Methyl Alcohol

METHYL ALCOHOL, in a more or less impure form known in commerce as wood spirit, being produced by the destructive distillation of wood. The name methyl from the Greek kliev, wine, wood, explains its origin. Discovered in 1661 by R. Boyle, it was studied in greater detail by Dumas and Peligot in 1831, and its synthesis by M. Berthelot from methane through methyl chloride followed in 1858. It is the simplest alcohol (q.v.) of the aliphatic series (see CHEMISTRY : Organic) with the formula it is also known as methanol.

The older process of manufacture consists in distilling wood in iron retorts at about 500° C, when the aqueous distillate, contain ing methyl alcohol, acetic acid, acetone and methyl acetate, is neutralised with lime to fix the acetic acid and again distilled. Crude methyl alcohol thus obtained in the distillate can be purified by conversion into the calcium chloride methyl-alcoholate, which is separated and again decomposed by redistilling with water. Purified methyl alcohol is dehydrated over caustic potash or lime. Further purification may be effected by convert ing methyl alcohol into one of its esters (acetate, oxalate or benzo ate). Methyl alcohol is also obtained in the dry distillation of molasses.

Industrial Synthesis of Methanol.

A formidable rival to the wood distillation has arisen froni the modern development of pressure chemistry (q.v.). The thermochemical equation cal. shows that the synthesis of methyl alcohol from carbon monoxide and hydrogen will be fa voured by increased pressure and also by diminishing tempera ture, providing that the reaction is facilitated by a suitable cat alyst. These conditions have been realised by using a zinc oxide— chromic acid catalyst prepared by interaction between zinc oxide (3 mols.) and chromic acid (I mol.) with subsequent reduction in hydrogen at 350° C. A mixture of one volume of carbon monox ide and two volumes of hydrogen when passed over the heated catalyst at 350-400° C under a pressure of 20o atmospheres gave a liquid product consisting mainly of methyl alcohol (up to 9o%) ; the other ingredients are higher alcohols and water, the latter being formed during further condensation and also from the gradual reduction of the catalytic oxides. The catalytic chamber consists

of a strong steel cylinder lined with copper, and the inlet and exit tubes consist chiefly of the latter metal. The organic product contains smaller amounts of the higher primary alcohols among which n-propyl alcohol and isobutyl alcohol, have been identified (Morgan, Taylor and Hedley, J. Soc. Chem. Ind., 1928). From these higher alcohols and water, methyl alcohol is readily separated by fractional distillation. When purified from traces of aldehydes by successive digestion with 2 :4-dinitro phenyl-hydrazine and sodium and again rectified by distillation, it is obtained as a colourless, almost inodorous liquid, boiling at 66-67° C and having a specific gravity of 0.8142 at o° C. It mixes in all proportions with water, ethyl alcohol or ether. Its chief industrial uses are as follows :—(i) starting material for formaldehyde, (2) denaturant for ethyl alcohol (wine spirit), (3) in varnish manufacture, (4) as a fuel, (5) as a chemical reagent in the fine chemical and synthetic colour industries.

The following derivatives have some industrial importance: Methyl chloride, a colourless gas boiling at —23° C, ob tained by chlorinating methane, or preferably by passing hydrogen chloride into methyl alcohol in presence of zinc chloride. It is soluble in water and more so in alcohol. Methyl bromide, simi larly prepared by the use of hydrogen bromide, is a volatile liquid boiling at '3° C (sp. gravity, 1.73). Methyl iodide boils at C (sp. gravity 2.19). Dimethyl sulphate, prepared by adding chlorosulphonic acid or sulphur trioxide to methyl alcohol diluted with carbon tetrachloride, is a colourless oily liquid boiling at 187-188° C (sp. gravity 1.327). It is greatly used as a methylat ing agent in spite of its poisonous character. The inhalation of its vapours should be avoided. (G. T. M.)