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5-Methyl-4-isoxazolecarboxylic acid

5-Methyl-4-isoxazolecarboxylic acid structure

CAS No.: 42831-50-5

Chemical Name:: 5-Methyl-4-isoxazolecarboxylic acid

Synonyms: 5-METHYLISOXAZOLE-4-CARBOXYLIC ACID;TIMTEC-BB SBB005909;Leflunomide Impurity D;Lefluonamide Impurity D;LeflunoMide EP IMpurity D;Leflunomide impurities1343;Methylisoxazole-4-carboxylic;5-Methyl-4-isoxazolecarboxyl;5-METHYLISOXAZOLE-4-CARBOXYLIC;5-methylisoxazole-4-formic acid

CBNumber:: CB8342928

Molecular Formula:: C5H5NO3

Molecular Weight:: 127.1

MDL Number:: MFCD00955655

MOL File:: 42831-50-5.mol

MSDS File:: SDS

TDS File:: TDS

Last updated:2026-04-24 14:58:19

Product description	Number	Pack Size	Price
5-Methylisoxazole-4-carboxylic acid 97%	633771	10g	$247
5-Methylisoxazole-4-carboxylic acid 97%	633771	1g	$34.7
5-Methylisoxazole-4-carboxylic Acid >98.0%(T)(HPLC)	M1740	5g	$22
5-Methylisoxazole-4-carboxylic Acid >98.0%(T)(HPLC)	M1740	25g	$71
5-Methylisoxazole-4-carboxylic acid	M315000	1g	$50
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5-Methyl-4-isoxazolecarboxylic acid Properties

Melting point	144-148 °C(lit.)
Boiling point	308.3±22.0 °C(Predicted)
Density	1.348±0.06 g/cm3(Predicted)
storage temp.	Sealed in dry,Room Temperature
solubility	DMSO (Slightly), Methanol (Slightly)
pka	2.85±0.25(Predicted)
form	Solid
color	White to Pale Brown
BRN	116000
InChI	1S/C5H5NO3/c1-3-4(5(7)8)2-6-9-3/h2H,1H3,(H,7,8)
InChIKey	VQBXUKGMJCPBMF-UHFFFAOYSA-N
SMILES	Cc1oncc1C(O)=O
CAS DataBase Reference	42831-50-5(CAS DataBase Reference)
FDA UNII	BL2Q213Q2M
UNSPSC Code	12352100
NACRES	NA.22

SAFETY

Risk and Safety Statements

Symbol(GHS)

GHS07

Signal word

Warning

Hazard statements

H315-H319-H335

Precautionary statements

P261-P280a-P304+P340-P305+P351+P338-P405-P501a

PPE

Eyeshields, Gloves, type N95 (US)

Hazard Codes

Xi,F

Risk Statements

36/37/38-37/38-36-10

Safety Statements

22-26-36/37/39-36-16

WGK Germany

HazardClass

IRRITANT

HS Code

29349990

Storage Class

11 - Combustible Solids

NFPA 704

	0
2		0

5-Methyl-4-isoxazolecarboxylic acid price More Price(26)

Manufacturer	Product number	Product description	CAS number	Packaging	Price	Updated	Buy
Sigma-Aldrich	633771	5-Methylisoxazole-4-carboxylic acid 97%	42831-50-5	10g	$247	2026-03-19	Buy
Sigma-Aldrich	633771	5-Methylisoxazole-4-carboxylic acid 97%	42831-50-5	1g	$34.7	2023-06-20	Buy
TCI Chemical	M1740	5-Methylisoxazole-4-carboxylic Acid >98.0%(T)(HPLC)	42831-50-5	5g	$22	2026-03-19	Buy
TCI Chemical	M1740	5-Methylisoxazole-4-carboxylic Acid >98.0%(T)(HPLC)	42831-50-5	25g	$71	2026-03-19	Buy
TRC	M315000	5-Methylisoxazole-4-carboxylic acid	42831-50-5	1g	$50	2021-12-16	Buy

Product number	Packaging	Price	Buy
633771	10g	$247	Buy
633771	1g	$34.7	Buy
M1740	5g	$22	Buy
M1740	25g	$71	Buy
M315000	1g	$50	Buy

5-Methyl-4-isoxazolecarboxylic acid Chemical Properties,Uses,Production

Chemical Properties

Cream to brown Solid

Uses

5-Methylisoxazole-4-carboxylic Acid (Leflunomide EP Impurity D) is an intermediate for synthesis of Leflunomide (L322750). Herbicidal activities towards Digitaria ciliaris.

