110877-64-0

Basic information

• Product Name: 2-Chloro-4,5-difluorobenzoic acid
• Synonyms: RARECHEM AL BO 1000;TIMTEC-BB SBB003616;2-CHLORO-4,5-DIFLUOROBENZOIC ACID;2-CHLORO-4 5-DIFLUOROBENZENE ACID 98%;2-Chloro-4,5-difluorobenzoic acid, 99+%;2-Chloro-4,5-difluorobenzoic acid 99%;2-chloro-4,5-difluorophenyl acid;2-CHLORO-4,5-DIFLUOROBENZOIC ACID,98%
• CAS NO: 110877-64-0
• Molecular Formula: C₇H₃ClF₂O₂
• Molecular Weight: 192.55
• EINECS: 405-380-5
• Product Categories: Aromatic Carboxylic Acids, Amides, Anilides, Anhydrides & Salts;Aromatic compound;Benzoic acid;C7;Carbonyl Compounds;Carboxylic Acids;Fluorine series
• Mol File: 110877-64-0.mol
• Article Data: 12

Chemical Properties

• Melting Point: 103-106 °C(lit.)
• Boiling Point: 258 °C
• Flash Point: 257-259°C
• Appearance: White/Fine Crystalline Powder
• Density: 1.4821 (estimate)
• Vapor Pressure: 0.00273mmHg at 25°C
• Storage Temp.: Sealed in dry,Room Temperature
• PKA: 2.50±0.25(Predicted)
• Water Solubility: 5.0 g/L (20 ºC)
• BRN: 4247522
• CAS DataBase Reference: 2-Chloro-4,5-difluorobenzoic acid(CAS DataBase Reference)
• NIST Chemistry Reference: 2-Chloro-4,5-difluorobenzoic acid(110877-64-0)
• EPA Substance Registry System: 2-Chloro-4,5-difluorobenzoic acid(110877-64-0)

Safety Data

• Hazard Codes: Xi,Xn
• Statements: 36/37/38-41-43-21/22-20/21/22
• Safety Statements: 26-39-36/37/39-36
• WGK Germany: 3
• HazardClass: IRRITANT
• Hazardous Substances Data: 110877-64-0(Hazardous Substances Data)

Usage

Chemical Properties

white to light yellow crystal powder

General Description

2-Chloro-4,5-difluorobenzoic acid is an important intermediate in medicinal compounds and pesticides. Lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been prepared and their crystal structures have been studied. Efficient synthesis of 2-chloro-4,5-difluorobenzoic acid v-difluororbenzene has been reported.

InChI:InChI=1/C7H3ClF2O2/c8-4-2-6(10)5(9)1-3(4)7(11)12/h1-2H,(H,11,12)/p-1

Synthetic route

2'-chloro-4',5'-difluoroacetophenone (121872-94-4) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With sodium hypochlorite Oxidation;	90%
With hydrogenchloride; sodium hypochlorite In dichloromethane	85.1%
With hydrogenchloride; sodium hypochlorite In dichloromethane	85.1%
With sodium hypochlorite for 6h; Heating;	80%
With hydrogenchloride; sodium hydroxide; sodium hypobromide; bromine; sodium hydrogensulfite In 1,4-dioxane; dichloromethane; water

2-chloro-5-fluoro-4-nitrobenzoic acid + 4-chlorosulfonyl chloride → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With KF; benzenesulfonyl chloride In sulfolane; thionyl chloride	75%

2-chloro-4,5-difluoro-α-chloroacetophenone (133117-00-7) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With sodium hypochlorite Oxidation;

4-chloro-1,2-difluorobenzene (696-02-6) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 2 steps 1: 80 percent / AlCl3 2: 90 percent / 5 percent NaOCl View Scheme
Multi-step reaction with 2 steps 1: 95 percent / AlCl3 2: 5 percent NaOCl View Scheme
Multi-step reaction with 2 steps 1: 75 percent / AlCl3 / 9 h / 60 °C 2: 80 percent / NaOCl / 6 h / Heating View Scheme

2-fluoro-5-chloronitrobenzene (345-18-6) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 5 steps 1: H2 / 5 percent Pt/C / 1,2-dimethoxy-ethane / 24 h / 2585.74 Torr 2: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 3: 49 percent / 0.5 h / 170 °C 4: 80 percent / AlCl3 5: 90 percent / 5 percent NaOCl View Scheme
Multi-step reaction with 5 steps 1: H2 / 5 percent Pt/C / 1,2-dimethoxy-ethane / 24 h / 2585.74 Torr 2: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 3: 49 percent / 0.5 h / 170 °C 4: 95 percent / AlCl3 5: 5 percent NaOCl View Scheme

