accessibility menu, dialog, popup

UserName
Viewing profile as user:

Organic acids and derivatives

Organic compounds with acidic properties, and will commonly have carboxylic acids or similar functional groups in their structure. Derived compounds are also included.
Carboxylic acids and derivatives (11,880)
Boronic acid derivatives (3,163)
Acrylic acids and derivatives (2,773)
Organic sulfonic acids and derivatives (2,664)
Organic phosphoric acids and derivatives (1,869)
Organic sulfuric acids and derivatives (1,232)
Alpha-halocarboxylic acids and derivatives (847)
Organic carbonic acids and derivatives (836)
Organic phosphonic acids and derivatives (702)
Hydroxy acids and derivatives (610)
Vinylogous acids (568)
Cyclopropanecarboxylic acids and derivatives (416)
Carboximidic acids and derivatives (198)
Carbothioic Derivatives (95)
C24-propyl sterols and derivatives (84)
Orthocarboxylic acid derivatives (81)
Organic nitric acids and derivatives (58)
Phloroglucinols and derivatives (44)
Borinic Acid Derivatives (39)
Thiocarboxylic acids and derivatives (21)
Seleninic acids and derivatives (4)
Organic dithiophosphoric acids and derivatives (2)
Organic thiophosphoric acids and derivatives (2)

Filtered Search Results

Products from some of our suppliers do not display in filtered search results. Please clear all filters to see these products.

Narrow Results

Narrow Results

category

special offers

  • (1)
  • (4,894)
  • (30)

brands

  • (2)
  • (2)
  • (1)
  • (156)
  • (2)
  • (1)
  • (73)
  • (3)
  • (9)
  • (2)
  • (1)
  • (2)
  • (8)
  • (89)
  • (532)
  • (2)
  • (4,779)
  • (386)
  • (1)
  • (7)
  • (1)
  • (5)
  • (44)
  • (18)
  • (3)
  • (1)
  • (1)
  • (1)
  • (10)
  • (4)
  • (10)
  • (8)
  • (12)
  • (7)
  • (98)
  • (3)
  • (1)
  • (282)
  • (27)
  • (4)
  • (257)
  • (10)
  • (1)
  • (258)
  • (2)
  • (1)
  • (1)
  • (15)
  • (2)
  • (2)
  • (12)
  • (4)
  • (9)
  • (3,427)
  • (2)
  • (1)
  • (15)
  • (2)
  • (16)
  • (67)
  • (17)
  • (122)
  • (33)
  • (6)
  • (1)
  • (3)
  • (2)
  • (1)
  • (3)
  • (5)
  • (2)
  • (9)
  • (2)
  • (7)
  • (21)
  • (1)
  • (84)
  • (2)
  • (5)
  • (3,308)
  • (43)
  • (60)
  • (1)
  • (3)
  • (239)
  • (1)
  • (1)
  • (50)
  • (8)
  • (5)
  • (3)
  • (1)
  • (14)
  • (39)
  • (1)
  • (6)
  • (2)
  • (1)
  • (2)
  • (312)
  • (914)
  • (959)
  • (4)
  • (503)
  • (1)
  • (49)
  • (1)
  • (6)
  • (1)
  • (1)
  • (2)
  • (4,337)
  • (1)
  • (6)
  • (11)
  • (5,754)
  • (7)
  • (31)
  • (1)
  • (2)
  • (7)
  • (4)
  • (1)
  • (14)

special interests

  • (19)
  • (48)
  • (5)
  • (192)
  • (25)
  • (5,910)

Quantity

  • (1)
  • (3)
  • (6)
  • (1)
  • (2)
  • (121)
  • (1,559)
Show all

Molecular Weight (g/mol)

  • (20)
  • (50)
  • (2)
  • (3)
  • (15)
  • (23)
  • (17)
Show all

Percent Purity

  • (2)
  • (2)
  • (3)
  • (1)
  • (1)
  • (2)
  • (6)
Show all

Physical Form

  • (4)
  • (3)
  • (2)
  • (2)
  • (16)
  • (2)
  • (67)
Show all

Boiling Point

  • (2)
  • (2)
  • (3)
  • (4)
  • (4)
  • (1)
  • (2)
Show all

Grade

  • (1)
  • (103)
  • (3)
  • (36)
  • (2)
  • (25)
  • (3)
Show all

Product Line

  • (33)
  • (7)
  • (1)
  • (2)

