Org. Synth. 1966, 46, 120
DOI: 10.15227/orgsyn.046.0120
TRIMETHYLOXONIUM FLUOBORATE
[Oxonium compounds, trimethyloxonium tetrafluoroborate]
Submitted by H. Meerwein
1
Checked by O. Vogl, B. C. Anderson, and B. C. McKusick.
1. Procedure
Freshly prepared
triethyloxonium fluoborate2 (170 g., 0.90 mole) is dissolved in
500 ml. of anhydrous methylene chloride in a
1-l. three-necked flask equipped with a
stirrer,
gas-inlet tube, and
drying tube (Note 1). The reaction flask is immersed in an
ice bath, the stirrer is started, and
138 g. (3.00 moles) of dry dimethyl ether is passed into the solution from a
tared cylinder over a period of about 2 hours. The reaction mixture is allowed to stand overnight at room temperature. An hour after the addition of
dimethyl ether is complete,
trimethyloxonium fluoborate begins to separate. The initially liquid product solidifies slowly.
The stirrer is replaced by a filter stick, and the supernatant methylene chloride is withdrawn from the crystalline mass of trimethyloxonium fluoborate; nitrogen is admitted through a bubbler during this operation to prevent atmospheric moisture from entering the flask. The crystals are washed with three 100-ml. portions of anhydrous methylene chloride. The flask is transferred to a dry box, and trimethyloxonium fluoborate is collected on a sintered-glass filter, dried for 2 hours in a vacuum desiccator at 25° (1 mm.), and bottled in a stream of dry nitrogen. The fluoborate is colorless; yield 114–124 g. (86–94%). Rapidly heated in an open capillary tube, it sinters and darkens, with decomposition, at 141–143° (Note 3).
2. Notes
1.
In order to obtain maximum yields, all operations must be carried out under rigorously dry conditions. The apparatus should be dried in an
oven at 110°, assembled while hot, and cooled in a stream of dry
nitrogen. The checkers dried the
methylene chloride over PA 100 silica gel (12–28 mesh) obtained from Davison Chemical Co., Baltimore, Maryland.
2.
Trimethyloxonium fluoborate is less hygroscopic and keeps better than
triethyloxonium fluoborate, but it should be stored at 0–5° in a
tightly closed screw-cap bottle.
2 So stored, it can be kept at least a few weeks.
3.
The decomposition point varies widely, depending on rate of heating and apparatus. Professor S. H. Pine, California State College at Los Angeles, informed the checkers that he observed decomposition at
210–220°, with the salt totally disappearing and (CH
3)
2OBF
3 forming on the wall of the capillary tube above the bath. This prompted the checkers to study the decomposition by differential thermal analysis. At a heating rate of 30°/min., there was an endotherm peak at 142°, with sample all gone by 200°. At 15°/min., the peak was at 155°, with sample all gone by 180°.
Working with Hazardous Chemicals
The procedures in Organic Syntheses are intended for use only by persons with proper training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011; the full text can be accessed free of charge at http://www.nap.edu/catalog.php?record_id=12654). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
In some articles in Organic Syntheses, chemical-specific hazards are highlighted in red "Caution Notes" within a procedure. It is important to recognize that the absence of a caution note does not imply that no significant hazards are associated with the chemicals involved in that procedure. Prior to performing a reaction, a thorough risk assessment should be carried out that includes a review of the potential hazards associated with each chemical and experimental operation on the scale that is planned for the procedure. Guidelines for carrying out a risk assessment and for analyzing the hazards associated with chemicals can be found in Chapter 4 of Prudent Practices.
The procedures described in Organic Syntheses are provided as published and are conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
The paragraphs above were added in September, 2014. The statements above do not supersede any specific hazard caution notes and safety instructions included in the procedure.
3. Discussion
The procedure used is essentially that described by Meerwein and co-workers.
3 The salt has also been prepared from the same reagents in a
sealed tube.
4
Curphey has described a convenient synthesis from
boron trifluoride diethyl etherate,
dimethyl ether, and
epichlorohydrin.
5
4. Merits of the Preparation
This facile preparation is suitable for preparation of large amounts of salt. Like
triethyloxonium fluoborate,
2 trimethyloxonium fluoborate is a potent alkylating agent. In comparison with
trimethyloxonium 2,4,6-trinitrobenzenesulfonate,
6 trimethyloxonium fluoborate is easier to make but does not keep quite as well on storage.
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Epichlorohydrin (106-89-8)
nitrogen (7727-37-9)
dimethyl ether (115-10-6)
methylene chloride (75-09-2)
boron trifluoride diethyl etherate (109-63-7)
Triethyloxonium fluoborate (368-39-8)
trimethyloxonium fluoborate (420-37-1)
Trimethyloxonium 2,4,6-trinitrobenzenesulfonate (13700-00-0)
Oxonium compounds, trimethyloxonium tetrafluoroborate
Copyright © 1921-2025, Organic Syntheses, Inc. All Rights Reserved