Compuestos fluorados

En esta categoría, puede encontrar una amplia variedad de compuestos que contienen uno o más átomos de flúor en su estructura. Estos compuestos fluorados son altamente valiosos en la síntesis orgánica y el análisis químico debido a sus propiedades químicas únicas, como mayor estabilidad, reactividad y lipofilia. Los compuestos fluorados se utilizan ampliamente en el desarrollo de productos farmacéuticos, agroquímicos y materiales avanzados. En CymitQuimica, ofrecemos una selección completa de compuestos fluorados de alta calidad para apoyar sus aplicaciones de investigación e industriales, asegurando un rendimiento preciso y confiable.

100
- 20
- 50
- 200

productos por página. Hay 57320 productos en esta categoría.

Datos del producto	Pureza	Rango de precios	Entrega estimada
4-Methoxy-3-methyl-5-(trifluoromethyl)benzamide REF: 10-F343364CAS: 1431329-75-7	- - -	- - -	Producto descatalogado
1-(3,4-dimethylphenyl)-3-(trifluoromethyl)-1H-pyrazol-5-amine REF: 10-F428479CAS: 1226268-82-1	- - -	- - -	Producto descatalogado
8-Bromo-2-(difluoromethyl)imidazo[1,2-a]pyridine REF: 10-F783246CAS: 2248343-49-7	98%	- - -	Producto descatalogado
3-Methoxy-4-(2-nitro-4-(trifluoromethyl)phenoxy)benzaldehyde REF: 10-F751735CAS: 5509-72-8	98%	- - -	Producto descatalogado
2-(Trifluoromethyl)-1,3-benzoxazol-6-amine REF: 10-F658127CAS: 1039334-81-0	95%	- - -	Producto descatalogado
3-Methyl-2-((3-(trifluoromethyl)phenyl)sulfonamido)pentanoic acid REF: 10-F708668CAS: 1008214-80-9	95%	- - -	Producto descatalogado
3-(Trifluoromethyl)-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide REF: 10-F610430CAS: 112107-46-7	98%	- - -	Producto descatalogado
4-Amino-N-(2-(2,2,2-trifluoroethoxy)ethyl)benzamide REF: 10-F752013CAS: 924710-26-9	97%	- - -	Producto descatalogado
Ethyl 2-((4-(1-ethyl-3-methyl-1h-pyrazol-4-yl)-6-(trifluoromethyl)pyrimidin-2-yl)sulfonyl)acetate REF: 10-F710860CAS: 1006328-62-6	98%	- - -	Producto descatalogado
1-[4-(difluoromethoxy)phenyl]piperidin-3-amine REF: 10-F675423CAS: 1282711-39-0	95%	- - -	Producto descatalogado
[5-chloro-2-(difluoromethoxy)phenyl]methanamine REF: 10-F675883CAS: 1094236-98-2	98%	- - -	Producto descatalogado
methyl 3-[4-bromo-3-(trifluoromethyl)-1H-pyrazol-1-yl]propanoate REF: 10-F427139CAS: 1006432-21-8	- - -	- - -	Producto descatalogado
3-(Difluoromethoxy)-4-methoxybenzaldehyde REF: 10-F770167CAS: 153587-11-2	98%	- - -	Producto descatalogado
3-[3-(trifluoromethyl)phenyl]-1h-pyrazole-4-carbaldehyde REF: 10-F651003CAS: 1152541-77-9	98%	- - -	Producto descatalogado
3-Chloro-N-(3-methoxypropyl)-5-(trifluoromethyl)pyridin-2-amine REF: 10-F714479CAS: 338406-33-0	95+%	- - -	Producto descatalogado
7-Benzyl-4-chloro-2-(trifluoromethyl)-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine REF: 10-F430289CAS: 647863-01-2	95.0%	- - -	Producto descatalogado
4-((2-Oxo-5-(trifluoromethyl)pyridin-1(2H)-yl)methyl)benzoic acid REF: 10-F751796CAS: 339024-98-5	90%	- - -	Producto descatalogado
{[2-ethyl-4-(trifluoromethyl)-2H-pyrazolo[3,4-b]pyridin-6-yl]thio}acetic acid REF: 10-F427966CAS: 1018166-25-0	- - -	- - -	Producto descatalogado
4'-Ethoxy-3'-methyl-2,2,2-trifluoroacetophenone REF: 10-F395855CAS: 1369012-94-1	97.0%	- - -	Producto descatalogado
