Building Blocks

Esta sección contiene productos fundamentales para la síntesis de compuestos orgánicos y biológicos. Los bloques de construcción son los materiales de partida esenciales utilizados para construir moléculas complejas a través de diversas reacciones químicas. Desempeñan un papel crítico en el descubrimiento de fármacos, la ciencia de materiales y la investigación química. En CymitQuimica, ofrecemos una gama diversa de bloques de construcción de alta calidad para apoyar sus investigaciones innovadoras y proyectos industriales, asegurando que tenga los componentes esenciales para una síntesis exitosa.

Subcategorías de "Building Blocks"

Ácidos borónicos y derivados del ácido borónico

Building Blocks quirales

Building Blocks de hidrocarburos

Building Blocks orgánicos

Productos de "Building Blocks"

100
- 20
- 50
- 200

productos por página. Hay 263118 productos en esta categoría.

Datos del producto	Pureza	Rango de precios	Entrega estimada
6-Chloro-1-methyl-1H-1,3-benzodiazole-2-carbaldehyde REF: 3D-GGA21281CAS: 156212-81-6	Min. 95%	A consultar	Mié 13 Nov 24
2-(4-Fluoro-2-methylphenyl)piperazine REF: 3D-WEB59600CAS: 746596-00-9	Min. 95%	A consultar	Mié 13 Nov 24
2-(2-Oxopropyl)-1λ⁶-thiolane-1,1-dione REF: 3D-REA15494CAS: 116154-94-0	Min. 95%	A consultar	Mié 13 Nov 24
2-Methoxy-3-nitro-phenol REF: 3D-VAA73471CAS: 20734-71-8	Min. 95%	A consultar	Mié 13 Nov 24
Ethyl 3-(4-oxopiperidin-1-yl)propanoate REF: 3D-ZGA77490CAS: 174774-90-4	Min. 95%	A consultar	Mié 13 Nov 24
3-Pyrrolo[2,3-b]pyridin-1-yl-propionic acid REF: 3D-EBC20247CAS: 1279202-47-9	Min. 95%	A consultar	Mié 13 Nov 24
tert-Butyl 3-iodo-1H-pyrrolo[2,3-b]pyridin-5-ylcarbamate REF: 3D-QQB60919CAS: 1015609-19-4	Min. 95%	A consultar	Mié 13 Nov 24
3-(Tert-butoxy)aniline REF: 3D-YUB16958CAS: 1123169-58-3	Min. 95%	A consultar	Mié 13 Nov 24
4-(3-Bromophenyl)oxane-4-carbonitrile REF: 3D-VJA43936CAS: 245439-36-5	Min. 95%	A consultar	Mié 13 Nov 24
5-Cyclopropylfuran-2-sulfonyl chloride REF: 3D-NKD10456CAS: 2138104-56-8	Min. 95%	A consultar	Mié 13 Nov 24
8-Chloro-3,4-dihydro-2H-benzo[b][1,4]dioxepin-7-ylamine REF: 3D-DKB21762CAS: 878217-62-0	Min. 95%	A consultar	Mié 13 Nov 24
4-(2-Bromophenoxy)piperidine REF: 3D-RLB97129CAS: 916971-29-4	Min. 95%	A consultar	Mié 13 Nov 24
2-(4-Oxo-1,4-dihydroquinolin-1-yl)acetamide REF: 3D-VWB06049CAS: 1170060-49-7	Min. 95%	A consultar	Mié 13 Nov 24
6-(Oxolan-3-yloxy)pyridin-3-amine REF: 3D-RDC83337CAS: 1341833-37-1	Min. 95%	A consultar	Mié 13 Nov 24
