluminate anion... 

Most commonly known as a Schlenk line (see Fig. 7.19), this vacuum line/appa-ratus allows easy evacuation and purging of Schlenk items (see Fig. 7.20). The concept for Schlenk procedures is very simple One simply evacuates an item connected by a thick-walled tube to the bottom of the three way stopcock. Then by... 

I strongly encourage anyone seeking more information on Schlenk lines and other oxygen sensitive chemistry to examine The Manipulation of Air-sensitive Compounds by D.F. Shriver and M.A. Drezdzon (Wiley-Interscience, 1986). 

Schlenk apparatus (also called a Schlenk line) 597... 

Representative Procedure for the Use of Benzophenone Imine as an Ammonia Equivalent (Excerpted with permission from [108]. 1996 Pergamon Press) A Schlenk tube was charged with sodium tert-butoxide (1.4 mmol), Pd2(dba)3 (0.00125 mmol), and BINAP (0.00375 mmol). The Schlenk tube was fitted with a septum and attached to a Schlenk line. After the air atmosphere was replaced with argon, toluene (4 ml), 4-tert-butylbromobenzene (1.0 mmol), and benzophenone imine (1.2 mmol) were added by syringe. After the septum was replaced with a teflon valve, the reaction was sealed and heated to 80 °C with stirring until starting material was consumed as judged by GC analysis. The reaction mixture was cooled to room temperature, diluted with ether (40 ml), filtered, and concentrated. The crude reaction mixture was then recrystallized from MeOH to furnish the desired product in 90% yield. 

All reactions and operations must be carried out under dinitrogen or under vacuum, using standard Schlenk line techniques. Diethyl ether, THF, and hexane are freshly distilled from sodium benzophenone ketyl under nitrogen. Toluene is freshly distilled from sodium under nitrogen. The compounds [Mo(t) -C5Hs)(CO)3]2, r-Bu2PH, and Me2AsH are prepared as described in the literature cited. 

---