Study On Deoximation

Doximation is an important reaction, because oximation serves as anefficient protective method for carbonyl compounds. At the same time,oximes could be prepared from non-carbonyl compounds, such asα-halogen esters,β-keto esters, and malonic ester derivatives. So theregeneration of carbonyl compounds from these oximes representpotential route for synthesis of ketches and aldehydes. Furthermore,Ketone and aldehyde oximes can be easily purified through recrystallition,an efficient method for deoximation can, therefore, be used forpurification of carbonyl compounds. As a result, chemists have beenpaying interest in the development of procedures for the effectiveregeneration of carbonyl compounds from the corresponding oximes,especially, under mild conditions.General process for dcoximation can be described as follow.There are many practical procedures for deoximation, includinghydrolytic, reductive, oxidative and photosensitized deoximation.In this thesis, we systemically studied acid-catalyzed deoximationunder liquid state with perillartine (1, 8-p-menthadiene-7-oxime) assubstrate. This procedure is equivalent to an acid-catalyzed exchangingreaction between perilartine and formaldehyde. The influences of reactionvariables on yield, such as temperature, time, catalyst, catalyst's property,solvent, dosage of catalyst and formaldehyde, were evaluated. Finally, weput the optimized condition into the practice of synthesizing high purityperilaldehyde. The results show that: 1. The most suitable reactiontemperature was at 80℃. Higher temperature will strengthen the sidereaction. While lower temperature will lower down the reaction speed orlead to incomplete reaction. 2. The yield of perilly aldehyde was thehighest when the amount of the catalyst, nitro acid, was 5～10ï¼…. Sidereaction will be enhanced when more dosage used. Less dosage makesthe reaction time longer. Catalysts with middle acidity showed good catalysis. 3. The best molar ratio of formaldehyde, to perillartine fordeoximation was 2:1. More dosage makes no difference. 4. Generallyspeaking, the stronger is polarity of solvent, the better result ofdeoximation shows. Nitromethane is more suitable for deoximatiom.However, when DMF works as solvent, there is an exception due to itsalkalescence, which weakened the effect of catalyst. The optimumcondition is as follow: 96ï¼…yield of the product, perillaldehyde, wasobtained in the presence of nitric acid as catalyst at 80℃for 4h inuitromethaue, when the molar ratio of formaldehyde to perillartine was2:1. It provides a convenient way for the synthesis of highly pureperillaldehyde.At the same time, we studied solid state, method for deoximation,then used it for deoximation with a series of substrates. We synthesized aseries of aromatic and alkyl oximes. The result show that: Oximes ofketoues and aldehydes were efficiently converted to the correspondingcarbonyl compounds, using a combination of NaHSO₄·H₂O andparaformaldehyde in good to excellent yields under solid state conditionsat room temperature for 10 minutes, when the molar ratio offormaldehyde to perillartine was 2:1. Converting aldoximes to thecorresponding carbonyl compounds was easier than ketoximes. It is noteworthy thatα,β-unsaturated oximes underwent deoximation veryefficiently without rearrangement of the C=C bond. The electrondonatinggroups such as MeO, OH on the aromatic ring were inert to the reagent,and enhanced the yield of products. The oximes with more stericalhinderence were more difficult to hydrolysis to the correspondingcarbonyl compounds. Hydrate water in sodium hydrogen sulfatemonohydrate plays a very important role in deoximation. Without hydratewater, the yields of carbonyl compounds would decrease obviously. Theadvantages of this system are easier work-up, cheaper reagents andshorter reaction times.