Amines dissolving metals

Ion exchange, in which cation and/or anion resins are used to replace undesirable anionic species in liquid solutions with nonhazardous ions. For example, cation-exchange resins may contain nonhazardous, mobile, positive ions (e g., sodium, hydrogen) which are attached to immobile acid groups (e.g., sulfonic or carboxylic). Similarly, anion-exchange resins may include nonhazardous, mobile, negative ions (e.g., hydroxyl or chloride) attached to immobile basic ions (e.g., amine). These resins can be used to eliminate various species from wastewater, such as dissolved metals, sulfides, cyanides, amines, phenols, and halides. 

Catalytic reduction of fluormated aliphatic and aromatic nitro compounds to give oximes and amines was described previously, as was the use of dissolving metals to prepare amines [Si] Refmement of these techniques has resulted in optimized yields and, as indicated in equations 69 and 70, in selective reductions [S6, 87]... 

The anolyte, containing about 75gdm CD at pFI 2, is fed to a solvent extraction circuit for the separation of Fe—Co and Fe—Ni with a tertiary alkyl amine, dissolved in kerosene. The separation is based on the tendency of the metals to form metal-chloride-amine complexes (Fig. 11.2). At low chloride ion concentration (about 75gdm ), Fe(III) is extracted to the organic solvent, while Co(II) and Ni(II) remain in the aqueous raffinate. If the chloride ion concentration is then increased to about 250 gdm, cobalt is extracted, leaving nickel behind in the raffinate. 

Benzene and its homologs can be converted to the corresponding cyclo-hexadienes and cyclohexenes, and even cyclohexanes, by treatment with dissolving metals lithium, sodium, potassium or calcium in liquid ammonia or amines. Conversions are not complete, and the ratio of cyclohexadienes to cyclohexenes depends on the metal used, on the solvent, and on the presence of hydrogen donors (alcohols) added to the ammonia or amine [392, 393, 394]. 

This method involves formation of reverse micelles in the presence of surfactants at a water-oil interface. A clear homogeneous solution obtained by the addition of another amine or alcohol-based cosurfactant is termed a Microemulsion. To a reverse micelle solution containing a dissolved metal salt, a second reverse micelle solution containing a suitable reducing agent is added reducing the metal cations to metals. The synthesis of oxides from reverse micelles depends on the coprecipitation of one or more metal ions from... 

The SR substituent can be displaced nucleophilically by amines and hydroxide (867 — 868) and removed reductively by dissolving metals, e.g. from (869) with Zn/H+. Oxidation gives the corresponding sulfoxide and sulfone, in which nucleophilic displacement is easier. Thus, 2- and 4-(phenylsulfonyl)pyrimidines give the corresponding replacement products with various nitrogen and... 

The issue became one of selective reduction of the 1,3 diene moiety, and various conditions for 1,4 hydrogen addition were examined. Unfortunately, all of these failed. For 43, complex, difficult to purify mixtures of various reduction products were generated under various hydrogenation and dissolving metal conditions (Scheme 21).42 The amines 46 and 47 had the additional problem of the readily reducible alkenyl iodide segment. Indeed, exposure to hydride reagents led to quite facile hydrodehalogenation, with products such as 52. Thus, it became... 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

Dissolving metals have been used as reducing agents in organic synthesis for well over a century and for many years metal-alcohol or metal amalgam-water systems were the principal methods employed for the reduction of aldehydes and ketones to primary and secondary alcohols, respectively. The same reagents were employed for the reduction of imines and oximes to the corresponding amines. Catalytic hy-... 

The stereochemical course of these, and other similar reductions, led Barton to suggest that dissolving metal reductions of ketones and oximes to secondary alcohols and primary amines would lead to mixtures of products rich in the thermodynamically more stable product. However, in the early 1960s a number of reports appeared in which the reduction of ketones gave primarily the thermodynamically less stable epimeric alcohol. These observations have prompted a continuing series of investigations into the mechanism of these reductions. 

The metal-NHs reductions of carbonyl groups are exceedingly fast reactions for the reaction of acetone with an ammoniated electron the rate is 9 x 10 M" s". Although many, particularly older, published experimental procedures for the metal-NHs reduction of ketones employ prolonged reaction times with excess metal, these conditions are unnecessarily harsh. The reactions of carbonyl compounds with metals in NH3 are effectively instantaneous and by using short reaction times it appears that reduction of terminal alkenes and disubstituted alkynes can be avoided.In addition to the functional groups mentioned above, alcohols, amines and ethers, other than epoxides, are usually stable to reductions of aldehydes and ketones by dissolving metals. " ... 

The reduction of imines to amines (equation 21) by dissolving metals is usually carried out using active metals in a protic solvent, typically Na-alcohol, Zn-NaOH and A1 or Mg in alcohols. - ""- Although the mechanism of these reductions has not been investigated in detail it is almost certainly analogous to that of the reduction of ketones (Section 1.4.2). It has been established that radical anions are intermediates in these reductions and in the absence of a proton donor reductive dimerization is the principal reaction path. ... 

The reduction of oximes to primary amines by dissolving metals, usually Na-alcohol, is an established synthetic procedure which has been employed for many years. Although in some cases LAH reduction is superior, the reduction of many oximes with LAH leads either to aziridines or Beckman-type rearrangements. ... 

In conclusion, nitriles may be reduced electrochemically or with dissolving metal to produce amines. Nonetheless, such reactions must be used with caution. In addition to competitive decyanation, aldehyde or 2,4,6-trialkyIhexahydro-l,3,5-triazine formation and reductive dimerization are waiting to overwhelm the unwary. 

Extensive investigations have been made into further methods for the reduction of aromatic rings based on the use of dissolving metals in other solvents, especially the lower molecular weight amines (the Benkeser reduction), electrochemical methods (cathodic reductions), photochemical methods and the reaction of radical anions with silylating reagents rather than proton sources. The aim of much of this work has been to produce the normal Birch products more conveniently or cheaply, but very often the outcome has been quite distinct. The alternative method may then provide access to products which are not so easily obtained by the standard metal-liquid ammonia methodology. 

Benzylic amines are particularly susceptible to hydrogenolysis by catalytic hydrogenation or dissolving metal reduction. " Note that the Wolff-Kishner reduction in 19-61 involved formation of a hydrazone and deprotonation by base led to loss of nitrogen and reduction. Ceric ammonium nitrate in aqueous acetonitrile has also been shown to reductively cleave the V-benzyl group. Primary amines have been reduced to RH with hydroxylamine-O-sulfonic acid and... 

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