Sodium amalgam, as reductant

A preparation of fra/ -[Mo(N2)2(dppe)2] (dppe = Ph2PCH2CH2PPh2) that uses triethylaluminum as reductant has already been reported in Inorganic Syntheses,3 but it is less convenient and gives much lower yields than that described below. Other reported methods, using sodium amalgam as reductant, involve a more difficult work-up procedure.4... 

There has been considerable research into the electrolytic reduction of aromatic carboxylic acids to the corresponding aldehydes. A general procedure has been described in which key elements are the use of the ammonium salt of the acid, careful control of the pH and the presence of an organic phase (benzene) to extract the aldehyde and thus minimize overreduction. The method appears to work best for relatively acidic substrates for example, salicylaldehyde was obtained in 80% yield. Danish workers have shown that, under acidic conditions, controlled electrolytic reductions are possible for certain pyridine-, imidazole- and thiazole-carboxylic acids. In these cases, it is thought that the product aldehydes are protected by geminal diol formation. A chemical method which is closely related to electrolysis is the use of sodium amalgam as reductant. Although not widely used, it was successfully employed in the synthesis of a fluorinated salicylaldehyde. ... 

The reduction of the p-acyloxy sulfone is most often carried out with sodium amalgam, as the examples below indicate. The reductive elimination can be buffered with disodium hydrogenphosphate for sensitive substrates. In certain applications it has proven advantageous to utilize lithium or sodium in ammonia. For example, Keck s synthesis of pseudomonic acid C made use of the lithium/ammonia reductive elimination to simultaneously form an alkene and deprotect a benzyl ether.In studies directed toward the same target, Williams made use of a reductive elimination procedure developed by Lythgoe, involving the formation of the xanthate ester followed by reduction with tri-n-butyltin hydride. ... 

The reduction of a-benzoylaminoacrylic acids with an equivalent amount of 3% sodium amalgam as originally described by Erlenmeyer has been improved in several ways. - In a modification of the pro-cedure, a-benzoylaminopropionic acids are obtained in 62-80% yields by treating aqueous solutions of the sodium salts of a-benzoylaminoacrylic acids with a large excess of sodium amalgam. This method is not always satisfactory 2-phenyl-4-(3, 4, 5 -trimethoxybenzal)-5-oxazolone is not reduced, 1 and a-benzoylamino-d-(4-methoxy-l-naphthyl)-... 

Reduction of propylene oxide to propylene is accompHshed by use of metallocenes, such as Ti(AH5)2Cl2, and sodium amalgam (88). 

Xyhtol is synthesized by reduction of D-xylose catalyticahy (40), electrolyticahy (41), and by sodium amalgam (42). D-Xylose is obtained by hydrolysis of xylan and other hemiceUulosic substances obtained from such sources as wood, com cobs (43), almond shells, hazelnuts, or oHve waste (44). Isolation of xylose is not necessary xyhtol results from hydrogenation of the solution obtained by acid hydrolysis of cottonseed hulls (45). 

Dithionites. Although the free-dithionous acid, H2S2O4, has never been isolated, the salts of the acid, in particular zinc [7779-86-4] and sodium dithionite [7775-14-6] have been prepared and are widely used as industrial reducing agents. The dithionite salts can be prepared by the reaction of sodium formate with sodium hydroxide and sulfur dioxide or by the reduction of sulfites, bisulfites, and sulfur dioxide with metallic substances such as zinc, iron, or zinc or sodium amalgams, or by electrolytic reduction (147). 

Aluminum or sodium amalgam reduces 3-ones to 1,2-dihydro derivatives (71TH21500), as does borohydride (63JCS5156) and catalytic hydrogenation (Pd/SrCOs) (71TH21500). Catalytic (Pd/C) reduction of a 5-one also gave a 1,2-dihydro compound (74JMC553). 