2-(5-Oxopyrrolidin-2-yl)propanoic acid REF: 3D-ZAA45463CAS: 24454-63-5	Min. 95%	A consultar	Mié 13 Nov 24
1-(6-Methylpyridin-2-yl)acetone REF: 3D-QCA70208CAS: 65702-08-1	Min. 95%	A consultar	Mié 13 Nov 24
5-(Aminomethyl)-1H-1,2,4-triazol-3-amine hydrochloride REF: 3D-WSB62599CAS: 1071625-99-4	Min. 95%	53,00 €~483,00 €	Mié 13 Nov 24
2-(4-Dimethylaminomethyl-piperidin-1-yl)-ethylamine REF: 3D-TBC11559CAS: 1293115-59-9	Min. 95%	A consultar	Mié 13 Nov 24
2-(2-Bromoethoxy)-1,1-difluorocyclopropane REF: 3D-FDD52391CAS: 1955523-91-7	Min. 95%	A consultar	Mié 13 Nov 24
5-(3-(Trifluoromethyl)phenyl)nicotinaldehyde REF: 3D-MKB97363CAS: 887973-63-9	Min. 95%	A consultar	Mié 13 Nov 24
6-Methoxy-5-methylpicolinohydrazide REF: 3D-DFC38141CAS: 1378381-41-9	Min. 95%	A consultar	Mié 13 Nov 24
2-[3-(Trifluoromethyl)-1H-pyrazol-1-yl]ethan-1-amine hydrochloride REF: 3D-HHC03483CAS: 1432034-83-7	Min. 95%	A consultar	Mié 13 Nov 24
DL-2,4-dimethoxyphenylalanine REF: 3D-RDA24817CAS: 91248-17-8	Min. 95%	A consultar	Mié 13 Nov 24
8-Bromo-2,5-dichloroquinoline REF: 3D-PKC15598CAS: 1514155-98-6	Min. 95%	A consultar	Mié 13 Nov 24
2-(4-Amino-2-chlorophenoxy)-N,N-dimethylacetamide REF: 3D-UGA28690CAS: 169286-90-2	Min. 95%	A consultar	Mié 13 Nov 24
{4-[(Methylsulfanyl)methyl]phenyl}methanamine REF: 3D-EJB30448CAS: 854304-48-6	Min. 95%	A consultar	Mié 13 Nov 24
6-Methoxy-1-phenyl-1H,2H,3H,4H,9H-pyrido[3,4-b]indole hydrochloride REF: 3D-NAA63747CAS: 13637-47-3	Min. 95%	A consultar	Mié 13 Nov 24
Methyl 4-methanesulfonyl-2-nitrobenzoate REF: 3D-IGA58107CAS: 158581-07-8	Min. 95%	49,00 €~1.126,00 €	Mié 13 Nov 24
2-Hydroxypyrimidine-5-carboxylic acid REF: 3D-NBA32483CAS: 38324-83-3	Min. 95%	A consultar	Mié 13 Nov 24
(4-Cyclopropyl-4-methyl-2,5-dioxo-imidazolidin-1-yl)-acetic acid REF: 3D-GNB35540CAS: 956355-40-1	Min. 95%	A consultar	Mié 13 Nov 24
1-(m-Tolyl)cyclopropanamine REF: 3D-DVA41730CAS: 503417-30-9	Min. 95%	A consultar	Mié 13 Nov 24
1-[(3,5-Dimethyl-1H-pyrazol-1-yl)methyl]-3,5-dimethyl-1H-pyrazol-4-amine REF: 3D-EQB19285CAS: 1004192-85-1	Min. 95%	A consultar	Mié 13 Nov 24
Diethyl (5-[2-(3-methylbutyl)-1,3-dithian-2-yl]-2-furyl)phosphonate REF: 3D-ZXB58968CAS: 1199589-68-8	Min. 95%	A consultar	Mié 13 Nov 24
(2R)-1-[(2-Methyl-2H-1,2,3,4-tetrazol-5-yl)methyl]pyrrolidine-2-carboxylic acid hydrochloride REF: 3D-MKD02901CAS: 2137029-01-5	Min. 95%	A consultar	Mié 13 Nov 24
1-(3-Pyridin-3-ylisoxazol-5-yl)methanamine REF: 3D-TWA71343CAS: 543713-43-5	Min. 95%	A consultar	Mié 13 Nov 24
