Purification, general procedures

GENERAL PROCEDURES FOR THE PURIFICATION OF SOME CLASSES OF ORGANIC COMPOUNDS... 

N -Ethyl-jK-toluidine has been obtained by passing m-toluidine and ethyl alcohol over a catalyst at high temperatures,1 and by the use of ethyl />-toluenesulfonate 2 as an alkylating agent. The present method of purification is a modification of a general procedure for secondary amines developed by Diepolder.3... 

The general procedure described here was originally published by the submitters.3 Both ketones and aldehydes may be prepared, and this method is particularly effective when the mild conditions of the Moffat oxidation are required, but the dicyclohexylurea by-product formed with the usual reagents causes purification problems. 

Puig O, Caspary F, Rigaut G, et al. The tandem affinity purification (TAP) method a general procedure of protein complex purification. Methods 2001 24 218-229. 

General Procedure for the Hydroformylation/Carbonyl ene Reaction/O,O-acetal Forma-tion/Dehydration. Synthesis of Chromane Derivatives. A solution of the substrate (1 eq) RhCl(PPh3)3 (1 mol %) and PPh3 (3 mol %) in dry dioxane was heated for 70 h to 120 °C und an atmosphere of CO/H2 (1 1, 100 bar). The crude product was filtered through basic alumina (eluated with MTBE). After evaporation of the solvent further purification by column chromatography (silica, PE/MTBE) furnished the title compounds. 

Alkynylphenyl tellurides from arylteUurolates and alkynyliodonium salts (general procedure) To a stirred solution of PhLi in Et20/cyclohexane at room temperature under N2, tellurium powder was added and the solution was stirred for 1 h. The appropriate iodonium triflate was added and the solution was stirred for 2 h. The product was eluted through a small portion of silica gel with CHjCN and the volume was reduced in vacuo followed by purification via radial chromatography. 

This general procedure was applied to a variety of scaffolds to produce a small library of compounds. After the work-up and preparative HPLC, the final yields were in the range of 40-63%, which is comparable to the previously reported batch procedures. A typical 35 min run finally gave 0.5 mmol of the product that afforded 40-80 mg after the HPLC purification this accounts to approximately 80-160 mg/h productivity. 

General Procedure for Preparation of Triazones 5a-f. 264 mg (3 mmol) /V,/V-di-metliylurea, 1 g paraformaldehyde, 3 mmol primary amine 4a-f and 2 g montmorillonite K-10 were irradiated by microwave in a Teflon vessel. The reaction mixture was filtered and washed with water. The organic phase was separated and dried with Na2S04 and concentrated by vacuum distillation. Purification of the... 

General Procedure for Microwave-Induced Fries Rearrangement. Neat substrate (0.01 mol) was mixed with the support (1 3, w/w) in a beaker and was exposed to microwave irradiation for 7 min. After cooling to room temperature the product was extracted with diethyl ether. Evaporation of the solvent gave almost pure product. Further purification was carried out by recrystallization or column chromatography on silica gel. 

Derivative preparation involves the application of a concisely described general procedure to a specific compound (possibly at this stage of uncertain identity), and its success may well depend upon the use of intuition and initiative in the preparative and purification stages. As such it must be regarded as making an important contribution to the training of the organic chemist. 

Secondly, the description of the general procedures given below, as distinct from the specific experimental procedures of the preparations described in earlier chapters, provides an excellent opportunity for the student to explore on the small scale the optimum reaction conditions, the chromatographic monitoring of the reaction, the methods of isolation and purification procedures (solvent extraction, recrystallisation, etc.) for the successful completion of the preparation. The small-scale nature of the experiments is of particular importance in providing experience of those techniques of reaction work-up in which mechanical loss is frequently the reason for failure. Such experience is vital to the synthetic chemist since many of the new chemo-, regio- and stereo-specific reagents are expensive and used in small-scale reactions. 

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