Acetals 1.3- dioxans

It was decided to construct a D-ring acylating agent bearing a latent C-8 vinyl group. To this end, benzylation of the known 5-bromo-orr/to-vanillin (22),14 followed by protection of the aldehyde carbonyl in the form of a cyclic acetal (1,3-dioxane), affords com-... 

A 2-methoxyethoxymethyl ether (MEMOR) is normally prepared under non-acidic conditions in methylene chloride solution or under basic conditions. The MEM ether group can be removed in excellent yield with trifluoroacetic acid (TEA) in dichloromethane (1 1). The MEM group can also be removed by treatment with zinc bromide (ZnBr2), titanium chloride (TiCU) or bromocatechol borane. When MEM-protected diols are treated with zinc bromide (ZnBr2) in ethyl acetate, 1,3-dioxane is formed and a mechanism of this reaction is given in Scheme 1.23. 

Malinowski and T. Urbanski (60J advanced a suggestion that a hydrogen bond can exist between the nitro and the hydroxy group in nitro alcohols. This was based on the experimental fact that 2-nitropropane-l,3-diol (I) formed cyclic acetals-1,3-dioxane derivatives (II) and ketals with great difficulty, while on the contrary the triol 2-hydroxymethyI-2-nitro-propane-l,3-diol (11 ) forms the corresponding cyclic acetal (IV) and ketal with great ease. 

Like all acetalizations, 1,3-dioxane formation is reversible it finds wide appHcation for establishing the 1,3-dioxane moiety as protective group for carbonyl compounds, as well as for systems with a 1,3-diol structural element. 

The smallest ring of a cyclic acetal contains five atoms. Ring-opening polymerization of cyclic monomers with rings composed of more than four atoms is a reversible process due to a relatively low negative AHp (enthalpy of polymerization) value (Table 1) [see Chapter 4.02). Thus, monomer-polymer equilibrium is established, and if the equilibrium monomer concentration [M]e is higher than its starting concentration, polymerization is not possible. This is the case with the six-membered cyclic acetal 1,3-dioxane. 

OB to C02 —85.04%, needles from glac AcOH, mp 262—63° (decomp). Sol in glac AcOH, acet, dioxane py si sol in benz, toluene, xylene amyl ale. Prepn from l-nitro-2-. me thy lnaphthalene by nitration using mixed acids of nitric (d 1.52g/cc), sulfuric (d 1.84 g/cc) oleum (20—25% SO5 free), and heating for one hour at 80° on a water bath. Two other isomers which do not decompose are prepd simultaneously viz, mp (I) 230° ... 

In pale yel crysts mp, decompn above 200° without melting, Sol in acet, dioxane and acetic anhydride. Prepn of the polymer by vigorous stirring of the monomer with a satd aq soln of K bicarbonate. The crude prod is purified by w washing and air drying. The yield is... 

Purify the derivatized dendrimer using gel filtration (size exclusion chromatography) on a desalting column or through use of ultrafiltration spin-tubes (for G-4 and above). For smaller dendrimers, the derivatives may be purified by repeated precipitation from a meth-anolic solution by addition of ethyl acetate, dioxane, or benzene. The SPDP-dendrimer may be dried by lyophilization (if in water or buffer) or by solvent evaporation in vacuo (if the precipitation method was used). 

On the other hand, Matsuzaki et al studied TLC behavior of a PMMA prepared with a phenylmagnesium bromide-tetrahyrofuran complex in toluene79). Good separation into two components was achieved using either ethyl acetate singly or a binary ethyl acetate + dioxane. However, these components could not be identified with either isotactic or syndiotactic PMMA, and the separation took place rather... 

Solv. Ref. C- Cholesteryl acetate Dioxane/CHCl3 [65 a] Cholesteryl methyl ether Dioxane/CHCl3 [65 a] 7-Dehydro- cholesteryl acetate Dioxane/CHCl3 [65 a] Ergostcrol Dioxane/CHCl3 [65 a] Lanosterol CDC13 [587] Dihydro- lanosterol CDC13 [587]... 

Solv. Ref. C- Cholestan-3-one Dioxane/CHClj [65 a] Cholesta-3,5- dien-7-one Dioxane/CHCl3 [65 a] Cholest-5-en-7-on-3/J-yl acetate Dioxane/CHCl3 [65 a] 2/ ,3/ ,14oc- Trihydroxy- 5/i-cholest- 7-en-6-one Pyridine-d5 [588] a-Ecdysone Pyridine-d3 [588] a-Ecdysone triacetate Pyridine-d5 [588]... 

Phenols, m-cresol, concentrated mineral acids, formic acid Ethanolamine, dioxane, chlorinated hydrocarbons, cyclohexanone Dichlorobenzene, pentachloroethylene, dichloroethylene, tetralin Cresol, concentrated sulfuric acid, chlorophenol, trichloroacetic acid Dichlorobenzene, DMF, chlorophenol, benzyl alcohol Aromatic and chlorinated hydrocarbons, pyridine, ethyl acetate, dioxane, chloroform, acetone Fluorocarbon oil... 

In view of the fact that the methanol-phenyl isocyanate reaction is known to be an auto-catalytic reaction due to the weakly basic character of the phenylurethane formed, one would expect an upward drift of the second-order plot if the reaction were truly of the second order. This is apparently the case in n-butyl acetate and dioxane. The straight line plot in MEK and acetonitrile and the downward curvature found in toluene and nitrobenzene were taken to indicate an order greater than 2 with respect to the reactants. It appeared that the deviations from second-order kinetics toward higher order in the sequence toluene > nitrobenzene > acetonitrile > MEK > n-butyl acetate > dioxane increased with an increase in the hydrogen bonding capacity of the solvent. 

Iodine Potassium Iodide Dodecylbenzene Tridecyibenzene Hydroquinone Propionaldehyde Methylform amide Diacetone Alcohol Isoamyl Alcohol Pentanedione (2,4-) Acetylacetone Paraldehyde Butylaldehyde Butyraldehyde Levulinic Acid Dioctyl Adipate Acetic Acid Butyl Ester Butyl Acetate Dioxane (1,4-) Dioxane Dioxane (p-) Isoamyl Acetate Thiodiacetic Acid Butyl Stearate Santoprene 201-73 Kamax T-260 Adipic Acid Ethylene Chloroformate Caprylic Acid Octanoic Acid Hexamethylenediamine Butyl Carbitol Acetate Decane Carbon Dioxide Dimethylamine Sodium Methylate Freon 114B2 Tetrachloropentane Santicizer 141 Santoprene 201-64 Ecolan Hetron 99P Calcium Hydride Triton Sulfolane Tributyl Phosphate Tributylphosphate Sodium Diacetate Methacrylonitrile... 

For polystyrene at a concentration of 5 wt. % gelation occurs on irradiation only in ethyl acetate, dioxane and methylethylketone, the first two being poor solvents for polystyrene. Degradation was found by Ikada and Schnabel [459] to occur almost exclusively in benzene below the critical concentration. 

Large, blue-green, deliquesc, orthorhombic crystals. Sublimes at 150-225. mp 255-256", Sol in water, ethyl acetate, dioxane dissolves in and reacts vigorously with ether. Keep well closed. 

Canary-yellow, very deliquescent crystals. Begins to sublime at 250". mp 300.3 bp 360.3 Smith el at. J. Am. Chem Soc. 74, 4964 (1952). Freely sol in water, alcohol, ether, ethyl acetate, dioxane, pyridine. Readily absorbs water forming perrhenic acid, HRiO,. 

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