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外観
赤色～暗赤紫色, 結晶～結晶性粉末
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性質
三酸化クロムの融点は197℃、沸点 (分解) は250℃、密度は2.70g/cm3です。三酸化クロムは高温で分解して酸素を遊離し、最終的にを生成可能です (4CrO3 → 2Cr2O3+3O2)。
水には極めて溶けやすく、水溶液は酸性を示します。強力な酸化剤である三酸化クロムは、アルコールなどの有機材料に接触すると点火します。
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反応
有機合成では酸化剤として用いられますが、多くの場合酢酸の溶液として、ジョーンズ酸化の場合はアセトンに溶かして使用されます。これらの酸化において、Cr(VI)は第一級アルコールを対応するカルボン酸に、第二級アルコールをケトンに変換します。
4CrO3 + 3RCH2OH + 12H+ → 3RCOOH + 4Cr3+ + 9H2O
2CrO3 + 3R2CHOH + 6H+ → 3R2C = O + 2Cr3+ + 6H2O
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溶解性
水に易溶 (163.37g/100ml, 20℃), エタノール, エーテルに可溶。注意:エタノールと混合すると発火爆発する。
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解説
二クロム酸カリウム，または二クロム酸ナトリウム，酸化クロム(Ⅵ)の水溶液と濃硫酸との混合物．強い酸化力があり，理化学用ガラス器具の洗浄，とくに有機物による汚れの除去に利用される．液ははじめ赤橙色であるが，使用するにつれて，CrⅢを生じて赤褐色になり，さらに緑色に近づく．CrⅥの毒性と硫酸の腐食性という問題点があるため，現在ではほかの界面活性洗剤にとってかわられて使用は減っている．
森北出版「化学辞典（第2版）
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用途
酸化剤、有機合成原料、触媒。
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用途
金属表面仕上げ剤
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構造
三酸化クロムは固体状態では、頂点を共有する四面体配位のクロム原子が鎖状に並んだ構造をしています。
各中心は1つの酸素原子を隣のクロムと共有していますが、3つの酸素原子は共有されておらず、全体的な化学量論は1:3です。三酸化クロム単量体の構造は、密度汎関数理論を用いて計算されており、平面 (点群D3h) ではなくピラミッド型 (点群C3v) であると予測されています。
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製法
三酸化クロムは、か二クロム酸ナトリウムをと反応させることによって得られます。
H2SO4 + Na2Cr2O7 → 2CrO3 + Na2SO4 + H2O
この製法で工業的には毎年数百万kg生産されています。
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使用上の注意
潮解性がある。可燃性の有機溶剤と接すると発火の危険がある。
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説明
Chromium hydroxide (Cr2O(OH)4) is a bright bluish-green pigment prepared by the calcinations of bichromate with boric acid at 500°C. The mass during cooling is hydrolyzed with water, which yields the hydrate.
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化学的特性
Chromium trioxide is a dark-red crystalline substance. It is odorless
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物理的性質
Dark-red crystals, flakes or granular powder; bipyramidal prismatic system; density 2.70 g/cm3; melts at 197°C; decomposes on further heating; highly soluble in water, 61.7 g and 67 g/100 mL at 0°C and 100°C, respectively; soluble in sulfuric and nitric acids.
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使用
Chromium(VI) oxide is widely used in chromium electroplating, and as protective coatings in corrosion/oxidation resistance of metals. It is also employed in CDs and DVDs. It is useful as an oxidant in Jones oxidation in acetic acid or acetone. It is used in the oxidation of primary alcohols into carboxylic acids, and secondary alcohols into ketones. With phosphoric acid, it is used as a stripping agent for anodic coatings of all types and in the production of syntheric rubies.
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定義
chromium trioxide: A redcompound, CrO3; rhombic; r.d. 2.70;m.p. 196°C. It can be made by carefuladdition of concentrated sulphuricacid to an ice-cooled concentratedaqueous solution of sodium dichromatewith stirring. The mixture isthen filtered through sintered glass,washed with nitric acid, then dried at120°C in a desiccator.
