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性質
アレンの化学的性質は、一般的なアルケンとは大きく異なります。共役ジエンや孤立ジエンなどと比較すると、アレンはとても不安定です。アレンのC–H結合は、ビニル基のC-H結合よりも弱く、酸性が強いです。
アレンは[2+2]環化付加反応や[4+2]環化付加反応を起こします。遷移金属触媒を用いると、形式的環化付加反応が進行します。
アレンのうち最も基本的な構造を有するプロパジエンは、甘い臭気を持つ無色の気体です。融点は-136.3°C、沸点は-34.4°Cです。水にはほとんど溶解しません。分解しやすいですが、安定性は高く、メチルアセチレンとともに溶接燃料に使用されます。
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解説
プロパジエン，無色の気体．融点－136.3 ℃，沸点－34.5 ℃．C=C0.131 nm．異性体であるプロピン(メチルアセチレン)へ転化しやすい．
森北出版「化学辞典（第2版）
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構造
アレンのように、二重結合が2つ以上連続した構造を集積二重結合と呼びます。化学式はR2C=C=CR2と表わされます。二重結合が3個以上連続した構造を持つ化合物の呼称は、クムレン (英: Cumulene) です。アレンのRをアルキル基としたR2C=C=CR–のような置換基は、アレニル基 (英: allenyl group) と呼ばれます。
最も基本的な構造を有するアレンである、プロパジエンの化学式はH2C=C=CH2です。プロパジエンは、化学式がH3C-C3≡CHのメチルアセチレンとの平衡状態として存在しています。アレンの合成には特殊な合成法が、必要な場合も多いです。ただし工業的にプロパジエンは、メチルアセチレンとの混合物から合成されています。
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合成
図2. アレンの合成
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製造
プロパジエン，石油系炭化水素の高温熱分解生成物に含まれる．実験室的には，2,3-ジブロモ-1-プロペン，2,3-ジクロロ-1-プロペンに亜鉛末を作用させる製法がある．構造は二つの連続した二重結合により，末端炭素に結合した水素原子は直交した二つの平面上にそれぞれ位置する．このため，末端水素原子を異なる置換基で置き換えると，分子不斉となり，光学異性体が存在するようになる．
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説明
MAPP Gas is a stabilized mixture of methylacetylene
and propadiene. Alkane and alkene
hydrocarbons are added as stabilizers. The stabilizers
serve to render the methylacetylene and
propadiene shock insensitive and to ensure that
their concentrations remain nearly uniform at all
times during vaporization of the mixture.
MAPP Gas is transported and stored as a liquid
under its own vapor pressure. Its transportation,
storage, and handling characteristics are
the same as those of liquefied petroleum gas. It
has a characteristic odor detectable at concentrations
as low as 100 ppm in air. Stabilized
liquefied MAPP Gas and MAPP Gas vapor are
insensitive to shock.
Its vapor is not subject to exothermic decomposition
from a 100-J energy source to 419°F
(215°C) and 285 psig (1970 kPa). With a probe
temperature of 825°F (441°C), the gas is stable
up to 600°F (316°C) and 1100 psig (7580 kPa).
Thus, it can be safely used up to full cylinder
pressure.
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化学的特性
Allene is colorless with a sweet odor. It is a flammable gas and may cause fl ash fi re at room
temperature. Allene is the simplest member of the 1,2-diene class of compounds of hydrocarbons
of the aliphatic chemical family. It is a benzene and petroleum ether. Allenes are
not as stable as conjugated dienes or isolated dienes. Allene is slightly more strained than
the isomeric methylactylene. Allene is chiefl y used in organic synthesis. It is incompatible
with metals and oxidizing materials, therefore it is important to avoid copper and silver
and their alloys when used under high pressure or temperature.
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使用
- Allene is extensively used in a variety of photochemical, thermal, and transition metal-mediated cycloadditions.
- It can be lithiated to obtain allenyllithium which reacts with alkyl halides to afford terminal allenes.
- Additional application includes the preparation of reagents such as isopropenylsilanes and isopropenylstannanes by reacting with stannyl and silyl cuprates respectively.
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定義
Any hydrocarbon or hydro-
carbon derivative produced by substitution that has
two double bonds from one carbon and to two oth-
ers.
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一般的な説明
A colorless flammable gas. May become unstable. Not toxic but asphyxiation may occur because of displacement of oxygen. Under prolonged exposure to fire or heat the containers may rupture violently and rocket.
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空気と水の反応
Highly flammable.
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反応プロフィール
The unsaturated aliphatic hydrocarbons, such as PROPADIENE, are generally much more reactive than the alkanes. Strong oxidizers may react vigorously with them. Reducing agents can react exothermically to release gaseous hydrogen. In the presence of various catalysts (such as acids) or initiators, compounds in this class can undergo very exothermic addition polymerization reactions. Many of these compounds undergo autoxidation upon exposure to the air to form explosive peroxides. Violent explosions have occurred at low temperatures in ammonia synthesis gas units. These explosions have been traced to the addition products of dienes and oxides of nitrogen, produced from the interaction of nitrogen oxide and oxygen [Bretherick, 1995].
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健康ハザード
Allene is a simple asphyxiant with slight narcotic properties. Exposures to allene cause
irritation to the skin and eyes, nausea, vomiting, headache, symptoms of drunkenness,
suffocation, convulsions, and coma.
