Roe, Arthur published the artcileThe preparation of some fluoro- and trifluoromethylphenothiazines, and some observations regarding determination of their structure by infrared spectroscopy, Application of Ethyl 3,5-difluorobenzoate, the publication is Journal of Organic Chemistry (1955), 1577-90, database is CAplus.
A number of fluorophenothiazines which may be of interest as antioxidants in lubricating oils are prepared Adding slowly with stirring 16 g. Br in 25 cc. AcOH to 12.9 g. 2,4-F2C6H3NH2 in 75 cc. AcOH at 25°, removing after 0.5 hr. any excess Br with Na2S2O3, then adding 11.2 g. NaOAc in 100 cc. H2O, and cooling the mixture in an ice bath give 81% 2,4,6-F2BrC6H2NH2 (I), m. 41-2°. I has a high vapor pressure [N-Ac derivative (II), 90%, prepared with Ac2O, m. 156-7°]. 2,4-F2C6H3NHAc cannot be brominated in AcOH. Deamination of I with H3PO2 gives 74% 3,5-F2C6H3Br (III), b. 140°, d23 1.676, nD23 1.4989. Adding a Grignard reagent of 14.5 g. III and 1.9 g. Mg in 50 cc. Et2O to Dry Ice in Et2O gives 64% 3,5-F2C6H3CO2H, m. 121-2°, also obtained when 18 g. 3,5-(H2N)2C6H3CO2Et in 480 g. 45% HBF4 is treated at -10° with 15 g. NaNO2, the bis(diazonium fluoborate) (40 g., decomposing about 175°) is decomposed at 30 mm., and the Et ester, b46 103-5°, b760 200°, nD25 1.4670, d25 1.201, saponified with KOH. Stirring 23 g. 2,6-ClFC6H3CO2H in 100 cc. concentrated H2SO24 1 hr. at 60°, adding (1.5 hrs.) 10 g. NaN3 in small portions at 65°, keeping the mixture overnight, making it basic with NH4OH, and steam distilling it give 70% 2,6-ClFC6H3NH2 (IV), b30 91°, nD23 1.5511, d23 1.316 (Ac derivative, prepared in 71% yield by refluxing 6 g. IV 1.5 hrs. in 25 cc. AcOH and 4.2 g. Ac2O, platelets, m. 134-5°). Adding 9.1 g. NaNO2 in small portions to 24 g. 2,3-O2N(H2N)C6H3CF3 in 300 cc. 50% H2SO4 at 0°, stirring the mixture 15 min., pouring it into 160 cc. 10% CuCl at 20°, keeping it 1 hr. at 20°, diluting it with 100 cc. H20, and steam distilling it give 52% 3-Cl analog, b27 125-6°, nD24 1.4782, d24 1.531. 3,4-Cl(O2N)C6H3CF3, prepared in the same way in 53% yield, b28 116°, nD24 1.4864, d24 1.527. Refluxing 17 hrs. 0.1 mole of the appropriate acetanilide, 0.2 mole PhBr, 0.1 mole anhydrous K2CO3, 20 cc. PhNO2, 6 g. catalyst mixture (consisting of equal parts by weight of CuI, KI, and Cu powder), and a crystal of iodine, steam distilling the mixture, extracting the distillation residue with Et2O, refluxing the Et2O residue 3.5 hrs. in 100 cc. 20% alc. KOH, pouring the solution into 800 cc. saturated NaCl solution, and extracting with Et2O give the fluorodiphenylamine of which the following are prepared: 2-F (V), 80%, yellow oil, b3 111.5°, d23 1.165, nD23 1.6171 (N-Bz derivative, m. 129-30°); 3-F (VI), 56%, yellow oil, b10 149-50°, d23 1.176, nD23 1.6203; 2,5-di-F (VII), 68%, b9 138°, m. 45-5.5°; 2,4-di-F (VIIa), 63%, b3 110-13°, m. 42-2.5°; 3,5-di-F (VIII), 51%, b4 121-4°, m. 45-5.5°; 2,3′,5-tri-F, 63%, b2.5 105-6°, m. 31.5-2°; 2,4′,5-tri-F, 71%, b2.5 104-5°, m. 39.2-40°; 3,3′,5-tri-F (VIIIa), 49%, b3.5 121°, m. 27.5-8.5°; 3,4′,5-tri-F (IX), 65%, b4 127-8°, m. 60-1°; 3,3′,5,5′-tetra-F (X), 43%, m. 117-18°; 2,6-ClF (XI), 34%, b4 138-40°, m. 69-9.3°. Adding 4 g. NaOH in 30 cc. H2O to 12.5 g. o-H2NC6H4SH in 300 cc. absolute EtOH, then adding 0.1 mole of the appropriate halonitrobenzene in 100 cc. absolute EtOH, refluxing the mixture 0.5 hr. (3.5 hrs. in the preparation of XIII below), adding 100 cc. H2O to the boiling filtered solution, and cooling it slowly give the substituted o-H2NC6H4SC6H3RNO2-x,2 (XII) of which the following are prepared: R = 3-CF3(XIII), 67%, m. 72-3°; 4-CF3 (XIV), 