DA Reaction To Synthesize Methyl Pyran And Its Catalyst Regeneration And Waste Water Recovery

Leaf alcohol possess a clean fresh grassy note with strong permeability and imfectivity.It's raw material for ester derivatives,such as cis-3-hexenyl acetate,cis-3-hexenyl n-butyrate,cis-3-hexenyl salicylate,which can be used to produce fruity note with banana or apple taste.The natural leaf alcohol is too low.Japan and some other countries have the monopoly on it.China has to import a lot of leaf alcohol.In recent years,leaf alcohol is widely used in many high-ends aroma chemicals and household chemicals.2-methyl-5,6-dihydro-2H-pyran,as a key intermediate,possess an advantage of short route to the synthesis.Thus it's very important to do the research on this topic.In the second chapter,we studied the reaction conditions for the synthesis of 2-methyl-5,6-dihydro-2H-pyran using 1,3-pentadiene and paraformaldehyde as raw maternals.We explored reaction influence factors such as catalysts&feeding ratio,relationships between solvent selection and feeding ratio,reaction temperature and time,stirring speed,reaction pressure,polymerization inhibitor and other conditions.The optimum feed mass ratio of paraformaldehyde:p-pentadiene:zinc bromide:tetrahydrofuran is 100:270:64.5:200,and the reaction is carried out without the use of a polyrmerization inhibitor,slowly raising the temperature to 140? for 8 hours.After completion of the reaction,the material is extruded from the autoclave with nitrogen.The solvent is recovered by distillation.The catalyst is removed by washing,and the waste is removed by steam distillation to obtain the target product in a yield of not less than 65%.The third chapter discusses the recovery and regeneration of the catalyst of zinc bromide.The regeneration of zinc bromide can be achieved by three steps of rough steaming dehydration,azeotropic dehydration,and activation.70%of aqueous solution can be recovered by vacuuming,and then use toluene to do azeotropic dehydration.The autoclave temperatureis raised to 110 0C to complete dehydration.Afterwards,hydrobromic acid is added to do activation to achieve the regeneration of catalyst.This can completely solve the problem that waste water from zinc bromide can not be handled.