Chromium(VI) oxide is an extremelypowerful oxidizing agent,especially to organic matter; it immediatelyinflames ethanol. It is anacidic oxide and dissolves in water toform ‘chromic acid’, a powerful oxidizingagent and cleansing fluid forglassware. At 400°C, chromium(VI)oxide loses oxygen to givechromium(III) oxide.
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製造方法
Chromium(VI) oxide is prepared by heating sodium dichromate dihydrate with a slight excess of sulfuric acid in a steel tank or cast iron container:
Na2Cr2O7 + 2H2SO4 → 2CrO3 + 2NaHSO4 + H2O
The temperature of the mixture is kept above the melting point of chromium(VI) oxide to evaporate water and separate the top layer of sodium bisulfate from the molten chromium(VI) oxide at the bottom. Temperature control and duration of heating is very crucial in the process. Temperatures over 197°C (melting point), or allowing the molten mass to stand for a longer time, may result in decomposition of the product.
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一般的な説明
Chromium(VI) oxide (CrO3) is a hexavalent chromium that is majorly used as an oxidizing agent. It oxidizes the C-H bonds in the aromatic rings to form benzoic acid from alkyl benzene. It can be prepared by adding concentrated sulphuric acid in potassium dichromate.
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空気と水の反応
Deliquescent. Water soluble, giving acidic solutions.
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反応プロフィール
CHROMIUM TRIOXIDE is a powerful oxidizing agent. Can react violently upon contact with reducing reagents, including organic matter, leading to ignition or explosion. Dangerously reactive with acetone, alcohols, alkali metals (sodium, potassium), ammonia, arsenic, dimethylformamide, hydrogen sulfide, phosphorus, peroxyformic acid, pyridine, selenium, sulfur, and many other chemicals [Sax, 9th ed., 1996, p. 852]. Noncombustible but can accelerate the burning of combustible materials. Sufficient heat may be generated from the reaction with combustible materials to ignite the mass. Aqueous solutions corrode many metals rapidly. Often mixed with sulfuric acid to make "cleaning solution" for glass. Used cleaning solution in closed bottles may explode due to the build up of gaseous carbon dioxide arising from oxidation of organic impurities [Bryson, W. R., Chem. Brit., 1975, 11, p. 377].
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健康ハザード
Chromium(VI) oxide and other chromium(VI) salts are moderately toxic substances by ingestion; 1 to 15 g may be a fatal dose in humans. Ingestion of nonlethal doses of these compounds can cause stomach, liver, and kidney damage; symptoms may include clammy, cyanotic skin, sore throat, gastric burning, vomiting, and diarrhea. Chromic acid is irritating to the skin, and prolonged contact can cause ulceration. Inhalation of chromate dust or chromic acid mist can result in severe irritation of the nose, throat, bronchial tubes, and lungs and may cause coughing, labored breathing, and swelling of the larynx. Eye contact with chromium trioxide and its solutions can cause severe burns and possible loss of vision.
Occupational exposure to chromium(VI) compounds has been related to an increased risk of lung cancer. Several hexavalent compounds of chromium, including chromium trioxide, are listed in IARC Group 1 ("carcinogenic to humans") and are classified as "select carcinogens" under the criteria of the OSHA Laboratory Standard. Long-term exposure to chromium trioxide or chromium(VI) salts may cause ulceration of the respiratory system and skin. Exposure to chromium trioxide by inhalation or skin contact may lead to sensitization. Chromium trioxide has exhibited teratogenic activity in animal tests.
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火災危険
These substances will accelerate burning when involved in a fire. May explode from heat or contamination. Some may burn rapidly. Some will react explosively with hydrocarbons (fuels). May ignite combustibles (wood, paper, oil, clothing, etc.). Containers may explode when heated. Runoff may create fire or explosion hazard.
