Croconic acid

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Croconic acid
Croconic acid.svg
Croconic-acid-3D-balls.png
Croconic-acid-3D-spacefill.png
Names
Preferred IUPAC name
4,5-Dihydroxycyclopent-4-ene-1,2,3-trione
Other names
Crocic acid
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.201.686 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/C5H2O5/c6-1-2(7)4(9)5(10)3(1)8/h6-7H Yes check.svgY
    Key: RBSLJAJQOVYTRQ-UHFFFAOYSA-N Yes check.svgY
  • O=C1C(O)=C(O)C(=O)C1=O
Properties
C5H2O5
Molar mass 142.07
Melting point >300 °C (572 °F; 573 K) (decomposes)
Acidity (pKa)0.80, 2.24
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Croconic acid (also known as 4,5-dihydroxycyclopentenetrione, crocic acid or pentagonic acid) 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]

Contents

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.

History

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 orthorhombic 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]

Croconate dianion Croconate dianion.svg
Croconate dianion

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

Related Research Articles

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In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group or hydrogen in the case of formyl group. In organic chemistry, the acyl group is usually derived from a carboxylic acid, in which case it has the formula R−C(=O)−, where R represents an organyl group or hydrogen. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond.

<span class="mw-page-title-main">Cyanate</span> Anion with formula OCN and charge –1

The cyanate ion is an anion with the chemical formula OCN−. It is a resonance of three forms: [O−−C≡N] (61%) ↔ [O=C=N−] (30%) ↔ [O+≡C−N2−] (4%).

<span class="mw-page-title-main">18-Crown-6</span> Chemical compound

18-Crown-6 is an organic compound with the formula [C2H4O]6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M−1). The point group of 18-crown-6 is S6. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is 2.76 ± 0.06 D in cyclohexane and 2.73 ± 0.02 in benzene. The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen.

<span class="mw-page-title-main">Carbenium ion</span> Class of ions

A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with carbon atom having three covalent bonds, and it bears a +1 formal charge. But IUPAC confuses coordination number with valence, incorrectly considering carbon in carbenium as trivalent.

Pyrylium is a cation with formula C5H5O+, consisting of a six-membered ring of five carbon atoms, each with one hydrogen atom, and one positively charged oxygen atom. The bonds in the ring are conjugated as in benzene, giving it an aromatic character. In particular, because of the positive charge, the oxygen atom is trivalent. Pyrilium is a mono-cyclic and heterocyclic compound, one of the oxonium ions.

<span class="mw-page-title-main">Keggin structure</span> Best known structural form for heteropoly acids

The Keggin structure is the best known structural form for heteropoly acids. It is the structural form of α-Keggin anions, which have a general formula of [XM12O40]n−, where X is the heteroatom, M is the addendum atom, and O represents oxygen. The structure self-assembles in acidic aqueous solution and is a commonly used type of polyoxometalate catalysts.

<span class="mw-page-title-main">Potassium ferrioxalate</span> Chemical compound

Potassium ferrioxalate, also called potassium trisoxalatoferrate or potassium tris(oxalato)ferrate(III) is a chemical compound with the formula K3[Fe(C2O4)3]. It often occurs as the trihydrate K3[Fe(C2O4)3]·3H2O. Both are crystalline compounds, lime green in colour.

A carbon–oxygen bond is a polar covalent bond between atoms of carbon and oxygen. Carbon–oxygen bonds are found in many inorganic compounds such as carbon oxides and oxohalides, carbonates and metal carbonyls, and in organic compounds such as alcohols, ethers, carbonyl compounds and oxalates. Oxygen has 6 valence electrons of its own and tends to fill its outer shell with 8 electrons by sharing electrons with other atoms to form covalent bonds, accepting electrons to form an anion, or a combination of the two. In neutral compounds, an oxygen atom can form up to two single bonds or one double bond with carbon, while a carbon atom can form up to four single bonds or two double bonds with oxygen.

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Tetrahydroxy-1,4-benzoquinone, also called tetrahydroxy-p-benzoquinone, tetrahydroxybenzoquinone, or tetrahydroxyquinone, is an organic compound with formula C6O2(OH)4. Its molecular structure consists of a cyclohexadiene ring with four hydroxyl groups and two ketone groups in opposite (para) positions.

