無水酢酸

外観

無色澄明の液体

性質

酢酸の沸点が118度であるのに対し、無水酢酸の沸点は139.8度と高く、発生した蒸気は催涙性があり、皮膚に付着すると水ほうや炎症が発生します。そのため、素手で取り扱わないようにし、無水酢酸を熱するときは目を保護することが必要です。

多くの酸無水物と同様に、無水酢酸も加水分解してカルボン酸が生成します。無水酢酸の場合、酢酸が形成され、酢酸は水に完全混和します。
(CH3CO)2O + H2O → 2 CH3COOH

溶解性

ジエチルエーテルに極めて溶けやすい。エタノールには溶けるが、反応して酢酸エチルとなる。水にはすぐには溶けないが、徐々に反応して酢酸になる。

解説

無水酢酸，酢酸の酸無水物。化学式(CH3CO)2O。融点－68℃，沸点140.0℃の強烈な刺激臭をもつ無色の液体。クロロホルム，エーテルなどの有機溶媒に易溶。皮膚に触れると水ぶくれを生じる。水と徐々に反応して酢酸になるが，無機酸が存在すると急激に反応する。また無機塩基と激しく反応して酢酸塩となる。第三アミンの存在下にアルコールと反応して酢酸エステルを生じ，アンモニアまたはアミンと反応してアセトアミドを生じる(アセチル化)。

用途

酢酸エステル原料、染料等原料

用途

酢酸繊維素の製造、アスピリン、その他薬品、香料、染料、酢酸エステル類、有機合成原料

用途

アセチル化剤。コレステロールの定量。

用途

汎用分析用試薬。薬品、香料、染料等の有機合成原料。

製法

歴史的には、1852年にフランスの化学者シャルル・フレデリック・ゲルハルトが、をで加熱することで、無水酢酸を初めて合成しました。

工業的には、無水酢酸はケテンと酢酸を45～55℃かつ低圧下で反応させて製造します。
H2C=C=O + CH3COOH → (CH3CO)2O

無水酢酸は、のカルボニル化によっても生成します。
CH3CO2CH3 + CO → (CH3CO)2O

使用上の注意

アルゴン封入

説明

Acetic anhydride (chemical formula: (CH3CO)2O) is the simplest isolable anhydride of a carboxylic acid, is widely used as a reagent in organic synthesis. It has an internal asymmetric structure, leading to its potent electrophilicity. In organic chemistry, it is mainly used in acetylation for the manufacture of commercially significant materials, e.g. it can be used for the conversion of cellulose to cellulose acetate and aspirin. It can also be used as a wood preservative. In starch industry, it is a common acetylation compound for acetylation of monoglyceride. It is also an esterification agent for the production of modified starches. It is produced by carbonylation of methyl acetate or the reaction between ketene and acetic acid.

化学的特性

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis. It is a combustible, colorless, strongly refractive, liquid that smells strongly of acetic acid, formed by its reaction with the moisture in the air. Acetic anhydride is an esterification agent used in the preparation of modified starch and for acetylation of acetylated monoglycerides.

物理的性質

Acetic anhydride is a colorless, very mobile liquid with a very strong, acetic acid-like odor. Experimentally determined detection and recognition odor threshold concentrations were <600 μg/m3 (<140 ppbv) and 1.5 mg/m3 (360 ppbv), respectively (Hellman and Small, 1974). Acetic anhydride is miscible with polar solvents and dissolves in cold alcohol with slow decomposition. The solubility of acetic anhydride in water at 20°C is 2.6wt%, with slow decomposition; the solubility of water in acetic anhydride at 15°C is 10.7 wt%, with gradual decomposition.

天然物の起源

Reported found in watercress (Nasturtium officinale r. br.).

使用

Acetic anhydride is an important solvent and acetylation agent. It is used for the manufacture of acetylcellulose, acetylsalicylic acid, acetanilide, nitrofurane, sulfonamides, vitamin B6 etc. As acetulizer and solvent in examining wool fat, glycerol, fatty and volatile oils, resins; detection of rosin. Widely used in organic syntheses, e.g., as dehydrating agent in nitrations, sulfonations and other reactions where removal of water is necessary.

定義

ChEBI: Acetic anhydride is an acyclic carboxylic anhydride derived from acetic acid. It has a role as a metabolite and a reagent.

