Acetylene, preparation from calcium

Mercuric oxide (5 g.) is dissolved for the most part in a still warm mixture of 110 c.c. of water and 50 c.c. of concentrated sulphuric acid. The mixture is brought into a large hydrogenation flask (Fig. 58, p. 377) and shaken for some time with acetylene prepared from calcium carbide, purified with acid solutions of dichromate and copper nitrate, and collected over saturated sodium chloride solution in a glass gas-holder (capacity 10-15 litres). Before shaking is begun the air present must be displaced by the hydrocarbon. 

Acetylene prepared from calcium carbide and purified by passing (1) through copper sulphate solution, and (2) through a tower packed... 

Acetylene was discovered m 1836 by Edmund Davy and characterized by the French chemist P E M Berthelot m 1862 It did not command much attention until its large scale preparation from calcium carbide m the last decade of the nineteenth century stim ulated interest m industrial applications In the first stage of that synthesis limestone and coke a material rich m elemental carbon obtained from coal are heated m an electric furnace to form calcium carbide... 

Historically, the use of acetylene as raw material for chemical synthesis has depended strongly upon the avadabihty of alternative raw materials. The United States, which until recendy appeared to have limitless stocks of hydrocarbon feeds, has never depended upon acetylene to the same extent as Germany, which had more limited access to hydrocarbons (1). During Wodd War 1 the first manufacture of a synthetic mbber was undertaken ia Germany to replace imported natural mbber, which was no longer accessible. Acetylene derived from calcium carbide was used for preparation of... 

It is scarcely necessary to remove the flask for weighing until near the end of the experiment, since the volume of acetylene is known and practically complete absorption takes place. If a tank of compressed gas is not available, the acetylene may be prepared from calcium carbide by the usual laboratory methods.1... 

In some forms of generators for the gas, which are used commercially, the finely powdered carbide runs slowly into a reservoir of water. A better regulation of the gas supply is effected by using this method, and overheating, which may lead to an explosion, is avoided. Acetylene prepared from commercial calcium carbide contains ammonia, hydrogen sulphide, and phosphine. These substances must be removed when the gas is to be used for indoor illumination. The purification is effected by washing the gas with water and a mixture of slaked lime and bleaching powder, or with a solution of chromic acid in hydrochloric acid. In the laboratory a solution of mercuric chloride in dilute hydrochloric acid can be conveniently used for the purpose. 

Acetylene can be prepared by other methods which are analogous to those used to prepare ethylene. While these methods lack practical value in the case of this hydrocarbon, which can be so readily prepared from calcium carbide, they are of importance since similar methods must be used to prepare the homologues of acetylene. Moreover, compounds other than hydrocarbons may contain carbon atoms held together in the way in which these atoms are united in acetylene, and the methods about to be described can be used to prepare such compounds. 

The simplest alkene is ethene, the compound which has previously been called ethylene . Ethene is produced in large quantities because it is one of the most important substances in the production of a wide variety of organic compounds and technological materials. The parent alkyne is ethyne which is marketed under the trade name of acetylene . This substance is also a very important industrial product. Both ethene and ethyne are flammable ethyne mixed with oxygen produces a very hot flame so acetylene is used for gas welding. Ethyne can be easily prepared from calcium carbide and water ... 

Acetylene is also prepared from calcium carbide, CaC2. Calcium carbide is obtained by heating calcinm oxide and coke (carbon) in an electric furnace ... 

Acetylene was discovered in 1836 but did not command much attention until its large-scale preparation from calcium carbide near the end of the nineteenth century stimulated interest in... 

Tests and experience with acetylene generators have shown that this gas has no action on aluminium, even in the presence of humidity. This also applies to gas that contains the classic impurities due to its preparation from calcium carbide, namely hydrogen sulphide and phosphine. The dissolution rate is very low, in the order of 0.10 mm per year [3]. 

