Study On Synthesis Of(R)-2-[4-(6-Chlor-2-benzoxazolyloxy)-phenoxy]-propionic Acid

(R)-2-[4-(6-chlor-2-benzoxazolyloxy)-phenoxy] propionic acid is an important intermediate in the synthesis of The aryloxyphenoxy propionate herbicides. In china, there is no efficient method to synthesis (R)-2-[4-(6-chlor-2-benzoxazolyloxy)-phenoxy] propionic acid, correspondently the cost of manufacturing is very high.In terms of lots of study and research at home and abroad,2,6-Dichlorobenzoxazole was synthesis through carbonylation, two chlorination choosing ortho-aminophenol as start material; at the same time, R-(+)-2-(4-hydroxyphenoxy) propionate was synthesis through chlorination and etherification choosing Methyl (R)-(+)-Lactate as start material. at last, The title compound was obtained from2,6-Dichlorobenzoxazole and R-(+)-2-(4-hydroxyphenoxy) propionate. All products were characterized by melting point, IR,1H-NMR and MS, which proves the construction is the same as target product. Meanwhile, This essay studied the influence of six reactions conditions. In the end, the yield was over55%, we obtained a simple, low-cost, high conversion, low pollution way of manufacturing (R)-2-[4-(6-chlor-2-benzoxazolyloxy)-phenoxy] propionic acid.According to the experimental results, ortho-aminophenol was used as material reacting with urea, dimethyl carbonate and triphosgene synthesis2-Benzoxazolinone, Method reacting with urea, is much better in any aspect, it may be the best way for manufacturing of2-Benzoxazolinone. The optimum condition for the synthesis of6-chlorobenzoxazolone was obtained as follows:2-Benzoxazolinone and hydrochloric acid (1M:1.5-2M) reacted in HAc,40-50℃for3h to prepare, the yield of6-chlorobenzoxazolone was91.1%, the purity was98.0%; The optimum conditions for the synthesis of2,6-Dichlorobenzoxazole were as follows: the molar ratio of6-chlorobenzoxazolone to phosphorus pentachloride was1:2, the amount of the O-dichlorobenzene was60ml (relative to0.1mol6-chlorobenzoxazolone), the temperature was150～160℃; reaction time was2.5h, so that The yield of2,6-Dichlorobenzoxazole was over72.4%, the purity was99.0%.The optimum conditions for (S)-2-Chloropropionate methyl ester were as follows:the molar ratio of Methyl (R)-(+)-Lactate to vilsmeier reagent is1:1.15, the amount of dimethyl formamide is1.0or1.5time more than Methyl (R)-(+)-Lactate, dimethyl formamide is Catalyst and solvent, the best reaction temperature is50～60℃, reaction time is5h, the productivity of is over89%, e.e%is over98.2%. The optimum conditions for (R)-2-(4-hydroxylphenoxy) propionic acid were as follows:the quantity of sodium hydrosulfite was equal to1%of hydroquinone. the amount of sodium hydroxide is1.0or1.5time more than hydroquinone. the molar ratio of hydroquinone to S-2-Chloropropionate methyl ester is1:1.15, the best reaction temperature is65℃, reaction time is4h The maximum yield is84.8%, the maximum purity is98.3%.The optimum conditions of (R)-2-[4-(6-chlor-2-benzoxazolyloxy)-phenoxy]-propionic acid were as follows:the molar ratio of R-(+)-2-(4-hydroxyphenoxy) propionic acid to2,6-Dichlorobenzoxazole is1:1.2, reacted4h at50℃, refluxed1h. The yield of (R)-2-[4-(6-chlor-2-benzoxazolyloxy)-phenoxy]-propionic acid is over90.1%, the purity is98.4%.