The present procedure was developed from those of Wallach and Freylon, based upon the general method discovered by Leuckart. a-Phenylethylamine also can be prepared satisfactorily by the reduction of acetophenone oxime with sodium and absolute alcohol or sodium amalgam, but the reagents are more expensive and the processes less convenient. The amine has been obtained by reducing acetophenone oxime electro-lytically, by reducing acetophenone phenylhydrazone with sodium amalgam and acetic acid, from a-phenylethyl bromide and hexamethylenetetramine, and by the action of methyl-magnesium iodide upon hydrobenzamide, as well as by other methods of no preparative value. 

This, on reduction with zinc dust and acetic acid, yielded the corresponding oxime, which was further reduced by sodium amalgam to -3 4 5-trimethoxyphenylethylamine, CgHjj(OMe)3. CH. CH. NHg, and this proved to be identical with mezcaline (I). Like the latter, it behaves on analysis as if it contained the grouping —NHMe but this had already been disproved by Heffter. Interest in the remarkable physiological properties attributed to mezcaline has led to many syntheses of this alkaloid and of its isomerides and analogues. ... 

Thebainol (Pschorr Dihydrometathebainone (Schopf i), CigHjgOjN, is obtained by the reduction of metothebainone, with sodium amalgam in dilute alkali. Crystallised from methyl alcohol, it melts at 54-5° and re-melts at 76-8°, but after crystallisation from dry ether it has m.p. 135-6° and [a]f ° + 67-05° (EtOH). The oxime has m.p. 217-8° and [a][, ° + 104-2° (acetic acid, 10%). The benzylidene derivative forms yellow needles, m.p. 100-2°. An amorphous dipiperonylidene derivative has been described by Gulland and Robinson.The methyl ether is amorphous, but yields a crystalline methiodide, m.p. 245°. Thebainol is represented as (L), produced by saturation of the ethylenic (C -C ) linkage in meta-thebainone (LII). 

On reduction with sodium amalgam the acid adds on two atoms of hydrogen the resulting amorphous aeid yields a crystalline dimethyl ester, C2iH2gOgN2, colourless prisms, m.p. 143-7° dec.). On hydrogenation in presenee of platinic oxide as catalyst 2 mols, of hydrogen are absorbed to form the acid, CjgHjgOgNj, colourless prisms, [ajo - -17-7° (HjO). On oxidation with chromic acid the Cjg acid is converted into Wieland s Ci7 acid and Hanssen s Cjg acid. ... 

Toluene from Toluidine.—It is often desirable to obtain tbe hydiocarbon from the base. The process of diazotisntion offers the only convenient method. The diazonium salt may be reduced by alcohol (Reaction 1, p. 162) or, as in the piesent instance, by sodium stannite. Less direct methods are the con-veision of the diazonium compound into (i) the hydrazine (see p. 174), (2) the acid and distillation with lime (p. 200), (3) the halogen derivative and reduction with sodium amalgam, 01, finally (4) the phenol and distillation with zinc dust. 

Similar results were obtained on reduction of 3,4,5-trimethylisoxa-zole/ Further examples of such a cleavage were found later. Thus, j8-(3-halogenoisoxazol-5-yl) propionic acids (163) on treatment with sodium amalgam give a mixture of S-cyano-y-ketovaleric and succinic acids (163—> 164) The reaction can be interpreted as a result of... 

Phenyl-propyl alcohol, CgH. CHj. CH.2. CHj. OH, is the next highest homologue of phenyl-ethyl alcohol, and is also known as hydro-cinnamyl alcohol. Like the last described bodies it has been known for many years, its first preparation being described in the Aivnalen (188, 202). It occurs as a cinnamic acid ester in storax, and as an acetic ester in cassia oil. It is prepared synthetically by the reduction of cinnamyl alcohol with sodium amalgam and water, or by the reduction of cinnamic or benzyl acetic esters with sodium and absolute alcohol. It has the following characters —... 

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