Acetic anhydride

Last updated
Acetic anhydride
Acetic anhydride2DACS.svg
Acetic-anhydride-from-xtal-2003-3D-balls.png
Names
Preferred IUPAC name
Acetic anhydride
Systematic IUPAC name
Ethanoic anhydride
Other names
Ethanoyl ethanoate
Acetic acid anhydride
Acetyl acetate
Acetyl oxide
Acetic oxide
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.241 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 203-564-8
PubChem CID
RTECS number
  • AK1925000
UNII
UN number 1715
  • InChI=1S/C4H6O3/c1-3(5)7-4(2)6/h1-2H3 Yes check.svgY
    Key: WFDIJRYMOXRFFG-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C4H6O3/c1-3(5)7-4(2)6/h1-2H3
    Key: WFDIJRYMOXRFFG-UHFFFAOYAH
  • O=C(OC(=O)C)C
  • CC(=O)OC(=O)C
Properties
C4H6O3
Molar mass 102.089 g·mol−1
Appearancecolorless liquid
Density 1.082 g cm−3, liquid
Melting point −73.1 °C (−99.6 °F; 200.1 K)
Boiling point 139.8 °C (283.6 °F; 412.9 K)
2.6 g/100 mL, reacts (see text)
Vapor pressure 4 mmHg (20 °C) [1]
-52.8·10−6 cm3/mol
1.3901
Thermochemistry [2]
−624.4 kJ·mol−1
Pharmacology
Legal status
Hazards
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-acid.svg GHS-pictogram-exclam.svg
Danger
H226, H302, H314, H330
P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P330, P363, P370+P378, P403+P235, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
2
1
W
Flash point 49 °C (120 °F; 322 K)
316 °C (601 °F; 589 K)
Explosive limits 2.7–10.3%
Lethal dose or concentration (LD, LC):
1000 ppm (rat, 4 hr) [3]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5 ppm (20 mg/m3) [1]
REL (Recommended)
C 5 ppm (20 mg/m3) [1]
IDLH (Immediate danger)
200 ppm [1]
Safety data sheet (SDS) ICSC 0209
Related compounds
Propionic anhydride
Related compounds
 Acetic acid
Acetyl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac 2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, which is formed by its reaction with moisture in the air.

Contents

Structure and properties

Acetic anhydride in a glass bottle Acetic anhydride.jpg
Acetic anhydride in a glass bottle

Acetic anhydride, like most acid anhydrides, is a flexible molecule with a nonplanar structure. [4] The pi system linkage through the central oxygen offers very weak resonance stabilization compared to the dipole-dipole repulsion between the two carbonyl oxygens. The energy barriers to bond rotation between each of the optimal aplanar conformations are quite low. [5]

Like most acid anhydrides, the carbonyl carbon atom of acetic anhydride has electrophilic character, as the leaving group is carboxylate. The internal asymmetry may contribute to acetic anhydride's potent electrophilicity as the asymmetric geometry makes one side of a carbonyl carbon atom more reactive than the other, and in doing so tends to consolidate the electropositivity of a carbonyl carbon atom to one side (see electron density diagram).

Production

Acetic anhydride was first synthesized in 1852 by the French chemist Charles Frédéric Gerhardt (1816-1856) by heating potassium acetate with benzoyl chloride. [6]

Acetic anhydride is produced by carbonylation of methyl acetate: [7]

CH3CO2CH3 + CO → (CH3CO)2O

The Tennessee Eastman acetic anhydride process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium chloride in the presence of lithium iodide is employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene (ethenone) with acetic acid at 45–55 °C and low pressure (0.05–0.2 bar). [8]

H2C=C=O + CH3COOH → (CH3CO)2O
(ΔH = −63 kJ/mol)

The route from acetic acid to acetic anhydride via ketene was developed by Wacker Chemie in 1922, [9] when the demand for acetic anhydride increased due to the production of cellulose acetate.

Due to its low cost, acetic anhydride is usually purchased, not prepared, for use in research laboratories.

Reactions

Acetic anhydride is a versatile reagent for acetylations, the introduction of acetyl groups to organic substrates. [10] In these conversions, acetic anhydride is viewed as a source of CH3CO+.

