Croconic acid or 4,5-dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or (C=O)3(COH)2. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms. It is sensitive to light,[1] soluble in water and ethanol[2] and forms yellow crystals that decompose at 212 °C.[3]
The compound is acidic and loses the protons from the hydroxyl groups (pKa1 = 0.80±0.08 and pKa2 = 2.24±0.01 at 25 °C).[4][5] The resulting anions, hydrogencroconateC5HO−5[1] and croconateC5O2−5 are also quite stable. The croconate ion, in particular, is aromatic[6] and symmetric, as the double bond and the negative charges become delocalized over the five CO units (with two electrons, Hückel's rule means this is an aromatic configuration). The lithium, sodium and potassium croconates crystallize from water as dihydrates[7] but the orange potassium salt can be dehydrated to form a monohydrate.[1][4] The croconates of ammonium, rubidium and caesium crystallize in the anhydrous form.[7] Salts of barium, lead, silver, and others[specify] are also known.[1]
Croconic acid also forms ethers such as dimethyl croconate where the hydrogen atom of the hydroxyl group is substituted with an alkyl group.
Croconic acid and potassium croconate dihydrate were discovered by Leopold Gmelin in 1825, who named the compounds from Greek κρόκος meaning "crocus" or "egg yolk".[7] The structure of ammonium croconate was determined by Baenziger et al. in 1964. The structure of K2C5O5·2H2O was determined by Dunitz in 2001.[8]
Structure
In the solid state, croconic acid has a peculiar structure consisting of pleated strips, each "page" of the strip being a planar ring of 4 molecules of C5O5H2 held together by hydrogen bonds.[7] In dioxane it has a large dipole moment of 9–10 D, while the free molecule is estimated to have a dipole of 7–7.5 D.[9] The solid is ferroelectric with a Curie point above 400 K (127 °C), indeed the organic crystal with the highest spontaneous polarization (about 20 μC/cm2). This is due to proton transfer between adjacent molecules in each pleated sheet, rather than molecular rotation.[9]
In the solid alkali metal salts, the croconate anions and the alkali cations form parallel columns.[7] In the mixed salt K3(HC5O5)(C5O5)·2H2O, which formally contains both one croconate dianion C5O2−5 and one hydrogencroconate monoanion (HC5O−5), the hydrogen is shared equally by two adjacent croconate units.[7]
Salts of the croconate anion and its derivatives are of interest in supramolecular chemistry research because of their potential for π-stacking effects, where the delocalized electrons of two stacked croconate anions interact.[10]
Infrared and Raman assignments indicate that the equalization of the carbon–carbon bond lengths, thus the electronic delocalization, follows with an increase in counter-ion size for salts.[6] This result leads to a further interpretation that the degree of aromaticity is enhanced for salts as a function of the size of the counter-ion. The same study provided quantum mechanical DFT calculations for the optimized structures and vibrational spectra which were in agreement with experimental findings. The values for calculated theoretical indices of aromaticity also increased with counterion size.
The croconate anion forms hydrated crystalline coordination compounds with divalent cations of transition metals, with general formula M(C5O5)·3H2O; where M stands for copper (yielding a brown solid), iron (dark purple), zinc (yellow), nickel (green), manganese (dark green), or cobalt (purple). These complexes all have the same orthorombic crystal structure, consisting of chains of alternating croconate and metal ions. Each croconate is bound to the preceding metal by one oxygen atom, and to the next metal through its two opposite oxygens, leaving two oxygens unbound. Each metal is bound to three croconate oxygens and to one water molecule.[11]Calcium also forms a compound with the same formula (yellow) but the structure appears to be different.[11]
The croconate anion also forms compounds with trivalent cations such as aluminium (yellow), chromium (brown), and iron (purple). These compounds also include hydroxyl groups as well as hydration water and have a more complicated crystal structure.[11] No indication was found of sandwich-type bonds between the delocalized electrons and the metal (as are seen in ferrocene, for example),[11] but the anion can form metal complexes with a large variety of bonding patterns, involving from only one to all five of its oxygen atoms.[12][13][14]
^ abcdYamada, K.; Mizuno, N.; Hirata, Y. (1958). "Structure of croconic acid". Bulletin of the Chemical Society of Japan. 31 (5): 543–549. doi:10.1246/bcsj.31.543.