1-(Bromomethyl)-4-(trifluoromethyl)cyclohexane REF: 10-F637829CAS: 858121-96-7	95+%	- - -	Producto descatalogado
6-(2-Fluorophenoxy)-1,1,1-trifluoro-hexan-2-one REF: 10-F542561	96.0%	- - -	Producto descatalogado
6-Trifluoromethyl-naphthalen-1-ol REF: 10-F736917CAS: 33533-45-8	98%	- - -	Producto descatalogado
tert-Butyl[3-(5'-(trifluoromethyl)pyridin-2'-yl)-[1,2,4]methyl]-carbamate REF: 10-F047528CAS: 1160994-72-8	95%	- - -	Producto descatalogado
2-Fluoro-4-methyl-3-(trifluoromethyl)benzaldehyde REF: 10-F476008CAS: 1824270-96-3	- - -	- - -	Producto descatalogado
2-Methyl-6-(trifluoromethyl)morpholine REF: 10-F619398CAS: 1342385-23-2	95+%	- - -	Producto descatalogado
(5-Methyl-2-(trifluoromethyl)furan-3-yl)methanamine REF: 10-F721660CAS: 306935-05-7	97%	- - -	Producto descatalogado
2-Methoxy-4-(trifluoromethoxy)benzyl alcohol REF: 10-F342417CAS: 886500-30-7	- - -	- - -	Producto descatalogado
6-(3,4-Dimethylphenoxy)-1,1,1-trifluoro-hexan-2-one REF: 10-F542574	96.0%	- - -	Producto descatalogado
(3-Chloro-4-(difluoromethoxy)phenyl)methanamine REF: 10-F699760CAS: 1249925-84-5	98%	- - -	Producto descatalogado
9-Phenanthryl trifluoromethyl ketone REF: 10-F207036CAS: 163082-41-5	97.0%	- - -	Producto descatalogado
3-Ethoxy-2-fluoro-5-(trifluoromethoxy)phenylboronic acid REF: 10-F623177CAS: 1793003-82-3	95%	- - -	Producto descatalogado
4-[5-(trifluoromethyl)-1h-pyrazol-1-yl]aniline REF: 10-F665381CAS: 215500-56-4	95%	- - -	Producto descatalogado
2-[2-(difluoromethoxy)phenyl]acetaldehyde REF: 10-F655596CAS: 1343623-94-8	98%	- - -	Producto descatalogado
1-[3,5-bis(trifluoromethyl)benzenesulfonyl]piperazine hydrochloride REF: 10-F643341CAS: 97630-12-1	98+%	- - -	Producto descatalogado
methyl 4-bromo-1-(3,3,3-trifluoropropyl)-1H-pyrazole-3-carboxylate REF: 10-F508893	- - -	- - -	Producto descatalogado
1,1,1-Trifluoro-2-(trifluoromethyl)pentan-2-ol REF: 10-F765480CAS: 10315-75-0	98%	- - -	Producto descatalogado
4-Chloro-6-methyl-2-(2,2,2-trifluoroethyl)-2H-pyrazolo[3,4-d]pyrimidine REF: 10-F610140CAS: 2163771-92-2	98%	- - -	Producto descatalogado
3-(4-(3-Chloro-5-(trifluoromethyl)pyridin-2-yl)-1,4-diazepan-1-yl)propanoic acid REF: 10-F776456CAS: 1227954-72-4	98%	- - -	Producto descatalogado
2-Methyl-4-(4-trifluoromethyl-phenoxy)-phenylamine REF: 10-F032970CAS: 102766-74-5	95.0%	- - -	Producto descatalogado
2-Hydroxy-2-[2-(trifluoromethyl)phenyl]acetic acid REF: 10-F655976CAS: 339-93-5	97%	- - -	Producto descatalogado
1-Amino-3,3-bis(trifluoromethyl)cyclobutane-1-carboxylic acid REF: 10-F701583CAS: 1186237-66-0	98%	- - -	Producto descatalogado
1,1,1-Trifluoro-4-phenylbutan-2-ol REF: 10-F744539CAS: 90550-18-8	98%	- - -	Producto descatalogado
methyl 4-iodo-1-(3,3,3-trifluoropropyl)-1H-pyrazole-3-carboxylate REF: 10-F508895	- - -	- - -	Producto descatalogado
1,1,1-Trifluoro-3-(3-methylpyridin-2-yl)propan-2-ol REF: 10-F746295CAS: 1526768-72-8	98%	- - -	Producto descatalogado
2-(3'-(Trifluoromethyl)-[1,1'-biphenyl]-4-yl)acetic acid REF: 10-F235544CAS: 877607-26-6	95.0%	- - -	Producto descatalogado
1-(3-(TRIFLUOROMETHYL)PHENYL)CYCLOBUTANAMINE HCL REF: 10-F304995CAS: 1094218-35-5	95.0%	- - -	Producto descatalogado
2-(5-Methoxy-2-nitro-4-(trifluoromethyl)phenyl)acetonitrile REF: 10-F620316CAS: 178896-77-0	97%	- - -	Producto descatalogado
