Arylammonium salts

Amines react with strong acids to form amine salts. The pKas of amine salts are related to the base strength of the corresponding amines. Alkylammonium salts have pKas of 9-10 while arylammonium salts have pKas of 4-5. The fact that these salts are usually water-soluble can be exploited in separating amines from neutral or acidic contaminants. Chiral amines can be used to resolve enantiomeric acids, through the formation of diastereomeric salts. 

The carbonate itself can be used as solvent and the reaction is very selective as no methylation or arylation products of the amine are found. The catalyst can be easily and quantitatively recovered as arylammonium salt at the end of the reaction and recycled. Thereof, the carbamate is not contaminated with P. These features make Ph2P(0)0H) very attractive from a practical point of view. This represents the first example of non-metal catalysis for the synthesis of carbamates from carbonates. Kinetic experiments support the "nucleophilic catalysis" depicted below. 

The reactions indicated by Eqs. (1) and (7) show that weak bases such as aniline behave similarly to ammonia. They unite with water to form weakly dissociated bases, e.g., arylammonium hydroxides. These, like ammonium hydroxide, precipitate the hydroxides of the heavy metals from solutions of their salts. The last step [Eq. (6)] shows the completion of the catalytic cycle and emphasizes the role of iron in the regeneration of the catalyst, ferrous chloride,. and. the amine. This reaction is in accord with practical observations that aqueous solutions of aniline hydrochloride, or other salts that are hydrolyzed in the presence of metals with the formation of hydrogen ions, are useful catalysts/ The over-all reaction can be represented as... 

Bases LiOH. NaOH. KOH... Salts Na2C03,... Molecules amines,. .. Acids HF, H2SiF6,. Salts LiF, NaF, NH4F Molecules alkyl and arylammonium.. 

Correlations of the oxygen balance of a parent energetic compound and its impact sensitivity (a thermal decomposition phenomenon) are well known 11-31. Hammett correlations with the explosive sensitivity in arylammonium perchlorate salts have been uncovered [4]. Relationships between the composition [5] and decomposition [6,7] of explosives and their detonation velocity are known. Extensive studies have been made relating molecular structure to the kinetics and thermolysis trends for aliphatic nitro compounds [8J, azides [9,10], and nitramines [11]. Correlations of the melting point with burn-rate [12], functional group with decomposition temperature [13], and various structural parameters with stability [14] have been proposed. 

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