5-chloro-2-fluoroaniline (2106-05-0) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 4 steps 1: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 2: 49 percent / 0.5 h / 170 °C 3: 80 percent / AlCl3 4: 90 percent / 5 percent NaOCl View Scheme
Multi-step reaction with 4 steps 1: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 2: 49 percent / 0.5 h / 170 °C 3: 95 percent / AlCl3 4: 5 percent NaOCl View Scheme

2,5-dichloronitrobenzene (89-61-2) + potassium-compound of 1-<4-hydroxy-phenyl>-ethanone → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 6 steps 1: 52 percent / KF; 18-crown-6 / tetrahydrothiophene 1,1-dioxide / 32 h / 180 °C 2: H2 / 5 percent Pt/C / 1,2-dimethoxy-ethane / 24 h / 2585.74 Torr 3: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 4: 49 percent / 0.5 h / 170 °C 5: 80 percent / AlCl3 6: 90 percent / 5 percent NaOCl View Scheme
Multi-step reaction with 6 steps 1: 52 percent / KF; 18-crown-6 / tetrahydrothiophene 1,1-dioxide / 32 h / 180 °C 2: H2 / 5 percent Pt/C / 1,2-dimethoxy-ethane / 24 h / 2585.74 Torr 3: BF3*Et2O; t-BuONO / 1,2-dimethoxy-ethane / 1 h / -5 °C 4: 49 percent / 0.5 h / 170 °C 5: 95 percent / AlCl3 6: 5 percent NaOCl View Scheme

2-Fluoro-5-chlorophenyldiazonium tetrafluoroborate → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 3 steps 1: 49 percent / 0.5 h / 170 °C 2: 80 percent / AlCl3 3: 90 percent / 5 percent NaOCl View Scheme
Multi-step reaction with 3 steps 1: 49 percent / 0.5 h / 170 °C 2: 95 percent / AlCl3 3: 5 percent NaOCl View Scheme

ortho-difluorobenzene (367-11-3) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
Multi-step reaction with 3 steps 1: 90 percent / FeCl3, Cl2 / 3 h / 50 °C 2: 75 percent / AlCl3 / 9 h / 60 °C 3: 80 percent / NaOCl / 6 h / Heating View Scheme

2-chloro-4,5-difluorobenzotrichloride (136364-59-5) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With sulfuric acid
With sulfuric acid

ammonium persulfate + 2-chloro-4,5-difluorobenzophenone → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With sulfuric acid In water; acetic acid

2-chloro-4,5-difluoro-α,α-dichloroacetophenone + sodium disulfite + water (7732-18-5) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With hydrogenchloride; sodium hydroxide; bromine In sodium hypobromide

sodium disulfite + 2-chloro-4,5-difluoro-α-chloroacetophenone (133117-00-7) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With hydrogenchloride In sodium hypobromide

2-chloro-4,5-difluoro-α,α-dichloroacetophenone + sodium disulfite → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With hydrogenchloride In sodium hypochlorite

tert.-butylnitrite (540-80-7) + 2-amino-4,5-difluorobenzoic acid (83506-93-8) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With hydrogenchloride In water; acetonitrile

2-amino-4,5-difluorobenzoic acid (83506-93-8) → 2-chloro-4,5-difluorobenzoic acid (110877-64-0)

Conditions	Yield
With sodium nitrate; copper(l) chloride In hydrogenchloride; water

2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2-chloro-4,5-difluorobenzoyl chloride (121872-95-5)

Conditions	Yield
With pyridine; thionyl chloride In toluene	92.1%
With N,N-dimethyl-formamide In dichloromethane for 3h; Ambient temperature;
With thionyl chloride; N,N-dimethyl-formamide for 2h; Heating;

methanol (67-56-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2-Chloro-4,5-difluorobenzoic acid methyl ester (128800-36-2)

Conditions	Yield
With sulfuric acid at 60℃; for 48h;	86.6%
With acetyl chloride at 0℃;	84%
With acetyl chloride at 20℃; Cooling with ice;
With acetyl chloride for 65h; Reflux;

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + acetyl chloride (75-36-5) → 2-Chloro-4,5-difluorobenzoic acid methyl ester (128800-36-2)

