Organic Syntheses, CV 5, 1080
Submitted by H. Meerwein
1
Checked by B. C. Anderson, O. H. Vogl, and B. C. McKusick.
1. Procedure
A
2-l. three-necked flask, a
stirrer, a
dropping funnel, and a
condenser provided with a drying tube are dried in an
oven at 110°, assembled while hot, and cooled in a stream of dry
nitrogen.
Sodium-dried ether (500 ml.) and
284 g. (252 ml., 2.00 moles) of freshly distilled boron fluoride etherate (Note
1) and (Note
2) are placed in the flask.
Epichlorohydrin (140 g., 119 ml., 1.51 moles) is added dropwise to the stirred solution at a rate sufficient to maintain vigorous boiling (about 1 hour is needed). The mixture is refluxed an additional hour and allowed to stand at room temperature overnight. The stirrer is replaced by a filter stick, and the supernatant
ether is withdrawn from the crystalline mass of
triethyloxonium fluoborate;
nitrogen is admitted through a bubbler during this operation to prevent atmospheric moisture from entering the flask. The crystals are washed with three
500-ml. portions of sodium-dried ether. The flask is transferred to a
dry box, and
triethyloxonium fluoborate is collected on a
sintered-glass filter and bottled in a stream of dry
nitrogen. The fluoborate is colorless; m.p.
91–92° (dec.), yield
244–272 g. (
85–95%) (Note
3).
2. Notes
2. It is convenient to measure the liquids with syringes using the densities:
epichlorohydrin d425 1.179;
boron fluoride etherate,
d425 1.125.
3.
Triethyloxonium fluoborate is very hygroscopic. It should be stored in a
tightly closed screw-cap bottle at 0–5° and should be used within a few days of the time it is made. It should be weighed and transferred in a dry box. It can be stored indefinitely under ether or at −80°.
3. Discussion
4. Merits of the Preparation
This simple procedure easily provides large amounts of
triethyloxonium fluoborate.
Triethyloxonium fluoborate readily ethylates such compounds as ethers, sulfides, nitriles, ketones, esters, and amides on
oxygen,
nitrogen, or
sulfur to give onium fluoborates (often isolable) that can react with nucleophilic reagents to give useful products.
5 For example,
dimethylformamide gives the imino ether fluoborate [(CH
3)
2NCH-OC
2H
5]
+ BF4−, which is converted to (CH
3)
2NCH(OC
2H
5)
2 by
sodium ethoxide.
5 Since an imino ether fluoborate is easily hydrolyzed to the corresponding amine and ester,
triethyloxonium fluoborate is a useful reagent for converting amides to amines under mild conditions.
6 Curphey provides a fuller discussion of the alkylating properties of trialkyloxonium fluoborates.
7
This preparation is referenced from:
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