Organic Reactions Volume 4 - Sciencemadness Dot Org

40 ORGANIC REACTIONS
rated linkages in oils and fats. 303 " 814 The determination of these constants
is subject, however, to certain inherent errors. 315-319
EXPERIMENTAL CONDITIONS AND PROCEDURES
Perhaps the most striking characteristic of the Diels-Alder reaction
is the ease and rapidity with which it may take place. No condensing
agents are required, although trichloroacetic acid, trimethylamine, anaphthoquinone,
and, possibly, dimethylaniline and s^/m-trinitrobenzene
have been found to catalyze the reaction in certain instances. 102 ' 118-120 A
vigorous reaction frequently ensues when the components are merely
mixed in about equimolecular proportions at room temperature. Inert
solvents, such as benzene or ether, are sometimes added to dissolve the
components or to moderate the reaction. Under such conditions a
quantitative yield of adduct often separates from solution in nearly pure
form. Heat of reaction can also be dissipated effectively in certain instances
by allowing the reaction to proceed with emulsified dienes in
an aqueous medium. 320
Less reactive dienes form adducts when solutions of the components
are refluxed at appropriate temperatures. Although high-boiling solvents,
such as anisole, o-dichlorobenzene, and nitrobenzene, have been
used for some reactions, this procedure is often of no avail because of
the reversible nature of the Diels-Alder reaction. It is evident from
examination of Table II (p. 28) that the equilibrium at high temperatures
is decidedly unfavorable for the preparation of adducts from certain
polycyclic hydrocarbons. This disadvantage may be overcome, however,
by lowering the temperature of reaction or by use of excess maleic
803
Kaufmann and Baltes, Fette u. Seifen, 43, 93 (1936) [C. A., 30, 7885 (1936)].
304
Kaufmann and Baltes, Ber., 69, 2676 (1936).
805
Kaufmann and Baltes, Ber., 69, 2679 (1936).
306
Kaufmann, Ber., 70, 900 (1937).
307
Kaufmann, Baltes, and Biiter, Ber., 70, 903 (1937).
308
Kaufmann, Baltes, and Josephs, Ber., 70, 908 (1937).
309
Kaufmann, Baltes, and Biiter, Ber., 70, 2535 (1937).
31° Kaufmann and Hartweg, Ber., 70, 2554 (1937).
311
Kaufmann, Baltes, and Hartweg, Ber., 70, 2559 (1937).
3 2
1 Ellis, Analyst, 61, 812 (1936).
313
Dyachkov and Ermolova, Caoutchouc and Rubber U.S.S.R., No. 3, 24 (1937) [C. A.,
31, 6138 (1937)].
314
Grosse-Oetringhaus, Petroleum Z., 35, 567 (1939) [C. A., 34, 975 (1940)].
315
Sabetay and Naves, Bull. soc. chim. France, [5] 4, 2105 (1937).
316 Bruce and Denley, Chemistry & Industry, 937 (1937).
317
Bickford, Dollear, and Markley, /. Am. Chem. Soc, 59, 2744^(1937).
318
Bickford, Dollear, and Markley, Oil & Soap, 15, 256 (1938) [C. A., 33, 421 (1939)].
319
Norris, Kass, and Burr, Oil & Soap, 18, 29 (1941) [C. A., 35, 2351 (1941)].
320
Hopff and Rautenstrauch, U. S. pat. 2,262,002 [C. A., 36, 1046 (1942)].