The discovery of acetylene in 1836(or 1837) is attributed to Edmond Davy, but it was not until I860 that Berthelot definitely identified and named it(Ref 9, p 101 Ref 16, p 469). The compd obtained by Berthelot from cuprous acetylide was not pure because it contained some vinyl chloride. Acetylene was not produced commercially until Ca carbide was produced in the lab in 1899 by Morehead Willson, by heating a mixt of lime and coke in an electric furnace. They expected to prepare metallic calcium... 

In the early days of the chemical industry, acetylene was a key starting material for many important products. Initially it was obtained for chemical purposes by reaction of calcium carbide with water but that practice has given way to acetylene recovery from hydrocarbon cracking, so that now 86 percent of acetylene used in chemical manufacturing is made in this way. Owing to difficulty in its safe collection and transport, it is almost always used where it is prepared. 

A by-product from the reaction of acetone and sodium acetylide is the acetylenic diol, (CHj)2C(OH)C= C(OH)(CH,)j, formed by condensation of two molecules of acetone with one molecule of sodium acetylide. A general method for the preparation of acetylenic diols of this type is from calcium carbide, potassium hydroxide, and ketones. Ciethynyl glycols in which the triple bonds are separated by two or four carbon atoms are made from sodium acetylide and a- or /S-diketones. ... 

Acetylene(D3) has been prepared on numerous occasions from calcium carbide and DjO. Generally it is necessary to enrich the acetylene obtained by repeated... 

NOTES.—(a) The acetylene prepared in this way from commercial calcium carbide contains impurities, such as hydrogen sulphide and phosphine. If the gas is to be used to prepare other compounds, it should be purified by passing it through a wash-bottle containing a solution of mercuric chloride in hydrochloric acid. 

Preparation of acetylene from calcium carbide in the laboratory gives a product that is difficult to purify. The literature485 should be consulted for methods of purifying this material. 

Figure 5.3 illustrates a process to manufacture acetylene from calcium carbide. The carbide is introduced by a screw conveyor into a perforated horizontal cylinder housed in a concentric envelope. Water is sprayed inside the internal shell. The acetylene formed passes upstream through the screw conveyor to a scrubbing tower, where, a new water spray carries off most, of the solids conveyed by the gas. The residual lime and carbide impurities are removed by a screw conveyor to a sludge receiver. The acetylene is cooled to — 10°C to condense most of the water. It is then purified by contact with dilute sulfuric acid in a liquid liquid absorber, and then with sodium hypochlorite prepared by the action of chlorine on caustic soda, to. remove impurities. The acetylene is then cooled to 0°C for the more complete separation of moisture. The final product nevertheless still contains 0.4 per cent by weight of water, which is suitable for most uses. More intensive dehydratation can be achieved by passage over silicagel. 

While this synthesis lacks industrial significance at present, it is of interest in that it makes it possible to synthesize the rubber from coal, through the preparation of calcium carbide, acetylene, and acetaldehyde. These latter steps in the process have been put on an industrial basis. 

Recently, the Yankee Atomic Electric Company, Environmental Laboratory, has determined the tritium levels in water samples from the environs of several nuclear generating facilities in the New England area by liquid scintillation analysis of high purity tritiated benzene prepared from the water samples to be quantified. A commercially available unit was utilized to facilitate the synthesis of benzene by reacting the water sample with calcium carbide to form tritiated acetylene which is subsequently trimerized on a vanadium catalyst to high purity tritiated benzene. 

This preparation of calcium carbide requires enormous amounts of energy so as the cost of energy rose, acetylene ceased to be an economical feedstock from which to manufacture acetic acid. 

An attempt to reproduce synthesis of 0-vinyl oximes according to the protocol [326] from oximes and acetylene (generated in situ from calcium carbide) in aqueous medium has led to pyridines instead of the expected products [174], For example, 2,4,6-trimethylpyridine in -10% yield is prepared from acetoxime (Scheme 1.150). 

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