出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2017/07/04 13:21:51」(JST)
硝酸 | |
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共鳴構造式
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IUPAC名
Nitric acid |
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識別情報 | |
CAS登録番号 | 7697-37-2 |
PubChem | 944 |
ChemSpider | 919 |
UNII | 411VRN1TV4 |
EINECS | 231-714-2 |
国連/北米番号 | 2031 |
KEGG | D02313 C00244 |
MeSH | Nitric+acid |
ChEBI | CHEBI:48107 |
ChEMBL | CHEMBL1352 |
RTECS番号 | QU5775000 |
Gmelin参照 | 1576 |
3DMet | B00068 |
SMILES
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InChI
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特性 | |
化学式 | HNO3 |
精密質量 | 62.995642903 g mol-1 |
外観 | 無色の液体 |
密度 | 1.5129 g cm-3 |
融点 |
-41.6 °C, 232 K, -43 °F |
沸点 |
82.6 °C, 356 K, 181 °F (68 % 溶液は 121 °Cで沸騰) |
水への溶解度 | 完全に溶解 |
酸解離定数 pKa | -1.4 |
屈折率 (nD) | 1.397 (16.5 ℃) |
双極子モーメント | 2.17 ± 0.02 D |
危険性 | |
安全データシート(外部リンク) | ICSC 0183 PCTL Safety Website |
EU分類 | 有害 (T) 腐食性 (C) |
EU Index | 007-004-00-1 |
NFPA 704 |
0
4
0
OX
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Rフレーズ | R8 R35 |
Sフレーズ | S1/2 S23 S26 S36 S45 |
引火点 | 不燃性 |
関連する物質 | |
その他の陰イオン | 亜硝酸 |
その他の陽イオン | 硝酸ナトリウム 硝酸カリウム |
関連物質 | 五酸化二窒素 |
出典 | |
ICSC | |
特記なき場合、データは常温 (25 °C)・常圧 (100 kPa) におけるものである。 |
硝酸(しょうさん、nitric acid)は窒素のオキソ酸で、化学式 HNO3 で表される。代表的な強酸の1つで、様々な金属と反応して塩を形成する。有機化合物のニトロ化に用いられる。硝酸は消防法第2条第7項及び別表第一第6類3号により危険物第6類に指定され、硝酸を 10 % 以上含有する溶液は医薬用外劇物にも指定されている。
濃硝酸に二酸化窒素、四酸化二窒素を溶かしたものは発煙硝酸、赤煙硝酸と呼ばれ、さらに強力な酸化力を持つ。その強力な酸化力を利用してロケットの酸化剤や推進剤として用いられる。
五酸化二窒素(無水硝酸、N2O5)を水に溶かすと得られる、一価の強酸性の液体で、金属と反応して硝酸塩(水に可溶)を作る。任意の割合で水に溶け、通常「硝酸」という場合には水溶液を指す。
濃度の低い硝酸を希硝酸という[注 1]。市販の濃硝酸は 60 %(d = 1.360 g cm−3, 13.0 mol dm−3)あるいは 70 % (d = 1.406 g cm−3, 15.6 mol dm−3) の水溶液が普通である。69.8 % の水溶液は共沸混合物となり 123 ℃で沸騰する。
濃硝酸と濃硫酸の混合物である混酸を用いたニトロ化合物の合成などから爆薬が作られ、他にも染料、肥料などの製造に用いる。
強酸化剤で、木炭の粉末とともに熱すれば木炭は酸化されて二酸化炭素となる。
二酸化窒素や四酸化二窒素を吸収させて発煙硝酸や赤煙硝酸とし、ロケットエンジンの推進剤の酸化剤として用いられる。有機系の燃料と混合するだけで点火する。
硝酸に触れるとキサントプロテイン反応によって皮膚が黄変する。
光に弱く、長時間光を浴び続けると分解し黄色を帯びる。
そのため褐色瓶中で保管する。
希塩酸とは異なり、酸化作用により希硝酸であっても水素よりイオン化傾向の小さい金属を溶かすことが可能である。白金、金を溶かすことはできないが、濃硝酸と濃塩酸を混ぜて王水を作ることにより、これらの金属も溶かすことが可能になる。また、アルミニウム、クロムおよび鉄などは濃硝酸中で表面に酸化皮膜を形成し不動態が形成されるため反応が進行しない。
極めて薄い硝酸水溶液の場合、マグネシウムは初期において水素ガスを発生する[1]。
しかし、希硝酸中であっても亜鉛などの比較的イオン化傾向の大きな金属は硝酸イオンをアンモニウムイオンまで還元する[2]。
また希硝酸はよりイオン化傾向の小さな金属の場合は主に一酸化窒素を発生する。
濃硝酸では二酸化窒素の発生が主反応となり、発熱により反応は次第に激しくなる。
硝酸は硫酸中では塩基として挙動しプロトン化を受け、脱水によりニトロイルイオン (nitroyl / NO2+) を生成する。濃硝酸と濃硫酸を混合した混酸中では以下のような化学平衡が成立している。
このニトロイルイオンが芳香族化合物などに対し求電子置換反応を起こしニトロ化が進行する。
純粋な遊離酸も 0 ℃で硝酸カリウムと純硫酸を反応させ、真空蒸留により単離することが可能である。
しかし不安定であり光反応などにより分解し、二酸化窒素などを発生させる[1]。
純硝酸は遊離酸として知られているものの中ではもっとも強く自己解離し、さらに生成するリオニウムイオンは脱水されニトロイルイオンとなり、その平衡定数は 25 ℃ で以下のようである
高い電気伝導度を示し、25 ℃ における比電気伝導度は 3.72 × 10−2 Ω−1 cm−1 であり、純硫酸よりさらに高い[1]。
