Zinc powder distillation with

R. Mellon (19) but using anhydrous reagents. He obtained an oil that reacted exothermically with hydroxylamine (oxime of m.p. 135°) and that isomerized to 2-oxy-4-methylthiazole (14) upon heating with diluted hydrochloric acid. The thiazolic nature of oxymethylthiazole was clearly demonstrated by its reduction by zinc powder distillation into 4-methylthiazole (23), the first free thiazole ever described. 

Preparation of REAOENTS.t It is essential for this preparation that the zinc powder should be in an active condition. For this purpose, it is usually sufficient if a sample of ordinary technical zinc powder is vigorously shaken in a flask with pure ether, and then filtered off at the pump, washed once with ether, quickly drained and without delay transferred to a vacuum desiccator. If, however, an impure sample of zinc dust fails to respond to this treatment, it should be vigorously stirred in a beaker with 5% aqueous sodium hydroxide solution until an effervescence of hydrogen occurs, and then filtered at the pump, washed thoroughly with distilled water, and then rapidly with ethanol and ether, and dried as before in a vacuum desiccator. The ethyl bromoacetate (b.p. 159 ) and the benzaldehyde (b.p. 179 ) should be dried and distilled before use. 

Phthalide. In a 1 litre bolt-head flask stir 90 g. of a high quality zinc powder to a thick paste with a solution of 0 5 g. of crystallised copper sulphate in 20 ml. of water (this serves to activate the zinc), and then add 165 ml. of 20 per cent, sodium hydroxide solution. Cool the flask in an ice bath to 5°, stir the contents mechanically, and add 73-5 g. of phthalimide in small portions at such a rate that the temperature does not rise above 8° (about 30 minutes are required for the addition). Continue the stirring for half an hour, dilute with 200 ml. of water, warm on a water bath imtil the evolution of ammonia ceases (about 3 hours), and concentrate to a volume of about 200 ml. by distillation vmder reduced pressure (tig. 11,37, 1). Filter, and render the flltrate acid to Congo red paper with concentrated hydrochloric acid (about 75 ml. are required). Much of the phthalide separates as an oil, but, in order to complete the lactonisation of the hydroxymethylbenzoic acid, boil for an hour transfer while hot to a beaker. The oil solidifles on cooling to a hard red-brown cake. Leave overnight in an ice chest or refrigerator, and than filter at the pump. The crude phthalide contains much sodium chloride. RecrystaUise it in 10 g. portions from 750 ml. of water use the mother liquor from the first crop for the recrystaUisation of the subsequent portion. Filter each portion while hot, cool in ice below 5°, filter and wash with small quantities of ice-cold water. Dry in the air upon filter paper. The yield of phthalide (transparent plates), m.p. 72-73°, is 47 g. 

Zinc powder (32.8 g,0.5 moles) is washed successively with hydrochloric acid (3%, 4 X 25 ml), distilled water (4 x 30 ml), aqueous copper sulfate (2%, 2 X 50 ml), distilled water (4 x 30 ml), absolute ethanol (4 x 30 ml) and absolute ether (5 x 25 ml). The washings are performed conveniently by stirring a mixture of the zinc powder and each wash solution with a porcelain spatula in an open beaker and then decanting the supernatant liquid. The couple is finally transferred to a Buchner funnel, washed with additional anhydrous ether, and then vacuum-dried in a round-bottom flask. 

Zinc-Copper Couple A 500-ml Erlenmeyer flask equipped for magnetic stirring is charged with a mixture of zinc powder (49.2 g, 0.75 g-atom) and hydrochloric acid (40 ml of 3 % aqueous solution). The contents of the flask are rapidly stirred for 1 minute, and the liquid is decanted. Similarly, the zinc is washed with the following three times with 40 ml of 3% hydrochloric acid solution, five times with 100 ml of distilled water, five times with 75 ml of 2 % aqueous copper sulfate solution, five times with 100 ml of distilled water, four times with 100 ml of absolute ethanol, and five times with 100 ml of absolute ether. These last ethanol and ether washes are decanted onto a Buchner funnel to prevent loss. The residue is collected by suction filtration, washed again with anhydrous ether, and dried in air. Finally, the zinc-copper couple is stored (20-24 hours) in a vacuum desiccator over phosphorous pentoxide. 

