Cuprous salts reagents

With two equivalents of an organomagnesium hahde, a Gtignard reagent is formed, capable of use in further syntheses (35,36). Cuprous salts cataly2e oxidative dimerization of propargyl alcohol to 2,4-hexadiyne-l,6-diol [3031-68-3] (37). 

The addition of Grignard reagents to unsaturated ketones gives mixtures resulting from 1,2-addition and 1,4-addition. In the presence of cuprous salts, however, the conjugate (1,4) addition is enhanced to the extent that the reaction becomes synthetically useful (11). Two examples of this procedure are given. 

The central C—C bond in bicyclo[ 1.1.0] butane has a high -character and is known to behave as an olefin. Thus, 1-arylsulfonylbicyclobutanes 312 reacted with Grignard reagents in the presence of lithium dialkylcuprates or cuprous salts (Me2S, CuBr or CuCl) giving 3-alkyl-1-arylsulfonylcyclobutanes 313406. 

Propargyl alcohols may be converted to allenes by several methods, for example, (a) through the intermediate formation of propargyl halides which are not isolated but react directly with cuprous salts and hydrogen halide [60, 72-73] or cyanide [71] (b) typical alcohol reactions with thionyl chloride [74a-d] phosphorus halides [75-77], and miscellaneous reagents (see Scheme 3). 

The precipitation of cuprous acetylide was introduced into analytical chemistry for the quantitative determination of copper. Since cupric acetylide was dangerous to handle, Makowka [108] worked out a method in which cupric salts are previously reduced, e.g. with hydroxylamine, to cuprous salts, when the acetylide is precipitated. Cuprous salts in a solution of hydroxylamine are employed as reagents for acetylene (e. g. Pietsch and Kotowski [114]). 

The most important finding for the synthetic applications of the Sandmeyer reaction is the clear experimental evidence of Galli that both oxidation states of copper ion are necessary for high yields. This claim is understandable on the basis of the reaction mechanism cupric ions are a ligand transfer reagent (see reviews ). The fact that the presence of Cu" ions was not realized much earlier is understandable, because cuprous salts are rarely completely free of cupric impurities. In aqueous systems they form cupric ions by equilibration as well as by air oxidation. The following comparative experiments of Gain in the chloro-de-diazoniation of benzenediazonium sulfate in water at room temperature are instructive. Yields of chlorobenzene are with 0.25 M CuCl 45% with 0.25 M CuCl -F 0.25 M Cu(N03)2 63% with 0.25 M Cu(N03)2 <0.1%. 

Aniline reacts with nitrous acid to give benzenediazonium salts, which react with a variety of reagents via a substitution reaction. These reagents include cuprous salts, aqueous acid, iodide, hypophosphorous acid, and activated benzene derivatives. Nucleophilic substitution at the sp carbon of a halo-benzene derivative does not occur unless high heat and pressure are used. Electron-withdrawing substituents on the benzene ring significantly lower the temperature required for the reaction. Nucleophiles for this nucleophilic aromatic substitution reaction include water, hydroxide, alkoxide, and amines. 

Organocuprates are generated from an organolithium reagent (see Chapter 15, Section 15.5) and a cuprous salt such as Cul (cuprous iodide). When two equivalents of n.-butyllithium are mixed with Cul in ether at -10°C, the product is lithium dibutylcuprate, 52. When 52 reacts with a conjugated ketone such as methyl vinyl ketone (10), the product is enolate anion 53, which gives 54... 

Procedure II. A drop of the test solution is precipitated with the reagent, either on a spot plate or on filter paper, and then a few drops of dilute hydrochloric acid or ammonium chloride are added. The mercury compound dissolves while the red silver precipitate remains. Procedure II is recommended when copper as well as mercury is present, since the cuprous cyanide is sufficiently dissociated (when potassium cyanide is used) to react with the reagent to give a red insoluble cuprous salt, which resembles the silver compound. 

---