また、純硝酸のハメットの酸度関数は H 0 = − 6.3 であり純硫酸などに比べるとかなり酸性度は低い[3]。
硝酸の第一水和エンタルピー変化および溶解エンタルピー変化は以下の通りであり、過塩素酸および硫酸などより発熱量は少ない[4]。
硝酸は水溶液中では強酸として挙動し、0.1 mol/dm3 程度の水溶液ではほぼ完全に解離し塩酸および過塩素酸などと電離度に大きな差は認められないが、濃厚溶液ではこれらの酸との電離度に差が認められ、2 - 4 mol/dm3 溶液については糖転化の触媒作用についてこれらより弱いことが示され、非解離の硝酸分子が存在することが示されている[5][6]。
濃厚溶液中における非解離の硝酸分子の濃度とデバイ-ヒュッケルの拡張理論などから硝酸の酸解離定数は K = 21 (pKa = −1.32) と求められ、またメタノール中 (pKa = 3.2) の値より水中では pKa = −1.8 とする推定値もある[7]。
また、水溶液中の解離に関する熱力学的な数値も報告されており、そのギブスの自由エネルギー変化によればpKa = −1.44である[8]。
−13.81 kJ mol−1 | −8.24 kJ mol−1 | −18.4 J mol−1 K−1 |
8世紀のアラビアの科学者ジャービル・イブン=ハイヤーンによって緑礬 FeSO4・7H2O または明礬 KAl(SO4)2・12H2O と硝石 KNO3 とを混ぜて蒸留によって合成されることが発見された。17世紀にはいってヨハン・ルドルフ・グラウバーがこれを改良し、硫酸と硝石との混合物を蒸留し、純粋な硝酸を作っている。銅・銀などをも溶かし金属に対する作用は硫酸よりも強いということから、強い水という意味のラテン語をとり aqua fortis と呼ばれた。イギリスでは硝石の精という意味の spirit of nitre ともいわれていた。硝酸という言葉は1789年にアントワーヌ・ラヴォアジエによってフランス語で acide nitrique と命名されて以来用いられるようになった。
2004年度日本国内生産量は 630,290 t、消費量は 331,347 t である。ヴィルヘルム・オストヴァルト考案のオストワルト法(アンモニア酸化法とも[9])による生産が一般的である。
アンモニアを白金触媒の存在下で 900 ℃ 程度に加熱すると一酸化窒素が得られる。この反応においては触媒とアンモニアの接触時間が重要であり、接触時間が長いとアンモニアと一酸化窒素とが反応して窒素が生成されてしまう[9]。触媒にはこのほかに CuO-MnO2 系や、Fe2O3-Bi2O3 系などの金属酸化物触媒も、かつては用いられたことがあったが、触媒活性で劣っていたり、反応中に触媒が微粉化してしまうため、現在では、白金に 10 % ほどのロジウムを加えた金網状の触媒が用いられている。白金-ロジウム触媒を用いた際には反応温度 800 °C、接触時間 0.001 秒の反応条件で一酸化窒素への転化が起こり、その収率は 95 – 98 % である[9]。そのほかに粘土によっても酸化に成功した事例もあるが、収率は半分以下である。
一酸化窒素は自発的に空気中の酸素と反応し二酸化窒素となる。空気酸化によるこの工程での収率はおよそ 50 % であり、純粋な酸素を用いて酸化させることでその収率は 62 % まで向上する[9]。
二酸化窒素を水(温水)と反応させると硝酸と一酸化窒素が発生する(一酸化窒素は最初のサイクルに戻る)(冷水との反応は「二酸化窒素」を参照)。常圧で反応させた場合は硝酸の濃度が低いため、ポーリング式硝酸濃縮法と呼ばれる方法を用いて硝酸濃度を 98 %になるまで濃縮が行われる。また、10 気圧 (106 Pa) ほどの圧力を加えて反応させる高圧法を用いれば、濃縮の必要なく直接 98 %の硝酸が得られる[9]。
全体として、
窒素酸化物は大気中でもこのような反応を起こし、酸性雨の原因の一つとなる。ただし僅かなレベルであれば植物の栄養源となる。
硝酸イオン(しょうさんイオン、NO3−, nitrate)は硝酸およびその化合物の電離、分解によって主に生じる1価の陰イオン、窒素化合物であり、硝酸塩中にも存在し、平面正三角形型構造で N−O 結合距離は硝酸三水和物中において 124.7 – 126.5 pm である[7]。
硝酸は強い酸化剤であり、多くの金属と反応するため多種の塩を生成する。また一般に、金属の硝酸塩は水に溶解しやすい。
希薄水溶液中における標準酸化還元電位は以下の通りである。
硝酸イオンは白金電極を用いた水溶液の電解により陰極でアンモニアまで還元される。
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消防法により硝酸塩類は危険物 第1類 酸化性固体に分類される。硝酸イオンは本来無色透明であるが、遷移金属イオンを含むものは有色であることが多い。
主に火薬、肥料、食品添加物(発色剤)などに用いられる。
水溶性であるため雨量の多い日本国内での産出は確認されていないが、南米チリが主な原産国である。
硝酸は好気性菌によって生物の屍骸等からアンモニア、亜硝酸を経て生成される。さらに嫌気性菌によって窒素等に分解され空気中等に放出されていく。なお、アクアリウムの生態系において嫌気性菌の発生は困難であり、水槽中に硝酸が分解されないまま溜まっていくので、高濃度となる以前の適度な水換えが必要となる。ただし一般的に、アクアリストにとって硝酸はアンモニアや亜硝酸との比較において毒性の低い物質と認識されている。
ウィキメディア・コモンズには、硝酸に関連するカテゴリがあります。 |
ウィキメディア・コモンズには、硝酸塩に関連するカテゴリがあります。 |
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Names | |||
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IUPAC name
Nitric acid
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Other names
Aqua fortis, Spirit of niter, Eau forte, Hydrogen nitrate, Acidum nitricum
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Identifiers | |||