Acetylation of alcohols and amines

Alcohols and amines are readily acetylated. [11] For example, the reaction of acetic anhydride with ethanol yields ethyl acetate:

(CH3CO)2O + CH3CH2OH → CH3CO2CH2CH3 + CH3COOH

Often a base such as pyridine is added to function as catalyst. In specialized applications, Lewis acidic scandium salts have also proven effective catalysts. [12]

Acetylation of aromatic rings

Aromatic rings are acetylated by acetic anhydride. Usually acid catalysts are used to accelerate the reaction. Illustrative are the conversions of benzene to acetophenone [13] and ferrocene to acetylferrocene: [14]

(C5H5)2Fe + (CH3CO)2O → (C5H5)Fe(C5H4COCH3) + CH3CO2H

Preparation of other acid anhydrides

Dicarboxylic acids are converted to the anhydrides upon treatment with acetic anhydride. [15] It is also used for the preparation of mixed anhydrides such as that with nitric acid, acetyl nitrate.

Precursor to geminal diacetates

Aldehydes react with acetic anhydride in the presence of an acidic catalyst to give geminal diacetates. [16] A former industrial route to vinyl acetate involved the intermediate ethylidene diacetate, the geminal diacetate obtained from acetaldehyde and acetic anhydride: [17]

CH3CHO + (CH3CO)2O → (CH3CO2)2CHCH3

Hydrolysis

Acetic anhydride dissolves in water to approximately 2.6% by weight. [18] Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give carboxylic acids. In this case, acetic acid is formed, this reaction product being fully water miscible: [19]

(CH3CO)2O + H2O → 2 CH3COOH

Applications

As indicated by its organic chemistry, acetic anhydride is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to cellulose acetate, which is a component of photographic film and other coated materials, and is used in the manufacture of cigarette filters. Similarly it is used in the production of aspirin (acetylsalicylic acid), which is prepared by the acetylation of salicylic acid. [20] It is also used as an active modification agent via autoclave impregnation and subsequent acetylation to make a durable and long-lasting timber. [21]

In starch industry, acetic anhydride is a common acetylation compound, used for the production of modified starches (E1414, E1420, E1422)

Because of its use for the synthesis of heroin by the diacetylation of morphine, acetic anhydride is listed as a U.S. DEA List II precursor, and restricted in many other countries. [22] [23]

Safety

Acetic anhydride is an irritant and combustible liquid; it is highly corrosive to skin and any direct contact will result in severe burns. Because of its reactivity toward water and alcohol, foam or carbon dioxide are preferred for fire suppression. [24] The vapour of acetic anhydride is harmful. [25]

Related Research Articles

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a compound derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

<span class="mw-page-title-main">Acetyl group</span> Chemical group, –C(=O)CH₃

In organic chemistry, acetyl is a functional group with the chemical formula −COCH3 and the structure −C(=O)−CH3. It is sometimes represented by the symbol Ac. In IUPAC nomenclature, acetyl is called ethanoyl.

<span class="mw-page-title-main">Acetate</span> Salt compound formed from acetic acid and a base

An acetate is a salt formed by the combination of acetic acid with a base. "Acetate" also describes the conjugate base or ion typically found in aqueous solution and written with the chemical formula C
2H
3O−
2. The neutral molecules formed by the combination of the acetate ion and a positive ion are also commonly called "acetates". The simplest of these is hydrogen acetate with corresponding salts, esters, and the polyatomic anion CH
3CO−
2, or CH
3COO−
.

<span class="mw-page-title-main">Chloroacetic acid</span> Chemical compound

Chloroacetic acid, industrially known as monochloroacetic acid (MCA), is the organochlorine compound with the formula ClCH2CO2H. This carboxylic acid is a useful building block in organic synthesis. It is a colorless solid. Related compounds are dichloroacetic acid and trichloroacetic acid.

In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

<span class="mw-page-title-main">Acyl halide</span> Oxoacid compound with an –OH group replaced by a halogen

In organic chemistry, an acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

In chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed acetate esters or simply acetates. Deacetylation is the opposite reaction, the removal of an acetyl group from a chemical compound.

