Synthesis Of Paclobutrazol

Paclobutrazol is a highly active plant growth regulator with very good fungicidal activity.It enables the growth of woody plants and grasses dwarfing delay or increase its lodging capacity;prevents excessive growth of fruit trees and other horticultural crops,promotes germination,reduces pruning and improves the light transmittance.In addition,it has a bactericidal effect on rice blight,powdery mildew rust,apple powdery mildew and has broad application prospects in agriculture,horticulture and so on.So how to improve the process to improve the yield of Paclobutrazol has important significance.This paper reviews the synthesis of Paclobutrazol and designs synthesis process route of Paclobutrazol through theoretical analysis and research,With 1-Chloropina-colone as raw material,polyethylene glycol 600 as phase transfer c-atalyst,3,3-Dim-ethyl-1-?1H-1,2,4-triazol-1-yl?butan-2-one is prepared in ethyl acetate solution with tri azole sodium via condensation reaction.Then with 4-Chlorobenzyl chloride,the 1-?4-Chlorophenyl?-4,4-dimethyl-2-?1,2,4-triazol-1-yl?pentan-3-one is prepared via conden-sation reaction,then the target product Paclobutrazol is gained by reduction reaction.The key factors effecting the above reactions are studied through single factor exper iments,and the optimum condition is gained.Study results:during the synthesis of 3,3-Dimethyl-1-?1H-1,2,4-triazol-1-yl?butan-2-one,n?1-Chloropinacolone?:n?Triazole sodium?=1:1.1,n?1-Chloropinacol-one?:n?Polye thylene glycol 600?=1:0.03,the temperature is the reflux temperature,the feeding way of 1-Chloropinacolone is dropwise addition,the solvent ethyl acetate is in an a mount of 120mL and can be recycled.Under these conditions,the yield of 3,3-Di-methyl-1-?1H-1,2,4-triazol-1-yl?butan-2-one is 96.71%,GC purity is 99.15%;during the synthesis of 1-?4-Chlorophenyl?-4,4-dimethyl-2-?1,2,4-triazol-1-yl?pentan-3-one,n?3,3-Dimethyl-1-?1H-1,2,4-triazol-1-yl?butan-2-one?:n?4-Chlorobenzyl chloride?=1:1.0,n?3,3-Dimethyl-1-?1H-1,2,4-triazol-1-yl?butan-2-one?:n?TEBA?=1:0.05,the feeding mode of4-Chlorobenzyl chloride is that use benzene dissolved before the dropwise adding,and m?4-Chlorobenzyl?:m?benzene?=3:1,the mass fraction of NaOH in alkaline sol-ution is 20%,the action temperature is 60⁶5?.Under these conditions,the yield of 1-?4-Chlorophenyl?-4,4-dimethyl-2-?1,2,4-triazol-1-yl?pentan-3-one is up to 95.96%,GC purity is 93.91%.In the reduction process of paclbutrazol,compared with five different reductions:KBH₄,sodium hyposulfite,TD,Mg-NH₄Cl and catalytic hydrog-enation,the last one is the best method.Hydrogen as reducing agent,3%Pd/C as catalyst,isopropyl alcohol as solvent,the optimum conditions are that the pressure is 2MPa,m?1-?4-Chlor-ophenyl?-4,4-dimethyl-2-?1,2,4-triazol-1-yl?pentan-3-one?:m?3%Pd/C?=100:5,the temperature is 70?,the reaction time is 2h.Under these conditions,the yield of Paclobutrazol is 96.03%,GC purity is 98.61%.In summary,the total yield?calculated by 1-Chloropinacolone?of Paclobutrazol is 89.12%.The synthetic method is simple and economic,and the target product has high purity and easy be separated.The structure of Paclobutrazol and intermediates are confirmed via ¹H N MR and IR,which was consistent with the standard features.