主な応用

As indicated by its organic chemistry, Ac₂O 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. Similarly it is used in the production of aspirin (acetylsalicylic acid), which is prepared by the acetylation of salicylic acid.It is also used as a wood preservative via autoclave impregnation to make a longer lasting timber.
In starch industry, acetic anydride is a common acetylation compound, used for the production of modified starches
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.

反応性

introduction of acetyl groups to organic substrates . In these conversions, acetic anhydride is viewed as a source of CH3CO+. Alcohols and amines are readily acetylated. 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.
Aromatic rings are acetylated, usually in the presence of an acid catalyst. Illustrative is the conversion of benzene to aceto phenone:
(CH3CO)₂O + C₆H₆ → CH₃COC₆H₅ + CH₃CO₂H
Ferrocene can be acetylated as well:
Cp₂Fe + (CH₃CO)₂O → CpFe(C₅H₄COCH₃).

用途

エーテルなどの有機溶媒に溶ける。アセチル化剤として広く使用され、セルロースをアセチル化してアセチルセルロースをつくるのに使われるほか、アスピリンなどの医薬、染料、クマリンなどの香料の合成に用いられる。特定麻薬向精神薬原料に指定されている。「氷酢酸」とよばれている水の含有量が低い高純度の酢酸とは別物である。

一般的な説明

A clear colorless liquid with a strong odor of vinegar. Flash point 129°F. Corrosive to metals and tissue. Density 9.0 lb /gal. Manufacture of cellulose esters, plastics, pharmaceuticals, photographic films, cigarette filters, and magnetic tape; inorganic synthesis as an acetylating agent, bleaching agent, and dehydrating agent.

空気と水の反応

Flammable. Reacts violently with water to generate acetic acid . This reaction is heightened by the presence of mineral acids (nitric, perchloric, sulfuric acid, etc.) [Chem. Eng. News 25, 3458].

反応プロフィール

Acetic anhydride reacts violently on contact with water, steam, methanol, ethanol, glycerol and boric acid. Reaction with water is particularly dangerous in presence with mineral acids (e.g., nitric, perchloric, chromic, sulfuric acid) [Chem. Eng. News 25, 3458]. Potentially explosive reactions with oxidizing reagents such as barium peroxide, chromium trioxide, chromic acid, hypochlorous acid, nitric acid, perchloric acid, peroxyacetic acid, potassium permanganate, hydrogen peroxide. [Sax, 9th ed., 1996, p. 15]. Reacts violently with metal nitrates used as nitrating agents [Davey W. et al., Chem. & Ind., 1948, p. 814].

健康ハザード

Liquid is volatile and causes little irritation on uncovered skin. However, causes severe burns when clothing is wet with the chemical or if it enters gloves or shoes. Causes skin and eye burns and irritation of respiratory tract. Nausea and vomiting may develop after exposure.

使用用途

無水酢酸は、有機化合物にアセチル基を導入するアセチル化のための広く用いられる薬品です。以下の反応において、無水酢酸はアセチル基(CH3CO−)の供給源として用いられています。

アルコール類やセルロースのアセチル化

無水酢酸とアルコールを反応させると酢酸エステルが得られます。例えば、と反応させると、が得られます。
(CH3CO)2O + CH3CH2OH → CH3CO2CH2CH3 + CH3COOH
セルロースと無水酢酸を反応させることで、アセチルセルロースを得られます。アセチルセルロースは、タバコのフィルター製造、写真やフィルム、合成繊維やプラスチック、各種コーティング材などの用途で使用されています。

芳香族環のアセチル化

酸触媒を用いて反応を促進させ、芳香族環を無水酢酸でアセチル化します。例として、フェロセンからアセチルフェロセンへの変換があります。
(C5H5)2Fe + (CH3CO)2O → (C5H5)Fe(C5H4COCH3) + CH3COOH

その他の酸無水物の調製

ジカルボン酸は、無水酢酸で処理すると無水物に変換されます。

また、無水酢酸を薄めて布や花びらなどを染める染料としても使用されています。この他にも、の製造、医薬、香料などでも利用されます。

近年では、LCD用偏光板保護フィルム向けとしての酢酸セルロースや、液晶ポリマー、ウレタン弾性繊維用など新しい分野に用途が拡大しています。

化学反応性

Reactivity with Water: Reacts slowly with water, but considerable heat is liberated when contacted with spray water; Reactivity with Common Materials: Corrodes iron, steel and other metals; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Dilute with water and use sodium bicarbonate solution to rinse; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.