<span class="mw-page-title-main">Anisole</span> Organic compound (CH₃OC₆H₅) also named methoxybenzene

Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly made synthetically and is a precursor to other synthetic compounds. Structurally, it is an ether with a methyl and phenyl group attached. Anisole is a standard reagent of both practical and pedagogical value.

<span class="mw-page-title-main">Acetyl chloride</span> Organic compound (CH₃COCl)

Acetyl chloride is an acyl chloride derived from acetic acid. It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl.

<span class="mw-page-title-main">Organic acid anhydride</span> Any chemical compound having two acyl groups bonded to the same oxygen atom

An organic acid anhydride is an acid anhydride that is also an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))2O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride. Thus, (CH3CO)2O is called acetic anhydride.Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride").

The Pummerer rearrangement is an organic reaction whereby an alkyl sulfoxide rearranges to an α-acyloxy–thioether (monothioacetal-ester) in the presence of acetic anhydride.

The Monsanto process is an industrial method for the manufacture of acetic acid by catalytic carbonylation of methanol. The Monsanto process has largely been supplanted by the Cativa process, a similar iridium-based process developed by BP Chemicals Ltd which is more economical and environmentally friendly.

<span class="mw-page-title-main">Palladium(II) acetate</span> Chemical compound

Palladium(II) acetate is a chemical compound of palladium described by the formula [Pd(O2CCH3)2]n, abbreviated [Pd(OAc)2]n. It is more reactive than the analogous platinum compound. Depending on the value of n, the compound is soluble in many organic solvents and is commonly used as a catalyst for organic reactions.

<span class="mw-page-title-main">Propionic anhydride</span> Chemical compound

Propionic anhydride is an organic compound with the formula (CH3CH2CO)2O. This simple acid anhydride is a colourless liquid. It is a widely used reagent in organic synthesis as well as for producing specialty derivatives of cellulose.

Acetyl iodide is an organoiodine compound with the formula CH3COI. It is a colourless liquid. It is formally derived from acetic acid. Although far rarer in the laboratory than the related acetyl bromide and acetyl chloride, acetyl iodide is produced, transiently at least, on a far larger scale than any other acid halide. Specifically, it is generated by the carbonylation of methyl iodide in the Cativa and Monsanto processes, which are the main industrial processes that generate acetic acid. It is also an intermediate in the production of acetic anhydride from methyl acetate.

<span class="mw-page-title-main">Ethenone</span> Organic compound with the formula H2C=C=O

In organic chemistry, ethenone is the formal name for ketene, an organic compound with formula C2H2O or H2C=C=O. It is the simplest member of the ketene class. It is an important reagent for acetylations.

<span class="mw-page-title-main">Acetic acid</span> Colorless and faint organic acid found in vinegar

Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH3COOH. Vinegar is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water. It has been used, as a component of vinegar, throughout history from at least the third century BC.

<span class="mw-page-title-main">Ethylidene diacetate</span> Chemical compound

Ethylidene diacetate is an organic compound with the formula (CH3CO2)2CHCH3. A colorless low-melting solid, it once served as a precursor to vinyl acetate.

<span class="mw-page-title-main">Acetyl nitrate</span> Chemical compound

Acetyl nitrate is the organic compound with the formula CH3C(O)ONO2. It is classified as the mixed anhydride of nitric and acetic acids. It is a colorless explosive liquid that fumes in moist air.

<span class="mw-page-title-main">Acetyl hypochlorite</span> Chemical compound

Acetyl hypochlorite, also known as chlorine acetate, is a chemical compound with the formula CH3COOCl. It is a photosensitive colorless liquid that is a short lived intermediate in the Hunsdiecker reaction.

