Solvent purification dioxane

A mixture of 1.38 grams of the above compound and 15 cc of dioxane was treated with 1.9 cc of a 0.5 N aqueous solution of perchloric acid and 600 mg of N-bromoacetamide, adding the latter in the dark, in three portions, in the course of half an hour and under continuous stirring. It was then stirred for a further 1% hours in the dark, then the excess of reagent was decomposed by the addition of aqueous sodium bisulfite solution and ice water was added the product was extracted with methylene chloride, washed with water, dried over anhydrous sodium sulfate and the solvent was evaporated under reduced pressure, thus giving a yellow oil consisting of the 16,21-diacetate of 6a-fluoro-9a-bromo-16o-hydroxy-hydrocortisone which was used for the next step without further purification. 

The pKs value of acetic acid is about the same as that of water therefore, in order to obtain high accuracy and greater differentiation in potentiometric titrations, Pifer and Wollish91 preferred to use acetic acid mixed with dioxan in the solvent and also in the perchloric acid titrant in view of the possible presence of peroxide, the previous purification requires great care40. Similarly, Fritz92 recommended acetic acid mixed with acetonitrile (pKs = 19.5 at 25° C)93 in both the solution and the titrant. 

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. 

Figure 1.6 ICH Class 2 solvents measured using GC. Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [15], copyright 2004, with permission from Elsevier. (Column 30 m X 0.53 mm i.d. 3 pm OVI-G43 (Supelco) carrier gas helium at 5 ml/min injection in split mode total flow 25 ml/min injector temperature 140 C flame ionization detector temperature 25C C and oven temperature 40°C for 20 min, to 240°C at 10°C/min, maintain at 240 C for 20 min. The components are 1 methanol, 3 acetonitrile, 4 dichloromethane, 5 hexane, 6 cw-l,2-dichloroeth-ylene, 7 nitromethane, 8 chloroform, 9 cyclohexane, 13 1,2-dimethoxyethane, 15 1,1,2-trichloroethyl-ene, 16 methylcyclohexane, 17 1,4-dioxane, 18 pyridine, 19 toluene, 20 2-hexanone, 21 chlorobenzene, 22 ethylbenzene, 23 m-xylene, 24p-xylene, 25 o-xylene, and 26 tetralin. The solvents are dissolved in DMF and heated at 80X for 60 min, and a sample of the headspace is injected.)...

Tellurium tetrachloride and tetrabromide react with equimolar quantities of aryl mercury chlorides to produce aryl tellurium trihalides in high yields. This reaction is useful when the trichlorotelluro group is required at a specific position in the aromatic molecule or when tellurium tetrachloride does not condense in an acceptable manner with the aromatic hydrocarbon. The solvent of choice is dioxane, because mercury dichloride precipitates as the dioxane adduct, facilitating the isolation and purification of the aryl tellurium trichlorides. 

The reversible dissociation of antigen-antibody bonds by nonaqueous solvents such as dioxane may prove of considerable practical use in procedures for the isolation and purification of specific antibodies (cf. Singer et al., 1960). 

Twenty-one grams (0.225 mol) of phenol is dissolved in 150 ml. of dioxane, and 5.1 g. (0.222 mol) of sodium is added. The mixture is boiled under reflux in a 500-ml. round-bottomed flask until all the sodium is dissolved. Ten grams (0.0215 mol) of octachlorocyclotetraphosphaza-tetraene is added slowly to the cold solution and the mixture is boiled for 3 hours. The cold mixture is diluted with 300 ml. of diethyl ether, then placed in a separatory funnel and washed with 120 ml. of water. It is then washed successively with dilute aqueous solutions of hydrochloric acid (5%) and sodium hydrogen carbonate (5%), and again with water. The solution is dried over sodium sulfate and the solvents are evaporated. The crude product solidifies slowly and melts at about 56°. The yield is 17 g. (85%). Purification is effected by one recrystallization from a benzene-petroleum ether mixture m.p. 85 to 86°. Anal. Calcd. C, 62.3 H, 4.3 N, 6.1. Found C, 62.0 H, 4.3 N, 6.0. 

A simple one-pot procedure for the synthesis of Fmoc-protected aspartic and glutanoic acid tert-butyl esters is shown in Scheme tert-Butylation of unprotected Asp and Glu can be effected in dioxane with excess isobutene using 4-toluenesulfonic add as catalyst. Subsequent Fmoc derivatization results in a mixture of the mono-tert-butyl esters (co/a 65/35 for Glu and 50/40 for Asp) with an overall yield of 55-60% contaminated with small amounts of d -tert-butyl esters. This procedure has the advantage that the Fmoc group is introduced without prior isolation or purification of the aspartic and glutamic tert-butyl esters. Whilst the diesters are readily removed by extraction with organic solvents, the Fmoc-Asp/Glu(OtBu)-OH derivatives are isolated by crystallization from dichloromethane/petroleum ether. 

To a stirred ice-cold soln of Fmoc-Xaa-OH (2.0 mmol) and HOPfp (2.0 mmol) in dry dioxane, EtOAc, or dioxane/DMF (5-10 mL), DCC (2.0 mmol) was added and stirring was continued for 1 h at 0°C and 1 h at rt. The DCU was removed by filtration, the solvent was removed, the residue was triturated with hexane, and the product was recrystallized (EtOAc or EtOAc/hexane). Fmoc-Asn-OPfp was prepared in dioxane/DMF (24 1) using HOPfp (6 mmol) yield 90% mp 164-165 °C (EtOAc/hexane). Fmoc-Ser-OPfp was purified by chromatography (silica gel, dried at 120 °C for 24 h, 33% EtOAc/petroleum ether). Fmoc-Ser(tBu)-OPfpP and Z-Lys(Z)-OPfp also required purification on silica gel. 

Purification. Benson, McBee, and Rand, in submitting an Organic Syntheses procedure for the preparation of N-iodosuccmimide, purify dioxane only by use of sodium chips and distillation (reference to Fieser"). Checkers B. C. McKusick and T. J. Kealy used a newly opened bottle of spectroquality Reagent (MCB). In purifying the solvent for a kinetic study Burstein and Ringold state that they applied the method of Fieser and then stored the solvent over a Linde molecular sieve for at least a week. Aetually Fieser cited two methods from the literature, the first of which is designed to eliminate water and glycol acetal by hydrolysis to acetaldehyde. The methods are as follows ... 

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