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火災危険
EXTREMELY FLAMMABLE. Will be easily ignited by heat, sparks or flames. Will form explosive mixtures with air. Silane will ignite spontaneously in air. May polymerize explosively when heated or involved in a fire. Vapors from liquefied gas are initially heavier than air and spread along ground. Vapors may travel to source of ignition and flash back. Cylinders exposed to fire may vent and release flammable gas through pressure relief devices. Containers may explode when heated. Ruptured cylinders may rocket.
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使用用途
狭義の「アレン」であるプロパジエンは、MAPPガスの成分として利用されています。MAPPガスとは、プロパジエンとメチルアセチレンの混合物のことです。MAPPガスはや溶接などに用いられています。安全性が高く輸送しやすいですが、コストパフォーマンスが悪いです。
広義の「アレン」に分類される化合物は、あまり工業的に利用されていません。しかし、アレンは反応性に富みさまざまな付加反応を起こすため、有用な化学反応への応用が期待されています。アレンの特徴として、軸方向にキラリティーを持つことなどが挙げられます。
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幾何構造
アレンの中心炭素原子は、σ結合とπ結合を2個ずつ持っています。末端にある炭素原子2個は、sp2混成軌道を有します。炭素原子3個は直線構造を形成しており、結合角は180°です。末端炭素原子2個は平面構造を形成し、各平面は配置が90°ねじれています。
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分子対称性
アレン分子は、2枚羽のプロペラに例えられることが多いです。すなわちアレンは4個の置換基を有し、中心炭素原子を通って2種類の末端CH2平面から、45°傾いた2本の2回回転対称軸C2が存在します。
C=C=C結合軸に沿って3個目の2回回転対称軸を有し、2個のCH2平面はいずれも鏡映対称面になっています。以上のことから、アレン分子の対称性は点群D2dに属し、置換基を持たないアレンは総双極子モーメントがない非極性分子です。
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異性体
図3. アレンの異性体
アレン分子の持つ炭素原子2個が、異なる置換基2種類と結合した誘導体は、鏡像異性体を有します。アレン分子を軸に沿って見た際の置換基の優先順位によって、R配置とS配置を決定可能です。奥側より手前側が優先され、手前と奥の相対配置によって決まっています。
このように、アレンは珍しい光学特性を有するため、有機材料の合成でビルディングブロックに利用されます。
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材料の用途
Piping systems for MAPP Gas must be made of
steel as stated in NFPA 51, Standard for the
Design and Installation of Oxygen-Fuel Gas
Systems for Welding, Cutting, and Allied Processes. Schedule 40 pipe is suitable if joints
are welded. Schedule 80 pipe is recommended
for threaded joints. In no case shall threaded
joints be welded after assembly. Fittings may be
rolled, forged or cast steel, malleable iron, or
modular iron. Gray or white cast iron fittings
must not be used.
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職業ばく露
Used in chemical synthesis and
as a component in mixtures with methyl acetylene, which
make up specialty welding gases.
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貯蔵
MAPP Gas should be treated with the same care
and caution as any other flammable gas. Cylinders
in storage or use should always be secured
in an upright position. Do not transport cylinders
in a closed vehicle.
MAPP Gas cylinder storage inside buildings,
except those in actual use, is limited to 368 lb
(167 kg). Larger quantities must be stored outside,
in a special building, or in a separate room
in accordance with NFPA 51.
MAPP Gas can be used with most commonly
available torches, hoses, and regulators. Acetylene
regulators can be used for working pressures
up to 15 psig (103 kPa). If a working
pressure of more than 15 psig (103 kPa) is required,
a suitable LP-gas regulator should be
used. If cylinders are manifolded, do not use
acetylene pigtails with dry flash arrestors. The
flash arrestors are not necessary and will impede
the flow of MAPP Gas.
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輸送方法
UN2200 Propadiene, stabilized, Hazard Class:
2.1; Labels: 2.1-Flammable gas. Cylinders must be trans-
ported in a secure upright position, in a well-ventilated
truck. Protect cylinder and labels from physical damage.
The owner of the compressed gas cylinder is the only entity
allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill
compressed gas cylinders without the express written
permission of the owner.
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純化方法
Freeze allene in liquid nitrogen, evacuate, then thaw out. This cycle is repeated several times, then the allene is frozen in a methylcyclohexane/liquid nitrogen bath and pumped for some time. It has also been purified by HPLC. [Cripps & Kiefer Org Synth 42 12 1962, Beilstein 1 IV 966.]
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不和合性
Extremely flammable gas or liquid.
Vapor or liquid forms explosive mixture with air.
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, nitrogen oxides.
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廃棄物の処理
Return refillable compressed
gas cylinders to supplier. Return refillable compressed
gas cylinders to supplier. Nonrefillable cylinders should be
disposed of in accordance with local, state and federal
regulations. Allow remaining gas to vent slowly into atmo-
sphere in an unconfined area or exhaust hood. Refillable-
type cylinders should be returned to original supplier
with any valve caps and outlet plugs secured and valve
protection caps in place.
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予防処置
Allene is a flammable gas and the container must be kept stored away from open flame
and smoking areas. Allene should be stored in well-ventilated areas with valve protection
caps in place. The gas cylinders should not be dragged or rolled, and the compressed gas
cylinders should not be refi lled without express written permission. Allene decomposes
violently at increased temperature/heat and/or pressure and the containers should be protected
from rupture and explosion.