1-(5-Ethylthiophen-2-yl)-4,4,4-trifluorobutane-1,3-dione REF: 10-F026071CAS: 438222-02-7	- - -	- - -	Producto descatalogado
5-Nitro-2-(trifluoromethoxy)benzonitrile REF: 10-F767148CAS: 1214341-32-8	98%	- - -	Producto descatalogado
2-methyl-3-[3-(trifluoromethyl)-4,5,6,7-tetrahydro-2H-indazol-2-yl]propanenitrile REF: 10-F427135CAS: 937601-64-4	- - -	- - -	Producto descatalogado
1-(2-Ethylphenyl)-2,2-difluoroethanone REF: 10-F401347CAS: 1352209-78-9	97.0%	- - -	Producto descatalogado
3-Bromo-5-(trifluoromethoxy)cinnamic acid REF: 10-F342966CAS: 1092460-68-8	- - -	- - -	Producto descatalogado
4-Bromo-2-(4-fluoro-phenyl)-5-trifluoromethyl-1H-pyrrole-3-carbonitrile REF: 10-F480541	- - -	- - -	Producto descatalogado
(4-(3-Chloro-5-(trifluoromethyl)pyridin-2-yl)piperazin-1-yl)(3-methylthiophen-2-yl)methanone REF: 10-F706682CAS: 1024338-68-8	90%	- - -	Producto descatalogado
3-(trifluoromethyl)-2H-pyrazolo[4,3-b]pyridine REF: 10-F602663CAS: 1211517-40-6	98%	- - -	Producto descatalogado
1-methyl-5-(trifluoromethyl)-1H-pyrazole-4-sulfonyl chloride REF: 10-F508066	- - -	- - -	Producto descatalogado
6-(Trifluoromethyl)-2H-spiro[1-benzofuran-3,4'-piperidine] hydrochloride REF: 10-F476425	- - -	- - -	Producto descatalogado
Ethyl 2-(4-(difluoromethyl)-3,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-1-yl)acetate REF: 10-F732574CAS: 1011380-61-2	97%	- - -	Producto descatalogado
4'-Chloro-3'-methyl-2,2,2-trifluoroacetophenone REF: 10-F023167CAS: 286017-71-8	97.0%	- - -	Producto descatalogado
Ethyl 2-(4-(difluoromethyl)-6-(furan-2-yl)-3-methyl-1H-pyrazolo[3,4-b]pyridin-1-yl)acetate REF: 10-F732575CAS: 1011373-83-3	97%	- - -	Producto descatalogado
1-(2,2-difluoroethyl)-5-(methoxymethyl)-1H-pyrazole REF: 10-F508915	- - -	- - -	Producto descatalogado
2-[(2,2,2-trifluoroethyl)sulfanyl]-5-(trifluoromethyl)aniline REF: 10-F673794CAS: 1094403-82-3	95%	- - -	Producto descatalogado
(s)-2-Amino-2-(2-(trifluoromethoxy)phenyl)ethan-1-ol REF: 10-F746522CAS: 1212964-05-0	98%	- - -	Producto descatalogado
1,2,4,5-Tetrachloro-3-trifluoromethyl-benzene REF: 10-F032977CAS: 7656-99-7	- - -	- - -	Producto descatalogado
1-(2,2,2-Trifluoroethyl)pyrrolidin-3-one REF: 10-F742860CAS: 1096881-58-1	95%	- - -	Producto descatalogado
4-Pyrrolidin-1-yl-3-trifluoromethyl-benzaldehyde REF: 10-F031216CAS: 886500-73-8	- - -	- - -	Producto descatalogado
2-(1,3-Dioxolan-2-yl)-1-(4-trifluoromethyl-phenyl)-ethanone REF: 10-F208496CAS: 1263366-02-4	97.0%	- - -	Producto descatalogado
4-Chloro-1-oxo-1-(4-trifluoromethylphenyl)butane REF: 10-F203715CAS: 327617-82-3	97.0%	- - -	Producto descatalogado
(E)-2-(3-(trifluoromethyl)benzylidene)hydrazine-1-carbothioamide REF: 10-F732851CAS: 264148-89-2	98%	- - -	Producto descatalogado
6-Chloro-3-(2-(trifluoromethyl)phenyl)-[1,2,4]triazolo[4,3-b]pyridazine REF: 10-F765914CAS: 1094452-66-0	98%	- - -	Producto descatalogado
1-ETHYL-6-ETHYLSULFANYL-3-(2,2,2-TRIFLUORO-ETHYL)-1H-[1,3,5]TRIAZINE-2,4-DIONE REF: 10-F479054	- - -	- - -	Producto descatalogado
5-(Difluoromethoxy)-2-fluorobenzyl bromide REF: 10-F342915CAS: 1017779-36-0	- - -	- - -	Producto descatalogado
2'-Ethoxy-4'-fluoro-2,2,2-trifluoroacetophenone REF: 10-F397061CAS: 1443307-51-4	97.0%	- - -	Producto descatalogado
2-[1-(chloroacetyl)-3-oxopiperazin-2-yl]-N-[3-(trifluoromethyl)phenyl]acetamide REF: 10-F371583CAS: 1306738-22-6	- - -	- - -	Producto descatalogado
