preparation of methylbenzothiophene-2-carbaldehyde_kain industrial additive

background and overview^[1]

methylbenzothiophene-2-carboxaldehyde is an organic synthesis intermediate that can be used in laboratory research and development processes and chemical and pharmaceutical synthesis. it can be obtained by esterification of benzothiophene-2-carboxylic acid.

preparation^[1]

dissolve 14.25 g (80 mmol) indole-2-carboxylic acid in 500 ml methanol, add 2 ml concentrated sulfuric acid, reflux for 24 hours at 75 °c, and monitor the reaction progress with tlc (5% water-acetonitrile). reaction after completion, most of the solvent was evaporated under reduced pressure, and the solution was cooled and left to stand for about 10 hours at 0°c. needle-like crystals precipitated and filtered to obtain 15.36 g of benzothiophene-2-carboxylic acid methyl ester (1), with a yield of 93%.

apply^[1]

can be used to synthesize 2-substituted-1,3,4-oxadiazinone compounds – compound 4. such compounds have good herbicidal activity, especially against crabgrass (digitaria sanguinalis) and amaranth (ambrosia tricolor linn).

1. synthesis of compound 2

dissolve 7.68 g (40 mmol) 1 in 500 ml methanol, add 23.12 g (0.36 mol) hydrazine hydrate, reflux the reaction at 80 °c for 20 h, and monitor the reaction with tlc (5% water-acetonitrile). after the reaction is completed , most of the solvent was evaporated under reduced pressure, and the solution was cooled and left to stand for about 10 hours at 0°c. needle-like crystals precipitated and filtered to obtain 7.06 g of benzothiophene-2-carboxylic hydrazide (2), with a yield of 92%.

2. synthesis of compound 3

dissolve 4.5 g (25 mmol) 2 in 160 ml dmf, add 2.92 g (27.5 mmol) triethylamine, cool the solution to 0 ℃, slowly add 4.90 g (37.5 mmol) chloroacetyl chloride, 0 ℃ react for 4 hours, and monitor the reaction with tlc (50% ethyl acetate-petroleum ether). after the reaction, filter to remove the white precipitate, evaporate about 2/3 of the solvent under reduced pressure, cool and let stand at room temperature if solid precipitates, filter a white solid was obtained, which was recrystallized from ethyl acetate to obtain 5.36 g of 1-(benzothiophene-2-formyl)-2-(chloroacetyl)hydrazine (3), with a yield of 80%.

3. synthesis of compound 4

heat and dissolve 2.69 g (10 mmol) 3 in 50 ml dmf, add 6.9 g (50 mmol) potassium carbonate, react at 80 °c for 6 h, and monitor the reaction with tlc (50% ethyl acetate-petroleum ether). after the reaction is completed, filter to remove the precipitate. add 50 ml of water to the filtrate. the solid will immediately precipitate into a suspension. cool and let stand overnight. filter to obtain a light yellow solid 2-(2-benzothienyl)-4h-1. ,3,4-oxadiazin-5(6h)-one(4) 1.11 g, yield 48%.

main reference materials

[1] sun hongshun, wang jianqiang, tan wenwen, yang haidong, li yulong, shen linjiang, guo cheng. synthesis and crystal structure of a new 1,3,4-oxadiazinone compound [j]. organic chemistry, 2016, 36(03):622-625.