Weygand/Hilgetag Preparative Organic Chemistry

806 Formation of metal-carbon bonds (organometallic compounds)
Trialkyl-arsines and -stibines, and triarylarsines, add alkyl iodides, yielding
quaternary arsonium and stibonium iodides, R4MI or R3R'MI.
Organic derivatives of the quinquevalent metals include examples of the
following types: halides, RMX4, R2MX3, R3MX2, and R4MX; oxygen compounds,
RMO(OH)2, R2MO(OH), R3M0, R4MOH; and pentaalkyl and
pentaaryl derivatives MR5.
Organic halide derivatives of the quinquevalent metals lose alkyl or aryl
halide when heated, and thus pass into derivatives of the trivalent element,
e.g.:
R3MX2 —> R2MX + RX
This reaction occurs particularly readily with the compounds RMX4 and
R2MX3, some of which decompose in this way even at room temperature.
1. Organoarsenic compounds 483
A great deal of work has been devoted to organic derivatives of arsenic,
particularly in the search for pharmacologically useful substances.
Organoarsenic compounds can be prepared from arsenic trihalides and
organic derivatives of other metals. For example, trialkylarsines are obtained
in good ^ yield from dialkylzincs and arsenic trichloride, 484 and dichloro-
(ethyl)arsine can be prepared from diethylmercury and arsenic trichloride: 485
Hg(C2H5)2 + AsCl3 • C2H5HgCl + C2H5AsCl2
Dichloro(ethyl)arsine: 485 Diethylmercury (150 g) is dropped into ice-cooled arsenic trichloride
(150 g); a strongly exothermic reaction occurs and crystals separate. The mixture
is finally heated for 0.5 h on a water-bath, then treated with anhydrous ether, filtered from
the precipitated ethylmercuric chloride, and freed from ether. By repeated fractional distillation
the dichloro(ethyl)arsine is separated from the excess of arsenic trichloride; the yield
of the former, b.p. 145-150°/760 mm, is 90 g.
The most convenient method, and thus that most often used, is treatment
of arsenic halides with alkyl- or aryl-Grignard reagents or organolithium
compounds. 486 ' 487
Triethylarsine: 488 Arsenic trichloride (50 g), diluted with anhydrous ether (120 ml), is
added to a cooled Grignard solution from ethyl bromide (93 g) and magnesium (21 g); then
ice and dilute hydrochloric acid are added until there is clear separation of two layers. The
ether layer is removed, dried over calcium chloride, and freed from ether cautiously below
38° in a stream of carbon dioxide. The residue of the ether is removed in a vacuum and the
arsine is distilled in a vacuum into a distilling flask from which it is refractionated in a stream
of carbon dioxide. The b.p. is 140°/736 mm and the yield is 40% (18 g).
483 W. R. Cullen, Advan. Organometal. Chem., 4, 145 (1966).
484 A. W. Hofmann, Ann. Chem., 103, 357 (1857); R.R.Renshaw and G. E. Holm, /.
Amer. Chem. Soc, 42, 1468 (1920).
485 W. Steinkopf and W. Mieg, Ber. Deut. Chem. Ges.9 53, 1013 (1920).
486 H. Hibbert, Ber. Deut. Chem. Ges., 39, 160 (1906); P. Pfeiffer, Ber. Deut. Chem.
Ges., 37, 4620 (1904).
487 J. Seifter, /. Amer. Chem. Soc, 61, 530 (1939); W. R. Cullen and P. E. Yates, Can.
J. Chem., 41, 1625 (1963).
488 Ref. 1, pp. 456-457.