Benzoic Anhydride

[93-97-0]  · C14H10O3  · Benzoic Anhydride  · (MW 226.23)

(primarily used as an acylation reagent;1 can be added to alkynes2 and carbon-nitrogen double3 and single bonds4,5)

Physical Data: mp 42-43 °C; bp 360 °C; d 1.199 g cm-3.

Solubility: insol H2O; sol alcohol, ether, CHCl3, acetone, EtOAc, benzene, toluene, glacial acetic acid, acetic anhydride; slightly sol pet ether.

Form Supplied in: white crystalline solid; widely available.

Purification: benzoic acid is removed by washing with NaHCO3, then water, followed by drying. The reagent can be recrystallized from benzene (0.5 mL g-1) by adding a small amount of pet ether (bp 40-60 °C) and cooling. It can also be distilled at 210-220 °C at 20 mmHg.

Handling, Storage, and Precautions: irritating to eyes, respiratory system, and skin. May decompose on exposure to moist air or water.

Acylation.

The most common use of this reagent is as a protecting group for oxygen1a,b and nitrogen1c functional groups. The ease of benzoylation and the ready removal of the protecting group under mildly basic conditions render it valuable in organic synthesis.1a In addition, this reagent has found many uses as an acylating agent for stabilized carbanions.1d,e Its participation in the Friedel-Crafts acylation reaction1f is well known and has been extended to processes involving Lewis acid catalysts.1g In the presence of Titanium(IV) Chloride and Silver(I) Perchlorate as catalysts, this reagent reacts with silyl derivatives of acids and alcohols to give esters via intermediate mixed anhydrides (eq 1).1h

Addition Reactions.

Addition of an excess of this reagent to alkynes, promoted by a Lewis acid, results in formation of 1,3-dicarbonyl compounds (eq 2).2 This reagent can also add across carbon-nitrogen double3 and single bonds4 (eqs 3 and 4). Tertiary amines are dealkylated in the presence of metal salts, resulting in the formation of tertiary amides (eq 5).5

Miscellaneous Uses.

This reagent has been shown to decarboxylate a-keto acids upon heating with an excess of pyridine, avoiding Perkin-type condensations.6 Cyclopropenone oximes have been activated by this reagent to study the Beckmann rearrangement of the O-benzoylated derivatives.7 Substitution of an allylic phenyl ether using this reagent, catalytic Palladium(II) Acetate, and Triphenylphosphine gives mixtures of allylic benzoates (eq 6).8


1. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 2nd ed.; Wiley: New York, 1991. (b) Oku, A.; Nakaoji, S.; Kadono, T.; Imai, H. BCJ 1979, 52, 2966. (c) Shipton, M. R. SL 1992, 491. (d) Brownbridge, P.; Durman, J.; Hunt, P. G.; Warren, S. JCS(P1) 1986, 1947. (e) Houghton, R. P.; Lapham, D. J. S 1982, 451. (f) Olah, G. A. Friedel-Crafts Chemistry; Wiley: New York, 1973. (g) Harada, T.; Ohno, T.; Kobayashi, S.; Mukaiyama, T. S 1991, 1216. (h) Mukaiyama, T.; Shiina, I.; Miyashita, M. CL 1992, 625.
2. Tanabe, Y.; Mukaiyama, T. CL 1985, 673.
3. Kobayashi, S.; Isobe, M.; Saegusa, T. BCJ 1982, 55, 1921.
4. Loewrigkeit, P.; DelFranco, G. J.; Georgalas, N.; Resnick, P. JOC 1968, 33, 3344.
5. Khai, B. T.; Arcelli, A. JOM 1983, 252, C9.
6. Cohen, T.; Sung, I. H. JACS 1965, 87, 3780.
7. Yoshida, H.; Yoshida, K.; Totani, H.; Ogata, T.; Matsumoto, K. BCJ 1990, 63, 3579.
8. Takahashi, K.; Hata, G.; Miyake, A. BCJ 1973, 46, 1012.

Kevin Daniels

The Ohio State University, Columbus, OH, USA



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