VINYL FLUORIDE

Description

Vinyl fluoride (VF) was first synthesized by Frederic Swarts, a Belgian chemist in 1901, by the reaction between zinc and 1,1-difluoro-2-bromoethane. Modern preparation involves the reaction of acetylene and hydrogen fluoride (HF) in the presence of a mercury- or aluminum-based catalyst. The US Environmental Protection Agency (EPA) listed VF as a highproduction- volume chemical in 1990. According to National Toxicology Program (NTP), 2005, the annual production of VF in the United States was above 1 million pounds (454 000 kg) in 1990 and approximately 3.3 million pounds (1.5 million kg) in 2001.

Chemical properties

Colorless gas. Insoluble in water; soluble in alcohol and ether.

Chemical properties

Vinyl fluoride is a colorless gas.

The Uses of VINYL FLUORIDE

Vinyl fluoride is used primarily in the production of polyvinyl fluoride and other fluoropolymers. Polymers of vinyl fluoride are resistant to weather and exhibit great strength, chemical inertness, and low permeability to air and water. Polyvinyl fluoride is laminated with aluminum, galvanized steel, and cellulose materials and is used as a protective surface for the exteriors of residential and commercial buildings. Polyvinyl fluoride laminated with various plastics has been used to cover walls, pipes, and electrical equipment and inside aircraft cabins (IARC 1995).

The Uses of VINYL FLUORIDE

Since the 1960s, VF has mainly been used in the production of polyvinyl fluoride (PVF) and other fluoropolymers. Polymers of VF have excellent resistance to degradation by sunlight, chemical attack, and water absorption and exhibit great strength, chemical inertness, and low permeability to air and water. PVF is laminated with aluminum, galvanized steel, and cellulose materials and is used as a protective surface for the exteriors of residential and commercial buildings. PVF laminated with various plastics has been used to cover walls, pipes, and electrical equipments and inside aircraft cabins. PVF is sold under the trademarks Tedlar PVF film and Dalvor. Due to increase in demand for solar panels, the demand for photovoltaic materials such as Tedlar is high, forcing the manufacturer to boost VF production.

Production Methods

The first preparation of VF in the early 1900s was by reacting zinc with 1,1-difluoro-2-bromomethane.
VF was considered to be a high production volume chemical according to the U.S. Environmental Protection Agency with annual production exceeding 1million lb in 1990. In 2001, annual U.S. production was estimated approximately 3.3 million lb. In 1994, VF was produced by one company each in Japan and the United States. More recently, only one U.S. manufacturer of VF was identified . Information on European manufacturer is not available.
The modern production is by the addition of hydrogen fluoride to acetylene over a mercury- or aluminum-based catalyst.

Preparation

Vinyl fluoride may be obtained from acetylene by either of the two following routes:

In the first method, acetylene is heated with hydrogen fluoride in the presence of a catalyst of mercuric chloride on charcoal at about 40??C to yield vinyl fluoride directly. In the second method, acetylene is treated with an excess of hydrogen fluoride to form difluoroethane which is then pyrolysed at about 700??C in a platinum tube to give vinyl fluoride, which is separated by distillation under pressure.
Vinylidene fluoride is obtained from vinylidene chloride by the following route:

In the first stage, vinylidene chloride undergoes addition with hydrogen chloride at about 30??C and atmospheric pressure in the presence of a FriedelCrafts type catalyst. The resulting trichloroethane is then treated with hydrogen fluoride at about 180??C and 3 MPa (30 atmospheres) in the presence of antimony pentachloride to give chlorodifluoroethane. Pyrolysis of this product yields vinylidene fluoride. Vinylidene fluoride is a gas, b.p. -84??C.

Definition

ChEBI: Fluoroethene is a monohaloethene and a gas molecular entity.

General Description

A colorless gas with a faint ethereal odor. Shipped as a confined liquid under its vapor pressure. Any leak can either be liquid or vapor. Contact with the liquid can cause frostbite. Easily ignited. Vapors are heavier than air. Can asphyxiate by the displacement of air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket.