Search Within Results
Keyword Search:
4,861 – 4,875 of 22,242 results
4,861

Ethyl Formate 98.0+%, TCI America™

CAS: 109-94-4 Molecular Formula: C3H6O2 Molecular Weight (g/mol): 74.08 MDL Number: MFCD00003294 InChI Key: WBJINCZRORDGAQ-UHFFFAOYSA-N Synonym: areginal,formic acid, ethyl ester,ethyl methanoate,formic acid ethyl ester,aethylformiat,ethyl formic ester,ethylformate,ethylformiaat,formic ether,ethylformiat PubChem CID: 8025 ChEBI: CHEBI:52342 IUPAC Name: ethyl formate SMILES: CCOC=O

PubChem CID 8025
CAS 109-94-4
Molecular Weight (g/mol) 74.08
ChEBI CHEBI:52342
MDL Number MFCD00003294
SMILES CCOC=O
Synonym areginal,formic acid, ethyl ester,ethyl methanoate,formic acid ethyl ester,aethylformiat,ethyl formic ester,ethylformate,ethylformiaat,formic ether,ethylformiat
IUPAC Name ethyl formate
InChI Key WBJINCZRORDGAQ-UHFFFAOYSA-N
Molecular Formula C3H6O2
4,862

Ethyl Phthalyl Ethyl Glycolate 95.0+%, TCI America™

CAS: 84-72-0 Molecular Formula: C14H16O6 Molecular Weight (g/mol): 280.28 MDL Number: MFCD00059377 InChI Key: PZBLUWVMZMXIKZ-UHFFFAOYSA-N Synonym: Ethoxycarbonylmethyl Ethyl Phthalate, Phthalic Acid Ethoxycarbonylmethyl Ethyl Ester PubChem CID: 6785 IUPAC Name: ethyl 2-[(2-ethoxy-2-oxoethoxy)carbonyl]benzoate SMILES: CCOC(=O)COC(=O)C1=CC=CC=C1C(=O)OCC

PubChem CID 6785
CAS 84-72-0
Molecular Weight (g/mol) 280.28
MDL Number MFCD00059377
SMILES CCOC(=O)COC(=O)C1=CC=CC=C1C(=O)OCC
Synonym Ethoxycarbonylmethyl Ethyl Phthalate, Phthalic Acid Ethoxycarbonylmethyl Ethyl Ester
IUPAC Name ethyl 2-[(2-ethoxy-2-oxoethoxy)carbonyl]benzoate
InChI Key PZBLUWVMZMXIKZ-UHFFFAOYSA-N
Molecular Formula C14H16O6
4,863

Ethyl all cis-5,8,11,14,17-Eicosapentaenoate 96.0+%, TCI America™

CAS: 86227-47-6 Molecular Formula: C22H34O2 Molecular Weight (g/mol): 330.512 MDL Number: MFCD00673476 InChI Key: SSQPWTVBQMWLSZ-AAQCHOMXSA-N Synonym: all cis-5,8,11,14,17-Eicosapentaenoic Acid Ethyl Ester, EPA Ethyl Ester, Ethyl all cis-5,8,11,14,17-Icosapentaenoate PubChem CID: 9831415 ChEBI: CHEBI:84883 IUPAC Name: ethyl (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoate SMILES: CCC=CCC=CCC=CCC=CCC=CCCCC(=O)OCC

PubChem CID 9831415
CAS 86227-47-6
Molecular Weight (g/mol) 330.512
ChEBI CHEBI:84883
MDL Number MFCD00673476
SMILES CCC=CCC=CCC=CCC=CCC=CCCCC(=O)OCC
Synonym all cis-5,8,11,14,17-Eicosapentaenoic Acid Ethyl Ester, EPA Ethyl Ester, Ethyl all cis-5,8,11,14,17-Icosapentaenoate
IUPAC Name ethyl (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoate
InChI Key SSQPWTVBQMWLSZ-AAQCHOMXSA-N
Molecular Formula C22H34O2
4,864