^Miller, W. A. (1868). Elements of Chemistry: Theoretical and Practical (4th ed.). Longmans.[page needed]
^ abSchwartz, L. M.; Gelb, R. I.; Yardley, J. O. (1975). "Aqueous dissociation of croconic Acid". Journal of Physical Chemistry. 79 (21): 2246–2251. doi:10.1021/j100588a009.
^Gelb, R. I.; Schwartz, L. M.; Laufer, D. A.; Yardley, J. O. (1977). "The structure of aqueous croconic acid". Journal of Physical Chemistry. 81 (13): 1268–1274. doi:10.1021/j100528a010.
^ abGeorgopoulos, S. L.; Diniz, R.; Yoshida, M. I.; Speziali, N. L.; Dos Santos, H. F.; Junqueira, G. M. A.; de Oliveira, L. F. C. (2006). "Vibrational spectroscopy and aromaticity investigation of squarate salts: A theoretical and experimental approach". Journal of Molecular Structure. 794 (1–3): 63–70. Bibcode:2006JMoSt.794...63G. doi:10.1016/j.molstruc.2006.01.035.
^ abcdefBraga, D.; Maini, L.; Grepioni, F. (2002). "Croconic acid and alkali metal croconate salts: Some new insights into an old story". Chemistry – A European Journal. 8 (8): 1804–1812. doi:10.1002/1521-3765(20020415)8:8<1804::AID-CHEM1804>3.0.CO;2-C. PMID 11933108.
^Dunitz, J. D.; Seiler, P.; Czechtizky, W. (2001). "Crystal structure of potassium croconate dihydrate, after 175 years". Angewandte Chemie International Edition. 40 (9): 1779–1780. doi:10.1002/1521-3773(20010504)40:9<1779::AID-ANIE17790>3.0.CO;2-6. PMID 11353510.
^Faria, L. F. O.; Soares, A. L., Jr.; Diniz, R.; Yoshida, M. I.; Edwards, H. G. M.; de Oliveira, L. F. C. (2010). "Mixed salts containing croconate violet, lanthanide and potassium ions: Crystal structures and spectroscopic characterization of supramolecular compounds". Inorganica Chimica Acta. 363 (1): 49–56. doi:10.1016/j.ica.2009.09.050.
^ abcdWest, R.; Niu, H. Y. (1963). "New aromatic anions. VI. Complexes of croconate ion with some divalent and trivalent metals (Complexes of divalent transition metal croconates and trivalent metal croconates)". Journal of the American Chemical Society. 85 (17): 2586. doi:10.1021/ja00900a013.
^Carranza, J.; Sletten, J.; Lloret, F.; Julve, M. (2009). "Manganese(II) complexes with croconate and 2-(2-pyridyl)imidazole ligands: Syntheses, X-ray structures and magnetic properties". Inorganica Chimica Acta. 362 (8): 2636–2642. doi:10.1016/j.ica.2008.12.002.
^M., S. C.; Ghosh, A. K.; Zangrando, E.; Chaudhuri, N. R. (2007). "3D supramolecular networks of Co(II)/Fe(II) using the croconate dianion and a bipyridyl spacer: Synthesis, crystal structure and thermal study". Polyhedron. 26 (5): 1105–1112. doi:10.1016/j.poly.2006.09.100.
^Wang, Chih-Chieh; Ke, Meu-Ju; Tsai, Cheng-Hsiao; Chen, I-Hsuan; Lin, Shin-I; Lin, Tzuen-Yeuan; Wu, Li-Mei; Lee, Gene-Hsiang; Sheu, Hwo-Shuenn; Fedorov, Vladimir E. (2009-02-04). "[M(C5O5)2(H2O)n]2− as a Building Block for Hetero- and Homo-bimetallic Coordination Polymers: From 1D Chains to 3D Supramolecular Architectures". Crystal Growth & Design. 9 (2): 1013–1019. doi:10.1021/cg800827a. ISSN 1528-7483.
