Formic acid, lithium salt

The reduction of the double bond of an enamine is normally carried out either by catalytic hydrogenation (MS) or by reduction with formic acid (see Section V.H) or sodium borohydride 146,147), both of which involve initial protonation to form the iminium ion followed by hydride addition. Lithium aluminum hydride reduces iminium salts (see Chapter 5), but it does not react with free enamines except when unusual enamines are involved 148). 

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

A very interesting modification of method B was applied to the stereospecific synthesis of ( )-pseudoheliotridane.27 Condensation of ethyl bromoacetate with l-methyl-2-ethyl-4,5-dihydropyrrole (42) afforded the quaternary salt 43, which was reduced, without isolation, with formic acid to give ethyl /3-(Ar-methyl-2-pyrrolidyl)butyrate (44). The amino alcohol (45), obtained by reduction of 44 with lithium... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

A general CE method using an imidazole-formic acid buffer has been validated [22] for analysis of the potassium counter-ion of an acidic drug. Sodium was used as the internal standard. The method was also applied to calcium, magnesium and lithium salts. The method can also be applied to the characterisation and identification of ionic raw materials and excipients such as sodium saccharin and sodium phosphate buffers. 

These salts are soluble in DMSO and can be Isolated. Polymerization of the di-salts was carried out by heating them in DMSO under nitrogen and is accompanied by liberation of lithium tr if late. The pol3nners were treated with formic acid yielding polyamides with a phenol group on one end. 

Depending on their specific compositions and the procedures by which they are produced, protein polymers may be soluble or insoluble in aqueous solution. The BetaSilk and ProNectin polymers are insoluble in water. Prom a lyophilized powder they can be dissolved in concentrated chaotropic solvents such as aqueous formic acid or lithium halide salt solutions. For example, SLP3 is soluble in 88% formic acid at 10 w t% or greater. If the formic acid is either diluted by addition of water or if its pH is neutralized, SLP3 will precipitate. SLPF is soluble in 4.5 M lithium perchlorate solution at 1 w t%. Once dissolved the solution can be diluted wadi water or phosphate buffer to 0.1 w t% or less. It will remain in solution temporarily depending on its concentration (O.OI wa% solution will precipitate in about 8 hours). 

Reduction. A variety of metal hydride reducing agents can be employed to reduce jr-allylpalladium dimers. These include sodium borohydride, sodium cyanoborohydride, lithium triethylborohydride, lithium aluminum hydride, lithium tri-ferf-butoxyaluminum hydride, polymethylhydrosiloxane, and RsSiH (eq Formic acids and formate salts also reduce... 

The reaction between ethyl Hthiopropiolate and the N-acylpyridinium salt formed by reaction of 4-methoxy-3-methyl-5-(triisopropylsilyl)pyridine 2363 with (+)-frafis-2-(a-cumyl)-cyclohexyl chloroformate (TCC chloro-formate) was the starting point in the synthesis of (-l-)-aUopumihotoxin 267A (1718) by Comins et al. (Scheme 301). The dihydropyridone product (—)- 2364 was obtained diastereoselectively (>96%) before hydrogenation to the saturated ester (+)-2365. However, some epimerization of the methyl substituent was apparent after cleavage of the TCC carbamate with lithium methoxide and cyclization to the indolizidinone (—)-2366 (dr 8 1). Acetoxylation at C-8 with lead tetraacetate was stereoselective, and introduced the acetate from the axial direction, possibly by stereoelec-tronicaUy-controUed intramolecular transfer of acetate from a lead—enol intermediate. The acetoxy product (—)-2367 was protodesilylated with formic acid, after which a one-pot tandem reduction with K-Selectride followed by hthium aluminum hydride gave diol (- -)-2368 with complete... 

Chitin is a white, amorphous solid, insoluble in water, dilute acids, dilute and concentrated alkali, and organic solvents. It readily dissolves in concentrated hydrochloric, sulfuric, nitric, and phosphoric acids, in anhydrous formic acid, with difficulty in liquid ammonia, but not in Schweizer s reagent. Hot, concentrated solutions of neutral salts, like lithium and calcium thiocyanate, dissolve chitin, which can then be reprecipitated by dilution with alcohol or acetone, without apparent degradation. 

Inorganic salts of organic acids and inorganic addition compounds of organic compounds (hydrohalides, perchlorates, sulfates, etc.) are not given separate entries but are indicated in modifying phrases under the formula of the compounds from which they are derived (under the acid in the case of a salt). Salts of formic, acetic, and oxalic acids are exceptions these are entered under their own formulas, and lithium acetate is found under C2H3Li02. 

In the survey article [174], devoted to a generalization of the data on the use of soaps for the stabilization of pol3rvinyl chloride, it is noted that in recent years salts of inorganic acids have been gradually displaced by soaps, the most widespread among which are lead stearate and barium and cadmium laurates. Salts of lead, tin, barium, calcium, cadmium, strontium, sodium, and lithium of such acids as formic, oxalic, maleic, caprylic, imdecylenic, lauric, stearic, ricinoleic, etc., have... 

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