Ethyl 3-Ethoxyacrylate (cis- and trans- mixture) 98.0+%, TCI America™

CAS: 1001-26-9 Molecular Formula: C7H12O3 Molecular Weight (g/mol): 144.17 MDL Number: MFCD00009863 InChI Key: ITQFPVUDTFABDH-AATRIKPKSA-N PubChem CID: 5366269 IUPAC Name: ethyl (E)-3-ethoxyprop-2-enoate SMILES: CCOC=CC(=O)OCC

PubChem CID 5366269
CAS 1001-26-9
Molecular Weight (g/mol) 144.17
MDL Number MFCD00009863
SMILES CCOC=CC(=O)OCC
IUPAC Name ethyl (E)-3-ethoxyprop-2-enoate
InChI Key ITQFPVUDTFABDH-AATRIKPKSA-N
Molecular Formula C7H12O3
4,865

Ethanesulfonic Acid 90.0+%, TCI America™

CAS: 594-45-6 Molecular Formula: C2H5O3S Molecular Weight (g/mol): 109.12 MDL Number: MFCD00007529 InChI Key: CCIVGXIOQKPBKL-UHFFFAOYSA-M Synonym: ethylsulfonic acid,ethanesulphonic acid,ethane sulfonate,ethane sulfonic acid,ethane sulphonic acid,ethansulfonic acid,ethylsulphonic acid,1-ethanesulfonic acid,2-ethanesulfonic acid,ethanesulfonicacid PubChem CID: 11668 ChEBI: CHEBI:42465 IUPAC Name: ethanesulfonate SMILES: CCS([O-])(=O)=O

PubChem CID 11668
CAS 594-45-6
Molecular Weight (g/mol) 109.12
ChEBI CHEBI:42465
MDL Number MFCD00007529
SMILES CCS([O-])(=O)=O
Synonym ethylsulfonic acid,ethanesulphonic acid,ethane sulfonate,ethane sulfonic acid,ethane sulphonic acid,ethansulfonic acid,ethylsulphonic acid,1-ethanesulfonic acid,2-ethanesulfonic acid,ethanesulfonicacid
IUPAC Name ethanesulfonate
InChI Key CCIVGXIOQKPBKL-UHFFFAOYSA-M
Molecular Formula C2H5O3S
4,866

Ethyl 4-Hydroxy-3-methoxycinnamate 97.0+%, TCI America™

CAS: 4046-02-0 Molecular Formula: C12H14O4 Molecular Weight (g/mol): 222.24 MDL Number: MFCD00009190 InChI Key: ATJVZXXHKSYELS-FNORWQNLSA-N Synonym: ethyl ferulate,ferulic acid ethyl ester,ethyl 3-4-hydroxy-3-methoxyphenyl acrylate,unii-5b8915uelw,ethyl 4'-hydroxy-3'-methoxycinnamate,e-ethyl 3-4-hydroxy-3-methoxyphenyl acrylate,ethyl 2e-3-4-hydroxy-3-methoxyphenyl prop-2-enoate,ethyl 4-hydroxy-3-methoxycinnamate,e-3-4-hydroxy-3-methoxy-phenyl-acrylic acid ethyl ester,ethyl 4-hydroxy-3-methoxycinnamate ferulic acid ethyl ester PubChem CID: 736681 IUPAC Name: ethyl (E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate SMILES: CCOC(=O)C=CC1=CC(=C(C=C1)O)OC

PubChem CID 736681
CAS 4046-02-0
Molecular Weight (g/mol) 222.24
MDL Number MFCD00009190
SMILES CCOC(=O)C=CC1=CC(=C(C=C1)O)OC
Synonym ethyl ferulate,ferulic acid ethyl ester,ethyl 3-4-hydroxy-3-methoxyphenyl acrylate,unii-5b8915uelw,ethyl 4'-hydroxy-3'-methoxycinnamate,e-ethyl 3-4-hydroxy-3-methoxyphenyl acrylate,ethyl 2e-3-4-hydroxy-3-methoxyphenyl prop-2-enoate,ethyl 4-hydroxy-3-methoxycinnamate,e-3-4-hydroxy-3-methoxy-phenyl-acrylic acid ethyl ester,ethyl 4-hydroxy-3-methoxycinnamate ferulic acid ethyl ester
IUPAC Name ethyl (E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate
InChI Key ATJVZXXHKSYELS-FNORWQNLSA-N
Molecular Formula C12H14O4
4,867

6-Ethoxy-2-naphthaleneboronic Acid (contains varying amounts of Anhydride), TCI America™

CAS: 352525-98-5 Molecular Formula: C12H13BO3 Molecular Weight (g/mol): 216.04 MDL Number: MFCD03427009 InChI Key: INXXVGFSXYJGHI-UHFFFAOYSA-N IUPAC Name: (6-ethoxynaphthalen-2-yl)boronic acid SMILES: CCOC1=CC2=CC=C(C=C2C=C1)B(O)O

CAS 352525-98-5
Molecular Weight (g/mol) 216.04
MDL Number MFCD03427009
SMILES CCOC1=CC2=CC=C(C=C2C=C1)B(O)O
IUPAC Name (6-ethoxynaphthalen-2-yl)boronic acid
InChI Key INXXVGFSXYJGHI-UHFFFAOYSA-N
Molecular Formula C12H13BO3
4,868

4-(Ethoxycarbonyl)phenylboronic Acid (contains varying amounts of Anhydride), TCI America™

CAS: 4334-88-7 Molecular Formula: C9H11BO4 Molecular Weight (g/mol): 193.99 MDL Number: MFCD02179441 InChI Key: ZLNFACCFYUFTLD-UHFFFAOYSA-N PubChem CID: 2734350 IUPAC Name: [4-(ethoxycarbonyl)phenyl]boronic acid SMILES: CCOC(=O)C1=CC=C(C=C1)B(O)O

PubChem CID 2734350
CAS 4334-88-7
Molecular Weight (g/mol) 193.99
MDL Number MFCD02179441
SMILES CCOC(=O)C1=CC=C(C=C1)B(O)O
IUPAC Name [4-(ethoxycarbonyl)phenyl]boronic acid
InChI Key ZLNFACCFYUFTLD-UHFFFAOYSA-N
Molecular Formula C9H11BO4
4,869

Trimethyl 1,3,5-Benzenetricarboxylate 98.0+%, TCI America™

CAS: 2672-58-4 Molecular Formula: C12H12O6 Molecular Weight (g/mol): 252.222 MDL Number: MFCD00008434 InChI Key: RGCHNYAILFZUPL-UHFFFAOYSA-N Synonym: trimethyl 1,3,5-benzenetricarboxylate,trimethyl trimesate,trimesic acid trimethyl ester,1,3,5-benzenetricarboxylic acid, trimethyl ester,1,3,5-benzenetricarboxylic acid trimethyl ester,trimethylbenzene-1,3,5-tricarboxylate,1,3,5-trimethyl benzene-1,3,5-tricarboxylate,methyl 3,5-bis methoxycarbonyl benzoate,benzene-1,3,5-tricarboxylic acid trimethyl ester,timtec-bb sbb007766 PubChem CID: 75881 IUPAC Name: trimethyl benzene-1,3,5-tricarboxylate SMILES: COC(=O)C1=CC(=CC(=C1)C(=O)OC)C(=O)OC

PubChem CID 75881
CAS 2672-58-4
Molecular Weight (g/mol) 252.222
MDL Number MFCD00008434
SMILES COC(=O)C1=CC(=CC(=C1)C(=O)OC)C(=O)OC
Synonym trimethyl 1,3,5-benzenetricarboxylate,trimethyl trimesate,trimesic acid trimethyl ester,1,3,5-benzenetricarboxylic acid, trimethyl ester,1,3,5-benzenetricarboxylic acid trimethyl ester,trimethylbenzene-1,3,5-tricarboxylate,1,3,5-trimethyl benzene-1,3,5-tricarboxylate,methyl 3,5-bis methoxycarbonyl benzoate,benzene-1,3,5-tricarboxylic acid trimethyl ester,timtec-bb sbb007766
IUPAC Name trimethyl benzene-1,3,5-tricarboxylate
InChI Key RGCHNYAILFZUPL-UHFFFAOYSA-N
Molecular Formula C12H12O6
4,870