4-(Prop-2-en-1-yl)piperidin-4-ol hydrochloride REF: 3D-UID51970CAS: 2094519-70-5	Min. 95%	A consultar	Mié 13 Nov 24
2-[2-(4-Bromophenyl)acetamido]-2-phenylacetic acid REF: 3D-DUB84095CAS: 1103840-95-4	Min. 95%	A consultar	Mié 13 Nov 24
(2E)-3-{1-[(4-Methylphenyl)methyl]-3-phenyl-1H-pyrazol-4-yl}prop-2-enoic acid REF: 3D-HNB02285CAS: 957022-85-4	Min. 95%	A consultar	Mié 13 Nov 24
6-Fluoro-2,3-dihydro-1H-inden-1-amine hydrochloride REF: 3D-RXB90844CAS: 1191908-44-7	Min. 95%	A consultar	Mié 13 Nov 24
4-(1,2,3,4-Tetrahydroisoquinolin-2-yl)pyrrolidin-3-ol dihydrochloride REF: 3D-DXC58411CAS: 1803584-11-3	Min. 95%	A consultar	Mié 13 Nov 24
Dibenzofuran-3-ylamine hydrochloride REF: 3D-RDA49329CAS: 91493-29-7	Min. 95%	A consultar	Mié 13 Nov 24
5-Methyloxazolo[4,5-b]pyridin-2(3H)-one REF: 3D-FCA65625CAS: 55656-25-2	Min. 95%	A consultar	Mié 13 Nov 24
±-Methoxyphenylacetic acid REF: 3D-HAA02109CAS: 7021-09-2	Min. 95%	A consultar	Mié 13 Nov 24
2-((5-Bromo-4-methylpyridin-2-yl)amino)ethanol REF: 3D-UYB98286CAS: 1219982-86-1	Min. 95%	A consultar	Mié 13 Nov 24
2-Thienyl-carbamic acid ethyl ester REF: 3D-FEA99516CAS: 105995-16-2	Min. 95%	A consultar	Mié 13 Nov 24
rac-Methyl (1R,3S)-3-aminocyclohexane-1-carboxylate REF: 3D-CIA12010CAS: 202120-10-3	Min. 95%	A consultar	Mié 13 Nov 24
(1S)-4-Chloro-2,3-dihydro-1H-inden-1-amine hydrochloride REF: 3D-JJD87407CAS: 2109874-07-7	Min. 95%	A consultar	Mié 13 Nov 24
1,1,1-Trifluoro-3-(4-fluorophenyl)propan-2-ol REF: 3D-UDC00694CAS: 1344006-94-5	Min. 95%	A consultar	Mié 13 Nov 24
2-(2,3-Dihydro-1H-isoindol-2-yl)ethan-1-ol hydrochloride REF: 3D-EEC95020CAS: 1354950-20-1	Min. 95%	A consultar	Mié 13 Nov 24
[2-(4-Bromophenyl)propan-2-yl](2-methylpropyl)amine hydrochloride REF: 3D-HPC27768CAS: 1607277-68-8	Min. 95%	A consultar	Mié 13 Nov 24
1-(2-Chloro-3-methoxyphenyl)ethan-1-ol REF: 3D-HCC25536CAS: 1307255-36-2	Min. 95%	A consultar	Mié 13 Nov 24
2-[3-(5-Phenyl-2H-1,2,3,4-tetrazol-2-yl)adamantan-1-yl]acetic acid REF: 3D-NSA22139CAS: 438221-39-7	Min. 95%	A consultar	Mié 13 Nov 24
1-Ethynyl-3-isothiocyanatobenzene REF: 3D-UJA24695CAS: 244246-95-5	Min. 95%	A consultar	Mié 13 Nov 24
2-Amino-3-(4-chlorophenyl)propanamide hydrochloride REF: 3D-DHC14931CAS: 1428149-31-8	Min. 95%	A consultar	Mié 13 Nov 24
(S)-tert-Butyl 3-methanesulfonamidopiperidine-1-carboxylate REF: 3D-CQB35992CAS: 1002359-92-3	Min. 95%	A consultar	Mié 13 Nov 24
2-Bromo-3-fluoro-4-iodopyridine REF: 3D-EXC91090CAS: 1804910-90-4	Min. 95%	A consultar	Mié 13 Nov 24