CAS Number
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3D model (JSmol)
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3DMet | B00068 | ||
ChEBI |
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ChemSpider |
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ECHA InfoCard | 100.028.832 | ||
EC Number | 231-714-2 | ||
Gmelin Reference
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1576 | ||
KEGG |
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MeSH | Nitric+acid | ||
PubChem CID
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RTECS number | QU5775000 | ||
UNII |
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UN number | 2031 | ||
InChI
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SMILES
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Properties | |||
Chemical formula
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HNO3 | ||
Molar mass | 63.01 g·mol−1 | ||
Appearance | Colorless, yellow or red fuming liquid[1] | ||
Odor | acrid, suffocating[1] | ||
Density | 1.5129 g cm−3 | ||
Melting point | −42 °C (−44 °F; 231 K) | ||
Boiling point | 83 °C (181 °F; 356 K) 68% solution boils at 121 °C (250 °F; 394 K) | ||
Solubility in water
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Completely miscible | ||
Vapor pressure | 48 mmHg (20 °C)[1] | ||
Acidity (pKa) | -1.4[2] | ||
Magnetic susceptibility (χ)
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−19.9·10−6 cm3/mol | ||
Refractive index (nD)
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1.397 (16.5 °C) | ||
Dipole moment
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2.17 ± 0.02 D | ||
Thermochemistry | |||
Std molar
entropy (S |
146 J·mol−1·K−1[3] | ||
Std enthalpy of
formation (ΔfH |
−207 kJ·mol−1[3] | ||
Hazards | |||
Safety data sheet | ICSC 0183 PCTL Safety Website |
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EU classification (DSD) (outdated)
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C O T+ | ||
R-phrases (outdated) | R8 R35 | ||
S-phrases (outdated) | (S1/2) S23 S26 S36 S45 | ||
NFPA 704 |
0
4
0
OX
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Flash point | Non-flammable | ||
Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration)
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138 ppm (rat, 30 min)[1] | ||
US health exposure limits (NIOSH): | |||
PEL (Permissible)
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TWA 2 ppm (5 mg/m3)[1] | ||
REL (Recommended)
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TWA 2 ppm (5 mg/m3) ST 4 ppm (10 mg/m3)[1] | ||
IDLH (Immediate danger)
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25 ppm[1] | ||
Related compounds | |||
Other anions
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Nitrous acid | ||