References

  1. 1 2 3 4 NIOSH Pocket Guide to Chemical Hazards. "#0003". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99th ed.). CRC Press. pp. 5–3. ISBN   978-1138561632.
  3. ↑ "Acetic anhydride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. ↑ Seidel, R. W.; Goddard, R.; Nöthling, N.; Lehmann, C. W. (2016), "Acetic anhydride at 100 K: the first crystal structure determination", Acta Crystallographica Section C, 72 (10): 753–757, doi:10.1107/S2053229616015047, PMID   27703123.
  5. ↑ Wu, Guang; Van Alsenoy, C.; Geise, H. J.; Sluyts, E.; Van Der Veken, B. J.; Shishkov, I. F.; Khristenko (2000), "Acetic Anhydride in the Gas Phase, Studied by Electron Diffraction and Infrared Spectroscopy, Supplemented with ab Initio Calculations of Geometries and Force Fields", The Journal of Physical Chemistry A, 104 (7): 1576–1587, Bibcode:2000JPCA..104.1576W, doi:10.1021/jp993131z.
  6. ↑ Charles Gerhardt (1852) “Recherches sur les acides organiques anhydres” (Investigations into the anhydrides of organic acids), Comptes rendus … , 34 : 755-758.
  7. ↑ Zoeller, J. R.; Agreda, V. H.; Cook, S. L.; Lafferty, N. L.; Polichnowski, S. W.; Pond, D. M. (1992), "Eastman Chemical Company Acetic Anhydride Process", Catal. Today, 13 (1): 73–91, doi:10.1016/0920-5861(92)80188-S
  8. ↑ Arpe, Hans-Jürgen (2007-01-11), Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte (6th ed.), Weinheim: Wiley-VCH, pp. 200–1, ISBN   978-3-527-31540-6 [ permanent dead link ].
  9. ↑ Milestones in the history of WACKER, Wacker Chemie AG, retrieved 2009-08-27.
  10. ↑ "Acid Anhydrides", Understanding Chemistry, retrieved 2006-03-25.
  11. ↑ Shakhashiri, Bassam Z., "Acetic Acid & Acetic Anhydride", Science is Fun…, Department of Chemistry, University of Wisconsin, archived from the original on 2006-03-03, retrieved 2006-03-25.
  12. ↑ Macor, John; Sampognaro, Anthony J.; Verhoest, Patrick R.; Mack, Robert A. (2000). "(R)-(+)-2-Hydroxy-1,2,2-Triphenylethyl Acetate". Organic Syntheses . 77: 45. doi:10.15227/orgsyn.077.0045 ; Collected Volumes, vol. 10, p. 464.
  13. ↑ Roger Adams and C. R. Noller "p-Bromoacetophenone" Org. Synth. 1925, vol. 5, p. 17. doi : 10.15227/orgsyn.005.0017
  14. ↑ Taber, Douglass F., Column chromatography: Preparation of Acetyl Ferrocene, Department of Chemistry and Biochemistry, University of Delaware, archived from the original on 2009-05-02, retrieved 2009-08-27.
  15. ↑ B. H. Nicolet and J. A. Bender "3-Nitrophthalic Anhydride" Org. Synth. 1927, vol. 7, 74. doi : 10.15227/orgsyn.007.0074
  16. ↑ R. T. Bertz "Furfuryl Diacetate" Org. Synth. 1953, 33, 39. doi : 10.15227/orgsyn.033.0039
  17. ↑ G. Roscher "Vinyl Esters" in Ullmann's Encyclopedia of Chemical Technology, 2007 John Wiley & Sons: New York. doi : 10.1002/14356007.a27_419
  18. ↑ Acetic Anhydride: Frequently Asked Questions (PDF), British Petroleum, archived from the original (PDF) on 2007-10-11, retrieved 2006-05-03.
  19. ↑ Acetic Anhydride: Material Safety Data Sheet (PDF) (PDF), Celanese, archived from the original (PDF) on 2007-09-27, retrieved 2006-05-03.
  20. ↑ Acetic anhydride (PDF), SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, p. 5[ dead link ]
  21. ↑ Tullo, Alexander (2012-08-06). "Making Wood Last Forever With Acetylation". Chemical and Engineering News. No. 32. American Chemical Society. ISSN   0009-2347 . Retrieved 2022-09-17.
  22. ↑ "§ 1310.02 - Substances Covered". e-CFR . 2022-02-15. Archived from the original on 2022-02-15.
  23. ↑ UN Intercepts Taliban's Heroin Chemical in Rare Afghan Victory, Bloomberg, archived from the original on 22 October 2012, retrieved 2008-10-07.
  24. ↑ "Data Sheets". International Occupational Safety and Health Information Centre. Retrieved 2006-04-13.
  25. ↑ "NIOSH". Pocket Guide to Chemical Hazards. Archived from the original on 22 April 2006. Retrieved 2006-04-13.
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