Ethyl 2-Thiophenecarboxylate 98.0+%, TCI America™

CAS: 2810-04-0 Molecular Formula: C7H8O2S Molecular Weight (g/mol): 156.20 MDL Number: MFCD00005436 InChI Key: JZGZKRJVTIRPOK-UHFFFAOYSA-N Synonym: ethyl 2-thiophenecarboxylate,ethyl 2-thenoate,ethyl-2-thiophenecarboxylate,thiophene-2-carboxylic acid ethyl ester,2-thiophenecarboxylic acid ethyl ester,thiophene, 2-ethyl carboxylate,thiophenecarboxylic acid, ethyl ester,ethylthiophen-2-carboxylat,ethyl2-thiophenecarboxylate,acmc-209h0w PubChem CID: 76052 IUPAC Name: ethyl thiophene-2-carboxylate SMILES: CCOC(=O)C1=CC=CS1

PubChem CID 76052
CAS 2810-04-0
Molecular Weight (g/mol) 156.20
MDL Number MFCD00005436
SMILES CCOC(=O)C1=CC=CS1
Synonym ethyl 2-thiophenecarboxylate,ethyl 2-thenoate,ethyl-2-thiophenecarboxylate,thiophene-2-carboxylic acid ethyl ester,2-thiophenecarboxylic acid ethyl ester,thiophene, 2-ethyl carboxylate,thiophenecarboxylic acid, ethyl ester,ethylthiophen-2-carboxylat,ethyl2-thiophenecarboxylate,acmc-209h0w
IUPAC Name ethyl thiophene-2-carboxylate
InChI Key JZGZKRJVTIRPOK-UHFFFAOYSA-N
Molecular Formula C7H8O2S
4,871

Octadecyl Thioglycolate 50.0+%, TCI America™

CAS: 10220-46-9 Molecular Formula: C20H40O2S Molecular Weight (g/mol): 344.60 MDL Number: MFCD00022084 InChI Key: JQTFPHLEQLLQOT-UHFFFAOYSA-N Synonym: Mercaptoacetic Acid Octadecyl Ester, Thioglycolic Acid Octadecyl Ester, Stearyl Thioglycolate, Thioglycolic Acid Stearyl Ester PubChem CID: 82462 IUPAC Name: octadecyl 2-sulfanylacetate SMILES: CCCCCCCCCCCCCCCCCCOC(=O)CS

PubChem CID 82462
CAS 10220-46-9
Molecular Weight (g/mol) 344.60
MDL Number MFCD00022084
SMILES CCCCCCCCCCCCCCCCCCOC(=O)CS
Synonym Mercaptoacetic Acid Octadecyl Ester, Thioglycolic Acid Octadecyl Ester, Stearyl Thioglycolate, Thioglycolic Acid Stearyl Ester
IUPAC Name octadecyl 2-sulfanylacetate
InChI Key JQTFPHLEQLLQOT-UHFFFAOYSA-N
Molecular Formula C20H40O2S
4,872

2-(p-Toluenesulfonyloxy)acetic Acid 97.0+%, TCI America™

CAS: 39794-77-9 Molecular Formula: C9H10O5S Molecular Weight (g/mol): 230.234 MDL Number: MFCD00021764 InChI Key: NSORSORRXHLKQV-UHFFFAOYSA-N Synonym: 2-(Tosyloxy)acetic Acid PubChem CID: 226266 IUPAC Name: 2-(4-methylphenyl)sulfonyloxyacetic acid SMILES: CC1=CC=C(C=C1)S(=O)(=O)OCC(=O)O

PubChem CID 226266
CAS 39794-77-9
Molecular Weight (g/mol) 230.234
MDL Number MFCD00021764
SMILES CC1=CC=C(C=C1)S(=O)(=O)OCC(=O)O
Synonym 2-(Tosyloxy)acetic Acid
IUPAC Name 2-(4-methylphenyl)sulfonyloxyacetic acid
InChI Key NSORSORRXHLKQV-UHFFFAOYSA-N
Molecular Formula C9H10O5S
4,873

Tetradecyldimethyl(3-sulfopropyl)ammonium Hydroxide Inner Salt 98.0+%, TCI America™