1-Bromo-2-fluoro-3-(butylaminomethyl)benzene REF: 3D-FEC24701CAS: 1355247-01-6	Min. 95%	A consultar	Mié 13 Nov 24
(S)-3-Carboxymethoxy-pyrrolidine-1-carboxylic acid benzyl ester REF: 3D-EEC00032CAS: 1354000-32-0	Min. 95%	A consultar	Mié 13 Nov 24
5-[(4-Chloro-5-methyl-3-nitro-1H-pyrazol-1-yl)methyl]furan-2-carboxylic acid REF: 3D-CRA61416CAS: 402614-16-8	Min. 95%	A consultar	Mié 13 Nov 24
(2,4-Difluoro-5-methoxyphenyl)methanol REF: 3D-RAC11465CAS: 1266114-65-1	Min. 95%	A consultar	Mié 13 Nov 24
2-(4-Bromothien-2-yl)-1,3-dioxolane REF: 3D-ICA26785CAS: 58267-85-9	Min. 95%	A consultar	Mié 13 Nov 24
2-Chloro-7-methoxyquinoline REF: 3D-ZBA60915CAS: 49609-15-6	Min. 95%	A consultar	Mié 13 Nov 24
2,8-Dimethylimidazo[1,2-a]pyridine-3-carbaldehyde REF: 3D-VHB24585CAS: 820245-85-0	Min. 95%	A consultar	Mié 13 Nov 24
3-[1-(4-Bromophenyl)-2,5-dimethyl-1H-pyrrol-3-yl]-2-cyanoprop-2-enoic acid REF: 3D-BJB16950CAS: 851169-50-1	Min. 95%	A consultar	Mié 13 Nov 24
1-boc-2-methyl-3-azetidone REF: 3D-IGC07636CAS: 1408076-36-7	Min. 95%	A consultar	Mié 13 Nov 24
3-chloro-4-(prop-2-en-1-yloxy)benzaldehyde REF: 3D-ICA23691CAS: 58236-91-2	Min. 95%	A consultar	Mié 13 Nov 24
Methyl 2-(3-methylpyridin-2-yl)acetate REF: 3D-STB47778CAS: 1092477-78-5	Min. 95%	A consultar	Mié 13 Nov 24
5-Bromo-8-(bromomethyl)-2-methoxyquinoline REF: 3D-KKB68781CAS: 885687-81-0	Min. 95%	A consultar	Mié 13 Nov 24
3-Cyano-4-methyl-benzenesulfonamide REF: 3D-DPA46848CAS: 353468-48-1	Min. 95%	A consultar	Mié 13 Nov 24
3-(Benzyloxy)-2,2-dimethylcyclobutan-1-one REF: 3D-CAA06392CAS: 2063-92-5	Min. 95%	A consultar	Mié 13 Nov 24
3-Amino-3-(2,3-dimethylphenyl)propanoic acid REF: 3D-MRA92512CAS: 412925-12-3	Min. 95%	A consultar	Mié 13 Nov 24
(6-Aminohexyl)(methyl)amine dihydrochloride REF: 3D-PED67236CAS: 1989672-36-7	Min. 95%	A consultar	Mié 13 Nov 24
1-Methyl-5-(trifluoromethyl)-1H-pyrazol-3-amine REF: 3D-ZFA97842CAS: 149978-42-7	Min. 95%	A consultar	Mié 13 Nov 24
3-Azetidinyl 3-methylbutanoate REF: 3D-UYB94857CAS: 1219948-57-8	Min. 95%	A consultar	Mié 13 Nov 24
2-Fluoro-3-iodo-6-(pyrrolidin-1-yl)pyridine REF: 3D-DYB49932CAS: 1203499-32-4	Min. 95%	A consultar	Mié 13 Nov 24
5-(Benzyloxy)-1-methyl-1H-indole REF: 3D-CAA43968CAS: 2439-68-1	Min. 95%	A consultar	Mié 13 Nov 24
ethyl (2E)-3-(5-methylpyridin-2-yl)prop-2-enoate REF: 3D-QGC13209CAS: 1415132-09-0	Min. 95%	A consultar	Mié 13 Nov 24
8-Chloro-2-(chloromethyl)-4(1H)-quinolinone REF: 3D-WMB69243CAS: 946692-43-9	Min. 95%	A consultar	Mié 13 Nov 24
3-Chloro-1,2,4-benzotriazine REF: 3D-RDA66921CAS: 91669-21-5	Min. 95%	A consultar	Mié 13 Nov 24
