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ChemicalBook CAS DataBase List 3,5-Diethyl-1,2-dihydro-1-phenyl-2-propylpyridine
34562-31-7

3,5-Diethyl-1,2-dihydro-1-phenyl-2-propylpyridine synthesis

4synthesis methods
3,5-diethyl-1,2-dihydro-1-phenyl-2-propylpyridine (DHP) was prepared using methods shown below. A 1000 mL four neck flask was equipped with a mechanical stirrer, a reflux condenser, a thermometer, and an addition funnel. An ice-water bath was used to cool the flask as needed. The flask was charged with 86 g de-ionized water, 9.8 g (0.16 mole) acetic acid, and 216 g (3.0 mol) butyraldehyde. With cooling and stirring, 60 g (0.64 mole) aniline was added over a 35-minute period while maintaining the reaction temperature at 20℃. The reaction mixture was stirred for one hour at less than 25℃. The reaction mixture was then heated to 750C and held for two hours. Finally, the reaction mixture was heated to reflux (~90°C) and was held for five hours. The reaction mixture was cooled and the layers were separated. The top, organic layer was distilled through a 14" packed column under reduced pressure. The fraction taken at a head temperature of 140-1430C and 5 mm Hg pressure weighed 104 grams and was analyzed to contain 73% DHP for an overall yield of 46%.
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Yield:34562-31-7 69.8 %Chromat.

Reaction Conditions:

Stage #1: butyraldehyde;anilinewith acetic acid at 75; for 5 h;
Stage #2: with sodium carbonate in water; for 5 h;Product distribution / selectivity;Heating / reflux;

Steps:

III.4

EXAMPLE III; Several parameters were changed between Example I and Example II. To isolate the effects of each parameter, a series of runs was made wherein in each run only one parameter was changed. As shown in Table 1, runs were made to compare the reaction temperature after completion of the addition of the reactants and the effect of neutralizing the reaction mixture prior to refluxing. All reported yields are based on the weight of the recovered top layer from the reaction mixtures and a gas chromatograph (GC) analysis of the top layer. Thus, these are chemical yields of DHP made and not isolated recovered yields.Runs 1, 2, and 3 are a comparison of reaction temperature after the addition of the reactants. In run 1 the reaction was immediately heated to reflux, in run 2 the reaction was immediately heated to 75° C., and in run 3 the reaction was held at <45° C. for one hour before heating to 75° C. No difference in chemical yield was seen between runs 1 and 2. However, subsequent recovery of DHP from the crude mixture was greater with DHP prepared according to run 2 (data not shown), perhaps due to a decrease in the production of other compounds that make purification more difficult. In run 3, an improvement in the chemical yield of DHP was seen in addition to the improvement in recovery during subsequent purification. Thus, it has been found that holding the reaction mixture at a lower temperature for a period of time is beneficial to formation and purification of DHP. Without being bound to any particular theory, it is thought that the lower temperature may suppress the formation of other products that consume materials that could have been converted to DHP. Runs 4 and 5 are comparisons of the effect of base neutralization prior to refluxing on DHP yield. Previous work had shown DHP to decompose under acidic conditions when heated, especially at high temperature. By neutralizing the acidic catalyst before heating to reflux temperatures, decomposition of DHP can be suppressed. No difference in DHP chemical yield was seen in runs 4 and 5 but, again, subsequent recovery of DHP from the crude mixture was greater with DHP prepared according to run 4 than with run 5 (data not shown). Neutralization with a base allows the excess butryaldehyde to be reduced via base-catalyzed self-condensation, which is faster than acid catalyzed self-condensation. Also, the base neutralized run appeared to give improved layer separation. The top layer was relatively clear as compared to the other runs in which the top layers were cloudy. It was also noted that top layers from the non-neutralized runs would form small water droplets or layers in the sample bottles after standing for a few days. Neutralization of the acid catalyst is particularly useful when the product is distilled under high temperatures. Distillation of a neutralized DHP crude mixture produces fewer decomposition products and leads to increased recovered yields of purified DHP.

References:

US2006/178517,2006,A1 Location in patent:Page/Page column 3