Conditions	Yield
In methanol	84%

copper (I) acetate (598-54-9, 142-71-2, 4180-12-5, 24381-58-6, 66760-61-0, 66760-62-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 3-methyl-1-(2-pyridinyl)-1H-pyrazol-5-ylamine (19541-96-9) → 4,5-difluoro-2-[[3-methyl-1-(2-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid (364727-90-2)

Conditions	Yield
With potassium carbonate; acetic acid In N,N-dimethyl-formamide	81%
With potassium carbonate; acetic acid In N,N-dimethyl-formamide	81%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + metronidazole (443-48-1) → 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl 2-chloro-4,5-difluorobenzoate (1403815-92-8)

Conditions	Yield
With dmap; dicyclohexyl-carbodiimide In dichloromethane at 0 - 20℃;	80%

3-methyl-1-(6-methylpyridin-2-yl)-1H-pyrazol-5-amine (364728-13-2) + copper (I) acetate (598-54-9, 142-71-2, 4180-12-5, 24381-58-6, 66760-61-0, 66760-62-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 4-chloro-6,7-difluoro-3-methyl-1-(6-methyl-2-pyridinyl)-1H-pyrazolo[3,4-b]quinoline (364728-21-2) + 4,5-difluoro-2-[[3-methyl-1-(6-methyl-2-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid (364728-20-1)

Conditions	Yield
With hydrogenchloride; potassium carbonate In N,N-dimethyl-formamide	A 39% B 79%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 4-amino-5-(3-pyridyl)-4H-1,2,4-triazole-3-thiol (78027-00-6) → 6-(2-chloro-4,5-difluorophenyl)-3-(pyridin-3-yl)[1,2,4]-triazolo[3,4-b][1,3,4]thiadiazole

Conditions	Yield
With trichlorophosphate for 6h; Reflux;	79%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + phenylmethanethiol (100-53-8) → 4-(benzylthio)-2-chloro-5-fluorobenzoic acid

Conditions	Yield
With caesium carbonate In N,N-dimethyl-formamide at 70℃; for 6h;	79%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2-chloro-4,5-difluorobenzamide (296274-32-3)

Conditions	Yield
Stage #1: 2-chloro-4,5-difluorobenzoic acid With 1-hydroxy-pyrrolidine-2,5-dione; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride In N,N-dimethyl-formamide at 0 - 20℃; for 1h; Stage #2: With ammonia In water; N,N-dimethyl-formamide at 0 - 20℃; for 0.5h;	76%
Stage #1: 2-chloro-4,5-difluorobenzoic acid With thionyl chloride In toluene at 60℃; for 1.5h; Heating / reflux; Stage #2: With pyridine In toluene at 60℃; for 1.5h; Stage #3: With ammonia In toluene at 20 - 35℃;

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + benzylamine (100-46-9) → N-benzyl-2-chloro-4,5-difluorobenzamide (710981-36-5)

Conditions	Yield
Stage #1: 2-chloro-4,5-difluorobenzoic acid With triethylamine; isobutyl chloroformate In dichloromethane for 0.25h; Inert atmosphere; Schlenk technique; Stage #2: benzylamine In dichloromethane at 0℃;	76%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 4-amino-3-(2-furyl)-5-mercapto[4H]-1,2,4-triazole (80809-38-7) → 6-(2-chloro-4,5-difluorophenyl)-3-(furan-2-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole

Conditions	Yield
With trichlorophosphate Reflux;	75%

4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol (36209-51-5) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 6-(2-chloro-4,5-difluorophenyl)-3-(pyridin-4-yl)[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (1607018-29-0)

Conditions	Yield
With trichlorophosphate Reflux;	74%

2-Amino-4,6-dimethylpyridine (5407-87-4) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → N-(4,6-dimethylpyridin-2-yl)-2-chloro-4,5-difluorobenzamide

Conditions	Yield
With O-phenyl phosphorodichloridate; triethylamine In 1,2-dichloro-ethane at 20℃; for 24h;	72%

3-ethyl-1-(2-pyridinyl)-1H-pyrazol-5-ylamine (364728-11-0) + copper (I) acetate (598-54-9, 142-71-2, 4180-12-5, 24381-58-6, 66760-61-0, 66760-62-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 4-chloro-3-ethyl-6,7-difluoro-1-(2-pyridinyl)-1H-pyrazolo[3,4-b]quinoline (364727-14-0) + 4,5-difluoro-2-[[3-ethyl-1-(2-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid (364728-18-7)

