Ammonium salts, alkyl cleavage

You have read (Unit 10, Class Xll) that the carbon - halogen bond In alkyl or benzyl haUdes can be easily cleaved by a nucleophile. Hence, an allqrl or ben l haUde on reaction with an ethanollc solution of ammonia undergoes nucleophilic substitution reaction m which the halogen atom Is replaced by an amino (-NHJ group. This process of cleavage of the C-X bond by ammonia molecule Is known as ammonolysis. The reaction Is carried out In a sealed tube at 373 K. The primary amine thus obtained behaves as a nucleophile and can further react with allqrl halide to form secondary and tertiary amines, and finally quaternary ammonium salt. 

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. 

Concerning the hydrolytic cleavage conditions, one method was reported by Enders in his seminal study in 1976 [8]. The latter consists in the alkylation of the nitrogen with an excess of iodomethane to form the corresponding ammonium salt, which is hydrolyzed in a biphasic HCl 1 M/n-pentane system. In 1998, Enders described very mild conditions using a saturated aqueous solution of oxalic acid in ether, which allowed to hydrolyze the hydrazones without racemization [12]. This protocol has also the advantage of recycling the chiral SAMP hydrazine. 

Complexation with zinc effectively separates the C3S5 dianion from the trithiocarbonate ion in high yield, and the material obtained is sufficiently pure for further reactions. The quaternary ammonium zincate salt is alkylated slowly but smoothly by many halides at room temperature in solvents such as acetone or tetrahydrofuran. Reaction of the zincate with benzoyl chloride followed by cleavage of the resulting benzoate by sodium ethoxide in ethanol provides the much more reactive species NajCaSs. The sodium salt is, however, very air sensitive,5 whereas the zinc salt is completely stable. 

Trimethyl tetrathiophosphate heated 12 hrs. in a closed flask on a water bath with a 28% soln. of trimethylamine in anhydrous acetone tetramethyl-ammonium dimethyl tetrathiophosphate. Y 85%. — The salts produced give mixed esters by reaction with alkyl halides. Also cleavage of trimethyl trithiol-phosphate s. P. Ghabrier and T. N. Thanh, G. r. 261, 2229 (1965). 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

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