Ammonium salts, alkyl reduction

In reviewing the intrinsic electrochemical behavior of nonaqueous systems, it is important to describe reactions of the most common and unavoidable contaminants. Some contaminants may be introduced by the salts (e.g., HF in solutions of the MFX salts M = P, B, As, etc.). Other possible examples are alcohols, which can contaminate esters, ethers, or alkyl carbonates. We examined the possible effect of alcoholic contaminants such as CH3OH in MF and 1,2-propylenegly-col at concentrations of hundreds of ppm in PC solutions. It appears that the commonly used ester or alkyl carbonate solvents are sufficiently reactive (as described above), and so their intrinsic reactivity dominates the surface chemistry if the concentration of the alcoholic contaminant is at the ppm level. We have no similar comprehensive data for ethereal solutions. However, the most important contaminants that should be dealt with in this section, and which are common to all of these solutions, are the atmospheric ones that include 02, H20, and C02. The reduction of these species depends on the electrode material, the solvent used, and their concentration, although the cation plays the most important role. When the electrolyte is a tetraalkyl ammonium salt, the reduction products of H20, 02 or C02 are soluble. As expected, reduction of water produces OH and... 

The Leuckart reaction uses formic acid as reducing agent. Reductive alkylation using formaldehyde, hydrogen, and catalyst, usually nickel, is used commercially to prepare methylated amines. These tertiary amines are used to prepare quaternary ammonium salts. 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

Diphenylisoinclole (29) can be prepared by a modified Leuckart reaction of o-dibenzoylbenzene (46), using an ammonium salt of formic acid the process is essentially a reductive alkylation of ammonia, accompanied by cyclization, and leads to 29 in 44% yield with ammonium formate, and 47 in 28% yield with methylammonium formate. 1,3-Diphenylisoindole. (29) can also be obtained in good yield by the reaction of 46 with 1,1-dimethylhydrazine. ... 

A thio-substituted, quaternary ammonium salt can be synthesized by the Michael addition of an alkyl thiol to acrylamide in the presence of benzyl trimethyl ammonium hydroxide as a catalyst [793-795]. The reaction leads to the crystallization of the adducts in essentially quantitative yield. Reduction of the amides by lithium aluminum hydride in tetrahydrofuran solution produces the desired amines, which are converted to desired halide by reaction of the methyl iodide with the amines. The inhibitor is useful in controlling corrosion such as that caused by CO2 and H2S. 

The reaction of methylenesulphones with allyl halides in the presence of quaternary ammonium salts produces the 1-allyl derivatives [52], unlike the corresponding reaction in the absence of the catalyst in which the SN- product is formed (Scheme 6.5). In contrast, alkylation of resonance stabilized anions derived from allyl sulphones produces complex mixtures [51] (Scheme 6.6). Encumbered allyl sulphones (e.g. 2-methylprop-2-enyl sulphones) tend to give the normal monoalkyl-ated products. Methylene groups, which are activated by two benzenesulphonyl substituents, are readily monoalkylated hydride reduction leads to the dithioacetal and subsequent hydrolysis affords the aldehyde [61]. 

Now comes the key step intramolecular conjugate addition of the nitroalkane anion to the unsaturated ester. When catalysed by CsF and a tetra-alkyl ammonium salt, this is selective (1.5 1) for the all equatorial products 100. Reduction and cyclisation give the lactam 102 having the right stereochemistry for (Llycorane 72. 

Reduction of 3 -iodopropionitrile at the potential of the first polarographic (1 e) wave yields Hg (CH2 CH2 CN)2, Sn2 (CH2 CH2CN)6, Pb(CH2 CH2 CN)4 and T1(CH2CH2CN)2I at Hg, Sn, Pb, or T1 cathodes 481 When ethyl or butyl iodide is reduced at platinum or copper cathodes in DMF dimers R2 and disproportionation products, RH, RH(-H2), are formed 482,483,48S Formation of these are attributed to radicals originating both from tire cathodic cleavage of the R-I and the R2-N(CH3)2 bond 482 The ammonium salt is formed by alkylation of DMF. 

