SU1594169A1 - Method of producing 5-promopentanic acid - Google Patents

Abstract

The invention relates to carboxylic acids, in particular the preparation of 5-bromopentanoic acid used in fine organic synthesis. The goal is to increase the yield of the target product and simplify the process. The latter is oxidized with cyclopentanone with H 2 O 2 at 0–30 ° C and the molar ratio of reagents is 1: (4–7), followed by treatment of the reaction mixture with copper salt (2+) and alkali metal bromide at a pH of 1.7–3, 5 and 5-30 ° C. The molar ratio of cyclopentanone, copper salt and bromide = 1: (0.05-1) :( 1: 2.5). These conditions increase the yield of the target acid from 45-52 to 61-69% and simplify the process by eliminating HVH, methanol (solvent). 1 tab.

Description

This invention relates to organic chemistry, in particular, to a method for producing 5-bromopentanoic acid, which is used in fine organic synthesis.

The aim of the invention is to simplify the process, reduce its risk of explosion and increase the output of the target product.

Example 1. At 50 ° C, 450 ml of 31% aqueous (perhydrol) hydrogen peroxide (4.1 mol) is added to 50.4 g of cyclopentanone (0.6 mol) with stirring. The molar ratio of cyclopentanone: hydrogen peroxide is 1: 6.8. After 12 h, the resulting solution was added dropwise with stirring to a solution of 30 g of CuBr (0.1 mol) and 100 g of KBr (0.84 mol) in 300 ml of water, maintaining the temperature of the reaction mass of 15 C and pH of the medium 2.6 by addition during the reaction hydrobromic

acids (a total of 2.5 ml of 20% HBr was added).

After the completion of the dropping, the reaction mass is stirred for 30 minutes, acidified with hydrobromic acid to pH = -2 and extracted with ether (3x100 ml). The ether extracts are combined, dried with MgSO4 and the solvent and unreacted cyclopentanone (20.7 g, 0.2 mol) are distilled off on a rotary evaporator under vacuum. The residue is washed with 10 ml of hexane cooled to 0-5 ° C and 46.6 g of 5-bromopentanoic acid are obtained (purity 95% according to GLC).

The yield of 5-bromopentanoic acid is 69% o.t. of the theoretical on reacted cyclopentanone.

Examples 2-6. It is carried out as in Example 1.

The conditions for and the yield of 5-bromopentanoic acid are given in the table below.

with

about X

face. The purity of 5-bromopentanoic acid obtained is 95% in all experiments.

Examples 7-10 (comparative). Confirm the selected intervals of molar content of reagents, pH of the medium and temperature.

As can be seen from the table, the use of more than 7-fold excess and more than 2.5-fold excess of alkali metal bromide (Example 8) is impractical because it does not increase the yield of the desired product. Conducting the oxidation at a temperature below and treating the reaction mass with a solution of a salt of copper and alkali metal bromide at a temperature below is difficult, since under these conditions the reaction mixture ceases to be homogeneous.

PRI me R 11 (comparative). The procedure is carried out as in Example 1, but with a known molar ratio of cyclopentanone O, 1: 1.5. INPUT of the target product drops sharply to 19%.

Example 12 (comparative). It is carried out as in Example 1, but during the oxidation of cyclopeitanone, 1.5 g of concentrated HBr is additionally introduced (i.e., as in the known method, the molar ratio of cyclopentanone: HBr 1: 0.05). When the target product is removed by distilling off the solvent and unreacted cyclopentanone, a strong release occurs, which is characteristic of the decomposition of cyclic cyclopentanone peroxides. Under these conditions (i.e., when

. The relative ratio of cyclopentanone is 1: 4-7 and the reaction mass is also acid qQ 0.

five

d

five

0

HBg, as in the known method, the process of oxidation of cyclopentanone with hydrogen peroxide occurs predominantly towards the formation of cyclic peroxides, which makes it explosive.

The proposed method for producing 5-bromopentanoic acid allows to increase the yield of the target product to 61-69% (in the known method 45- 52%) and simplify the process (exclusion of the catalyst — hydrobromic acid, and the solvent — methanol) by carrying out the process at x cyclopentanone: other than the known (including by a known method), and. Also pH of the medium is 1.7-3.5.

Claims (1)

Invention Formula Method for producing 5-bromopentanoic acid by oxidizing with cyclopentano on hydrogen peroxide at 0-3Q C followed by treating the reaction mass with copper salt and alkali metal bromide at a temperature of 5-30 ° C and molar ratio of cyclopentanone: copper salt: alkali bromide metal 1: (O, 05-1):: (1-2,5), about t l - and the fact that, in order to simplify the process, reduce its explosiveness and increase the yield of the target product, the oxidation of cyclopentanone with hydrogen peroxide is carried out molar ratio cyclopentanone: n rekis hydrogen of 1: (4-7) and subsequent treatment of the reaction mass cupric salt and alkali metal bromide is carried out at pH 1.7-3.5. Table continuation  The yield of 5-bromopentanoic acid is given taking into account the purity in% of theory based on the reacted cyclopentanone.