Acid-washed zinc powder

The original procedure using acid-washed zinc powder in aqueous alcohols at reflux is still the most used protocol, but some other metallic sources were also employed in the past few years [19,20], For example, the use of more reactive zinc sources, as zinc-Rieke [21] or zinc-silver graphite [22,23], allowed the fragmentation to be carried out in tetrahydrofuran (THF) at room temperature. On the contrary, the fragmentation can also be effected by treatment of the halosugar with n-BuLi in THF at -80°C, as depicted in Scheme 3.3 for iodoftiranoside 3 [24]. 

Dialkyl bromodifluoromethylphosphonates are treated with acid washed zinc dust or powder in ethereal solvents at room temperature to 60 °C to give the corresponding dialkoxyphosphinydifluoromethyl zinc reagents in good yields [274] (Scheme 94). 

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. 

Activate the zinc by stirring 400 g. of zinc powder with 150 ml. of 10 per cent, hydrochloric acid for 2 minutes, filter and wash with 300 ml. of water, followed by 100 ml. of acetone. 

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. 

Reduction of 6p, 9-Oxidoprogesterone to 9-Hydroxyprogesterone. Zinc powder Note 2) (4. g) is added in small portions to a solution of 2 g of 6)5,19-oxidoprogesterone in 40 ml glacial acetic acid Note i). The mixture is stirred for 40 min, then an additional 4 g zinc is added and stirring is continued for another 40 min at 30°. The cooled solution is filtered, the inorganic residue washed with methanol and the filtrate evaporated under reduced pressure. The resultant crude product is dissolved in 60 ml of chloroform and filtered. Concentrated hydrochloric acid (0.6 ml) is added and the solution stirred for 10 min at 25°. The reaction mixture is diluted with ether, washed successively with water, sodium bicarbonate solution and again with water, dried and evaporated under reduced pressure. The... 

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. 

Methylacridinium-9-carboxylic ester trifluoromethanesulfonate (100 mg) was dissolved in dichloromethane (100 mL). To this solution perchloric acid (20 drops) and zinc powder (6 g) were added. The mixture was placed in an ultrasonic bath for 3 h and filtered. The solution was washed with water (1 x) and hydrochloric acid (2X, 0.1 M), dried over MgS04, and concentrated. 

Zinc powder, obtainable from Mallinckrodt Chemical Works, St. Louis, Missouri, and Merck and Co., Rahway, New Jersey, is placed in a beaker and is washed consecutively and rapidly ( 10 seconds) with three 100-ml. portions of 3% hydrochloric acid, two 100-ml. portions of water, two 200-ml. portions of 2% aqueous copper sulfate (until blue color disappears), two 200-ml. portions of water, two 100-ml. portions of acetone, two 100-ml. portions of dimethylformamide, and is washed into the reaction vessel with dimethylformamide. This procedure is a modification of one described by Hennion and Sheehan.3... 

Bis-[tellura-9-xanthenyl] ° Zinc powder (1.0 g, 15 mmol) is added to a refluxing solution of 1.5 g (4.9 mmol) of telluraxanthone in 30 mL of glacial acetic acid. Then, 1.5 mL of concentrated hydrochloric acid are added to the stirred, refluxing mixture over 1 h. The resultant mixture is poured into 200 mL of 6 M hydrochloric acid, and stirred until the zinc has dissolved. The mixture is filtered, and the precipitate is washed with water and dried. Yield 1.0 g (74%) m.p. >300°C (from chlorobenzene). 

Zinc. Next to sodium, zinc is the most used reductant. It is available in powder, dust, and granular (mossy) forms. Zinc gets coated by a l er of zinc oxide which must be removed to activate it before it can reduce effectively. It can easily be activated by shaking 3 to 4 min. in a 1% to 2% hydrochloric acid solution. This means for every 98 ml of water volume, add 2 ml of coned hydrochloric acid. Then wash this solution with water, ethatiol, acetone, and ether. Ot activation can be accomplished by washing zinc in a solution of anhydrous zinc chloride (a very small amount) in ether, alcohol, or tetrahydrofuran. Another way is to stir 180 g of zinc in a solution of 1 g copper sulfate pentahydrate. Personally, I like the HCl acid method. 

Dihalodifluoromethanes react readily with acid-washed cadmium or zinc powder in DMF at room temperature to produce stable solutions of trifluoromethyl cadmium and zinc reagent, respectively in high yields [42], which undergo a metathesis reaction with copper (I) salts to give a trifluoromethylcopper solution [92] (Scheme 30). 

A. Zinc-copper couple. In a 500-ml. Erlenmeyer flask fitted with a magnetic stirrer are placed 49.2 g. (0.75 g. atom) of zinc powder (Note 1) and 40 ml. of 3% hydrochloric acid. The mixture is stirred rapidly for 1 minute, then the supernatant liquid is decanted. In a similar manner, the zinc powder is washed successively with three additional 40-ml. portions of 3% hydro-... 

---