Preparation of ethyl 4-fluorobenzoate
Ethyl 4-aminobenzoate (165 g) is warmed, with shaking, on a water-bath with hydrochloric acid (d 1.19; 204 ml) and water (300 ml), this yielding a colorless paste of the ethyl 4-aminobenzoate hydrochloride. The mixture is cooled in ice-salt to 0°, and a solution of sodium nitrite (72.6 g, = 1 mole of 95 % sodium nitrite) in a little water is allowed to run in slowly with stirring until the starch-iodide reaction remains weakly positive for 10 min; the temperature should not exceed 7°. Meanwhile, a solution of tetrafluoroboric acid is prepared. Boric acid (68 g, 1.1 moles) is dissolved in 60% hydrogen fluoride (133 g) in a paraffin-coated or plastic beaker or a lead jar, with ice-cooling to keep the temperature below 25° (so that the paraffin wax does not melt); alternatively, commercial 40% hydrogen fluoride (200 g) may be used. The ice-cold solution is allowed to run into the diazonium solution fairly fast, although the temperature should remain below 10°. After this addition the mixture is stirred for a further 20-30 min and the diazonium fluoroborate that has separated as a thick paste is filtered off, washed successively with cold water (300 ml), methanol (300 ml), and ether (200 ml), with good suction in each case, and then dried in a vacuum over concentrated sulfuric acid. This affords a 75-78% yield (198-205 g) of ethyl 4-fluorobenzoate diazonium tetrafluoroborate, dec. 93-94°. Thermal decomposition of the diazonium tetrafluoroborate involves losses due to resinification unless the salt is completely dry!!!. 85 g portions of the fluoroborate are placed in a 2-liter flask which is connected by a bent glass wide tube to a 1-liter flask, and the uncondensed vapors of boron trifluoride are led over water; the unabsorbed gas is fed into an efficient fume cupboard. The diazonium fluoroborate is heated from above with a luminous Bunsen flame until white fumes of boron trifluoride appear, then decomposition is allowed to proceed spontaneously. If the reaction slackens it is hastened again by temporary heating, until finally on substantial heating the solid mass is completely liquified. Most of the ethyl 4-fluorobenzoate, b.p. 105-106°/25 mm, remains in the reaction vessel but a small part of it is carried into the receiver. It is taken up in ether, filtered, and freed from ether in vacuo and purified by fractionation collecting fraction boiling at b.p. 105-106°/25 mm or 210 °C.
Org. Syn., Coll. Vol. II, 299 (1943).
Ethyl 4-fluorobenzoate, 451-46-7, 4-Fluorobenzoic acid ethyl ester, Ethyl p-fluorobenzoate, Benzoic acid, 4-fluoro-, ethyl ester, p-Fluorobenzoic acid, ethyl ester, ETHYL4-FLUOROBENZOATE, 4-fluoro-benzoic acid ethyl ester, UMPRJGKLMUDRHL-UHFFFAOYSA-N, MFCD00000351, SBB063137, Benzoic acid, p-fluoro-, ethyl ester, PubChem3471, ethyl-4-fluorobenzoate, ACMC-1AEKF, ethyl 4-fluoro-benzoate, Ethyl para-fluorobenzoate, 4-Fluorobenzoic acid ethyl, SCHEMBL62862, KSC490A7P, 102644_ALDRICH, AC1L28R8, PARAGOS 390198, RARECHEM AL BI 0076, DTXSID6060006, 46610_FLUKA, CTK3J0077, 4-fluoro benzoic acid ethyl ester, 4-Fluorobenzoic acid, ethyl ester, ZINC388045, 4-fluoro benzoic acid ethyl ester;, ACT01143, EBD37497, EINECS 207-194-8, ANW-30217, NSC190692, ZINC00388045, AKOS004911144, AS01264, CS21694, MCULE-8333373853, NSC 190692, NSC-190692, PF10983, PS-8725, RP23085, VZ32143, P-FLUOROBENZOIC ACID ETHYL ESTER, TRA-0184256, AC-15551, AJ-20399, AK-46539, AN-44958, BR-46539, CJ-03088, KB-51253, OR002175, SC-04598, ZB011243, AB1010809, KB-242167, ST2419351, TL8003131, TR-017211, AM20060907, F0203, FT-0618510, ST50406228, Benzoic acid, p-fluoro-, ethyl ester (8CI), C-4528, 65126-EP2286811A1, 65126-EP2308812A2, I01-0532, W-106162
Benzoic acid, ethyl ester, C9H9FO2, MolPort-000-155-246, CID67976, RTR-017211