Aluminum-mercury amalgam, reduction

In contrast, the latter. ryw-isomer, ethyl (TS,2R)-2-(1 -hydroxymethyl)-4-pentenoate. was recently prepared as the only product of a reduction with an enzyme fraction obtained from baker s yeast176. Introduction of a sulfur-containing functional group into the substrate increases stereocontrol in baker s yeast reduction of many ketonesI2e>. 2-Methylthio-3-keto esters are selectively reduced to the (3S)-3-hydroxy esters (Table 5)123,127. The 2-methylthio group is easily removed by 3-chloroperbenzoic acid oxidation to the corresponding sulfoxide followed by subsequent reduction with aluminum-mercury amalgam. Thus, these compounds can also be used for the preparation of optically pure 2-unsubstituted 3-hydroxy esters. 

Strontium metal also can be prepared by thermal reduction of its oxide with aluminum. Strontium oxide-aluminum mixture is heated at high temperature in vacuum. Strontium is collected by distillation in vacuum. Strontium also is obtained by reduction of its amalgam, hydride, and other salts. The amalgam is heated and the mercury is separated by distillation. If hydride is used, it is heated at 1,000°C in vacuum for decomposition and removal of hydrogen. Such thermal reductions yield high—purity metal. 

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

It is alloyed with about 4% A1 and 0.02% Mg. The aluminum strengthens the zinc and also prevents the molten alloy from attacking the steel pressure casting dies. Zinc readily reacts with mercury or will displace mercury from a mercury(II) salt to form an amalgam that is usefril for reductions, as in the preparation of compounds of the lower oxidation states of transition metals and lanthanides (e.g. Cr , V , Eu°, dimeric Mo ) and in analytical chemistry (e.g. in the Jones reductor see Analytical Chemistry of the Transition Elements). 

Compared with copper, iron, gold, and lead, which were known in antiquity, aluminum is a relative newcomer. Sir Humphry Davy obtained it as an alloy of iron and proved its metallic nature in 1809. It was first prepared in relatively pure form in 1825 by H. C. Oersted through reduction of aluminum chloride with an amalgam of potassium dissolved in mercury,... 

Use of Aluminum Amalgam. Aluminum amalgam is widely used in the che-moselective reduction of a-sulfonylated carbonyl groups because of the high tolerance shown by this reagent towards other functional groups (Eq. 85).143 Use of a large excess of toxic mercury is one of the main drawbacks associated with this method. 

Selective defluorination of 1,3-difluorobenzene to fluorobenzene has been successfully carried out by use of cathodic reduction at mercury in diglyme containing Bu4NBp4and a catalytic amount of a dimethylpyrrolidinium (DMP ) salt. In this reaction, DMP is first reduced to form an amalgam, which reduces difluorobenzene catalyti-cally as shown in Scheme 1. Also, cathodic reduction of perfluoroben-zene at an aluminum cathode in aqueous DMF provides benzene in moderate yield (Eq. 4). 

Alum was used by the Greeks and Romans in medicines and in dying processes. In 1807, Davey proposed the name alumine for the as yet undiscovered metal in alum. Finally, in 1825 Hans Christian Oersted isolated an impure sample of aluminum by heating AICI3 with potassium amalgam and boiling off the mercury at the end of the reduction. 

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