Sulphonic acids protonation

The pKa values of thirteen naphthylamine-sulphonic acids (proton lost constants only) are available to supplement the anilinesulphonic acids of Table 8.11 (Bryson, 1951). 

The kinetics of desulphonation of sulphonic acid derivatives of m-cresol, mesitylene, phenol, p-cresol, and p-nitrodiphenylamine by hydrochloric or sulphuric acids in 90 % acetic acid were investigated by Baddeley et a/.701, who reported (without giving any details) that rates were independent of the concentration of sulphuric acid and nature of the catalysing anion, and only proportional to the hydrogen ion concentration. The former observation can only be accounted for if the increased concentration of sulphonic acid anion is compensated by removal of protons from the medium to form the undissociated acid this result implies, therefore, that reaction takes place on the anion and the mechanism was envisaged as rapid protonation of the anion (at ring carbon) followed by a rate-determining reaction with a base. 

One potentially important example of CIDNP in products resulting from a radical pair formed by electron transfer involves a quinone, anthraquinone j5-sulphonic acid (23). When irradiated in the presence of the cis-syn dimer of 1,3-dimethylthymine (24), enhanced absorption due to vinylic protons and emission from the allylic methyls of the monomer (25) produced can be observed (Roth and Lamola, 1972). The phase of the polarizations fits Kaptein s rules for intermediate X... 

Fig. 3.3f(/) shows the use of a combination of ion-pairing and ion-suppression to separate a mixture of acids and bases. The pH of the mobile phase is about 2.5, as at this pH the maleic acid is unionised and elutes quickly as a very polar molecule on the reverse phase column. The other solutes are all weak bases which at pH 2.5 are fully protonated and pair with the pentane sulphonic acid anion. 

Example 3 Sulphonic acids rapidly pair with a plethora of protonated amines to form an easily extractable complex... 

It is technically possible, but very difficult, to measure the exact frequency of a radio signal, and in practice the frequency of the energy absorbed by a test compound (usually called the resonance frequency) is measured relative to that of a reference compound. This reference may be mixed with the sample (direct referencing), or if contamination of the sample is undesirable it may be placed in a separate container within the sample tube (external referencing). In proton and 13C NMR, the reference compound usually used is TMS (tetra-methyl silane) or its water-soluble derivative DSS (2,2-dimethylsilapentane 5-sulphonic acid). These compounds give a sharp proton peak at the right-hand side of a typical NMR spectrum (Figure 2.39). 

Fig. 5.22 Proton-conducting membrane based on benzyl sulphonic acid siloxane.

Hydroxyazobenzene and 4-hydroxyazobenzene-4 -sulphonic acid become diprotonated in 100% sulphuric acid, the second proton going on the phenolic 0-site, rather than on carbon (Strachan et al., 1969). 

Both lyotropic and thermotropic liquid-crystalline synthetic polymers have been widely studied. Aromatic polyamides constitute the most important class forming liquid-crystalline solutions the solvents are either powerfully protonating acids such as 100% sulphuric acid, chloro-, fluoro- or methane-sulphonic acid, and anhydrous hydrogen fluoride, or aprotic dipolar solvents such as dimethyl acetamide containing a small percentage, usually 2-5 %, of a salt such as lithium chloride or calcium chloride. Such solutions constitute a nematic phase within certain limits. Some criteria for formation of a nematic instead of an isotropic phase are ... 

When sulphonic acids are not completely dissociated, so that both protonated and dissociated forms exist in solution, 33S parameters measured experimentally have intermediate values between those of the two forms ... 

The solubility of the electrically conductive form, the protonated EM salt, is poor in common solvents, and so, initially, EM base was used to form films from NMP solution before conversion to the salt with HC1. Attempts to increase solubility by incorporating pendent alkyl chains were counterproductive as such polymers had significantly lower electrical conductivity. Better solubility is obtained for salts produced with sulphonic acids. Thus the camphor sulphonic acid salt dissolves in m-cresol and the 2-acrylamido-2-methyl-l-propanesulphonic acid salt dissolves in dichloro-acetic acid. The use of these systems, and polymer synthesised below room temperature, has facilitated the spinning of fibres with oriented polymer chains and conductivity along the fibre as high as 2x 105f2-Im-1 (Pomfret et ai, 1998). 

One case of apparent defiance of the trans requirement for oxetane formation has recently been reported in the solvolysis of the 3"tosylate (i6) of 3j5,5jS dihydroxycholestan"6"One [ 138]. Under strictly anhydrous conditions the major product was the 3 ff,5j5 oxetane (17), although aqueous solvents gave mainly the 3a,5jS-diol. The mechanism of internal cis substitution at C(3) is not known. Various possibilities include the formation of an internally "solvated ion-pair (18), as a consequence of the extra acidity imposed upon the 5i -hy-droxylic proton by the 6 oxo group this could be followed by oxetane formation with extrusion of a molecule of toluene- -sulphonic acid. 

Where the template has been an aromatic amine of low basidty, interaction with carboxylic acid groups has proved too weak to allow selective imprinting. However, Sherrington et al. [112] have shown that the sulphonic add residue in 2-acrylamido-2-methylpropane sulphonic acid is very useful under these circumstances the much higher acidity of this add allows protonation of the weak base template, and hence sufficiently strong electrostatic interaction for imprinting to be achieved. 

Dupont de Nemours) or analogous perfluorosulphonic acid membranes have been the dominating choice. The structure of the repeat structure of the polymer fluorocarbon backbone and a side chain with sulphonic acid ends upon which Nafion is based is shown in Fig. 3.42 (the commercial product is sold with various thicknesses and dimensions denoted by a number code such as "Nafion-117", related to non-SI units). The membranes should have high protonic conductivity, low gas permeability and, of course, a suitable mechanical strength and low temperature sensitivity. 

Replacement of hydrogen by alkali-metal disrupts the hydrogen bonding necessary for the concerted mechanism, but the relatively high activity of -SOali was attributed to failure to remove all the water of hydration under the conditions used for drying the catalyst. Hence -SOali could act as a proton-donor acceptor of sufficient strength to act in the concerted mechanism, but was unable to catalyse the carbonium ion mechanism. The soluble toluene-p-sulphonic acid was less active at high concentration because it could not act in a concerted mechanism. 

Fischer-Speier esterification to give a salt of an amino acid ester (by refluxing an alkanol with anhydrous HC1 or hot benzyl alcohol with toluene-/>-sulphonic acid) is straightforward. The fact that the nearby amino group is protonated when the carboxy group reacts to give a-amino acid esters does not slow the reaction down unduly a nearby positive site might have been expected to reduce the electrophilic character of the carboxy carbon atom. Without an acid catalyst, Walkylation can accompany esterification (Equation 4.6). 

Fig. 6 Illustration of Nafion-acid functionalized zeolite Beta nanocomposite membranes helping to increase the proton conductivity and decrease the methanol crossover (A) H2O and CH3OH diffusion reduced by zeolite flow resistance (B) sulphonic acid functionalized zeolite nanoparticles increases proton conductivity of composite membranes. (View this art in color at www. dekker. com.)...

The Chemistry of Rii% b.— The 9— 6p lactone (44, R = H) of the 12-methoxy-podocarpa-8,ll,13-triene series was obtained by the successive dehydration of the 7a- and 7)3-hydroxy-lactones with toluene-p-sulphonic acid in acetic anhydride and hydrogenation of the resulting A -enol-lactone over palladium-charcoal. Examination of the width of the C-6 proton resonance led to the... 

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