Study On Synthesis Of Hindered Amine Light Stabilizer 625 And Pentamethylpiperidinol

Hindered amine light stabilizers are widely used in coatings,fibers and organic polymer materials by possessing excellent light stabilizer properties.In recent years,the research on hindered amine light stabilizers and their intermediates has become a hot topic field.Hindered amine light stabilizer 625 is a light stabilizer with suitable molecular weight,low alkalinity and suitable mobility.Because it can be used in harsh acidic environments,it is greatly welcomed in the field of polymer materials.In addition,hindered amine light stabilizer GW-540 and HS-508 are commonly used light stabilizers.Pentamethylpiperidinol is a key intermediate in the synthesis of GW-540 and HS-508.It is also of great significance to study its synthetic technology.By using hindered amine light stabilizer 360 as a raw material,the hindered amine light stabilizer 625 was synthesized in this paper by the formaldehyde/formic acid method and the formaldehyde method,and the reaction conditions were also optimized.In the formaldehyde/formic acid method,the problem of salt caking of light stabilizer 360 and formic acid in the former formaldehyde/formic acid process was solved,and the methylation rate was increased by 5.6%.On this basis,the light stabilizer 625 was synthesized by the formaldehyde method.This method is simple in operation,mild in condition,without salt caking,and it has certain industrialization potential.(1)For the formaldehyde/formic acid method,we studied two operating conditions,in water and in anhydrous medium.?The best reaction conditions in the presence of water were:using toluene as the solvent,the amount of water added was 27.78%of the total mass,the molar ratio was n(light stabilizer 360):(formic acid):(paraformaldehyde):1:3.1:3.1,and formic acid was slowly added at 70?.Then,the temperature was raised to 80? after adding formic acid.The reaction time was 4 hours.The pH of the reaction solution was adjusted with a 10%sodium hydroxide solution.Under these conditions,the methylation rate was 97.6%.?The optimal process conditions in anhydrous medium were:using toluene as solvent,molar ratio was n(light stabilizer 360):(formic acid):(paraformaldehyde)=1:3.1:3.1,formic acid and paraformaldehyde were divided into three times add alternately.Formic acid was added dropwise very slowly.Under laboratory conditions,2-3 drops were added in 6-8 min,and the reaction was incubated at 80? for 3 hours.Under this optimized condition,the methylation rate was 98.3%.(2)The preferred conditions of the formaldehyde method were:using toluene as solvent,the molar ratio was n(light stabilizer 360):n(formaldehyde)=1:4.6,the reaction temperature was 90?,and the reaction time was 5 h.Under optimized conditions,the methylation rate was 97.3%.By using tetramethylpiperidinol as a raw material,pentamethylpiperidinol was synthesized in this paper by formaldehyde/formic acid method and formaldehyde method.And the reaction conditions were optimized.In the formaldehyde/formic acid method,compared with the previous methods,there were advantages such as short reaction time and low temperature.In the formaldehyde method,the reaction mechanism of formaldehyde and tetramethylpiperidinol was discussed.Firstly,Formaldehyde reacts with tetramethylpiperidinol to form a reductive hemiacetal,then the hemiacetal is oxidized to a formate,and then it is eliminated to form reductive formate.Then,under the action of formate and hemiacetal,the imine salt formed from tetramethylpiperidinol and formaldehyde is reduced,finally,pentamethylpiperidinol was synthesized.The equation for the synthesis of pentamethylpiperidinol by the formaldehyde method was determined,which greatly reduced the feed amount of paraformaldehyde and improved certain industrial economic benefits.(3)The conditions of the formaldehyde/formic acid method were:n(tetramethylpiperidinol):n(paraformaldehyde):n(formic acid)=1:1.05:1.05,the reaction temperature was 80?,and the reaction time was 2.5 h.Under optimal operating conditions,solvent water can be recycled for 3 times.The average yield of pentamethylpiperidol was 97.9%,and the purity was 99.7%.(4)Solvent method and neat method are discussed in the formaldehyde method.?The preferred process conditions in the solvent method were:using water as solvent,the molar ratio n(tetramethylpiperidinol):n(paraformaldehyde)=1:1.6,the reaction temperature was 85?,and the reaction time was 3 h,solvent water can be recycled for 3 times.Under these conditions,the average yield of pentamethylpiperidol was 96.3%,and the purity was 99.6%.?The optimal process conditions for the solvent-free method were:the molar ratio n(tetramethylpiperidinol):n(paraformaldehyde)=l:1.6,the reaction temperature was 80?.Paraformaldehyde was added in three batches with a reaction time of 3 h.Under these conditions,the average yield of pentamethylpiperidol was 97.8%,and the purity was 99.4%.