Methyl 2-cyclopropyl-2-sulfamoylacetate REF: 3D-JSD46096CAS: 2309460-96-4	Min. 95%	A consultar	Mié 13 Nov 24
tert-Butyl 4-amino-4-(pyridin-3-yl)piperidine-1-carboxylate REF: 3D-HTC58061CAS: 1707580-61-7	Min. 95%	A consultar	Mié 13 Nov 24
N-[(4-Bromophenyl)sulfonyl]-β-alanine REF: 3D-REA03558CAS: 116035-58-6	Min. 95%	A consultar	Mié 13 Nov 24
2-(4-Bromophenyl)-1-methylpiperidin-4-one REF: 3D-ZJC21113CAS: 1499211-13-0	Min. 95%	A consultar	Mié 13 Nov 24
4-Amino-5-nitronicotinamide REF: 3D-LLB46118CAS: 911461-18-2	Min. 95%	A consultar	Mié 13 Nov 24
6-(tert-Butyl)-2-thioxo-2,3-dihydro-4(1H)-pyrimidinone REF: 3D-RCA69866CAS: 66698-66-6	Min. 95%	A consultar	Mié 13 Nov 24
Methyl 3-bromo-6-chloropicolinate REF: 3D-PYB32896CAS: 1214328-96-7	Min. 95%	A consultar	Mié 13 Nov 24
2-(2-Dimethylamino-cyclohexylamino)-ethanol REF: 3D-DEC95904CAS: 1353959-04-2	Min. 95%	A consultar	Mié 13 Nov 24
3-Chlorophenyl methyl sulfone REF: 3D-WAA38300CAS: 21383-00-6	Min. 95%	A consultar	Mié 13 Nov 24
Ethyl 2-azepan-1-ylpropanoate REF: 3D-BGB99391CAS: 776993-91-0	Min. 95%	A consultar	Mié 13 Nov 24
4-[2-(4-Methoxy-phenyl)-ethyl]-piperidine REF: 3D-YFA13592CAS: 148135-92-6	Min. 95%	A consultar	Mié 13 Nov 24
7-Bromothieno[2,3-c]pyridine-2-carboxylic acid REF: 3D-PID32575CAS: 2089325-75-5	Min. 95%	A consultar	Mié 13 Nov 24
4-{4-Chloro-5H,6H,7H-cyclopenta[D]pyrimidin-2-yl}pyridine REF: 3D-ZZB85385CAS: 1249853-85-7	Min. 95%	A consultar	Mié 13 Nov 24
Methyl({[1-(2-methylpropyl)cyclopropyl]methyl})amine hydrochloride REF: 3D-FLD85305CAS: 2155853-05-5	Min. 95%	A consultar	Mié 13 Nov 24
(4-Aminobutyl)(benzyloxy)amine dihydrochloride REF: 3D-JDA62729CAS: 84627-29-2	Min. 95%	A consultar	Mié 13 Nov 24
5-Carbamoyl-2-fluorobenzeneboronic acid pinacol ester REF: 3D-MGC90542CAS: 1412905-42-0	Min. 95%	A consultar	Mié 13 Nov 24
5H,6H,7H,8H-[1,2,4]Triazolo[1,5-a]pyridine-7-carboxylic acid hydrochloride REF: 3D-VAD58565CAS: 1895585-65-5	Min. 95%	A consultar	Mié 13 Nov 24
N-Ethyl-1-methyl-1H-pyrrole-2-carboxamide REF: 3D-ZEA72522CAS: 124725-22-0	Min. 95%	A consultar	Mié 13 Nov 24
N'-(7-Chloro-4-methoxy-1,3-benzothiazol-2-yl)-N,N-dimethylethane-1,2-diamine REF: 3D-FUB18890CAS: 1105188-90-6	Min. 95%	A consultar	Mié 13 Nov 24
trans-Chloro(1-naphthyl)bis(triphenylphosphine)-nickel REF: 3D-ECA80625CAS: 54806-25-6	Min. 95%	A consultar	Mié 13 Nov 24
2-Ethyl-5H,6H,7H,8H-imidazo[1,2-a]pyridine-7-carboxylic acid hydrochloride REF: 3D-KQD93075CAS: 2260930-75-2	Min. 95%	A consultar	Mié 13 Nov 24

