Tetramethyl dioxane

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form etliylidene diacetate [542-10-9] , boron fluoride also catalyzes the reaction (78). Etliylidene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutylene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-m-dioxanes 2,4,4,6-tetramethyl- -dioxane [5182-37-6] is produced in yields up to 90% (82). 

For molecules containing a weak bond, say, HOOH, it is possible to provide enongh energy by an overtone excitation of an O—H bond so as to dissociate the molecnle. For exoergic processes it is only necessary to provide enough energy to surmount the barrier. A well-studied example is the dissociation of die cyclic peroxide tetramethyl dioxane (TMD) that fragments over a barrier of about 110 kJ mol (about three quanta of C—H stretch) to two acetone molecules... 

A kinetic isotope effect, kH/kD = 1.4, has been observed in the bromination of 3-bromo-l,2,4,5-tetramethylbenzene and its 6-deuterated isomer by bromine in nitromethane at 30 °C, and this has been attributed to steric hindrance to the electrophile causing kLx to become significant relative to k 2 (see p. 8)268. A more extensive subsequent investigation304 of the isotope effects obtained for reaction in acetic acid and in nitromethane (in parentheses) revealed the following values mesitylene, 1.1 pentamethylbenzene 1.2 3-methoxy-1,2,4,5-tetramethyl-benzene 1.5 5-t-butyl-1,2,3-trimethylbenzene 1.6 (2.7) 3-bromo-1,2,4,5-tetra-methylbenzene 1.4 and for 1,3,5-tri-f-butylbenzene in acetic acid-dioxan, with silver ion catalyst, kH/kD = 3.6. All of these isotope effects are obtained with hindered compounds, and the larger the steric hindrance, the greater the isotope... 

A l,l,2,2-tetrachloro-l,2-digermacyclobutene, 113, has been obtained282 by the reaction of the dioxane complex of GeCl2 with 3,3,6,6-tetramethyl-l-thiacyclohept-4-yne ... 

An admittedly enigmatic result involves the thermolysis of solution phase di-f-butyl diperoxyoxalate and a cyclic counterpart, 7,7,10,10-tetramethyl-l,2,5,6-tetraoxacyclodecane-3,4-dione. While the former reaction was shown to be exothermic by 238.5 8.4 kJmol and the latter by 414.2 8.4 kJmol , the latter is slower by a factor of some 3000. The latter decomposition results in acetone, ethylene, CO2 and 3,3,6,6-tetramethyl-l,2-dioxacyclohexane. The enthalpy of formation measurements of the cyclic peroxyoxalate and the 1,2-dioxane are coupled if we knew the enthalpy of formation of 1,2-dioxane it would allow us to derive the enthalpy of formation of 7,7,10,10-tetramethyl-l,2,5,6-tetraoxacyclodecane-3,4-dione and the other way around. 

The photochemical reactions of l,l,4,4-tetramethyl-2,3-dioxotetralin (14) have been studied in methanol, isopropyl alcohol, cyclohexane, toluene, -butyraldehyde, methyl formate, acetic acid, dioxane, and benzene.75 In isopropyl alcohol the reduced ketone (15) is formed almost exclusively, while... 

Noise and single frequency off-resonance decoupled CMR spectra of disopyramide phosphate in deuterated water solution are shown in Figures 4 and 5.2 Shifts are reported in ppm downfield from the shift of tetramethyl silane as referenced to a shift of 67.4 ppm for dioxane which was used as an internal reference. 

The reaction of 7-chloro-p-xylene with potassium tert-butoxide in p-xylene in the presence of stable N-oxy biradicals such as 2,2,6,6-tetramethylpiperidinoxy-4-spiro-2 -(r,3 -dioxane)-5 -spiro-5"-(r, 3"-dioxane)-2"-spiro-4 -(2 ",2", 6", 6 "-tetramethyl piperidinoxy) gives the corresponding copolymer 36 indicating the formation of QM as a reaction intermediate. 

Kinetic data are available for the hydrolysis of benzophenone diethyl ketal in various dioxane—water mixtures [164]. General catalysis cannot be detected with certainty [165, 188,189]. The activation parameters for the H30+ catalyzed reaction are AH = 13.9 kcal. mole-1 and AS = +1.4 eu as expected for an A1 reaction. Another interesting example is the acid catalyzed hydrolysis of the tetramethyl ketal of p-benzoquinone which takes place in two stages [190]... 

Furthermore, Masuda et al. have shown that dialkoxyhydroborane can replace diboron 55 in converting aryl halides and triflates into arylboronates [30]. In one example, treatment of 2-methoxyquinolinyl-8-triflate with 4,4,5,5-tetramethyl-[l,3,2]dioxaborolane in the presence of PdCl2 (dppf) and Et N in dioxane at 80°C for 4 h produced 2-methoxy-... 

LiBp4, wet CH3CN. Unsubstituted 1,3-dioxolanes are cleaved slowly under these conditions (40% in 5 h). The 4,5-dimethyl- and 4,4,5,5-tetramethyl-dioxolane and 1,3-dioxane are inert under these conditions. Dimethyl ketals are readily cleaved. 

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