Other cations
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Sodium nitrate Potassium nitrate |
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Related compounds
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Dinitrogen pentoxide | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Y verify (what is YN ?) | |||
Infobox references | |||
Nitric acid (HNO3), also known as aqua fortis and spirit of niter, is a highly corrosive mineral acid.
The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%.
Nitric acid is the primary reagent used for nitration – the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.
Commercially available nitric acid is an azeotrope with water at a concentration of 68% HNO3, which is the ordinary concentrated nitric acid of commerce. This solution has a boiling temperature of 120.5 °C at 1 atm. Two solid hydrates are known; the monohydrate (HNO3·H2O) and the trihydrate (HNO3·3H2O).
Nitric acid of commercial interest usually consists of the maximum boiling azeotrope of nitric acid and water, which is approximately 68% HNO3, (approx. 15 molar). This is considered concentrated or technical grade, while reagent grades are specified at 70% HNO3. The density of concentrated nitric acid is 1.42 g/cm3[inconsistent]. An older density scale is occasionally seen, with concentrated nitric acid specified as 42° Baumé.[4]
Nitric acid is subject to thermal or light decomposition and for this reason it was often stored in brown glass bottles: 4 HNO3 → 2 H2O + 4 NO2 + O2. This reaction may give rise to some non-negligible variations in the vapor pressure above the liquid because the nitrogen oxides produced dissolve partly or completely in the acid.
The nitrogen dioxide (NO2) remains dissolved in the nitric acid coloring it yellow or even red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors, leading to the common name "red fuming acid" or "fuming nitric acid" – the most concentrated form of nitric acid at Standard Temperature and Pressure (STP). Nitrogen oxides (NOx) are soluble in nitric acid.
A commercial grade of fuming nitric acid contains 90% HNO3 and has a density of 1.50 g/cm3. This grade is often used in the explosives industry. It is not as volatile nor as corrosive as the anhydrous acid and has the approximate concentration of 21.4 molar.
Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide (NO2) leaving the solution with a reddish-brown color. Due to the dissolved nitrogen dioxide, the density of red fuming nitric acid is lower at 1.490 g/cm3.
An inhibited fuming nitric acid (either IWFNA, or IRFNA) can be made by the addition of 0.6 to 0.7% hydrogen fluoride (HF). This fluoride is added for corrosion resistance in metal tanks. The fluoride creates a metal fluoride layer that protects the metal.
