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Method of manufacturing alkyl iodides
US3053910A
"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]
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Peacock and Menon, Quart, J. Indian Chem. Soc. 2, 240 (1925)
The Preparation of Methyl and Ethyl lodides from the Corresponding Toluene Sulphonates
BY David Henry Peacock and Bala Krishna Menon.
The preparation of methyl iodide from dimethyl
sulphate is a well established method but suffers from
the disadvantage that only one methyl group is converted
to methyl iodide. It has been found that the dimethyl
sulphate can be replaced by methyl toluene sulphonate
with satisfactory results. Ethyl iodide can be prepared
by a similar method.
EXPERIMENTAL
(1) Methyl Iodide.—42 gms. of potassium iodide were
dissolved in 42 c.c. of water and 47 grams of methyl-p-toluene
sulphonate added. The mixture was distilled
from a sand-bath. The yield of dry, redistilled methyl
iodide was 30 grams or 84,5% .
(2) Ethyl Iodide.—42 gms. of potassium iodide were
dissolved in 42 c.c. of water and boiled on a sand-bath
under a reflux condenser. During the course of two
hours 50 grams of ethyl-p-toluene sulphonate were added ;
when the addition was complete the mixture was heated
for a further half hour. The ethyl iodide was then
distilled from a water-bath. The yield of dry, redistilled
product was 26 grams or 66% of theory. When the
ethyl toluene sulphonate was added all at once and the
reaction completed by boiling for 2 1/2 hours, the yield was
25 grams. The gradual addition of the ethyl toluene
sulphonate effects very little improvement in the yield.
UNIVERSITY COLLEGE,
RANGOON. Received, August 3, 1925.
[Edited on 31-10-2021 by Mush]
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