4-[4-(trifluoromethyl)-1,3-thiazol-2-yl]piperidine REF: 10-F655653CAS: 1248983-30-3	95%	- - -	Producto descatalogado
2-((Benzyloxy)carbonyl)-4-(trifluoromethyl)-2-azabicyclo[2.1.1]hexane-1-carboxylic acid REF: 10-F617718CAS: 1050886-63-9	98%	- - -	Producto descatalogado
3-Amino-4-methyl-n-[3-(trifluoromethyl)phenyl]benzene-1-sulfonamide REF: 10-F643279CAS: 565209-22-5	95%	- - -	Producto descatalogado
2-(Hydroxymethyl)-6-(trifluoromethyl)phenol REF: 10-F761192CAS: 773873-13-5	97%	- - -	Producto descatalogado
2-(((4-Chloro-3-(trifluoromethyl)phenyl)amino)methyl)-6-ethoxyphenol REF: 10-F734521CAS: 1232803-68-7	98%	- - -	Producto descatalogado
(E)-4-(2-(Trifluoromethyl)phenyl)but-3-en-2-one REF: 10-F680913CAS: 852527-28-7	98%	- - -	Producto descatalogado
4-(2,2,2-Trifluoroethyl)morpholine-3-carboxylic acid REF: 10-F705020CAS: 1478442-66-8	95%	- - -	Producto descatalogado
1-Oxa-7-azaspiro[3.4]octane 2,2,2-trifluoroacetic acid REF: 10-F624684CAS: 1392804-83-9	95+%	- - -	Producto descatalogado
3-[7-(difluoromethyl)-5-(1-ethyl-5-methyl-1H-pyrazol-4-yl)[1,2,4]triazolo[1,5-a]pyrimidin-2-yl]propanoic acid REF: 10-F428209CAS: 1174869-32-9	95.0%	- - -	Producto descatalogado
3,4-Dichloro-5-(trifluoromethoxy)benzaldehyde REF: 10-F475934CAS: 1706430-32-1	- - -	- - -	Producto descatalogado
5-Methyl-7-pentafluoroethyl-pyrazolo[1,5- a ]pyrimidine-2-carboxylic acid REF: 10-F027993CAS: 676469-64-0	- - -	- - -	Producto descatalogado
2-((1-Ethyl-3-(trifluoromethyl)-1h-pyrazol-5-yl)methoxy)ethan-1-amine REF: 10-F710808CAS: 1170513-11-7	97%	- - -	Producto descatalogado
Tert-butyl 5-cyano-3-formyl-6-(trifluoromethyl)-1H-indole-1-carboxylate REF: 10-F768878CAS: 1353877-93-6	98%	- - -	Producto descatalogado
3-Bromo-4-methoxy-5-(trifluoromethyl)aniline REF: 10-F343315CAS: 1373920-70-7	- - -	- - -	Producto descatalogado
4-[(2,2,3,3-tetrafluoropropoxy)methyl]benzohydrazide REF: 10-F425346CAS: 438473-25-7	- - -	- - -	Producto descatalogado
Methyl 3-methoxy-5-(trifluoromethyl)benzoate REF: 10-F765236CAS: 1003843-90-0	98%	- - -	Producto descatalogado
6-(4-(Trifluoromethyl)phenyl)pyridazin-3-amine REF: 10-F777029CAS: 1215073-83-8	98%	- - -	Producto descatalogado
4-Chloro-2-(trifluoromethyl)phenylhydrazine, HCl REF: 10-F638458CAS: 502496-20-0	95+%	- - -	Producto descatalogado
2-{[3-chloro-5-(trifluoromethyl)pyridin-2-yl]oxy}benzoic acid REF: 10-F517838	- - -	- - -	Producto descatalogado
4-Bromo-1-(difluoromethyl)-5-(isobutoxymethyl)-1H-pyrazole REF: 10-F509152CAS: 1856089-39-8	- - -	- - -	Producto descatalogado
2-Chloro-N-ethyl-N-(3-trifluoromethyl-benzyl)-acetamide REF: 10-F086234CAS: 1353982-20-3	- - -	- - -	Producto descatalogado
6-Amino-5-(trifluoromethyl)nicotinic acid REF: 10-F785476CAS: 1476762-30-7	98%	- - -	Producto descatalogado
4'-(Trifluoromethyl)-[1,1'-biphenyl]-3-amine hydrochloride REF: 10-F776871CAS: 1211195-38-8	98%	- - -	Producto descatalogado
4-(2,2,2-Trifluoroethoxy)pyridin-3-amine REF: 10-F697439CAS: 1039822-70-2	98%	- - -	Producto descatalogado
3-[4-(difluoromethyl)-2,3-dimethyl-6-oxo-2,6-dihydro-7H-pyrazolo[3,4-b]pyridin-7-yl]propanoic acid REF: 10-F427838CAS: 1018126-77-6	- - -	- - -	Producto descatalogado
n-Isopropyl-3-(trifluoromethoxy)aniline REF: 10-F715120CAS: 1020966-65-7	95%	- - -	Producto descatalogado