Conditions	Yield
With hydrogenchloride; potassium carbonate In N,N-dimethyl-formamide	A 50% B 66%

ethanamine hydrochloride (557-66-4) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2-(ethylamino)-4,5-difluorobenzoic acid

Conditions	Yield
With potassium phosphate; copper(l) iodide In N,N-dimethyl-formamide at 140℃; for 1.5h; Microwave irradiation;	65%

3-methyl-1-(3-pyridinyl)-1H-pyrazol-5-ylamine dihydrochloride + copper (I) acetate (598-54-9, 142-71-2, 4180-12-5, 24381-58-6, 66760-61-0, 66760-62-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 4-chloro-6,7-difluoro-3-methyl-1-(3-pyridinyl)-1H-pyrazolo[3,4-b]quinoline (364727-16-2) + 4,5-difluoro-2-[[3-methyl-1-(3-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid

Conditions	Yield
With hydrogenchloride; potassium carbonate In N,N-dimethyl-formamide	A 8% B 63%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 1,1,1,3,3,3-hexamethyl-disilazane (999-97-3) → trimethylsilyl 2-chloro-4,5-difluorobenzoate

Conditions	Yield
With iodine In neat (no solvent) at 20℃; for 96h; Green chemistry;	62%

1-(tert-butyl)-2-iodobenzene (62171-59-9) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → C16H14F2

Conditions	Yield
With tetrabutyl-ammonium chloride; palladium diacetate; potassium carbonate; Tri(p-tolyl)phosphine In N,N-dimethyl-formamide at 140℃; for 12h; Schlenk technique; Inert atmosphere;	58%

2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 1,2-cyclooctene (931-88-4, 22770-27-0, 3958-30-3) → 2-bromocyclooctyl 2-chloro-4,5-difluorobenzoate

Conditions	Yield
With N-Bromosuccinimide; 5,6-difluoro-2-(1-phenylethyl)benzo[d][1,2]selenazol-3(2H)-one In dichloromethane at 20℃; for 8h;	56%

copper (I) acetate (598-54-9, 142-71-2, 4180-12-5, 24381-58-6, 66760-61-0, 66760-62-1) + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) + 1-(2-pyridinyl)-1H-pyrazol-5-ylamine (89977-46-8) → 4,5-difluoro-2-[[1-(2-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid (364728-10-9)

Conditions	Yield
With hydrogenchloride; potassium carbonate In N,N-dimethyl-formamide	55%

methanol (67-56-1) + dysprosium(III) nitrate hexahydrate + N-Methyldiethanolamine (105-59-9) + chromium(III) chloride hexahydrate + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2Cr(3+)*2Dy(3+)*1.4CH3O(1-)*0.6HO(1-)*4C7H2ClF2O2(1-)*2C5H11NO2(2-)*2NO3(1-)*0.6CH4O

Conditions	Yield
Stage #1: dysprosium(III) nitrate hexahydrate; N-Methyldiethanolamine; chromium(III) chloride hexahydrate; 2-chloro-4,5-difluorobenzoic acid With triethylamine In acetonitrile for 2h; Stage #2: methanol In diethyl ether	49%

methanol (67-56-1) + terbium(III) nitrate hexahydrate + N-Methyldiethanolamine (105-59-9) + chromium(III) chloride hexahydrate + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2Cr(3+)*2Tb(3+)*0.8CH3O(1-)*1.2HO(1-)*4C7H2ClF2O2(1-)*2C5H11NO2(2-)*2NO3(1-)*1.2CH4O

Conditions	Yield
Stage #1: terbium(III) nitrate hexahydrate; N-Methyldiethanolamine; chromium(III) chloride hexahydrate; 2-chloro-4,5-difluorobenzoic acid With triethylamine In acetonitrile for 2h; Stage #2: methanol In diethyl ether	42%

methanol (67-56-1) + holmium(III) nitrate hexahydrate + N-Methyldiethanolamine (105-59-9) + chromium(III) chloride hexahydrate + 2-chloro-4,5-difluorobenzoic acid (110877-64-0) → 2Cr(3+)*2Ho(3+)*1.16CH3O(1-)*0.84HO(1-)*4C7H2ClF2O2(1-)*2C5H11NO2(2-)*2NO3(1-)*0.84CH4O

Conditions	Yield
Stage #1: holmium(III) nitrate hexahydrate; N-Methyldiethanolamine; chromium(III) chloride hexahydrate; 2-chloro-4,5-difluorobenzoic acid With triethylamine In acetonitrile for 2h; Stage #2: methanol In diethyl ether	39%

