Alcohols controlled decomposition

Olefins can be prepared by the dehydrogenation of paraffins, dehydration of alcohols, or decomposition of ethers and halides, if vapours of these substrates are passed over metals or metal oxides at elevated temperatures (300-600°C). Dehydration reactions have been most widely studied and by careful selection of the catalyst and the reaction conditions the direction and stereochemistry of elimination can be controlled. However, dehydration often has to compete with dehydrogenation, and isomerisation of olefinic products by the acidic sites on the catalyst can reduce the synthetic utility of these reactions. Most frequently alumina has been used as the catalyst and the advantages and complexities of the method are amply illustrated by the dehydration of alcohols. Surface-catalysed eliminations have been the subject of several reviews "". ... 

An alternate method for the preparation of such dusters [213] is based on the impregnation of a dehydrated zeolite with alcoholic solutions of sodium azide, followed by the controlled decomposition of the azide. The ionic sodium clusters were shown by ESR spectroscopy to be Na4 and are formed in the zeolite pores. The clusters exhibit catal)dic properties for both isomerization and hydrogenation reactions of alkenes and alkynes. 

Equip a 1-litre three-necked flask with a powerful mechanical stirrer, a separatory funnel with stem extending to the bottom of the flask, and a thermometer. Cool the flask in a mixture of ice and salt. Place a solution of 95 g. of A.R. sodium nitrite in 375 ml. of water in the flask and stir. When the temperature has fallen to 0° (or slightly below) introduce slowly from the separatory funnel a mixture of 25 ml. of water, 62 5 g. (34 ml.) of concentrated sulphuric acid and 110 g. (135 ml.) of n-amyl alcohol, which has previously been cooled to 0°. The rate of addition must be controlled so that the temperature is maintained at 1° the addition takes 45-60 minutes. AUow the mixture to stand for 1 5 hours and then filter from the precipitated sodium sulphate (1). Separate the upper yellow n-amyl nitrite layer, wash it with a solution containing 1 g. of sodium bicarbonate and 12 5 g. of sodium chloride in 50 ml. of water, and dry it with 5-7 g. of anhydrous magnesium sulphate. The resulting crude n-amyl nitrite (107 g.) is satisfactory for many purposes (2). Upon distillation, it passes over largely at 104° with negligible decomposition. The b.p. under reduced pressure is 29°/40 mm. 

C. When heated it partially volatilizes, though a greater part decomposes. At a pressure of 1.6 kPa it boils at 170 °C. In an atmosphere of steam it distils without decomposition at atmospheric pressure. It is soluble in water and alcohol in all proportions, but not in ether [8]. Compared with the hydrocarbon feedstocks currently used in classic petrochemistry, it is already a highly functionalized molecule. Obviously, new (catalytic) transformations of glycerol will require controlled defunctionalization. 

Table 9.1). The rate of dehydrobromination from the intermediate bromoalkenes follows the pattern 2-bromoalkenes > Z-l-bromoalkenes > E- -bromoalkenes the corresponding chloro derivatives react more slowly. For optimum yield, the reaction temperature should be <100°C to reduce decomposition of the catalyst, and the concentration of base should be kept low to prevent isomerization of the resulting alkynes. [3-Elimination of HBr from 1,2-dibromo-1 -phenylethane can be controlled to yield 1-bromo-l-phenylethene in 83% yield [15]. The addition of alcohols and diols have a co-catalytic effect on the elimination reaction, as the alkoxide anions are transferred more effectively than the hydroxide ions into the organic phase [13]. 

At elevated temperature alkyl hydroperoxides undergo thermal decomposition to alcohols [Eqs. (9.9)—(9.11)]. This decomposition serves as a major source of free radicals in autoxidation. Because of side reactions, such as p scission of alkylperoxy radicals, this process is difficult to control. Further transformation of the alkoxy... 

In contrast, the acid-catalyzed hydrolysis of alkyl selenates is A-2158. The actual species which undergoes decomposition to alcohol and sulfur trioxide is probably the zwitterion as in the case of phosphate monoester monoanions. Evidence for sulfur trioxide as the reactive initial product of the A-1 solvolysis is obtained from the product compositions arising with mixed alcohol-water solvents. The product distribution is identical to that found for sulfur trioxide solvolysis, with the latter exhibiting a three-fold selectivity for methanol. Although the above entropies of activation and solvent deuterium isotope effects do not distinguish between the conventional A-l mechanism and one involving rate-limiting proton transfer, a simple calculation, based on the pKa of the sulfate moiety and the fact that its deprotonation is diffusion controlled. 

Carbenoids derived from the metal catalysed decomposition of diazo compounds undergo various chemical transformations. Control of chemoselectivity by choice of the appropriate catalyst has significantly increased the synthetic viability of catalytic cyclopropanation reactions. Intermolecular reaction of unsaturated alcohols with carbenoids derived from catalytic decomposition of alkyl diazoesters has been reported by Noels and... 

The high-pressure cells and temperature control units are similar to the ones described by Betts and Bright (29). Samples for analysis were prepared by directly pipetting the appropriate amount of stock solution into the cell. To remove residual alcohol solvent, the optical cell was placed in a heated oven (60 °C) for several hrs. The cell was then removed from the oven, connected to the high-pressure pumping system (29), and a vacuum (50 pm Hg) maintained on the entire system for 10-15 minutes. The system was then charged with CF3H and pressurized to the desired value with the pump (Isco, model SFC-500). Typically, we performed experiments at 10 /xM PRODAN and there was no evidence for primary or secondary interfilter effects. HPLC analysis of PRODAN subjected to supercritical solvents showed no evidence of decomposition or additional components. 

This compound is a useful chlorinating reagent, and although relatively stable, its purification by distillation is not normally attempted. Primary and secondary hypochlorites readily explode when exposed to light, and even in the absence of light rapid decomposition occurs at room temperature. t-Butyl hypochlorite may be prepared by the interaction of t-butyl alcohol, sodium hydroxide and chlorine at low temperature, which must be carefully controlled during the reaction... 

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

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