Weygand/Hilgetag Preparative Organic Chemistry

330 Formation of carbon-oxygen bonds
the dark for 3 h between 5° and 10°, and then poured into 5 % sodium sulfite solution. Extraction
with methylene chloride, drying and evaporation of the extract, and crystallization
of the residue gave the dione.
Dehydrogenation by iV-halo imides has been reviewed by Filler. 420 Mild
dehydrogenation of various alcohols can be achieved, not merely by iVh-alo
imides, but also by diethyl azodicarboxylate C2H5O2CN:NCO2C2H5 458
and 4-phenyl-l,2,4-triazole-3,5-dione; 459 equivalent amounts of the triazole
and alcohol are used in benzene at room temperature, reaction being complete
within a few hours and yields being good; examples are 90% of benzophenone
from benzhydrol, and 84% of cyclohexanone from cyclohexanol.
Heyns et al.* 27 have worked out a method for oxidation of cyclic alcohols
to ketones (e.g., cyclohexanol to cyclohexanone) by means of oxygen in the
presence of platinum (see page 324); with bicyclic systems composed of two
fused five-membered rings, only endo-hydroxyl groups are attacked. 460
Polyols of six-membered ring systems, including those of the cyclitol and
pentopyranoside series, are oxidized only at axial hydroxyl groups, reaction
ceasing at the monoketone stage even if other axial hydroxyl groups are
present. 461 For example, benzyl /?-D-arabopyranoside gives 29% of benzyl
/?-D-fAre0-pentopyran-4-uloside (as monohydrate).
Among other details given 427 are the conditions under which this reaction
converts primary alcohols into (a) aldehydes or (b) carboxylic acids, and
secondary alcohols into ketones, with special recommendation of the process
for preparation of long-chain aldehydes from the corresponding alcohols.
For catalytic dehydrogenation of secondary alcohols in the vapor phase
the same catalysts are successful as for primary alcohols, but here the reaction
is even easier because ketones form fewer by-products. Hurd, Greengard, and
Roe 462 obtained 60% of cyclohexanone from cyclohexanol by using Adkin's
copper chromite catalyst. Also secondary alcohols can be dehydrogenated in
the liquid phase, for which, e.g., Raney nickel was used as catalyst; in such
cases it is useful to add a hydrogen acceptor such as cyclohexanone, reaction
being effected by short heating of the alcohol, solvent, catalyst, and hydrogen
acceptor. 463
Phenols can be oxidized to quinones by a variety of oxidants: for instance,
hydroquinone is converted into /7-benzoquinone by chromic-sulfuric acid 464
or by sodium chlorate in the presence of V2O5, 465 yields exceeding 90% in
both cases. Substituted hydroquinones have been oxidized to quinones by
iron(m) salts 466 and by Ag2O. 467t 468 The xeaction is effected in media such
458 F. Yoneda, K. Suzuki, and Y. Nitta, /. Amer. Chem. Soc, 88, 2328 (1966).
459 R. C. Cookson, I. D. R. Stevens, and C. T. Watts, Chem. Commun., 1966, 744.
460 K. Heyns, W.-P. Trautwein, and H. Paulsen, Chem. Ber., 96, 3195 (1963).
461 K. Heyns, J. Lenz, and H. Paulsen, Chem. Ber., 95, 2964 (1962).
462 C. D. Hurd, H. Greengard, and A. S. Roe, /. Amer. Chem. Soc, 61, 3359 (1939).
463 E. C. Kleiderer and E. C. Kornfeld, /. Org. Chem., 13, 455 (1948); cf. Brit. Pat.
767,093 {Chem. Abstr., 51, 13928 (1957); /. Appl. Chem. {London), 8, 615 (1958).
464 E. B. Vliet, Org. Syn., 2, 85 (1922).
465 H. W. Underwood and W. L. Walsh, Org. Syn., Coll. Vol. II, 553 (1943).
466 L. I. Smith and P. F. Wiley, /. Amer. Chem. Soc, 68, 889 (1946).
467 J. W. Bruce and F. K. Sutcliffe, /. Chem. Soc, 1956, 3820.
468 M. F. Ansell and co-workers, /. Chem. Soc, 1963, 3028.