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Organic Synthess - McKusick B.C.

McKusick B.C., Boekelheide V., Emmons W.D. Organic Synthess - New York, 1963. - 134 p.
Download (direct link): boekelheide1963.pdf
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66
ORGANIC SYNTHESES, VOL. 43
Purification of the crude iodoxybenzene is effected by grinding it to a powder in a mortar, macerating it with 70 ml. of chloroform, and separating the solid by filtration. The chloroform extraction is repeated and the solid is dried; weight 17-19 g. (72-80%); purity 99.0-99.9% by iodometric titration.3
2. Notes
1. For a source and the specifications of 40% peracetic acid and precautions in handling it, see Notes 3 and 1 under the preparation of iodosobenzene diacetate, p. 62.
2. If the temperature of the bath is not raised slowly, foaming is difficult to control. Although the gradual rise in temperature causes considerable foaming, the reaction mixture remains within the flask.
3. The filtrate must not be evaporated to dryness because iodoxybenzene explodes when heated.
4. The major by-products in this reaction are iodobenzene and iodosobenzene diacetate. An excess of 20 ml. of peracetic acid over the 65 ml. recommended results in an increase in the amount of iodobenzene. Both impurities are removed from the product by washing with chloroform.
3. Methods of Preparation
Iodoxybenzene has been prepared by the disproportionation of iodosobenzene,4"® by oxidation of iodosobenzene with hypo-chlorous acid or bleaching powder,7 and by oxidation of iodobenzene with hypochlorous acid or with sodium hydroxide and bromine.8 Other oxidizing agents used with iodobenzene include air,3 chlorine in pyridine,9 Caro’s acid,10,11 concentrated chloric acid,12 and peracetic acid solution.13 Hypochlorite oxidation of iodobenzene dichloride has also been employed.14
4. Merits of the Preparation
This one-step method of preparing iodoxybenzene is preferable to earlier methods because it is simpler and the yield is substantially higher. The procedure seems general for iodoxyarenes,
IODOXYBENZENE
67
at least those with electron-releasing substituents, for the submitters have used it to obtain good yields of o-, m- and />iodoxy-toluene, 2- and 4-iodoxy-w-xylene, 2-iodoxy-^-xylene, o-iodoxy-phenetole, 4-iodoxybiphenyl, and o-iodoxybenzoic acid.
Iodoxyarenes are useful in the preparation of iodonium salts, Ar2I+X~.16
1 Department of Chemistry, Brooklyn College of the City University of New York, Brooklyn 10, New York.
2 H. J. Lucas and E. R. Kennedy, Org. Syntheses, Coll. Vol. 2, 351 (1943).
3 C. Willgerodt, Chem. Ber., 25, 3500 (1892); 26, 358 (1893).
‘ C. Willgerodt, Chem. Ber., 26, 1307, 1806 (1893).
6 P. Askenasy and V. Meyer, Chem. Ber., 26, 1356 (1893).
* H. J. Lucas and E. R. Kennedy, Org. Syntheses, Coll. Vol. 3, 485 (1955).
’ C. Willgerodt, Chem. Ber., 29, 1568 (1896).
* C. Willgerodt, Chem. Ber., 29, 1571 (1896).
9 G. Ortoleva, Chem. Zentr., 1900, 723.
10 E. Bamberger and A. Hill, Chem. Ber., 33, 534 (1900).
111. Masson, E. Race, and F. E. Pounder, J. Chem. Soc., 1935, 1678.
12 R. L. Datta and J. K. Choudhury, J. Am. Chem. Soc., 38, 1085 (1916).
13 B. A. Arbusov, J. Prakt. Chem., 131, 357 (1931).
14 M. W. Formo and J. R. Johnson, Org. Syntheses, Coll. Vol. 3, 486 (1955).
15 C. Hartman and V. Meyer, Chem. Ber., 27, 504 (1894).
68
ORGANIC SYNTHESES, VOL. 43
2-MERCAPTOPYRIMIDINE (2-Pyrimidinethiol)
NaOH
CH(OC2H6)2
+ NaCl + H20
SH
Submitted by Donald G. Crosby, Robert V. Beethold, and Herbert E. Johnson.1
Checked by B. Bellin, J. L. Gibbs, and V. Bqekelheide.
1. Procedure
A. 2-Mercaptopynmidine hydrochloride. Thiourea (61 g., 0.80 mole) and 600 ml. of ethyl alcohol (Note 1) are placed in a 2-1. three-necked flask equipped with a sealed mechanical stirrer, a reflux condenser, and a stopper. The stirrer is started, and 200 ml. of concentrated hydrochlori* acid is added in one portion through the open neck. After several minutes, when the warm mixture has become homogeneous, 176 g. (0.80 mole) of com-mercial-grade 1,1,3,3-tetraethyoxypropane (Note 2) is added rapidly, the open neck is stoppered, and the yellow solution is boiled for about 1 hour with continuous stirring. During this period the reaction mixture darkens in color and the product separates (Note 3).
The reaction mixture is chilled to about 10° by immersing it in an ice bath for about 30 minutes, and the yellow crystalline precipitate is collected on a Buchner funnel. It is then washed with 100 ml. of cold alcohol and air-dried at room temperature. The yield of 2-mercaptopyrimidine hydrochloride is 71-76 g.
CH(OC2Hg)2 NH2
I______[ hci N-HC1
CH2 + С S _4C2H5OH >
2-MERCAPTOPYRIMIDINE
69
(60-64%). The product is pure enough for most purposes (Note 4), but it may be recrystallized by dissolving it in 12N hydrochloric acid (10 ml. per gram of solid) at about 75°, filtering the hot solution through glass wool or a sintered glass filter, chilling the filtrate in ice, and collecting the golden-yellow crystals on a sintered glass filter. Recovery is 60-65% (Note 5).
B. 2-Mercaptopyrimidine. Crude 2-mercaptopyrimidine hydrochloride (25 g., 0.17 mole) is suspended in 50 ml. of water in a beaker and stirred rapidly while a 20% aqueous solution of sodium hydroxide (about 27 ml.) is added until the pH of the mixture is 7—8 (Note 6). The precipitated solid is collected on a Buchner funnel and washed on the funnel with 50 ml. of cold water. The damp product is dissolved by heating it in a mixture of 300 ml. of water and 300 ml. of alcohol on the steam bath, and the hot solution is filtered through a fluted paper and allowed to cool slowly to room temperature. The crystals of 2-mercaptopyrimidine are collected, washed with about 50 ml. of the aqueous alcohol, and dried either at room temperature overnight or for several hours in an oven at 110°. The yield is 15-16 g. (80 85%) of yellow needles, m.p. 218-219° (sealed tube).
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