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燃焼性と爆発性
Chromium(VI) oxide is not combustible but is a strong oxidizing agent and can accelerate the burning rate of combustible materials. Contact with easily oxidized organic or other combustible materials (including paper and oil) may result in ignition, violent combustion, or explosion. The use of dry chemical, carbon dioxide, Halon, or water spray extinguishers is recommended for fires involving chromium (VI) compounds.
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使用用途
主に用の工業原料として使用され、や、その他の金属と反応させ、耐腐食性のクロム保護膜を形成する方法がよく用いられます。
また、赤外域に透過波長域を持つという特徴があり、光学系材料として、吸収膜、エレクトロクロミック用途などに使われます。光学特性 (屈折率、透過率) は基板の温度によって、強い影響を受けます。三酸化クロムの膜質は丈夫で、耐腐蝕、酸化防止、耐磨耗性、密着力を付与するためにも使用可能です。
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法規情報
国内法規上において、毒物及び劇物取締法では「劇物、包装等級2」、消防法では「危険物第一類 クロムの酸化物、危険等級Ⅰ」に該当します。
労働安全衛生法では「名称等を表示・通知すべき危険有害物」および「リスクアセスメントを実施すべき危険有害物」に該当し、化学物質排出把握管理促進法 (PRTR法) では「第1種指定化学物質」に、労働基準法では「疾病化学物質」に指定されているので、取り扱いには注意が必要です。
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取扱いおよび保管上の注意
取扱い及び保管上の注意は、下記の通りです。
- 直射日光を避け、換気の良いなるべく涼しい場所に容器を密栓して保管する。
- 屋外や換気の良い区域のみで使用する。
- 危険を伴うため、高温と直射日光、熱、炎、火花、静電気、スパークとの接触を避ける。
- 発火のおそれがあるため、有機物との直接の接触は避ける。
- 使用時は保護手袋、保護衣、保護眼鏡を着用する。
- 取扱い後はよく手を洗浄する。
- 皮膚に付着した場合は、大量の水で洗い流す。
- 眼に入った場合は、水で15～20分間注意深く洗う。
参考文献
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職業ばく露
Chromium trioxide is used in plating and metal treatment, as a corrosion inhibitor; and as an oxidant; in aluminum anodizing, dye; ink, and paint manufacturing, tanning, engraving; and photography.
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貯蔵
Chromium trioxide should be handled in a fume hood to avoid the inhalation of dust, and impermeable gloves should be worn at all times to prevent skin contact. The practice of using chromate solutions to clean glassware should be avoided. Chromium trioxide should be stored in areas separated from readily oxidized materials.
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輸送方法
UN1463 (anhydrous), Chromium trioxide, anhydrous, Chromium trioxide, anhydrous, Hazard Class: 5.1; Labels: 5.1-Oxidizer, 6.1-Poisonous materials, 8-Corrosive material. UN1755 (solution), Hazard class: 8; Labels: 8-Corrosive material.
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純化方法
It separates when potassium or sodium dichromate are dissolved in conc H2SO4. Dry it in a vacuum desiccator over NaOH pellets. It is a hygroscopic, powerful oxidant and can ignite with organic compounds. It is a skin and pulmonary IRRITANT. [Keyes et al. Industrial Chemicals (Lowenheim & Moran eds.) 4th edn J. Wiley pp 270-274 1975.] CANCER SUSPECT.
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不和合性
Chromium trioxide is a strong oxidizer. The solution in water is a strong acid. Reacts violently with bases and is corrosive. Contact with reducing agents; fuels, organic chemicals, flammable and combustible materials, causing fire and explosion hazard. This chemical decomposes above 250C to chromic oxide and oxygen with increased fire hazard. Attacks metals in the presence of moisture.
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廃棄物の処理
Reduce to Cr(III). If material cannot be recovered and recycled, dispose of sludge in a chemical waste landfill.
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参考文献
A. Byström, K.-A. Wilhelmi, Acta Chem. Scand., 4, 1131 (1950), DOI: 10.3891/acta.chem.scand.04-1131.