External links
Media related to Croconic acid at Wikimedia Commons
January 20, 2023
croconic, acid, confused, with, crocinic, acid, dihydroxycyclopentenetrione, chemical, compound, with, formula, c5h2o5, cyclopentene, backbone, with, hydroxyl, groups, adjacent, double, bond, three, ketone, groups, remaining, carbon, atoms, sensitive, light, s. Not to be confused with Crocinic acid Croconic acid or 4 5 dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or C O 3 COH 2 It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms It is sensitive to light 1 soluble in water and ethanol 2 and forms yellow crystals that decompose at 212 C 3 Croconic acid NamesPreferred IUPAC name 4 5 Dihydroxycyclopent 4 ene 1 2 3 trioneOther names Crocic acidIdentifiersCAS Number 488 86 8 Y3D model JSmol Interactive imageChemSpider 476003 NECHA InfoCard 100 201 686PubChem CID 546874UNII 6HGY35UXAA YCompTox Dashboard EPA DTXSID20878763InChI InChI 1S C5H2O5 c6 1 2 7 4 9 5 10 3 1 8 h6 7H NKey RBSLJAJQOVYTRQ UHFFFAOYSA N NInChI 1 C5H2O5 c6 1 2 7 4 9 5 10 3 1 8 h6 7HKey RBSLJAJQOVYTRQ UHFFFAOYATSMILES O C1C O C O C O C1 OPropertiesChemical formula C5H2O5Molar mass 142 07Melting point gt 300 C 572 F 573 K decomposes Acidity pKa 0 80 2 24Except where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa N verify what is Y N Infobox references The compound is acidic and loses the protons from the hydroxyl groups pKa1 0 80 0 08 and pKa2 2 24 0 01 at 25 C 4 5 The resulting anions hydrogencroconate C5HO 5 1 and croconate C5O2 5 are also quite stable The croconate ion in particular is aromatic 6 and symmetric as the double bond and the negative charges become delocalized over the five CO units with two electrons Huckel s rule means this is an aromatic configuration The lithium sodium and potassium croconates crystallize from water as dihydrates 7 but the orange potassium salt can be dehydrated to form a monohydrate 1 4 The croconates of ammonium rubidium and caesium crystallize in the anhydrous form 7 Salts of barium lead silver and others specify are also known 1 Croconic acid also forms ethers such as dimethyl croconate where the hydrogen atom of the hydroxyl group is substituted with an alkyl group Contents 1 History 2 Structure 3 See also 4 References 5 External linksHistory EditCroconic acid and potassium croconate dihydrate were discovered by Leopold Gmelin in 1825 who named the compounds from Greek krokos meaning crocus or egg yolk 7 The structure of ammonium croconate was determined by Baenziger et al in 1964 The structure of K2C5O5 2H2O was determined by Dunitz in 2001 8 Structure EditIn the solid state croconic acid has a peculiar structure consisting of pleated strips each page of the strip being a planar ring of 4 molecules of C5O5H2 held together by hydrogen bonds 7 In dioxane it has a large dipole moment of 9 10 D while the free molecule is estimated to have a dipole of 7 7 5 D 9 The solid is ferroelectric with a Curie point above 400 K 127 C indeed the organic crystal with the highest spontaneous polarization about 20 mC cm2 This is due to proton transfer between adjacent molecules in each pleated sheet rather than molecular rotation 9 In the solid alkali metal salts the croconate anions and the alkali cations form parallel columns 7 In the mixed salt K3 HC5O5 C5O5 2H2O which formally contains both one croconate dianion C5O2 5 and one hydrogencroconate monoanion HC5O 5 the hydrogen is shared equally by two adjacent croconate units 7 Salts of the croconate anion and its derivatives are of interest in supramolecular chemistry research because of their potential for p stacking effects where the delocalized electrons of two stacked croconate anions interact 10 Infrared and Raman assignments indicate that the equalization of the carbon carbon bond lengths thus the electronic delocalization follows with an increase in counter ion size for salts 6 This result leads to a further interpretation that the degree of aromaticity is enhanced for salts as a function of the size of the counter ion The same study provided quantum mechanical DFT calculations for the optimized structures and vibrational spectra which were in agreement with experimental findings The values for calculated theoretical indices of aromaticity also increased with counterion size The croconate anion forms hydrated crystalline coordination compounds with divalent cations of transition metals with general formula M C5O5 3H2O where M stands for copper yielding a brown solid iron dark