The asymmetric organocatalytic transformation of a ketone into an alcohol may be realized with the combination achiral silanexhiral phase-transfer catalyst, such a quaternary ammonium salt. The final alcohol is then recovered by an additional hydrolytic step. The asymmetric reduction of aryl alkyl ketones with silanes has been reported (ee-values up to 70%), the catalysts utilized being ammonium fluorides prepared from the quinine/quinidine series (e.g., 18 in Scheme 11.6) [19]. (For experimental details see Chapter 14.21.1). The more appropriated silanes were (Me3SiO)3SiH or (MeO)3SiH (some examples are... 

Besides the effect of the electrode materials discussed above, each nonaqueous solution has its own inherent electrochemical stability which relates to the possible oxidation and reduction processes of the solvent,the salts, and contaminants that may be unavoidably present in polar aprotic solutions. These may include trace water, oxygen, CO, C02 protic precursor of the solvent, peroxides, etc. All of these substances, even in trace amounts, may influence the stability of these systems and, hence, their electrochemical windows. Possible electroreactions of a variety of solvents, salts, and additives are described and discussed in detail in Chapter 3. However, these reactions may depend very strongly on the cation of the electrolyte. The type of cation present determines both the thermodynamics and kinetics of the reduction processes in polar aprotic systems [59], In addition, the solubility product of solvent/salt anion/contaminant reduction products that are anions or anion radicals, with the cation, determine the possibility of surface film formation, electrode passivation, etc. For instance, as discussed in Chapter 4, the reduction of solvents such as ethers, esters, and alkyl carbonates differs considerably in Li or in tetraalkyl ammonium salt solutions [6], In the presence of the former cation, the above solvents are reduced to insoluble Li salts that passivate the electrodes due to the formation of stable surface layers. However, when the cation is TBA, all the reduction products of the above solvents are soluble. 

Figure 6 presents a scheme of an electrolysis cell for the isolation of reduction and oxidation products of nonaqueous solutions [15]. The electrolyte of the W.E. solution must be an alkyl ammonium salt because the reduction products of most of the commonly used solvents in the presence of metal cations precipitate as insoluble metal salts. The counter- and reference electrode compartments are separated from the working electrode compartment by two frits each. The separating units have pipes which enable the sampling of their solutions in order... 

For instance, the reduction potential of many solvents depends on the salt used and, in particular, on the cation. The reduction potentials of alkyl carbonates and esters in the presence of tetraalkyl ammonium salts (TAA) are usually much lower than in the presence of alkaline ions (Li+, Na+, etc.). Similar effects were observed with the reduction potential of some common contaminants (e.g., H20, 02, C02). Moreover, the reduction products of many alkyl carbonates and esters are soluble in the presence of tetraalkyl ammonium salts, while in the presence of lithium ions, film formation occurs, leading to passivation of the electrode [3],... 

The advantages of PTC reactions are moderate reaction conditions, practically no formation of by-products, a simple work-up procedure (the organic product is exclusively found in the organic phase), and the use of inexpensive solvents without a need for anhydrous reaction conditions. PTC reactions have been widely adopted, including in industrial processes, for substitution, displacement, condensation, oxidation and reduction, as well as polymerization reactions. The application of chiral ammonium salts such as A-(9-anthracenylmethyl)cinchonium and -cinchonidinium salts as PT catalysts even allows enantioselective alkylation reactions with ee values up to 80-90% see reference [883] for a review. Crown ethers, cryptands, and polyethylene glycol (PEG) dialkyl ethers have also been used as PT catalysts, particularly for solid-liquid PTC reactions cf. Eqs. (5-127) to (5-130) in Section 5.5.4. 

The alkylation of amines (including polyamines formed by reduction of polypeptides) was a highly popular method of derivatization in peptide chemistry before the appearance of contemporary mass-spectro-metric techniques for analysis of nonvolatile compounds (FFAB, MALDI, etc.). Direct alkylation of amines by alkyl halides (Hoffman reaction) can lead to the final nonvolatile ammonium salts and, hence, other soft reagents must be used. For example, exhaustive methylation can be provided by the mixtures CH20/NaBH4/H+ or CH20/formic add. 

In the reactions of sodium in liquid ammonia with quaternary ammonium salts with different alkyl groups the methyl group is always cleaved first (except for the 2-butyl group). This behavior is similar to LAH reductions 33> and to thermal decompositions of halide salts 2h... 

---