50mg		217,00 €
500mg		865,00 €

10mg		180,00 €
100mg		677,00 €

25mg		200,00 €
250mg		797,00 €

1g		765,00 €
100mg		194,00 €

Building Blocks

Subcategorías de "Building Blocks"

Ácidos borónicos y derivados del ácido borónico

Building Blocks quirales

Building Blocks de hidrocarburos

Building Blocks orgánicos

Productos de "Building Blocks"

6-Chloro-1-methyl-1H-1,3-benzodiazole-2-carbaldehyde

Ref: 3D-GGA21281

2-(4-Fluoro-2-methylphenyl)piperazine

Ref: 3D-WEB59600

2-(2-Oxopropyl)-1λ⁶-thiolane-1,1-dione

Ref: 3D-REA15494

2-Methoxy-3-nitro-phenol

Ref: 3D-VAA73471

Ethyl 3-(4-oxopiperidin-1-yl)propanoate

Ref: 3D-ZGA77490

3-Pyrrolo[2,3-b]pyridin-1-yl-propionic acid

Ref: 3D-EBC20247

tert-Butyl 3-iodo-1H-pyrrolo[2,3-b]pyridin-5-ylcarbamate

Ref: 3D-QQB60919

3-(Tert-butoxy)aniline

Ref: 3D-YUB16958

4-(3-Bromophenyl)oxane-4-carbonitrile

Ref: 3D-VJA43936

5-Cyclopropylfuran-2-sulfonyl chloride

Ref: 3D-NKD10456

8-Chloro-3,4-dihydro-2H-benzo[b][1,4]dioxepin-7-ylamine

Ref: 3D-DKB21762

4-(2-Bromophenoxy)piperidine

Ref: 3D-RLB97129

2-(4-Oxo-1,4-dihydroquinolin-1-yl)acetamide

Ref: 3D-VWB06049

6-(Oxolan-3-yloxy)pyridin-3-amine

Ref: 3D-RDC83337

2-(5-Oxopyrrolidin-2-yl)propanoic acid

Ref: 3D-ZAA45463

1-(6-Methylpyridin-2-yl)acetone

Ref: 3D-QCA70208

5-(Aminomethyl)-1H-1,2,4-triazol-3-amine hydrochloride

Ref: 3D-WSB62599

2-(4-Dimethylaminomethyl-piperidin-1-yl)-ethylamine

Ref: 3D-TBC11559

2-(2-Bromoethoxy)-1,1-difluorocyclopropane

Ref: 3D-FDD52391

5-(3-(Trifluoromethyl)phenyl)nicotinaldehyde

Ref: 3D-MKB97363

6-Methoxy-5-methylpicolinohydrazide

Ref: 3D-DFC38141

2-[3-(Trifluoromethyl)-1H-pyrazol-1-yl]ethan-1-amine hydrochloride

Ref: 3D-HHC03483

DL-2,4-dimethoxyphenylalanine

Ref: 3D-RDA24817

8-Bromo-2,5-dichloroquinoline

Ref: 3D-PKC15598

2-(4-Amino-2-chlorophenoxy)-N,N-dimethylacetamide

Ref: 3D-UGA28690

{4-[(Methylsulfanyl)methyl]phenyl}methanamine

Ref: 3D-EJB30448

6-Methoxy-1-phenyl-1H,2H,3H,4H,9H-pyrido[3,4-b]indole hydrochloride

Ref: 3D-NAA63747

Methyl 4-methanesulfonyl-2-nitrobenzoate

Ref: 3D-IGA58107

2-Hydroxypyrimidine-5-carboxylic acid

Ref: 3D-NBA32483

(4-Cyclopropyl-4-methyl-2,5-dioxo-imidazolidin-1-yl)-acetic acid

Ref: 3D-GNB35540

1-(m-Tolyl)cyclopropanamine

Ref: 3D-DVA41730

1-[(3,5-Dimethyl-1H-pyrazol-1-yl)methyl]-3,5-dimethyl-1H-pyrazol-4-amine

Ref: 3D-EQB19285

Diethyl (5-[2-(3-methylbutyl)-1,3-dithian-2-yl]-2-furyl)phosphonate

Ref: 3D-ZXB58968

(2R)-1-[(2-Methyl-2H-1,2,3,4-tetrazol-5-yl)methyl]pyrrolidine-2-carboxylic acid hydrochloride

Ref: 3D-MKD02901

1-(3-Pyridin-3-ylisoxazol-5-yl)methanamine

Ref: 3D-TWA71343

4-(Prop-2-en-1-yl)piperidin-4-ol hydrochloride

Ref: 3D-UID51970

2-[2-(4-Bromophenyl)acetamido]-2-phenylacetic acid