Water-dioxane

Xanthylamides. Dissolve 0 25 g. of xanthhydrol in 3-5 ml. of glacial acetic acid if an oil separates (as is sometimes the case with commercial material), allow to settle for a short time and decant the supernatant solution. Add 0-25 g. of the amide, shake and allow to stand. If a crystalline derivative does not separate in about 10 minutes, warm on a water bath for a period not exceeding 30 minutes, and allow to cool. Filter oflF the solid xanthylamide (9-acylamidoxanthen) and recrystallise it from dioxan - water or from acetic acid - water, dry at 80° for 15 minutes and determine the m.p. 

The best results are obtained with freshly prepared xanthhydrol (reduction of xanthone with sodium amalgam. Section VII,16). Dissolve 0 -25 g. of xanthhydrol and 0 -25g. of the primary sulphonamide in 10 ml. of glacial acetic acid. Shake for 2-3 minutes at the laboratory temperature and allow to stand for 60-90 minutes. Filter oflf the derivative, recrystallise it from dioxan-water (3 1), and dry at room temperature under water pump suction for 30 minutes. 

The /-butoxycarbonyl group (Boc, "t-box ) has been eMens vely used in peptide synthesis, and Boc derivatives of many amino acids are commercially available. The customary reagent for the preparation from the amine is t-butyl azidoformate in water, dioxane/water, DMSO, or DMF. The cleavage by acids of medium strength proceeds with concomitant loss of isobutene and carbon dioxide (L.A. Carpino, 1957, 1973 see section 4.1.2.2). 

The above product (24 g, 0.067 mol) was dissolved in 90 10 dioxane-water (300 ml) and sodium borohydride (92.5 g, 0.067 mol) was added. The mixture was refluxed for 4h. The cooled solution was poured into 0.1 N HCl (1.11). A solid precipitated and was collected by filtration, dried and recrystallized from ether hexane to give 6,7-dibromo-4-methoxyindole (18.5 g, 90%). 

D. R. Burfield,/ Org. Chem. 49, 3852—3854 (1984). Part 9, efficiency of dryiag 1,4-dioxane, water-saturated diethylether, and acetonitrile with CaSO, CaCl2, and molecular sieves 3A and 4A. 

Sulfobenzyl esters were prepared (cesium salt or dicyclohexylammonium salt, Na03SC6H4CH2Br, DMF, 37-95% yield) from A -protected amino acids. They are cleaved by hydrogenolysis (H2/Pd), or hydrolysis (NaOH, dioxane/water). Treatment with ammonia-or hydrazine results in formation of the amide or hydrazide. The ester is stable to 2 M HBr/AcOH and to CF3SO3H in CF3CO2H. The relative rates of hydrolysis and hydrazinolysis for different esters are as follows ... 

The enamines, enol ethers and enol acetates of A -3-keto steroids provide important substrates for fluorination with FCIO3. Reaction of such A -enol ethers and acetates (6) with perchloryl fluoride results in 6a- and 6jff-fluoro-A -3-ketones (7) and (8), the latter representing the more abundant isomer. Tetrahydrofuran or dioxane-water mixtures appear to be particu-... 

A novel reaction of perchloryl fluoride with aromatic substrates was discovered by Neeman and Osawa, the oxofluorination reaction. These authors found that reaction of indene with perchloryl fluoride in dioxane-water yields five products, the major product being, 2-fluoroindanone. When applied to 6-dehydroestradiol diacetate (24) there is obtained as the major product the 7a-fluoro-6-ketone (25). Borohydride reduction of the... 

Hydrochloric acid, 80% dioxane/water. Cleavage rates for various ring sizes were examined. 

Schneider and Busch have showed that tetraazafS 1 8 l paracyclophane catalyzes the nitration of alkyl bromides with sodiiun nitrite In dioxane-water d l at 30 C, the reaction of 2-bromomethylnaphthalene with sodiiun nitrite is accelerated by a factor of 20 in the presence of the catalyst Concomitantly, the product ratio of [R-ONO [RNO-, changes from 0 50 1 to 016 1 Thus, an acciuruiladon of nitrite ions at the positively charged cyclophanes or IRA-900-nitrite form provides a new method for selective nitration of alkyl halides... 

Alternatively, starting with water, the number of dipoles per cubic centimeter may be progressively diminished by diluting the water with a nonpolar liquid, such as dioxane. Values for dioxane-water mixtures... 

In discussing the loss of entropy in an electric field, we may consider a charged sphere immersed either in an alcohol or in a dioxane-water mixture. In (19) in Sec. 8 we obtained an expression for the total amount... 

The merocyanine dye mentioned above shows solvatochromism, which means that the absorption band maximum of the quinoid form (D form) is sensitive to solvent polarity [40,41]. In Fig. 3, the absorption maximum of the solvatochromic band for M-Mc (a low molecular weight merocyanine analog) is plotted against the dielectric constant of 1,4-dioxane/water mixtures [42]. With the relationship... 

If one limits the consideration to only that limited number of reactions which clearly belong to the category of nucleophilic aromatic substitutions presently under discussion, only a few experimental observations are pertinent. Bunnett and Bernasconi30 and Hart and Bourns40 have studied the deuterium solvent isotope effect and its dependence on hydroxide ion concentration for the reaction of 2,4-dinitrophenyl phenyl ether with piperidine in dioxan-water. In both studies it was found that the solvent isotope effect decreased with increasing concentration of hydroxide ion, and Hart and Bourns were able to estimate that fc 1/ for conversion of intermediate to product was approximately 1.8. Also, Pietra and Vitali41 have reported that in the reaction of piperidine with cyclohexyl 2,4-dinitrophenyl ether in benzene, the reaction becomes 1.5 times slower on substitution of the N-deuteriated amine at the highest amine concentration studied. 

A number of investigations concerning the effect of added electrolytes and change in the solvent polarity have been reported (see ref. 25 pp. 17-19 for a more detailed account). The addition of neutral salts causes a large increase in the rate of reaction in both the one and two-proton mechanisms. In addition, the effect of increasing the water content in a dioxan-water solvent, provided that the concentration of water is above a certain threshold value, also produces a large increase in... 

An example of a cyclophane-type cavity is the azacyclophane CP66 supra-molecular system which provides a lipophilic cavity with an internal width of approximately 6.5 A, as well as positive charges which accelerate and increase the selectivity of the process. The Diels-Alder reaction of cyclopentadiene with diethylfumarate at 20 °C in 10% and 50 To dioxane-water is accelerated by the presence of CP66 by 2.9 and 1.5 times, respectively [65c] (Equation 4.12). 

The solvents were as follows A, aqueous dioxane B, aqueous acetone C, methanol-dioxane-water, 15 5 10. 

Atkinson, G. Kor, S. K. (1965). The kinetics of ion association in manganese sulphate solutions. I. Results in water, dioxane-water mixtures, and methanol-water mixtures at 25 °C. Journal of Physical Chemistry, 69, 128-33. 

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