Vinyl acetate


Vinyl acetate is an organic compound with the formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, an important industrial polymer.

Production

The worldwide production capacity of vinyl acetate was estimated at 6,969,000 tonnes/year in 2007, with most capacity concentrated in the United States, China, Japan and Taiwan. The average list price for 2008 was $1600/tonne. Celanese is the largest producer, while other significant producers include China Petrochemical Corporation, Chang Chun Group, and LyondellBasell.
It is a key ingredient in furniture glue.

Preparation

Vinyl acetate is the acetate ester of vinyl alcohol. Since vinyl alcohol is highly unstable, the preparation of vinyl acetate is more complex than the synthesis of other acetate esters.
The major industrial route involves the reaction of ethylene and acetic acid with oxygen in the presence of a palladium catalyst.
2 C2H4 + 2 CH3CO2H + O2 -> 2 CH3CO2CHCH2 + 2 H2O
The main side reaction is the combustion of organic precursors.

Mechanism

Isotope labeling and kinetics experiments suggest that the mechanism involves PdCH2CH2OAc-containing intermediates. Beta-hydride elimination would generate vinyl acetate and a palladium hydride, which would be oxidized to give hydroxide.

Alternative routes

Vinyl acetate was once prepared by hydroesterification. This method involves the gas-phase addition of acetic acid to acetylene in the presence of metal catalysts. By this route, using mercury catalysts, vinyl acetate was first prepared by Fritz Klatte in 1912. Another route to vinyl acetate involves thermal decomposition of ethylidene diacetate:
2CHCH3 -> CH3CO2CHCH2 + CH3CO2H

Polymerization

It can be polymerized to give polyvinyl acetate. With other monomers it can be used to prepare various copolymers such as ethylene-vinyl acetate, vinyl acetate-acrylic acid, polyvinyl chloride acetate, and polyvinylpyrrolidone. Due to the instability of the radical, attempts to control the polymerization via most 'living/controlled' radical processes have proved problematic. However, RAFT polymerization offers a convenient method of controlling the synthesis of PVA by the addition of a xanthate or a dithiocarbamate chain transfer agent.

Other reactions

Vinyl acetate undergoes many of the reactions anticipated for an alkene and an ester. Bromine adds to give the dibromide. Hydrogen halides add to give 1-haloethyl acetates, which cannot be generated by other methods because of the non-availability of the corresponding halo-alcohols. Acetic acid adds in the presence of palladium catalysts to give ethylidene diacetate, CH3CH2. It undergoes transesterification with a variety of carboxylic acids. The alkene also undergoes Diels-Alder and 2+2 cycloadditions.
Vinyl acetate undergoes transesterification, giving access to vinyl ethers:

Toxicity evaluation

Tests suggest that vinyl acetate is of low toxicity. For rats LD50 is 2920 mg/kg.
On January 31, 2009, the Government of Canada's final assessment concluded that exposure to vinyl acetate is not harmful to human health. This decision under the Canadian Environmental Protection Act was based on new information received during the public comment period, as well as more recent information from the risk assessment conducted by the European Union.
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.