White fuming nitric acid, pure nitric acid or WFNA, is very close to anhydrous nitric acid. It is available as 99.9% nitric acid by assay. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved NO2. Anhydrous nitric acid has a density of 1.513 g/cm3 and has the approximate concentration of 24 molar. Anhydrous nitric acid is a colorless mobile liquid with a density of 1.512 g/cm3, which solidifies at −42 °C to form white crystals. As it decomposes to NO2 and water, it obtains a yellow tint. It boils at 83 °C. It is usually stored in a glass shatterproof amber bottle with twice the volume of head space to allow for pressure build up, but even with those precautions the bottle must be vented monthly to release pressure.
The molecule is planar. Two of the N–O bonds are equivalent and relatively short (this can be explained by theories of resonance; the canonical forms show double-bond character in these two bonds, causing them to be shorter than typical N–O bonds), and the third N–O bond is elongated because the O atom is also attached to a proton.[5][6]
Nitric acid is normally considered to be a strong acid at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the pKa value is usually reported as less than −1. This means that the nitric acid in diluted solution is fully dissociated except in extremely acidic solutions. The pKa value rises to 1 at a temperature of 250 °C.[7]
Nitric acid can act as a base with respect to an acid such as sulfuric acid:
The nitronium ion, NO2+, is the active reagent in aromatic nitration reactions. Since nitric acid has both acidic and basic properties, it can undergo an autoprotolysis reaction, similar to the self-ionization of water:
Nitric acid reacts with most metals, but the details depend on the concentration of the acid and the nature of the metal. Dilute nitric acid behaves as a typical acid in its reaction with most metals. Magnesium, manganese and zinc liberate H2:
Nitric acid can oxidize non-active metals such as copper and silver. With these non-active or less electropositive metals the products depend on temperature and the acid concentration. For example, copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry:
The nitric oxide produced may react with atmospheric oxygen to give nitrogen dioxide. With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry:
Upon reaction with nitric acid, most metals give the corresponding nitrates. Some metalloids and metals give the oxides; for instance, Sn, As, Sb, and Ti are oxidized into SnO2, As2O5, Sb2O5, and TiO2 respectively.[8]
Some precious metals, such as pure gold and platinum-group metals do not react with nitric acid, though pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid. However, some less noble metals (Ag, Cu, ...) present in some gold alloys relatively poor in gold such as colored gold can be easily oxidized and dissolved by nitric acid, leading to colour changes of the gold-alloy surface. Nitric acid is used as a cheap means in jewelry shops to quickly spot low-gold alloys (< 14 carats) and to rapidly assess the gold purity.
Being a powerful oxidizing agent, nitric acid reacts violently with many non-metallic compounds, and the reactions may be explosive. Depending on the acid concentration, temperature and the reducing agent involved, the end products can be variable. Reaction takes place with all metals except the noble metals series and certain alloys. As a general rule, oxidizing reactions occur primarily with the concentrated acid, favoring the formation of nitrogen dioxide (NO2). However, the powerful oxidizing properties of nitric acid are thermodynamic in nature, but sometimes its oxidation reactions are rather kinetically non-favored. The presence of small amounts of nitrous acid (HNO2) greatly enhance the rate of reaction.[8]
Although chromium (Cr), iron (Fe), and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal-oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called passivation. Typical passivation concentrations range from 20% to 50% by volume (see ASTM A967-05). Metals that are passivated by concentrated nitric acid are iron, cobalt, chromium, nickel, and aluminium.[8]
Being a powerful oxidizing acid, nitric acid reacts violently with many organic materials and the reactions may be explosive. The hydroxyl group will typically strip a hydrogen from the organic molecule to form water, and the remaining nitro group takes the hydrogen's place. Nitration of organic compounds with nitric acid is the primary method of synthesis of many common explosives, such as nitroglycerin and trinitrotoluene (TNT). As very many less stable byproducts are possible, these reactions must be carefully thermally controlled, and the byproducts removed to isolate the desired product.