Flammability and Explosibility

Non flammable

Synthesis

51135-73-0

42831-50-5

Example 4 Preparation of 5-methylisoxazole-4-carboxylic acid To a two-necked flask equipped with a mechanical stirrer and a horizontal condenser for distillation were added 40.0 g of crude ethyl 5-methyl-4-isoxazolecarboxylate and 44 g of 60% sulfuric acid solution. The mixture was heated to 85°C while the ethanol generated from the reaction was continuously distilled. After 4 hours of reaction, thin layer chromatography (TLC) analysis showed complete disappearance of spots of ester compounds. After cooling the reaction mixture to room temperature, the solid product (16.5 g) was collected by filtration. The filtrate was retained for a second product collection at room temperature. The resulting crude acid was dissolved in 60 mL of 2% acetic acid-toluene mixed solvent and crystallized to give 5-methylisoxazole-4-carboxylic acid (9.5 g) of about 99.9% purity. The crystallized mother liquor was retained for subsequent batch processing. The crystallization process was performed as follows: the crude acid was added to 2% acetic acid-toluene solvent mixture and heated for 30 minutes until dissolved. Separate and remove the brown oil from the bottom of the flask. The upper clear organic phase was carefully transferred to another container and left to crystallize.

References

[1] Patent: US2003/139606, 2003, A1
[2] Letters in Drug Design and Discovery, 2016, vol. 13, # 9, p. 912 - 920
[3] Journal of Heterocyclic Chemistry, 1991, vol. 28, # 2, p. 453 - 457
[4] Yakugaku Zasshi, 1959, vol. 79, p. 836
[5] Chem.Abstr., 1960, p. 1493

5-Methyl-4-isoxazolecarboxylic acid Preparation Products And Raw materials

Raw materials

Ethyl 5-methylisoxazole-4-carboxylate 2-Methylphenylacetic acid Sulfuric acid

Preparation Products

4-Isoxazolecarboxamide, N-(4-aminophenyl)-5-methyl- 3-Isoxazoleaceticacid,4-cyano-5-methyl-(9CI)

5-Methyl-4-isoxazolecarboxylic acid Suppliers

Global( 442)Suppliers

Supplier	Tel	Email	Country	ProdList	Advantage
Capot Chemical Co.,Ltd.	+86-（0）57185586718; +8613336195806	sales@capot.com	China	29640	60
Shanghai Daken Advanced Materials Co.,Ltd	+86-2158073036	info@dakenam.com	China	13815	58
Beijing Cooperate Pharmaceutical Co.,Ltd	010-60279497	sales01@cooperate-pharm.com	CHINA	1803	55
Hi-Tech Chemistry Corp	0519-86626038	yuhh@hitechem.com	CHINA	810	58
Henan Tianfu Chemical Co.,Ltd.	+86-0371-55170693 +86-19937530512	info@tianfuchem.com	China	21592	55
ATK CHEMICAL COMPANY LIMITED	+undefined-21-51877795	ivan@atkchemical.com	China	33024	60
career henan chemical co	+86-0371-86658258 +8613203830695	sales@coreychem.com	China	29821	58
Jinan Finer Chemical Co., Ltd	+86-531-88989536 +86-15508631887	sales@finerchem.com	China	2949	58
Standardpharm Co. Ltd.	86-714-3992388	overseasales1@yongstandards.com	United States	14332	58
Alchem Pharmtech,Inc.	8485655694	sales@alchempharmtech.com	United States	63687	58

Supplier	Advantage
Capot Chemical Co.,Ltd.	60
Shanghai Daken Advanced Materials Co.,Ltd	58
Beijing Cooperate Pharmaceutical Co.,Ltd	55
Hi-Tech Chemistry Corp	58
Henan Tianfu Chemical Co.,Ltd.	55
ATK CHEMICAL COMPANY LIMITED	60
career henan chemical co	58
Jinan Finer Chemical Co., Ltd	58
Standardpharm Co. Ltd.	58
Alchem Pharmtech,Inc.	58

View Lastest Price from 5-Methyl-4-isoxazolecarboxylic acid manufacturers

Update time	Product	Price	Min. Order	Purity	Supply Ability	Manufacturer
2026-04-27	5-Methyl-4-isoxazolecarboxylic acid 42831-50-5			0.99		RongNa Biotechnology Co.,Ltd
2026-04-27	5-Methyl-4-isoxazolecarboxylic acid 42831-50-5	US $0.00-0.00 / Kg/Drum	1KG	99%min	1000KGS	WUHAN FORTUNA CHEMICAL CO., LTD
2026-01-04	5-Methyl-4-isoxazolecarboxylic acid 42831-50-5	US $0.00-0.00 / kg	0.1kg	99.0%min	2000kg	Hangzhou ICH Biofarm Co., Ltd

