[33100-27-5] · C10H20O5 · 15-Crown-5 · (MW 220.27)
(sodium-selective complexing agent used for the activation of various sodium salts such as the hypochlorite, sulfide, hydroxide, and imidazolide; phase transfer catalyst; activation of potassium and magnesium reagents)
Physical Data: bp 78 °C/0.05 mmHg; IR (CCl4, 0.1 mm NaCl cell) 2875, 1445, 1350, 1280, 1250, 1185, 975, and 925 cm-1; 1H NMR (CCl4) 3.58 ppm (sharp singlet); 13C NMR (CDCl3) 70.621 ppm.
Preparative Methods: 15-crown-5 has been synthesized by a variety of methods involving modified Williamson ether procedures;1,2 in addition, 15-crown-5 is formed from the cyclic oligomerization of Ethylene Oxide in the presence of gaseous Boron Trifluoride;3 commercially available.
Handling, Storage, and Precautions: use in a fume hood.
The cavity diameter of 15-crown-5 is estimated to be 1.7-2.2 Å, which is ideal for complexing with a sodium cation (ionic diameter of 1.94 Å). While the selectivity of 15-crown-5 for sodium salts is well documented, this macrocyclic multidentate ligand will also effectively complex with other alkali metal cations.4
The cycloaddition of 2-phenylallylmagnesium phenoxide and trans-stilbene in THF is better catalyzed by 15-crown-5 than 12-crown-4.4 No reaction takes place in the absence of a ligand or in the presence of 18-crown-6 (eq 1).
The benzylation of Potassium Thiocyanate yields benzyl thiocyanate as the kinetic product and benzyl isothiocyanate as the thermodynamic product. Solid-liquid phase-transfer catalytic reaction of Benzyl Chloride with potassium thiocyanate produces approximately a 50/50 mixture of the two products in the presence of 15-crown-5.5 Dibenzo-18-crown-6 produces substantially more of the isothiocyanate (eq 2).
The preparation of N-(arylsulfonyl)sulfoximines by oxidation of the sulfilimines with Sodium Hypochlorite in an aqueous methylene chloride-ethyl acetate two-phase system in the presence of 15-crown-5 has been reported (eq 3).6
4,4´-Dicyanodiphenyl thioether was prepared in excellent yield from the reaction of 4-cyanochlorobenzene and Sodium Sulfide in dipolar, aprotic solvents (DMF, o-dichlorobenzene) at 200 °C in the presence of 15-crown-5 (eq 4).7
The Wittig rearrangement of the phenyl ether of 9-fluorenol was investigated under solid-liquid phase transfer catalytic conditions using solid, powdered base and an organic phase in the presence of crown ethers (eq 5). In the presence of Potassium Hydroxide the order of effectiveness is: dibenzo-18-crown-6 < Dicyclohexano-18-crown-6 < 15-crown-5 < 18-Crown-6. In the presence of Sodium Hydroxide the order of effectiveness is: 12-Crown-4 < 18-crown-6 < 15-crown-5.8
The sodium salt of theophylline undergoes N-alkylation with 1-chloro-4-iodobutane in acetonitrile in the presence of 15-crown-5. The resulting chloride reacts smoothly with the potassium salt of 2-nitroimidazole, again in the presence of 15-crown-5, to give the second N-alkylation (eq 6).9
The polymerization of phenylmethyldichlorosilane with sodium metal (Wurtz Coupling) in toluene/heptane solvent has been found to be catalyzed by 15-crown-5.10
Charles L. Liotta & Joachim Berkner
Georgia Institute of Technology, Atlanta, GA, USA