3) Of course, the molecule actually contains two similar C K~S S K~ conjugated systems, permitting a greater number of possible products. accordine to whether one or both react in each treatment.

In connection with another investigation under way in this Laboratory, use of the common reagents for a carbonyl group failed to give a solid derivative. At about the same time it was noted that there was no reliable rapid reagent for preparing solid derivatives of most of the aliphatic aldehydes and ketones. As a rule the reagents that form crystalline products with aromatic carbonyl compounds give oils with most of the corresponding aliphatic substances; in spite of this, Laboratory manuals in illustrating

Details are reported for the preparation of the three chlorotoluquinones• Raiford's work on the chlorination of 4-nitro-m-cresol to give 2-chIoro-4-nitrom-cresol has been corroborated in all details.A high-yield method has been developed for synthesis of 3-chlorotoluquinone from 6-chloro-2-nitrotoluene, proceeding by way of electrolytic reduction to the corresponding p-aminophenol and oxidation of this intermediate to the quinone. Berkeley, California

The hydrochlorides of 27 Michael adducts, formed from alkylthiols and chalco~les monosubstituted successively in each ring by nitro, chloro, and ~nethoxy groups, were thermally cleaved by hot water. T h e amount of cleavage was readily determined iodimetrically.A syste~natic study of the thermal reversibility of Michael adducts, formed by the addition of mercaptans to the conjugated system of double bonds present in ketones, esters, and the like, is believed to be new. The only instances on record are those described in one of our previous papers (1). The current account is limited to adducts which are formed from chalcones and which have @-alkylmercapto substituents. They comprise a new class that can be used for a study of therinal cleavage. A follo\ving paper will contain an account of similar adducts derived froin unsaturated esters, nitriles, ketones with fewer substituents, and the like. I t has been found that they are not sufficiently active to reverse therinally.The extent of thermal cleavage is susceptible to quantitative estimation, since the mercapto addends regenerated can be titrated against standard iodine solutions. This operation is much more convenient than the use of gas chromatography, as previously employed (1). Since these adducts can give only normal cleavage, it inaltes possible an exalnination of the effect, if any, of substituents in different positions of both benzene rings on the extent of the reversal. The extent of cleavage of all the adducts is summarized in Table I.The adducts investigated were inainly those (11) forined from @-morpl~olinoethanetl~iol, because of its availability (2), because the hydrochloride salts are easily crystallized solids, because of their increased solubility, and because they give good cleavage rates.A few prelinlinary experirllents showed that other thiols could be so used (Table I, Nos. 1, 2, 3, 7, S), that the reversal was general, and that it was not confined to @-mercaptoethylainines. Three kinds of ring substituents were employed-nitro (strong electronwithdrawing), chloro (weak electron-withdrawing), and methoxy (electron-donating). These groups, one a t a time, were located in ortho-, meta-, and para-positions in both rings.The process may depend upon (a) the activity of the a-hydrogen atom of the adduct, For personal use only.

No abstract