The Synthesis Study Of 2,7-dimethy-2,4,6-octatriene-1,8-dialdehyde

2,7-dimethyl-2,4,6-octatriene-1,8-dialdehyde is the key intermediate for synthesis of carotenoids.A five-step route including chlorination,isomerization,condensation Wittig-Horner reaction and hydrolysis is proposed to prepare 2,7-dimethyl-2,4,6-octatriene-1,8-dialdehyde in this thesis from 1,4-butenediol,thionyl chloride,dimethoxyacetone and triethyl phosphite,and optimum synthesis conditions are obtained through systematical single-factor optimization.The first chlorination from 1,4-butenediol and thionyl chloride is carried out under molar ratio of thionyl chloride to 1,4-butenediol 2.2,pyridine to thionyl chloride 1.3,temperature 10?,to obtain cis-1,4-dichloro-2-butene,thionyl chloride was added dropwise for 6 hours,which is followed by temperature keeping for 8 hours to give the yield of 95.5%.Catalyzed by N-bromosuccinimide,trans-1,4-dichloro-2-butene is obtained through the second isomerization which is optimized and the yield is 90.2%under the conditions of mass ratio of N-bromosuccinimide to cis-1,4-dichloro-2-butene 0.024,temperature 55? and reaction time 3 hours.The optimum conditions for the third condensation from triethyl phosphite and trans-1,4-dichloro-2-butene to 2-butene-1,4-tetraethyl phosphite are:molar ratio of triethyl phosphite to trans,-1,4-dichloro-2-butene 2.3,temperature 150?,reaction time 3 hours,addition time of trans-1,4-dichloro-2-butene 3 hours,which gives the yield of 95.4%.The fourth Wittig-Horner reaction gives 1,1,8,8-tetramethoxy-2,7-dimethyl-2,4,6-octriene from 1,1-dimethoxyacetone and 2-butene-1,4-tetraethyl phosphite.The optimum conditions are molar ratio of 1,1-dimethoxyacetone to 2-butene-1,4-tetraethyl phosphite 2.1,sodium tert-butoxide to 1,1-dimethoxyacetone 1.2.addition time of sodium tert-butoxide 6 hours at 40?,temperature keeping for 4 hours,solvent molar ratio of cyclohexane to 1,1-dimethoxyacetone 4.2,toluene to cyclohexane 1.1,and the yield is 91.6%.Catalyzed by acid the fifth hydrolysis of 1,1,8,8-tetramethoxy-2,7-dimethyl-2,4,6-octriene to 2,7-dimethy 1-2,4,6-octatriene-1,8-dialdehyde gives the yield of 96.6%under the optimum conditions:molar ratio of 1,1,8,8-tetramethoxy-2,7-dimethyl-2,4,6-octriene to hydrochloric acid 3.5,1,1,8,8-tetramethoxy-2,7-dimethyl-2,4,6-octriene to methanol 25,the concentration of hydrochloric acid solution 5%,temperature 30? and reaction time an hour.The total yield of the five-step reaction is 72.7%,which exceeded the total yield of 39%reported in the literature and has industrial application potentially.Furthermore,the structure of 2,7-dimethyl-2,4,6-octatriene-1,8-dialdehyde is characterized by gas chromatography-mass spectrometer,nuclear magnetic resonance spectrometer,infrared spectrometer and uv-visible spectrophotometer.