Upstream product

• 121872-94-4 2'-chloro-4',5'-difluoroacetophenone 
• 133117-00-7 2-chloro-4,5-difluoro-α-chloroacetophenone 
• 696-02-6 4-chloro-1,2-difluorobenzene 
• 345-18-6 2-fluoro-5-chloronitrobenzene 
• 2106-05-0 5-chloro-2-fluoroaniline 
• 89-61-2 2,5-dichloronitrobenzene 
• 367-11-3 ortho-difluorobenzene 
• 136364-59-5 2-chloro-4,5-difluorobenzotrichloride 
• 83506-93-8 2-amino-4,5-difluorobenzoic acid 
• 540-80-7 tert.-butylnitrite 
• 7732-18-5 water 

Downstream Products

• 128800-37-3 ethyl 2-chloro-4,5-difluorobenzoate 

Related news

Determination of 2-Chloro-4,5-difluorobenzoic acid (cas 110877-64-0) and related impurities by liquid chromatography08/19/2019

2-Chloro-4,5-difluorobenzoic acid (CDFBA) and related impurities are determined using liquid chromatography (LC). Separations are achieved using a reversed-phase isocratic system with an ion-pair reagent (tetrabutylammonium hydroxide). Unique isomeric impurities observed in commercially produced...detailed

Relevant articles and documents

Syntheses of 2-chloro-4,5-difluorobenzoic acid

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Method of preparing fluoroaromatic compounds

The present invention provides a method of preparing ortho-difluorobenzene derivatives, which comprises (a) providing a mixture of cyclohexenes by reacting chlorotrifluoroethylene (CTFE) and 1,3-diene in a flow reactor and distilling the resultant, and (b) dehydrohalogenating the mixture of cyclohexenes with a phase transition catalyst in the presence of alkali metal hydroxide at temperature range of 40 to 150 °C without using any organic solvent. The distillate having low boiling point, which is obtained during distillation of the resultant, is recycled into the flow reactor. The present invention also provides a method of preparing 2-chloro-4,5-difluorobenzoic acid, which comprises (a) providing a mixture of 4-chloro-1-methyl-4,5,5-trifluorocyclohexene and 5-chloro-1-methyl-4,4,5-trifluorocyclohexene by reacting chlorotrifluoroethylene (CTFE) and isoprene and distilling the resultant, (b) dehydrohalogenating said mixture in the presence of alkali metal hydroxide and a phase transition catalyst to form 3,4-difluorotoluene, (c) reacting said 3,4-difluorotoluene with chlorine gas without using any organic solvent to form 2-chloro-4,5-difluorotoluene, (d) photo-reacting said 2-chloro-4,5-difluorotoluene with chlorine gas under a lighting mercury lamp without using any organic solvent to form 2-chloro-4,5-difluorobenzotrichloride, and (e) reacting said 2-chloro-4,5-difluorobenzotrichloride with aqueous acid solution without using any organic solvent. The present invention also provides a method of preparing 2-chloro-4,5-difluorobenzoyl chloride by reacting the 2-chloro-4,5-difluorobenzotrichloride of step (e) above with zinc oxide.

Process for the preparation of halogenated benzoic acids

A process for the preparation of halogenated benzoic acids of formula (1): STR1 in which R1, R2, R3, R4 and R5 are hydrogen, fluorine, chlorine or bromine atoms or C1 -C6 -alkyl, C1 -C6 -alkoxy, nitro, cyano, trifluoromethyl, aidehyde, C1 -C4 -alkoxycarbonyl, -SO2 -C1 -C4 -alkyl, -SO2 -phenyl, -CONH2, -CON(C1 -C4 -alkyl)2, hydroxy, carboxy, -NH2 or -N(C1 -C4 - alkyl)2 groups, at least one of the substituents R1 -R5 being one of said halogen atoms, which comprises reacting 1 mol of a benzophenone, asymmetrically substituted on the benzene rings A and B, of general formula (2): STR2 in which R1 -R10 are as defined above for R1 -R5, with about 1 to about 10 mol of an oxidizing agent selected from the group comprising hydrogen peroxide, urea/hydrogen peroxide addition product, an alkali metal peroxide, ammonium, alkali metal or alkaline earth metal peroxodisulfates, pertungstates, perborates or percarbonates, ozone, alkyl- or aryl-percarboxylic acids, alkyl- or aryl-persulfonic acids or persulfuric acid, at temperatures from about -20° to about +100° C.