Sciencemadness Discussion Board

Ethyl Iodide

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Mush - 14-3-2020 at 07:38

Method of manufacturing alkyl iodides

"The synthesis of alkyl iodides is not new to the art.
Dumas and Peligot, Ann. 15, 20 (1835), first reported the preparation of methyl iodide by the reaction of an alcohol with phosphorus and iodine. A furtherance of their early work is reported by Ipatieu, J. Russ. Phys. Chem. Soc. 27 I, 364 (1895); Crisner, 717 (1892); and Walker and Johnson, J. Chem. Soc. 87, 1592 (1905). Adams and Voorhees, J. Am. Chem. Soc. 41, 789-98 (1919), improved upon the red phosphorus-yellow phos phorus-alcohol iodine synthesis of Walker, and by equip ment modification were able to prepare larger amounts of the several lower alkyl iodides in yields of 90-100% of the theoretical. Hunt, J. Chem. Soc. 177, 1592-4 (1920), verified the work of Beilstein and Rieth, Ann. 126, 250 (1863), that one atom of phosphorus reduces five atoms of iodine in stead of the assumed three atoms reported in much of the earlier work. As late as 1931, Hirao, J. Chem. Soc. Japan 52, 269-70 (1931) disclosed a more rapid method of converting an alcohol, phosphorus and iodine to an alkyl halide in 90% yield.In addition to the classical phosphorus and iodine synesis of alkyl iodides, given in excellent detail by King in Organic Synthesis, Collective Vol. II, pp. 399-404, John Wiley and Sons, Inc., Weinland and Schmidt, German Patent 175,209, describe the preparation of methyl iodide and ethyl iodide by reacting dimethylsulfate with an aqueous solution of potassium iodide in the following are:

(CH3)2SO4 +KI -> K(CH3)SO4 +CH3I

Peacock and Menon, Quart, J. Indian Chem. Soc. 2, 240 (1925), employed a similar approach by converting the methyl and ethyl esters of p-toluenesulfonic acid to the corresponding alkyl iodides with potassium iodide in 84.5 and 66.6% yields, respectively. This work was substantiated by Rodionov, Bull. Soc. Chem. 39, 305-25 (1926). In two works, Jones and Green, J. Chem. Soc. 1926, 270; J. Chem. Soc. 1927, 928, report the reaction of aluminum with three atoms of iodine, with hydrolysis of the aluminum tri-iodide in the presence of an alcohol and water to produce the corresponding alkyl iodide. These workers state aluminum can advantageously be used in stead of phosphorus in the synthesis. To avoid the use of phosphorus, an element of pyrophoric nature, numerous workers have since devised methods for synthesis of alkyl iodides which, although expensive and cumbersome in operation, eliminate the hazards encountered in using phosphorus as an intermedi ate chemical. Kimball, J. Chem. Education 10, 747 (1933) reacted iodoform with potassium hydroxide in 95% ethanol, distilled off the ethanol solvent, acidified the resultant mixture prior to filtering, and then rendered the filtrate alkaline with sodium hydroxide followed by heat ing with commercial dimethylsulfate to obtain methyl iodide in 78% yield. To obtain ethyl iodide in 80% yield, Kimball teaches heating the alkaline filtrate described above with commercial diethylsulfate. Dangyan, J. Chem. Gen. (USSR) 10, 1668-9 (1940), obtained methyl iodide in 50.3% yield by heating methanol with iodine and iron, ethyl iodide in 96% yield by fusing ethylacetate with iodine in the presence of iron. In a later work, Dangyn, J. Gen. Chem. (USSR) 11, 314-18; 11, 616-18 (1941), describes the utilization of aluminum and ethylacetate with iodine at 110-210 C. to form ethyl iodide, and magnesium, iodine, and methyl benzoate to synthesize methyl iodide in 70-90% of theo retical yield. Dangyan further teaches that the reaction of aluminum, alcohol, and iodine to form alkyl iodides is an excellent method of preparation, but that extreme caution is required during the heating period of the Syn thesis. Landover and Rydon, J. Chem. Soc. 1953, 2224-34, report the preparation of ethyl iodide in 62% yield by the distillation of ethanol from silver iodide. In British Patent 695,648 of July 12, 1953, Landover and Rydon demonstrate a method for the synthesis of alkyl iodides whereby an alkyl, aryl or alkyl-aryl phosphate is heated with an alkyl halide and an alcohol to obtain an alkyl exchange of 77% in the case of ethyl alcohol. De Postes, Compt. Rend. 223, 681-2 (1946), proposes the preparation of methyl iodide by the introduction of gaseous hydrogen chloride at 20° C. into a mixture of zinc, methanol and iodine. Still other methods of preparation, Norris, Am. Chem. J. 38, 639 (1907), utilized the slow distillation of methanol from an excess of constant boiling hydriodic acid to form methyl iodide, and Peacock and Menon, Quart. J. Indian Chem. Soc. 2, 240 (1925), and Rodionov, Bull. Soc. Chem. (4) 39, 323 (1926), resorted to the electrolysis of aqueous potassium iodide in the presence of methyl p-toluene-sulfonate.
Commercially, the alkyl iodides, and more specifically methyl iodide and ethyl iodide, are produced by either the reaction of the corresponding alcohol with phosphorus and iodine, or by the reaction of a dialkylsulfate on a solution of sodium or potassium iodide. It is of especial interest that in the latter reaction, as described by Hart man, Organic Synthesis, Collective Vol. II, p. 404, John Wiley and Sons, calcium carbonate is added to the mix ture to insure a neutral or alkaline condition throughout the course of the reaction. To those skilled in the art, the inherent danger in commercial production of alkyl iodide by the use of phosphorus and iodine is quite obvi ous. Partington, Textbook of Inorganic Chemistry, Sixth Edition, Macmillan and Company, Ltd., pp. 566-567, states: “A characteristic property of white phosphorus is the ease with which it undergoes spontaneous oxidation when exposed to air at the ordinary temperature, accom panied by a green glow of phosphorescence. If warmed to about 50 it inflames in dry air and burns with a white flame, forming white fumes of the pentoxide P2O5. It inflames spontaneously in chlorine, explodes violently in contact with liquid bromine, and inflames in contact with solid iodine.' Furthermore, Partington discloses the so-called red-phosphorus of commerce contains about 0.5% of white phosphorus, from which it is prepared.

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[Edited on 14-3-2020 by Mush]

anti - 14-3-2020 at 10:41

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