Acetylenic Routes

Reaction of the ArC,o unit with 1-pentynylmagnesium bromide occurred smoothly in tetrahyrofuran containing cuprous chloride without formation of alienic impurities. An analogous type of route was used for the synthesis of 1,3-dimethoxy-5-[(ZZ)-pentadec-8,11-dienyl]benzene, (15 2)-cardol dimethyl ether (ref. 105). For the synthesis of (15 2)-urushiol, 1,2-dihydroxy-3-[(ZZ)-penta-dec-8.11-dienyl]benzene and its dimethyl ether, 7-(2,3-dimethoxyphenyl)heptyl bromide and the corresponding 2,3-dihydroxy compound, obtained by demethylation with boron tribromide, have been used (ref. 149). 

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The principal chemical markets for acetylene at present are its uses in the preparation of vinyl chloride, vinyl acetate, and 1,4-butanediol. Polymers from these monomers reach the consumer in the form of surface coatings (paints, films, sheets, or textiles), containers, pipe, electrical wire insulation, adhesives, and many other products which total biUions of kg. The acetylene routes to these monomers were once dominant but have been largely displaced by newer processes based on olefinic starting materials. 

On the laboratory scale, isothiazole is most conveniently prepared by the acetylenic route.On the other hand, the olefinic route has... 

Parker, W, Raphael, R.A., Wilkinson, D.l. (1959) Acetylenic Routes to Tropinone, pseudo-PeUetierine, and Lobelanine. Journal of the Chemical Society, 2433-2437. 

Parker, Raphael, and Wilkinson have investigated a synthetic approach to tropinone (124), which they call the acetylenic route (78). Reaction of hexa-1,5-diyne-l,6-dicarboxylate (145) with methylamine yields the pyrrolidine derivative (146), which by catalytic hydrogenation affords the diester 147 (79,50). 

Acetaldehyde is the product of the Wacker process. At the end of the fifties oxidation of ethene to ethanal replaced the addition of water to acetylene, because the acetylene/coal-based chemistry became obsolete, and the ethene/petrochemistry entered the commercial organic chemicals scene. The acetylene route involved one of the oldest organometallics-mediated catalytic routes started up in the 1920s the catalyst system comprised mercury in sulfuric acid. Coordination of acetylene to mercury(II) activates it toward nucleophilic attack of water, but the reaction is slow and large reactor volumes of this toxic catalyst were needed. An equally slow related catalytic process, the zinc catalysed addition of carboxylic acids to acetylene, is still in use in paint manufacture. 

Smaller but growing markets for PO include liquid detergents and surface coatings. The PO route to butanediol is replacing the acetylene route. 

Reppe process yields are about 80%, but the usual acetylene drawbacks are present hazardous materials handling and higher-cost raw materials. As a result the acetylene route plants are not being duplicated as they wear out, giving way to the newer technologies. 

Remirez, Raul, "Ethylene or Acetylene Route to VA, Chem. Eng. (Aug. 

Technological advances in the production of the vinyl chloride monomer (VCM) have contributed to the declining price of the polymer. Figure 4 illustrates this statement the price of the vinyl chloride monomer (1) over a period of 20 years is plotted against two curves that represent the annual production of monomer made from two different bases, acetylene and ethylene. The classic acetylene route was the first to be exploited commercially, but its popularity has declined as more processes were developed that could utilize ethylene, a cheaper base. 

This process is shown schematically in Figure 7. The ethylene part of the feed reacts with chlorine in the liquid phase to produce 1,2-di-chloroethane (EDC) by a simple addition reaction, in the presence of a ferric chloride catalyst (9). Thermal dehydrochlorination, or cracking, of the intermediate EDC then produces the vinyl chloride monomer and by-product HC1 (1). Acetylene is still needed as the other part of the over-all feed, to react with this by-product HC1 and produce VCM as in the all-acetylene route. 

Most of the simple monoalkyl- and arylisothiazoles may be prepared by direct ring synthesis either by the olefin route (Section I,C) or Wille s acetylenic route (Section I,D). 5-Alkylisothiazoles are accessible from isothiazolyllithium derivatives, and 3-alkyl- and arylisothiazoles are conveniently prepared by deamination of the readily available 5-aminoisothiazoles.37, 70,95 Arylisothiazoles have also been prepared from aminoisothiazoles by the Gomberg-Hey route.107... 

Meurer, P., The acetylene route to chemicals International Conference on Coal Cooversion. Pretoria, Sooth Aixica (16/20 August 1982V... 

A more effective acetylene hydrogenation catalyst to ethylene would also facilitate the development of coal to ethylene via the acetylene route, which is at present restricted to the use of acetylene for the production of vinyl chloride. 

A recent study indicates that if the Wacker process proves to be substantially cheaper than the acetylene route, no more vinyl acetate plants will be built in the United States, based on the latter process (38). Table XV gives estimated production costs for manufacturing vinyl acetate. Several companies are building or have already built plants to manufacture vinyl acetate from ethylene. These include Distillers Co., Ltd., British Celanese, Imperial Chemical Industries, and Celanese Corp., to name only a few. 

Acetylene routes have some peculiarities not shared by other alternative gas conversion routes. 

Ethylene or acetylene route to vinyl acetate Chan. Engng, 75 (17) 94 96 (1968). 

Meurer, P The acetylene route to chemicals" International Conference on Coal Conversion Pretoria South Africa (16/70 August 1982)... 

Celecoxib 24, a highly selective COX-2 inhibitor and a nonsteroidal anti-inflammatory drug (NS AID), is used for the treatment of arthritis and pain. The core skeleton of Celecoxib 24 is a 3-trifluoromethylpyrazole ring, which has been synthesized by [2 - - 3] cyclization and condensation of 1,3-diketones or their equivalents. Figure 12.3 summarizes three synthetic approaches toward 3-trifluoromethylpyrazole compounds via condensation of 1,3-diketones or a,[3-unsaturated ketones with arylhydrazine (route A, Schemes 12.1-12.3), via [2 - - 3] cycloaddition of trifluor-oacetamide with substituted ethenes or acetylene (route B, Schemes 12.4 and 12.5), and via cycloaddition of CFa-alkene with C-N=N unit (route C, Scheme 12.6). 

The use of acetylene is the most direct route the other methods are of secondary importance. The acetylene route is also used to prepare A -vinylcarba-zole [88]. 

The Wittig reaction is second in importance only to the acetylenic route as a means of synthesizing olefinic fatty acids and has also been used extensively in preparing long-chain alcohols and their esters which are important as insect pheromones. 

While the direct oxidative vinylation reaction shown above has many advantages over the acetylene route to the preparation of vinyl ethers, it has yet to be commercialized. 

In the older acetylene route, acetylene is first dimerized to monovinyl acetylene in a concentrated aqueous solution of a complex salt of cuprous chloride. 

This route is analogous to the acetylene route to chloroprene as also were the polymerization methods employed. The properties of the resulting elastomer, Fluoroprene, were far from outstanding and production was soon discontinued. 

Neoprene was manufactured via the acetylene route for many years. However, the technology is difficult and the starting material, acetylene, gradually increased in price over the years. By 1960 a second, less expensive method of chloroprene production had been developed and commercialized. The second, preferred method involves the production of chloroprene from butadiene via a chlorination step. 

Until the mid-1960s, vinyl acetate manufacture was based almost entirely on acetylene. Since that time, however, more economical ethylene-based processes have been developed and now very few manufacturers use the acetylene route. 

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