1g	Descatalogado	Solicitar información
5g	Descatalogado	Solicitar información
10g	Descatalogado	Solicitar información

1g	Descatalogado	Solicitar información
250mg	Descatalogado	Solicitar información
500mg	Descatalogado	Solicitar información

50mg	Descatalogado	Solicitar información
100mg	Descatalogado	Solicitar información
250mg	Descatalogado	Solicitar información

1g	Descatalogado	Solicitar información
2.5g	Descatalogado	Solicitar información
50mg	Descatalogado	Solicitar información
100mg	Descatalogado	Solicitar información
250mg	Descatalogado	Solicitar información
500mg	Descatalogado	Solicitar información

Compuestos fluorados

4-Methoxy-3-methyl-5-(trifluoromethyl)benzamide

Ref: 10-F343364

1-(3,4-dimethylphenyl)-3-(trifluoromethyl)-1H-pyrazol-5-amine

Ref: 10-F428479

8-Bromo-2-(difluoromethyl)imidazo[1,2-a]pyridine

Ref: 10-F783246

3-Methoxy-4-(2-nitro-4-(trifluoromethyl)phenoxy)benzaldehyde

Ref: 10-F751735

2-(Trifluoromethyl)-1,3-benzoxazol-6-amine

Ref: 10-F658127

3-Methyl-2-((3-(trifluoromethyl)phenyl)sulfonamido)pentanoic acid

Ref: 10-F708668

3-(Trifluoromethyl)-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide

Ref: 10-F610430

4-Amino-N-(2-(2,2,2-trifluoroethoxy)ethyl)benzamide

Ref: 10-F752013

Ethyl 2-((4-(1-ethyl-3-methyl-1h-pyrazol-4-yl)-6-(trifluoromethyl)pyrimidin-2-yl)sulfonyl)acetate