CAS: 14933-09-6 Molecular Formula: C19H41NO3S Molecular Weight (g/mol): 363.601 MDL Number: MFCD00036910 InChI Key: BHATUINFZWUDIX-UHFFFAOYSA-N Synonym: myristyl sulfobetaine,zwittergent 3-14,n-tetradecyl-n,n-dimethyl-3-ammonio-1-propanesulfonate,3-dimethyl tetradecyl ammonio propane-1-sulfonate,3-n,n-dimethylmyristylammonio propanesulfonate,dimethyl 3-sulphonatopropyl tetradecylammonium,zwittergent™ 3-14 detergent,3-myristyldimethylammonio propanesulfonate,3-n,n-dimethyltetradecylammonio propanesulfonate PubChem CID: 84705 ChEBI: CHEBI:10129 IUPAC Name: 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate SMILES: CCCCCCCCCCCCCC[N+](C)(C)CCCS(=O)(=O)[O-]

PubChem CID 84705
CAS 14933-09-6
Molecular Weight (g/mol) 363.601
ChEBI CHEBI:10129
MDL Number MFCD00036910
SMILES CCCCCCCCCCCCCC[N+](C)(C)CCCS(=O)(=O)[O-]
Synonym myristyl sulfobetaine,zwittergent 3-14,n-tetradecyl-n,n-dimethyl-3-ammonio-1-propanesulfonate,3-dimethyl tetradecyl ammonio propane-1-sulfonate,3-n,n-dimethylmyristylammonio propanesulfonate,dimethyl 3-sulphonatopropyl tetradecylammonium,zwittergent™ 3-14 detergent,3-myristyldimethylammonio propanesulfonate,3-n,n-dimethyltetradecylammonio propanesulfonate
IUPAC Name 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate
InChI Key BHATUINFZWUDIX-UHFFFAOYSA-N
Molecular Formula C19H41NO3S
4,874

Tetrakis(acetonitrile)palladium(II) Bis(trifluoromethanesulfonate) 95.0+%, TCI America™

CAS: 68569-14-2 Molecular Formula: C10H12F6N4O6PdS2 Molecular Weight (g/mol): 568.758 InChI Key: KXRMHIBEZBOSNG-UHFFFAOYSA-L Synonym: Tetrakis(acetonitrile)palladium(II) Ditriflate PubChem CID: 22755518 IUPAC Name: acetonitrile;palladium(2+);trifluoromethanesulfonate SMILES: CC#N.CC#N.CC#N.CC#N.C(F)(F)(F)S(=O)(=O)[O-].C(F)(F)(F)S(=O)(=O)[O-].[Pd+2]

PubChem CID 22755518
CAS 68569-14-2
Molecular Weight (g/mol) 568.758
SMILES CC#N.CC#N.CC#N.CC#N.C(F)(F)(F)S(=O)(=O)[O-].C(F)(F)(F)S(=O)(=O)[O-].[Pd+2]
Synonym Tetrakis(acetonitrile)palladium(II) Ditriflate
IUPAC Name acetonitrile;palladium(2+);trifluoromethanesulfonate
InChI Key KXRMHIBEZBOSNG-UHFFFAOYSA-L
Molecular Formula C10H12F6N4O6PdS2
4,875

Tetrabromo-o-sulfobenzoic Anhydride 98.0+%, TCI America™

CAS: 68460-01-5 Molecular Formula: C7Br4O4S Molecular Weight (g/mol): 499.749 MDL Number: MFCD00009745 InChI Key: QPGYGIVRJIICGZ-UHFFFAOYSA-N PubChem CID: 110335 IUPAC Name: 4,5,6,7-tetrabromo-1,1-dioxo-2,1$l^{6}-benzoxathiol-3-one SMILES: C12=C(C(=C(C(=C1Br)Br)Br)Br)S(=O)(=O)OC2=O

PubChem CID 110335
CAS 68460-01-5
Molecular Weight (g/mol) 499.749
MDL Number MFCD00009745
SMILES C12=C(C(=C(C(=C1Br)Br)Br)Br)S(=O)(=O)OC2=O
IUPAC Name 4,5,6,7-tetrabromo-1,1-dioxo-2,1$l^{6}-benzoxathiol-3-one
InChI Key QPGYGIVRJIICGZ-UHFFFAOYSA-N
Molecular Formula C7Br4O4S