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Deltic acid is a chemical substance with the chemical formula C3O(OH)2. It can be viewed as a ketone and double enol of cyclopropene. At room temperature, it is a stable white solid, soluble in diethyl ether, that decomposes between 140 °C and 180 °C, and reacts slowly with water.

<span class="mw-page-title-main">Rhodizonic acid</span> Chemical compound

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<span class="mw-page-title-main">Disulfite</span> Chemical compound

A disulfite, commonly known as metabisulfite or pyrosulfite, is a chemical compound containing the ion S
2O2−
5. It is a colorless dianion that is primarily marketed in the form of sodium metabisulfite or potassium metabisulfite. When dissolved in water, these salts release the hydrogensulfite HSO−
3 anion. These salts act equivalently to sodium hydrogensulfite or potassium hydrogensulfite.

<span class="mw-page-title-main">Croconate violet</span>

Croconate violet or 1,3-bis(dicyanomethylene)croconate is a divalent anion with chemical formula C
11N
4O2−
3 or ((N≡C−)2C=)2(C5O3)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of two oxygen atoms by dicyanomethylene groups =C(−C≡N)2. Its systematic name is 3,5-bis(dicyanomethylene)-1,2,4-trionate. The term croconate violet as a dye name specifically refers to the dipotassium salt K
2C
11N
4O
3.

<span class="mw-page-title-main">1,2-Bis(dicyanomethylene)squarate</span>

1,2-Bis(dicyanomethylene)squarate is a divalent anion with chemical formula C
10N
4O2−
2 or ((N≡C−)2C=)2(C4O2)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion C
4O2−
4 through the replacement of two adjacent oxygen atoms by dicyanomethylene groups =C(−C≡N)2.

<span class="mw-page-title-main">1,3-Bis(dicyanomethylene)squarate</span>

1,3-Bis(dicyanomethylene)squarate is a divalent anion with chemical formula C
10N
4O2−
2 or ((N≡C−)2C=)2(C4O2)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion C
4O2−
4 through the replacement of two opposite oxygen atoms by dicyanomethylene groups =C(−C≡N)2.

<span class="mw-page-title-main">Croconate blue</span>

Croconate blue or 1,2,3-tris(dicyanomethylene)croconate is a divalent anion with chemical formula C
14N
6O2−
2 or ((N≡C−)2C=)3(C5O2)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of three oxygen atoms by dicyanomethylene groups =C(−C≡N)2. The term Croconate Blue as a dye name specifically refers to the dipotassium salt K
2C
14N
6O
2.

<span class="mw-page-title-main">2-(Dicyanomethylene)croconate</span> Ion

2-(Dicyanomethylene)croconate is a divalent anion with chemical formula C
8N
2O2−
4 or ((N≡C−)2C=)(C5O4)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of one oxygen atom by a dicyanomethylene group =C(−C≡N)2.

<span class="mw-page-title-main">Pseudo-oxocarbon anion</span>

In chemistry, the term pseudo-oxocarbon anion is used to refer to a negative ion that is conceptually derived from an oxocarbon anion through replacement of one or more of the basic oxygen atoms by chemically similar elements or functional groups, such as sulfur (S), selenium (Se), or dicyanomethylene (=C(CN)2).

<span class="mw-page-title-main">Cerium nitrates</span> Chemical compound

Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist.

The nickel organic acid salts are organic acid salts of nickel. In many of these the ionised organic acid acts as a ligand.

References

  1. 1 2 3 4 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.
  2. ↑ Miller, W. A. (1868). Elements of Chemistry: Theoretical and Practical (4th ed.). Longmans.[ page needed ]
  3. ↑ Turner, E. Elements of Chemistry.[ page needed ]
  4. 1 2 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.
  5. ↑ 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.
  6. 1 2 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.
  7. 1 2 3 4 5 6 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<1804::AID-CHEM1804>3.0.CO;2-C. PMID   11933108.
  8. ↑ 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.
  9. 1 2 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.
  10. ↑ 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.
  11. 1 2 3 4 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.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ 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.
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