Ref: 10-F710860

1-[4-(difluoromethoxy)phenyl]piperidin-3-amine

Ref: 10-F675423

[5-chloro-2-(difluoromethoxy)phenyl]methanamine

Ref: 10-F675883

methyl 3-[4-bromo-3-(trifluoromethyl)-1H-pyrazol-1-yl]propanoate

Ref: 10-F427139

3-(Difluoromethoxy)-4-methoxybenzaldehyde

Ref: 10-F770167

3-[3-(trifluoromethyl)phenyl]-1h-pyrazole-4-carbaldehyde

Ref: 10-F651003

3-Chloro-N-(3-methoxypropyl)-5-(trifluoromethyl)pyridin-2-amine

Ref: 10-F714479

7-Benzyl-4-chloro-2-(trifluoromethyl)-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine

Ref: 10-F430289

4-((2-Oxo-5-(trifluoromethyl)pyridin-1(2H)-yl)methyl)benzoic acid

Ref: 10-F751796

{[2-ethyl-4-(trifluoromethyl)-2H-pyrazolo[3,4-b]pyridin-6-yl]thio}acetic acid

Ref: 10-F427966

4'-Ethoxy-3'-methyl-2,2,2-trifluoroacetophenone

Ref: 10-F395855

1-(Bromomethyl)-4-(trifluoromethyl)cyclohexane

Ref: 10-F637829

6-(2-Fluorophenoxy)-1,1,1-trifluoro-hexan-2-one

Ref: 10-F542561

6-Trifluoromethyl-naphthalen-1-ol

Ref: 10-F736917

tert-Butyl[3-(5'-(trifluoromethyl)pyridin-2'-yl)-[1,2,4]methyl]-carbamate

Ref: 10-F047528

2-Fluoro-4-methyl-3-(trifluoromethyl)benzaldehyde

Ref: 10-F476008

2-Methyl-6-(trifluoromethyl)morpholine

Ref: 10-F619398

(5-Methyl-2-(trifluoromethyl)furan-3-yl)methanamine

Ref: 10-F721660

2-Methoxy-4-(trifluoromethoxy)benzyl alcohol

Ref: 10-F342417

6-(3,4-Dimethylphenoxy)-1,1,1-trifluoro-hexan-2-one

Ref: 10-F542574

(3-Chloro-4-(difluoromethoxy)phenyl)methanamine

Ref: 10-F699760

9-Phenanthryl trifluoromethyl ketone

Ref: 10-F207036

3-Ethoxy-2-fluoro-5-(trifluoromethoxy)phenylboronic acid

Ref: 10-F623177

4-[5-(trifluoromethyl)-1h-pyrazol-1-yl]aniline

Ref: 10-F665381

2-[2-(difluoromethoxy)phenyl]acetaldehyde

Ref: 10-F655596

1-[3,5-bis(trifluoromethyl)benzenesulfonyl]piperazine hydrochloride

Ref: 10-F643341

methyl 4-bromo-1-(3,3,3-trifluoropropyl)-1H-pyrazole-3-carboxylate

Ref: 10-F508893

1,1,1-Trifluoro-2-(trifluoromethyl)pentan-2-ol

Ref: 10-F765480

4-Chloro-6-methyl-2-(2,2,2-trifluoroethyl)-2H-pyrazolo[3,4-d]pyrimidine

Ref: 10-F610140

3-(4-(3-Chloro-5-(trifluoromethyl)pyridin-2-yl)-1,4-diazepan-1-yl)propanoic acid

Ref: 10-F776456

2-Methyl-4-(4-trifluoromethyl-phenoxy)-phenylamine

Ref: 10-F032970

2-Hydroxy-2-[2-(trifluoromethyl)phenyl]acetic acid