Reaction with non-metallic elements, with the exceptions of nitrogen, oxygen, noble gases, silicon, and halogens other than iodine, usually oxidizes them to their highest oxidation states as acids with the formation of nitrogen dioxide for concentrated acid and nitric oxide for dilute acid.
or
Concentrated nitric acid oxidizes I2, P4, and S8 into HIO3, H3PO4, and H2SO4, respectively.[8]
Nitric acid reacts with proteins to form yellow nitrated products. This reaction is known as the xanthoproteic reaction. This test is carried out by adding concentrated nitric acid to the substance being tested, and then heating the mixture. If proteins that contain amino acids with aromatic rings are present, the mixture turns yellow. Upon adding a base such as ammonia, the color turns orange. These color changes are caused by nitrated aromatic rings in the protein.[9][10] Xanthoproteic acid is formed when the acid contacts epithelial cells. Respective local skin color changes are indicative of inadequate safety precautions when handling nitric acid.
Nitric acid is made by reaction of nitrogen dioxide (NO2) with water.
Normally, the nitric oxide produced by the reaction is reoxidized by the oxygen in air to produce additional nitrogen dioxide.
Bubbling nitrogen dioxide through hydrogen peroxide can help to improve acid yield.
Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid. Production of nitric acid is via the Ostwald process, named after German chemist Wilhelm Ostwald. In this process, anhydrous ammonia is oxidized to nitric oxide, in the presence of platinum or rhodium gauze catalyst at a high temperature of about 500 K and a pressure of 9 bar.
Nitric oxide is then reacted with oxygen in air to form nitrogen dioxide.
This is subsequently absorbed in water to form nitric acid and nitric oxide.
The nitric oxide is cycled back for reoxidation. Alternatively, if the last step is carried out in air:
The aqueous HNO3 obtained can be concentrated by distillation up to about 68% by mass. Further concentration to 98% can be achieved by dehydration with concentrated H2SO4. By using ammonia derived from the Haber process, the final product can be produced from nitrogen, hydrogen, and oxygen which are derived from air and natural gas as the sole feedstocks.[11]
Prior to the introduction of the Haber process for the production of ammonia in 1913, nitric acid was produced using the Birkeland–Eyde process, also known as the arc process. This process is based upon the oxidation of atmospheric nitrogen by atmospheric oxygen to nitric oxide at very high temperatures. An electric arc was used to provide the high temperatures, and yields of up to 4% nitric oxide were obtained. The nitric oxide was cooled and oxidized by the remaining atmospheric oxygen to nitrogen dioxide, and this was subsequently absorbed in dilute nitric acid. The process was very energy intensive and was rapidly displaced by the Ostwald process once cheap ammonia became available.
In laboratory, nitric acid can be made by thermal decomposition of copper(II) nitrate, producing nitrogen dioxide and oxygen gases, which are then passed through water to give nitric acid.
An alternate route is by reaction of approximately equal masses of any nitrate salt such as sodium nitrate with 96% sulfuric acid (H2SO4), and distilling this mixture at nitric acid's boiling point of 83 °C. A nonvolatile residue of the metal sulfate remains in the distillation vessel. The red fuming nitric acid obtained may be converted to the white nitric acid.[6]
The dissolved NOx are readily removed using reduced pressure at room temperature (10–30 min at 200 mmHg or 27 kPa) to give white fuming nitric acid. This procedure can also be performed under reduced pressure and temperature in one step in order to produce less nitrogen dioxide gas.[citation needed]
Dilute nitric acid may be concentrated by distillation up to 68% acid, which is a maximum boiling azeotrope containing 32% water. In the laboratory, further concentration involves distillation with either sulfuric acid or magnesium nitrate which act as dehydrating agents. Such distillations must be done with all-glass apparatus at reduced pressure, to prevent decomposition of the acid. Industrially, highly concentrated nitric acid is produced by dissolving additional nitrogen dioxide in 68% nitric acid in an absorption tower.[12] Dissolved nitrogen oxides are either stripped in the case of white fuming nitric acid, or remain in solution to form red fuming nitric acid. More recently, electrochemical means have been developed to produce anhydrous acid from concentrated nitric acid feedstock.[13]
The main industrial use of nitric acid is for the production of fertilizers. Nitric acid is neutralized with ammonia to give ammonium nitrate. This application consumes 75–80% of the 26M tons produced annually (1987). The other main applications are for the production of explosives, nylon precursors, and specialty organic compounds.[14]
In organic synthesis, industrial and otherwise, the nitro group is a versatile functional group. Most derivatives of aniline are prepared via nitration of aromatic compounds followed by reduction. Nitrations entail combining nitric and sulfuric acids to generate the nitronium ion, which electrophilically reacts with aromatic compounds such as benzene. Many explosives, such as TNT, are prepared this way.