B. Amalgamated, Zinc [Mercury alloy (Hg, Zn)]. Zinc powder (206 g., 3.15 moles) is placed in a 1-1. beaker, covered with 250 ml. of aqueous 10% hydrochloric acid, and stirred for 2 minutes. The acid is then decanted and replaced by distilled water, the mixture is stirred, and the supernatant is decanted. Washing is continued in this way until the water is neutral to litmus. A warm solution of 40 g. (0.15 mole) of mercuric chloride [Mercury chloride (HgCl2)] in 250 ml. of distilled water is then poured onto the zinc, and the mixture is stirred gently for 10 minutes. After filtration, the powder is washed with 250 ml. of distilled water, five 250-ml. portions of 95% ethanol, and five 250-ml. portions of anhydrous ether. Drying under vacuum gives 196 g. of zinc amalgam. 

The tissues were fixed in 0.05 M cacodylate buffer containing 2.5% glutaraldehyde and 1.5% formaldehyde (pH 7.0) for 16 h. The ZIO mixture was prepared as follows 3 g zinc (powder) and 1 g resublimed iodine crystals were dissolved in 20 mL distilled water. After stirring for 5 min, the zinc was filtered off. The filtered solution was mixed with an equal volume of 2% 0s04 solution and the solution used immediately. Treatment with the ZIO mixture was carried out for 4 h at room temperature. 

The tissue blocks were immersed in 0.1 M phosphate buffer containing 2% glutaraldehyde and 5% sucrose (pH 7.4). The tissue blocks were immersed in ZIO solution. The ZIO solution was prepared as follows 3 g of zinc (powder) was dissolved ultrasonically in 20 mL distilled water and 1 g of iodine crystals was slowly added to the zinc suspension with stirring. After cooling, 4 mL of the filtered solution was mixed with 2 mL of Tris-HCl buffer (pH 7.5) and 2 mL of 2% Os04 solution. Treatment with this ZIO mixture was carried out for 16-20 h at 4°C in the dark. 

First, when 1,1-dihaloalkanes are reduced with low-valent titanium derived from TiCU and zinc, it is necessary to add a catalytic amount of PbCU (or Pb) for reproducibility (Equations (5) and (6)). Two kinds of zinc powder are available for laboratory use electrolytic zinc derived by hydrometallurgy and distilled zinc derived by pyrometallurgy. 

Diethylzinc, one of the first organometallic compounds to be isolated (Fran-kland, 1849), epitomizes these characteristics. The compound is easily prepared by heating powdered zinc or zinc-copper alloy with ethyl iodide under an atmosphere of dry nitrogen or CO2 (the initial product is actually C2H5ZnI, which disproportionates on distillation to zinc iodide and diethylzinc) ... 

Benzofuran derivatives are rare in petroleum, where sulfurated heterocycles predominate among heterocyclic compounds. Benzofurans and 2,3-dihydrobenzofurans are found, however, in the 200°-270° fraction of the distillate of California crude oil, with dibenzofurans and naphthobenzofurans.123 Alkyl-dibenzofurans have been traced in the 275°-305° fraction of petroleum with alkylnaphthalenes, 4-methyl-dibenzofuran among others.124 The distillation of humic acids with zinc powder is said to give benzofuran and hydrobenzofuran derivatives.125... 

A mixture of 15 (4.2 g, 20 mmol), powdered Zn (14.5 g, 0.22 mol), H20 (15 mL), and 5 M NaOH (6.6 mL) was refluxed with stirring forca. 1.5 h(the progress of the reaction was followed by argentometric titration). The zinc was filtered off by suction, the oily layer was separated, and unreacted zinc was washed with EtOH (3 x 10 mL). The aqueous filtrate was extracted with benzene (3x10 mL) and the extract was mixed with the oil and EtOH washings. All solvents were removed in vacuo to give the crude product (2.5 g) that was purified by distillation to give pure 16 yield 2.2 g (72%) bp 97-100 C/l7 Torr. 

Perfluoro(l, 2,3,4,5,6,7.8-octahydronaphthalene) (7 10 g, 23.6 mmol) and activated zinc powder (6g, 91.7 mmol) were placed in solvent (60 mL either dioxane, MeCN or DMF) and stirred under the conditions given in the scheme. Then, the mixture was poured into ice water (50 mL) and acidified with dil HC1. The organic layer was separated and the aqueous solution extracted with Et20. All organic extracts were combined, dried and distilled to yield ... 

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