Uses of Vinyl Acetate

Most vinyl acetate is converted into polyvinyl acetate (PVA) which is used in the manufacture of dispersions for paints and binders and as a raw material for paints. It is also copolymerized with vinyl chloride and ethylene and to a lesser extent with acrylic esters. A substantial proportion of vinyl acetate is converted into polyvinyl alcohol by saponification or transesterification of polyvinyl acetate. The main applications for polyvinyl alcohol are either as raw material for adhesives or for fibres. It is also employed in textile finishing and paper glueing, and as a dispersion agent (protective colloid). The world production capacity of PVA was 4.35 Mt/a in 2005, of which 2.1 Mt were converted into polyvinyl alcohol. 

16 Enzymatic and Microbiological Oxidations. Microbial Hydroxylation of Progesterone 

The catalysts are bacteria, typically Acetobacter. Already cited in the Bible (see, e.g.. Numbers 6 3), vinegar is today produced at a rate around 1900 x 10 1/a with an average acetic acid content of 10% (see also Section 4.2.1 et seq.). 

The enzyme involved in the reaction is a heme-containing cytochrome P-450. Several relatives of it are involved in a large number of steroids hydroxylations and, overall, play an important role in steroidogenesis. 

The discovery of this stereoselective hydroxylation at C-11 and the introduction of diosgenin as a cheap raw material had dramatic effects in reducing the cost of steroid hormones. Thus in the early 1950 s, the price of progesterone dropped within just three years from 80 to 3/g. In its turn cortisone cost about 200/g in 1949 whereas today its cost is less than l/g. Several other steroids are also prepared by processes which include a microbiological oxidation step among them, cortexone and fluocortolone. 

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The commercial process for the production of vinyl acetate monomer (VAM) has evolved over the years. In the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate carbon-supported catalyst. This chemistry and process eventually gave way in the late 1960s to a more economically favorable gas-phase conversion of ethylene and acetic acid over a palladium-based silica-supported catalyst. Today, most of the world s vinyl acetate is derived from the ethylene-based process. The end uses of vinyl acetate are diverse and range from die protective laminate film used in automotive safety glass to polymer-based paints and adhesives. 

Diketones. Some years ago Heiba and Dessau reported that Mn(OAc), promotes oxidative addition of isopropenyl acetate to ketones to give 1,4-diketones in 20-35% yield (6, 356). Use of CAN as the oxidant results in higher yields (65-80%) and a regioselective reaction at the more substituted a-position of the ketone.1 Use of vinyl acetate results in the dimethyl acetal of 4-oxo aldehydes. 

All the above-mentioned processes are similar in a CH3CN-pyridine (v/v = 9/1) mixture32. However, the disproportionation rate of Co1 which is electrogenerated at — 1.30 V/SCE and its oxidative addition rate to various arylhalides are divided by a factor of two compared to the rate constants determined in DMF-pyridine. It has also been shown that the use of vinyl acetate stabilizes Co1 species. Under these conditions, the disproportionation rate constant is divided by a factor of seven whereas the oxidative addition rate constants are not much affected. 

Vinyl acetate is a dear colorless liquid. It has a boiling point of 72 °C and a flash point of -9 °C. In 1977 vinyl acetate production in the United States was 1.60 x 10 pounds (1 ). This gave vinyl acetate a rank of 45 among the 50 top-volume chemicals produced in the United States during 1977. The major end uses of vinyl acetate were adhesives (30 ), paints (20 ), textile finishes (15%), and paper coatings (10 ). Approximately 15 of the vinyl acetate produced was exported (2). 

In this resolution involving transesterification, the enzyme is catalysing the acetylation by vinyl acetate of the hydroxyl group of 42 with S configuration. This use of vinyl acetate is now fairly common in enzymatic resolution (see Chadha and Manohar12) hexanoic anhydride is also sometimes used in this context. 

An attempt to convert methyl levulinate to vinyl levulinate was unsuccessful (Figure 2). Heating methyl ester with vinyl acetate in acidic mercuric acetate gave a-angelica lactone as the major product rather than the vinyl ester. Vinyl levulinate was previously prepared by the mercuric ion-catalyzed reaction of levulinic acid with vinyl acetate (id), so this older preparation will be used for future studies. a-Angelica lactone can also be prepared by dehydration of the acid without the use of vinyl acetate (/ 7). 

A modification of the trans-esterification process has found favour with synthetic chemists. The use of vinyl acetate (often as the solvent) for the acetylation of chiral secondary alcohols leads to the formation of vinyl alcohol, which rapidly tautomerizes to acetaldehyde. Acetaldehyde does not take part in a back-reaction (but can form a Schiff base derivative with the enzyme, which may affect the catalyst s activity). For example, the alcohol (31) is readily formed from cyclopentadiene and is enantiospecifi-cally acylated under the influence of Pseudomonas fluorescens lipase (Scheme 3.20) to furnish the acetate (32) and the recovered, optically active alcohol. The unreacted alcohol (—)-(31) was chemically acetylated and converted into the biological active carbocyclic nucleoside aristeromycin. For another example involving this protocol, see Chapter 5 (p. 133). 

Vinyl Acetate Copolymers. Available only as emulsions for PSA applications, the use of vinyl acetate copolymers is still relatively small and confined almost entirely to permanent la-... 

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