Perrin titration method

Johnston et al. developed an ammonium salt (26), derived from cyclohexane diamine, and successfully employed it as a catalyst for the aza Henry reaction (Scheme 2.67) [127]. They estimated the pKa value of the ammonium salt to be 5.78 by the Perrin titration method [128]. 

PhCD2NH2,40,42 as well as the temperature independence of the Ap/f, for CD3M f and (CD3)2NH2,52 Perrin and coworkers reinvestigated these and other secondary IEs.30,31 The amines studied were methylamine (16-do,1,2,3), benzylamine (18-d), N,A -dimethy 1 ani 1 ine (19-d3), 1-benzyl-4-methylpiperidine (20-d3), pyrrolizidine (21-d), N-methy 1 norborny 1 amine (22-d2), and A -benzyl-norbornylamine (23-d). The NMR titration method [Equation (19)], which gives highly accurate results, was applied to the reporter H depicted in boldface on the molecular structures. The results are presented in Table 5. According to those data the ApK for methylamine (16) is proportional to the number of deuteriums, and for 16-18, 22, and 23 the Apper D or the AAG° per D is nearly constant, 24 cal mol-1. 

Kolthoff IM, The dissociation constants, solubility product and titration of alkaloids, Biochem. Z., 162,289-353 (1925). NB Cited in Perrin Bases no. 2906. The spectrophotometric method used colorimetric determination of the extent of ionization by use of an indicator of known pKa value. 

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