89%, yellow, m. 108-9°; 5-CF3, 80%, yellow, m. 110-11°; 4-F, 70%, red, m. 73-4°; 5-F, 54%, yellow, m. 115-16.5°. Refluxing XII with 10 times its weight of 90% HCO2H 9-10 hrs. gives the substituted N-formyl derivative, o-OHCNHC6H4SC6H3RNO2-x,2, of which the following are prepared: x-R = 3-CF3 (XV), 92%,m. 137-8°; 4-CF3(XVI), 88%, yellow, m. 132-3°; 5-CF3 (XVII), 83%, yellow, m. 95-6°; 4-F (XVIII), 74%, yellow, m. 128-9°; 5-F (XIX), 74%, yellow, m. 116-17°. Refluxing 6.3 g. XIV 1 hr. with 2.8 g. BzCl in 25 cc. C5H5N gives 89% 2-[4,2-CF3(O2N)C6H3S]C6H4NHBz (XX), m. 127.5-8°. Heating 15 g. V, 5 g. S, and a few crystals of iodine 3 hrs. at 200-10° under reflux, boiling the tar obtained with 20% Na2S (to remove the excess S), extracting it with Et2O, treating the Et2O solution with Norit and Zn dust, and distilling the residue of the filtered Et2O solution give 2.2 g. unchanged V and 3 g. of a yellow solid, b2.5 140°, from which 9.3% 1-fluorophenothiazine (XXI), m. 81.5-2°, and 1.4% phenothiazine (XXII), m. 180-2°, are isolated. XXI gives a blood-red color with concentrated HNO3. When 1.9 g. V, 0.6 g. S, and a crystal of iodine are heated 1.5 hrs. in a sealed tube at 310-40° a few mg. XXI and 0.175 g. XXII are obtained. When 2.2 g. XI, 0.6 g. S, and a crystal of iodine are heated 1.5 hrs. at 300°, no crystalline product can be isolated. Heating 5 g. VI, 1.7 g. S, and a few crystals of iodine 1 hr. at 180° ± 5° gives 52% 2-fluorophenothiazine (XXIII), light yellow powder, m. 199° (decomposition); it gives a blood-red color with HNO3. In an attempted synthesis of 1,4-difluorophenothiazine (XXIV), XXIII is obtained. Several other attempts to prepare XXIV from VII, from VIIa, or 1,3-difluorophenothiazine also failed. Heating a carefully purified VIII with S and a crystal of iodine 35 min. at 175° gives 43% 2,4-difluorophenothiazine, subliming 130°/2.5 mm., m. 129-30°. Attempts to prepare 1,4,7- and 1,4,8-trifluorophenothiazines by ring closure of the appropriate trifluorodiphenylamines failed. Ring closure of IX with S and iodine 1 hr. at 190° gives 20% 2,4,7-trifluorophenothiazine, m. 147-8° (decomposition); 6.1 g. VIIIa, 1.75 g. S, and a crystal of iodine 2.5 hrs. at 170° give 44% 2,4,8-trifluorophenothiazine, m. 142-3°; 1.2 g. X, 0.31 g. S, and a crystal of iodine 1 min. at 230° and 20 min. at 210° (or 1.5 hrs. at 210-40°) give 13% (or 20%) 2,4,6,8-tetrafluorophenothiazine, needles, m. 193-3.5°. Refluxing 15 g. XVI in 150 cc. Me2CO 0.5 hr. with 44 cc. N NaOH, evaporating the solution to dryness, and extracting the residue with boiling CCl4 give 52% 3-trifluoromethylphenothiazine, m. 217-18°, also obtained in much lower yield from XX. In a similar way, XVII gives 59% 2-trifluoromethylphenothiazine, m. 189-90°, and XVIII gives 43% 3-fluorophenothiazine, m. 178-9°. Attempts to prepare 4-trifluoromethylphenothiazine by treating 4.6 g. XV in 46 cc. Me2CO with NaOH, or 2-fluorophenothiazine by refluxing 4.4 g. XIX in Me2CO with NaOH were unsuccessful. The infrared absorption spectra of these compounds are determined and an attempt is made to see if a reliable method of structure determination of fluorophenothiazines can be made with these spectra. It is found that this kind of structural determination should be approached with discretion.
Journal of Organic Chemistry published new progress about 350-19-6. 350-19-6 belongs to esters-buliding-blocks, auxiliary class Fluoride,Benzene,Ester, name is Ethyl 3,5-difluorobenzoate, and the molecular formula is C9H8F2O2, Application of Ethyl 3,5-difluorobenzoate.
Referemce:
https://en.wikipedia.org/wiki/Ester,
Ester – an overview | ScienceDirect Topics