The precursor to nylon, adipic acid, is produced on a large scale by oxidation of cyclohexanone and cyclohexanol with nitric acid.[14]
Nitric acid has been used in various forms as the oxidizer in liquid-fueled rockets. These forms include red fuming nitric acid, white fuming nitric acid, mixtures with sulfuric acid, and these forms with HF inhibitor.[15] IRFNA (inhibited red fuming nitric acid) was one of 3 liquid fuel components for the BOMARC missile.[16]
In elemental analysis by ICP-MS, ICP-AES, GFAA, and Flame AA, dilute nitric acid (0.5 to 5.0%) is used as a matrix compound for determining metal traces in solutions.[17] Ultrapure trace metal grade acid is required for such determination, because small amounts of metal ions could affect the result of the analysis.
It is also typically used in the digestion process of turbid water samples, sludge samples, solid samples as well as other types of unique samples which require elemental analysis via ICP-MS, ICP-OES, ICP-AES, GFAA and flame atomic absorption spectroscopy. Typically these digestions use a 50% solution of the purchased HNO
3 mixed with Type 1 DI Water.
In electrochemistry, nitric acid is used as a chemical doping agent for organic semiconductors, and in purification processes for raw carbon nanotubes.
In a low concentration (approximately 10%), nitric acid is often used to artificially age pine and maple. The color produced is a grey-gold very much like very old wax or oil finished wood (wood finishing).[18]
The corrosive effects of nitric acid are exploited for a number of specialty applications, such as etching in printmaking, pickling stainless steel or cleaning silicon wafers in electronics.[19]
A solution of nitric acid, water and alcohol, Nital, is used for etching of metals to reveal the microstructure. ISO 14104 is one of the standards detailing this well known procedure.
Commercially available aqueous blends of 5–30% nitric acid and 15–40% phosphoric acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning). The phosphoric acid content helps to passivate ferrous alloys against corrosion by the dilute nitric acid.[citation needed]
Nitric acid can be used as a spot test for alkaloids like LSD, giving a variety of colours depending on the alkaloid.[20]
Nitric acid is a corrosive acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns as it carries out acid hydrolysis with proteins (amide) and fats (ester) which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin. These yellow stains turn orange when neutralized.[21] Systemic effects are unlikely, however, and the substance is not considered a carcinogen or mutagen.[22]
The standard first aid treatment for acid spills on the skin is, as for other corrosive agents, irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes to cool the tissue surrounding the acid burn and to prevent secondary damage. Contaminated clothing is removed immediately and the underlying skin washed thoroughly.
Being a strong oxidizing agent, reactions of nitric acid with compounds such as cyanides, carbides, or metallic powders can be explosive and those with many organic compounds, such as turpentine, are violent and hypergolic (i.e. self-igniting). Hence, it should be stored away from bases and organics.
The first mention of nitric acid is in Pseudo-Geber's De Inventione Veritatis, wherein it is obtained by calcining a mixture of niter, alum and blue vitriol. It was again described by Albert the Great in the 13th century and by Ramon Lull, who prepared it by heating niter and clay and called it "eau forte" (aqua fortis).[23]
Glauber devised a process to obtain it by distillate potassium nitrate with sulfuric acid. In 1776 Lavoisier showed that it contained oxygen, and in 1785 Henry Cavendish determined its precise composition and showed that it could be synthesized by passing a stream of electric sparks through moist air.[23]
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リンク元 | 「100Cases 10」「nitrate」 |
拡張検索 | 「dil. HNO3」「conc. HNO3」 |
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