安全性プロファイル

Moderately toxic by inhalation, ingestion, and skin contact. A skin and severe eye irritant. A flammable liquid. A fire and explosion hazard when exposed to heat or flame. Potentially explosive reactions with barium peroxide, boric acid, chromium trioxide, 1,3diphenyltriazene, hydrochloric acid + water, hypochlorous acid, nitric acid, perchloric acid + water, peroxyacetic acid, potassium permanganate, tetrafluoroboric acid, 4toluenesulfonic acid + water, and acetic acid + water. Reactions with ethanol + sodium hydrogen sulfate, and hydrogen peroxide form explosive products. Reactions with ammonium nitrate + hexamethylenetetrammonium acetate + nitric acid form as products the military explosives RDX and HMX. Reacts violently with N-tert-butyl-phthalimic acid + tetrafluoroboric acid, chromic acid, glycerol + phosphoryl chloride, and metal nitrates (e.g., copper or sodium nitrates). Incompatible with 2-aminoethanol, aniline, chlorosulfonic acid, (CrOs + acetic acid), ethylene-diamine, ethyleneimine, glycerol, oleum, HF, permanganates, NaOH, Na2O2, H2SO4, water, N2O2, (glycerol + phosphoryl chloride). When heated to decomposition it emits toxic fumes; can react vigorously with oxidizing materials, wdl react violently on contact with water or steam. Used in production of drugs of abuse. To fight fire, use CO2, dry chemical, water mist, alcohol foam. See also ANHYDRIDES.

職業ばく露

Acetic anhydride is used as an acetylating agent or as a solvent in the manufacture of cellulose acetate, acetanilide, aspirin, synthetic fibers, plastics, explosives, resins, perfumes, and flavorings; and it is used in the textile dyeing industry. It is widely used as a pharmaceutical intermediate and as a pesticide intermediate

概要

無水酢酸は、分子式C4H6O3、示性式(CH3CO)2Oで表される有機化合物です。無色の液体で、水と反応してを作ります。空気中において、水分と反応することで、酢酸の強い刺激臭を呈します。

純酢酸(高純度の酢酸)、氷酢酸(純度98%以上の酢酸)は、水分含有量の少ない酢酸(CH3COOH)であり、無水酢酸とは違う化合物であることに注意が必要です。

最も単離が容易なカルボン酸の無水物で、有機合成の原料として広く用いられています。例えば、アルコール、セルロースなどとエステルをつくります。

環境運命予測

Chemical/Physical. Slowly dissolves in water forming acetic acid. In ethanol, ethyl acetate is formed (Windholz et al., 1983).

輸送方法

UN1715 Acetic anhydride, Hazard class: 8; Labels: 8-Corrosive material, 3-Flammable liquid.

純化方法

Adequate purification can usually be achieved by fractional distillation through an efficient column. Acetic acid can be removed by prior refluxing with CaC2 or with coarse Mg filings at 80-90o for 5days, or by distillation from a large excess of quinoline (1% AcOH in quinoline) at 75mm pressure. Acetic anhydride can also be dried by standing with Na wire for up to a week, removing the Na and distilling it under vacuum. (Na reacts vigorously with acetic anhydride at 65-70o). Dippy & Evans [J Org Chem 15 451 1950] let the anhydride (500g) stand over P2O5 (50g) for 3hours, then decanted it and stood it with ignited K2CO3 for a further 3hours. The supernatant liquid was distilled and the fraction b 136-138o was further dried with P2O5 for 12hours, followed by shaking with ignited K2CO3, before two further distillations through a five-section Young and Thomas fractionating column. The final material distilled at 137.8-138.0o. It can also be purified by azeotropic distillation with toluene: the azeotrope boils at 100.6o. After removal of the remaining toluene, the anhydride is distilled [sample had a specific conductivity of 5 x 10-9 ohm-1cm -1]. [Beilstein 2 H 96, 2 I 39, 2 II 91, 2 III 134, 2 IV 94.] Rapid procedure: Shake with P2O5, separate, shake with dry K2CO3 and fractionally distil.

不和合性

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides, alcohols, chromic acid (violent reaction), amines, strong caustics; finely divided metals. Contact with water forms acetic acid and liberates a large amount of heat. Corrosive to iron, steel and other metals.

廃棄物の処理

Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed.