Chlorozincate

The mixed amines are dissolved in hydrochloric acid and zinc chloride solution added. The quinoline chlorozincate, (C H7N)2,HtZnCl, crystallises out, being almost insoluble in water, while the aniline chlorozincate remains in solution. The quinoline chlorozincate is then filtered off and decomposed by alkalis, and the liberated quinoline extracted with ether or steam-distilled. 

These chlorozincates must not be confused with the non-ionic compounds which quinoline and aniline bases give with neutral zinc chloride the latter have the formulae [(C,H7N)2ZnClt] and [(C,H7N)tZnCl ] respectively, and both are only slightly soluble in water. 

Transfer the quinoline chlorozincate to a beaker, add a small quantity of water, and then add 10% sodium hydroxide solution until the initial precipitate of zinc hydroxide completely redissolves, and the free quinoline separates. Transfer the mixture to a separating-funnel, wash out the beaker with ether, adding the washings also to the solution in the funnel, and then extract the quinoline twice with ether. Dry the united ethereal extracts by adding an ample quantity of powdered potassium hydroxide and... 

The success of this reaction was ascribed to the solubility of the chlorozinc intermediate, whereas other chloramine-T derivatives (e.g. the sodium salt) are insoluble. An alternative non-nitrene pathway was not eliminated from consideration. On the other hand, no aromatic substitution or addition, characteristic of a free sulphonyl nitrene (see below), took place on treatment of jV,lV-dichloromethanesulphonamides with zinc powder in benzene in the cold or on heating. The only product isolated was that of hydrogen-abstraction, methanesulphonamide 42>, which appears to be more characteristic of the behaviour of a sulphonyl nitrene-metal complex 36,37). Photolysis of iV.iV-dichloromethanesulphonamide, or dichloramine-B, or dichloramine-T in benzene solution led to the formation of some unsubstituted sulphonamide and some chlorobenzene but no product of addition of a nitrene to benzene 19>. 

On treating diisobutene with acetic anhydride and anhydrous zinc chloride, A. C. Byrns and T. F. Doumani had isolated in 1943 a crystalline compound to which they had ascribed the structure of a zinc complex with a 1,3-diketone 40 the correct pyrylium chlorozincate structure was established by A. T. Balaban et al.41 in 1961, after extended investigation on the formation of pyrylium salts by alkene diacylation.42 This formation again had remained undetected for many decades during which alkenes had been acylated but only the water-insoluble monoacylation products had been investigated, whereas the water-soluble pyrylium salts went into the sink with the Lewis or Bronsted acid catalysts that had been used in the acylation. 

Bromobicyclopropylidene (43 d) reacts with the chlorozinc compound 274 a produced by metal exchange from lithiated ethyl M-(diphenylmethylene)glyci-nate [151] under PdCl2(dppf) catalysis [152] to give the substituted diene 277 formed by an unusual ring opening (Scheme 62) [1531. 

TABLE 8. Preparation of chlorozinc allenyl reagents from iodoallenes... 

Conversion of the presumptive dialkyl allenylzinc intermediate to the corresponding chlorozinc species could be effected by exposure to ZnCl2. Subsequent addition of various aldehydes led to anti homopropargylic alcohols (Table 11). In contrast, reaction of the... 

Thus, the alkynyllithium derived from the propargylic ether 302 underwent allylzincation under the above-mentioned conditions and led to the dimetallic species 303. Whereas treatment with NBS resulted in the formation of the dibromoolefin 304, reaction of 303 with the less reactive benzenesulfonyl chloride produced an ce-chlorozinc sulfinate 305. The latter could in turn react with different electrophiles and afforded the corresponding tri- or tetra-substituted olefins of type 306 as single geometric isomers (equation 144)179. 

Similar complexes were prepared for L = 2-thiazolidinethiolate, 5-methyl-2-thiazolidinethiolate and l-methyl-4-imidazolethioIate. The following chlorozinc complexes have also been prepared [(pyS)3Zn2Cl], [(pyS)4Zn3Cl2] and [(pyS)ZnCl], The last compound is probably polymeric.8"... 

The composition of the various chlorozincate anions in the Lewis add ionic liquids was determined using potentiometry in an analogous manner to that used by Heerman and D Olislager [109] who measured the potential of the cell... 

Liu et al. [110] studied the crystal structures of chlorozincate-choline chloride complexes and identified that in an equimolar ratio the liquid is made up of two species. It was shown that two types of crystal could be grown from the super-cooled liquid, one rod-like and the other sheet-like, and these were thought to be due to the Zn2Cl5 and ZnCl3 salts, respectively. 

From a practical perspective the chlorozincate liquids are easier to make and handle than the corresponding chloroaluminates as they are less susceptible to hydrolysis. As with the aluminum-based liquids the electrochemistry is dominated by the complex anions present in the liquid, which depend upon the composition and the relative Lewis acidity. There is some evidence, however, that hydrolysis of zinc Lewis basic melts does occur as Hsiu et al. used fast atom bombardment mass spectroscopy (FAB MS) to show that some zinc species do contain oxygen [105]. 

Chlorozincate liquids have also been studied for the deposition of numerous zinc-containing alloys including Pt-Zn, Zn-Fe, Sn-Zn and Cd-Zn alloys. These alloys will all be discussed in greater detail in Chapter 5. 

As the chlorozincate anions are reduced at the electrode surface the liquid close to the electrode surface will become more Lewis basic... 

Electrodeposition of Zn-containing Alloys from Chlorozincate Ionic Liquids... 

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