Air & Water Reactions

Highly flammable, reacts with air to form peroxides

Reactivity Profile

VINYL FLUORIDE is light sensitive, peroxidizable monomer may initiate exothermic polymerization of the bulk material [Handling Chemicals Safely 1980. p. 958]. Sensitive to many oxidants.

Health Hazard

Inhalation of vapor causes slight intoxication, some shortness of breath. Liquid may cause frostbite of eyes or skin.

Safety Profile

Confirmed carcinogen. A poison. Mutation data reported. A very dangerous fire hazard. To fight fire, stop flow of gas. When heated to decomposition it emits toxic fumes of F-. See also FLUORIDES.

Potential Exposure

Vinyl fluoride’s primary use is as a chemical and polymer intermediate; used to make polyvinyl fluoride (Tedlar) film. Polyvinyl fluoride film is characterized by superior resistance to weather, high strength; and a high dielectric constant. It is used as a film laminate for building materials and in packaging electrical equipment. Polyvinyl fluoride film poses a hazard, so it is not recommended for food packaging. Polyvinyl fluoride evolves toxic fumes upon heating.

Carcinogenicity

Vinyl fluoride is reasonably anticipated to be a human carcinogenbased on sufficient evidence of carcinogenicity from studies in experimental animals.

Environmental Fate

VF is expected to exist solely as a gas in the ambient atmosphere. The gas-phase of VF is degraded in the atmosphere by reaction with photochemically produced hydroxyl radicals. The half-life for this reaction in air is estimated to be 3 days as calculated from its rate constant of 5.56 × 10^-12 cm3 molecule sec-^-1 at 25°C. VF also reacts with atmospheric ozone, leading to its atmospheric degradation (estimated half-life of about 16 days). The Henry’s Law constant of VF (0.118 atmm3 mol1) indicates that VF is expected to volatilize rapidly from water surfaces. Due to its volatile property, VF is not persistent in nature and adsorption to sediment is not considered to be a natural process for VF in water. The half-life for volatilization from a model river (1-m deep) and a model pond (2-m deep) are 2 and 23.5 h, respectively. VF is not expected to bioconcentrate in aquatic organisms as it has a bioconcentration factor (BCF) of 4.7, whereas a BCF value greater than 1000 is required for its significant bioaccumulation. As VF remains as a gas under normal conditions, it readily evaporates to the atmosphere when released into soil. When dissolved in an aqueous solution, VF is very mobile in soil. Lack of sufficient data prevents to predict its biodegradation fate in soils.

Shipping

UN1860 Vinyl fluoride, inhibited, Hazard Class: 2.1; Labels: 2.1-Flammable gas.

Toxicity evaluation

VF is readily absorbed after administration by inhalation. Its metabolism is saturable and dose dependent.
VF is metabolized via the same pathway as for other carcinogenic vinyl halides like vinyl chloride (VC) and vinyl bromide. VF is metabolized to DNA-reactive intermediates fluoroethylene oxide and fluoroacetaldehyde via a human cytochrome P450 2E1 (CYP) dependent pathway. These reactive metabolites react with DNA bases and form promutagenic DNA adducts mainly 1, N6-ethenoadenine and N2,3- -ethenoguanine and cause DNA miscoding by modifying base-pairing sites. These cyclic etheno adducts lead to misincorporation of bases upon replication or transcription and cause critical lesions in VF-induced carcinogenesis. The fluoroacetaldehyde is metabolized to fluoroacetic acid, a potent inhibitor of the Krebs cycle. As a consequence, its incorporation into the citric acid cycle disrupts energy metabolism and leads to increased production of mitochondrial acetyl coenzyme A and causes excretion of ketone bodies and free F. So, administration of VF has been shown to increase acetone exhalation and F excretion in urine of experimental animals. On the other hand, fluoroacetaldehyde alkylates the prosthetic heme group of CYP resulting irreversible inactivation of the enzyme, which catalyzes the VF metabolism. The alkylate has been identified as N-(2-oxoethyl) protoporphyrin IX or green porphyrin.

Incompatibilities

May polymerize. Inhibited with 0.2% terpenes to prevent polymerization. Violent reaction with oxidizers. May accumulate static electrical charges.