purple zinc yellow nickel green manganese dark green or cobalt purple These complexes all have the same orthorombic crystal structure consisting of chains of alternating croconate and metal ions Each croconate is bound to the preceding metal by one oxygen atom and to the next metal through its two opposite oxygens leaving two oxygens unbound Each metal is bound to three croconate oxygens and to one water molecule 11 Calcium also forms a compound with the same formula yellow but the structure appears to be different 11 The croconate anion also forms compounds with trivalent cations such as aluminium yellow chromium brown and iron purple These compounds also include hydroxyl groups as well as hydration water and have a more complicated crystal structure 11 No indication was found of sandwich type bonds between the delocalized electrons and the metal as are seen in ferrocene for example 11 but the anion can form metal complexes with a large variety of bonding patterns involving from only one to all five of its oxygen atoms 12 13 14 See also EditCroconate violet Croconate blue Rhodizonic acid Squaric acid Deltic acid Cyclopentanepentone leuconic acid References Edit a b c d Yamada K Mizuno N Hirata Y 1958 Structure of croconic acid Bulletin of the Chemical Society of Japan 31 5 543 549 doi 10 1246 bcsj 31 543 Miller W A 1868 Elements of Chemistry Theoretical and Practical 4th ed Longmans page needed Turner E Elements of Chemistry page needed a b Schwartz L M Gelb R I Yardley J O 1975 Aqueous dissociation of croconic Acid Journal of Physical Chemistry 79 21 2246 2251 doi 10 1021 j100588a009 Gelb R I Schwartz L M Laufer D A Yardley J O 1977 The structure of aqueous croconic acid Journal of Physical Chemistry 81 13 1268 1274 doi 10 1021 j100528a010 a b Georgopoulos S L Diniz R Yoshida M I Speziali N L Dos Santos H F Junqueira G M A de Oliveira L F C 2006 Vibrational spectroscopy and aromaticity investigation of squarate salts A theoretical and experimental approach Journal of Molecular Structure 794 1 3 63 70 Bibcode 2006JMoSt 794 63G doi 10 1016 j molstruc 2006 01 035 a b c d e f Braga D Maini L Grepioni F 2002 Croconic acid and alkali metal croconate salts Some new insights into an old story Chemistry A European Journal 8 8 1804 1812 doi 10 1002 1521 3765 20020415 8 8 lt 1804 AID CHEM1804 gt 3 0 CO 2 C PMID 11933108 Dunitz J D Seiler P Czechtizky W 2001 Crystal structure of potassium croconate dihydrate after 175 years Angewandte Chemie International Edition 40 9 1779 1780 doi 10 1002 1521 3773 20010504 40 9 lt 1779 AID ANIE17790 gt 3 0 CO 2 6 PMID 11353510 a b Horiuchi S Tokunaga Y Giovannetti G Picozzi S Itoh H Shimano R Kumai R Tokura Y 2010 Above room temperature ferroelectricity in a single component molecular crystal Nature 463 7282 789 92 Bibcode 2010Natur 463 789H doi 10 1038 nature08731 PMID 20148035 S2CID 205219520 Faria L F O Soares A L Jr Diniz R Yoshida M I Edwards H G M de Oliveira L F C 2010 Mixed salts containing croconate violet lanthanide and potassium ions Crystal structures and spectroscopic characterization of supramolecular compounds Inorganica Chimica Acta 363 1 49 56 doi 10 1016 j ica 2009 09 050 a b c d West R Niu H Y 1963 New aromatic anions VI Complexes of croconate ion with some divalent and trivalent metals Complexes of divalent transition metal croconates and trivalent metal croconates Journal of the American Chemical Society 85 17 2586 doi 10 1021 ja00900a013 Carranza J Sletten J Lloret F Julve M 2009 Manganese II complexes with croconate and 2 2 pyridyl imidazole ligands Syntheses X ray structures and magnetic properties Inorganica Chimica Acta 362 8 2636 2642 doi 10 1016 j ica 2008 12 002 M S C Ghosh A K Zangrando E Chaudhuri N R 2007 3D supramolecular networks of Co II Fe II using the croconate dianion and a bipyridyl spacer Synthesis crystal structure and thermal study Polyhedron 26 5 1105 1112 doi 10 1016 j poly 2006 09 100 Wang Chih Chieh Ke Meu Ju Tsai Cheng Hsiao Chen I Hsuan Lin Shin I Lin Tzuen Yeuan Wu Li Mei Lee Gene Hsiang Sheu Hwo Shuenn Fedorov Vladimir E 2009 02 04 M C5O5 2 H2O n 2 as a Building Block for Hetero and Homo bimetallic Coordination Polymers From 1D Chains to 3D Supramolecular Architectures Crystal Growth amp Design 9 2 1013 1019 doi 10 1021 cg800827a ISSN 1528 7483 External links Edit Media related to Croconic acid at Wikimedia Commons Retrieved from https en wikipedia org w index php title Croconic acid amp oldid 1117341667, wikipedia, wiki, book, books, library,