5-Methyl-4-isoxazolecarboxylic acid
42831-50-5
0.99
RongNa Biotechnology Co.,Ltd

5-Methyl-4-isoxazolecarboxylic acid
42831-50-5
US $0.00-0.00 / Kg/Drum
99%min
WUHAN FORTUNA CHEMICAL CO., LTD

5-Methyl-4-isoxazolecarboxylic acid
42831-50-5
US $0.00-0.00 / kg
99.0%min
Hangzhou ICH Biofarm Co., Ltd

5-Methyl-4-isoxazolecarboxylic acid Spectrum

5-Methyl-4-isoxazolecarboxylic acid(42831-50-5)MS 5-Methyl-4-isoxazolecarboxylic acid(42831-50-5)¹HNMR 5-Methyl-4-isoxazolecarboxylic acid(42831-50-5)¹³CNMR 5-Methyl-4-isoxazolecarboxylic acid(42831-50-5)IR1 5-Methyl-4-isoxazolecarboxylic acid(42831-50-5)IR2

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Methyl A77 1726 Leflunomide 3-Isomer

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5-Methyl-4-isoxazolecarboxylic acid, Tech. 5-methylisoxazole-4-carboxylic acid(SALTDATA: FREE) Methylisoxazole-4-carboxylic LeflunoMide EP IMpurity D 4-Carboxy-5-methylisoxazole ,4-Carboxy-5-methyl-1,2-oxazole 5-Methylisoxazole-4-carboxylic acid, 99%, 99% Leflunomide Impurity D 5-Methyl-isoxazol-4-carboxylic acid Leflunomide Impurity 4(Leflunomide EP Impurity D) TIMTEC-BB SBB005909 5-METHYLISOXAZOLE-4-CARBOXYLIC ACID 5-METHYL-4-ISOXASOLECARBOXYLIC ACID 5-METHYL-4-ISOXAZOLECARBOXYLIC ACID 5-Methyl-4-Isooxazolecarboxylic Acid 5-METHYLISOXAZOLE-4-CARBOXYLIC 5-MethylIsoxazole-4-CarboxalicAcid,Leflunomide 4-Isoxazolecarboxylic acid,5-Methyl 5-METHYLISOXAZOLE-4-CARBOXYLIC ACID 98% 5-Methylisoxazole-4-carboxylic acid, 98+% Imp. D (EP):5-Methylisoxazole-4-carboxylic Acid 5-Methylisoxazole-4-carboxylicAcid> 5-Methyl-4-isoxazolecarboxylic acid ISO 9001：2015 REACH 5-Methyl-4-isoxazolecarboxyl 5-methylisoxazole-4-formic acid Leflunomide EP Impurity D (5-Methylisoxazole-4-carboxylic Acid) Lefluonamide Impurity D Leflunomide impurities1343 5-Methyl-4-isoxaze-4-carboxylic AcidQ: What is 5-Methyl-4-isoxaze-4-carboxylic Acid Q: What is the CAS Number of 5-Methyl-4-isoxaze-4-carboxylic Acid Q: What is the storage condition of 5-Methyl-4-isoxaze-4-carboxylic Acid Q: What are the applications of 5-Methyl-4-isoxaze-4-carboxylic Acid CAS No.42831-50-5 5-Methyl-4-isoxazolecarboxylic acid MethylisoChemicalbookxazole-4-carboxylic 5-Methylisoxazole-4-carboxylic acid (Leflunomide Impurity) 42831-50-5 42931-50-5 C5H5NO3 C5H4NO3 CARBOXYLIC ACID Heterocyclic Building Blocks Isoxazoles Building Blocks Intermediates Intermediates & Fine Chemicals Pharmaceuticals Isoxazoles, Oxadiazoles, Oxazoles Acids and Derivatives Heterocycles Carboxylic Acids Oxazoles, Isoxazoles & Benzoxazoles Oxazole&Isoxazole Organic acids (intermediate of leflunomide) Heterocyclic Compounds Carboxylic Acids Oxazoles, Isoxazoles & Benzoxazoles Building Blocks Heterocyclic Building Blocks Isoxazoles