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Organic Synthess - McKusick B.C.

McKusick B.C., Boekelheide V., Emmons W.D. Organic Synthess - New York, 1963. - 134 p.
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2. The impurities present in the original allene are concentrated in the recovered material. If recovered allene is to be reused, it should be fractionated first.
3. The checkers isolated 167 g. of crude anhydride mixture boiling at 70-125°/3 mm. The large tarry residue contains allene polymers and small amounts of 1,2,3,4,5,6,7,8-octahydronaph-thalene-2,3,6,7-tetracarboxylic dianhydride, which can be recovered by diluting the residue with benzene and filtering.
4. Pot temperatures above 175°, which result from use of pressures above 25 mm., cause formation of high-boiling by-products.
5. Collection of the product fraction should begin after a few milliliters of an intermediate fraction has been collected at 155°/25 mm. This material has a low index of refraction.
6. The checkers found that the use of anhydride with «£? 1.4937-1.4945 led to a product with a low index of refraction «5 1.4616).
7. The temperature rises because of disappearance of methanol by conversion to the methyl ester. Attainment of equilibrium is signified by the pot temperature reaching a constant temperature.
8. The second treatment with methanol increases the yield from 60% to 90%.
9. Rapid distillation from the neutralized catalyst results in much smaller loss of ester than is encountered in the more usual procedure that includes washing with water and drying.
3. Methods of Preparation
The procedure used is essentially that described by Cripps, Williams, and Sharkey.5 The anhydride has been prepared in a similar manner by Alder and Ackermann.6 No other methods have been described for the preparation of these materials.
4. Merits of the Preparation
The first step of this procedure illustrates a general reaction, the addition of allenes to alkenes to form methylenecyclobutanes. The reaction has been reviewed recently.7
Since 3-methylenecyclobutane-l,2-dicarboxylic anhydride is easily converted to 3-methyl-2-cyclobutene-l,2-dicarboxylic acid,8 it is an intermediate to a variety of cyclobutenes. The dimethyl ester of 3-methylenecyclobutane-l,2-dicarboxylic acid is also a versatile compound; on pyrolysis it gives the substituted allene, methyl butadienoate,9 and on treatment with amines it gives a cyclobutene, dimethyl 3-methyl-2-cyclobutene-l,2-di-carboxylate.8
1 Contribution No. 567 from the Central Research Department, Experimental Station, E. I. du Pont de Nemours and Co., Wilmington, Delaware.
8 The Upjohn Company, Kalamazoo, Michigan.
* H. N. Cripps and E. Г. Kiefer, Org. Syntheses, 42, 12 (1962).
4 R. G. Nester, Anal. Chem., 28, 278 (1956).
* H. N. Cripps, J. K. Williams, and W. H. Sharkey, J. Am. Chem. Soc., 81, 2723
• К. Alder and 0. Ackermann, Chem. Ber., 90, 1697 (1957).
7 J. D. Roberts and С. M. Sharts, Org. Reactions, 12, 1 (1962).
8 H. N. Cripps, J. K. Williams, V. Tuffio, and W. H. Sharkey, J. Am. Chem. Soc., 81, 4904 (1959).
> J. J. Drysdale, H. B. Stevenson, and W. H. Sharkey, J. Am. Chem. Soc., 81, 4908 (1959); H. B. Stevenson and W. H. Sharkey, Org. Syntheses, this volume, p. 71.
(Carbodiimide, diphenyl-) CH3
2C6H5NCO -—-► C6H6N=C=NCeH6 + CO2
Submitted by T. W. Campbell 1 and J. J. Monagle. Checked by W. S. Wadsworth and W. D. Emmons.
1. Procedure
A 250-ml. four-necked flask is fitted with a sealed mechanical stirrer, a condenser protected by a drying tube, a thermometer, and a gas inlet. The flask is swept with a slow stream of nitrogen (Note 1) and dried by flaming. One hundred milliliters (108 g.,
0.91 mole) of phenyl isocyanate (Note 2) is pipetted into the flask. One gram (0.052 mole) of 3-methyl-l-phenyl-3-phos-pholene 1-oxide 2 is added (Note 3), and the reaction mixture is heated at 50° under nitrogen for 2.5 hours (Note 4); at this point only a faint test for carbon dioxide is obtained when the off-gas is passed through saturated calcium hydroxide solution. The reaction mixture is cooled and rapidly transferred to a Claisen flask. Distillation yields 72-82 g. (82-93%) of diphenylcarbodiimide, obtained as a clear water-white oil, b.p. 110-112°/0.2 mm., «ff 1.6360-1.6362 (Note 5).
2. Notes
1. Commercial nitrogen is dried by passage through concentrated sulfuric acid.
2. Best results were obtained with material obtained from
Eastman Kodak Company. Either freshly distilled material or material from a freshly opened bottle may be used. Material obtained from several other sources gave variable results even after redistillation.
3. Since the phosphine oxides are very hygroscopic and the reaction rate is sensitive to traces of moisture, the catalyst can be conveniently stored and added to the reaction mixture in longnecked, thin-walled glass ampoules. The catalyst may be dried by distillation (b.p. 168-170°/1.4 mm.) into a receiver containing the inverted ampoules. When sufficient catalyst has distilled to fill the ampoules, nitrogen is bled into the receiver, forcing the catalyst into the ampoules. An ampoule about 15 mm. in diameter will hold about 1 g. of catalyst. A small air space should be left to facilitate crushing the ampoule.
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