Chemical Properties
18-Crown-6 is a slightly yellow solid, it has a high affinity for the hydronium ion H3O+, as it can fit inside the crown ether. Thus, reaction of 18-crown-6 with strong acids gives the cation [H3O·18-crown-6]+.
Uses
18-Crown-6 is used as an efficient phase transfer catalyst and as a complexing agent with a variety of small cation. It is involved in the synthesis of diaryl ethers, diaryl thioethers, and diarylamines mediated by potassium fluoride-alumina and 18-crown-6. It facilitates the solubility of potassium permanganate in benzene, which is used for oxidizing the organic compounds. It is used to accelerate various substitution reactions as well as enhances the power of nucleophiles such as potassium acetate. It is utilized in the alkylation reactions in the presence of potassium carbonate, N-alkylation of glutarimide and succinimide with dimethylcarbonate. The complex formed by its reaction with potassium cyanide acts as a catalyst in the cyanosilylation of aldehydes, ketones and quinines with trimethylsilyl cyanide (TMSCN).
Uses
A useful phase transfer catalyst.
Uses
18-Crown-6 may be used to catalyze the
N-alkylation of heterocyclic compounds and allylation of functionalized aldehydes.
Definition
ChEBI: 18-crown-6 is a crown ether that is cyclooctadecane in which the carbon atoms at positions 1, 4, 7, 10, 13 and 16 have been replaced by oxygen atoms. It has a role as a phase-transfer catalyst. It is a crown ether and a saturated organic heteromonocyclic parent.
Synthesis Reference(s)
The Journal of Organic Chemistry, 39, p. 2445, 1974
DOI: 10.1021/jo00930a037
General Description
18-Crown-6 is the simplest crown ether that can be prepared by reacting triethylene glycol with triethylene glycol dichloride in the presence of potassium hydroxide as a base. 18-Crown-6 can solubilize metal salts, particularly potassium salts, in nonpolar and dipolar aprotic solvents. Thus, it is widely used as a phase transfer catalyst. It can also be used as a metal complexing agent to prepare a variety of molecular complexes.
Purification Methods
Recrystallise it from acetonitrile and dry it in a vacuum. Purify it also by precipitating the 18-crown-6/nitromethane 1:2 complex with Et2O/nitromethane (10:1 mixture). The complex is decomposed in vacuum whereby 18-crown-6 distils off under the reduced pressure. [Beilstein 19/12 V 601.]
