15-Crown-5

15-Crown-5 is a crown ether with the formula (C₂H₄O)₅. It is a cyclic pentamer of ethylene oxide that forms complex with various cations, including sodium (Na⁺)^[2] and potassium (K⁺);^[3] however, it is complementary to Na⁺ and thus has a higher selectivity for Na⁺ ions.

15-Crown-5

Names
Preferred IUPAC name 1,4,7,10,13-Pentaoxacyclopentadecane[1]
Identifiers
CAS Number	33100-27-5 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1618144
ChEBI	CHEBI:32401 Y
ChEMBL	ChEMBL156289 Y
ChemSpider	33416 Y
ECHA InfoCard	100.046.694
EC Number	251-379-6
Gmelin Reference	3897
MeSH	15-Crown-5
PubChem CID	36336
RTECS number	SB0200000
CompTox Dashboard (EPA)	DTXSID7067746
InChI InChI=1S/C10H20O5/c1-2-12-5-6-14-9-10-15-8-7-13-4-3-11-1/h1-10H2 Y Key: VFTFKUDGYRBSAL-UHFFFAOYSA-N Y InChI=1/C10H20O5/c1-2-12-5-6-14-9-10-15-8-7-13-4-3-11-1/h1-10H2 Key: VFTFKUDGYRBSAL-UHFFFAOYAH
SMILES C1COCCOCCOCCOCCO1
Properties
Chemical formula	C10H20O5
Molar mass	220.265 g·mol−1
Appearance	Clear, colorless liquid
Density	1.113 g cm−3 (at 20 °C)
Boiling point	93–96 °C (199–205 °F; 366–369 K) at 0.05 mmHg
log P	−0.639
Refractive index (nD)	1.465
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	−881.1 to −877.1 kJ mol−1
Std enthalpy of combustion (ΔcH⦵298)	−5.9157 to −5.9129 MJ mol−1
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H315, H319
Precautionary statements	P305+P351+P338
NFPA 704 (fire diamond)	2 1 0
Flash point	113 °C (235 °F; 386 K)
Safety data sheet (SDS)	msds.chem.ox.ac.uk
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis

15-Crown-5 can be synthesized using a modified Williamson ether synthesis:^[4]

(CH₂OCH₂CH₂Cl)₂ + O(CH₂CH₂OH)₂ + 2 NaOH → (CH₂CH₂O)₅ + 2 NaCl + 2 H₂O

It also forms from the cyclic oligomerization of ethylene oxide in the presence of gaseous boron trifluoride.^[5]

Properties

Analogous to 18-crown-6, 15-crown-5 binds to sodium ions. Thus, when treated with this complexing agent, sodium salts often become soluble in organic solvents.

First-row transition metal dications fit snugly inside the cavity of 15-crown-5. They are too small to be included in 18-crown-6. The binding of transition metal cations results in multiple hydrogen-bonded interactions from both equatorial and axial aqua ligands, such that highly crystalline solid-state supramolecular polymers can be isolated. Metal salts isolated in this form include Co(ClO₄)₂, Ni(ClO₄)₂, Cu(ClO₄)₂, and Zn(ClO₄)₂. Seven coordinate species are most common for transition metal complexes of 15-crown-5, with the crown ether occupying the equatorial plane, along with 2 axial aqua ligands.^[6]

The structure of the complex [Co(15-crown-5)(H₂O)₂]²⁺.

15-crown-5 has also been used to isolate salts of oxonium ions. For example, from a solution of tetrachloroauric acid, the oxonium ion [H₇O₃]⁺ has been isolated as the salt [(H₇O₃)(15-crown-5)₂][AuCl₄]. Neutron diffraction studies revealed a sandwich structure, which shows a chain of water with remarkably long O-H bond (1.12 Å) in the acidic proton, but with a very short OH•••O distance (1.32 Å).^[6]

Structure of [(H₇O₃)(15-crown-5)₂]⁺ ion

A derivative of 15-crown-5, benzo-15-crown-5, has been used to produce anionic complexes of carbido ligands as their [K(benzo-15-crown-5)₂]⁺ salts:^[6]

(Ar₂N)₃MoCH + KCH₂Ph + 2 (15-crown-5) → [K(15-crown-5)₂]⁺[(Ar₂N)₃MoC]⁻ + CH₃Ph

See also

• Host guest chemistry
• Phase transfer catalyst