Org. Synth. 1969, 49, 121
[Pyrylium tetrafluoroborate, 2,4,6-triphenyl-]
Submitted by K. Dimroth, C. Reichardt, and K. Vogel1
Checked by Saul Cerkofsky and Richard E. Benson.
In a 1-l. four-necked flask (or a three-necked flask with a Y-tube connector) equipped with a mechanical stirrer, a reflux condenser, a dropping funnel, and a thermometer are placed 208 g. (1.00 mole) of benzalacetophenone (Note 1), 60 g. (58.5 ml., 0.50 mole) of acetophenone, and 350 ml. of 1,2-dichloroethane. The contents of the flask are warmed to 70–75°, and 160 ml. of a 52% ethereal solution of fluoboric acid (Note 2) is added from the funnel with stirring during 30 minutes. With the first addition the mixture becomes orange; subsequently the color changes to brownish yellow. After the addition is completed, the mixture is stirred and heated under reflux for 1 hour (Note 3). The fluorescent mixture is allowed to stand overnight in a refrigerator. The crystalline product that separates is collected on a Buchner funnel and washed well with ether. By addition of 250 ml. of ether (Note 4) to the mother liquor an additional quantity of 2,4,6-triphenylpyrylium tetrafluoroborate is obtained. A total yield of 125–135 g. (63–68%) of yellow crystals results; m.p. 218–225° (Note 5). The product can be recrystallized from 650–700 ml. of 1,2-dichloroethane, when it separates in the form of yellow needles, m.p. 251–257° (Note 6). The yield of product dried at 80° (10 mm.) for 3 hours is 102.5–107 g. (52–54%) (Note 6).
Ethereal fluoboric acid
can be prepared as follows: 19 ml. (19 g., 0.95 mole) of anhydrous hydrofluoric acid
, b.p. 19.4° (760 mm.)
[Caution! Hydrofluoric acid in contact with the skin produces extremely painful burns. It is therefore necessary to use every precaution to protect exposed parts of the body, especially the hands and eyes. Cf. Org. Syntheses, Coll. Vol. 2, 295 (1943). Note 3
; this volume, p. 136, Note 1
] is added in small portions with shaking or stirring to 126 ml. (142 g., 1.00 mole) of distilled boron trifluoride etherate
, b.p. 126° (760 mm.)
, contained in a 500-ml. polyethylene flask
that is cooled in an ice bath
to 0°. The concentration of the resulting yellowish solution of fluoboric acid
is about 52% by weight (ca.
6.6 moles per l.).
used for washing the product may be added to the filtrate.
The 2,4,6-triphenylpyrylium tetrafluoroborate
resulting from this procedure is sufficiently pure for use in the preparation of 2,4,6-triphenylnitrobenzene
It is necessary to dry under reduced pressure in order to remove that portion of the solvent that is tightly held. Anal.
Calcd. for C23
O: C, 69.73; H, 4.33; B, 2.73; F, 19.18. Found: C, 69.38; H, 4.47; B, 3.07; F, 19.51. The n.m.r. spectrum (acetone-d6
) shows a singlet at 9.1 p.p.m. (2 H) and multiplets at 8.6 p.p.m. and 7.9 p.p.m. (15 H) (downfield from internal tetramethylsilane reference).
The present procedure is an improved modification of that described by Balaban3
for the corresponding perchlorate. 2,4,6-Triphenylpyrylium tetrafluoroborate
has also been prepared from the corresponding tetrachloroferrate4,5
with fluoboric acid
and boron trifluoride
and from acetophenone
, and boron trifluoride etherate
Additional methods for the preparation of pyrylium salts have been reviewed.5,8,9,10,11,12,13,14
is a versatile and useful stable starting material. Its reaction with nitromethane
under basic conditions has made 2,4,6-triphenylnitrobenzene
In addition, pyrylium salts are readily converted to a variety of pyridine derivatives16,17,18
including alkyl- and arylpyridinium slats,17,18
to thiopyrylium salts,19
and to substituted azulenes.20
The chemistry and transformation of pyrylium salts have been reviewed.5,8,9,10,11,21,14
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
hydrofluoric acid (7664-39-3)
boron trifluoride (7637-07-2)
boron trifluoride etherate (109-63-7)
Pyrylium tetrafluoroborate, 2,4,6-triphenyl- (448-61-3)
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved