High laboratory synthesis methods

From Boron Halides. Using boron haUdes is not economically desirable because boron haUdes are made from boric acid. However, this method does provide a convenient laboratory synthesis of boric acid esters. The esterification of boron haUdes with alcohol is analogous to the classical conversion of carboxyUc acid haUdes to carboxyUc esters. Simple mixing of the reactants at room temperature or below ia a solvent such as methylene chloride, chloroform, pentane, etc, yields hydrogen haUde and the borate ia high yield. 

In 1987, the successful startup of a new process was announced for the production of 10,000 tons/year of catechol and hydroquinone by the selective oxidation of phenol with H202 catalyzed by TS-1 at the Enichem plant in Ravenna, Italy (Notari, 1988). Soon thereafter, it was disclosed that another new process for the production of cyclohexanone oxime from cyclohexanone, H202, and NH3 with TS-1 as the catalyst was being developed (Roffia et al., 1990).The fact that a material with unusual catalytic properties had been obtained was then finally recognized, and the interest in titanium-containing catalysts spread rapidly in the scientific community, especially in industrial research laboratories. In the meantime, the synthesis method was studied and described in more detail and when all the necessary precautions were taken, TS-1 was reproduced in other laboratories, as were the highly selective catalytic reactions. The subsequent work confirmed that Ti v can assume the tetrahedral coordination necessary for isomorphous substitution of SiIV and added valuable information about the structure, properties and catalytic performance of the material. New reactions catalyzed by TS-1 have been discovered, and new synthetic methods... 

Therefore, for small-scale laboratory synthesis it seemed promising to develop alternative methods which avoid the inconvenient high temperature and yield the reactive, solvated form. For example, the THF adducts can readily be synthesized by treating lanthanide powders with CHC13 under ultrasonic conditions, as described by Eq. (1) [100], Redox transmetallation between lanthanide metals and mercury(II) halides are carried out in refluxing THF (Eq. 2) [108]. Recently ammonia was employed as an alternative solvent, e.g. in the synthesis... 

The synthesis of interlocked molecules has become commonplace over the past 25 years with the gradual development of a number of highly facile template methods for their construction. What were once laboratory curiosities have now taken a prominent place in the broad field of supramolecular chemistry, especially regarding their uses and further potential as molecular switches and machines [1], We present here an overview of the main synthetic approaches to these molecules, with a focus on methods in which macrocyclization reactions result in interlocked products. The analysis is by no means meant to be comprehensive or exhaustive in detail, but rather to convey the variety and utility of the selected synthetic strategies in generating abiotic rotaxane and catenane superstructures. 

The least expensive method for synthesizing simple symmetrical ethers is the acid-catalyzed bimolecular condensation (joining of two molecules, often with loss of a small molecule like water), discussed in Section 11-10B. Unimolecular dehydration (to give an alkene) competes with bimolecular condensation. To form an ether, the alcohol must have an unhindered primary alkyl group, and the temperature must not be allowed to rise too high. If the alcohol is hindered or the temperature is too high, the delicate balance between substitution and elimination shifts in favor of elimination, and very little ether is formed. Bimolecular condensation is used in industry to make symmetrical ethers from primary alcohols. Because the condensation is so limited in its scope, it finds little use in the laboratory synthesis of ethers. 

Despite using array-based technologies in combinatorial chemistry, most of the current synthesis methods in research laboratories or industry are based on highly automated plate-based technologies. The concept of parallel synthesis in combinatorial chemistry involves the generation of discrete compounds in spatial separated reaction compartments. The typical employed format is the 96-well microtiter plate. 

Tartarie acid [(/ ,/ )-20J is one of the most inexpensive chiral compounds available even the (.S. .S )-enantiomer, which does not occur so frequently in nature, is comparatively inexpensive, so there is no need for laboratory synthesis. Most diesters of both enantiomers are also inexpensive, at least for the C, - C3 alcohols. Tartaric acid itself has been used for the chiral modification of the surface of Raney nickel, which permits highly enantioselective reduction of carbonyl groups, e.g., of oxo esters, to the secondary alcohols (Section D.2.3.I.). The zinc salt of tartaric acid has been used for the asymmetric ring opening of epoxides by thiolates (Section C.). The diesters, e.g., 21-25, are conveniently obtained by acid-catalyzed esterification28-31, a method applicable to almost all alcohols as a typical example, dicyclohexyl (f ,tf)-tartrate is given32. 

Combinatorial chemistry can be carried out both in the solution phase or on a solid support. These two complementary approaches offer valuable solutions to the chemist either on a high throughput automated method or on a laboratory scale. Both solution- and solid-phase approaches present characteristics and requirements that have to be considered before deciding whether the planned synthesis should be carried out with one or the other technique. 

The direct synthesis of (arene)Mo(CO)3 complexes from arene and Mo(CO)g is much more limited than for chromium (Scheme 4) [11,51]. The long reaction times at elevated temperature (e.g., ten days for (benzene)Mo(CO)3) and the high sensitivity to oxygen often results in low yields for substituted arenes. While (benzene)Mo(CO)3 (40) has been reportedly obtained in near quantitative yield, the yield was based on liberated CO rather than isolated complex [11]. In the author s laboratory, an isolated yield of 50% is more realistic for this procedure. The reaction time can be shortened by reacting Mo(CO)g in benzene in the presence of pyridine in an autoclave [52]. Toma and coworkers have described a different procedure that uses a double condenser system, and decalin plus ethylformate as solvent [53]. With a bath temperature of 240 °C this cuts the preparation time of the aniline complex 42 to 1 h (55% yield) (Scheme 4). In the authors laboratory the method is used routinely for the synthesis of complex 40 (18 h, 60% yield). 

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