Allene

Description

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.

Chemical Properties

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.

Uses

• 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.

Definition

Any hydrocarbon or hydro- carbon derivative produced by substitution that has two double bonds from one carbon and to two oth- ers.

General Description

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.

Air & Water Reactions

Highly flammable.

Reactivity Profile

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].

Health Hazard

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.

Fire Hazard

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.

Materials Uses

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.

Potential Exposure

Used in chemical synthesis and as a component in mixtures with methyl acetylene, which make up specialty welding gases.

storage

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.

Shipping

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.

Purification Methods

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.]

Incompatibilities

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.

Waste Disposal

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.

Precautions

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.