Mercaptals metalation

More complicated systems can be synthesized by preparation of dimercaptopiperazinediones by method 1, followed by mercaptalization, metallation of the mercaptals, electrophilic substitution and finally generation of the disulfide from the mercaptal via the monosulfoxide 206—208). 

Two techniques, electrochemical reduction (section IIl-C) and Clem-mensen reduction (section ITI-D), have previously been recommended for the direct reduction of isolated ketones to hydrocarbons. Since the applicability of these methods is limited to compounds which can withstand strongly acidic reaction conditions or to cases where isotope scrambling is not a problem, it is desirable to provide milder alternative procedures. Two of the methods discussed in this section, desulfurization of mercaptal derivatives with deuterated Raney nickel (section IV-A) and metal deuteride reduction of tosylhydrazone derivatives (section IV-B), permit the replacement of a carbonyl oxygen by deuterium under neutral or alkaline conditions. 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

Formaldehyde diethyl thioacetal added dropwise with stirring to a suspension of NaNHg in liq. NHg, after a few min. n-butyl bromide added dropwise and allowed to stand overnight valeraldehyde diethyl thioacetal. Y 84.5% based on thioacetal.—Mercaptals can be metallated with remarkable ease. F. e. and reactions s. A. Froling and J. F. Arens, R. 81, 1009 (1962) s. a. W. E. Truce and F. E. Roberts, J. Org. Ghem. 28, 961 (1963). 

---